Biophysics Answers (dead link removed)

Use these as a guideline but be careful to make sure that the answers are correct according to the textbook. Remember that THESE ARE A STUDENT'S ANSWERS, NOT THE GOSPEL TRUTH!
The professors are very keen on equations and units so once you have learnt the theory, be sure to have at least one equation memorised per question where possible. If you can write down an equation they will love you!

Biophysics Answers

1. Wave properties of particles and quantum properties of waves
A - Wave property of particles: Particles can be show to exhibit wave like behaviour under certain conditions. All particles can be shown to have a wavelength that is proportional to its momentum.
λ = h/p
(Random Q) Q - Wave properties of particles (mass wave properties)
A - The energy E of photon (J) is related to the frequency f of the wave and to its wavelength λ (m) : E=hf = hc/λ h=6.63 x 10(-31) planks constant c=velocity of light.
Motion of each particle with mass m momentum p and energy E is related to the mass wave of the wavelengths : λ=h/p
And to the frequency f defined by eqn - f=E/h


The consequence of this is that an electron (normally considered as a particle) can be passed through a slit that is comparable with its DeBroglie wavelength to demonstrate wave like properties of the electron (diffraction and interference patterns)

Quantum properties of waves: The energy of a photon is related to the frequency of the wave and therefore its wavelength

E = h.f
= h.c / λ
Energy is released in discrete packets, and is not dependent on intensity. This suggests a particulate nature of em radiation where each light particle (photon) carries an energy that is proportional to its frequency.

Quantum numbers:
Quantum numbers are natural integers and determine the geology and symmetry of the electron cloud. There are 4:
1. Principle quantum number (n) determines total energy of electron, a natural number, the value of which estimates the shell in which the electron occurs.
2. Orbital quantum number (ℓ)=n-1 and determines form and symmetry of electron cloud i.e. the sublevels s,p,d,f,g,h. eg. Sublevel 4d is where n=4 and ℓ=2. Determined by angular momentum
3. Magnetic quantum number (m) = ±ℓ and determine the spatial position of orbital. Estimates direction of angular momentum, L.
4. Spin quantum number (s) is the electrons own internal angular momentum

Ionisation and excitation:
Excitation:
• Electrons with minimum energy are in the ground state, increase energy and becomes excited state
• Atom absorbs energy corresponding to difference between ground state and excited state
• Atom remains in excited state for short time (10-5-10-7s)
• Excitation energy emitted as one or more photons during deexcitation
• Metastable state of electron when it reaches an energy level from which transition to ground state is ‘forbidden’
• Deexcitation may be followed by radiation emission resulting in luminescence
Ionisation:
• Ionisation potential = binding energy of electron which is the energy required to remove the electron from the forces of the nucleus
• Always positive, equal in value to total energy of electron (with heavy atoms, other factors affect this)
• If electron gets energy greater than binding energy, some of this energy is used to remove electron from the system
• Results in formation of positive ion and increase in total energy of system
• Ionised atom is unstable and returns to ground state of minimum energy by emission of fluorescence radiation
Absorbed energy must be of order of eV for excitation or ionisation of outer electrons to take place, and keV for inner electrons. Excitation or ionisation of inner electrons may result in emission of UV light or Xrays

Structure of electron shells in atoms

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Some Examples:
Element Z Electron configuration
Titanium 22 1s2 2s2 2p6 3s2 3p6 4s2 3d2
Vanadium 23 1s2 2s2 2p6 3s2 3p6 4s2 3d3
Chromium 24 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Manganese 25 1s2 2s2 2p6 3s2 3p6 4s2 3d5
Iron 26 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Cobalt 27 1s2 2s2 2p6 3s2 3p6 4s2 3d7
Nickel 28 1s2 2s2 2p6 3s2 3p6 4s2 3d8
Copper 29 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Zinc 30 1s2 2s2 2p6 3s2 3p6 4s2 3d10
Gallium 31 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1

Atomic Nucleus:
• Formed by nucleons: protons and neutrons
• Atomic number (Z) = no. of protons
• Mass number (A) = no. of protons + neutrons
• Neutron number (N) = no. of neutrons
• Total electric charge of nucleus = 1.6 x 10-19C
• Isotope is atom with identical Z but different A
• Isobar is atom with different Z but identical A
• Isomer is atom with same Z and A but different energy
• Nuclear forces are result of strong interaction and do not exceed radius of nucleus, very strong

Binding energy in atomic nucleus
• Determines stability
• Estimated from total mass defect Δm = (Z.mp + N.mn) - mnucleus (measured mass of nucleus is lower than calculated mass.
• >Mass defect = >Binding energy
• Disintegration of nucleus into nucleons would require energy E = mc2

Potential Barrier of Atomic Nucleus
• At low r strong interactions overcome electromagnetic interactions
• Electric charge of nucleus (Ze) forms electrostatic force field around nucleus with potential (U(r)) which is a function of the distance (r) from nucleus
• Potential barrier exists due to electromagnetic interaction for positively charge particle entering nucleus
• Potential barrier must be overcome for positive particle to enter nucleus and come under strong interactions of nucleus

Physical Principles of Mass Spectrometry
• Determines isotopic composition of a sample
• Trajectory of charged particle in a magnetic field depends on its mass
• Method
1. Isotopes ionised to become +ve ions with charge q
2. Acceleration of ions to form beam of ions with energy qU (U is potential difference of longitudinal electric field)
3. Decomposition of ion beam into more beams according to specific charge (q/mass)
4. Detection of each beam and measurement of intensity
• Ions of different masses impact at different places according to their mass, measurement of relative amount of isotopes then yields isotopic composition of sample studied

Physical principles of nuclear magnetic resonance.
• Magnetic properties of atomic nuclei represent physical basis for nuclear magnetic resonance effect applied for imaging techniques
• Proton localised in external magnetic field with induction B can have one of two energy states ±μB (μ=magnetic moment of proton). Nuclear magnetic resonance is the resonance exchange of energy, two possibilities:
1. Proton energy = -μB, photon absorbed and transition into higher energy state with energy +μB
2. Proton energy = +μB, photon emitted and transition into lower energy state with energy -μB
• Frequency of resonance exchange called Lamor’s frequency
• Creates massive magnetic field to excite water particles, different tissues contain different quantities of water, so excitation varies from tissue to tissue so can be measured separately. Create an image of tissues of different water concentration.
• Complicate, expensive and noisy

2. Molecular Biophysics

SI units
All other units are based upon 7 base units
• Mass (kg)
• Current (A)
• Time (s)
• Temp (K)
• Amount of substance (mole)
• Length (m)
• Luminous intensity (Cd)
Magnitudes of unit
• 1015 = P (peta) 10-18 = a (atto)
• 1012 = T 10-15 = f (femto)
• 109 = G 10-12 = p (pico)
• 106 = M 10-9 = n
• 103 = k 10-6 = μ
• 102 = h 10-3 = m
• 101 = d 10-2 = c
• 100 = 1 10-1 = d

Phase states of matter
State is described by physical quantities (pressure, temp etc)
Gaseous, liquid, solid and plasma phases as well as transition states
Gaseous
• gas consists of large number of identical molecules with random velocities
• kinetic energy is energy of translation
• molecules don’t interact except brief elastic collisions with each other and container walls
• average distance between molecules greater than diameter
Liquid
• number of molecules per unit volume greater than in gaseous phase
• less compressible and volume changes with temperature lower than gases
• surface tension due to Van der Waals
Solid
• crystalline structure is feature of solids
• ions, atoms or molecules from lattice with special spatial arrangement
• components of lattice oscillate around equilibrium position and amplitude of vibrations is function of temperature
• supply of thermal energy increases amplitude of vibration and lattice may collapse at high temperatures

State equation of ideal gas
pV = nRT
R = 8.31 J.mol-1.K-1
Boltzmann’s constant k = R/NA = 1.38 x 10-23 J.K-1
∴pV = KkT
Boyles Law (Isothermal)
• T constant
• pV constant
Charles’ Law (Isobaric)
• p constant
• V/T constant
Therefore,
• V constant
• p/T constant

Bernoulli equation, equation of continuity
Bernoulli equation
• Work done on a flowing fluid is equal to the change of its mechanical energy:
p + ½ρv2 + hρg = const
• Sum of pressure and total mechanical energy of liquid per unit volume is constant everywhere in a flow tube. ½ρv2 represents kinetic energy, and hρg the potential energy of the fluid per unit volume
• Pressure at same depth at two places in a fluid at rest is the same
Equation of continuity
A1v1 = A2v2



Law of Laplace
Describes the relation between the pressure difference (ΔP) across the surface of a closed membrane and the wall tension T (N.m-1).
ΔP = T (1/R1+1/R2)
where R1 and R2 are the main radii of the membrane curvature at the given point. For a cylindrical form of the membrane, one of the radii is infinitely large and thus ΔPcylinder = T/R, for a sphere R1=R2=R and thus P = 2T/R

Gibbs phase rule, phase chart of water
Dispersion system consists of dispersive portion dispersed within dispersive medium
• Heterogeneous system; boundary between portion and medium e.g. oil in water
• Homogeneous system; no boundary
Relates the number of components (c), phases (p) and degrees of freedom (d)
p + d = c + 2
d of heterogeneous system is number of independent variables (pressure, temp, conc); when p = 3 no variable can be changed as equilibrium would be lost, this is the triple point (no degree of freedom)

An increase in pressure results in a decrease of melting point temperature, i.e. at a given temperature ice can be made to melt by the application of pressure
Three phase equilibrium lines intersect at the triple point; at this pressure and temperature the three phases can coexist in equilibrium





Water as a solvent
• water is a dipole
• polar solvent with good solvent power
• bond angle is 105°
• water molecules interconnected by hydrogen bonds in liquid and solid phases
• substantial component of all body liquids and organs and represent dispersion medium for macromolecules, molecules, and ions in cells and enables their interactions

Dispersion systems and their classifications.
Classification:
• Size of particles
1. Analytical dispersion <1nm (chemical analysis, not physical)
2. Colloidal dispersion 1-1000nm
3. Coarse dispersion >1μm
• Phase of dispersive medium
• Phase of dispersive portion
Analytical dispersions
• homogeneous
• dispersion portion is ions, molecules or atoms
• gas + gas
− Dalton’s law p = p1 + p2 + …
− Amagad’s law v = v1 + v2 + …
• liquid + gas
− Henry’s law states that the amount of a gas dissolved in a liquid is directly proportional to the partial pressure of the gas above the liquid when the gas and liquid do not chemically react
• liquid + liquid
− homogeneous analytical dispersion possible (not heterogeneous)
• solid + liquid
− solid dissociates into ions and organic compounds with polar groups
− solubility of solid increases with increasing temperature
− solidification of solid phase should appear on cooling
Colloidal dispersions
• highest biological importance
• lyophobic and lyophillic according to behaviour with solvent
• macromolecules (with chemical bonds) or micelles (particles without chemical bonds) form colloidal particles
• thermal motion of liquid molecules disturbs sedimentation process but after certain time interval sedimentation equilibrium is reached
• sedimentation rate depends on temperature (centrifugation accelerates sedimentation)
• permeability or impermeability of colloidal particles through membranes allows for separation from analytical portion of solution or dispersion medium
• measurement of intensity of scattered light can be applied for estimation of concentration (dependent on particle size)

Properties of colloid particles
• double layer of charged particles on surface distinguishing them from other dispersions
• arranged by electrolytical dissociation or by adsorption of an ion
− e.g. micelles of AgI (insoluble in water) prepared by missing KI with AgNO3 → K+ I- Ag+ NO3-
− excess of AgNO3 ∴overall production of AgI which coagulates with some AgI micelles remaining in solution. They attract the Ag+ ions, which then attract the NO3- ions forming a double layer
• adsorption forces and electrostatic forces with decrease with squared distance
• electric double layer gives colloidal particles an electrokinetic potential

Principle of electrophoresis, electrokinetic potential
Electrophoresis
• technique used to separate and sometimes purify macromolecules (especially proteins and nucleic acids) that differ in size, charge or conformation
• one of the most widely-used techniques in biochemistry and molecular biology
• when charged molecules are placed in an electric field, they migrate toward either the positive (anode) or negative (cathode) pole according to their charge
• proteins have either a net positive or net negative charge, whilst nucleic acids have a consistent negative charge imparted by their phosphate backbone, and migrate toward the anode
• relative movement of the charged macromolecule depends on mass: charge.
Electrokinetic potential
• potential across the interface of all solids and liquids
• specifically, potential across the diffuse layer of ions surrounding a charged colloidal particle, which is largely responsible for colloidal stability



Transport Phenomena
• related to motion of molecules and processes of interactions of molecules
• transport of some physical quantities occurs
− viscosity is transport of momentum
− conduction of heat is transport of energy
− diffusion is transport of molecules
• necessary condition for transport is presence of appertaining gradient of flow velocity, temperature or concentration

Viscosity and its Measurement
Fluids contain internal friction between adjacent layers (molecules) of liquids as they move past each other
Highest velocity vmax in centre of tube. Velocity equals zero just at the wall of the tube.


Kinetic Velocity v (m2s-1)
• dynamic velocity (Pa.s) divided by density (kg.m-3)
• v = η/ρ
Tangent tension σ (Pa)
• σ = η(Δv/Δr)
Hagen-Poiseuille’s law, flow rate Q (m3.s-1)
• increase of radius by 19% results in twofold increased flow rate
• Q = (πR4ΔP)/(8ηL)
Flow resistance Rf (Pa.s.m-3)
• Rf = ΔP/Q
• ratio of pressure drop to flow rate
Stokes law
• at constant velocity, the driving and frictional forces differ only in sign, and velocity is proportional to driving force
• Fr = 6πηrv
• Reynolds number Re defined by 2ρvavR/η. Re<2000 flow is laminar, Re>3000 flow is turbulent and some energy dissipated as sound (principle used in measuring blood pressure)

Diffusion, 1st Law of Fick
Diffusion
• net transport of molecules from high concentration to low concentration
• primary mechanism in body for absorbing and distributing substances required by living cells
• release of by products of cellular function (e.g. CO2) also proceeds by diffusion
• density of diffusion flux, n/Aτ (mol.m-2.s-1) is proportional to concentration gradien:
1st Law of Fick
• n/Aτ = -D Δc/Δx (D = diffusion coefficient, m2.s-1)
• -ve sign indicates that direction of flux in opposite direction to concentration gradient


Surface tension, adsorption

Colligative properties of Solutions
4 properties of solutions
• dependent only on the number of particles of solute dissolved
• independent on size, form, chemical behaviour, molecules, ions, or colloids
• described with help of physical properties
• if denoted Φ, then Φ = kCm (k = proportionality constant, Cm= molar conc)
• can be used to determine molar mass of solute particles, Φ = k(Cg/M) where M = molar mass

Osmotic Pressure
• extra pressure that must be applied to stop the flow of solvent molecules into solution
4th colligate property
• osmosis is the movement of solvent particles through a semi-permeable membrane until the number of molecules passing in both directions is the same
• tissues composed of cells containing complex solutions, fluid surrounding cells also complex but with different composition
• in equilibrium total osmotic pressures due to impermeable molecules or ions must be same outside and inside cell
• hypotonic solution = lower osmotic pressure
• hypertonic solution = higher osmotic pressure
• isotonic solution = same osmotic pressure
van’t Hoff’s law
• p = RTCm p = pressure (Pa), R = 8.31 J.mol-1.K-1, T = temp (K)
Osmotic pressure in capillaries
• arterial capillaries have higher blood pressure than osmotic pressure, therefore water leaves tube
• venous capillaries have lower blood pressure than osmotic pressure, therefore water enters tube

Blood pressure measurement
Influencing Factors
• force by which the blood is ejected from the left heart into the circulation during systole
• peripheral resistance of blood vessels
• amount of circulating blood
• blood viscosity
Pressure amplitude
• difference between systolic and diastolic pressure
Measured using mercury manometer (sphygmomanometer)
• sounds are transported from the place examined to the physicians ear with the help of stethoscope
• when the pressure is above systolic pressure, no sound can be heard through the stethoscope
• level at which sounds start to occur is considered as systolic pressure
• pressure at which the sounds begin to disappear is generally taken as an indication of diastolic pressure





3. Thermodynamics

Thermodynamic system
• a part of nature, separated from its surroundings by real or imaginary boundaries, containing a great number of interacting particles and being composed of a great number of subsystems
• heat, work, or a substance (moles) may penetrate the boundary
• isolated system: Q=0, W=0 and Σni=0
• closed system: Q≠0, W=0 and Σni=0 (only heat exchange)
• open system: Q≠0, W≠0 and Σni≠0 e.g. humans
• processes of energy transformation
• law of conservation – amount of energy in a closed and isolated system remains constant whenever any physical or chemical process occurs ΔU=Q-W
System parameters
• Global (extensive) – describe system as a whole and possess additive properties (total value of parameter is sum of individual parts)
• Local (intensive) – depend not only on time but also spatial coordinate (e.g. temp, pressure)
State quantities
• state of system determined by variables related by pV=nRT (R=8.314 J.mol.K-1)
• value of a state variable depends on the state of the system
• all physical and chemical processes occurring in a system are related to changes of variables and functions of state (enthalphy, internal energy etc, functions of state variables and value independent on path)
• equilibrium state - state achieved in an isolated system (most probable arrangement of system)

First Law of Thermodynamics
The internal energy of a system changes from an initial value Ui to a final value Uf due to heat (Q) and work (W):
ΔU = Uf – Ui = Q – W
Q>0 – system gains heat W>0 – work done by system
Q<0 – system loses heat W<0 – work done on system

Second Law of Thermodynamics:
• heat flows spontaneously from a substance at a higher temperature to a substance at a lower temperature and doesn’t flow in the reverse direction
• Total entropy of the universe does not change when a reversible process occurs (ΔS=0) and increases when an irreversible process occurs (ΔS>0)
Carnot principle
• no irreversible engine operating between two reservoirs at constant temperatures can have greater efficiency than a reversible engine operating between the same temperatures. All reversible engines operating between the same temperatures have the same efficiency

Definitions of Thermodynamic Functions. (U,H,S,F,G)
Functions of state describe the state of a thermodynamic system by state variables
Internal Energy (U) (J)
• ΔU = Uf – Ui = Q – W
Q>0 – system gains heat W>0 – work done by system
Q<0 – system loses heat W<0 – work done on system
• U changes when work is done on or by system, and when it exchanges heat with the environment

Enthalpy (H) (J.mol-1)
• H = U + pV
• ΔH represents the quantity of heat released/absorbed by the system
• exothermic reaction H decreases
• endothermic reaction H increases
Entropy (S) (J.K-1)
• ΔS = Sf – Si = Qrev/T (Qrev = amount of heat absorbed by system)
• thermodynamic function that describes a degradation of energy
• total entropy of the universe does not change when a reversible process occurs (ΔS=0) and increases when an irreversible process occurs (ΔS>0)
• entropy increases towards equilibrium, maximum at equilibrium
Free Energy (F) (J)
• a.k.a. Helmholtz function
• F = U – TS
• during spontaneous irreversible process at a constant temperature, free energy decreases and reaches minimum at equilibrium
Free Enthalpy (G) (J)
• G = H – TS
• isothermal isobaric processes only
• spontaneous isothermal isobaric process, decrease of free enthalpy and reaches minimum at equilibrium

Chemical potential
• each kind of energy can be expressed as a product of intensive and extensive factors
• chemical energy: intensive factor is increase of number of moles of given substance (i), extensive factor is chemical potential (μi)
• ΔE = μi.Δni (J.mol-1)
• measure of affinity of given substance
• dictates which reactions take place in a system and their rates (also dependent on amount of substance in system)

Thermoregulation in homoiothermic organisms:
Human body is an open thermodynamic system
• processes against thermodynamic equilibrium occur due to continuous uptake of nutrient, though no process contradicting thermodynamic laws may occur
• entropy changes due to internal entropy production (diS) and entropy exchange (deS) with its surroundings
• total change of entropy dS = diS + deS
• alive system has low entropy, energy in is used for conservation, increasing arrangement and to remove waste products
• alive system develops in time towards a stationary state so that its production of entropy decreases in time and reaches minimum just at the stationary state

Measurement of temperature
Know about Q=mc T and SI unit will be known as J/K. The specific heat capacity Q=nC T (molar specific heat)measured in Jkmol. Also look about latent heat Q=ml and can also measure temperature from eqn pV=nRT but wil only get the result of temperature difference.

Calorimetric measurements
Calorimeter
• device for measurement of heat
• most common is mixing calorimeter
Q = (M + K)cΔT
− K – water value, amount of water (kg) which requires same amount of heat to increase temperature by 1°C as that consumed by device (heating walls, thermometer and mixing device)
− Q – heat supplied (J)
− M – mass of heated water (kg)
− C – specific heat capacity
− ΔT – temperature difference before and after heating
Calorimetry
• method for measurement of amount of thermal energy
• applied for measurement of energy requirements of organisms as well as for evaluation of energy content in nutrients
Direct Calorimetry
• subject measured is situated in isolated space and heat fromed is measured by temperature of certain volume of water circulating in calorimeter
Values
• in adults 11 MJ/day
• proportional to body surface 5 MJ/m2/day
• energy exchange per unit mass in kidneys is about 20-25 times higher than in rest of body

Specific heat, Latent heat
Specific heat (c) J.kg-1.K-1
• ΔQ = mcΔT
• property of given substance that varies with temperature
• molar specific heat C = Mc (M = molar mass)
• c of body (37°C) is 3.5 J.kg-1.K-1
• Poisson’s constant cp/cv = Cp/Cv (cp - constant pressure, cv - constant temperature)
Latent heat (L) J. kg-1
• ΔQ = mL
• temperature remains constant when substance changes its phase

4. Physical and Physiological Acoustics

Physical Properties of Acoustic Waves
• mechanical waves
• produced by vibration source of suitable frequency which pass through different media with various velocities
• no transport of medium particles occurs but medium particles oscillate around their equilibrium positions
• gas and liquid longitudinal oscillations
• solid longitudinal and transverse oscillations
• velocity of sound propagation dependent on temperature
• wavelength related to velocity and frequency λ = c/f
Acoustic amplitude (a)
• amplitude of vibration motion of medium particles 0 < a < amax
Acoustic velocity (v)
• velocity of vibrating motion of medium particles 0 < v < vmax
• effective acoustic velocity vef = vmax/√2
Acoustic pressure (p)
• oscillations of medium particles result in periodical density change and induce periodically changing acoustic pressure
• effective acoustic pressure pef = pmax/√2; related to effective acoustic velocity, density of medium and velocity of sound propagation pef = vefρc

Acoustic impedance (z)
• ratio of effective acoustic pressure to effective acoustic velocity
• z = pef/vef = ρc (ρ - tissue density)
• zair = 440 Pa.s.m-1
• zsoft tissue = 1.5 x 106 Pa.s.m-1

Sound intensity and loudness, units
Intensity of sound (I) W.m-2
• amount of energy passing through the area of 1m2 perpendicular to direction of sound wave propagation within 1s
• I = pef.vef = p2ef/ρc
Intensity level (L) dB (relative unit)
• L = 10.log(I/I0) = 20.log(p/p0)
Loudness (Ph – phone)
• physiological quantity of perception of sound
• function of frequency
• human ear perceives sound of frequency 16Hz – 16kHz
• energy transformed into electric potentials in receptor of inner ear and conducted by acoustic nerve to brain
• loudness is NOT proportional to intensity
• speech = 40 – 60 Ph

Field of Hearing
• region of sound intensities and frequencies inducing effect of hearing
• plotted as intensity vs frequency
• threshold of pain ≈ 130dB
• region of speaking and region of music found between threshold of hearing and threshold of pain

Weber-Fechner’s Law in Acoustics
• change of loudness ∆L is proportional to relative change of stimulus ∆I/I
ΔL=k. ΔI/I
• describes the dependence of loudness on intensity of its stimulus
• sound perception is subjective, and human ear is sensitive for various frequencies to various extents
• a linear increase of intensity results in a logarithmic increase of loudness

Ultrasound Generators
• frequencies > 20kHz
• produced by mechanical, magnetic, or piezoelectric generators
− piezoelectric generators most important in medicine
− mechanical waves produced by materials vibrating due to an action of high-frequency alternated electrical field in a liquid medium (oil)
− intensities up to 10 W.m-2
• velocity of ultrasound is same as audible sound but has shorter wavelength and higher frequency

Physical principles and diagnostic use of ultrasound
Physical principles
• frequencies > 20kHz
• velocity of ultrasound is same as audible sound but has shorter wavelength and higher frequency
• absorption of ultrasound is frequency dependent
• absorption of ultrasound in gas media is much higher than in liquids
Effects of ultrasound
• mechanical (cavitations)
• thermal (increase of temperature within regions where ultrasound is absorbed)
• physical-chemical (coagulation)
• chemical-electrochemical (decomposition of some highly-molecular compounds, polymerisation)
• biological (structural changes, changes of membrane permeability and conductivity of nerves, changed pH values of tissues, analgesic or spasmolytic effects, increased metabolic exchange)
Diagnostic Use
• imaging techniques in internal medicine and gynaecology
• pulse echo technique; emission of ultrasonic pulses and recording of echo
• visual image of what pulse echoed on (absorption of ultrasound varies according to amount of water present in tissue)
• intensity of ultrasound must not exceed 1.5 W.m-2, or irreversible morphological changes may occur

Audiometry
• done using an audiometer which is a device producing sound waves with adjustable frequency and intensity
• a sound or vibration is produced and the patient indicates the intensity at which they hear/feel the sound waves

5. Optics in Medicine

General classification of electromagnetic waves
• transverse waves
• speed (c) 3 x 108 m.s-1 in a vacuum
• E =cB (E – intensity of electric field, B – intensity of magnetic field)
• no medium necessary for propagation, though field interact with atoms when passing through medium
• intensity of light W.m-2
• span immense range of frequencies/wavelengths
− radiowaves
− infrared λ 700nm – 1mm, vibration and rotation of molecules, perceived by us as heat, used in early detection of tumours (warmer than surrounding tissue)
− visible light λ 360nm – 760nm; violet (400 – 450nm), blue (450 – 520nm), green (520 – 560nm), yellow (560 – 600nm), orange (600 – 625nm), red (625 – 700nm)
− ultraviolet light λ 10 – 400nm, production of Vitamin D in skin (tanning), can kill bacteria and cause cancer in large doses

Planck’s Law, Stefan–Boltzmann Law, Wein’s Law
Planck’s Law
• E = hf = hc/λ
• Planck’s constant h = 6.63 x 10-34 J.s = 4.13 x 10-15 eV.s
• energy of a photon depends on the frequency and wavelength of the wave
Stefan-Boltzmann Law
• energy irradiated by a black body within a unit of time is directly proportional to the fourth power of its absolute temperature
• P/A = σ T4 (P – watts)
• Stefan-Boltzmann constant (s) = 5.67 x 10-8 W.m-2. K -4
• total energy emitted each second by the object, and does not provide any information about the distribution of energy as a function of frequency
Wein’s Law
• take the first derivative of Planck’s Lawsetting it equal to zero solving for wavelength
• Wein’s displacement law states that the wavelength of maximum emission is inversely proportional to temperature.
• λmax = a/T ( where a = Wein’s Constant)

Lens equation
• converging lens, central section thicker than rim. Causes parallel rays to be focused to a real point
• diverging lens, central section thinner than rim. Causes parallel rays to diverge
Thin Lens Formula
• 1/a + 1/b = 1/f (a = object distance, b = image distance, f = focal distance)
• f +ve for converging lens, -ve for diverging lens
Optical Power (dioptre)
• D = 1/f
• D +ve for converging lens, -ve for diverging lens
Transverse/Linear Magnification (m)
• m = -b/a
• if both b and a have same sign then image is inverted

Extinction, Lambert-Beer Law
Extinction
• absorbance
• applied in absorption photometry for measures of concentrations
Lambert-Beer Law
• E = εcmd = logI0/I (ε = molar extinction coefficient, mol-1.m-2)
• defines extinction
• value of molar extinction coefficient depends on kind of molecules of dissolved substance and of the solvent, also function of wavelength of light applied

Scattering of Light
Rayleigh scattering
• elastic scattering induced when light passes through diluted gas
• λ much greater than size of molecule of gas
• intensity of scattered in all directions is very low, though it can be applied to get information about scattering objects
• Is/Io = k(M2/λ4) (Is – intensity of scattered light, Io – incident intensity)
Raman scattering
• scattered light spectrum has shorter or longer wavelength than incident light
• changes to vibration and rotational energy of scattering molecules occur
• probability is low and intensity of spectral lines is weak and undetectable by human eye
• detected by photodetector

Dispersion of Light
• rate of change of refractive index with wavelength
• when a beam of white light (mixture of all visible wavelengths) is incident at an angle to a glass surface, it is dispersed into a spectrum of colours
• each colour has its own angle of deviation relative to the original ray, due to the relationship between refractive index and wavelength

Refraction and Its use in Spectroscopy
Snell’s Law
• n1.sinθ1 = n2.sinθ2
Refraction
• when light enters a medium with a higher refractive index, the ray bends towards the normal
• at some critical angle of incidence (αc) the refracted ray emerges parallel to the boundary
• angle of incidence > αc, light is totally reflected back into the medium of higher refractive index = total internal refraction (can be used in endoscopy)
• n1.sinαc = n2
Refractive index (n)
• ratio of the speed of light in vacuum (c) to the speed in medium (v)
• n = c/v
Spectroscopy
• dispersion of light according to wavelength
• rays refracted by prism, decomposed, pass the objective lens and form the spectrum on an indicator
• in the case of spectroscopy the indicator is the eyepiece
• can be used to identify different molecules according to how they refract light

Interference and light reflection
Interference
• only observed at coherent waves (same frequency/wavelength and differ only by constant phase shift that doesn’t change in time)
• constructive interference (maximum) occurs if the path difference is an integer multiple of the whole wavelength ∆δ = kλ (k = 1,2…)
• destructive interference (minimum) appears if the path difference is an odd number of half wavelength ∆δ = (2k + 1)λ/2
Reflection
• angle of incidence is equal to angle of reflection

Refractometry, Polarimetry
Refractometry
• determination of the power of refraction of the eye. This gives the degree to which the eye differs from normal, which will determine whether or not the patient needs glasses and, if so, how strong they should be
Polarimetry
• polarisation of light is the process of separation of linearly polarized light from the beam of natural light, achieved by reflection or by refraction in dielectrics and by birefringence
• polarimetry is the use of a polarimeter to determine the concentration of the optically active substance
• beam of light from source passes through a filter, polariser, cuvetter and analyser into the objective and eyepiece where it’s intensity is evaluated


Polarimetry:
Measurement of % concentration of polarized dispersion. Polarimetry is a sensitive, nondestructive technique for measuring the optical activity exhibited by inorganic and organic compounds. A compound is considered to be optically active if linearly polarized light is rotated when passing through it. The amount of optical rotation is determined by the molecular structure and concentration of chiral molecules in the substance. Each optically active substance has its own specific rotation as defined in Biots law:


The polarimetric method is a simple and accurate means for determination and investigation of structure in macro, semi-micro and micro analysis of expensive and non-duplicable samples. Polarimetry is employed in quality control, process control and research in the pharmaceutical, chemical, essential oil, flavor and food industries. It is so well established that the United States Pharmacopoeia and the Food & Drug Administration include polarimetric specifications for numerous substances.
Polarization is called the process of separation of linearly polarized light from the beam of natural light. It can be achieved by reflection, birefringerence or by refraction. In polarization by reflection the reflected ray is linearly polarized. At this angle of incidence, reflected and refracted rays are perpendicular therefore we get full eqn of tgøp = n2/n1 øp = known as brewsters angle
With polarization by birefringerence – if a ray of light enters a crystal then birefringerence is observed. Birefringerence occurs in optically anisotropic crystals.

Biophysics of vision
• rays of light from external objects are focused on retina and set up nerve impulses that are transmitted by the optic nerve to the visual area in the brain cortex
• pupil size controlled by iris to control intensity of light entering eye
• accommodation is the ability of the eye to focus objects at different distances by varying the focal length of the lens
• cones specialised to function in daylight, visual acuity best when pupil constricts, found in the fovea centralis for colour and detailed vision
• rod specialised to function in twilight and darkness, found only in periphery of retina
• eye is sensitive to light of wavelengths 400 – 750nm, though wavelengths in this range are not equally effective in stimulating the retina

Eye defects
Emmetropia
• ideal state of the eye in which no refractive error is present
Ametropia
• any deviation from the condition of emmetropia
Hyperopia (Long-sightedness)
• eyeball shorter than focal length
• image is focused behind the retina
• needs converging lens
Presbyopia (Long-sightedness with age)
• eye muscles get weaker or lens hardens
• optical power of the eye is too weak
• needs converging lens
Myopia (Short-sightedness)
• eyeball longer than focal length
• image is focused in front of the retina
• optical power of eye is too high
• needs diverging lens

Absorption Spectral Analysis
• absorption coefficient is a function of wavelength
• absorption is a selective process
• when light passes through a solution of a concentration cm (mol.m-3), the absorption coefficient is proportional to the concentration α = εcm
• E = εcmd = logI0/I (ε = molar extinction coefficient, mol-1.m-2)

Optical Properties of Colloids
Colloid particle
• macromolecule of micelle
• scattering of light takes place when a beam of light passes through a cell containing colloidal dispersion (Tyndal phenomenon)
• intensity of scattered light depends on particle size, therefore measurement of intensity of scattered light can be applied for estimation of concentration in monodisperse colloidal system

Principle of Laser (Light Amplified by Stimulated Emission Radiation)
• source of highly coherent light
• function based on stimulated emission of radiation
• ruby crystal doped with Cr3+ ions
• ions absorb energy and excited to metastable state, remain here for 10-3s, therefore many ions accumulate in this level and inversion occurs (more atoms in excited state than ground state)
• light of energy corresponding to difference between ground state and metastable state passes through crystal, all excited atoms transit to ground state simultaneously resulting in pulse of coherent light of that wavelength
• laser important in medicine in destruction of small size tissues, coagulation of tissues, healing of ulcers etc.

Optical and Electron Microscopes.
Optical microscope
• uses lenses to bend light and magnify and image
• operate in transmission or reflection
• images viewed in eyepiece or digitally captured
• horizontal and vertical controls accurate to a micron
• two incident light sources, halogen lamp and mercury arc lamp



















Electron microscope
• uses beam of electrons moved using magnets which act like lenses
• can magnify over 200,000 times
• scanning electron microscope uses electrons to form an image
• large depth of field, allowing a large amount of sample to be in focus at one time
• produces images of high resolution, closely spaced features can be examined at high magnification




6. Electricity in medicine

Coulomb Law, permittivity
Coulomb Law
• attractive/repulsive force (F) acting between 2 charges, q0 and q is directly proportional to their product and inversely proportional to the squared distance between them
• F = 1/4πε. q0q/r2
Permittivity
• ε is permittivity (F.m-1), ε0 (vacuum) = 8.854 x 10-12 F.m-1
• relative permittivity εrel = ε/ε0
• water has high εrel therefore good solubility of salts in water
• positive ions and smaller ions have a higher hydration number (number of water molecules that lose translation degrees of freedom due to interaction with given ion)
• therefore, cell membranes are more permeable for K+ than Na+

Intensity, voltage, resistance, impedance and their measurements and units
Intensity (I)
• amount of energy transmitted
• I = pef.vef = p2ef/ρc
• W.m-2
Voltage (V)
• electrical potential
• measured with two leads connected to a circuit across the two points defining the voltage to be measured
• volt = joule/coulomb
• V
Resistance (R)
• R = U/I
• total resistance of a conductor of length l and cross-section A, R = ρ( l /A)
Impedance (Z)
• measure for manner and degree a component resists flow of electrical current if a given voltage is applied
• Ohms’s Law Z = V/I
• ohms (Ω)
• differs from resistance in that it takes into account capacity and induction when an alternating voltage is applied to a conductor

Donnan’s equilibrium on cell membrane
Where an ion is on one side of a membrane and it can’t diffuse through the membrane, it will hinder the diffusion of other ions of the same charge towards it and encourage diffusion of opposite charged ions
Donnan’s equilibrium
• in the presence of a nondiffusible ion, the diffusible ions position themselves so that at equilibrium the product of the concentration of the diffusible ions on one side equals that on the other side

Rest membrane potential
• is the potential across the membrane when the cell is at rest (i.e. when there is no signalling activity), interior of cell is negatively charged
• Umem = RT/zF (F – Faraday constant, 96484 C/mol, z – number of elementary charges irrespective of size)
• sometimes called Donnan’s potential
• the potential difference between the internal and external membrane surface is determined by concentration difference of the given ion inside and outside the cell
• at rest, the membrane of nerve cell is significantly more permeable for potassium ions as compared to all other ions present in the intracellular and extracellular fluid
• active transport allows the concentration of potassium ions to be 20 times greater inside the cell than outside

Electrochemical potential
• µ i = µi + zi Fϕ
• work required for transport of 1 mole of the i-th component (ion or electron) inside the given phase, defined as the sum of chemical and electrostatic components

Nernst equation
• used to establish the standard cell potential when the reaction conditions are not standard state
• Ecell = E0 – RT/nF.lnKeq

Measurement of electrical conductivity in solutions
• if one chemical compound (electrolyte) is present in solution then electrical conductivity is proportional to concentration of compound (concentration can be estimated by measuring specific conductivity)
• specific conductivity (S.m-1) is inversely proportional to resistivity κ = 1/ρ, therefore κ = l/qR (R – resistance, l - length of conductor, q – cross section of conductor)
• measurement of specific conductivity realised by using conducting vessel containing two platinum electrodes
• the vessel is located in the Wheatstone bridge circuit (unknown resistance)
• find R by filling vessel with standard solution of known specific conductivity (e.g. 0.1M KCl solution); l/q known as capacity “C” of conducting vessel

Action potential and its detection.
Production of action potential
• during stimulation, ion channels in membrane open and permeability changes for several ions (little for K+, lots for Na+)
• substantial flux of Na+ ions into cell, transpolarisation occurs and the interior of the cell becomes +ve, potential increases from rest membrane potential (≈70mV) to zero
Detection
• axon can be stimulated using two electrodes and some external source of voltage, one electrode inside the axon and the other located on surface
• hyper polarisation – external electrode is +ve and positive charge on axon is increased
• depolarisation – internal electrode positive
• action potential – response when depolarisation reduces rest membrane potential (≈70mV) below threshold potential (≈60mV)

Action potential of heart muscles and their detection
Action potential
• action potential of heart muscle fibre possesses a wide plateau
• heart contracts due to electrical stimulation controlled by the SA node (pacemaker) in the right atrium causing a path of depolarisation to the rest of the heart and the AV nodes
• SA causes atrial contraction, AV causes ventricular contraction
• repolarisation occurs and the cycle repeats
Detection
• an electrocardiogram is used to detect the action potential of the heart
• P region responds to atrial depolarisation
• QRS corresponds to ventricular depolarisation

Principle of oscilloscope
• visualises the voltage that changes periodically in time
• cathode ray tube used, function based on the motion of electric charge in electric field (particle of mass m and charge q in an electric field of the intensity E experiences a force F = qE, and its acceleration is a = qE/m)
• electrons emitted from thin, heated filament, and accelerated by anode (with hole) that they pass through, and concentrated into a fine beam by a negatively charged cylinder
• beam passes between two paris of defection plates and strikes screen coated by phosphorescence material (e.g. ZnS)
• charge of plates deflects beam in horizontal plane and serves for ‘time basis’ of oscilloscope

Use of Electricity in Diagnosis
Electrocardiogram
• monitors heart
• abnormal heart rates: bradycardia = slower rate, tachycardia= faster rate, arrythmia= irregular rate;
Electroencepalogram
• measurement of brain waves; electrical potential across regions of the brain.
• a-wave(8-13 Hz) - light sleep, B-wave (14-100Hz) - neutral activity, ∆-wave (0.3-3.5Hz) - sleep, Omega-wave (4-7Hz) - sleep
• Diagnosis; epilepsy, sleep, brain death.

Use of Electricity in Therapy
• 3 effect of electric current which are Electrolytic/Stimulation/Thermal
• direct current is known to have electrolytic effects which can cause changed stimulation of nerves (high current density can lead to tissue damage)
• low frequency alternating current has weak electrolytic effects because polarity changes in time (not really used in therapy as the current can be dangerous to the heart; if current passes heart, the activity is disturbed and may lead to lethal effects
• high frequency alternating current though are use for thermal effects, it is applied safely for heating the tissues by diathermy

7. Use of X-rays in medicine

Production of x rays, energy spectra?
A - EM waves produced from electrons with high energy striking nuclei of atoms ; λ – 5-120pm E – 0.01 – 0.2 MeV - very high penetrability
Two types 1) Bremsstrahlung – continuos spectrum produced by electron interaction with atomic nuclei
2 - Characteristc – line spectrum produced by electron shells of anode from ionization by electron beam.
Produced in an x ray tube with heated cathode that emits electrons – beam accelerated to anode which emits x rays once struck by electron beam.
Primary effects are luminescence, photographic, ionizing.
Photon E=hf
Power = KU²IZ
Efficiency of x ray tube : ŋ = KUZ
Z variables can be controlled 1) Penetrability ability via accelerating voltage
2) Power via current of anode

Control of the energy and intensity of x rays
A - Energy – penetration ability controlled by the accelerating voltage of the tube, the higher the voltage higher the x ray energy
Intensity – controlled by the current flowing through the anodic current, therefore the intensity can be varied by changing the current in the circuit of the tube

X ray
A - Apparatus consists of x ray tube, cathode, anode, anode must be immersed in coolant (water, oil). A form of ionising radiation used to image some internal structures of the body. Electromagnetic radiation of very short wavelength and very high energy; x-rays have shorter wavelengths than ultraviolet light but longer wavelengths than cosmic rays.

X ray lamp:
A - energy of accelerated e- that strike an anode in the x ray tube is higher than the binding energy of e- in the e- shell of nucleus. Subsequent excitation are e- transition results in production of the line x – ray spectrum since electron energy levels are well defined. Increasing atomic number Z of the target material results in the shift of these line spectra to shorter wavelengths.

X- Ray absorption?
A - Talk about these 2 processes:
-Photoelectric effect – photon transfers its whole energy to an electron, therby ionising the atom. The electron ionises and excites further until energy dissipated producing characteristic x rays.
-compton scattering – in this only a fraction of photon is transferred to electron causing thus the scattering effect. In diagnostic proceses – all dense material in body can be detected by x ray such as bones. Can also detect tumors but x ray will show it as a shadow but it can detect them. (infra red is used as early detection of tumours)
A - X –rays are high energy em waves (high frequency) and therefore are highly penetrating. Therefore, they are only stopped by dense materials but pass though less dense materials. In medicine, the x – ray passes through the less dense soft tissues and is only absorbed by the denser bone tissue. The bone is seen as the unexposed region on the x-ray film (white).
The heavier atoms like metal absorb x-rays. A beam of high energy electrons crashes into a metal target and x-rays are produced. A filter near the x-ray source blocks the low energy rays so only the high energy rays pass through a patient toward a sheet of film. Along with the sheet of film, a second sheet of film prevents the scattered x-rays from fogging the picture. Calcium in bones is considered a type of metal and when photographic film is placed on the body, this allows the technician to take the picture and an x-ray is developed to solve or analyze the problem.

X ray contrast
A - contrast Cr of traditional x ray image resulting from different x ray absorption in various tissues (of various density and effect atomic number) is defined by
Cr = ln I2/I1
I2,I1 are different x ray intensities.

Since linear attenuation coef. Of a bone or soft tissue decreases with increasing incident photon energy, the contrast between bone and soft tissue decreases with increasing accelerating voltage installed on the x ray tube.
The following conclusions can be drawn according to the above equation:
A: contrast is negative
B: contrast doesn’t depend on irradiated object
C: for empty space of thickness Δx the resulting contrast will be positive

Use of X rays for diagnostic purposes

X ray Therapy
A - Used in therapy of malignant tumours. Low energy photons must be cut out from the x-ray beam because of causing surface damage. The HVL(half value layer) reduces initial intensity by 50%. The quality factor gained is : HVL1/HVL2→should be about 1.5. To avoid superficial damage, high energy photons are positioned sufficiently distant from the patient; to avoid deep damage we use law energy photons near to the skin →this is recommended for therapy of superficial lesions. Physicians also need to be protected by shielding. The radiation hazard has to be checked by film dosemeters.

Depth dose
A - This is one of the various types of dose (exposure).Depth dose is that absorbed at a certain depth below the surface. Since intensity of radiation from a point source of radiation decreases proportionally to the squared distance from the source, the depth dose (Dd) observed at a depth d is related to the surface dose (Ds) as: Dd/Ds = FS2/(FS+d)2 FS = distance between X ray tube and body surface.

Computed Tomography
A -This is basically known as a narrow beam that indicates a layer of patients body from various distinctions resulting in a 3-0image calculated by a computer from matrix intensities. I=I0e-^(n∆x+n∆x). In Hospital it is a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays – sometimes you have to inject or swallow readioactive dye – it makes it easier to see all structures – cool stuff.

8. Radioactivity and Ionising Radiation

Radioactive Decay
A - Atoms with unstable nuclei are radioactive →undergo spontaneous decay by emission of a particle or/& a quantum of electromagnetic radiation. “Natural” radioactive nuclei are divided into (1) Light: z ≤75 that have no decay series only stable nuclei. (2) Heavy: z>75 that have a decay series, also exist “artificial” nuclei produced acceleration.
Basic Law of Radioactive Decay: dN/dT= -λN → N=N0e^-λt
Activity : A0=λ No

Energy Spectra of α and β Radiation
A - Decay of heavy radionuclides results in emission of α particle. Paricle composed of 2 portons + 2neutrons. It is the nucleus of Helium 4,2. The nucleus changes according to the scheme : a,zX → 4,2He + a-4,z-2X. KE of α particles is in MeV.
Β decay is known to be an isbaric transmutation of the nucleus. There are 3 types of β decay:
Emisson of Electron: a,z,X→ a,z+1X + 0,-1e+0,0Ve 1,1n→1,1p +0,-1e +0,0Ve Emission of positron 1,1p→ 1,0n +0,1e+0,0Ve

Energy Spectrum of Y Radiation
A - This radiation is represented by photons emitted by the nuclei of radioactive elements. The cobalt gun is used as a source of radiation used in radiotherapy. The known intensity of y-radiation decreases slowly with time since the half-life of this radionuclide is about 5 years. It can serve as therapy by using ionising radiation.

Radioactive equilibrium
A - In a series of radioactive decay, an eqm will be reached where patient + daughter nuclei decay at equal states. Know rate of change of number of parent nuclei is ; dN1/df = λN
Rate of change of daughter nuclei is; dN/dt = λ2N-λ2N2
Know if T1<<T2 then there is no =ions
If T1>T2 then there is no =ion
But if T1>>T2 the=ion is achieved, therefore ratio of number of aren’t +daughter nucleotides equals ratio of their half lives: N1/Ni=T1/Ti

Physical, Biological and Effective Half-Life

Absorption of gamma radiation
A - Gamma radiation is high energy elemcromagnectic radiation, that is highly penetrating. Only dense materials such as lead are capable of absorbing such high energy em radiation.
Gamma rays are electromagnetic radiation given off by an atom as a means of releasing excess energy. They are bundles (quanta) of energy that have no charge or mass and can travel long distances through air (up to several hundred meters), body tissue, and other materials. A gamma ray can pass through a body without hitting anything, or it may hit an atom and give that atom all or part of its energy. This normally knocks an electron out of the atom, ionizing it.
This electron then uses the energy it receives from the gamma ray to create additional ions by knocking electrons out of other atoms. Because a gamma ray is pure energy, it no longer exists once it loses all its energy. The capability of a gamma ray to do damage is a function of its energy, where the distance between ionizing events is large on the scale of the nucleus of a cell.

Q - Absorption of α and β radiation:
A - α - due to relatively large mass and electric charge, the ionisation losses of energy are high and several 1000s of ion pairs may be formed during the absorption of one α particle. Energy losses due to ionisation and excitation are approx 50/50. range is v. small ie at E of 10MeV its about 10cm in air and several µm in soft tissue or water therefore little biological effect.
β- process of ionisation and excitation represents the highest energy losses of electrons during their passage through an absorber , their specific linear ionisation is lower than α because of the lower mass to charge. Bremsstrahlung (high E quanta of EM rad) may be produced due to the interaction of electrons with matter. Intensity of β- beam decreases according to:

I = I0 e -µd ←→ I = I0 e–mk/p (kgm-2)
µd –linear absorption constant,
µk/p mass attenuation coef

Energy loss due to Bremsstrahlung: (dE/dxrad)/(dE/dxion) = EZ/800

Nuclear reactions
A - Know that neutrons react very importantly when it is absorbed in the nucleus. This causes the molecule to become unstable and release particles.
Main formula: X + N = (X+N) = X + EM particles

Cosmic rays?
A - Ionising radiation that falls onto Earth from universe.
Intensity depends upon altitude and geographical width(increase up to 20km then decrease 50km, constant at higher alt.)
Important in nuclear medicine since it results in the background detection of devices used and suitable shielding can decrease its effects.
Primary component:
Radiation that did not interact with atmosphere (fast protons, α particles & 1% of light nuclei)
Proton energy of 10GeV (have detected 1018 eV)
Secondary component:
soft: e-, e+ , photons, protons & light nuclei (shielded by 10cm Pb)
hard: fast mesons, high energy secondary protons, neutrons and all elementary particles

Selective and integral detection of gamma radiation?
A - Selective detection at photopeak, only pulses with amplitude greater than the lower discrimination level and lower than the upper discriminatoion level are registered; good for spatial resolution of head, lowercosmic detection and lower scattered detection.
Integral – all pulses higher than set level are counted, total no of pulses proportional to area beneath curve of number of pulses plotted.

Principles of detection of ionizing radiation
Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because they have an excess of energy or mass or both.
Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation.
Types of ionizing radiation.
Alpha particles (He2+ nucleus)
Beta particles (β-)
Gamma rays (photons)
Neutrons (uncharged nucleon)
Geiger-Muller counter. This device consists of two parts, a detecting tube and a counter. The heart of the system is the detecting tube, which consists of a pair of electrodes surrounded by an ionizable gas. As radiation enters the tube, it ionizes the gas. The ions produced travel toward the electrodes, between which there is a high voltage. The ions cause pulses of current at the electrodes, which are picked up and recorded on the counter. The Geiger tube is most sensitive to beta radiation. Gamma radiation can pass right through the tube without being counted, and some alpha radiation can't make it through the window of the tube. The Geiger-Muller counter indicates the counts per minute of radiation entering the tube, but it doesn't tell you the energy of the radiation.
A scintillation counter is a device that not only counts radioactivity, but also enables the operator to determine the energy of the radiation.
Film badges are small portable devices that are worn by people such as x-ray technicians and nurses, who may be exposed to radiation. The badge contains a piece of photographic film that is removed monthly and developed. The darker the film badge, the greater the degree of exposure.

Detectors of ionising radiation?
A - Three types of detectors are present, these are the scintillation detector/Geiger muller and the cloud chamber. The scintillation detector consists of 3 parts: The scintillator/Photomultiplier and the last part is the electronic parts. What happens in the detector is that excitation of atoms from the scintillator and photons are emitted during dexitation. Photon hits cathode of photomultiplier causes electron emission from photoelectric effect. The electrons reach the first dynode with lowest voltage. After impact, secondary electrons are ejected and attracted to the second dynode with a higher more positive. Therfore many electrons are ultimately formed. Geiger muller tube is detection of beta radiation. It consists of a cathode and an anode. B enter ionisation chamber and ionise particles inside the GM tube – this causes electrical impulse to occur and therefore radiation can be detected.

Scintillation detector
A - Consists of 3 parts 1) Scintillator – radiation energy transferred to luminous E 2) Photomultiplier – detects scintillations 3) electronic parts.
Detection – excitation of atoms from radiation in scintillator
-photon hits cathode of photomultiplier causing electron emission from photoelectric effect. -photon emitted from deexitation
- 8-14 dyanodes of p.m. 1st dynode has lowest voltage, it ejects z electron more with higher voltage which leads to amplification (10)5 – (10)7
-avalanche of electrons come to final dyanode and create a pulse of voltage at anode, the pulse is amplified and measured.

Geiger muller tube function and its characteristics:
A - used for beta radiation, consists of a cathode and anode and tungsten wire,tube filled with inert gas. A high voltage is loaded between cathode and anode ( (10)2 – (10)3 V )
Beta enters causing ionisation of (Ar) accelerated ions cause further ionisation leading to an avalanche of electrons, the pulse is then registered.

Accelerators of particles

Ionization Chamber
A - This is basically a capacitor with 2 electrodes filled with air. Electrons +positively charged ions are produced in the ionisation chamber and then attracted to its electrodes. Therefore, an electric current flowing through the chamber can be registered. It particles are exposed to some radiation and 80 ionised. The produced ions can disappear at the electrodes/Chamber walls. Ions with charge e move in electric field due to force F=eE where E is intensity of electric field. This all cell due because of the presence of voltage difference between the electrodes. Ionisation chambers are used as pocket personal dosimeters for evaluation of exposure to radiation.

Methods of personal dosimetry
A - Based on 3 interactions of radiation with matter
(1) Film-Dosimetry” (photographic emulsion) – emulsion sensitive to ionizing radiation and does is measured based on its blackening, not accurate below mc/kg
(2) Thermoluminesence Dosimetry (excitation)- powdered LiF in rods 1mm &3mm^2 are excited permanently and subsequent heating to 100C causes dexcitation, good for 3mnths because resistant to humidity 7 t.
(3) “Pocket Dosimetry-ionizing- sml ionization chamber with loaded charge is slowly decharged by ionizing effects; very sensitive to humidity.

Units of exposition and absorbed dose of irradiation

Use these as a guideline but be careful to make sure that the answers are correct according to the textbook. Remember that these are a student's answers, not the gospel truth!The professors are very keen on equations and units so once you have learnt the theory, be sure to have at least one equation memorised per question where possible. If you can write down an equation they will love you!