Radiology is concerned with the application of radiation to Radiology is concerned with the application of radiation to the human body for diagnostically and therapeutically purposes.the human body for diagnostically and therapeutically purposes.This requires an understanding of:This requires an understanding of:

• the basic nature of radiationthe basic nature of radiation

• interaction between radiation and matterinteraction between radiation and matter

• radiation detectionradiation detection

• biological effects of radiationbiological effects of radiation

to evaluate the advantages and disadvantages of the various to evaluate the advantages and disadvantages of the various medical applications of radiation and its limitations.medical applications of radiation and its limitations.

There are various kind of radiation which can be classified in There are various kind of radiation which can be classified in electromagnetic radiation (EM) and particle radiation (p). The electromagnetic radiation (EM) and particle radiation (p). The X-raysX-rays and and -rays-rays are part of the electromagnetic spectrum; both have a wavelength are part of the electromagnetic spectrum; both have a wavelength range between range between 1010-4 -4 and 10and 1011 nm nm, they differ only in their origin., they differ only in their origin.

Nature and Origin of RadiationNature and Origin of Radiation

When interacting with matter EM-radiation shows particle like behavior.When interacting with matter EM-radiation shows particle like behavior.

The 'particles' are called photons. The energy of the photon The 'particles' are called photons. The energy of the photon and the frequency and the frequency (or wavelength (or wavelength ) of the EM-radiation are ) of the EM-radiation are determined by the Planck constant h:determined by the Planck constant h:

h=6.62h=6.62-34-34 J J s = 4.12 s = 4.12 1010-21-21 MeV MeVss

The photon energy for X-rays and The photon energy for X-rays and -rays is in the eV to MeV range.-rays is in the eV to MeV range.

X-rays originate either from characteristic deexcitation X-rays originate either from characteristic deexcitation processes in the atoms (Kprocesses in the atoms (K, K, K transitions) (Characteristic X-rays). transitions) (Characteristic X-rays). The photon energy corresponds to the difference in binding energy of The photon energy corresponds to the difference in binding energy of the electrons in the excited levels to the K-level.the electrons in the excited levels to the K-level.

X-rays also originate from energy loss of high energy X-rays also originate from energy loss of high energy charged particles (e.g. electrons) due to interaction with the charged particles (e.g. electrons) due to interaction with the atomic nucleus (atomic nucleus (bremsstrahlungbremsstrahlung))

The X-rays have a smooth energy spectrum, The X-rays have a smooth energy spectrum, due to the continues energy loss effects in the due to the continues energy loss effects in the Coulomb field of the nucleus.Coulomb field of the nucleus.

-rays have typically higher energies than X-rays. They -rays have typically higher energies than X-rays. They originate mainly from deexcitation processes within the nucleus. originate mainly from deexcitation processes within the nucleus. The nucleus of mass M is characterized by Z protons of mass The nucleus of mass M is characterized by Z protons of mass mp and N neutrons of mass mmp and N neutrons of mass mnn. The mass number A=Z+N.. The mass number A=Z+N.example:example: 1818

88OO1010. . AAZZElementElementZZ

The binding energy BE of the nucleus is the The binding energy BE of the nucleus is the difference between the mass of the nucleus and the difference between the mass of the nucleus and the mass of the Z protons and N neutrons.mass of the Z protons and N neutrons.

The mass is often expressed in terms of The mass is often expressed in terms of amu (atomic mass units) which is defined byamu (atomic mass units) which is defined by

As higher the binding energy as more stable is the As higher the binding energy as more stable is the nucleus. The binding energy is often calculated in terms of nucleus. The binding energy is often calculated in terms of the mass excess:the mass excess:

As higher the binding energy as more stable is the As higher the binding energy as more stable is the nucleus. The binding energy is often calculated in terms of nucleus. The binding energy is often calculated in terms of the mass excess:the mass excess:

EXAMPLE binding energy for EXAMPLE binding energy for 1818OO

Nuclei with equal Z but different A, N are called Nuclei with equal Z but different A, N are called isotopesisotopes

the three stable oxygen isotopes are:the three stable oxygen isotopes are: 161688OO88, , 1717

88OO99, , and and 181888OO1010

Nuclei with equal N but different A, Z are called Nuclei with equal N but different A, Z are called isotonesisotones

three N=10 isotones are: three N=10 isotones are: 171777NN1010, , 1818

88OO1010, and , and 191999FF1010

Nuclei with equal A but different Z, N are called Nuclei with equal A but different Z, N are called isobarsisobars

three A=18 isobars are: three A=18 isobars are: 181877NN1111, , 1818

88OO1010, and , and 181899FF99

All these nuclei have different binding energies All these nuclei have different binding energies because they differ in the number of protons and neutrons because they differ in the number of protons and neutrons from each other.from each other.

The nucleus can be in higher excitation if it rotates The nucleus can be in higher excitation if it rotates (rotational energy), if it vibrates ((rotational energy), if it vibrates (vibrationalvibrational energyenergy), if the single ), if the single particles are in higher quantum mechanically allowed states particles are in higher quantum mechanically allowed states (single particle excitation).(single particle excitation).

-emission-emission occurs by deexcitation of a high excitation occurs by deexcitation of a high excitation level of the nucleus to the ground state. The energy difference level of the nucleus to the ground state. The energy difference between the two excited states corresponds to the energy of between the two excited states corresponds to the energy of the the -radiation.-radiation.

Particle radiation is typically induced by decay processes of the Particle radiation is typically induced by decay processes of the nucleus. In these decay processes an internal reorganization of the nucleus. In these decay processes an internal reorganization of the nucleons takes place by which a more energeticallynucleons takes place by which a more energetically favorable state can favorable state can be reached (minimum of mass, maximum in binding energy).be reached (minimum of mass, maximum in binding energy).

In In -decay -decay processes a neutronprocesses a neutron is converted is converted into a proton by electroninto a proton by electron emissionemission ( (---decay-decay), or a ), or a proton is converted in proton is converted in a neutron by positron emissiona neutron by positron emission ( (++-decay-decay):):

-radiation are electrons which are emitted in the decay -radiation are electrons which are emitted in the decay process with a certain kinetic energy which originates from the process with a certain kinetic energy which originates from the energy difference between the decaying nucleus (energy difference between the decaying nucleus (mothermother) and the ) and the decay product (decay product (daughterdaughter). As part of the energy is distributed to a ). As part of the energy is distributed to a third particle (third particle (neutrinoneutrino) the ) the -spectrum of a particular decay -spectrum of a particular decay process is a smooth distribution.process is a smooth distribution.

The released energy is The released energy is translated into the kinetic energy of translated into the kinetic energy of the emitted a-particle and the heavy the emitted a-particle and the heavy recoil nucleus.recoil nucleus.

In In -decay-decay processes the nucleus reduces his mass by emitting a processes the nucleus reduces his mass by emitting a 4422HeHe22 (helium) nucleus ( (helium) nucleus (-particle) to reach a less massive state.-particle) to reach a less massive state.

-decay occurs in particular for heavy massive nuclei. The kinetic -decay occurs in particular for heavy massive nuclei. The kinetic energy of the emitted energy of the emitted a a particles is determined by the mass of the mother and particles is determined by the mass of the mother and daughter system.daughter system.

Neutron decayNeutron decay occurs either as consequence of a preceding occurs either as consequence of a preceding -decay-decay, , ((-delayed neutron decay-delayed neutron decay) or as a result of a reaction of fission ) or as a result of a reaction of fission process.process.

In most cases concerned with medical applications neutrons are In most cases concerned with medical applications neutrons are originated in fission, the splitting of a heavy nucleus in two approximately originated in fission, the splitting of a heavy nucleus in two approximately equally massed smaller nuclei.equally massed smaller nuclei.

oror

Natural Decay LawNatural Decay Law

The rate of the decay process is determined by the activity The rate of the decay process is determined by the activity A A (number of decay processes per second) of the radioactive sample. (number of decay processes per second) of the radioactive sample.

The activity is proportional to the number of radioactive nuclei (radionuclide)The activity is proportional to the number of radioactive nuclei (radionuclide)

is the decay constant!is the decay constant!

Differential equation for Differential equation for N(t)N(t) can be solved can be solved

N(tN(t00), ), AA(t(t00) are the initial number of radionuclides and ) are the initial number of radionuclides and initial activity, respectively.initial activity, respectively.

The half life The half life tt1/21/2 of a radionuclide is the time by which the of a radionuclide is the time by which the number of radionuclides has reduced to 50%.number of radionuclides has reduced to 50%.

This shows a direct correlation This shows a direct correlation between half life and decay constant for between half life and decay constant for each radionuclide.each radionuclide.

The lifetime The lifetime r r of a nucleus is defined by:of a nucleus is defined by:

Quite often the expression Quite often the expression “lifetime” can be found for radionuclides.“lifetime” can be found for radionuclides.

This means that after a period corresponding to the “lifetime”This means that after a period corresponding to the “lifetime” of a radioactive nucleus the initial abundance has decreased to 36.8% of of a radioactive nucleus the initial abundance has decreased to 36.8% of its initial value, of a nucleus can be found!its initial value, of a nucleus can be found!

Unit for Unit for exposure exposure EE is theis the Roentgen [R]Roentgen [R] which is defined by thewhich is defined by the ionization between EM-radiation and air. 1 ionization between EM-radiation and air. 1 Roentgen is the amount of EM-radiation which produces in 1 gram of air Roentgen is the amount of EM-radiation which produces in 1 gram of air 2.58 2.58 1010-7-7 C at normal temperature (22°C) and pressure (760 Torr) C at normal temperature (22°C) and pressure (760 Torr) conditions.conditions.

Dosimetry UnitsDosimetry Units

Due to the interaction between radiation and material Due to the interaction between radiation and material ionization occurs in the radiated material! (Energy transfer from the ionization occurs in the radiated material! (Energy transfer from the high energetic radiation photons or particles to atomic electrons.) The high energetic radiation photons or particles to atomic electrons.) The ionization can be used as measure for the amount of exposure which ionization can be used as measure for the amount of exposure which the material had to radiation.the material had to radiation.

1 R = 2.58 1 R = 2.58 1010-4-4 C/kg C/kg

The The exposure rate exposure rate ERER (= ionization/time) can be related (= ionization/time) can be related to the to the activity activity AA of a source (in units mCi) viaof a source (in units mCi) via::

F is the exposure constant in units F is the exposure constant in units [ (R[ (Rcmcm22) / (h) / (hmCi) ]mCi) ], , and d is the distance between source and material in units [cm]. The and d is the distance between source and material in units [cm]. The exposure constant is characteristical for the radiation source:exposure constant is characteristical for the radiation source:

TheThe absorbed doseabsorbed dose DD of radiation in any kind of of radiation in any kind of material depends on the typical ionization energy of the particular material depends on the typical ionization energy of the particular material. The absorbed dose is defined in terms of the absorbed material. The absorbed dose is defined in terms of the absorbed radiation energy per mass radiation energy per mass WW1P 1P ..

It therefore clearly depends on the energy loss behavior It therefore clearly depends on the energy loss behavior of the various kinds of radiation.of the various kinds of radiation.

The unit for the absorbed dose isThe unit for the absorbed dose is::

1 Gray 1 Gray = = 1Gy = 1 J/kg = 101Gy = 1 J/kg = 1044 erg/kg = 100 rad erg/kg = 100 rad

The average ionization energy for air is The average ionization energy for air is WW1P1P 34 eV/ion. With 34 eV/ion. With 1 eV = 1.6022 1 eV = 1.6022 1010-19-19J and the charge per ion is 1.6J and the charge per ion is 1.61010-19-19, this yields for , this yields for the absorbed dose in air D for 1 R exposure of EM radiation:the absorbed dose in air D for 1 R exposure of EM radiation:

D D = = 11 R • 34 J/C R • 34 J/C = = 2.58 2.58 1010-4-4 C/kg C/kg 34 J/C = 8.8 34 J/C = 8.8 1010-3-3 J/kg = J/kg =8.8 8.8 1010-3-3 Gy = 0.88 rad Gy = 0.88 rad

The average ionization energy depends critically on the material.The average ionization energy depends critically on the material.

There is an empirical relation between the amount of There is an empirical relation between the amount of ionization in air and the absorbed dose for a given photon ionization in air and the absorbed dose for a given photon energy and absorber (body tissue).energy and absorber (body tissue).

The absorbed dose in rads per roentgen of exposure is The absorbed dose in rads per roentgen of exposure is known as the known as the roentgen-to-rad conversion factor Croentgen-to-rad conversion factor C

C is approximately equal to one for soft body tissue in the C is approximately equal to one for soft body tissue in the energy range of diagnostic radiology.energy range of diagnostic radiology.

The increase for bone material is due to higher The increase for bone material is due to higher photoelectric absorption cross section for low energy photons.photoelectric absorption cross section for low energy photons.

Dose (rad) = Exposure (R) x R to Rad Conversion factorDose (rad) = Exposure (R) x R to Rad Conversion factor

Exposure, exposure rate and absorbed dose are independent of Exposure, exposure rate and absorbed dose are independent of the nature of radiation. Biological damage depends mainly on the energy the nature of radiation. Biological damage depends mainly on the energy loss of the radiation to the body material. These energy losses differ loss of the radiation to the body material. These energy losses differ considerably for the various kinds of radiation. To assess the biological considerably for the various kinds of radiation. To assess the biological effects of the different kind of radiations better, as new empirical unit the effects of the different kind of radiations better, as new empirical unit the dose equivalent Hdose equivalent H is introduced:is introduced:

DOSE EQUIVALENTDOSE EQUIVALENT

with the quality factor Q which depends strongly on the ionization power of the with the quality factor Q which depends strongly on the ionization power of the various kinds of radiation per path length. In first approximation Qvarious kinds of radiation per path length. In first approximation QZ of radiation Z of radiation particles, Q(particles, Q(, X, , X, ) ) 1.1.

As higher Q as higher the damage the radiation does!As higher Q as higher the damage the radiation does!

EFFECTIVE DOSEEFFECTIVE DOSE

The various body organs have The various body organs have different response to radiation. To different response to radiation. To determine the specific sensitivity to determine the specific sensitivity to radiation exposure a tissue specific radiation exposure a tissue specific organ weighting factor organ weighting factor wwTT has been has been established to assign a particular organ established to assign a particular organ or tissue or tissue TT a certain exposure risk.a certain exposure risk.

The given weighting factors in the table imply for example that an The given weighting factors in the table imply for example that an equivalent dose of 1 mSv to the lung entails the same probability of damaging equivalent dose of 1 mSv to the lung entails the same probability of damaging effects as an equivalent dose to the liver of (0.12/0.05) effects as an equivalent dose to the liver of (0.12/0.05) 1 mSv = 2.4 mSv1 mSv = 2.4 mSv

The sum of the products of the equivalent dose to the organ The sum of the products of the equivalent dose to the organ HHTT and the and the weighting factor weighting factor wwTT for each organ irradiated is called the effective dose for each organ irradiated is called the effective dose HH::

H HT TT

Like HLike HTT, H, H is expressed in units Sv or rem!. is expressed in units Sv or rem!.

Supernova remnants

Man is exposed to different kind of natural occurring Man is exposed to different kind of natural occurring radiation. That includes radiation from outer space as well as radiation. That includes radiation from outer space as well as radiation from natural sources on earth.radiation from natural sources on earth.

Outer space originated Outer space originated radiation is mainly absorbed by the radiation is mainly absorbed by the atmosphere.atmosphere.

Ultraviolet (UV) radiation in the sunlight Ultraviolet (UV) radiation in the sunlight as part of the solar spectrumas part of the solar spectrum

Cosmic Rays are high energetic Cosmic Rays are high energetic particles, originated in the solarparticles, originated in the solarflares at the surface of stars or in flares at the surface of stars or in supernova explosions over the supernova explosions over the lifetime of our galaxy.lifetime of our galaxy.

Sources of natural terrestrial radioactivitySources of natural terrestrial radioactivity

Radioactivity originating from the natural decay chains, Radioactivity originating from the natural decay chains, long lived long lived -emitters. -emitters.

There are four natural decay chains:There are four natural decay chains:

Uranium series: Uranium series: 2382389292U U 206206

8282PbPb

Actinium seriesActinium series : : 2352359292U U 207207

8282PbPb

Thorium seriesThorium series : : 2322329090Th Th 208208

8282PbPb

Neptunium seriesNeptunium series : : 2412419494Pu Pu 209209

8282PbPb

There are several long-lived members of the decay chain. The resulting radioactivity is found in natural environment, but particularly enriched in uranium and radium quarries.

Particularly important is the noble gas radon-222 Particularly important is the noble gas radon-222 2222228686Rn, Rn,

which is a member of the uranium series.which is a member of the uranium series.

It decays by It decays by -emission-emission with a half life of with a half life of tt1/21/2=3.82=3.82 days. Because of its gaseous character it can diffuse out of days. Because of its gaseous character it can diffuse out of the rock and mix into the air where it can be inhaled. the rock and mix into the air where it can be inhaled. Outside its concentration is low because of the dilution in Outside its concentration is low because of the dilution in air, but in closed rooms like basements its concentration air, but in closed rooms like basements its concentration can be quite large.can be quite large.

Once inhaled, the majority of the dose is Once inhaled, the majority of the dose is deposited in the trachea-bronchial region by the decay of deposited in the trachea-bronchial region by the decay of the short-lived daughters, the short-lived daughters, 218218PoPo and and 214214PoPo, which are both , which are both -emitters-emitters..

The radon-problem is therefore mainly due to -bombardment of sensitive lung tissue, which can cause cancer.

The second largest source for natural background activity The second largest source for natural background activity comes from the long-lived radioisotope comes from the long-lived radioisotope 4040K.K.

half life of thalf life of t1/21/2 = 1.28 = 1.28 101099 years. years.

natural isotopic abundance is natural isotopic abundance is 0.0118 %.0.0118 %.

It decays by It decays by decay, Edecay, E 1.3 1.3 MeV (89%) and by MeV (89%) and by -decay, E-decay, E = 1.46 MeV (11 %).= 1.46 MeV (11 %).

This isotope is a strong source for natural internal and external This isotope is a strong source for natural internal and external radiation exposure, since potassium is a natural constituent for body radiation exposure, since potassium is a natural constituent for body tissue like skeletal muscles and bones. It is also an important regulator for tissue like skeletal muscles and bones. It is also an important regulator for cell processes (see information transfer in nerve cells). In addition K is cell processes (see information transfer in nerve cells). In addition K is also frequent in external materials as stone or concrete.also frequent in external materials as stone or concrete.

NN 0.000118 0.0001180.00030.000380 kg = 0.00294 g.80 kg = 0.00294 g.40 g = 6.02240 g = 6.02210102323 atoms atomsNN 4.44 4.4410101919 4040K atoms K atoms in the whole body: in the whole body: AA 2.44 2.4410101010 decays/yr decays/yr

The whole body activity on 40K is:The whole body activity on 40K is:

A(A(4040K) = K) = N N = = 5.45.41010-10-10 [1/yr] N [1/yr] N 0.03% of the body 0.03% of the body material is kalium (25 g potassium).material is kalium (25 g potassium).

Therefore the natural abundance of 40K in body tissue is:Therefore the natural abundance of 40K in body tissue is:

This corresponds to a whole body activity of A This corresponds to a whole body activity of A 764 Bq 764 Bq

Assuming that the entire radiation is absorbed in the body tissue, the Assuming that the entire radiation is absorbed in the body tissue, the whole body exposure is: whole body exposure is: ERER ( A ( A 0.8 MeV) / 80 kg = 4 0.8 MeV) / 80 kg = 4 1.6 1.6 1010-15-15 J/kg = 3.8 J/kg = 3.8 1010-5-5 J/(kg J/(kg yr) = 3.80 yr) = 3.80 1010-5-5 Gy/yr = 38 mrad/yr Gy/yr = 38 mrad/yr

With an quality factor of With an quality factor of Q Q 1 1 the equivalent dose rate the equivalent dose rate DR DR is: is:

DR DR 38 mrem/year 38 mrem/year

The external dose from 40K is in the same order of magnitude 28 mrem/yr.

There is considerable exposure due to artificially produced sources!

Possibly largest contributor is tobacco which Possibly largest contributor is tobacco which contains radioactive contains radioactive 210210PoPo which emits 5.3 MeV which emits 5.3 MeV particles particles with an half life of with an half life of TT1/21/2=138.4days=138.4days..

During smoking process During smoking process 210210Po is absorbed by the bronchial systemPo is absorbed by the bronchial system

Lungs are exposed to radiation!

Only estimates are available which suggest that smokers Only estimates are available which suggest that smokers receive an equivalent dose rate of: receive an equivalent dose rate of: HRHRTT=16 rem/y = 160 mSv/year=16 rem/y = 160 mSv/year

Using the lung tissue weighting factor Using the lung tissue weighting factor TT==0.120.12::the total effective dose rate will be the total effective dose rate will be HRHR=1.9 rem/y =19 mSv/y=1.9 rem/y =19 mSv/y

Averaged over the entire smoking and nonsmoking US population this yields an annual effective dose of 280 mrem =2.8 mSv!

The other considerableThe other considerable exposureexposure sources are:sources are:

• fall-out from nuclear bomb testing between 1945 - 1980 (fall-out from nuclear bomb testing between 1945 - 1980 (1mrem/yr)1mrem/yr)

• nuclear power plants and nuclear laboratories (w 0.05 mrem/yr)nuclear power plants and nuclear laboratories (w 0.05 mrem/yr)

• inhaling radioactivity while smoking ( inhaling radioactivity while smoking ( 200 - 300 mrem/yr average) 200 - 300 mrem/yr average)

Often mentioned contributor to man-made radiation exposure is the fall-out from the 450 thermonuclear born tests performed between 1945 and 1980 (test ban).

Other products are Other products are 33H (12 y), H (12 y), 5454Mn Mn (312 d), (312 d), 136136Cs (13 d), Cs (13 d), 137137Cs (30 y) Cs (30 y) relatively relatively short-lived products in comparison with short-lived products in comparison with 1414C .C .Large fraction has since decayed.Large fraction has since decayed.

Main fall out product is Main fall out product is 1414C (70%) with TC (70%) with T1/21/2= 5730 y= 5730 y

Today's average effective dose 1 mrem = 10Sv

Estimated Average Total Effective Dose Rate in the United Estimated Average Total Effective Dose Rate in the United States from Various Sources of Natural Background RadiationStates from Various Sources of Natural Background Radiation

There is no direct evidence There is no direct evidence of radiation-induced genetic effects in of radiation-induced genetic effects in humans, even at high doses. Various humans, even at high doses. Various analyses indicate that the rate of analyses indicate that the rate of genetic disorders produced in genetic disorders produced in humans is expected to be extremely humans is expected to be extremely low, on the order of a few disorders low, on the order of a few disorders per million live born per rem of per million live born per rem of parental exposure.  parental exposure. 

The potential biological effects and damages caused by The potential biological effects and damages caused by radiation depend on the conditions of the radiation exposure.radiation depend on the conditions of the radiation exposure.

The different kinds of radiation have different energy loss effects The different kinds of radiation have different energy loss effects LET.LET.

It is determined by:It is determined by:

quality of radiation quality of radiation

quantity of radiation quantity of radiation

received dose of radiation received dose of radiation

exposure conditions (spatial distribution) exposure conditions (spatial distribution)

Energy loss effects depends on nature and probability of interactionEnergy loss effects depends on nature and probability of interactionbetween radiation particle and body material.between radiation particle and body material.

Particles with high energy loss effects cause typically greater damage.Particles with high energy loss effects cause typically greater damage.

To normalize these effects as an empirical parameter the To normalize these effects as an empirical parameter the RRelativeelative BBiologicaliological EEffectiveness ffectiveness RBERBE of radiation for producing a of radiation for producing a given biological effect is introduced:given biological effect is introduced:

The The RBERBE for different kinds of radiation can be expressed in terms of for different kinds of radiation can be expressed in terms ofenergy loss effects energy loss effects LETLET..

For low LET radiation, For low LET radiation, RBE RBE LET LET, for higher LET the RBE , for higher LET the RBE increases to a maximum, the subsequent drop is caused by the overkill increases to a maximum, the subsequent drop is caused by the overkill effect. effect.

These high energies are sufficient to kill more cells than actually available!These high energies are sufficient to kill more cells than actually available!

Radiation damage to body organs, tissue, and cells is a Radiation damage to body organs, tissue, and cells is a purely statistical effectpurely statistical effect

As higher the radiation dose as more likely some effects will As higher the radiation dose as more likely some effects will occur. As higher the occur. As higher the LETLET and/orand/or the the RBERBE as more likely damage may as more likely damage may occur. The effects are typically described by empirical occur. The effects are typically described by empirical dose-responsedose-response curvescurves..

Schematic representation of dose-response function Schematic representation of dose-response function E(D) E(D) at low doses D at low doses D for high-LET (curve H) and low-LET (curve Lfor high-LET (curve H) and low-LET (curve L11,) radiations. L,) radiations. L22 is the is the extension of the linear beginning of Lextension of the linear beginning of L11..

Radiation can cause immediate effects (Radiation can cause immediate effects (radiation radiation sicknesssickness), but also long term effects which may occur many ), but also long term effects which may occur many years (years (cancercancer) or several generations later () or several generations later (genetic effectsgenetic effects).).

Biological effects of radiation result from both direct and Biological effects of radiation result from both direct and indirect action of radiation.indirect action of radiation.

Direct action is based on direct interaction between Direct action is based on direct interaction between radiation particles and complex body cell molecules, (radiation particles and complex body cell molecules, (for example for example direct break-up of DNA moleculesdirect break-up of DNA molecules))

Indirect action is more complex and depends heavily on the Indirect action is more complex and depends heavily on the energy loss effects of radiation in the body tissue and the subsequent energy loss effects of radiation in the body tissue and the subsequent chemistry.chemistry.

1.1. Radiation deposits energy into the body tissue by energy Radiation deposits energy into the body tissue by energy loss effectsloss effects

compton scattering, photo-excitation for compton scattering, photo-excitation for - and X-rays- and X-rays

scattering and ionization processes for scattering and ionization processes for -, p, n-particles (LET)-, p, n-particles (LET)

2.2. Energy loss causes ionization and break-up of simple body Energy loss causes ionization and break-up of simple body molecules:molecules:

HH22O O H H++ + OH + OH

3.3. OHOH radical attacks DNA-molecule. radical attacks DNA-molecule.

4.4. Resulting biological damage depends on the kind of alteration andResulting biological damage depends on the kind of alteration andcan cause cancer or long-term genetic alterations.can cause cancer or long-term genetic alterations.

RADIATIONRADIATION

DIRECT IONIZATIONDIRECT IONIZATIONOF DNA OF DNA

IONIZATION OFIONIZATION OFOTHER MOLECULES, e.g.,HOTHER MOLECULES, e.g.,H22OO

radiation + Hradiation + H22O O H H22OO++ + e + e

HH22OO++ H H++ + OH + OH00

ee + H + H22O O H H00 + OH + OH

OXIDATION OF DNAOXIDATION OF DNA BY OH RADICALS BY OH RADICALS

NO EFFECTNO EFFECTENZYMATIC REPAIRENZYMATIC REPAIR

CHEMICALCHEMICALRESTORATIONRESTORATION

DNADNARESTOREDRESTORED

PERMANENT DAMAGE IN DNAPERMANENT DAMAGE IN DNA

BIOLOGICAL EFFECTSBIOLOGICAL EFFECTS1. GENETIC EFFECTS1. GENETIC EFFECTS

2. SOMATIC EFFECTS2. SOMATIC EFFECTSCANCERCANCER

STERILITYSTERILITY

The time scales for the short and long term effects of radiation are The time scales for the short and long term effects of radiation are symbolized in the figure and listed in the tablesymbolized in the figure and listed in the table

There are many biological effects a high dose of radiation can cause: There are many biological effects a high dose of radiation can cause:

The results are based on several data sources on radiation The results are based on several data sources on radiation exposure to humans exposure to humans

survivors of the atomic bomb detonations at Hiroshima and Nagasaki survivors of the atomic bomb detonations at Hiroshima and Nagasaki

medical exposure to patients (in particular in the early forties and fifties) medical exposure to patients (in particular in the early forties and fifties)

evaluations of populations with high occupational exposure evaluations of populations with high occupational exposure

evaluations of populations with high radiation background (high altitude) evaluations of populations with high radiation background (high altitude)

Skin EffectsSkin Effects

The first evidence The first evidence of biological effects of of biological effects of radiation exposure appears radiation exposure appears on the exposed skin. on the exposed skin.

The different stages The different stages depend on the dose and on depend on the dose and on the location of the exposure. the location of the exposure.

Acute Radiation SyndromeAcute Radiation Syndrome

The body consists of cells of different radiation sensitivity, a The body consists of cells of different radiation sensitivity, a large dose of radiation delivered acutely does larger damage than large dose of radiation delivered acutely does larger damage than the same does delivered over a long period of time. the same does delivered over a long period of time.

The body response to a large acute dose manifests itself in The body response to a large acute dose manifests itself in the the acuteacute radiation syndromeradiation syndrome..

The first (prodomal) symptoms show up after The first (prodomal) symptoms show up after 6 hours 6 hours

These symptoms subside during the These symptoms subside during the latent period, which lasts between one latent period, which lasts between one (high doses) and four weeks (low doses) (high doses) and four weeks (low doses) and is considered an incubation period and is considered an incubation period during which the organ damage is during which the organ damage is progressing progressing

The latent period ends with the onset of The latent period ends with the onset of the clinical expression of the biological the clinical expression of the biological damage, the damage, the manifest illness stagemanifest illness stage, , which which lasts two to three weeks lasts two to three weeks

Survival of the manifest illness stage practically guaranties full recovery Survival of the manifest illness stage practically guaranties full recovery of the patientof the patient

The severity and the timescale for the acute radiation syndromeThe severity and the timescale for the acute radiation syndromedepends on the maximum delivered dose. depends on the maximum delivered dose.

The first symptoms show up after The first symptoms show up after 6 hours 6 hours

If the whole body exposure exceeds a critical threshold rate of If the whole body exposure exceeds a critical threshold rate of 50 -100 rad the symptoms show up more rapidly and 50 -100 rad the symptoms show up more rapidly and

drastically.drastically.

Long term radiation risks are more difficult to assess. Long term radiation risks are more difficult to assess. The predictions are based on the use of risk models.The predictions are based on the use of risk models.

The main problem are the insufficient statistical long term data The main problem are the insufficient statistical long term data about radiation victims which make reliable model predictions difficult.about radiation victims which make reliable model predictions difficult.

In particular for low LET exposure linear and quadratic dose-In particular for low LET exposure linear and quadratic dose-response models differ considerably in their risk assessment response models differ considerably in their risk assessment

The risk assessment depends on the age of the exposed The risk assessment depends on the age of the exposed person, different organs have a different response to radiation, person, different organs have a different response to radiation, therefore the risk of cancer differs considerably. therefore the risk of cancer differs considerably.

The total lifetime detriment incurred each year from radiation The total lifetime detriment incurred each year from radiation by a worker exposed to the limits over his/her lifetime should be no by a worker exposed to the limits over his/her lifetime should be no greater than the annual risk of accidental death in a " safe" industrygreater than the annual risk of accidental death in a " safe" industryenvironment. environment.

Annual rate of fatal accidents ranges from 0.2Annual rate of fatal accidents ranges from 0.2101044 (service industries) (service industries) to 5to 5101044 (min in industries). (min in industries).

For an averaged measured effective dose of 2.1 mSv for For an averaged measured effective dose of 2.1 mSv for radiation workers, the total detriment to receive radiation damage is: radiation workers, the total detriment to receive radiation damage is:

21 21 101033 Sv/y Sv/y 4.0 4.0 101022 Sv Sv11 = 8.4 = 8.4 101044yy11 0.001 y 0.001 y11

This level is in the range of the average annual risk for This level is in the range of the average annual risk for accidental death for all industries. accidental death for all industries.

To control the distribution of exposure over a working career To control the distribution of exposure over a working career thethe annual effective doseannual effective dose is limited to is limited to 50 mSv50 mSv (not including medical (not including medical and natural background exposure) and natural background exposure)

To account for the cumulative effects of radiation, an age-dependent To account for the cumulative effects of radiation, an age-dependent limit of 10 mSv • age (y) is introduced. limit of 10 mSv • age (y) is introduced.

Workers at age of 64 at the end of their career with an Workers at age of 64 at the end of their career with an accumulated effective dose of 640 mSv would have a lifetime detriment of: accumulated effective dose of 640 mSv would have a lifetime detriment of:

0.64Sv • 4.0•100.64Sv • 4.0•10-2-2SvSv-1-1 = 2.6•10 = 2.6•10-2-2

in comparison their lifetime risk of a fatal accident over their 50 y working in comparison their lifetime risk of a fatal accident over their 50 y working career is of comparable order:career is of comparable order:

50y • 5.0•1050y • 5.0•10-4-4yy-1-1 = 2.5•10 = 2.5•10-2-2

For specific organs special limits for the annual equivalent For specific organs special limits for the annual equivalent dose are recommended.dose are recommended.

There are two kinds of radiation monitors used for medical purposes:There are two kinds of radiation monitors used for medical purposes:

survey monitors survey monitors

personal monitors personal monitors

Survey MetersSurvey Meters

Survey meters are used to determine the extend of possibleSurvey meters are used to determine the extend of possiblecontaminations.contaminations.

Most frequently used is the Most frequently used is the Geiger-Miller (GM) meter, which are Geiger-Miller (GM) meter, which are based on the ionization effects of based on the ionization effects of radiation in gas. The radiation is radiation in gas. The radiation is completely absorbed in the counter completely absorbed in the counter gas, creates a charged particles gas, creates a charged particles which are collected in the field of the which are collected in the field of the applied voltage and converted to an applied voltage and converted to an electrical pulse. electrical pulse.

The number of pulses corresponds to the number of absorbed The number of pulses corresponds to the number of absorbed particles, but is independent from the applied collection voltage.particles, but is independent from the applied collection voltage.

Therefore the GM detector is used for measuring the rate of the Therefore the GM detector is used for measuring the rate of the radiation not the absorbed dose (energy).radiation not the absorbed dose (energy).

Survey metersSurvey meters, field survey meters, rate meters, radiac meters, radiation , field survey meters, rate meters, radiac meters, radiation detection meters, low-range meters, high-range meters, airborne meters, fallout meters, detection meters, low-range meters, high-range meters, airborne meters, fallout meters, remote monitors, Geiger counters, and even 'dose rate meters' are all describing remote monitors, Geiger counters, and even 'dose rate meters' are all describing instruments that instruments that measure exposure ratemeasure exposure rate or the intensity of radiation at a location at some or the intensity of radiation at a location at some point in time. It's like the speedometer of a car; both present measurements relative to point in time. It's like the speedometer of a car; both present measurements relative to time. All of these above 'meters', the Geiger counter, too (which utilizes a Geiger tube time. All of these above 'meters', the Geiger counter, too (which utilizes a Geiger tube rather than an ion chamber), will show their radiation intensity readings relative to time, rather than an ion chamber), will show their radiation intensity readings relative to time, such as R/hr or mR/hr like the scale at the right, same as a car speedometer will show such as R/hr or mR/hr like the scale at the right, same as a car speedometer will show miles/hr. If you entered a radioactive area and your meter says 60 R/hr then that means if miles/hr. If you entered a radioactive area and your meter says 60 R/hr then that means if you were to stay there for a whole hour you would be exposed to 60 R. Same as driving a you were to stay there for a whole hour you would be exposed to 60 R. Same as driving a car for an hour at 60 mph, you'd be 60 miles down the road after that hour, car for an hour at 60 mph, you'd be 60 miles down the road after that hour, at that rateat that rate

CD V-715 Civil Defense High-Range Survey Meter CD V-715 Civil Defense High-Range Survey Meter 0-500 R/hr range0-500 R/hr range

3.25 pounds, die cast aluminum and drawn steel case, watertight, 3.25 pounds, die cast aluminum and drawn steel case, watertight, will float. Powered with one D-sized battery, continuously for 150 will float. Powered with one D-sized battery, continuously for 150 hours, longer if on intermittent basis. hours, longer if on intermittent basis. Instrument accuracy on any of its four ranges is within +- 20% of Instrument accuracy on any of its four ranges is within +- 20% of true dose rate. Accuracy maintained throughout temperature true dose rate. Accuracy maintained throughout temperature ranges of -20 F to +125 F, relative humidities to 100% and ranges of -20 F to +125 F, relative humidities to 100% and altitudes up to 25,000'.altitudes up to 25,000'.

The low-range Civil Defense survey meter is the CD V-700 The low-range Civil Defense survey meter is the CD V-700

In the proportional range the number of collected ions In the proportional range the number of collected ions (pulse height) is proportional to the applied potential. (pulse height) is proportional to the applied potential.

Proportional CounterProportional Counter

GM-counters are sensitive for low levels of radiation GM-counters are sensitive for low levels of radiation

GM counters are sensitive for GM counters are sensitive for -, -, -, and -, and -radiation provided the-radiation provided theparticle energy is sufficient for penetrating the detector entranceparticle energy is sufficient for penetrating the detector entrancewindow. window.

((WarningWarning the mR/hr reading of the GM-counter will be usually the mR/hr reading of the GM-counter will be usually lower than the real exposure rate due to the low energy absorption lower than the real exposure rate due to the low energy absorption in the monitor window.)in the monitor window.)

GM counters are best used for radiation detection not for measurement GM counters are best used for radiation detection not for measurement of dose of dose

GM counters can be calibrated for absorbed dose reading by usingGM counters can be calibrated for absorbed dose reading by usingcalibrated calibrated -sources. -sources.

Personnel Monitor DevicesPersonnel Monitor Devices

The most common monitor devices to determine the personal exposureThe most common monitor devices to determine the personal exposurehistory are: history are:

Radiation Film Badges Radiation Film Badges

Pocket Dosimeter Pocket Dosimeter

Radiation film badgesRadiation film badges are composed of two pieces of film, are composed of two pieces of film, covered by light tight paper in a compact plastic container. Various covered by light tight paper in a compact plastic container. Various filters in the badge holder allow areas to be restricted to X-ray, filters in the badge holder allow areas to be restricted to X-ray, -ray, -ray, -rays only. -rays only.

Radiation causes a blackening (silver) of the film material Radiation causes a blackening (silver) of the film material (mostly a silver bromide emulsion) The sensitivity of the film material is (mostly a silver bromide emulsion) The sensitivity of the film material is limitedlimited

For For -radiation the sensitivity is in the range of 10 - 1800 mrem. -radiation the sensitivity is in the range of 10 - 1800 mrem.

For For -radiation the sensitivity is in the range of 50 - 1000 mrem. -radiation the sensitivity is in the range of 50 - 1000 mrem.

Special film material is used for neutron monitoring. Special film material is used for neutron monitoring. The badge is usually not sensitive for The badge is usually not sensitive for radiation because the radiation because the -particles are absorbed in the light-tight paper. -particles are absorbed in the light-tight paper.

Pocket dosimeterPocket dosimeter

The pocket dosimeter or pen dosimeter is a common small sized The pocket dosimeter or pen dosimeter is a common small sized ion chamber which measures the originated charge by direct collection on a ion chamber which measures the originated charge by direct collection on a quartz fiber electroscope.quartz fiber electroscope.

The U-shaped fiber is close to a U-shaped wire. If the fiber is The U-shaped fiber is close to a U-shaped wire. If the fiber is charged it will be deflected away from the wire. The position of charged it will be deflected away from the wire. The position of deflection is a measure of the accumulated radiation dose.deflection is a measure of the accumulated radiation dose.

The dosimeter records total exposure from the initial The dosimeter records total exposure from the initial charging to the time of reading. charging to the time of reading.

It is an active device as the radiation exposure can be It is an active device as the radiation exposure can be read immediately as opposed to the passive film badge which is read immediately as opposed to the passive film badge which is only read after approximately six months.only read after approximately six months.

DosimetersDosimeters, which are also available in high or low ranges, can be in the , which are also available in high or low ranges, can be in the form of a badge, pen/tube type, or even a digital readout and all form of a badge, pen/tube type, or even a digital readout and all measure exposuremeasure exposure or the total accumulated amount of radiation to which you were exposed. (The Civil or the total accumulated amount of radiation to which you were exposed. (The Civil Defense pen/tube tube would show a reading like below when looking through it.) It's Defense pen/tube tube would show a reading like below when looking through it.) It's also similar to the odometer of a car; where both measure an accumulation of units. also similar to the odometer of a car; where both measure an accumulation of units. The dosimeter will indicate a certain total number of R or mR exposure received, just The dosimeter will indicate a certain total number of R or mR exposure received, just as the car odometer will register a certain number of miles traveled. as the car odometer will register a certain number of miles traveled.

Whole-Body CountingWhole-Body Counting

NaI Systems NaI Systems

Whole-Body CountingWhole-Body Counting

HPGe-Based SystemsHPGe-Based Systems

High-Purity Germanium detector systems offer many advantages High-Purity Germanium detector systems offer many advantages over their NaI counter parts which include: over their NaI counter parts which include: More robust analysis algorithmsMore robust analysis algorithms

Greater stability over long periods of useGreater stability over long periods of useSuperior identification capabilities for Superior identification capabilities for individual nuclide peaksindividual nuclide peaksAdvanced peak deconvolution, peak Advanced peak deconvolution, peak background subtraction, background subtraction, and peak interference correctionsand peak interference corrections

Total dose ranges (for Dose-Depth Total dose ranges (for Dose-Depth Monitors)Monitors) 5 krad to 1 Mrad5 krad to 1 Mrad

Proton cross-section (for Proton SEU Proton cross-section (for Proton SEU Monitor)Monitor) 5 105 10-7-7cmcm22

Input voltageInput voltage 12 - 40 V12 - 40 V

Power SEU / Dose Depth MonitorsPower SEU / Dose Depth Monitors 300 / 900 mW300 / 900 mW

Data interfaceData interface RS232 / RS 422RS232 / RS 422

Temperature rangeTemperature range -40 to + 55°C-40 to + 55°C

Mass SEU / Dose Depth MonitorsMass SEU / Dose Depth Monitors 350 / 500 g350 / 500 g

DimensionsDimensions SEUSEU 135 x 100 x 250 135 x 100 x 250 mmmm33

Dose-DepthDose-Depth 135 x 155 x 250 135 x 155 x 250 mmmm33

Optional data recorderOptional data recorder

Small, low powered real-time Radiation Monitors for manned Small, low powered real-time Radiation Monitors for manned and unmanned spacecraft applications. Total Dose and Dose-Depth and unmanned spacecraft applications. Total Dose and Dose-Depth Monitors for external and/or internal radiation environment monitoring for Monitors for external and/or internal radiation environment monitoring for electronics, materials and human radiation protection tasks. Single event electronics, materials and human radiation protection tasks. Single event upset (SEU) monitors for applications such as proton induced upset upset (SEU) monitors for applications such as proton induced upset monitoring for satellites in LEO. All monitors are based on unique silicon monitoring for satellites in LEO. All monitors are based on unique silicon radiation sensors and are small enough for on-board housekeeping radiation sensors and are small enough for on-board housekeeping tasks.tasks.