Chapter 2. Radiation

1.Radioactivity

2.Radiation interaction with Matter

3.Radiation Doses and hazard Assessment 

1) Overview2) Types of Radioactive Decay3) Energetics of Radioactive Decay4) Characteristics of Radioactive Decay5) Decay Dynamics6) Naturally Occurring Radionuclides

2.1 Radioactivity

3

c) Beta Decay Spectra and Neutrino

Pauli: Neutrino with spin 1/2 is emitted simultaneously with beta, carrying the missing energy.

A Typical Beta Spectrum

Intensityor # of

Energy of

E max

A Beta Decay Scheme

PZ DZ+1 + – + v

?

c)

The mass of the neutrino is negligibly small.

5

d) Positron Decay Energy

Positron Emission

+

–

3 ） 36CI decays into 36S (35.967081 u) and 36Ar. If the energy release is 1.142 MeV to 36S and 0.709 MeV to 36Ar, calculate the masses of 36CI and 36Ar. Describe the modes of decay.

5) The radionuclide 41Ar decays by β- emission to an excited level of 41K that is 1.293 MeV above the ground state. What is the maximum kinetic energy of the emitted β- particle?

Variation of N as a function of time t

N No

t

N = No e - t

Also A = Ao e - t

Radioactive Decay Kinetics -exponential

Number of radioactive nuclei decrease exponentially with time as indicated by the graph here.

As a result, the radioactivity vary in the same manner.

Note l N = A

l No = Ao

6) The activity of a radioisotope is found to decrease by 30% in one week. What are the values of its (a) decay constant, (b) half-life, and (c) mean life?

b) Three Component Decay Chains

Daughter Decays Faster than the Parent λI < λ2,

transient equilibrium: daughter's decay rate is limited by the decay rate of the parent.

λI << λ2,

The activity of the daughter approaches that of the parent. This extreme case is known as secular equilibrium( 久期平衡 ).

4 ） An initial number NA(0) of nuclei A decay into daughter nuclei

B, which are also radioactive. The respective decay probabilities areλA and λB. IfλB = 2λA , calculate the time (in terms of λA)when NB

is at its maximum. Calculate NB (max) in terms of NA(0)

1) overview2) Photon Interactions3) Neutron Interactions4) Interaction of Heavy Charged Particles with

Matter5) Scattering of Electrons in a Medium

2.2 Radiation interaction with Matter

1) overview

Intensity of Parallel Gamma Rays as aFunction of Absorber Thickness.

Thickness x

Intensity, I

I = Io e–μx

mean-free-path length

Half-Thickness

4) Interaction of Heavy Charged Particles with Matter

Sketch of Alpha Particle Paths in a Medium

source

Shield

Fast moving protons, 4He, and other nuclei are heavy charged particles.

Coulomb force dominates charge interaction.

They ionize and excite (give energy to) molecules on their path.

The Born-Bethe Formula for Energy Loss of Charged Particles.

- dE

dx =

KM zE

2

能量损失

ee b

v

NZmv

eZ

dx

dE)(2

lg4

~ 22

421

Range of Heavy Charged Particles in a Medium

Variation of Intensity as a Function of Thickness

Detector

Absorber

Intensity

thickness

sourcestraggling

Range

source

Shield

Particles lose all their energy at a distance called range.

A material is found to have a tenth-thickness of 2.3 cm for 1.25 MeV gamma rays, (a) What is the linear attenuation coefficient for this material? (b) What is the half-thickness? (c) What is the mean-free-path length for 1.25-MeV photons in this material?

The specific rate of energy loss (-dE/ρdx) of a 5 MeV proton in silicon is 59 keV mg-1 cm2 and its range R' is 50 mg cm-2 . Calculate values of (-dE/ρdx) and range R' for deuterons, tritons, 3He and a particles, all of which have the same speed as the proton.

1) Historical Roots

2) Dosimetric Quantities

3) Natural Exposures for Humans

4) Radiation Effects

2.3 Radiation Doses and hazard Assessment

Early workers exposed to X-rays developed dermatitis （皮炎） .

Uranium miners developed skin lesions.

People working with radioactivity experienced illness.

Researchers exposed to radioactivity suffered radiation sickness at advanced age.

Manhattan project workers in Los Alamos, Oak Ridge, Hanford, and atomic worker in the former USSR suffered anorexia （厌食） , fatigue, headache, nausea （反胃） , vomiting, and diarrhea.

1)Historical Roots

Collective Response to Radiation Risk

In 1928, the International Committee on X-ray and Radium Protection was formed to look into the risk of radiation. It is now called International Commission on Radiological Protection, ICRP.

In 1942, a group of health physicists had the responsibility to assess problems and implement safe operation procedures regarding radioactivity.

After WW2, the (American) National Council of Radiation Protection (NCRP) was formed in 1946.

Guidelines are given for radioactive material handling and applications.

Today, safety committee is set up to deal with radiation risks.

Mission Statement of the ICRPThe International Commission on Radiological Protection, ICRP, is an independent Registered Charity, established to advance for the public benefit the science of radiologicalprotection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation.

From www.icrp.comcheck with ICRP for up-to-date guidance regarding radiation

Protection standards

GB4792-84 放射卫生防护基本标准 卫生部发布GB8703-88 辐射防护规定 环保局发布GB 18871-2002 电离辐射防护与辐射源安全基本标准 2002-10-08 发布 2003-04-01 实施 中华人民共和国国家质量监督检验检疫总局发布

2) Dosimetric quantities

a physical measure correlated with a radiation effect.

...When you can measure what you are speaking about, and express it in numbers, you know something about it...

Lord Kelvin

Lord Kelvin

Radiation Absorption and DosageThe amount of energy absorbed from exposure to radiation is called a dose. The radiation effect measured by a dosimeter reflects an equivalence of certain dosage of X-rays. The amounts are defined in certain units as shown here.

type units

Radioactivity Bq, Ci

Exposure dose Gy, rad (R)

Quality factor Q

Biological dose Sv, rem

Units for Radiation Source (review)

The SI unit for radioactivity is Bq (1 becquerel = 1 dps).

The decay is not necessary all absorbed unless it’s internal.

1 curie = 3.7e10 Bq.

These units have nothing to do with energy, type ( , , a b g, X-rays, neutrons, protons or particles), and effect of radiation.

Commonly used unitsmegacuriekilocuriemillicurie

microcurienonocuriepicocurie

these modifiers are also used for other units.

disintegrations per second

the fluence is not closely enough related to most radiation effects to be a useful determinant.

Dose Units - roentgen, rad, and gray

Amounts of absorbed energy are not the same as exposed.The amount of radiation energy absorbed is called a dose.

A roentgen ( R) is a dose of X- or -rays that produce 1 esu charge at STP (negative and positive each or 2.1e9 ion pairs) in 1.0 L.

1 R = 352.1e9 = 7.35e10 eV (*1.6x10-12 erg/eV) = 0.12 erg (per 0.00123 g air)

= 1 rad (100 erg per g of any substance)

1 Gy = 1 J / kg (1 J per kg of any substance is a gray, Gy) = 1e7 erg / kg = 100(100 erg/g) ~ 100 rad

In air, the average energy required to produce an ion pair is 35 eV

average energy

1 Gy being equal to an imparted energy of 1 joule per kilogram.

corpuscular radiation

photons

A Dosage Evaluation ExampleA 5-MeV particle is absorbed by 1 gram of water, estimate the dosage in rad and rem.

The Q factor is 10 for particle, and thus the dose is 8e-7 rem or 8e-9 Sv.

If the a particle is absorbed by a of 10-9 g cell, then the dose is 109 times higher (0.8 Gy, 8 Sv), exceeded lethal ( 致命 ) dose for most living beings.

rad 108.0 = erg 100

rad 1

J 1

erg 10 MeV 1

J 101.6

g 1

5MeV 8-7-13

Integral Dose Used in Radiation Therapy

Total energy absorbed by an organ called integral dose is gram-rad or g-rad or g-Gy total dosage received by an organ.

g-Gy = dose * mass of the organ

Accumulated dose is the dose received over a period, but g-Gy is the total dose received in a single time.

The Quality Factor QF and Dosage Units

The factor reflecting the relative harmfulness of various types of radiation is called the quality factor (QF) or relative biological effectiveness (rbe)

Biological dose = QF * exposure dose

Exposure and Biological Dosage

SI unit cgs unitExposure unit 1 Gy = 100 rad (=100 R)Biological dose 1 Sv = 100 rem (= Qrad)

Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent man

Summary of Units for Radioactive Dosage

Quantity Symbol SI unit cgs unit Conversion factor

radioactivity A Bq Ci 1 Ci = 3.7e10 Bqexposure dose X C/kg R 1 C/kg = 3876 Rabsorbed dose D Gy (J/kg) rad 1 Gy = 100 rad

=6.24 eV/gbiological dose H Sv (QF*Gy) rem 1 Sv = 100 rem

C/kg charge produced by exposure to radiation

Effective Dose Equivalent

In a human, different organs have different radiological sensitivities,

To account for different organ sensitivities and the differentdoses received by the various organs a special dose unit, the effective dose equivalent HE, is used to describe better the hazard a human body experiences when placed in a radiation field.

Tissue weighting factors adopted by the ICRP [1977] for use in determining the effective dose equivalent.

Naturally occurring radionuclides in the human body deliveran annual dose to the various tissues and organs of the body as follows: lung 36 mrem, bone surfaces 110 mrem, red marrow 50 mrem, and all other soft tissues 36 mrem. What is the annual effective dose equivalent that a human receives?

Kerma kinetic energy of radiation absorbed per unit mass 比释动能

indirectly ionizing (uncharged) radiation

If Etr is the sum of the initial kinetic energies of all the charged ionizing particles released by interaction ofindirectly ionizing particles in matter of mass m, then

(a) Energy deposition for photon energy involved in the interactions in an incremental volume of material, (b) Formulas for the energy per unit mass of the material in the incremental volume, corresponding to the various energy increments in (a), (c) Linear coefficients defined by their proportionality to the mass energy relationships in diagrams (a) and (b).

total moss interaction coefficient

μtri which account for fewer secondary photons escaping from the interactionsite, are sometimes encountered.

the linear energy absorption coefficient

Photon Kerma and Absorbed Dose

If, at some point of interest in a medium, the fluenceof radiation with energy E is Ф, the kerma at that point is

f(E) is the fraction of the fraction of the incident radiation article's energy E that is transferred to secondary charged particles

μ(E)/ρ is the mass interaction coefficient for the detector material.

μtr(E)/ρ for charged secondary particles and excludes the energy carried away from the interaction site by secondary photons 一定物质对特定能量的间接致电离粒子的质量能量转移系数。

Example What are the iron kerma and absorbed dose rates from uncollided photons 1 meter from a point isotropic source emitting 1014 5 MeV gamma rays per second into an water medium? the total mass interaction coefficient for 5-MeV photons isfound to .

The uncollided flux density 1 meter from the source is,

Example : What is the dose equivalent 15 meters from a point source that emitted 1 MeV photons isotropically into an infinite air medium for 10 minutes at a rate of 109 photons per second?

neglect air attenuation over a distance of 15 m

QF = I

0.15 μSv

Dosimeters for Dosage MonitoringDosimeters are devices to measure exposed doses.

Film-badges, electroscopes, ionization chambers, biological and chemical dosimeters have been used for radiation monitors.

Plants, cells, bacteria, and viruses reacting to radiation are biological dosimeter candidates.

Ferrous sulfate, FeSO4, solution is a chemical dosimeter due to the reaction:

4 Fe2+ + energy + O2 4 Fe3+(brown) + 2 O2-

Some glasses and crystals serve as solid state dosimeters.

Shelf life, linearity, stability, usage simplicity, easy-to-read, dose-rate and equal responses to various radiation are some considerations.

Chemical 3-dimensional Dosimeter

Ferrous ions, Fe2+, are oxidized by ionizing radiation, and convert to ferric ions, Fe3+, which complexes with xylenol （二甲苯酚） orange dye to give an orange compound.

When the sample is prepared in a gel form, it serves as a 3-dimensional dosimeter, because the complexes are localized in the gel. These dosimeters are useful for planning radiation medical treatments such as radiation cancer treatment.

1) Historical Roots

2) Dosimetric Quantities

3) Natural Exposures for Humans

4) Radiation Effects

2.3 Radiation Doses and hazard Assessment

3) Natural Exposures for Humans

The uranium decay series.

222Rn is responsible for higher levels of background radiation in many parts of the world. because it is a gas and can easily seep out of the earth into unfinished basements and then into the house

Radioactivity in Nature

Radon

Summary of the annual effective dose equivalents from various sources of natural background radiation in the United States. Source: NCRP [1987].

Some Natural Occurring Radioactive Nuclides

Nuclides (t½ ~ 106-15 y) Radiation

235, 238U, 232Th and offsprings , ,

144Nd, 147, 148, 149Sm, 152Gd, 186Os, 190, 192Pt

()

40K, 87Rb, 115In, 123Te, 138La, 176Lu, 187Re, 210Bi etc.

+, , EC ()

Nuclides produced by cosmic rays14C (5730 y), 3T (15 y), 7Be (53 d), 10Be (2.7×106 y)

1) Historical Roots

2) Dosimetric Quantities

3) Natural Exposures for Humans

4) Radiation Effects

2.3 Radiation Doses and hazard Assessment

Radiation Effects

Somatic effects damages to cells passed on to succeeding cell generations, acute or chronic

Genetic effectsdamages to genes that affect future generations.Genes are units of hereditary information that occupy fixed positions (locus) on a chromosome. Genes achieve their effects by directing the synthesis of proteins.

Somatic Effects

Damages to cell membranes, mitochondria( 线粒体） and cell nuclei result in abnormal cell functions, affecting their division, growth and general heath.

Organs such as skin, lining of gastrointestinal tract （胃肠道） , embryos, and bone marrow, whose cells proliferate rapidly are easily damaged.

Bone marrow makes blood, and its damage leads to reduction of blood cell counts and anemia.

Damage to germinal ( 幼体 tissues reduces cell division, and induces sterility.

Cellular Effects

Cell death

Cell repair

Cell change

Is this change good or bad?

Dividing Cells are the Most Radiosensitive

• Rapidly dividing cells are more susceptible to

radiation damage.

• Examples of radiosensitive cells are;– Blood forming Cells

– The intestinal lining

– Hair follicles （毛囊）– A fetus

This is why the fetus has a exposure limit (over gestation period) of 500 mrem (or 1/10th of the annual adult limit)

Median effective absorbed doses D50 and threshold doses Dth for exposure of different organs and tissues in the human adult to gamma photons at dose rates < 0.06 Gy h-1.

Deterministic Effects in Organs and Tissues

Exposure Limit

Maximum permissible dosage of workers in radiation zone

Max. accumulated Max. dose/13 wk mSv mSv

Whole body 50(age-18) 30

Hands and 250 (750/y)forearms

1 Sv = 1000 mSv = 100 rem

We are facing many environmental toxic agents.The risk estimation of these agents should be based on dose response curve.

Dose

Resp

on

se

The response in a low dose range could be extrapolated fromhigh doses if it is a physical system.However, it is not true in biological systems.

Dose

Bio

log

ical

Resp

on

se

Biological response to low dose radiation is complicated.

Adaptive response

Bystander effect

ICRP (International Commission on Radiological Protection)

In the biological systems, the dose response at low dose level cannot be extrapolated from high dose response.

Instead, experimental as well as epidemiological studies are needed to clarify the dose response.

When a cell is damaged by radiation, it can send signals to bystander cells, which are the cells near the “hit” cell.

The signals sent by the damaged cell may disrupt the normal function of it’s neighboring cells, or it may stimulate them to respond with additional signals

back to the damaged cell or to other nearby cells.

The signals sent by the bystander cells may help repair the damaged cell, or it may trigger the cell to commit cell suicide.

Bystander Effects

Micronuclei

Cells were stained with two different dyes. Only the nuclei of the cells stained with pink dye were hit by alpha particles from a microbeam. The figures show the presence of broken chromosomes in the form of micronuclei (the smaller fragments of pink and blue). These micronuclei are present not only in the pink “hit” cells, but also in the blue non-exposed cells. Such studies provide direct evidence for bystander effects.

Geard

No bystander between organs exposed at low dose-rates

The site of deposition of the radioactive material is the site of cancer induction

•90SR - bone cancer

•144Ce – liver/bone cancer

•239 PuO2 (inhaled)- lung cancer

The influence of communication on radiation-induced micronuclei in lung

Khan et al 1998

Shielded Cells

Lower half of lungs irradiated with 10 Gy

400

Micronuclei/1000 Cells

800

Exposed Cells

Lung cells shielded from direct radiation

showed a major increase in the production of

micronuclei (one indicator of

chromosome damage) when other cells in the

lung tissue were irradiated, indicating

some type of communication between cells.

Why now?

• Standards have been set from high dose effects, but low dose effects have not been measurable until now

• New technological developments and biological discoveries have made it possible to study low dose effects

• A gradual deterioration due to accumulated radiation damage

• Transient malfunctions due to single particles hitting a sensitive node.

Single ion hit system

Does the bystander effect occur in animals as well as cell culture?

• The bystander effect occurs in animal

systems

• The bystander effect is limited to specific

organs or tissues

• No bystander effects seen between organs at

low dose rates

Genetic EffectsHuman cells contain 46 chromosomes( 染色体） . Germ or ovum cells contain 23.

A chromosome contains a deoxyribonucleic acid (DNA) molecule.

The double-helix DNA has two strands of phosphoric-acid and sugar linked bases of Adenine, Guanine Cytosine or Thymine.

The A-T and G-C pairs stack on top of each other.

The DNA codon transcripts mRNA, which directs the amino-acid sequences of protein. DNA Damages result in somatic and genetic effects.

When DNA molecules replicate (pass on to next generation), they are sensitive to radiation damage. Joining wrong ends of broken DNA is called Translocation, which cause mutation and deformation at birth.

Genetic effects increase frequency of mutation.

A simplified view of a portion of the DNA molecule, as well as the various types of damageit can experience. Four building blocks or bases combineto form the DNA molecule: adenine (A) （腺嘌呤） , guanine(G) （鸟嘌呤） , cytosine (C)（氧氨嘧啶） , and thymine (T)（胸腺嘧啶） .

Genomic InstabilityDelayed Genetic Effects

What is Genomic Instability?

• Often, after being damaged by radiation, cells are able to repair DNA damage and reproduce normally.

• However, sometimes damage may carry over for several generations before the unobserved damage causes the cell to lose control of its genome.

• At this point, cells may be unable to reproduce successfully. They may become genetically unstable, or become cancerous.

Genomic Instability

Gene mutation

Chromosome aberration

Mitotic failure-aneuploidy （ 非整倍

的）

Cell death Micronuclei

New ParadigmAfter a cell is exposed to radiation, biological changes are

produced that, after many cell divisions, result in loss of genetic control. This is a frequent event that can be modified.

Early effects seen in “hit” cell

Chromosomal rearrangements

Micronuclei

Gene mutations

Increased Reactive Oxygen Species (ROS)

Inflammatory responses

Change in gene expression

Effects seen in cell progeny

Chromosomal rearrangements

Micronuclei

Transformation

Chromosome amplification

Death inducing factors

Gene mutations

Cell death

Change in gene expression

Radiation-related Gene Induction

It has been shown that certain genes are inappropriately induced, or “turned on” or

“turned off” by radiation. The consequence of the

gene alteration sometimes shows up more frequently several generations after the

initial radiation exposure.

Genomic Instability can be demonstrated in some strains of mice

Hybrid Mouse Models

After only a few generations of apparently normal breast cell division, the cells of the sensitive mice, BALBc, show increased chromosome aberrations and genomic instability, while cells of the radiation resistant mice, C57BL/6, remain stable.

Cells of the sensitive BALBc mice are very sensitive to radiation-induced breast cancer. Other cells, such as those from the resistant C57BL/6 mice, are particularly resistance to this radiation-induced effect.

Genomic Instability can be demonstrated in cells of some strains of mice

B. Ponnaiya & R.L. Ullrich, 1998

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

4 8 12 16 20 24 28

Population Doublings

Ab

erra

tion

s/C

ell

Sensitive BALB/c miceResistant C57BL/6 mice

Impact on Standards

Genomic Instability• Provides a mechanism to explain how radiation can

produce the multiple steps needed to transform a normal cell to a malignant cell

• Supports the LNTH if cellular genomic instability can be shown to increase cancer frequency

Summary

• Radiation-induced genomic instability is defined as detrimental effects that occur several cell generations after radiation exposure.

• This may be due to factors produced by inflammatory response or a failure of genes to turn on or off properly.

• Signaling factors involved in genomic instability may be similar to those involved in bystander effects.

• Increased Reactive Oxygen Species (ROS) may also interfere with normal cellular processes and produce genomic instability.

Dose Ranges

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0 100 200 300 400 500 600 700 800 900 1000

0 10 20 30 40 50 60 70 80 90 100

0 1 2 3 4 5 6 7 8 9 10

0 0.1 0. 2 0.3 0. 4 0. 5 0.6 0.7 0.8 0. 9 1

0 0.01 0.02 0.03 0.04 0.05 0.0 6 0.0 7 0.08 0.0 9 0.1

(mSievert)

0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000

Cancer Radiotherapy

Experimental Radiobiology

Cancer Epidemiology

DOE Low Dose Program

Medical Diagnostics

Regulatory Standards

Total Body Therapy Total Tumor Dose

A-bomb survivors

Significant cancer risk at > 200 mSv (UNSCEAR)

Human LD50

Typical mission dose on Int. Space Station

Typical annual dose for commercial airline flight crews

Bone (Tc-99m)Thyroid (I-123)

Chest X-rayDental X-ray

ICRP Negligible Dose

NRC Dose Limit for PublicNatural background

Site Decommissioning/License Termination

3-Mile Island Ave Ind

Occupational Limit NRC, EPA

EPA Clean-up Standards NRC Clean-up Standards

0

1

2

3

4

5

6

0 2 4 6 8 10

Radiation-induced mutation in liver of gpt-delta mouse

MF

(1

0-6)

Dose (Gy)

920 mGy/min

1 mGy/min

12.5μGy/min

Direct and indirect action of radiation

Direct action: charged particle “directly” interacts with the target molecule, e.g. breaks bond in DNA molecule

Indirect action: charged particle interacts with a water molecule producing “free radicals” which then interact with the target molecule

For x and g radiations, indirect interactions cause about 80% of the biological damage

Direct and indirect action of radiation

Our Bodies Are Resilient• DNA damage is most important and can lead to

cell malfunction or death.

• Our body has ~ 60 trillion cells– Each cell takes “a hit” about every 10 seconds,

resulting in tens of millions of DNA breaks per cell each year.

– BACKGROUND RADIATION causes only a very small fraction of these breaks (~ 5 DNA breaks per cell each year).

• Our bodies have a highly efficient DNA repair mechanisms

1) Historical Roots

2) Dosimetric Quantities

3) Natural Exposures for Humans

4) Radiation Effects

2.3 Radiation Doses and hazard Assessment

The three key rules of radiation protection ： time, distance, and shielding.

ALARA principle ： As Low As Reasonably Achievable

justification of practice

optimization of radiation protectionwith

(annual radiation) dose limits

Radiationsy(i)(Bq-s)-1

E(i)(MeV) y(i)×E(i)

b- 1 9.47×10-01 1.743×10-01 * 1.65×10-01

b- 2 5.80×10-06 3.347×10-01 * 1.94×10-06

b- 3 5.30×10-02 4.163×10-01 * 2.21×10-02

g 1 5.80×10-06 2.835×10-01 1.64×10-06

g 2 8.51×10-01 6.617×10-01 5.63×10-01

55-CESIUM-137

With a frequency of 0.849 per decay