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Chapter 2. Radiation 1.Radioactivity 2.Radiation interaction with Matter 3.Radiation Doses and hazard Assessment.

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Presentation on theme: "Chapter 2. Radiation 1.Radioactivity 2.Radiation interaction with Matter 3.Radiation Doses and hazard Assessment."— Presentation transcript:

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2 Chapter 2. Radiation 1.Radioactivity 2.Radiation interaction with Matter 3.Radiation Doses and hazard Assessment

3 1)Overview 2)Types of Radioactive Decay 3)Energetics of Radioactive Decay 4)Characteristics of Radioactive Decay 5)Decay Dynamics 6)Naturally Occurring Radionuclides 2.1 Radioactivity

4 3 c) Beta Decay Spectra and Neutrino Pauli: Neutrino with spin 1 / 2 is emitted simultaneously with beta, carrying the missing energy. ?

5 c) The mass of the neutrino is negligibly small.

6 5 d) Positron Decay Energy

7 3 ) 36 CI decays into 36 S ( u) and 36 Ar. If the energy release is MeV to 36 S and MeV to 36 Ar, calculate the masses of 36 CI and 36 Ar. Describe the modes of decay. 5) The radionuclide 41 Ar decays by β - emission to an excited level of 41 K that is MeV above the ground state. What is the maximum kinetic energy of the emitted β - particle?

8 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 N = A N o = A o

9 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?

10 b) Three Component Decay Chains

11 Daughter Decays Faster than the ParentλI < 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 ).

12 4 ) An initial number N A (0) of nuclei A decay into daughter nuclei B, which are also radioactive. The respective decay probabilities are λ A and λ B. If λ B = 2 λ A, calculate the time (in terms of λ A )when N B is at its maximum. Calculate N B (max) in terms of N A (0)

13 1)overview 2)Photon Interactions 3)Neutron Interactions 4)Interaction of Heavy Charged Particles with Matter 5)Scattering of Electrons in a Medium 2.2 Radiation interaction with Matter

14 1) overview

15 I = I o e –μx mean-free-path length Half-Thickness

16 4) Interaction of Heavy Charged Particles with Matter Fast moving protons, 4 He, 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.

17 能量损失

18 Range of Heavy Charged Particles in a Medium  source Shield Particles lose all their energy at a distance called range.

19 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 cm 2 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.

20 1)Historical Roots 2)Dosimetric Quantities 3)Natural Exposures for Humans 4)Radiation Effects 2.3 Radiation Doses and hazard Assessment

21 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

22 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.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 Guidelines are given for radioactive material handling and applications. Today, safety committee is set up to deal with radiation risks.

23 Mission Statement of the ICRP The International Commission on Radiological Protection, ICRP, is an independent Registered Charity, established to advance for the public benefit the science of radiological protection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation. From check with ICRP for up-to-date guidance regarding radiation

24 Protection standards GB 放射卫生防护基本标准 卫生部发布 GB 辐射防护规定 环保局发布 GB 电离辐射防护与辐射源安全基本标准 发布 实施 中华人民共和国国家质量监督检验检疫总局发布

25 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

26 Radiation Absorption and Dosage The 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. typeunits  Radioactivity Bq, Ci    Exposure dose Gy, rad (R) Quality factor Q Biological dose Sv, rem

27 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 ( , X-rays, neutrons, protons or particles), and effect of radiation. Commonly used units megacurie kilocurie millicurie microcurie nonocurie picocurie 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.

28 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 = 35  2.1e9 = 7.35e10 eV (*1.6x erg/eV) = 0.12 erg (per 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

29 A Dosage Evaluation Example A 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  particle is absorbed by a of g cell, then the dose is 10 9 times higher (0.8 Gy, 8 Sv), exceeded lethal ( 致命 ) dose for most living beings.

30 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.

31 The Quality Factor Q F and Dosage Units The factor reflecting the relative harmfulness of various types of radiation is called the quality factor ( Q F ) or relative biological effectiveness ( rbe ) Biological dose = Q F * exposure dose

32 Exposure and Biological Dosage SI unit cgs unit Exposure unit1 Gy = 100 rad (=100 R) Biological dose1 Sv = 100 rem (= Q  rad) Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent man

33 Summary of Units for Radioactive Dosage QuantitySymbol SI unitcgs unitConversion factor radioactivity A BqCi1 Ci = 3.7e10 Bq exposure dose X C/kgR1 C/kg = 3876 R absorbed dose D Gy (J/kg)rad1 Gy = 100 rad =6.24 eV/g biological dose H Sv ( QF*Gy )rem1 Sv = 100 rem C/kg charge produced by exposure to radiation

34 Effective Dose Equivalent In a human, different organs have different radiological sensitivities, To account for different organ sensitivities and the different doses received by the various organs a special dose unit, the effective dose equivalent H E, is used to describe better the hazard a human body experiences when placed in a radiation field.

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

36 Naturally occurring radionuclides in the human body deliver an 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?

37 Kerma kinetic energy of radiation absorbed per unit mass 比释动能 indirectly ionizing (uncharged) radiation If E tr is the sum of the initial kinetic energies of all the charged ionizing particles released by interaction of indirectly ionizing particles in matter of mass m, then

38 (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 μ tri which account for fewer secondary photons escaping from the interaction site, are sometimes encountered. the linear energy absorption coefficient

39 Photon Kerma and Absorbed Dose If, at some point of interest in a medium, the fluence of 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. μ tr (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。

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

42

43 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 10 9 photons per second? neglect air attenuation over a distance of 15 m QF = I 0.15 μSv

44 Dosimeters for Dosage Monitoring Dosimeters 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, FeSO 4, solution is a chemical dosimeter due to the reaction: 4 Fe 2+ + energy + O 2  4 Fe 3+ (brown) + 2 O 2- 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.

45 Chemical 3-dimensional Dosimeter Ferrous ions, Fe 2+, are oxidized by ionizing radiation, and convert to ferric ions, Fe 3+, 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.

46 1)Historical Roots 2)Dosimetric Quantities 3)Natural Exposures for Humans 4)Radiation Effects 2.3 Radiation Doses and hazard Assessment

47 3) Natural Exposures for Humans

48 The uranium decay series. 222 Rn 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

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

50 Some Natural Occurring Radioactive Nuclides Nuclides (t ½ ~ y)Radiation 235, 238 U, 232 Th and offsprings , ,  144 Nd, 147, 148, 149 Sm, 152 Gd, 186 Os, 190, 192Pt  () () 40 K, 87 Rb, 115 In, 123 Te, 138 La, 176 Lu, 187 Re, 210 Bi etc.  +, , EC (  ) Nuclides produced by cosmic rays 14 C (5730 y), 3 T (15 y), 7 Be (53 d), 10 Be (2.7×10 6 y) 

51 1)Historical Roots 2)Dosimetric Quantities 3)Natural Exposures for Humans 4)Radiation Effects 2.3 Radiation Doses and hazard Assessment

52 Radiation Effects Somatic effects damages to cells passed on to succeeding cell generations, acute or chronic Genetic effects damages 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.

53 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.

54 Cellular Effects Cell death Cell repair Cell change Is this change good or bad?

55 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 1/10 th of the annual adult limit)

56 Median effective absorbed doses D 50 and threshold doses D th 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

57 Exposure Limit Maximum permissible dosage of workers in radiation zone Max. accumulated Max. dose/13 wk mSvmSv Whole body 50( age -18) 30 Hands and 250 (750/y) forearms 1 Sv = 1000 mSv = 100 rem

58 We are facing many environmental toxic agents. The risk estimation of these agents should be based on dose response curve. Dose Response The response in a low dose range could be extrapolated from high doses if it is a physical system. However, it is not true in biological systems.

59 Dose Biological Response Biological response to low dose radiation is complicated. Adaptive response Bystander effect ICRP (International Commission on Radiological Protection) Radiological Protection)

60 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.

61 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

62 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

63 No bystander between organs exposed at low dose-rates The site of deposition of the radioactive material is the site of cancer induction 90 SR - bone cancer 144 Ce – liver/bone cancer 239 PuO 2 (inhaled)- lung cancer

64 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.

65 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

66 A gradual deterioration due to accumulated radiation damage Transient malfunctions due to single particles hitting a sensitive node. Single ion hit system

67 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

68 Genetic Effects Human 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.

69 A simplified view of a portion of the DNA molecule, as well as the various types of damage it can experience. Four building blocks or bases combine to 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).

70 Genomic Instability Delayed Genetic Effects

71 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.

72 Genomic Instability Gene mutation Chromosome aberration Mitotic failure- aneuploidy ( 非整倍的) Cell death Micronuclei New Paradigm After 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.

73 Early effects seen in “hit” cell Chromosomal rearrangements Micronuclei Gene mutations Increased Reactive Oxygen Species (ROS) Inflammatory responses Change in gene expression

74 Effects seen in cell progeny Chromosomal rearrangements Micronuclei Transformation Chromosome amplification Death inducing factors Gene mutations Cell death Change in gene expression

75 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.

76 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.

77 Genomic Instability can be demonstrated in cells of some strains of mice B. Ponnaiya & R.L. Ullrich, Population Doublings Aberrations/Cell Sensitive BALB/c mice Resistant C57BL/6 mice

78 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

79 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.

80 Dose Ranges ( mSievert) Cancer Radiotherapy Experimental Radiobiology Cancer Epidemiology DOE Low Dose Program Medical Diagnostics Regulatory Standards Total Body TherapyTotal 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-ray Dental X-ray ICRP Negligible Dose NRC Dose Limit for Public Natural background Site Decommissioning/License Termination 3-Mile Island Ave Ind Occupational Limit NRC, EPA EPA Clean-up StandardsNRC Clean-up Standards

81 920 mGy/min 1 mGy/min 12.5μGy/min

82 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  radiations, indirect interactions cause about 80% of the biological damage

83 Direct and indirect action of radiation

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88 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

89 1)Historical Roots 2)Dosimetric Quantities 3)Natural Exposures for Humans 4)Radiation Effects 2.3 Radiation Doses and hazard Assessment

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

91 ALARA principle : As Low As Reasonably Achievable justification of practice optimization of radiation protectionwith (annual radiation) dose limits

92 Radiations y(i) (Bq-s) -1 E(i) (MeV)y(i)×E(i) b × × *1.65× b × × *1.94× b × × *2.21× g 15.80× × × g 28.51× × × CESIUM-137 With a frequency of per decay


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