Transcript chap2c.pptx

Chapter 2. Radiation
1.Radioactivity
2.Radiation interaction with Matter
3.Radiation Doses and hazard Assessment
2.1 Radioactivity
1)
2)
3)
4)
5)
6)
Overview
Types of Radioactive Decay
Energetics of Radioactive Decay
Characteristics of Radioactive Decay
Decay Dynamics
Naturally Occurring Radionuclides
c) Beta Decay Spectra and Neutrino
A Beta Decay Scheme
P D
Z
Z+1
A Typical Beta Spectrum
+  +v
–
Intensity
or # of 
?
E max
Energy of 
Pauli: Neutrino with spin 1/2 is emitted simultaneously with beta, carrying
the missing energy.
3
c)
The mass of the neutrino is negligibly small.
d) Positron Decay Energy
Positron Emission
–
+

5
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 βparticle?
Radioactive Decay Kinetics -exponential
Variation of N as a function of time t
No
N
N = No e
Also A = Ao e
- t
- t
t
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
 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) halflife, 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)
2.2 Radiation interaction with Matter
1)
2)
3)
4)
overview
Photon Interactions
Neutron Interactions
Interaction of Heavy Charged Particles with
Matter
5) Scattering of Electrons in a Medium
1) overview
Intensity of Parallel Gamma Rays as a
Function of Absorber Thickness.
Intensity, I
I = Io e–μx
Thickness x
mean-free-path length
Half-Thickness
4) Interaction of Heavy Charged Particles with Matter
Sketch of Alpha Particle Paths in a Medium
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.
 source
Shield
The Born-Bethe Formula for Energy
Loss of Charged Particles.
2
dE
KM z
=
dx
E
能量损失
dE
~
dx
v
2( )
e
4Z 12 e 4


NZ
lg
2
be
mv 2
Range of Heavy Charged Particles in a Medium
Variation of  Intensity as a Function of Thickness
Detector
Intensity
Range
Absorber
straggling
Particles lose
all their energy
at a distance
called range.
 source
 source
thickness
Shield
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 meanfree-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.
2.3 Radiation Doses and hazard Assessment
1)
2)
3)
4)
Historical Roots
Dosimetric Quantities
Natural Exposures for Humans
Radiation Effects
1)Historical Roots
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.
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 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 www.icrp.com
check 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
Lord Kelvin
2) Dosimetric quantities
...When you can measure what
you are speaking about, and
express it in numbers, you
know something about it...
Lord Kelvin
a physical measure correlated with a radiation effect.
Radiation Absorption and Dosage
type
Radioactivity
units
Bq, Ci
 
Exposure dose Gy, rad (R)
Quality factor
Biological dose
Q
Sv, rem
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.
Units for Radiation Source (review)
The SI unit for radioactivity is Bq
(1 becquerel = 1 dps). disintegrations per second Commonly used units
megacurie
The decay is not necessary all
kilocurie
absorbed unless it’s internal.
millicurie
1 curie = 3.7e10 Bq.
microcurie
nonocurie
These units have nothing to do
picocurie
with energy, type (, , g, X-rays,
neutrons, protons or particles),
these modifiers are also
and effect of radiation.
used for other units.
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.
average energy
A roentgen ( R) is a dose of X- or g-rays that produce 1 esu charge at STP
(negative and positive each or 2.1e9 ion pairs) in 1.0 L.
In air, the average energy required to produce an ion pair is 35 eV
1 R = 352.1e9
= 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)
photons
corpuscular radiation
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
1 Gy being equal to an imparted energy of 1 joule per kilogram.
A Dosage Evaluation Example
A 5-MeV  particle is absorbed by 1 gram of water,
estimate the dosage in rad and rem.
5MeV 1.6 10-13 J 107 erg 1 rad
= 8.0 10-8 rad
1g
1 MeV
1 J 100 erg
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 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.
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 unit
Exposure unit 1 Gy = 100 rad (=100 R)
Biological dose 1 Sv = 100 rem (= Qrad)
Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent man
Summary of Units for Radioactive Dosage
Quantity Symbol
SI unit
cgs unit
Conversion factor
1 Ci = 3.7e10 Bq
1 C/kg = 3876 R
1 Gy = 100 rad
=6.24 eV/g
1 Sv = 100 rem
radioactivity
exposure dose
absorbed dose
A
X
D
Bq
C/kg
Gy (J/kg)
Ci
R
rad
biological dose
H
Sv (QF*Gy)
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 different
doses 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 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?
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 of
indirectly ionizing particles in matter of mass m, then
total moss interaction coefficient
the linear energy absorption coefficient
μtri which account for fewer
secondary photons escaping from
the interaction
site, are sometimes encountered.
(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).
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.
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。
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 is
found to
.
Example
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 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, FeSO4, solution is a chemical dosimeter due to the
reaction:
4 Fe2+ + energy + O2  4 Fe3+(brown) + 2 O2Some 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 3dimensional dosimeter, because the complexes are localized in the
gel. These dosimeters are useful for planning radiation medical
treatments such as radiation cancer treatment.
2.3 Radiation Doses and hazard Assessment
1)
2)
3)
4)
Historical Roots
Dosimetric Quantities
Natural Exposures for Humans
Radiation Effects
3) Natural Exposures for Humans
Radioactivity in Nature
222Rn
is responsible for
higher levels of
background radiation in
many parts of the world.
Radon
The uranium decay series.
because it is a gas and
can easily seep out of
the earth into unfinished
basements and then into
the house
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
, , g
and offsprings
144Nd, 147, 148, 149Sm, 152Gd, 186Os, 190,
 (g)
192Pt
40K, 87Rb, 115In, 123Te, 138La, 176Lu,
187Re, 210Bi
+, , EC (g)
etc.
Nuclides produced by cosmic rays
14C
(5730 y), 3T (15 y), 7Be (53 d),
10Be (2.7×106 y)

2.3 Radiation Doses and hazard Assessment
1)
2)
3)
4)
Historical Roots
Dosimetric Quantities
Natural Exposures for Humans
Radiation Effects
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.
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)
Deterministic Effects in Organs and Tissues
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.
Exposure Limit
Maximum permissible dosage of workers in radiation zone
Max. accumulated
mSv
Whole body
Hands and
forearms
Max. dose/13 wk
mSv
50(age-18)
30
250 (750/y)
1 Sv = 1000 mSv = 100 rem
Response
We are facing many environmental toxic agents.
The risk estimation of these agents should be based
on dose response curve.
Dose
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.
Biological response to low dose radiation
is complicated.
Biological
Response
Bystander effect
ICRP (International Commission on
Radiological Protection)
Adaptive response
Dose
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.
Bystander Effects
The
When
signals
a cellsent
is damaged
by the bystander
by radiation,
cells itmay
canhelp
sendrepair
signals
thetodamaged
bystander
cell,
cells,
or it
may
which
trigger
are the
the cell
cellstonear
commit
the “hit”
cell suicide.
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.
Micronuclei
Geard
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.
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
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
Lower half of lungs
communication
irradiated with 10 Gy
between cells.
Shielded
Cells
400
Micronuclei/1000 Cells
800
Exposed Cells
Khan et al 1998
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
Single ion hit system
•A gradual deterioration
due to accumulated
radiation damage
•Transient malfunctions
due to single particles
hitting a sensitive node.
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 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.
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）.
Genomic Instability
Delayed 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
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.
Cell death
Gene
mutation
Chromosome
aberration
Micronuclei
Mitotic failureaneuploidy（ 非整倍的）
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
Aberrations/Cell
0.35
Sensitive BALB/c mice
Resistant C57BL/6 mice
0.3
0.25
0.2
0.15
0.1
0.05
0
4
8
12
16
20
24
28
Population Doublings
B. Ponnaiya & R.L. Ullrich, 1998
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
mSievert)
(
Total Body Therapy
0
10000
20000
1000
2000
Typical mission dose on Int. Space Station
0
100
30000
40000
3000
50000
4000
5000
Significant cancer risk at > 200 mSv
(UNSCEAR)
200
300
60000
70000
80000
90000
100000
Experimental Radiobiology
Human LD50
A-bomb survivors
0
Cancer Radiotherapy
Total Tumor Dose
400
500
6000
7000
8000
9000
10000
Cancer Epidemiology
600
700
800
900
1000
DOE Low Dose Program
Occupational Limit NRC, EPA
0
10
20
30
40
50
Typical annual dose for commercial airline flight crews
Thyroid (I-123)
0
Bone (Tc-99m)
1
2
3 background
4
Natural
Site Decommissioning/License Termination
60
70
80
90
100
Medical Diagnostics
5
6
7
8
9
10
NRC Dose Limit for Public
Dental X-ray
Chest X-ray
0
0.1
0. 2
EPA Clean-up Standards
0.3
0. 4
0. 5
0.6
0.7
0.8
NRC Clean-up Standards
0.01
0.02
3-Mile Island Ave Ind
0.03
0.04
0.05
1
Regulatory Standards
ICRP Negligible Dose
0
0. 9
0.0 6
0.0 7
0.08
0.0 9
0.1
Radiation-induced mutation
in liver of gpt-delta mouse
6
-6
MF (10 )
5
920 mGy/min
4
3
1 mGy/min
12.5μGy/min
2
1
0
0
2
4
6
Dose (Gy)
8
10
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
2.3 Radiation Doses and hazard Assessment
1)
2)
3)
4)
Historical Roots
Dosimetric Quantities
Natural Exposures for Humans
Radiation Effects
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
55-CESIUM-137
y(i)
Radiations (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
g1
5.80×10-06
2.835×10-01
1.64×10-06
g2
8.51×10-01
6.617×10-01
5.63×10-01
With a frequency of 0.849 per decay