radiation effects of a nuclear bombnsl/lectures/phys20061/pdf/18.pdf · damage radioactive...
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Radiation Effects of a Nuclear BombBeside shock, blast, and heat a nuclear bomb generates high intensity flux of radiation in form of γ-rays, x-rays, and
neutrons as well as large abundances of short and long-lived radioactive nuclei which contaminate the entire area of the
explosion and is distributed by atmospheric winds worldwide.
T1/2=5730y
Effective half-life ~5-10 y(photosynthesis)
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14C distribution+ nuclear test related 14C production
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Nuclear Bomb related Radiation Production
The units rad (rem) are a measure of radiation exposure!
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Monitoring radiation intensity
[ ]
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sdecays
dtdNCi 10107.31Classical Unit: 1 Curie [Ci]
[ ]
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sdecay
dtdNBq 11Modern Unit: 1 Becquerel [Bq]
The so-called dosimetry units (rad, rem) determine the amount of damage radioactive radiation can do to the human body. They depend on the kind and nature of the incident radiation
(X-rays, γ-rays, α-particles, β-particle, or neutrons).It also depends on the energy loss of the particular radiation and the associated ionisation effects in the human body material.
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Radiation Detection
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Radiation Exposure & Dosimetry
Dose: DEm
=Amount of energy E deposited by radiation into body part of mass m. unit Rad or Gray
Equivalent Dose: H Q D= ⋅ Radiation independent doseQ is normalization factorwhich accesses the individual body damage done by the particular kind of radiationUnit Rem or Sievert
Photons: Q=1Neutrons: E<10keV Q=5Neutrons: E>10keV Q=15Protons: Q=5Alphas : Q=20
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UNITS OF RADIATION MEASUREMENTDosage units:The Sievert (Gray) is a measure of biological effect.1 Gray (Gy) = 1 Joule/kg (Energy/mass)1 Sievert (Sv) = Gray x Q, where Q is a "quality factor" based on the type of particle.
Q for electrons, positrons, and x-rays = 1 Q = 3 to 10 for neutrons, protonsdependent upon the energy transferred by these heavier particles. Q = 20 for alpha particles and fission fragments.
Converting older units: 1 rad = 1 centigray = 10 milligrays ( 1 rad = 1cGy = 10 mGy ) 1 rem = 1 centisievert = 10 millisieverts ( 1 rem = 1cSv = 10 mSv )
Nominal background radiation absorbed dose of 100 mrad/year = 1 mGy/yr. Nominal background radiation dose biological equivalent of 100 mrem/year = 1mSv/yr. Occupational whole body limit is 5 rem/yr = 50 mSv/yr. 2.5 mrem/hr or 25 uSv/hr is maximum average working level in industry.
Exposure rate from Naturally Occurring Radioactive Material; an empirically derivedconversion factor for Ra-226 decay series: 1.82 microR/ hour = 1 picoCurie/gram.
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Exposure to Natural and Man-made Radioactivity
Total average annual dose:H ≈ 250-300 mrem
Tobacco contains α-emitter 210Po with T1/2=138.4 days. Through absorption in the bronchial system smoking adds 280 mrem/year to the annual dose of US populationAverage annual dose from nuclear
bomb test fallout Hfo ≈ 0.06 mrem.
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Sources of Natural and Radioactivity
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Spectrum of CR
Cosmic Rays origin from:• solar flares;• distant supernovae;
Cosmic Ray Bombardment
Low energy CR
High energy CR
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Cosmic Rays in High AltitudeEarth is relatively protected from cosmic rays through atmosphere shield; typical exposure is H=3.2 mrem/h. Mountain climbers and airline crews and passengers are exposed to higher doses of radiation. Dose doubles every 1500 m in height. At 10 km height dose is about 100 times sea-level dose H=0.32mrem/h.
Example: Total dose H:• after 10h of flight:H=3.2 mrem,
• for round trip:H=6.4 mrem
• Frequent flyer with about 10 transatlantic flights/yearH=64 mrem/year.
Compare to natural dose (~200 mrem/y) !
( ) ( )mhn
mnh DDn 15001500 0
2 =⋅= ⋅=
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Observable Effects!
Husband’s ringwith transatlantichigh altitude dose
8 times more dose
Wife’s ringwith groundlevel dose!
Au γ-activity
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Natural Radioactivity in the US
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Long lived 40K Radioactivity40K has a half-life of T1/2=1.28·109 yearsits natural abundance is 0.021 % 40K
40Ar 40Ca
β+ β-
γ
40Ar40K
Potassium decay to Argon
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Internal γ GlowingOn average, 0.27% of the mass of the human body is potassium K of which 0.021% is radioactive 40K
with a half-life of T1/2=1.25·109 [y]. Each decay releases an average of Eavg= 0.5 MeV β- and γ-radiation,
which is mostly absorbed by the body but a small fraction escapes the body.
Calculate, how many radioactive 40K atoms are in your body system!
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Some Mass and Number Considerations
[ ] [ ]
[ ]
[ ]particlesNkg
mN
gparticlesmN
Nparticlesm
gmm
atomsKg
m.m.m
m.m
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00270 :body in theK potassium of mass
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−−
−
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Example: 40KCalculate the absorbed body dose over an average human
lifetime of t = 70 y for this source of internal exposure.
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Dose DEm
t A KEm
Activity A K N T N
D y g mMeV
m
D MeV kg J kg Gy
with eV J
absorbed
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40
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4 88 1005
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λ
1.25 10 [y]9 (8.54
[ ] [ ] [ ]
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radGykgJkgMeVD
19
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• Radon is a radioactive inert gas.• Radon progenies build up in confined space – are breathed in, stick to surface
of airways and emit α-particles.• Basal cells in bronchial epithelium are believed to be target cells for cancer.
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Annual Average Total Effective Dose Equivalent to the U.S. Population
Natural Background, Radon 200 mremsCosmic and Terrestrial source 56Medical and Dental X-Rays 54Internal Source, 40K 40Tobacco Smoking 280Other Consumer Products 10
Total, All Population 640Total, Non-Smokers 360
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Comparing the Risks: Radiation, Smoking, and Driving
A full set of dental X-rays using a high energy X-ray machine and E-speed film has a relative cancer risk equivalent to that of smoking ~2-3 cigarettes.
31312817.5 x 10-6875 mremsBarium enema
2811.41.6 x 10-678 mremsSkull examination
3.61.52 x 10-710 mremsChest radiograph535722003 x 10-415 rems
131I treatments for thyrotoxicosis
From LeukemiaBone Marrow
Number of Highway Miles Driven
Number of Cigarettes SmokedChance of DeathDoseProcedure
Equivalent to
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Release of Radiation by Nuclear Bomb Nuclear bomb causes sudden release of a high flux on:
γ-rays E=hν≈1-10 MeV electromagnetic wavesx-rays E=hν≈1-100 keV electromagnetic wavesα-radiation 4He nucleiβ-radiation electrons and positronsneutrons neutronsheavy radioactive species (cause for delayed radiation)
The prompt radiation is absorbed in the surrounding atmosphere according to exponential absorption law
deIdI ⋅−⋅= µ0)( I0 is the initial intensity and µ is the
attenuation coefficient determined by the interaction probability of radiation with molecules and atoms in air.
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Hiroshima radiation spread dataPrimary γ ray originated low dose of <100 rad near the hypocenter,secondary γ-ray originated dose of >100 rad within 1500 m radius
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Absorption probabilityAttenuation coefficient µ depends on energy and natureof particle, medium and interaction probability. High Coulomb scattering probability for charged particles, causes high absorption probability, results in short range!
1 m Concrete1 m Concrete
AlphaAlphaBetaBeta
GammaGammaNeutronNeutron
Energy Range(α) Range(β)keV cm cm
10 0.01 0.2100 0.10 16.0
1000 0.50 330.010000 10.50 4100.0
Main component gammas & neutrons
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Neutrons originatedsecondary γ radiation by inelastic neutronscattering as well as by neutron captureon nitrogen isotopesin the surrounding air.Secondary γ-productionenhances radiation fluxand radiation extension.
Spread of prompt & secondary γ-radiation
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Fission products
127I
126Te
130Te129Xe128Te
126Cd
126Ag
128Cd
127In
127Cd
127Ag
128Sn
128In
130Sn129Sn
129In
125Te
e.g. 126Ag(β-,n)125Cdvs 126Ag(β-)126Cd
Production of neutron-richradioactive isotopes in themass 80-130 range whichdecay by β- decay or by β-delayed neutron emissionBack to stable isotopes.Decay time scale dependsOn the associated half-liveswhich determine the fluxand time scale for delayedradiation exposure.
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Decline by the “rule of seven”This rule states that for every seven-fold increase in time following a fission detonation (starting at or after 1 hour), the radiation intensity decreases by a factor of 10. Thus after 7 hours, the residual fission radioactivity declines 90%, to one-tenth its level of 1 hour. After 7·7 hours (49 hours, approx. 2 days), the level drops again by 90%. After 7·2 days (2 weeks) it drops a further 90%; and so on for 14 weeks.
The rule is accurate to 25% for the first two weeks, and is accurate to a factorof two for the first six months. After 6 months, the rate of decline becomes much more rapid.
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Dose received from bomb tests
http://ntsi131.nci.nih.gov/
Welcome to the Individual Dose & Risk Calculator for the Nevada test side fall out: 131I exposure