sizes. w. udo schröder, 2007 nuclear decay 2 decay types there are many unstable nuclei - in nature...
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W. Udo Schröder, 2007
Nu
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Deca
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Decay Types
There are many unstable nuclei - in nature Nuclear Science began with Henri Becquerel’s discovery (1896) of uranium radioactivity
and man-made:
+30 30 30 J oliot &Al( ,n) P Si ,1934
Th source
Curi
, E
e
6 MeV
Types of decay:
1 1
1 1 1
A A 4Z N Z 2 N 2
A AZ N Z 1 N 1 e
A AZ N Z 1 N 1 e
A AZ N Z 1 N 1 e
A A A x yAZ N Z N Z Z y N x
decay : X Y
decay : X Y e
decay : X Y e
e capture : X Y ( e )
Fission : X F F xn yp
Various rare heavy particle(cluster ) decays
“weak” decays
W. Udo Schröder, 2007
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Domains of Nuclear Decay Modes
N=126
Isotones
Z=82 Isotopes
A
Neutron Dripline
Bn = 0
SHE Z=118 discovered (?)
Proton Dripline Bp = 0
Ef = 0
Segré Chart
stable nuclide
A = 132 Isobars
Stable nuclides
W. Udo Schröder, 2007
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Example: ThB (212Pb) Decay Scheme
212Pb ground state decays spontaneously by e- emission (- decay)
212Bi ground state has branched ( and ) decays
208Pb ground state is stable
W. Udo Schröder, 2004
Pri
nci
ple
s M
eas
5
Measuring “Decay Curves”: Fast-Slow Signal Processing
Radiation
Source
Slow
Fast
PreAmp
Amp
Produce timing signal
electron. Clock(TAC)
Data Acquisition System
Energy
E-Tag
Produce analog signal Binary
data to computer
EnergyDiscriminator
TimeTrigger
Start
Stop
External Time reference signal t0
Detector
Measured: Energy and time of arrival t=t-t0 (relative to an external time-zero t0) for radiation (e.g., -rays), energy discriminator to identify events (A) in a certain energy interval E by setting an identifier “tag.”
Calibrate t axis channel # time units (s, y,..)Watch that t-channel .
0 100 200 300 4000.01
0.1
1
i
t
Act
ivit
y
A(
t)/
A(t
0)
t (Channel #)
t
A( t ) exp
W. Udo Schröder, 2007
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Example: Determination of the 198Au g.s. Lifetime
E. Norman et al., http://ie.lbl.gov/radioactivedecays/page2
411.8 keV
411.8 keV
Spectrum of delayed 198Au -rays
Spectrum of delayed 198Au -rays decay of 198Hg exc. state is prompt:
11 measurementsEach spectrum ran for 12 hours real time#11 taken 5 days after #1
# 1
# 11
Kinetics of Nuclear Decay: Logarithmic Decay Law
2.303
:
# /
( )
( 2.1828..)
( ) ( 0)
( 10)
( ) 1( 0)
( 2)
( 0
0
( )
1
)
t
t
e l
First order process
Activity of decays unit time
dA N N t N
dt
exponential law base e
N t N t
exponential law base
N t N t
exponential law b
ife time
ase
N t N t 0.
/ 2
1
1
6932
0.
:
6931
t
Deca
ha
y w
lf
idth
life t
0 100 200 300 4001 10 2
0.1
1
i
t
0 100
200
300
400
0
0.2
0.4
0.6
0.8
1
Disintegration of Radioactive Sample
i
ti
Sam
ple
Act
ivit
y A
(t)/
A(0
)
time t
time t
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Radio-Activity/Units
1
10
Number of nuclei in sample : N N(t ) changes in time
Differential probability for a nucleus to decay (dimension time )
Activity A(t ) : N(t )
Units of activity : 1Bq(Becquerel ) 1disintegration / s
Old : 1Ci (Curie) 3.7 10 di sintegr
226
3
ations / s ( 1g Ra)
radiation energy abs.Absorbed dose : D
mass of material m
Unit [D] 1Gy (Gray ) 100 rad 1J / kg
Old : 1R(Roentgen) 8.8 10 J / kg in air (material dependent )
Bio log ically equivalent dose H weight D
unit [H] 1Sv (
2
Sievert ) 1 J / kg
Old unit 1rem 10 Sv
19
18
1eV 1.602 10 J
1 J 6.242 10 eV
W. Udo Schröder, 2007
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Average Radiation Exposure
From Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001
(238U, 232Th, 40K)
(219Rn, 220Rn, 222Rn)
Tobacco absorbs Rn 210Pb, 210Po“hot spots” in lungs cancer risk
Note unit: Sv
W. Udo Schröder, 2007
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Biological EffectsAnn. ICRP 26, 1994
Heavy charged particles:High ionization density, localized: maximum near end of range (Bragg peak)
Electrons (+Bremsstrahlung):Long range, diffuse multiple scattering, low ionization density, delocalized absorption
Neutrons:Indirect ionization, capture H(n, ) for En<100 eV, keV-neutrons scatter elastically (np), 2-MeV neutrons have = 6 cm to thermalization and high ionization density. Photons:Like electrons, low ionization density, Compton scattering + photoelectric absorption, delocalized absorption
Indirect chemical effects:Free radicals (neutral atom or molecule with an unpaired e-)
2 2
2 2
2 2
2
2
RH OH
H O rad H O e
H O e H O
H O H OH
H O H OH
R organic
RH H R H
R O RO peroxy radical
2 2
Oxygen Effect (Chain Re ac
RO RH R
tion)
O H R
W. Udo Schröder, 2007
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Biologically Relevant Dose Weighting Factors
Type Energy Range
Weighting wR
e± all 1
neutrons < 10 keV 5
10-100 keV 10
100 keV – 2 MeV
20
2 - 20 MeV 10
>20 MeV 5
protons < 20 MeV 5
, FF, clusters
20
tissue radiation tissue,radiation
T R T ,R
T R T ,RR
T TT
Biol. equivalent dose (Damage due to energy deposition)
H w D
Brief : H w D
Combination of different rads,H w D
Combination of different tiss. Equivalent dose E w H
Tissue Weight wT
Gonads 0.20
Red bone marrow 0.12
Colon 0.12
Lungs 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Oesophagus 0.05
Thyroid 0.05
Skin 0.01
Bon surface 0.01
All remaining tissue 0.05
Ann. ICRP 26, 1994
W. Udo Schröder, 2007
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Effect on Complex Molecules
Enzyme deoxyribonuclease (DNAse)
Splits DNA
Rad exposure decreases activity exponentially with dose
•High DNAse concentrations: expect more direct hits, direct damage of molecule
•Low DNAse concentration: expect fewer direct hits, less direct damage.Observation due to more free OH. and H. radicals from H2O dissociation.
DNAse in Water
Recovery: DNA molecules can repair themselves after moderate damage by X rays and minimum ionizing radiation.
Approximately total recovery after small doses, no accumulation of effects
More damage and less recovery after irradiation with neutrons
X-rays, Assay at t0
t0+5hrs
Neutrons Assay at t0
t0+5hrs
DNA Survival Rate
After Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001
W. Udo Schröder, 2007
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Risk Factors
Tissue Effect Probability/Sv
Breast Cancer 2.0 x 10-3
Red bone marrow Leukemia 5.0 x 10-3
Lung Cancer 8.5 x 10-3
Thyroid Cancer 8.0 x 10-4
Bone surface Cancer 5.0 x 10-4
Other tissue Cancer 3.4 x 10-2
Whole body Cancer effects 5.0 x 10-2
After Lilley, Nuclear Physics, Principles and Applications, J. Wiley & Sons, Ltd., 2001
W. Udo Schröder, 2007
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clear
Deca
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Intrinsic Nuclear Spin
Nuclei can be deformed can rotate quantum mech. collective spin and magnetic effects (moving charges)
Intrinsic spin? Nucleons have spin-1/2Demonstrate via interaction with external B
odd-A : I= half-integer multiple of ħeven-A: I= integer multiple of ħeven-Z & even-N: I = 0
Quantum mechanical spin:
2 2, ,
, ,
1 3ˆ ( 1) 0, ,1, ,....2 2
ˆ ( 1)
2 1
ˆ
I m I mI I
z I m I I m II I
I I I I
I I I I
I different magnetic substates
I m I m I
“good” quantum numbers: I, mI
2B Ip
eW B g I B
m
Interactions via magnetic moment
mIħ
z
x
yI
quanti
zati
on
axis
I
I 2Np
em
Nuclear Magneton
expt fact
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