Alpha Decay. Radioactive Decay Alpha Decay Radioactive Decay Alpha Decay Beta Decay.
NE 301 - Introduction to Nuclear Science Spring 2012 Classroom Session 4: Radioactive Decay Types...
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Transcript of NE 301 - Introduction to Nuclear Science Spring 2012 Classroom Session 4: Radioactive Decay Types...
NE 301 - Introduction to Nuclear ScienceSpring 2012
Classroom Session 4:
•Radioactive Decay Types•Radioactive Decay and Growth•Isotopes and Decay Diagrams•Nuclear Reactions
• Energy of nuclear reactions• Neutron Cross Sections• Activation Calculations
2
Reminder
Load TurningPoint Reset slides Load List
The Energy Released (or consumed), Q
Change in BE:
Or since BE is related to mass defect
Change in M:
A + B C + D + E
( )C D A BQ BE BE BE BE BE
( )A B C DQ M M M M M
Preferred!because we have table B.1.
Remember: The Equation Has to Be
BALANCED!
Please remember…
BALANCE!
Before starting to work
5
Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)
Decay Type Description Emission
Gamma () Decay of excited nucleus
Gamma photon
alpha ()Alpha particle is emitted
Alpha particle
negatron (-) np++e-+ Electron and anti-neutrino
positron (β+) p+n+e++ Positron and neutrino
Electron Capture (EC)
Orbital e- absorbed: p++e-n +
Neutrino
proton (p) Proton ejected Proton
neutron (n) Neutron ejected Neutron
Internal Conversion (IC)
Electron (K-Shell) ejected*
Electron
Spontaneous Fission
(sf)
Fission fragments
*A AZ ZP P
1A AZ ZP D
42
A AZ ZP D
1A AZ ZP D
*1
A AZ ZP e D
*A AZ ZP P e
1 2 nAZ P D D x
6
7
Kinetic Energy of Radioactive Decay Products
Parent nucleus is at rest (Eth~ 0.025 eV~17 oC)
Conservation of Linear Momentum and Kinetic Energy requires products to travel in opposite directions (2 product).
m1v1=m2v2
Q=½ m1v12
+ ½ m2v22
What is the energy of emitted particle? (it is what we measure)
v1
m2
v2
m1
m1
m2
Original atom that will split in 2 pieces
8
Kinematics of radioactive decay…
2 21 1 2 2 1 1 2 2
2 21
1
2 22 21 2 2
1
2 22 22 2
2 2 2 2 21
22 2 2
1
2
1 1m v =m v Q= m v m v
2 2m v
v = replacing...m
m v1 1m ( ) m v
2 m 2
m v1 1 1m v and replacing m v by KE
2 m 2 2
m solving for KE
m
Q
Q
Q KE KE
KE Q
1 21
1 2 1 2
similarly: m m
KE Qm m m m
Notice 2:1
9
10
Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)
Decay Type Description Emission
Gamma () Decay of excited nucleus
Gamma photon
alpha ()Alpha particle is emitted
Alpha particle
negatron (-) np++e-+ Electron and anti-neutrino
positron (β+) p+n+e++ Positron and neutrino
Electron Capture (EC)
Orbital e- absorbed: p++e-n +
Neutrino
proton (p) Proton ejected Proton
neutron (n) Neutron ejected Neutron
Internal Conversion (IC)
Electron (K-Shell) ejected*
Electron
Spontaneous Fission
(sf)
Fission fragments
*A AZ ZP P
1A AZ ZP D
42
A AZ ZP D
1A AZ ZP D
*1
A AZ ZP e D
*A AZ ZP P e
1 2 nAZ P D D x
11
Beta Decay
Remember:’s DO NOT have
exactly defined energies
3 body interactionsMax energy =
neutrino took zero energy away…
What is this energy?Page 554
Page 98-Shultis
-, + produce three products:
Cannot say energy of Neutrinos by Fermi (1933)We only can say maximum energy of
13
Similarly for ’s
14
Kinetic Energy of De-excitation Decay
Details of the decays are needed to predict the correct spectrum.
Radioactive Decay Diagrams (e.g. book)
Write all 3 rxn shown
NiNi 6028
*6028
In principle gamma () photons would have Q of the reaction, but…
Q=2.50 MeV
16
Radioactive Decay Diagrams…In figure 5.6 Write all the reactions indicated in the
diagram.
If initially we have 100 g of 64Cu, how much Zn and Ni will we have after all Cu has decayed?
17
Branching Decay Example
1ln 20.0546
12.7h
h
?
?
?
?
EC
EC
1/ 2( )
1/ 2( )
1/ 2( )
1/ 2( )
?
?
?
?
EC
EC
T
T
T
T
1/2 T1/2 i
: is the frequency fraction or
TT
i T i i
i
f f
f
18
Branching Decay Example
-1ln 20.0546 h
12.7
1
1
1
1
0.005 0.0546 0.000273
0.431 0.0546 0.023533
0.174 0.0546 0.009500
0.390 0.0546 0.021294
EC
EC
h
h
h
h
1
0.000273 0.023533 0.009500 0.021294
0.0546
EC EC
h
19
On to
Binary Nuclear Reactions
Binary = 2 reactants (many times 2 products too)
Most important type of nuclear reactionMost elements produced by binary rxns. in stars
Nomenclature:
20
x X Y y Light nuclide usually projectile
Heavy nuclide usually target
Heavy Product
Light Product
21
Binary Reactions
(,p) First reaction reported by Rutherford:
Nitrogen in air bombarded by alphas producing protons
(,n) In 1932, the neutron was discovered (Chadwick).
Rxn. still used in some neutron generators today
24He 7
14N 817O1
1H or
714N(, p) 8
17O
24He4
9Be 612C0
1n or
49Be(,n) 6
12C
y)YX(x, or yYXx
22
Example Binary Reactions, cont.
(,n) Photo-nuclear rxns: Highly energetic gamma rays
can knock neutrons out of the nucleus.
(n,p) Fast neutrons react with oxygen in the water in a
reactor core producing radioactive 16N.
12H 1
1H01n or
12H(,n)1
1H
01n 8
16O 716N1
1p or
816O(n, p) 7
16C
or
12H(, p)0
1n
Mechanisms of Nuclear Reactions
Direct Interactions Projectiles w/
KE>40MeV have de Broglie wavelengths ~ size of a nucleon in target nucleus
Usually interact with individual nucleons
Near surface of nucleus (peripheral reactions)
Compound Nucleus Projectiles w/ KE ~
MeV have de Broglie wavelengths ~ size of the whole target nucleus
Usually interact with whole nucleus
Forms compound, highly excited nucleus
Products have no “memory” of the reactants.
23
( )*x X x X Y y
Reaction Nomenclature:
Transfer Reactions (,d) (d,n)
Scattering Reactions (x,x) elastic (x,x’) inelastic
Knockout Reactions (n,2n) (n,3n) (n,np)
Capture (n,)
Photo-Nuclear (,n)
24
Direct Reactions 1-2 nucleons transfer between projectile and target
projectile and target remain the same (it is a collision)
Direct Reaction: Original projectile emerges and is accompanied by other nucleons (i.e. spallation: SNS)
Projectile is absorbed by target nucleus (usually leaving it excited)
Strong gamma kicks nucleon from the target nucleus
25
For Binary Reactions: x +X Y + yx is a projectile with KE (Ex). X is a target stationary nucleus EX=0
simplification
y Cosy
0, RealyE
26
y Cosy
0, RealyE
A 5.5 MeV particle is incident on Li causing 7Li(,n)10B. What is the KE of neutron scattered 30o?
A 5.5 MeV particle is incident on Li causing 7Li(,n)10B. What is the KE of neutron scattered 30o?
27
0, RealyE
y Cosy
1. 0 MeV2. 0.31 MeV3. 1.31 MeV4. 2.31 MeV5. 3.31 MeV6. 5.5 MeV
7Li(alpha,n)10B
28
FIRST BALANCE THE EQUATION!!!
Endothermic Rxn
Neutron Energy = 1.31MeV
What would be the neutron energy if incident alpha particle is 1MeV instead?
Can’t happen…
Solution exists only if 0, RealyE
Potential “” Factors Q<0 Heavy projectiles (mY-mx<0) Large scattering angles Cos <0
Big enough Ex can guarantee Physical meaning: Threshold
Energy
0, RealyE
Argument of root >0