ne 301 - introduction to nuclear science spring 2012
DESCRIPTION
NE 301 - Introduction to Nuclear Science Spring 2012. Classroom Session 3: Radioactive Decay Types Radioactive Decay and Growth Isotopes and Decay Diagrams Nuclear Reactions Energy of nuclear reactions Neutron Cross Sections Activation Calculations. Reminder. Load TurningPoint - PowerPoint PPT PresentationTRANSCRIPT
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NE 301 - Introduction to Nuclear ScienceSpring 2012
Classroom Session 3:
•Radioactive Decay Types•Radioactive Decay and Growth•Isotopes and Decay Diagrams•Nuclear Reactions
• Energy of nuclear reactions• Neutron Cross Sections• Activation Calculations
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ReminderLoad TurningPoint Reset slides Load List
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Let’s do some accounting…Mass of Oxygen Atom:
Mp=1.007276 amuMn=1.008665 amuMe=5.48e-4 amu
3
168
16.131912 amu
8 1.007276 amu
( ) 8 1.008665 amu 15.994915 amu8 5.48 4 amu
p
n O
e
Zm
A Z m MZm e
Mass Defect = Binding
Energy (BE)
1 amu = 931.49 MeV
168O
16 O
931.49 MeVBE = (16.131912-15.994915 amu) 127.61 MeV1 amu
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Chart of the Nuclides
Z
N
IsobarsIsotopes
Isotones
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Notice radioactive decay stabilizes atoms:
Question:
Do fission products normally have - or + decay?
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Reaction EnergeticsReaction reactants and products
If E is positive: reaction exothermic
releases energyIf E is negative, reaction endothermic
requires energyEndoergic and exoergic is sometimes used
A + B C + D + E
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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!
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Please remember…
BALANCE!
Before starting to work
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Balancing Reactions
nucleons 1 +16 = 16+1Charges
01n 8
16O 716N1
1p
1 16 16 0 10 8 7 1 1
1 16 16 10 8 7 1
n O N e p or
n O N H
(+) 0 + 8 = 7 + 1(-) -0 -8 = -7 -0 e- missing
0 1So in reality the reaction is:
Calculating Q…
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Q-value for the reaction is:
Using atomic mass tables:
1 16 16 10 8 7 1n O N H
( )1.008665 15.994915 16.006101 1.007825 0.010346 amu
931.494 MeV 0.010346 amu 9.637 MeV1 amu
A B C DM M M M MM
Endothermic reaction. Only a few fission neutrons can do it
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A beryllium target is irradiated in a proton accelerator to produce 10B. What is Q of the reaction?
11 5.5 M
eV
4.5 MeV
3 MeV
6.5 MeV
85 MeV
14%
0%7%
79%
0%
1 9 101 4 5p Be B
1. 5.5 MeV2. 4.5 MeV3. 3 MeV4. 6.5 MeV5. 85 MeV
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For clicker
1 9 101 4 5
(1.007825 9.012182 10.012937) 931.494 6.586H Be BQ MeV
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Excited NucleiMany reactions involve excited nucleiSometimes long lived states (isomers)Excitation energy has to be added to the mass of the excited nuclei when calculating Q
e.g. The mass of 22Ne* at 1274 MeV is:
M ZAX * M Z
AX E *
c 2
22 2210 10*
1amu* 21.991386 1274 MeV 23.3591 amu931.494MeVNe Ne
M M
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Decay SeriesThe radioactive minerals contain many nuclidesAll of them decay by either or decay A changes by 4, Z by 2 A does not change, A by 1
Th has one long lived isotope 232ThU has two long lived 235U, 238U
Series identified by relation Parent to Dauthers mass:
A in multiples of 4
There are 3 natural series
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NoticeBranching
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Series are:A = 4n --- Thorium Series
A = 4n+2 -- Uranium Series
A = 4n+3 – Actinium Series
Which one is missing?
A = 4n+1 – Neptunium Series (Artificial)
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It was there from the beginning… but notice: half life of 237Np is relatively low.
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Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)
Decay Type Description EmissionGamma ()
Decay of excited nucleusGamma 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 Protonneutron (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
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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
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Comments:, +, - are common modes of decayLong T1/2 usually are -emittersn, p emission are rare (excess p+ atoms) is predominant for Z>83 (above Bismuth) and atoms away from the line of -stability.Some high Z atoms (Z>96) have dominant spontaneous fission mostly dominates again at Z>105
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Modes of Decay, +, - are common modes of decayLong T1/2 usually are -emittersn, p emission are rare (excess p+ atoms) is predominant for Z>83 (above Bismuth) and atoms away from the line of -stability.Some high Z atoms (Z>96) have dominant spontaneous fission mostly dominates again at Z>105
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Solving momentum and KE equations
2 11 2
1 2 1 2
m mKE Q KE Qm m m m
Remember the conditions:1. Parent nucleus at rest (usually the case)2. Binary products only (not -decay, but OK to
Emax)3. Calculate the correct Q (excited states are
prevalent, and balance)4. Finally, there usually reaction paths with
many outcomes, therefore multiple Q-values
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Kinetic Energy of Radioactive Decay ProductsParent 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
m1m1
m2
Original atom that will split in 2 pieces
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Kinematics of radioactive decay…2 2
1 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 v2 2
m vv = replacing...m
m v1 1m ( ) m v2 m 2
m v1 1 1m v and replacing m v by KE2 m 2 2m solving for KEm
Q
Q
Q KE KE
KE Q
1 21
1 2 1 2
similarly: m mKE Qm m m m
Notice 2:1
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Warm up:What % of the energy should go to the -particle?
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98% 2%50%
10% 1%
20% 20% 20%20%20%
HeThU 42
23490
23892
1 22 1
1 2 1 2
m mKE Q KE Qm m m m
1. 98%2. 2%3. 50%4. 10%5. 1%
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Example of -spectroscopy?
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237Pa 237U
237Np 237Pu
237Am 237Cm
0% 0% 0%0%0%
100%241 ?Am
1. 237Pa2. 237U3. 237Np4. 237Pu5. 237Am6. 237Cm
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Find Q for:
28 3.638 M
eV
4.638 MeV
5.638 MeV
6.638 MeV
7.638 MeV
20% 20% 20%20%20%
241 237 495 93 2Am Np He
1. 3.638 MeV2. 4.638 MeV3. 5.638 MeV4. 6.638 MeV5. 7.638 MeV
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For Clicker slide:Q=(241.056823-237.048167-
4.002603)*931.494=5.638MeV
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What is the KE of the particle in the radioactive decay of 241Am? (3 min)
30 0.09 M
eV
0.98 MeV
5.54 MeV
5.64 MeV
25% 25%25%25%
1. 0.09 MeV2. 0.98 MeV3. 5.54 MeV4. 5.64 MeV
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For Clicker slide:
KE=5.638*237/(237+4)=5.545 MeV
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Notice:If alpha particle ALWAYS leaves with exactly the same energy.We would expect to detect a monoenergetic beam of ’s.
In reality…
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The real alpha spectrum of 241Am is:
At least 5 different energies…
Why?
Excited Nuclei!
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The real decay path of 241AmThere are actually 6 alpha peaksLast two peaks are too close to be resolvedNotice frequencies (%’s)Every decay path happens all the time but not with equal probabilityLook in your book:
Page 578. 241AmTaken from J. K. Beling, et al. Phys. Rev. 87 (1952) 670-671
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Diagram means:
Energy of the -particle?
Same old same old
But Q is different each time
24195
*170 KeV
24195
*114 KeV
24195
*71 KeV
24195
*43 KeV
24195
*11 KeV
24195
237 * 493 2
237 * 493 2
237 * 493 2
237 * 493 2
237 * 493 2
237 493 2
Am
Am
Am
Am
Am
Am
Np He
Np He
Np He
Np He
Np He
Np He
2
mKE Qm m
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3.6
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4.0
By the wayNotice also
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4.0
There are a lot more hard to see peaks
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So how is the “real” diagram?For that we need the
TABLE OF ISOTOPES
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Diagram 241Am - 1 of 2
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Diagram 241Am - 2 of 2
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The Table also includes a more complete list of particles emitted during decay
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’s
’s
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Main Radioactive Decay Modes (Table 5.1 -page 89-Shultis)
Decay Type Description EmissionGamma ()
Decay of excited nucleusGamma 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 Protonneutron (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