resonance reactions
DESCRIPTION
Resonance Reactions. HW 34. In the 19 F ( p , ) reaction: The Q-value is 8.??? MeV. The Q-value for the formation of the C.N. is 12.??? MeV. For a proton resonance at 668 keV in the lab system, the corresponding energy level in the C.N. is at 13.??? MeV. - PowerPoint PPT PresentationTRANSCRIPT
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
1
Resonance Reactions
In the 19F(p,) reaction:• The Q-value is 8.??? MeV.• The Q-value for the formation of the C.N. is 12.??? MeV.• For a proton resonance at 668 keV in the lab system, the corresponding energy level in the C.N. is at 13.??? MeV.• If for this resonance the observed gamma energy is 6.13 MeV, what is the corresponding alpha particle energy?• If for this resonance there has been no gamma emission observed, what would then be the alpha particle energy?
HW 34HW 34
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
2
Neutron Resonance Reactions
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
3
Neutron Activation Analysis
(Z,A) + n (Z, A+1)-
(Z+1, A+1)
(-delayed -ray)
http://ie.lbl.gov/naa
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
4
Neutron Attenuation
Neutrons
ndxI
dIt
TargetThickness “x”
nxo
teII
Similar to -attenuation. Why?
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
5
Neutron Moderation
Show that, after elastic scattering the ratio between the final neutron energy E\ and its initial energy E is given by:
For a head-on collision:
After n s-wave collisions:
where
HW 35HW 35
2
2\
)1(
cos21
A
AA
E
E CM
2
min
\
1
1
A
A
E
E
nEEn lnln \
1
1ln
2
)1(1ln
2
\
A
A
A
A
E
E
av
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
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HW 35 HW 35 (continued)(continued)
How many collisions are needed to thermalize a 2 MeV neutron if the moderator was:
1H 4He 238U
Discuss the effect of the thermal motion of the moderator atoms.
Neutron Moderation
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
7
Nuclear Fission
~200 MeV
Fission
Fusi
on
Coulomb effectSurface effect
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
8
Nuclear Fission• B.E. per nucleon for 238U (BEU) and 119Pd (BEPd) ?• 2x119xBEPd – 238xBEU = ?? K.E. of the fragments 1011 J/g• Burning coal 105 J/g• Why not spontaneous?• Two 119Pd fragments just touching The Coulomb barrier is:
• Crude …! What if 79Zn and 159Sm? Large neutron excess, released neutrons, sharp potential edge…!
MeVMeVfm
fmMeVV 2142502.12
)46(.44.1
2
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
9
Nuclear Fission
• 238U (t½ = 4.5x109 y) for -decay.• 238U (t½ 1016 y) for fission.• Heavier nuclei??• Energy absorption from a neutron (for example) could form an intermediate state probably above barrier induced fission.• Height of barrier above g.s. is called activation energy.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
10
Nuclear Fission
Liquid Drop
Shell
Act
iva
tion
Ene
rgy
(MeV
)
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
11
Nuclear Fission
Surface Term Bs = - as A⅔
Coulomb Term BC = - aC Z(Z-1) / A⅓
3
3
4R
2
3
4ab=
1
)1(
Rb
Ra23 abR
...)1( 252
...)1( 251
Volume Term (the same)
32
31
52
51 )1( AaAZZa SC fission
47~2
A
Z
Crude: QM and original shape could be different from spherical.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
12
Nuclear Fission
48300
)120( 2
Extrapolation to 47 10-20 s.
Consistent with activation energy curve for A = 300.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
13
Nuclear Fission
235U + n
93Rb + 141Cs + 2nNot unique.
Low-energy fission
processes.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
14
Nuclear Fission
Z1 + Z2 = 92Z1 37, Z2 55
A1 95, A2 140Large neutron excess
Most stable:Z=45 Z=58
Prompt neutronsPrompt neutrons within 10-16 s.Number depends on nature of
fragments and on incident particle energy.The average number is characteristic of
the process.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
15
Nuclear Fission
The average number of neutrons is
different, but the
distribution is Gaussian.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
16
Delayed neutronsDelayed neutrons
Higher than Sn?
~ 1 delayed neutron per 100 fissions, but essential for control
of the reactor.
Follow -decay and find the most
long-lived isotope (waste) in this
case.
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
17
Nuclear Fission
Nuclear and Radiation Physics, BAU, 1st Semester, 2006-2007 (Saed Dababneh).
18
Nuclear Fission
1/v
235U thermal cross sectionsfission 584 b.scattering 9 b.
radiative capture 97 b.
Fast neutrons should be
moderated.
Fission Barriers