Transcript PPT-presentation

LOMONOSOV MOSCOW STATE UNIVERSITY,
SKOBELTSYN INSTITUTE OF NUCLEAR PHYSICS
Multi-particle photodisintegration of heavy nuclei
A.N. Ermakov, B.S. Ishkhanov, I.M. Kapitonov, I.V. Makarenko, V.N. Orlin
[email protected]
GDR
QD
Experimental complex
A compact accelerator with maximum electron energy of
70 MeV, built with the use of permanent magnets based
on rare-earth magnetic materials. It can be used as a
source of bremsstrahlung with maximum γ-quanta energy
of up to 70 MeV.
Electron racetrack microtron RTM-70
Skobeltsyn Institute of Nuclear Physics,
Moscow State University
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Electron accelerator microtron RTM-70
Canberra HPGe detector with efficiency of 30%
Automated system for collecting and analysis of γ-spectra
Nuclear data bases
GEANT Monte-Carlo simulation
Theoretical models of multi-particle photonuclear reactions
CDFE
The Centre for Photonuclear Experiments Data
of the Moscow Lomonosov State University
http://www.cdfe.sinp.msu.ru
CDFE is the member of the Nuclear Reaction Data Centres Network (NRDCNW), a world-wide
cooperation of nuclear data centers from various countries under the auspices of the International
Atomic Energy Agency (IAEA).
The CDFE is responsible for compilation, analysis and evaluation of photonuclear data and
dissemination of nuclear data
209Bi(γ,4n)205Bi
Channel identification:
• γ-transition energy Eγ
• γ-transition relative intensity Iγ
• half-life T1/2
These quantities were compared to tabular ones
This method allows to determine photonuclear reaction channels definitely
Microtron RTM-70
Electron energy 67.7 MeV
Current: 4-5 mA
Pulse duration: 4 μs
Pulse frequency: 10 Hz
HPGe detector Canberra GC3019
Resolution:
0.9 keV (122 keV),
1.9 keV (1332 keV).
Comparing of irradiated 209Bi sample residual activity spectrum (curve 1) and background spectrum (curve 2).
Spectra were measured during 2 h
Relative method
Use of relative methods is the most effective when investigated and monitor reactions
cross sections are measured in the same target and at the same geometry.
The method allows to investigate up to 10 reactions simultaneously at the same
experimental conditions. This increases relative accuracy of reactions yields
determination.
Reaction
Reaction
Final nucleus
threshold,
half-life
MeV
209Bi(γ,n)208Bi
7.46
3.68∙105 y
209Bi(γ,2n) 207Bi
14.35
32.9 y
209Bi(γ,3n) 206Bi
22.45
6.243 d
209Bi(γ,4n) 205Bi
29.48
15.31 d
209Bi(γ,5n) 204Bi
37.95
11.22 h
209Bi(γ,6n) 203Bi
45.15
11.76 h
209Bi(γ,7n) 202Bi
54.03
1.71 h
Irradiation duration: 4.3 h.
314 series of γ-spectra measurement were made
Sample exposition: 245 d
Bremsstrahlung γ-spectrum for the max electron energy Еe = 67.7 MeV.
Reaction thresholds in 209Bi nucleus
Reaction yield
 (E)  reaction cross section
W(E,Em)  number of bremsstrahlung photons with energy E in elementary energetic interval
that are produced by monochromatic electrons Ее  Ет
Ет –γ-quanta max energy
M – total number of scattering centers in the irradiated part of the target
The following factors are taken into account:
• detector efficiency energy dependence
• self-absorption in investigated sample
• time factors (dependence on irradiation, decay, and measurement time)
Sγ –γ-peak area
εγ –HPGe detector efficiency
Iγ – γ-transition relative intensity
λ – decay constant of final nucleus
ti, td, tm – irradiation, decay, and measurement time relatively
Photonuclear reactions yields in 209Bi
Reaction
(γ, 2n)
(γ, 3n)
(γ, 4n)
(γ, 5n)
(γ, 6n)
(γ, 7n)
Exp. yield
(rel. un.)
1.00 ± 0.05
0.15 ± 0.03
0.09 ± 0.02
0.017 ± 0.003
0.007 ± 0.002
0.00012 ± 0.00006
Photonuclear reactions yields in 203,205Tl
Reaction
Exp. yield
(rel. un.)
1.00 ± 0.03
0.18 ± 0.06
0.029 ± 0.003
0.011 ± 0.002
0.004 ± 0.001
0.0012 ± 0.0005
0.0035 ± 0.0012
203Tl(γ, 5n)198Tlm + 205Tl(γ, 7n)198Tlm
0.0012 ± 0.0004
203Tl(γ,
n)202Tl + 205Tl(γ, 3n)202Tl
203Tl(γ, 2n)201Tl + 205Tl(γ, 4n)201Tl
203Tl(γ, 3n)200Tl + 205Tl(γ, 5n)200Tl
203Tl(γ, 4n)199Tl + 205Tl(γ, 6n)199Tl
203Tl(γ, 5n)198Tl + 205Tl(γ, 7n)198Tl
203Tl(γ, 6n)197Tl + 205Tl(γ, 8n)197Tl
205Tl(γ, pn)203Hg
1.
2.
3.
4.
Levinger J.S. // Phys. Rev. 84, 43 (1951)
Chadwick M.B. et al. // Phys. Rev. C 44, 814 (1991)
Ishkhanov B.S., Orlin V.N. // ЭЧАЯ, 38, 84 (2007)
Ishkhanov B.S., Orlin V.N. // Phys. At. Nucl., 71, 517 (2008)
209Bi
Solid curves – reactions cross sections
dashed curves – QD cross sections.
Photonuclear reactions yields in
203,205Tl
Reaction
Exp. yield
(rel. un.)
n)202Tl + 205Tl(γ. 3n)202Tl
1.00 ± 0.03
203Tl(γ, 2n)201Tl + 205Tl(γ, 4n)201Tl
0.18 ± 0.06
203Tl(γ, 3n)200Tl + 205Tl(γ, 5n)200Tl 0.029 ± 0.003
203Tl(γ, 4n)199Tl + 205Tl(γ, 6n)199Tl 0.011 ± 0.002
203Tl(γ, 5n)198Tl + 205Tl(γ, 7n)198Tl 0.004 ± 0.001
203Tl(γ, 6n)197Tl + 205Tl(γ, 8n)197Tl 0.0012 ± 0.0005
205Tl(γ, pn)203Hg
0.0035 ± 0.0012
203Tl(γ,
Theor. Yield Theor. Yield
GDR+QD
GDR
(rel. un.)
(rel. un.)
1.0000
0.21
0.032
0.013
0.003
0.0008
0.0040
1.0000
0.19
0.019
0.006
0.001
0.0004
0.0026
Photonuclear reactions yields in 209Bi
Reaction
Exp. yield
(rel. un.)
(γ. 2n)
(γ. 3n)
(γ. 4n)
(γ. 5n)
(γ. 6n)
(γ. 7n)
1.00 ± 0.05
0.15 ± 0.03
0.09 ± 0.02
0.017 ± 0.003
0.007 ± 0.002
0.00012 ± 0.00006
Theor. Yield
GDR+QD
(rel. un.)
1.00
0.113
0.051
0.016
0.0041
0.00012
Theor. Yield
GDR
(rel. un.)
1.00
0.080
0.025
0.007
0.0020
0.00007
Photonuclear reactions yields in 197Au
Reaction
Exp. yield
(rel. un.)
(γ,n)
(γ,2n)
(γ,3n)
(γ,4n)
(γ,5n)
(γ,6n)
1.0000
0.16 ± 0.03
0.023 ± 0.002
0.0074 ± 0.0013
0.0025 ± 0.0002
0.00050 ± 0.00007
Theor. Yield
GDR+QD
(rel. un.)
1.0000
0.2039
0.0214
0.0097
0.0027
0.0006
Theor. Yield
GDR
(rel. un.)
1.0000
0.1940
0.0141
0.0043
0.0010
0.0002
Conclusions
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A research complex for multiparticle photonuclear reactions investigation is used in
Skobeltsyn Institute of Nuclear Physics of Moscow State University
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New experimental data on the multinucleon photodisintegration of heavy nuclei in the
energy region behind the maximum of the giant dipole resonance up to a photon
energy of 67.7 MeV have been obtained by the method of gamma spectroscopy of
residual beta-active nuclei.
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This method has made it possible to observe, for the first time, the entire set of
multineutron photonuclear reactions (γ, in) in heavy nuclei, where i ranges between
one and seven.
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It has been established that the data obtained in our experiment can be described
only by simultaneously taking into account both photodisintegration mechanisms—
that of the excitation (and decay) of a giant dipole resonance and that of
quasideuteron photodisintegration. As the photon energy and the neutron multiplicity
increase, the contribution of quasideuteron photodisintegration grows, becoming
dominant for reactions involving the emission of not less than four neutrons.