Lomonosov%20Moscow%20State%20University,%20Skobeltsyn%20Institute%20of%20Nuclear%20Physics

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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
• irina_at_depni.sinp.msu.ru

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(No Transcript)
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GDR
QD
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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 ?-quanta energy of up
to 70 MeV.
Electron racetrack microtron RTM-70 Skobeltsyn
Institute of Nuclear Physics, Moscow State
University

• Electron accelerator microtron RTM-70
• Canberra HPGe detector with efficiency of 30
• Automated system for collecting and analysis of
  ?-spectra
• Nuclear data bases
• GEANT Monte-Carlo simulation
• Theoretical models of multi-particle photonuclear
  reactions

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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

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209Bi(?,4n)205Bi

• Channel identification
• ?-transition energy E?
• ?-transition relative intensity I?
• half-life T1/2
• These quantities were compared to tabular ones
• This method allows to determine photonuclear
  reaction channels definitely

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• 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
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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.
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Bremsstrahlung ?-spectrum for the max electron
energy ?e  67.7 MeV.Reaction thresholds in
209Bi nucleus
Reaction Reaction threshold, MeV Final nucleus half-life
209Bi(?,n)208Bi 7.46 3.68105 y
209Bi(?,2n)207Bi 14.35 32.9 y
209Bi(?,3n)206Bi 22.45 6.243 d
209Bi(?,4n)205Bi 29.48 15.31 d
209Bi(?,5n)204Bi 37.95 11.22 h
209Bi(?,6n)203Bi 45.15 11.76 h
209Bi(?,7n)202Bi 54.03 1.71 h
Irradiation duration 4.3 h. 314 series of
?-spectra measurement were made Sample
exposition 245 d
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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 ?? ? ?? ?? ?-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)

S? ?-peak area e? HPGe detector efficiency I?
?-transition relative intensity ? decay
constant of final nucleus ti, td, tm
irradiation, decay, and measurement time
relatively
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Photonuclear reactions yields in 209Bi
Reaction Exp. yield (rel. un.)
(?, 2n) 1.00 0.05
(?, 3n) 0.15 0.03
(?, 4n) 0.09 0.02
(?, 5n) 0.017 0.003
(?, 6n) 0.007 0.002
(?, 7n) 0.00012 0.00006
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Photonuclear reactions yields in 203,205Tl
Reaction Exp. yield (rel. un.)
203Tl(?, n)202Tl  205Tl(?, 3n)202Tl 1.00 0.03
203Tl(?, 2n)201Tl  205Tl(?, 4n)201Tl 0.18 0.06
203Tl(?, 3n)200Tl  205Tl(?, 5n)200Tl 0.029 0.003
203Tl(?, 4n)199Tl  205Tl(?, 6n)199Tl 0.011 0.002
203Tl(?, 5n)198Tl  205Tl(?, 7n)198Tl 0.004 0.001
203Tl(?, 6n)197Tl  205Tl(?, 8n)197Tl 0.0012 0.0005
205Tl(?, pn)203Hg 0.0035 0.0012
203Tl(?, 5n)198Tlm  205Tl(?, 7n)198Tlm 0.0012 0.0004
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1. Levinger J.S. // Phys. Rev. 84, 43 (1951)
2. Chadwick M.B. et al. // Phys. Rev. C 44, 814
   (1991)
3. Ishkhanov B.S., Orlin V.N. // ????, 38, 84 (2007)
4. Ishkhanov B.S., Orlin V.N. // Phys. At. Nucl.,
   71, 517 (2008)

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209Bi
Solid curves reactions cross sections dashed
curves QD cross sections.
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Photonuclear reactions yields in 203,205Tl
Reaction Exp. yield (rel. un.) Theor. Yield GDRQD (rel. un.) Theor. Yield GDR (rel. un.)
203Tl(?, n)202Tl  205Tl(?. 3n)202Tl 1.00 0.03 1.0000 1.0000
203Tl(?, 2n)201Tl  205Tl(?, 4n)201Tl 0.18 0.06 0.21 0.19
203Tl(?, 3n)200Tl  205Tl(?, 5n)200Tl 0.029 0.003 0.032 0.019
203Tl(?, 4n)199Tl  205Tl(?, 6n)199Tl 0.011 0.002 0.013 0.006
203Tl(?, 5n)198Tl  205Tl(?, 7n)198Tl 0.004 0.001 0.003 0.001
203Tl(?, 6n)197Tl  205Tl(?, 8n)197Tl 0.0012 0.0005 0.0008 0.0004
205Tl(?, pn)203Hg 0.0035 0.0012 0.0040 0.0026
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Photonuclear reactions yields in 209Bi
Reaction Exp. yield (rel. un.) Theor. Yield GDRQD (rel. un.) Theor. Yield GDR (rel. un.)
(?. 2n) 1.00 0.05 1.00 1.00
(?. 3n) 0.15 0.03 0.113 0.080
(?. 4n) 0.09 0.02 0.051 0.025
(?. 5n) 0.017 0.003 0.016 0.007
(?. 6n) 0.007 0.002 0.0041 0.0020
(?. 7n) 0.00012 0.00006 0.00012 0.00007
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Photonuclear reactions yields in 197Au
Reaction Exp. yield (rel. un.) Theor. Yield GDRQD (rel. un.) Theor. Yield GDR (rel. un.)
(?,n) 1.0000 1.0000 1.0000
(?,2n) 0.16 0.03 0.2039 0.1940
(?,3n) 0.023 0.002 0.0214 0.0141
(?,4n) 0.0074 0.0013 0.0097 0.0043
(?,5n) 0.0025 0.0002 0.0027 0.0010
(?,6n) 0.00050 0.00007 0.0006 0.0002
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Conclusions

• A research complex for multiparticle photonuclear
  reactions investigation is used in Skobeltsyn
  Institute of Nuclear Physics of Moscow State
  University
• 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.
• This method has made it possible to observe, for
  the first time, the entire set of multineutron
  photonuclear reactions (?, in) in heavy nuclei,
  where i ranges between one and seven.
• It has been established that the data obtained in
  our experiment can be described only by
  simultaneously taking into account both
  photodisintegration mechanismsthat 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.