Photodissociation studies of p-process nuclei with bremsstrahlung at ELBE

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Photodissociation studies of p-processnuclei
with bremsstrahlung at ELBE

• R. Beyer, M. Erhard, E. Grosse1 , A.R. Junghans,
• J. Klug, K. Kosev, C. Nair, N. Nankov, G. Rusev,
• K.D. Schilling, R. Schwengner, A. Wagner
• Forschungszentrum Rossendorf, Institut für Kern-
  und Hadronenphysik,
• Postfach 51 01 19, 01314 Dresden, Germany
• 1 also at Technische Universität Dresden

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Normalized overproduction factors

• Mo, Ru are consistently underproduced in network
  calculations .
• Are the photodissociation crosssections correct
  in this region ?
• e.g. 92Mo(?,p) (PhD work of Martin Erhard)
• 93Mo(?,n) (GSI experiment, S. Müller, TU
  Darmstadt)

M. Arnould, S. Goriely / Physics Reports 384
(2003) 184.
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Photoactivation and Nuclear Resonance
Fluorescence at ELBE

• Photon flux
• electron-beam dump ? 1010 (scm²MeV)-1
• NRF-target site ? 108 (scm²MeV)-1

R. Schwengner et al., NIM A555 (2005) 211
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Photo-activation measurements
Yield integral from continuous bremsstrahlung
activation
Activation yield determined by decay
?-spectroscopy, including decay corrections

• 197Au(?,n) as calibration reaction
• Renormalize theoretical ??,n(197Au) with
  197Au(?,n) yield and photon flux at target site.
• Use ??,n(197Au) to determine absolute photon flux
  at photoactivation site
• Determine ??,x for p-process nuclei from
  comparison with activation yield.

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Bremsstrahlung spectra

• Description of Bremsstrahlung spectra with
  different models ? Accuracy about 5 (Atomic
  screening included)
• Larger deviations at the high energy end (ca.
  20)

A.A.Al-Beteri,D.E.Raeside NIM B 44 (1989) 149 S.
Seltzer, M.J. Berger ADNDT 35 (1986) 345
L.I.Schiff, PR 83 (1951) 252 E.Haug priv.
comm. H.BetheW.HeitlerQuantum Theory of
Radiation, Dover 1984 G.Roche, C.Ducos,
J.Proriol Phys. Rev. A 5 (1972) 2403
(higher-order coulomb correction terms)
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Comparison of bremsstrahlung calculations
H.BetheW.HeitlerQuantum Theory of Radiation,
Dover 1984 A.A.Al-Beteri,D.E.Raeside Nucl.
Instr. Meth. B 44 (1989) 149G.Roche, C.Ducos,
J.Proriol Phys. Rev. A 5 (1972) 2403
(higher-order coulomb correction terms) S.
Seltzer, M.J. Berger ADNDT 35 (1986) 345

• Yield Integral uncertainty increases for
  end-point energy close to the reaction threshold
  T0 ? Eth 0.5 MeV

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MC simulated bremsstrahlung (thin target)

• GEANT3 Bremsstrahlung production not optimized
  for ?10 MeV energy range
• GEANT4 MCNP4C2 use Seltzer Berger tables
• MCNP used for simulation of bremsstrahlung
  spectrum at photoactivation site (thick Carbon
  target)

Seltzer Berger
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Bremstrahlung at beam dump activation site

• MCNP 4C2 to simulate thick target (C)
  bremsstrahlung (Seltzer Berger)
• Analytical parametrization of thick target
  bremsstrahlung
• Roche formula has a more precise Coulomb
  correction than Seltzer Berger (work in
  progress)

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End-point energy from d(?,p)n
Deuteron breakup ? Bremsstrahlung-spectrum via
? Determination of end point energy (80 keV
FWHM) Proton kinematics energy width of the
electron beam determine the spectral shape.
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Photon-flux distribution derived from 11B strength
Au samples irradiated at both sites as activation
standards 197Au(?,n)
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197Au as calibration standard
Au activation described well by TALYS code. Look
for (g,n) data with monoenergetic photons
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92Mo(?,p/n) reaction - decay scheme
n
p
?
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Activation yield and comparison with theory

• Experiment (data points)Ratio of activation
  yields.
• TALYS (dashed), Non Smoker (full
  lines)Hauser-Feshbach model cross sections ?
  photon energy distribution up to end point energy
  
• Both normalized to photodissociation cross
  section standard of 197Au.
• Absolute Photon flux at photoactivation site
  still under analysis

Talys A. Koning et al., Proc. Int. Conf. Nuclear
Data Science and Technology, ND2004, Santa Fe,
NM, USA, AIP Conf. Proc. 769, 177 (2005) T.
Rauscher and F.-K. Thielemann, Atomic Data and
Nuclear Data Tables, 88 (2004) 1
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92Mo(?,n)91Mo decay measurement

• Decay of 91gMo(7 h photoactivation of 677
  mg natMoat 16.5 MeV Ie- 350 µA)
• Literature T½ 15.49(1) min
• Isomeric state decays quickly (91mMo
  T½ 65 s)

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Outlook the pneumatic delivery system
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Nuclear resonance fluorescence on 92,98,100Mo
Energy distributions
Angular distributions
Dipole transitions dominate.
About 300 isolated transitions detected in each
nucleus.
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Nuclear resonance fluorescence on 92,98,100Mo
(g,g) - corrected
(g,n) - expt
(g,g) - not corrected
? Dipole strength distributions merge between
(g,g)- and (g,n)-measurements.
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Summary

• Photoactivation Experiments
• Endpoint energy derived from 2H break-up reaction
  .
• Photon flux distribution using NRF measurements
  with 11B transition strength.
• Determination of activation yield of
  92Mo(?,p)91mNb up to Sn(92Mo) by
  decay of 91mNb(EC)91Zr(1205 keV) ? unique
  signature.
• ? Similarity of relative data from 92Mo(?,p) and
  100Mo(?,n) with Statistical Models suggests that
  the predicted underproduction of Mo and Ru
  isotopes might not be due to wrong
  photodissociation rates.
• 92Mo(?,?)88Zr on heavy nuclei at these low
  energies ( 13 MeV) measured.

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