Neutron Production at the GSI Fragment Separator

1
Neutron Production at the GSI
Fragment Separator

• G. Fehrenbacher, J.G. Festag,
• F. Gutermuth, T. Radon,
• K. Gunzert-Marx, D. Schardt
• GSI Darmstadt

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Neutron Production from Uranium
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Neutron production near the targets
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Measurement of Radiation Dose
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Neutron dosimetry based on TL
Measurement TLD-700 7LiF sensitive to
?-Radiation TLD-600 sensitive to n and
?-Radiation
Diameter 30-32 cm
TLD-600 6LiF n6Li3H4He, exoth. 4.78
MeV Signal difference Neutron dose
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Response of PE-Sphere / 6LiF (FLUKA)
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TLD Measurements at GSI-FRS
TL-Elements in PE-Spheres for neutron dosimetry
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Dose Rate modelled by Moyer
Interaction proportion in the target Ion
current Distance to source Angular dependence of
the neutron production Effective dose conversion
factor Buildup factor Layer thickness of the
absorber Attenuation parameter
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Dose Rate for Ne in Fe, 2 GeV/u
108 Ions/sec, mSv/h
Ne beam
Fe target
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Examples for TL-Dosimetry (1)
U-beam, 1014 Ions 15.7. 22.8.2002, Emean 800
MeV/u
Example 1 2 3
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Examples for TL-Dosimetry (2)
Pos. Dose Inside TLD/TLD-Pb in µSv Dose Roof TLD in µSv Concrete Shielding in m
1 1.6E06 1.7E07 9.3E00 3.2
2 2.1E06 1.8E06 8.0E01 4.0
3 2.0E06 9.2E05 - 4.0
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Neutron Production by 238U at FRS-GSI
Isodose distribution along the FRS without
shielding, in µSv
TLDModell calculation
Target, 107 µSv
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Dose distribution, GSI target hall, 2001
Results of area monitoring outside shielding by
means of TLD
(Background 0,009 mSv/a)
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Shielding of the FRS

• U-beam with energies from 100 MeV/u to 900 MeV/u,
  mean 800 MeV
• total number of U-ions in the synchrotron 1,14
  ?1014 (average 6 107/sec) target 0,8 ?1014
• TLD at FRS target /roof 107 µSv / in the
  range 10 and 80 µSv
• Super-FRS 1012 Ions/sec at 1 GeV/u, additional 4
  m concrete shielding

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TOF-Measurements Cave B, GSI
BaF2
238U
1 GeV/u, 106 /s
LAND
Target
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Measurement of Neutron Spectra, TOF
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Detector for TOF-Measurements, BaF2
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Neutrons from 238U in Fe, 1 GeV/u
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Neutrons, 12C and 238U in Fe, 1 GeV/u
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Comparison C / U - beam

• Total neutron production for C in Fe, 1 GeV/u
  45 neutrons per C-ion (En gt 25 MeV)
• Total neutron production for U in Fe, 1 GeV/u
  140 neutrons per U-ion (En gt 25 MeV)
• Scaling with the number of nucleons, overestimate
  the neutron production

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Conclusion / Proposal for developments

• TLD measurements give a first estimate on the
  needs of the shielding, TLD based on 6LiF and
  PE/Pb-spheres must be improved for the response
  to neutrons for the ambient dose equivalent
• Basis for neutron data in thick target
  approximation for U-beam (1-2 GeV/u) must be
  broadened by a) further measurements and b)
  Extension of MC-Codes for heavy ions, f.e. Fluka
• Development of Parameters of Moyer-Modells for
  heavy ions in thick target appr. (U etc.) for the
  shielding design of simple geometries