γ-Ray Strength Functions and GDR Cross Sections in the IAEA Photonuclear. . .
167
consisting of three concentric rings of 4, 9, and 18 3 He counters embedded in a
polyethylene moderator at 5.5, 13.0, and 16.0 cm from the γ-ray beam axis [5]. The
detector is designed to be of flat response to neutron kinetic energies by tuning
the distance and the number of 3 He counters for individual rings by GEANT4
simulation. The total detection efficiency is 36.5% with 1.6% uncertainty in one
standard deviation over an energy range from 10 keV to 5.0 MeV.
The partial photoneutron cross section with the neutron multiplicity x is determined from the number of reactions (γ, xn) that took place, N x (x = 1, 2, 3,..),
in an experiment. However, the number of reactions is not a direct experimental
observable. Instead, the number of neutron coincidence events is the experimental
observable. In general, a moderator-based neutron detector has a strong dependence
of the detection efficiency on neutron kinetic energy. In this case, the ring-ratio
technique which was originally developed by the Lawrence Livermore National
Laboratory [6] cannot determine the average neutron kinetic energy for the individual (γ, xn) reactions. In view of the fact that the neutron kinetic energy is different in
(γ, xn) reactions with a different x and in the emission order of neutrons in the same
(γ, xn) reactions, one encounters a difficulty in neutron-multiplicity sorting with the
ring-ratio technique.
The best way for overcoming the difficulty is to utilize a flat-efficiency detector
to determine the number of reactions N x by solving a set of equations for the
experimental observables, the number of neutron coincidence events. One can refer
to Ref. [5] for details of the direct neutron-multiplicity sorting with a flat-efficiency
detector.
3 Data Acquisition, Evaluation, and Compilation
We have successfully acquired all the data as originally time-scheduled as follows.
The institute which is responsible for the data reduction of (γ, xn) cross sections is
shown in the parentheses. The data reduction of (γ, n) cross sections is undertaken
by the University of Oslo.
I. (γ, xn) data on 11 nuclei
2015: 9 Be(Konan), 208 Bi(ELI-NP/IFIN-HH)
2016: 89 Y(SINP-MSU), 169 Tm(ELI-NP/IFIN-HH), 197 Au(Konan)
2017: 59 Co(SINP-MSU), 165 Ho(ELI-NP/IFIN-HH), 181 Ta(Konan)
2018: 103 Rh(SINP-MSU), 139 La(Konan), 159 Tb(ELI-NP/IFIN-HH)
II. (γ. n) data on 21 nuclei
2015: 89 Y, 203 Tl, 205 Tl
2016: 13 C, 58 Ni, 60 Ni, 61 Ni, 64 Ni, 137 Ba, 138 Ba, 185 Re, 192 Os
2017: 64 Zn, 66 Zn, 68 Zn, 182 W, 183 W, 184 W
2018: 156 Gd, 157 Gd, 158 Gd, 160 Gd
167
consisting of three concentric rings of 4, 9, and 18 3 He counters embedded in a
polyethylene moderator at 5.5, 13.0, and 16.0 cm from the γ-ray beam axis [5]. The
detector is designed to be of flat response to neutron kinetic energies by tuning
the distance and the number of 3 He counters for individual rings by GEANT4
simulation. The total detection efficiency is 36.5% with 1.6% uncertainty in one
standard deviation over an energy range from 10 keV to 5.0 MeV.
The partial photoneutron cross section with the neutron multiplicity x is determined from the number of reactions (γ, xn) that took place, N x (x = 1, 2, 3,..),
in an experiment. However, the number of reactions is not a direct experimental
observable. Instead, the number of neutron coincidence events is the experimental
observable. In general, a moderator-based neutron detector has a strong dependence
of the detection efficiency on neutron kinetic energy. In this case, the ring-ratio
technique which was originally developed by the Lawrence Livermore National
Laboratory [6] cannot determine the average neutron kinetic energy for the individual (γ, xn) reactions. In view of the fact that the neutron kinetic energy is different in
(γ, xn) reactions with a different x and in the emission order of neutrons in the same
(γ, xn) reactions, one encounters a difficulty in neutron-multiplicity sorting with the
ring-ratio technique.
The best way for overcoming the difficulty is to utilize a flat-efficiency detector
to determine the number of reactions N x by solving a set of equations for the
experimental observables, the number of neutron coincidence events. One can refer
to Ref. [5] for details of the direct neutron-multiplicity sorting with a flat-efficiency
detector.
3 Data Acquisition, Evaluation, and Compilation
We have successfully acquired all the data as originally time-scheduled as follows.
The institute which is responsible for the data reduction of (γ, xn) cross sections is
shown in the parentheses. The data reduction of (γ, n) cross sections is undertaken
by the University of Oslo.
I. (γ, xn) data on 11 nuclei
2015: 9 Be(Konan), 208 Bi(ELI-NP/IFIN-HH)
2016: 89 Y(SINP-MSU), 169 Tm(ELI-NP/IFIN-HH), 197 Au(Konan)
2017: 59 Co(SINP-MSU), 165 Ho(ELI-NP/IFIN-HH), 181 Ta(Konan)
2018: 103 Rh(SINP-MSU), 139 La(Konan), 159 Tb(ELI-NP/IFIN-HH)
II. (γ. n) data on 21 nuclei
2015: 89 Y, 203 Tl, 205 Tl
2016: 13 C, 58 Ni, 60 Ni, 61 Ni, 64 Ni, 137 Ba, 138 Ba, 185 Re, 192 Os
2017: 64 Zn, 66 Zn, 68 Zn, 182 W, 183 W, 184 W
2018: 156 Gd, 157 Gd, 158 Gd, 160 Gd