CNRS Université Bordeaux

Accueil du site > ANGLAIS > Research > ACEN: nuclear data for nuclear energy, new fuel cycle and nuclear waste transmutation > Activities > direct neutron measurements > 232Th(n,γ)


The ACEN group has been formally consitued after a first experiment performed at the end of the last century at the 4-MV Van de Graaff facility of CENBG. The neutron capture cross section of 232Th in the energy range from 60 keV to 2 MeV. It was in this energy range that the discrepancies between the various databases were the largest (20-30%).

Neutrons were produced by the 7Li(p,n) and T(p,n) reactions. The measurement was performed using the activation technique of thorium foils. The irradiation time per sample was of the order of 20 hours. The production rate of 233Th as a function of neutron energy was deduced from delayed γ—ray spectroscopy of the 312 keV transition de-exciting the first excited state of 233U, which was populated after two β-decays (T1/2: 27 d).

Below 1 MeV, the flux of fast neutrons was determined via activation of gold foils placed in front and behind the thorium target and shielded against possible thermal neutrons by a cadmium box of 1 mm thickness. The transmutation of 197Au was signed with the 412 keV γ-ray emitted from the first excited state of 198Hg populated after β-decay of 198Au (T1/2: 2.7 d) and detected out of beam with a 40% high purity Ge detector. Above 1 MeV neutron energy, the flux was furthermore determined by measuring the fission rate of a thin 235U target with solar cell detec- tors. For those two samples, the cross sections 197Au(n,γ) and 235U(n,f) are known to better than 4% and therefore provide excellent probes to accurately monitor the neutron flux.

The results, after applying the appropriate corrections, indicate that the cross sections are close to the JENDL-3 database values up to 800 keV and over 1.4 MeV. For energies in the intermediate range, our values are slightly lower than those from all the libraries.

The experiment and the results are presented in D. Karamanis et al..

Related publications:

Neutron radiative capture cross section of 232 Th in the energy range from 0.06 to 2 MeV
D. Karamanis et al., Nuclear Science and Engineering 139, 282-292 (2001)

In the same section :