Measurements of Neutron Photoproduction Cross Sections for 232Th and 238U Using Capture Gamma Rays

• Published in: Nuclear science and engineering 1999-05, Vol.132 (1), p.135-147
• Main Authors: Gonçalez, O. L., Geraldo, L. P., Semmler, R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Installations for energy generation and conversion: thermal and electrical energy
• ISSN: 0029-5639; 1943-748X
• DOI: 10.13182/NSE99-A2055

Neutron photoproduction studies for 232 Th and 238 U were carried out from 5.61 to 10.83 MeV, by using up to 30 neutron capture gamma rays with high resolution in energy (4 to 20 eV), produced in an experimental arrangement at the IPEN-IEA-R1 2-MW research reactor. Samples of U 3 O 8 depleted to 0.34% in 235 U and natural ThO 2 were irradiated inside a 4π sr long-counter neutron detector system, 520.5 cm away from the capture target. The gamma-ray flux was determined by means of a coaxial solid state Ge(Li) detector (EG&G ORTEC, 25 cm 3 , 5%) previously calibrated with capture gamma rays from a standard target of nitrogen (melamine). The compound neutron photoproduction cross section was measured for the gamma-ray spectrum produced by each capture target. Two methods to unfold the set of experimental data were proposed in order to obtain the differential cross sections at the main gamma line energies: the iterative and the least-squares methods. The calculated neutron photoproduction cross sections for 232 Th and 238 U were compared with experimental data reported by other authors who have employed different gamma-ray sources. A good overall agreement was observed among the experimental data, however, marked discrepancies were identified for some data points, indicating the possibility of narrow structures showing up at these excitation energies.