Measurement For Thermal Cross Section Of⁷⁸Se（n,γ）⁷⁹Se By AMS

SChemical symbol Se is the Chinese name of selenium, symbolized as Se, has six stable isotopes in nature,74Se、76Se、77Se、78Se、80Se and82Se。79Se is a radioactive isotope with half-life of (2.80+0.40)×105y.79Se is one fission product nuclide of235U and can be produced by neutron capture reaction,78Se(n,y)79Se. After a long time of storage of the spent fuel, radioactivity from79Se will become significant because of its relative long half-life. Relevant researches on79Se are important in fields of nuclear waste storage, nuclear astrophysics, biological medicine and environmental monitoring. Accurate thermal cross section of78Se(n,y)79Se reaction are needed. In this work, the thermal cross section of78Se(n,y)79Se reaction was measured by activation method, by using the AMS technic to determine the yield of79Se. SeO2slice sample, pressed by the SeO2powder, was irradiated in the miniature neutron source reactor (MNSR) at China Institute of Atomic Energy (CIAE), lasted for8hours. The thermal and epithermal neutron flux was monitored by zirconium slice, by measuring the specific activity of the95Zr and98Zr, produced in the reaction94Zr(n,y)95Zr and97Zr(n,γ)98Zr, respectively. Different samples, the irradiated, the blank and the experimental standard, were measured by AMS technology, based on the HI-13tandem accelerator at Beijing Nuclear Physics National Laboratory.In the end,78Se(n,γ)79Se thermal reaction cross section was obtained as a result of (0.35±0.05)b。Within the range of errors, values of this work and the references are in agreement with each other.The measurement can be detailed as following:(1) Sample irradiation in the MNSR. (2) Thermal neutron flux monitoring.(3) Sample preparations.(4) Isotope ratio (79Se/78Se) measurement by AMS method.(5) Data analysis.