Contribution of External Gamma Rays to SPND at HANARO

Self-Powered Neutron Detectors (SPNDs) have been widely used for monitoring the neutron flux in reactors as well as in irradiation facilities. In its simplest form, the detector operates on the basis of directly measuring the beta decay current following neutron capture. The neutron capture cross-section of ¹⁰³Rh, which is used for an emitter of the SPND, is 142.13 barns for thermal neutron (0.0253 eV). After neuron capture of ¹⁰³Rh, the compound nuclei of ¹⁰⁴Rh (92.6%) and ¹⁰⁴mRh (7.4%) are produced. The sensitivity of SPND is generally defined as. The influence of water in the irradiation basket on the external gamma rays is determined by calculations of neutron capture reaction and photon interaction rates at various irradiation positions in HANARO. Since it is not easy to correct the contribution of the external gamma rays to the current signal by measurements at the research reactor, it is advantageous to reduce materials such as water at the irradiation position