Experimental Research on Cold Neutron Prompt Gamma-ray Activation Analysis System at CARR

Prompt gamma-ray activation analysis (PGAA) is a neutron beam technique in which the gamma rays are measured during sample irradiation, which is used for the analysis of light elements such as H, B, C, N, as well as for the heavy elements Cd, Sm, Gd. PGAA can be performed using either a cold or thermal beam of neutrons. Due to the advantages of minimizing gamma-ray background and maximizing neutron flux by cold neutron guide, the cold neutron prompt gamma-ray activation analysis (CNPGAA) is used primarily for certification of inorganic standard reference materials (SRMs) and measurement of trace hydrogen and boron in materials. The CNPGAA experiment was firstly carried out at China Institute of Atomic Energy (CIAE) using the China Advanced Research Reactor (CARR) with cold neutron source (CNS). In the experiment, a customized and extended electro-mechanical cooler for high purity germanium (HPGe) detector and advanced digital multichannel spectrometer DSPEC®-502 were used to measure the cold neutron prompt gamma-ray spectrums of system background and NH₄Cl sample. The energy calibration was constructed for HPGe detector in the energy range from 0.1 MeV to 8 MeV using decay gamma rays produced by ¹⁵²Eu, ¹³⁷Cs, ⁶⁰Co and prompt gamma rays produced by NH₄Cl sample with neutron capture. In order to reduce the background of ambient radiation, the HPGe detector was surrounded successively by an annual bismuth germinate compton (BGO) suppressed spectrometer, 10 cm lead and materials for neutron beam collimator including elements of ⁶Li and ¹⁰B. In addition, the neutron flux was measured with and without CNS using the gold activation method at one meter far from cold neutron beam guide B (CNGB) exit of CARR under operating power of 15 MW. The results show that the neutron flux can be increased more than one order of magnitude by adding the CNS.