Evaluation of neutron and gamma dose in a new deuterium-deuterium fusion neutron generator facility using MCNP and experimental methods

Simulation of the cement measurement based on the pulse DT neutron generator: A Monte Carlo study

The PGNAA system for the cement measurement was simulated based on Monte Carlo method. The sizes of the moderator and reflector for the 14 MeV DT neutron generator were optimized for fast and thermal neutron outputs. The DT neutron generator was simulated at the pulse mode, and the gamma-ray detector was set as LaBr₃(Ce) scintillator. The characteristic peaks of the major elements (Ca, Si, Al, Fe) can be identified from the gamma-ray spectra which induced at the different time intervals of the neutron radiation. For the different thicknesses of the cement sample the ratios of the gamma-ray peaks were observed, and the result showed that when the thickness was between 20 to 30 cm, the ratios became stable. With the ratios, we can calculate the iron modulus, silica modulus and lime saturation factor.

Characterisation of neutron field in the polyethylene neutron irradiator

The paper describes neutron field characterisation of low-flux multipurpose educational irradiator developed at Czech Technical University in Prague. The irradiator is aimed for demonstration experiments including neutron activation analysis, delayed neutron counting, or studies related to neutron and/or gamma detection and spectrometric devices. It may accommodate various neutron sources including ²⁵²Cf or AmBe radionuclide sources, D-D generator, or in-reactor irradiated nuclear material serving as delayed neutron source, or gamma sources including radionuclide ones or short-lived sources produced in the adjacent reactor. The characterisation was performed based on neutron activation technique using gold foils. It included two experimental parts. The first one verified the level of response symmetry in the four irradiation channels and characterisation of the axial distribution in the irradiation channels. Within the second one, the responses to thermal and epithermal neutrons and the cadmium ratio in the central irradiation position were determined. Whereas the former was determined solely with the ²⁵²Cf source, the latter was performed for all available sources: ²⁵²Cf, AmBe, and the D-D generator. The experimental results were further compared to calculations by the MCNP Monte Carlo code.

Neutron and Photon Dose Rates in a D-T Neutron Generator Facility: MCNP Simulations and Experiments

The deuterium-tritium neutron generator is a common neutron source for fast neutron activation analysis. The 14.1 MeV neutrons emitted from a deuterium-tritium neutron generator are difficult to shield due to their strong penetrability and the induced secondary gamma rays in the shield. A rough calculation based on attenuation factors shows that when 14.1 MeV neutrons with a yield of 1 × 10 ns penetrate the designed shielding layers, which consist of a 0.5-m-thick concrete layer and a 0.5-m-thick water layer, the neutron ambient dose equivalent rate is 2.48 μSv h. A geometric model of a neutron shielding room is constructed based on the calculation. Monte Carlo simulations indicate that the highest neutron ambient dose equivalent rate outside the neutron shielding room is 0.73 μSv h, and the neutron ambient dose equivalent rate at the detector position in the shielding room is 2.12 μSv h. The experimental results show that the highest neutron ambient dose equivalent rate outside the neutron shielding room is 1.43 μSv h, and the neutron ambient dose equivalent rate at the detector position inside the shielding corridor is 2.74 μSv h. Comparative investigations show that the experimental results are basically consistent with the results of the Monte Carlo simulations, except for some positions with large proportions of fast neutrons where it is too difficult for the neutron dose equivalent meter to provide reliable values. Moreover, the radiation dose rate outside the designed shielding room is lower than the occupational exposure dose limit, which is in line with the design expectations. Finally, the gamma spectrum at the position of the gamma detectors is measured by a high-purity germanium detector. The analyzed results show that many secondary gamma rays are generated by the interaction of neutrons with the shield materials and detector probe crystals, and some gamma rays are produced from natural background radionuclides such as K, Tl, Bi, Bi, Pb, Pb, and Ac.