Abstract
Accurate neutron flux values in irradiation channels of research reactors are very essential to their usage. The total neutron flux of the Ghana Research Reactor-1(GHARR-1) was measured after a beryllium reflector was added to its shim to compensate for excess reactivity loss. The thermal, epithermal and fast neutron fluxes were determined by the method of foil activation. The experimental samples with and without a cadmium cover of 1-mm thickness were irradiated in the isotropic neutron field of the irradiation sites of Ghana Research Reactor-1 facility. The induced activities in the sample were measured by gamma ray spectrometry with a high purity germanium detector. The necessary correction for gamma attenuation, thermal neutrons and resonance neutron self-shielding effects were taken into account during the experimental analysis. By defining cadmium cutoff energy of 0.55eV, Al-0.1% Au wires of negligible thickness were irradiated at 3kW to determine the neutron fluxes of two irradiation channels, outer channel 7 and inner channel 2 whose Neutron Shaping Factor (α) were found to be (0.037 ± 0.001) and (–0.961 ± 0.034). The neutron flux ratios at the inner irradiation site 2 were found to be, (25.308 ± 3.201) for thermal to epithermal neutrons flux, (0.179 ± 0.021) for epithermal to fast neutrons flux and (4.528 ± 0.524) for thermal to fast neutrons flux, in the outer irradiation site 7, the neutron flux ratios were found to be, (40.865 ± 3.622) for thermal to epithermal neutrons flux, (0.286 ± 0.025) for epithermal to fast neutrons flux and (11.680 ± 1.030) for thermal to fast neutrons flux.
Highlights
Neutrons are readily obtained by the action of alpha particles on some light elements, example, beryllium, boron, or lithium
The determination of neutron fluxes in an irradiation channel is necessary to monitor the continuous stability of the nuclear reactor flux, characterize a new channel and re-characterize an old channel [15] after refueling and/or core configuration change [16]
By using the Al-0.1%Au wire to measure the thermal, epithermal and fast neutron fluxes of the Ghana Research Reactor-1 (GHARR-1), the fluxes obtained in this work are in good agreement with the neutron flux values obtained when the reactor was less than five (5) years old
Summary
Neutrons are readily obtained by the action of alpha particles on some light elements, example, beryllium, boron, or lithium. Neutrons have high energies covering a wide range, example, from 1 MeV to 10 MeV or more. The sources are said to be polyenergetic [1]. Many of the techniques for production of homogeneous neutrons are used in neutron energy measurement. The most important source of thermal neutrons is the nuclear reactor [2]. The inner irradiation sites in the research reactor are usually used to irradiate and analyze unknown samples, using the neutron activation technique through (n, γ) thermal neutron reactions. The inner irradiation site in the MNSR contains both the fast and the thermal neutron fluxes
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