Dose measurements around spallation neutron sources

Abstract

Neutron dose measurements and calculations around spallation sources appear to be of great importance in shielding research. Two spallation sources were irradiated by high-energy proton beams delivered by the Nuclotron accelerator (JINR), Dubna. Neutrons produced by the spallation sources were measured by using solid-state nuclear track detectors. In addition, neutron dose was calculated after polyethylene and concrete, using a phenomenological model based on empirical relations applied in high-energy physics. The study provides an analytical and experimental neutron benchmark analysis using the transmission factor and a comparison between the experimental results and calculations.

Neutron Production in Thick Targets Irradiated with High-Energy Ions

“…The irradiation lasted 11 hours with a total fluence of 10 13 protons of 1 GeV on target, corresponding to an average of 2.5 * 10 8 protons/sec. The experimental neutron ambient dose equivalent behind the concrete wall was 37 μSv/h [6], which is too much to be tolerated by humans. The ICRP 66 (International Commission on Radiological Table 2: Experimental neutron ambient dose equivalent from the irradiation of a Pb target in "Gamma-2" and "Energy plus Transmutation" (E + T) with 10 13 protons and a comparison with model calculations [6].…”

“…They also investigated the same thick Pb target as the one employed in [11]. The observed neutron numbers [6] from experiments at the Nuclotron accelerator in JINR describes measurements of the neutron dose from 1 GeV protons around two thick Pb target assemblies, called "Gamma-2" and "Energy plus Transmutation" (E + T). The neutron dose measurements were carried out close to the targets and in addition behind a 1.0 m thick concrete shielding wall of the experimental setups as shown in Figure 1.…”

“…The Pb core in the "Energy plus Transmutation" (E + T) target has a diameter of 8.4 cm and a length of 45 cm, and it is surrounded by a blanket of 206.4 kg natural uranium plus also a massive neutron shield. A detailed description can be found in [6,[13][14][15].…”

“…The neutron dose measurements were carried out with solid state nuclear track detectors (SSNTD's) by Fragopoulou et al [6]. Their experimental techniques allow to obtain separate results for (i) low-energy neutrons with E(n) < 1 eV, (ii) epithermal neutrons with 1 eV < E(n) < 10 keV, and…”

“…(c) This diagram illustrates the positions of the spallation sources, the concrete shielding wall, and the locations of the SSNTDs (solid state nuclear track detectors) that serve to determine the neutron ambient dose equivalent. Distances can be estimated from the thickness of the concrete wall which is 1.00 m (Figure taken from [6]).…”