C. Sunil

Directional distribution of the ambient neutron dose equivalent from 145-MeV 19F projectiles incident on thick Al target

The directional distribution of the ambient neutron dose equivalent from 145-MeV (19)F projectiles bombarding a thick aluminium target is measured and analysed. The measurements are carried out with a commercially available dose equivalent meter at 0°, 30°, 60° and 90° with respect to the beam direction. The experimental results are compared with calculated doses from EMPIRE nuclear reaction code and different empirical formulations proposed by others. The results are also compared with the measured data obtained from an earlier experiment at a lower projectile energy of 110 MeV for the same target-projectile combination.

Direction distribution of ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets

Ambient neutron dose equivalent from 20 MeV protons incident on thick Be and Cu targets are measured at 0 degrees, 30 degrees, 60 degrees and 90 degrees with respect to the beam direction using a conventional dose equivalent meter. The neutron spectra calculated using nuclear reaction model codes ALICE, PRECO and earlier reported empirical expressions are converted to the ambient dose equivalent using the ICRP fluence-to-dose conversion coefficients and are compared with the measured values. The experimental energy spectra reported in the literature for 19.08 MeV protons incident on a thick Be target are also converted to ambient neutron dose equivalent and are compared with the present experimental results. It is observed that the values estimated from the neutron spectra obtained from the nuclear reaction codes are unable to predict the measured values. The results obtained from the reported experimental energy spectra compare well with the results obtained here. An empirical relation that was used to calculate the directional dependence of the measured neutron dose equivalent from heavy ion-induced reactions is used in this study to check its effectiveness for proton-induced reactions.

Estimation of41 Ar production in 0.1–1.1.0-GeV proton accelerator vaults using FLUKA Monte Carlo code

The FLUKA Monte Carlo simulations are carried out to estimate the (41)Ar concentration inside accelerator vaults of various sizes when proton beams of energy 0.1-1.0 GeV are incident on thick copper and lead targets. Generally (41)Ar concentration is estimated using an empirical formula suggested in the NCRP 144, which assumes the activation is caused only by thermal neutrons alone. It is found that while the analytical and Monte Carlo techniques give similar results for the thermal neutron fluence inside the vault, the (41)Ar concentration is under-predicted by the empirical formula. It is also found that the thermal neutrons contribute ∼41 % to the total (41)Ar production while 56 % production is caused by neutrons between 0.025 and 1 eV. A modified factor is suggested for the use in the empirical expression to estimate the (41)Ar activity 0.1-1.0-GeV proton accelerator enclosures.

Measurement of Neutron Energy Distributions From p+Be Reaction at 20 MeV Using Threshold Activation Foils

Energy distributions of neutrons emitted from the interaction of 20 MeV protons incident on a thick Be target were estimated at two angles (0° and 90°) with respect to the incident beam using activation foils as threshold detectors. A recently developed unfolding code GAMCD based on Genetic Algorithm and Monte Carlo methods was used to estimate the neutron spectra by unfolding the counts obtained from the activation foils. These results were compared with the unfolding codes, MAXED and GRAVEL. In the GAMCD code, a guess spectrum as a-priori information need not be provided as input unlike in MAXED and GRAVEL. Results obtained from all these codes matched each other reasonably well. Out of 30 reactions studied experimentally only the selected 15 were found sufficient to generate acceptable spectra in the case of neutrons emitted from the p+Be reaction at 20 MeV. A peak in the energy distributions around 3 MeV at both the measured angles is contributed by the three body breakup process while a broad hump between 6 MeV and 10 MeV only in the forward direction suggests contribution from the pre-equilibrium emissions from the 9Be(p, n)9B channel, which also contributes to the small peak observed around 15 MeV. The code GAMCD was found to perform satisfactorily for the present data set.

Selection of neutron-absorbing materials to improve the low-energy response of a Zr-based extended neutron monitor using Monte Carlo simulations

Monte Carlo simulations have been carried out using the FLUKA code to improve the neutron ambient dose equivalent [H*(10)] response of the ZReC (zirconium-lined portable neutron counter responding satisfactorily to neutrons up to 1 GeV) by introducing various neutron absorbers in the system such as cadmium, gadolinium, natural boron, enriched (10)B and borated polythene. It was found that ZReC can be effectively used as a portable neutron monitor by introducing any one of the following perforated layers: 5 mm thick natural boron, 0.5 mm thick enriched (10)B or 1 cm high-density polythene mixed with 50 % boron by weight. The integral response of the instrument was also calculated for some typical reference neutron fields. The relative ambient dose equivalent response of the said system is also found comparable with that of the existing LINUS neutron monitor.