Determination of the spatial response of neutron based analysers using a Monte Carlo based method

Evaluation the nonlinear response function of a 3×3in NaI scintillation detector for PGNAA applications

Response functions of the 3 x 3 in NaI detector, which is mainly used in PGNAA applications, have been calculated by using MCNP-4C code. Calculated results are compared with measured data by using standard gamma-ray sources and prompt gamma-rays from pure element samples to check their accuracy. Prompt gamma-rays from pure element samples were used for this determination in the range from 1.942 to 10.829 MeV by use of (241)Am-Be neutron source and gamma-rays from radioisotope sources were used in the range from 0.081 to 4.438 MeV. Through the precise modeling of the detector structure, the agreement between both results has been improved. A surprising result is that in the PGNAA method the agreement between the MCNP simulation and experiment will be better by using a suitable neutron shield for NaI detector in order to prevent the activation of NaI (Tl) and a proper gamma-shield to attenuate the high-rate 4.438 MeV gamma-ray, (241)Am-Be gamma-ray component.

Performance improvement of keV Neutrons-based PGNAA setups

The performance of keV neutrons based Prompt Gamma Ray Neutron Activation Analysis (PGNAA) setups have been observed to improve by enclosing its neutron source inside the moderator. The keV neutrons were produced via (7)Li(p,n) reaction and (3)H(p,n) reactions. For the two PGNAA setups, the maximum intensity of the prompt gamma-ray yield was observed for a 5cm long moderator with the neutron source positioned at a distance of 0.5cm from the moderator-end facing the sample. Due to enclosing the source inside the moderator, the prompt gamma-ray yield from the (7)Li(p,n) reaction and (3)H(p,n) reaction based PGNAA setups have increased by a factor of three as compared to that achieved from these setups with the source outside the moderator. This study provides a theoretical basis for the measurement of performance of (7)Li(p,n) reaction and the (3)H(p,n) reaction based PGNAA setups.

Prompt gamma analysis of chlorine in concrete for corrosion study

Measurement of chlorine in concrete is very important for studying of corrosion of reinforcing steel in concrete. Corrosion of reinforcing steel is primarily ascribed to the penetration of chloride ions to the steel surface. Preventive measures for avoiding concrete structure reinforcement corrosion requires monitoring the chloride ion concentration in concrete so that its concentration does not exceed a threshold limit to initiate reinforcement concrete corrosion. An accelerator based prompt gamma neutron activation analysis (PGNAA) setup has been developed for non-destructive analysis of elemental composition of concrete samples. The setup has been used to measure chlorine concentration in concrete samples over a 1-3 wt% concentration range. Although a strong interference has been observed between the chlorine gamma-rays and calcium gamma-rays from concrete, the chlorine concentration in concrete samples has been successfully measured using the 1.164 and 7.643 MeV chlorine gamma-rays. The experimental data were compared with the results of the Monte Carlo simulations. An excellent agreement has been achieved between the experimental data and results of Monte Carlo simulations. The study has demonstrated the successful use of the accelerator-based PGNAA setup in non-destructive analysis of chlorine in concrete samples.

Monte Carlo simulations to advance characterisation of landmines by pulsed fast/thermal neutron analysis

The performance of a detection system based on the pulsed fast/thermal neutron analysis technique was assessed using Monte Carlo simulations. The aim was to develop and implement simulation methods, to support and advance the data analysis techniques of the characteristic gamma-ray spectra, potentially leading to elemental characterisation of innocuous objects using the full spectrum analysis (FSA) approach. The simulations were carried out with a simplified tool, based on a 14MeV DT pulse-neutron source and a bismuth-germanate detector. A MCNP-based method for de-coupling the radiation transport in mixed (n,gamma) fields, to generate separate sets of standard detector gamma-ray responses for individual elements, is outlined. When normalised and experimentally benchmarked in terms of the pulse-neutron source production rate, the standard spectra can be incorporated into algorithms for the FSA of in situ measurements and elemental fingerprinting of the inspected object.

Monte Carlo simulations as a feasibility tool for non-metallic land-mine detection by thermal-neutron backscattering

The use of Monte Carlo simulations is presented for modelling a simplified land-mine detector system with thermal neutron backscattering (TNB) analysis based on a 252Cf-neutron source. Different aspects and a variety of external conditions, related to localisation and identification of a buried object have been investigated. In particular, the influence of moisture in a formation has been assessed, as moisture can be a serious interference for hydrogen as an indicator for explosives. The results of sensitivity calculations confirm that land-mine detection methods, based on an analysis of TNB may be applicable in homogeneous formations with low porosity provided that pore-water remains <5% by weight. In dry limestone, the TNT-based explosives can be well distinguished from other hydrogen-rich materials, except wood. However, in dry siliciclastic sands TNT explosives and wood are distinguishable.

An on-belt elemental analyser for the cement industry

On-line control of raw mill feed composition is a key factor in the improved control of cement plants. A new and improved on-conveyor belt elemental analyser for cement raw mill feed based on neutron inelastic scatter and capture techniques has been developed and tested successfully in Adelaide Brighton's Birkenhead cement plant on highly segregated material with a depth range of 100 to 180 mm. Dynamic tests in the plant have shown analyser RMS total errors of 0.49, 0.52, 0.38 and 0.23 wt% (on a loss free basis) for CaO, SiO2, Al2O3 and Fe2O3 respectively, when 10-minute counting periods are used.