Shielding studies on a total-body neutron activation facility

Prompt gamma neutron activation analysis [PGNAA] is known as a non-invasive technique capable of measuring elemental concentration in voluminous samples in a short period of time. Also it is a valuable diagnostic tool for total body elemental measurements. 252Cf and 241Am-Be sources which are usually used in this method, generate not only neutrons, but also emit high-energy and unwanted gamma-rays. Because the patient must be located against the neutron source, patient dose during an analysis is an important concern when using this technique. Gamma-rays were attenuated without losing the neutron flux or significant alteration in the neutron spectrum. A relatively safe body chemical composition analyzer was designed with an optimal spherical gamma-ray shield, enclosed to the neutron source. Effects of gamma-ray shielding and optimum radius of spherical Pb shield was investigated and compared with the unfiltered bare source, using MCNP4C code. Then, the gamma ray dose equivalent per source neutron rate [user defined parameter] in the soft tissue is calculated for different radiuses of spherical Pb shield, for both neutron sources. A decreasing flux of gamma-ray was observed when the radius of the spherical Pb shields increased. The value of this reduction was about 94% for 252Cf source when a lead spherical shield of radius 4 cm was used; while the reduction was about 50% for 241Am-Be source with the same spherical shield. For a spherical Pb shield of radius 4 cm, reduction of the gamma dose equivalent per source neutron rate was about 8.44_10-17 Sv when the neutron source was 252Cf and about 1.24_10-16 Sv when the neutron source was 241Am-Be. Results show using optimum gamma-ray shield geometry can reduce the patient absorbed dose per incident neutron in a body chemical composition analyzer

safety of a landmine detection system using graphite and polyethylene moderator

Several landmine detection methods, based on nuclear techniques, have been suggested up to now. Neutron-induced gamma emission, neutron and gamma attenuation, and fast neutron backscattering are the nuclear methods used for landmine detection. In this paper an optimized [safe and effective] moderating structure using an [241]Am-Be neutron source for detecting landmines has been investigated by experiment and MCNP simulation. The experimental set up was composed of a lead [Pb] cylindrical shell enclosing the neutron source, embedded in a fixed size high-density polyethylene [HDPe] cylinder with the variable thickness of the upper and lower moderator/reflector. Some experimental groups were used to measure several moderator configurations' responses by replacing a thermal neutron detector with the mine and counting the neutron capture events the total experimental results led to the introduction of optimum moderator geometry for landmine detection. A safe landmine detection system was obtained which enabled the operator to use it for 950 h/year, regarding the dose limit recommended by ICRP. The novel method for optimization applied in this work is more applicable than the usual approach that is based on measuring the prompt gamma rays emitted by the landmine. Results showed that the method can be optimized in short time, without the usual difficulties of the other methods