A. Dubi

Self-shielding factors for TLD-600 and TLD-100 in an isotropic flux of thermal neutrons

Monte Carlo calculations have been carried out to determine the absorption probability (and consequently the self-shielding factor) for an isotropic flux of neutrons impinging on different sized cylindrical samples of TLD-100 and TLD-600.

Limitations of the paired LiF TLD-600, 700 technique for the estimation of gamma ray dose in mixed n-γ radiation fields: The effect of thermal neutrons

Abstract Two significant limitations of the paired LiF thermoluminescent (TL) technique for the determination of γ dose in mixed n-γ radiation fields are discussed. These are; (i) the likelihood of large variations in the behaviour of the TL sensitivity as a function of neutron energy from dosimeter batch to dosimeter batch due to minute variations in the dosimeter preparation and (2) the likelihood of large absorbed dose in TLD-600 due to thermal neutrons (compared to the fast neutron or γ dose) resulting in the necessity of a third independent experimental dose or fluence measurement of the thermal neutrons. It is estimated that for radiation fields where φ th φ f > 0.05 , even the angular distribution of the thermal neutrons at the point of interest must be determined to enable adequately accurate calculation of the thermal neutron selfshielding factor in TLD-600.

Contribution of epithermal activation in neutron in vivo activation

It is pointed out that epithermal activation is not negligible in the in vivo neutron activation analysis (IVNAA) technique for the measurement of skeletal Ca. Multi-group calculations have been carried out to determine the ratio of epithermal to thermal flux and the epithermal activation was measured using the Cd subtraction technique.

Solid-angle and self-absorption factors for an inclined cylindrical source viewed by a cylindrical detector

Abstract A Monte Carlo method is presented for the calculation of the self absorption of γ radiation in an inclined cylindrical source and for the calculation of the solid angle of the source subtended by a cylindrical detector. The source is centered on the symmetry axis of the detector and can be rotated through an angle from 0° to 90° around an axis perpendicular to the detector axis. Typical corrections to angular correlation measurements in multi-detector goniometers are presented and discussed.

The Interpretation of Conditional Monte Carlo as a Form of Importance Sampling

Conditional Monte Carlo has been recognized as a potentially useful method in various Monte Carlo applications. It seems, however, that the method has not gained widespread popularity, presumably due to the complexity involved in the formulation and operation of the technique. We present herein what we believe to be an original and simplified approach to conditional Monte Carlo interpreting it as a modified form of importance sampling. This provides a straightforward framework by which any conditional sampling problem can be handled. The benefits are demonstrated by applying our approach to two problems; one of a general statistical nature and the other concerning the neutron transport equation.

The Monte Carlo Nonuniform Sampling Technique Applied to the Klein-Nishina Probability Density Function

The Monte Carlo generalized rejection technique provides a continuous passage from the inverse equation sampling method to the uniform sampling rejection method; it is well known that the nonuniform rejection method can be used to achieve very significant increases in sampling efficiency. The nonuniform rejection method was applied to the Klein--Nishina probability density function, and improved efficiencies were obtained over the uniform sampling method of up to 100 percent at high gamma-ray energies and 10 to 60 percent improved efficiencies in the energy range from 0.3 to 1.5 MeV, respectively.

Comment on the use of thermoluminescence dosimeters as thermal neutron detectors

Abstract The importance of accurate knowledge of the self-shielding factor when using strongly absorbing thermoluminescence dosimeters as thermal neutron detectors is illustrated.

An analytic expression for the gamma-ray self absorption in the perpendicular-axes configuration

Abstract An analytic expression for the self absorption of gamma rays emitted from a point source on the face of a cylindrical absorber is constructed. The symmetry axis of the cylindrical absorber makes an angle of 90° with the symmetry axis of the cylindrical detector.

Gamma-ray self-absorption corrections for Eγ>0.6 MeV and μ<3 cm−1

Abstract The Monte Carlo method was used to calculate the self-absorption correction for a large number of cylindrical source-cylindrical detector configurations in the energy range Eγ greater than 0.6 MeV and for values of the total attenuation coefficient (μ) up to 3 cm−1. The corrections are thus applicable to all possible materials and compounds and are presented in a functional form which allows easy calculation and interpolation. The error introduced by using the self-absorption correction multiplied by a non-absorbing source-detector efficiency is discussed and shown to be usually negligible. The problem of forward-scattered Compton γ-rays from the source contributing to the photopeak efficiency in NaI(Tl) detectors is shown to be increasingly significant for Eγ