Monte Carlo simulation of an HPGe detector for detection of 239Pu in waste assay system.

This paper discusses the modeling of HPGe detector used in waste assay system using Monte Carlo code FLUKA to determine its detection limits. The modeled detector is validated using experimental point sources efficiencies in the energy range 60 keV-2000 keV. The numerical estimation of efficiency values for 239Pu present inside a 230 L cotton filled waste drum at various locations along the axis of the detector is discussed. Estimation of the minimum detectable activity (MDA) for 239Pu at these locations in the presence of 1 MBq of 137Cs/60Co again along the axis of the detector is examined. The efficiency of 239Pu decreases from 6.1 × 10-10 to 7.5 × 10-11 cps/Bq as the location of 239Pu moves away from the detector. MDA of 239Pu increases as the position of 239Pu and 137Cs/60Co in the waste drum shifts away from the detector while it decreases as the location of 137Cs/60CO moves away from 239Pu along measurement axis. It is observed that for all locations of 137Cs/60Co with 239Pu located up to 200 mm from the edge of the drum, the detection limit is within 140.3 mg (allowed limit).

Gamma photon techniques for detection of nucleation in superheated emulsion detectors for neutron dosimetry.

Application of transmission and scattering gamma photon techniques for calibration of superheated emulsion detectors used for neutron dosimetry is described. The bubbles nucleated in the detector due to neutron exposure generate detectable changes in both attenuation and scattering properties of the medium, and the magnitude of change in properties depends on population density of bubbles nucleated and in turn is proportional to neutron dose. The experimental set-up consists of (137)Cs and (241)Am sources and an HPGe detector-based gamma-ray spectrometer. An indigenously developed bubble detector and a commercially available one (BTI, Canada) are used in the present study. Theoretical models for the variation in transmitted and scattered intensities through the bubble detector as a function of neutron dose are formulated, and the experimental results obtained are found to be in good agreement with the models. In the neutron dose region studied, the transmission technique shows better sensitivity than scattering technique.

Application of gamma ray scattering technique for non-destructive evaluation of voids in concrete.

This paper describes application of the gamma ray scattering technique for NDE of concrete voids. A novel nonlinear extrapolation method is employed to correct for self-absorption and multiple scattered intensities. The attenuation data obtained from transmission method is employed for reconstruction of scattered images and the results show a good agreement in size and position of the voids with good spatial resolution. Intercomparison of the results of scattering and transmission techniques shows a good agreement in the position of the voids.

An improved Compton scattering method for determination of concentration of solutions.

An improved Compton scattering method for determination of concentration of low-Z solutions is presented. The Monte Carlo (MC) numerical simulation of the scattering phenomena is done using the MCNP code. A unique non-linear extrapolation method is followed in correcting the scattered intensity for self-absorption and multiple scattering. The density ratios obtained using non linear extrapolated scattered intensity values are free from self-absorption and multiple scattering and agree well with the standard ones within experimental errors. The sensitivity study of transmission and scattering methods for determination of concentration of solutions having closer attenuation parameters at 661.6 keV is carried out to predict the range of effectiveness and suitability of these methods. The slopes (sensitivity/unit concentration) of the curves obtained from scattering method are higher by a factor of 1.26 compared to those of the transmission method in the measured range of concentrations.

Intercomparison of gamma ray scattering and transmission techniques for fluid-fluid and fluid-air interface levels detection and density measurements.

This paper focuses on the fluid-fluid, fluid-air interface level detection and density determination by gamma scattering method and intercomparison with transmission (gammatography) technique. The Monte Carlo (MC) numerical simulation of the scattering phenomena is done using the MCNP code. The obtained accuracies and resolution of the level detections and density measurements are higher in case of gamma scattering method compared to transmission method.

Intercomparison of gamma scattering, gammatography, and radiography techniques for mild steel nonuniform corrosion detection.

This paper focuses on the mild steel (MS) corrosion detection and intercomparison of results obtained by gamma scattering, gammatography, and radiography techniques. The gamma scattering non-destructive evaluation (NDE) method utilizes scattered gamma radiation for the detection of corrosion, and the scattering experimental setup is an indigenously designed automated personal computer (PC) controlled scanning system consisting of computerized numerical control (CNC) controlled six-axis source detector system and four-axis job positioning system. The system has been successfully used to quantify the magnitude of corrosion and the thickness profile of a MS plate with nonuniform corrosion, and the results are correlated with those obtained from the conventional gammatography and radiography imaging measurements. A simple and straightforward reconstruction algorithm to reconstruct the densities of the objects under investigation and an unambiguous interpretation of the signal as a function of material density at any point of the thick object being inspected is described. In this simple and straightforward method the density of the target need not be known and only the knowledge of the target material's mass attenuation coefficients (composition) for the incident and scattered energies is enough to reconstruct the density of the each voxel of the specimen being studied. The Monte Carlo (MC) numerical simulation of the phenomena is done using the Monte Carlo N-Particle Transport Code (MCNP) and the quantitative estimates of the values of signal-to-noise ratio for different percentages of MS corrosion derived from these simulations are presented and the spectra are compared with the experimental data. The gammatography experiments are carried out using the same PC controlled scanning system in a narrow beam, good geometry setup, and the thickness loss is estimated from the measured transmitted intensity. Radiography of the MS plates is carried out using 160 kV x-ray machine. The digitized radiographs with a resolution of 50 µm are processed for the detection of corrosion damage in five different locations. The thickness losses due to the corrosion of the MS plate obtained by gamma scattering method are compared with those values obtained by gammatography and radiography techniques. The percentage thickness loss estimated at different positions of the corroded MS plate varies from 17.78 to 27.0, from 18.9 to 24.28, and from 18.9 to 24.28 by gamma scattering, gammatography, and radiography techniques, respectively. Overall, these results are consistent and in line with each other.