S.R. Hashemi-Nezhad

Determination of energetic neutron spatial distribution using neutron induced nuclear recoil events

Abstract Neutron induced nuclear recoils were used to determine the spatial distribution of the weakly moderated spallation neutrons produced in the interaction of 1 GeV protons with lead and uranium–lead targets. CR39 plastic track detectors were used to record neutron-induced recoil tracks. The track density measurements were carried out using a fully automated optical microscope. The experimental results were compared with Monte Carlo simulations using MCNPX-2.1.5 code and an extension code that was written for this purpose. A good agreement was found between the experiment and calculations for normalised results. Applicability of the MCNPX-2.1.5 code for absolute recoil track density determination is discussed.

Background neutron flux determination at a depth of 3200 mwe underground

Abstract Measurements of the background neutron flux at a depth of 1230 m (3200 mwe) in a silver, lead and zinc mine at Broken Hill, New South Wales, Australia are reported. using 3He neutron counters, the thermal neutron flux and epithermal neutron flux have been determined. The effect of background gamma radiation on the resultant pulse height spectra is discussed and a procedure is given for the correction of the obtained spectra for the effects of this gamma background. In addition, the internal counts originating from radioactive trace elements in the construction material of the detectors are discussed and appropriate corrections are determined. Using Monte Carlo calculations the response of 3He detectors for neutrons of different energies is examined. The upper energy limit for detection of neutrons using 3He detectors directly (in absence of any moderator) is calculated.

Geometry of etched charged particle tracks in crystalline detectors

Studies on the shape of etched fission tracks in crystalline detectors show that the track geometry carries valuable information on the crystal structure of the detector involved. The geometry of the etched tracks in crystalline detectors is a prism formed of certain crystal planes. In mica detectors, for given etching conditions the type and number of the planes depend on the incident angle and the extent of the radiation damage along the track. In a single track the type of crystal planes forming the track prism may change along the track resulting in dramatic variations of the track geometry at certain depth of focus.

A computer controlled optical microscope for three dimensional track analysis

Abstract A Computer Controlled Optical Microscope (CCOM) system has been developed that is capable of producing consecutive optical micro-images of transparent micro-objects, each image corresponding to a different depth of focus. The combination of the images can be used to produce a three dimensional (3D) image of the object. Multiple slices at arbitrary angles may be deduced from the 3D image. The system consists of an optical microscope with a computer controlled stage with 3D movement, a CCD camera, a frame grabber, three digital position gauges and counters (for X, Y and Z directions), an interface board for driving the stage and reading the counters and a personal computer with appropriately developed software for Windows. CCOM can be used successfully in particle identification in solid state nuclear track detectors as well as in the detailed track geometry analysis along the etched damage trails. Preliminary results on the use of the CCOM in analysing of the charged particle tracks in plastic and mica detectors are presented.

Sensitivity and uncertainty analysis of the simulation of 123I and 54Mn gamma and X-ray emissions in a liquid scintillation vial.

Radiation transport simulations of the most probable gamma- and X-ray emissions of (123)I and (54)Mn in a three photomultiplier tube liquid scintillation detector have been carried out. A Geant4 simulation was used to acquire energy deposition spectra and interaction probabilities with the scintillant, as required for absolute activity measurement using the triple to double coincidence ratio (TDCR) method. A sensitivity and uncertainty analysis of the simulation model is presented here. The uncertainty in the Monte Carlo simulation results due to the input parameter uncertainties was found to be more significant than the statistical uncertainty component for a typical number of simulated decay events. The model was most sensitive to changes in the volume of the scintillant. Estimates of the relative uncertainty associated with the simulation outputs due to the combined stochastic and input uncertainties are provided. A Monte Carlo uncertainty analysis of an (123)I TDCR measurement indicated that accounting for the simulation uncertainties increases the uncertainty of efficiency of the logical sum of double coincidence by 5.1%.

Experimental and Monte-Carlo studies of the spatial distribution of neutrons around extended Pb-spallation target

Abstract The spatial distribution of thermal and fast neutrons on the surface of a paraffin moderator surrounding a cylindrical lead target, irradiated with 1 GeV protons was studied. The lead target had 8 cm diameter and 20 cm length. The thickness of the paraffin around the target was 6 cm . The slow and fast neutron distributions were determined using LR 115 2B and CR-39 detectors via the 10 B ( n ,α) reaction and neutron induced nuclear recoils, respectively. The observed slow and fast neutron distributions on the surface of the paraffin were compared with Monte-Carlo simulations using the MCNPX-2.1.5 code.

Research into accelerator driven systems using particle track detectors

Abstract In the interaction of relativistic protons with heavy and extended targets such as lead, large number of neutrons is produced in the course of the so-called spallation process. These neutrons can be used to drive a sub-critical nuclear assembly for energy generation and/or for the transmutation of the long-lived nuclear waste isotopes to environmentally safer nuclear species. Such nuclear assemblies are referred to as accelerator driven systems (ADS). Knowledge of the neutron yield in the spallation process and an understanding of the behaviour of these neutrons in the desired sub-critical assembly are the most important and determining factors in the design and operation of these systems. Many parameters related to the neutronics of an ADS can be studied qualitatively as well as quantitatively using solid-state nuclear track detectors (SSNTD). In some circumstances SSNTDs provide the best and the most logical detector option for these investigations. In this paper applications of the SSNTDs into research related to ADS are discussed and some experimental and theoretical results presented.

Temperature-related effects in radon dosimetry using plastic track detectors

Abstract The effects of temperature-related phenomena in radon dosimetry using CN-85 cellulose nitrate track detectors are reported. In isothermal annealing of α-tracks in CN-85 exposed to radon gas in equilibrium with its daughters, the track density as a function of annealing time follows a curve which is step-like. Such a step-like behaviour has been confirmed by computer simulation of α-tracks from radon both for post-irradiation annealings and for simultaneous irradiation and annealing. Studies on the effect of irradiation temperature on the registration efficiency η of CN-85 detectors show that η is a decreasing function of temperature in the temperature range 26–90°C studied in this work.