Gamma-ray Backscatter Research Articles

Measurement of the response of a [formula omitted]Li-glass detector to gamma rays by a coincidence method

The response of a gamma-ray spectrometer is generally determined by analyzing full-energy peaks. However, full-energy peaks cannot be measured easily in the case of scintillation detectors that consist of light elements, such as glass scintillators. Only a strong Compton plateau appears in the spectrum of such detectors. Therefore, Compton edgers were used to evaluate the response of these detectors. The response of a low-resolution 6Li-glass detector to gamma rays was measured for the first time by a coincidence method with a high-resolution LaBr3:Ce detector using cascade gamma rays (2.75 and 1.37 MeV) from a 24Na source. Coincidence gates were applied at the peaks of the spectrum of the LaBr3:Ce detector at the 0.51 MeV annihilation peak, and the sum peaks of a gamma ray and a backscattered gamma ray. By analyzing the gated spectra of the 6Li-glass detector, the energy-dependent detector response (i.e., the output strength and its dispersion) was determined.

Experiment and Monte Carlo simulation of gamma-ray backscattering from materials for nondestructive testing

Experiment and Monte Carlo simulation of gamma-ray backscattering from materials for nondestructive testing

The criterion for self-sustaining production of relativistic runaway electron avalanches by the positron feedback in thunderstorms

Relativistic runaway electron avalanches (RREA) occurring in thunderstorm large-scale electric fields are one of the sources of atmospheric gamma radiation. Relativistic feedback is the generation of RREAs by positrons or backscattered gamma rays of the previously produced RREAs. In strong electric fields, relativistic feedback can make RREAs self-sustainable that hypothetically can cause a terrestrial gamma-ray flash (TGF). This paper introduces a kinetic approach to study the positron relativistic feedback, which is predominant for the directly observed conditions within thunderstorms. The criterion for self-sustaining production of RREAs by the positron feedback in thunderstorms is derived. The discovered criterion allows one to obtain the parameters of the thunderstorm electric field required for self-sustaining RREA development with positron feedback for any altitude. It is shown that the derived conditions of self-sustainable RREA development are not achieved for the parameters of electric field observed in real thunderclouds.

Activity standardization by means of liquid scintillation counting and determination of the half-life of 89Zr

A89Zr solution was measured by means of liquid scintillation counting techniques in order to determine the activity concentration. Two methods were used: the CIEMAT/NIST efficiency tracing method with 3H as a tracer, and the triple-to-double coincidence ratio method. The counting efficiencies were computed with a stochastic model. The very detailed investigation showed that a few corrections are particularly important: Asymmetries in the photodetector responses as well as the backscattering of high-energy gamma rays must be taken into account. Corresponding corrections have therefore been applied. In addition, a detailed uncertainty analysis was carried out and the uncertainties compared with those determined by other research groups.The activity concentrations obtained from the two methods agree well and a combined result was used to establish calibration factors for ionization chambers, which are important secondary standardization instruments. The ionization chambers were combined with a new high-precision current measurement device to provide outstanding linearity. Measurement data from one chamber were used to determine the half-life, which was found to be T1/2=(78.373 ± 0.023) h.

Intrinsic noise reduction of a Gamma-ray Backscattering imaging device

In order to increase the contrast and to improve the imaging capabilities of a Gamma-ray Backscattering device some changes are proposed with the aim of achieving a reduction of the intrinsic noise of the device. Simulated results suggest that the shielding system proposed, in addition to the use of a 68 Ge -γ ray source, produce a considerable reduction of the intrinsic noise of the device.

Simulation of Void Detection System using Gamma-Ray Compton Scattering Technique

A simple void detection system for concrete was successfully developed using high-penetration gamma rays with Compton scattering. This research attempted to identify a void in the subsurface of a concrete volume that could not be accessed from any of the sides. Monte Carlo simulation using GEANT4 toolkit was performed to investigate the gamma-ray backscattering events. An NaI(Tl) detector was used with 60Co and 137Cs as gamma-ray sources. The void's location was successfully detected during material target scanning. Density discrepancies conduce variance of the backscattering peak produced due to the presence of a void. Compared to 60Co as the gamma-ray source, 137Cs is a better choice for application in NDT systems using Compton scattering.

Conceptual design of an orphan gamma source finder

In this paper, a conceptual design of a gamma finder including four identical NaI (Tl) cylindrical scintillation detectors has been presented. This gamma finder can determine the position and the energy (in the energy range of 35 keV to 3 MeV) of an orphan gamma-ray point source in a limited space such as a treatment room or industrial lab. The novelty of this work is the ability to determine the activity of the source without directly using the efficiency calibration data. Being lightweight (portable), precision of 5° in determining angular position, error less than 10% in distance estimation, and suitable precision in calculating activity are the features of this system. Effects of walls and floor in a typical room (for considering backscattered gamma-rays) and the height shift of a source from the plane of array in different cases have been studied. Whole procedure has been based on the net counting rate of photopeak in gamma spectrum, so it can be applied for different energies as well. All aspects of this design have been simulated in presence of a 137Cs point source with MCNPX2.6 code.

Detection of scales and its thickness determination in industrial pipes using Compton backscattering system.

The ability to detect and quantify scales in pipes has been an important yardstick for efficient transfer of fluids in domestic as well as in application related industries. Knowledge of different kinds of scales formed has become a precondition for trouble-shooting in operational lines. In this paper, collimated Compton backscattered gamma rays from a radioactive source have been used to inspect the scales by automatic scanning in steps along the axial direction of different pipes. The methodology has been extended for the quantification of scales that prevails in the real functionality of extensive usage of fluids. To aid for descaling processes, the desideratum is the density determination of scales and this parameter is quantified non-destructively and is also validated with the standard density. The described non-intrusive gamma ray densitometry is quite promising, efficient and has highly reliable results for scale detection with the squared correlation coefficient of 0.98. The proposed technique shows a better linearity than the gammatography technique.

Use of Gamma Ray Back Scattering Method for Corrosion Assessment in Insulated Pipes

Corrosion of insulated pipes is a major problem in nuclear,petrochemical and other industries.This type of corrosion is difficult to measure by the available techniques of ultrasound and transmission gamma or x-ray radiography due to the presence of insulating material and limited accessibility to both sides. Gamma-ray backscattering technique is a non-contactmethod and is highly suitable for buried insulated pipes where access is limited to one side only.In the present work, MCNP5 code was used to simulate a case where pipe corrosion (i.e., wall thinning) was measured by gamma backscattered technique. A steel pipe is bombarded by collimated gamma ray beam of 1 cm diameter from an 8 mCi137Cs source. The pipehad different wall thicknesses and was wrapped with a commercially available insulator. Upon interaction with the pipe wall, a 2x2 cm NaI (Tl) scintillation detector was used to measure the scattered radiation due to Compton scattering. The codewas used to evaluate the sensitivity of the device to predict pipe wall thinning as an indication for pipe corrosion. Then, parametric analysis was done to investigate the effects of pipe diameter, insulator thickness, source collimator diameter, source shield thickness as well as the thickness of the shied between the source and the detector on the device response. Effect of empty vs. water-filled pipes on the device response was also investigated. Results indicate that Gamma-ray backscattering technique can be used successfully as a non-destructive test for measuring wall thinning of insulated pipes as an indication of their corrosion.

Toroidal proportional gas flow counter for conversion X-ray Mössbauer spectroscopy

Abstract This paper presents a new prototype of a toroidal proportional gas flow counter. This detector has been developed to be used in the Mossbauer spectroscopy for characterizing the surfaces of the iron bearing samples. The presented proportional counter allows to register both conversion X-rays (6.4 keV) and the backscattered gamma rays (14.4 keV) in the almost 2π geometry with the sufficient efficiency. This paper demonstrates the structure description of the detector and the optimization process of its use in the backscattering Mossbauer spectroscopy. The energy resolution of the detector is presented via the series of the multichannel analyses with different filters, where both energy peaks (6.4 keV and 14.4 keV) were observed. The measured Mossbauer spectra confirm the regularity of the energy assignment. The utilization of the aluminum filter enables to achieve a higher resonance effect, whereas the backscattered Mossbauer spectra were measured. The detector could be also used to measure in the transmission geometry with high efficiency.

High energy and high brightness laser compton backscattering gamma-ray source at IHEP

Based on the LINAC of BEPCII, a high-polarized, high bightness, energy-tunable, monoenergetic laser compton backscattering (LCS) gamma-ray source is under construction at IHEP. The gamma-ray energy range is from 1 MeV to 111 MeV. It is a powerful and hopeful research platform to reveal the underlying physics of the nuclear, the basic particles and the vacuum or to check the exist basic physical models, quantum electrodynamic (QED) theories. In the platform, a 1.064 μm Nd:YAG laser system and a 10.6 μmCO2 laser system are employed. All the trigger signals to the laser system and the electron control system are from the only reference clock at the very beginning of the LINAC to make sure the temporal synchronization. Two optical transition radiation (OTR) targets and two charged-couple devices (CCD) are used to monitor and to align the electron beam and the laser beam. With the LCS gamma-ray source, it is proposed to experimentally check the gamma-ray calibrations, the photon-nuclear physics, nuclear astrophysics and some basic QED phenomena.

Application of artificial neural networks for the prediction of volume fraction using spectra of gamma rays backscattered by three-phase flows

The determination of the volume fraction percentage of the different phases flowing in vessels using transmission gamma rays is a conventional method in petroleum and oil industries. In some cases, with access only to the one side of the vessels, attention was drawn toward backscattered gamma rays as a desirable choice. In this research, the volume fraction percentage was measured precisely in water-gasoil-air three-phase flows by using the backscatter gamma ray technique andthe multilayer perceptron (MLP) neural network. The volume fraction determination in three-phase flows requires two gamma radioactive sources or a dual-energy source (with different energies) while in this study, we used just a 137Cs source (with the single energy) and a NaI detector to analyze backscattered gamma rays. The experimental set-up provides the required data for training and testing the network. Using the presented method, the volume fraction was predicted with a mean relative error percentage less than 6.47%. Also, the root mean square error was calculated as 1.60. The presented set-up is applicable in some industries with limited access. Also, using this technique, the cost, radiation safety and shielding requirements are minimized toward the other proposed methods.

Experimental investigation of effective atomic numbers for some binary alloys

Abstract In the present work, the gamma ray backscattering technique was used to determine the effective atomic numbers for certain binary alloys. With the help of a muffle furnace, the binary alloys were synthesized using the melt quenching technique with different compositions of 82 Pb, 50 Sn, and 30 Zn. The intensity distribution of backscattered photons from radioactive isotope 22 Na (511 keV) was recorded with the help of GAMMARAD5 [76 mm × 76 mm NaI(Tl) scintillator detector] and analyzed as a function of both atomic number and thickness of the target material. The effective atomic numbers for the same binary alloys were also computed theoretically using the atomic to electronic cross-section method with the help of the mass attenuation coefficient database of WinXCom (2001). Good agreement was observed between theoretical and experimental results for the effective atomic numbers of all the selected alloys.

Nondestructive Inspection System for Special Nuclear Material Using Inertial Electrostatic Confinement Fusion Neutrons and Laser Compton Scattering Gamma-Rays

A Neutron/Gamma-ray combined inspection system for hidden special nuclear materials (SNMs) in cargo containers has been developed under a program of Japan Science and Technology Agency in Japan. This inspection system consists of an active neutron-detection system for fast screening and a laser Compton backscattering gamma-ray source in coupling with nuclear resonance fluorescence (NRF) method for precise inspection. The inertial electrostatic confinement fusion device has been adopted as a neutron source and two neutron-detection methods, delayed neutron noise analysis method and high-energy neutron-detection method, have been developed to realize the fast screening system. The prototype system has been constructed and tested in the Reactor Research Institute, Kyoto University. For the generation of the laser Compton backscattering gamma-ray beam, a race track microtron accelerator has been used to reduce the size of the system. For the NRF measurement, an array of LaBr3(Ce) scintillation detectors has been adopted to realize a low-cost detection system. The prototype of the gamma-ray system has been demonstrated in the Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology. By using numerical simulations based on the data taken from these prototype systems and the inspection-flow, the system designed by this program can detect 1 kg of highly enriched 235U (HEU) hidden in an empty 20-ft container within several minutes.

Monte Carlo Modeling of Gamma Ray Backscattering for Crack Identification in the Aluminum alloy Plate

A Monte Carlo simulation study has been conducted of the Cs-37 gamma ray backscattering in the aluminum alloy plate. This simulation was performed in order to identify the existence of the crack in the aluminum alloy plate, the correlation between the backscattering peak and the crack width. We are able to analyze the absorbed energy distribution in the NaI(Tl) scintillation detector. For the experimental measurement, we are using 5 μCi of a Cs-137 gamma source and 2 in. x 2in. NaI(Tl) scintillation detector with the PMT. The aluminum alloy dimension is about 8 cm x 6 cm x 1 cm. The crack model is represented by the slit with the varying width (1 mm, 2 mm, 4 mm, and 6 mm). The existence of a crack is identified by the decreasing intensity of the gamma backscattering energy peak. These predicted results have a good agreement with the experimental measurement.

Evaluation of Multiple Backscattering and Saturation Thickness of Gamma Rays

A Monte Carlo code was written to determine the saturation thickness for multiply scattered gamma rays from aluminium targets. Interactions of incident gamma rays with the energies of 123, 279, 360, 511, 662, 1115, and 1250 keV were simulated. This work aims to design a convenient code which can be used in investigations on gamma backscattering. Obtained results for saturation thickness values have been compared with experimental ones and the Monte Carlo N-particle (MCNP) code results, and showed good agreement. Also, based on the similar behavior of number of multiple scattered photons between these three methods, the expected spectrum of singly or multiply scattered photons which is not possible to observe with experiment has been presented.

Optimization of energy window for gamma densitometer based backscatter method in oil industry

In this paper, we describe the results of various calculations performed for a design of the interference gauges that use the gamma-ray backscattering method with different scatter windows. The Pb barrier as shielding placed between 4 mCi 137Cs sealed radioactive source and a NaI (Tl) scintillation detector (1 inch in diameter—2 inch in height). Upon interaction with the material the scattered radiation, due to Compton process, was measured by NaI(Tl) detector. Using Compton scattered photons and review of the scattered photons in substance, by measuring of gamma-ray photons distributed, the density of materials can be obtained accurately. The results present for different scatter energy windows which 39–273 and 39–390 keV scatter windows have the best ΔX, STD and signal to noise.

Corrosion Imaging and Thickness Determination Using Micro-Curie Radiation Sources Based on Gamma-Ray Backscattering: Experiments and MCNP Simulation

Gamma radiography is used to monitor the corrosion of pipelines in remote locations; usually high radioactivity (1011–1012 Bq) is used. The technique is also not useful for imaging pipes with thick walls or large vessel walls. In this work, Compton backscattered radiation was used for the wall-thickness determination and corrosion imaging of pipe and flat materials using extremely-low-activity sources with radioactivities on the order of 104–105 Bq. A two-dimensional scanning system was designed to scan object surfaces, and the signals from a NaI(Tl) scintillation detector were fed into a computer for image construction using the LabView program. Thicknesses greater than 1 cm and 1.5 cm could be measured for Fe and Al and for polyvinyl chloride (PVC) and poly methyl methacrylate (PMMA), respectively. It was also possible to detect changes of less than 1 mm in depression depth for depressions measuring 3 mm in diameter. One- and two-dimensional images artificial defects on a pipe surface were successfully constructed.

Inspection of reinforced concrete samples by Compton backscattering technique

Reinforced concrete structures require frequent monitoring to ensure the concrete quality during its service life and for evaluation of in situ existing conditions. Compton backscattering of gamma rays is a nondestructive technique used for material characterization and detection of defects and inclusions in materials and can be employed on reinforced concrete. The methodology allows one-sided inspection of large structures, is relatively inexpensive and can be portable. The concept is based on detection of backscattered radiation produced from a collimated beam aimed at the sample. By measuring the spectrum of these scattered gamma rays it is possible to determine local density perturbations. In this work we used the Compton backscattering technique to locate and measure steel, defects and crushed stone inside concrete. The samples were irradiated with gamma rays from a Ø2mm diameter collimated 241Am (100mCi) source and the inelastically scattered photons were recorded at an angle of 135° by a high resolution CdTe semiconductor detector. Scanning was achieved by lateral movement of the sample blocks across the source and detector field of view in steps of 1mm. A previous optimization of the experimental setup was performed with Monte Carlo simulation. The results showed that it was possible to locate inclusions and defects with Ø8mm positioned at a depth of 20mm below the surface of the sample. It was observed that aggregates such as crushed stone could mask defects at specific points due to high attenuation of the incident and scattered beam.

Monte Carlo analyses of multiple backscattering of gamma rays

We have written a Monte Carlo code to simulate the experimental results of a previously reported study. We were able to analyse the energy distributions of photons that reached the detector system after suffering several successive Compton scatterings in the target. We have also investigated how the number of multiply backscattered events depends on the target thickness and the energy of the primary photons.