Gamma-ray Backscatter Research Articles

Analysis of ergonomic quality coefficients of contraband detectors

The article concerns the world market contraband detectors of backscattered gamma rays that are part of the search and examination equipment at customs and specialized units, where the ergonomic coefficients of contraband detectors are investigated. The quality of items is assessed from the standpoint of competitiveness and global technological level. Determining the level of item, the comparison of the quality coefficients of future products and the base sample is carried out. The analysis of the ergonomic properties of portable devices of inspection control, presented as one-block designs with optional display, two-block designs and corresponding normative documentation, made it possible to form the basic coefficients of the sample quality according to the subgroup of ergonomic coefficients, including physiological, psychophysiological and health indicators for two-block contraband detector.

Demonstration of imaging via backscattering of annihilation gamma rays

Imaging via backscattering of annihilation gamma rays (IBAG) is a technique for three-dimensional gamma ray imaging of objects when only one side is accessible, such as for objects behind a wall or other barrier. This technique utilizes a positron source to produce nearly collinear, 511-keV gamma rays in opposite directions. One of these provides timing and directionality tagging, while the other backscatters off the object to be imaged. The scattering location can be reconstructed using the relative timing of the two gamma ray signals and the positions at which they are detected. Excellent timing resolution is required, since the time-of-flight information is essential for reconstruction. Three-dimensional imaging requires two arrays of detectors, one for the 511-keV tagging gamma ray and one for the backscattered gamma ray. We are studying the feasibility of an IBAG system using LaBr 3 to give good timing resolution and energy-based event selection. This paper presents one-dimensional position reconstruction measurements from our laboratory system for a variety of objects and barriers.

Experimental evaluation of multiple Compton backscattering of gamma rays in copper

The gamma ray photons continue to soften in energy as the number of scatterings increases in thick target, and results in the generation of singly and multiply scattered events. The number of these multiply scattered events increases with an increase in target thickness and saturates beyond a particular target thickness known as saturation depth. The present experiment is undertaken to study the saturation depth for 279 and 320 keV incident gamma ray photons multiply backscattered from copper targets of varying thickness. The backscattered photons are detected by a Nal(Tl) gamma detector whose pulse-height distribution is converted into a photon spectrum with the help of an inverse matrix approach. To extract the contribution of multiply backscattered photons only, the spectrum of singly scattered photon is reconstructed analytically. We observe that the numbers of multiply scattered events increases with an increase in target thickness and then saturate. The saturation depth is found to be decreasing with increase in incident gamma energy.

Optimization of a Detector Collimator for Use in a Gamma-Ray Backscattering Device for Anti-Personal Landmines Detection

Optimization of a Detector Collimator for Use in a Gamma-Ray Backscattering Device for Anti-Personal Landmines Detection

Response function of NaI(Tl) detectors and multiple backscattering of gamma rays in aluminium

The response function, converting the observed pulse-height distribution of a NaI(Tl) detector to a true photon spectrum, is obtained experimentally with the help of an inverse matrix approach. The energy of gamma-ray photons continuously decreases as the number of scatterings increases in a sample having finite dimensions when one deals with the depth of the sample. The present experiments are undertaken to study the effect of target thickness on intensity distribution of gamma photons multiply backscattered from an aluminium target. A NaI(Tl) gamma-ray detector detects the photons backscattered from the aluminium target. The subtraction of analytically estimated singly scattered distribution from the observed intensity distribution (originating from interactions of primary gamma-ray photons with the target) results in multiply backscattered events. We observe that for each incident gamma photon energy, the number of multiply backscattered photons increases with increase in target thickness and then saturates at a particular target thickness called the saturation thickness (depth). Saturation thickness for multiply backscattering of gamma photons is found to decrease with increase in energy of incident gamma-ray photons.

Analysis of gamma ray incoherent scattering for non-destructive testing

An approach for the analysis of gamma ray incoherent scattering on free and binding electrons is presented for Non-destructive Testing (NDT). The method is based on computational simulation and backscattering gamma ray measurements for carbon steel walls. The results of thickness measurements for steel walls are described by the theory of the energy transfer model.

Experimental and numerical analyses on LiSO 4 and Li 2TiO 3 pebble beds used in a ITER test blanket module

One of the possible configurations of test blanket module (TBM) which will be tested during the ITER operation phase is made up of neutron multiplier and breeder as pebble beds. This paper describes an experimental device for the determination of the pebble bed conductivity in presence of interstitial air. The tests were performed with a simultaneous compression of the bed in order to obtain the effective bed conductivity versus the axial deformation for several values of the temperature. The effective conductivities of LiSiO 4 and Li 2TiO 3 pebble beds, both in air and in vacuum, were determined. The packing factors of the beds were measured by means an ad hoc built instrumentation, based on the gamma ray backscattering. The experimental results have been compared with those of a theoretical model developed by the authors, obtaining a good agreement in terms of bed conductivity and stiffness.

Gamma-Ray Backscattering Tomography Approach Based on the Lidar Principle

An approach is proposed, and its potentialities are studied, for single-sided gamma-ray in-depth sensing and tomography of dense opaque media. The approach is based on lidar (LIgth Detection And Ranging) principle or, in the present case, graydar (Gamma RAY Detection And Ranging) principle, that is, time-to-range resolved detection of the backscattering-due radiative returns from the probed object irradiated by pulsed gamma-photon pencil beams. The basic analysis and data processing delta-pulse single-scattering graydar equation is formulated by analogy with the lidar equation and is shown to be applicable, under some determinate conditions, to the problems of gamma-ray in-depth profiling of dense media. It is shown analytically and by computer simulations that the approach developed in the work would enable one, at large-enough but reasonable sensing photon fluxes and measurement time intervals, to determine with good controllable accuracy and resolution the location, the material content, and the mass density of different homogeneous ingredients inside the probed object as well as the mass (or electron) density distribution within one-material objects. This approach can be widely applied, e.g., for nondestructive material examination in industry and aviation, detection of landmines and explosives, investigating the constitution of archeological artifacts, etc

レーザー逆コンプトンγ線によるコンクリート内部の検査

コンクリート構造物内部の調査・診断に各種非破壊検査手法が用いられている。しかしながら, 現在用いられている手法では, その測定範囲や精度等に制限があり, 正確に内部の情報を得ることは難しい。昨今, 耐震強度偽装問題やドリル削孔時の主鉄筋の切断等の問題が表面化し, 非破壊で配筋状態を正確に検査できる手法が望まれている。レーザー逆コンプトンγ線は高エネルギー, 高透過力, 高指向性という特徴を持ち, コンクリート中の鋼材や欠陥部の検出に有効であると考えた。そこで, レーザー逆コンプトンγ線によるコンクリート内部調査の適用性を検証するために, 供試体を用いて実験を行った。その結果, コンクリート内部の配筋, 空隙, 0.2mm幅以上のひび割れを鮮明にとらえることができた。

Flaw detection by spatially coded backscatter radiography

Backscatter imaging is useful for inspecting structures that are accessible only from one side. However, indications provided by scattered radiation are typically weak, convoluted and difficult to interpret. This paper explores the use of the coded aperture technique to detect flaws using gamma-ray backscatter imaging. The viability of this approach is demonstrated with indications obtained from Monte Carlo simulations of radiation scattering measurements. The results show that, with a 2 mm wide beam of 137Cs photons, flaws as small as 1.5 mm in width can be detected using this technique. Indications of changes in flaw size, location, multiplicity and density were also observable. In addition, it is possible to quantify, from the decoded indications, the flaw location and its size.

Comparison between (n–γ), (γ–γ) and natural γ-ray activity techniques for ash measurement of coal samples

A comparison between neutron capture gamma (n–γ), compton backscattering gamma ray (γ–γ) and natural radioactivity techniques was performed to measure the ash content of coal samples from coal mines in the north of Iran. The results proved that the neutron–gamma technique is superior to the other two techniques. The standard deviation between the chemical assays and the neutron–gamma, gamma–gamma and natural gamma predictions are 1.44, 5.68 and 1.71% ash, respectively.

Gamma-ray backscatter for body composition measurement

The purpose of this study was to examine the potential of using backscatter information to assess regional body composition at selected sites. Two measurement techniques are examined: the measurement of the ratio of coherent to Compton scatter, and the measurement of the Compton scatter profile. Two possible applications are considered: the measurement of trabecular bone mineral density, and the measurement of the average fat/muscle ratio in a tissue volume. The results presented indicate that the analysis of coherent and Compton backscattered γ-ray spectra from an 241Am source has the potential for measuring both trabecular bone mineral density and average fat/muscle ratio in a tissue volume, with a low absorbed dose to the subject.

Measuring physical properties at the surface of a comet nucleus

The European Space Agency’s cornerstone mission Rosetta is due for launch in January 2003. It will perform a rendezvous with comet 46P/Wirtanen beyond 3 AU and, following an initial mapping phase, deploy a lander to a selected site on the nucleus surface. The Rosetta Lander will provide unprecedented access to cometary material. Some of the most uncertain characteristics of the nucleus material are physical properties such as its density, the structure of the surface layers and its mechanical strength. MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science) is one of the experiment packages selected for the Lander payload which will address certain physical properties and their evolution with time. This thesis focuses on the in situ measurement of the density of the surface layers by a radiation densitometer incorporated into the MUPUS thermal probe, and on the penetrometry measurements to be performed by an accelerometer mounted in the Lander’s anchoring harpoon. A concept for incorporation of a gamma ray attenuation densitometer into the thermal probe is presented and explored. A 137Cs radioisotope source will be mounted near the tip of the probe and semiconductor radiation detectors situated at the top of the probe will monitor the transmitted count rate during probe insertion, as the intervening material attenuates the radiation. Preliminary experiments to evaluate cadmium telluride (CdTe) detectors for this purpose are presented, as well as results from a specially-developed Monte Carlo computer code designed to model the absorption and scattering of photons in bulk material. Also presented is a control algorithm to dynamically re-budget the integration time and depth resolution of the instrument as it is inserted by the hammering mechanism. This is required due to: a) the wide range of possible densities the instrument may encounter, b) the variation vs. depth of required integration time, and c) the limited time in which the measurement must be performed. For lower than nominal densities, integration time may be wasted when it could be used to improve the accuracy and depth resolution. For higher densities the integration time at particular depths may not be sufficient to obtain acceptable accuracy; in this case some depth resolution could be sacrificed to improve the accuracy. The proposed algorithm uses the density measured at each point to update the time budget and depth resolution for the remaining stages of penetration. Although the use of the gamma ray backscatter type of densitometer was eventually rejected in favour of the aforementioned attenuation technique, investigation of the backscatter technique resulted in an extension to the Single Scattering Model– an analytic approximation of its operation. This extended model adds to our understanding of these devices' response to spatial inhomogeneity. Calculations show that anchoring of the Lander is necessary to avoid possible ejection from the nucleus by gas drag in the case of a landing in an active area. The use of the Lander’s anchoring harpoon to perform penetrometry measurements is reported, including the results of preliminary experiments and techniques for analysing the accelerometry data. It is shown that layers with distinctly different strengths may be identified, and that the mean deviatoric stress– a strength parameter– may be constrained to within a factor of about 2.2. This would be a significant improvement on current estimates, which vary by several orders of magnitude. Together with other investigations on the Rosetta mission the densitometry and penetrometry measurements will serve to constrain models of the physical state and evolution of the cometary material found at the landing site. In particular both instruments are sensitive to near-surface layering, which may be expected from theoretical models of cometary activity.

Preparation of a 6Li 0.74Mg 0.26 alloy target

For a neutron-lifetime experiment at the National Institute of Standards and Technology (NIST), an alloy of 6Li and Mg was prepared as a disk 2.8 mm thick and 37.9 mm in diameter. Three-plus grams of a homogeneous alloy with a 6Li content approaching 74 at%, a very low hydrogen content and a low oxygen content were required. A sealed stainless-steel crucible was used for the alloying, in consideration of the chemical activities and vapor pressures of Li and Mg at the alloy-formation temperature (≥925 K). This report includes design details of the weld-sealed crucible, adaptations made to a radio-frequency (RF) induction furnance and the process used to prepare 4.5 g of the alloy, recover the alloy from the crucible and shape it into a disk. For ten months, the disk was stored successfully by continous vacuum pumping at 1.3 kPa. Back-scattered gamma rays revealed the alloy had acceptably low levels of hydrogen and oxygen. No other contaminants were detected.

Backscattering of Gamma rays from the natural turkish marbles

Backscattering of the gamma radiation from the natural Turkish marbles were measured as a function of the scatterer thickness using the standard gamma sources, such as Na-22, Co-60 and Cs-137. For comparison, each measurement has been repeated for ordinary concrete in place of the Turkish marbles. The results have been expressed graphically.

Local densitometry of wood by gamma back-scattering

Density of wood is one of the major material property. The article presents a simple, quick and precise local density measurement based on the gamma back-scattering technique. The equipment works with an 1GBq activity Am-241 ring source. Linear relationship was found between the back-scattered gamma ray intensity and the density of wood within the density range of 350–900 kg/m3. Using this technique non-contact local densitometry is possible. If the specimen thickness is less than 70 mm (saturation thickness) the specimen thickness must be well known, because in this thickness range the back-scattered gamma ray intensity depends on the thickness. A calibration curve should be determined for all thicknesses below 70 mm. Another limitation is that the equipment contains radioactive material. The user needs a special licence and permission from the authorities responsible for radioactive materials.

Use of the Gamma-Ray Back-Scattering Technique to Monitor Corrosion in a Circulating Rig

Abstract The gamma back-scattering technique (GBST) was used to monitor general corrosion in situ in a steel tube installed in a circulating rig. The circulating aggressive environment was 1 wt% hydrochloric acid (HCl, pH = 0.8) at a flow rate corresponding to Reynolds number (Re) = 7,675. The final wall thickness of the steel tube resulting from accelerated corrosion as measured by GBST was 1.7 mm (0.067 in.) vs an original wall thickness of 2.8 mm (0.110 in.). This method was compared with the standard ultrasonic technique, which gave a final thickness of 1.8 mm (0.071 in.). The theoretical thickness calculated from weight loss and the change of tube diameter was 1.92 mm (0.076 in.). The percentage of error against the theoretical thickness was 11.5% for GBST and 6% for the ultrasonic method. The small extra error in the GBST could be acceptable in certain situations in view of its ease of use, noncontact, and nondestructive nature.

Non-destructive exploratory tests of corrosion of steel embedded in cement-paste and mortar by gamma-ray backscattering : 50719 Sekine, I.; Yuasa, M.; Hotta, A. Corrosion Engineering, Vol. 41, No. 3, pp. 203–214 (1992)

Non-destructive exploratory tests of corrosion of steel embedded in cement-paste and mortar by gamma-ray backscattering : 50719 Sekine, I.; Yuasa, M.; Hotta, A. Corrosion Engineering, Vol. 41, No. 3, pp. 203–214 (1992)

後方散乱γ線によるコンクリート中の鉄筋の位置決め

後方散乱γ線によるコンクリート中の鉄筋の位置決め

Determination of the Double Angular and Energy Differential Gamma-Ray Albedo for Iron Material by Using the Monte Carlo Method

The Monte Carlo method can be used to compute the gamma-ray backscattering albedo. This method was used by Raso to compute the angular differential albedo. Raso’s results have been used by Chilton ...