keV Gamma Radiation Research Articles

Investigation of self-attenuation of 210Pb (46 keV) gamma ray in sediment, certified reference material and high-density minerals: Implication to precise measurement of 210Pb

High resolution gamma spectrometry is one of the most widely used techniques in the measurements of environmental level 210Pb in sediment from coastal and freshwater environments and such measurements are needed to establish 210Pb chronology for the past 100–150 years. Precise measurement of 210Pb in sediment and soil requires appropriate self-absorption correction for its low-energy (46.5 keV) gamma radiation due to differences in the matrix between the sample and standard used to calibrate the instrument. Here we report a method that involves precise determination of 210Pb activity in sediment sample by calibrating the HPGe well detector with RGU-1-IAEA Certified Reference Material for well-defined geometries. A comparison of the 210Pb activity obtained from gamma-ray spectrometry with that obtained from alpha spectrometry via 210Po, using 209Po as yield tracer, indicates good agreement. We propose an empirical relation between the absolute efficiencies and packing densities of sample in a well-defined geometry (cylindrical counting vial) by affecting the count rate of 210Pb and its progenitor, 226Ra (via 214Pb and 214Bi). The effects of self-attenuation of 46.5 keV (210Pb), for naturally-occurring high-density minerals (apatite, titanite, monazite, and cerite) are evaluated. Specific activity of 210Pb on apatite measured by alpha and gamma spectrometry are compared. This study is relevant and useful for precise measurements of gamma-emitting environmental radionuclides such as 210Pb, 7Be, 137Cs as well as 226Ra.

Evaluation of electric arc furnace slag high strength shielding concrete on exposure to gamma 662 KeV

Production of electricity from nuclear fission – or fusion in nuclear power plants is becoming an attractive solution to face the scarcity in different natural energy resources. This paper presents the first outcome from an NRC funded project investigating the production of concrete with an improved 662 KeV gamma radiation linear attenuation coefficient, using alternatives as Electric Arc Furnace Slag (EAFS), to traditional aggregates as crushed stone (Dolomite), and those known for their heaviness as barite and hematite. An insight research program is conducted using blended cements along with these variety of aggregates to produce different concrete mixes. The mechanical and physical properties of these concretes are thoroughly assessed. In addition, gamma attenuation coefficient (μ) of concrete of all mixes is measured. The results confirm significant improvement in most of the investigated properties by increasing (EAFS) percentage. Full replacement of coarse and fine aggregates by EAFS lead to highest values in all properties, as the compressive strength improved by 43 % and 40 %, for 7 and 28 days tests control values - respectively. Moreover, enhancement in linear attenuation coefficient (LAC) reached 22 %.

Measuring the internal activity of the neutron emitter 252Cf in-vivo: Basics and potentials based on measurements in phantoms

The possibility to determine internal activities of 252Cf in vivo in humans was studied by means of measurements of anthropomorphic phantoms. For this purpose, neutron capture by abundant hydrogen with subsequent emission of 2223 keV gamma radiation was used. The counting efficiency per emitted neutron for a 70 kg phantom was only 21% that for primary gamma radiation of the same energy. Detection limits were determined as 230 Bq and in a fictitious measurement chamber without background at the 2223 keV peak as 140 Bq. Several methods to enhance the measurement effect, all by capturing further neutrons outside the body by hydrogen or by cadmium, were investigated. The smallest activities that can be detected yield committed effective doses of 23 mSv and of 110 mSv if the results of the phantom measurements were adopted to adult humans and children, respectively.

Fluorescence-based method for estimating the dead layer thickness of a broad-energy germanium detector

A fluorescence-based method is proposed in this paper to estimate the front dead layer thickness of a broad-energy germanium detector. The germanium fluorescence was induced by the 57Co 14.4 keV gamma radiation incident on the dead layer. The count ratio between germanium fluorescence and the transmitted probe photons was experimentally measured and then compared with a series of Geant4 calculations for thickness determination. The method is sensitive to dead layer thickness owing to direct measurement of the thickness-dependent fluorescence and is independent of probe intensity and materials intervened between the source and the detector by using count ratio. The approach is anticipated to have a general application to surface studies of various types of germanium detectors.

Performance of lead and iron oxides nanoparticle materials on shielding properties for γ-rays

The objectives of this work are preparation and study of properties of some shielding materials to protect public and personnel from the effect of ionizing radiation. In the present work the increment in mass attenuation coefficients (μm) by using Lead oxide (PbO) and/or Iron oxide (Fe2O3) nanoparticles instead of bulk lead and iron oxides was investigated. Lead oxide nanostructure was synthesized by citrate precursor method, through the reaction of citric acid [C6H7O8.H2O] and lead acetate trihydrate [Pb (CH3COO) 2.3H2O]. Iron oxide nanostructure was synthesized by citrate precursor method, through the reaction of ferric nitrate [Fe(NO3)3.2H2O] and citric acid [C6H7O8.H2O]. The prepared nanostructure materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Different gamma radiation interaction parameters used for radiation shielding design were computed theoretically and measured experimentally at, 295 keV, 325 keV, 609 keV, 934 keV, 1378 keV and 1764 keV gamma radiation energy using narrow transmission geometry and using High Purity Germanium (HPGe) detector. Our results show that the mass attenuation coefficient (μm) of lead oxide (pbO) nanostructure was greater than that of bulk Lead oxide, while in the case of iron oxide there is little change between nano and bulk materials.

Collimators for Gamma Dual Energy CT Arch-Detector: A Simulation Study

The image resolution of computed tomography (CT) scan system can be affected by numbers of factors such as collimator material, collimator design, stopping power of detector and scatter photons rejection and/or correction technique. The scatter photons are one of the major sources of background noise that can immensely degrade the image quality of the CT system. The image quality, in turn, affects the discrimination and identification performance of the system especially in the case of dual-energy CT systems for material decomposition. Therefore, for material identification, acquisition of raw data with minimal noise is of immense importance. In this simulation study, the performance of two types of collimators was evaluated to come up with a better collimator design for background noise compression. Both collimators were made of tungsten with similar length of 30 mm but with different hole shapes (fan and parallel). In both cases, results suggest that there is a clear improvement in terms of spatial resolution. In a comparison of grids structure, fan grid performed slightly better than parallel for most of the cases. The peak-to-valley (PV) ratio for 122 keV gamma radiation source improved on average ∼0.16 (16%) and ∼0.23 (23%) for fan collimator and parallel collimator respectively. For 60 keV gamma source, the improvements were ∼0.14 (14%) and ∼0.17 (17%) respectively. Thus, from the results, it can be concluded that fan grid collimator can provide superior performance compared to parallel grid collimator.

Pulse length and amplitude filtration of gamma radiation detection, utilization in the 57Fe Mössbauer spectroscopy

In this paper we present a pulse signal processing which combines the pulse amplitude and length discrimination. The introduced technique improves the signal-to-noise ratio, especially in case of low energy gamma radiation. The effectiveness of this approach is demonstrated on the discrimination of 6.3 keV X-ray and 14.4 keV gamma radiation of 57Co and its utilization in Mössbauer spectroscopy. The presented signal analysis process can be easily implemented to other applications that are based on pulse detection, particularly to those, where the signals are very close to the noise level.

Measurement of the effective atomic number of some transition and rare earth compounds using the Rayleigh to Compton scattering ratio of gamma radiation

ABSTRACTThe effective atomic numbers of some transition and rare earth compounds have been determined by measuring the ratio of Rayleigh to Compton scattering signal using 59.5 keV gamma radiation from americium-241 radioactive source. The scattered gamma photons from the elements and compounds at an angle of 90° were detected using an ORTEC high-purity germanium detector coupled with 16K multi-channel analyzer. By measuring the ratio of Rayleigh to Compton scattered signal (momentum transfer 3.38 Å−1), the effective atomic numbers of the transition and rare earth compounds have been determined and compared with theoretical values predicted by AutoZeff, power law, and direct method.

Application of the Böhm chamber for reference beta dose measurements and the calibration of personal dosimeters

Abstract Thermoluminescent dosimeters (TLDs) currently used in personal and area dosimetry are often utilized to measure doses of ionizing radiation in fields with a more complex structure and therefore they should be calibrated in relation to different radiation types. The results of such calibration presented for UD-813 TLDs allowed for evaluation of their capability in relation to different radiation types like the beta and photon radiation of different energies and neutron radiation generated by the 241Am-Be source. The detector response for 60 keV photons was 10% higher than for the 662 keV gamma radiation of 137Cs. There were also response differences in relation to photon and beta radiation between detectors with an enhanced concentration of lithium 6Li and boron 10B and detectors containing a natural level of these isotopes. Measurements of the reference beta doses were performed with the help of the Böhm chamber. This method is relatively more complicated compared to determining the reference photon and neutron doses and is described thoroughly in this paper. The corrected current measured by the Böhm chamber for the chosen parameters was a linear function for an entire available range of the chamber depths. The percentage of errors related to the evaluated reference beta doses were below 2% despite a rather large number of corrections that should be taken into account. The calibration distances varied from 11 cm to 50 cm. For this range and beta particle energy, the absorption of radiation in the air was negligible and their attenuation had a predominantly geometric character.

Reassessment of the electron density in Cu2O using γ-ray diffraction.

The electron-density distribution in Cu2O has been critically reexamined to test controversial conclusions from earlier experimental and theoretical studies. The electron density is derived via multipole refinement of high-quality single-crystal diffraction data, collected at room temperature with 316.5 keV gamma radiation. Four γ-lines in the energy range 200-600 keV have been used to extrapolate extinction-free low-order structure factors. The remaining extinction corrections refine to a crystal mosaicity identical to the observed one. There is no support for anharmonic contributions to the thermal parameters. Important features of the derived electron density are (i) a partially filled d_{z^2} orbital, (ii) an incomplete ionization of Cu and O, and (iii) no interstitial Cu-Cu charge pileup, thereby refuting the covalent bonding hypothesis.

Optical properties of some modified plant compound after 662 keV gamma radiation

Plant-isolated compounds, Osthol [7-methoxy-8-(3-methylbut-2-enyl) coumarin], were subjected to modification in the isopentenyl side chain to get an aldehyde of 2-methyl-4 (7-methoxy-2-oxo-2H-chromen-8-yl)-but-2-en-1-al. This modified compound was exposed to γ-radiation produced by 137Cs source at room temperature. Pre- and post-irradiation study was carried out by ultraviolet–visible spectroscopy. The compound shows a sharp absorption peak at 322 nm. This observed absorption band decreases with irradiation up to a certain dose and then increases with a further increase in the radiation dose. This compound exhibits almost a linear response up to 7 Gy. From the optical data analysis, this compound follows indirect allowed transition and the optical gap was found around 3.58 eV. The systematic decrease in the band gap was found with an increase in the radiation dose. Urbach energy is also found to decrease with radiation. This parameter gives a clear indication of the defects and free radical created in the system after irradiation. The present features shown by this compound may be exploited as sensitive dosimeter in 0–7 Gy γ-radiation environment.

Development of a randomized 3D cell model for Monte Carlo microdosimetry simulations

The objective of the current work was to develop an algorithm for growing a macroscopic tumor volume from individual randomized quasi-realistic cells. The major physical and chemical components of the cell need to be modeled. It is intended to import the tumor volume into GEANT4 (and potentially other Monte Carlo packages) to simulate ionization events within the cell regions. A MATLAB© code was developed to produce a tumor coordinate system consisting of individual ellipsoidal cells randomized in their spatial coordinates, sizes, and rotations. An eigenvalue method using a mathematical equation to represent individual cells was used to detect overlapping cells. GEANT4 code was then developed to import the coordinate system into GEANT4 and populate it with individual cells of varying sizes and composed of the membrane, cytoplasm, reticulum, nucleus, and nucleolus. Each region is composed of chemically realistic materials. The in-house developed MATLAB© code was able to grow semi-realistic cell distributions (~2 × 10(8) cells in 1 cm(3)) in under 36 h. The cell distribution can be used in any number of Monte Carlo particle tracking toolkits including GEANT4, which has been demonstrated in this work. Using the cell distribution and GEANT4, the authors were able to simulate ionization events in the individual cell components resulting from 80 keV gamma radiation (the code is applicable to other particles and a wide range of energies). This virtual microdosimetry tool will allow for a more complete picture of cell damage to be developed.

Electron density distribution in hexagonal cobalt: Aγ-ray diffraction study

The electron density distribution of ferromagnetic hexagonal cobalt is studied at room temperature using high-quality single-crystal diffraction data measured up to $\text{sin}\text{ }\ensuremath{\theta}/\ensuremath{\lambda}=1.9\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ with 316.5 keV gamma radiation. A highly anisotropic mosaic-block orientation was found. The ensuing anisotropy in secondary extinction could be fairly well described by the Thornley-Nelmes formalism, with adjusted mosaicities close to the directly observed ones. The structure factors have been analyzed by a multipole expansion model within the Hartree-Fock framework. Thermal mean-square atomic amplitudes are distinctly different along the $a$ and $c$ axes. The total $3d$ charge exhibits appreciable anisotropy with an excess of density in the singlet ${a}_{\text{g}}$ along the $c$ axis and a deficiency in the two doublet ${e}_{\text{g}}$ orbitals. The $3d$ shell in the metal shows a slight contraction of 1.2% relative to the free atom. Agreement with low-order form factors from critical-voltage electron diffraction reaches 0.1%. No difference of $d$-electron count is found between metal and atom. A $3{d}^{7}$ configuration implies incomplete filling of the majority-spin band. The directed metallic bonds are characterized in terms of the electron density topology.

Compton profiles of p‐Si and n‐Si in an external electric field

AbstractThe Compton profiles of p‐Si and n‐Si have been measured in an external electric field with 59.54 keV gamma radiation from an Am‐241 source. The external electric field of intensities +167 kV/m and –167 kV/m were used to change the surface charge density of the samples. Comparison of the profiles of p‐Si and n‐Si in the same magnitude but opposite direction of the electric field gives information about the Compton scattering of gamma rays from holes. Furthermore, the Compton profile experiments in an external electric field can be used to identify the type of semiconductor. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Performance of 1-${\hbox {mm}}^{2}$ Silicon Photomultiplier

A silicon photomultiplier (SPM) is a large area detector consisting of a parallel array of photon counting microcells. Each microcell consists of a Geiger Mode photodiode with an integrated quenching element. Each microcell is then connected to a common output. The microcells have a uniform gain of up to 10 and provide an identical charge output signal for each photon detected. Under illumination the summed output of the detector is proportional to the number of Geiger pulses and hence proportional to the incident photon flux. This combination gives extremely high performance comparable to that of a conventional photomultiplier tube (PMT). We report on the characterization of two different 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> SPM detector designs with 620 and 920 microcells at room temperature (20 deg) and down to . We assess detection efficiency, breakdown voltage, gain, dark rate, crosstalk, timing jitter and dynamic range. The SPM detector operates over the visible region of the spectrum, characterized here from 400 to 800 nm. The peak photon detection efficiency of 15% occurs at 500 nm with a cooled () dark rate of 600 at a bias voltage of 31 V. In a test for positron emission tomography (PET), an energy resolution of 25% was recorded for the detection of 511 keV gamma radiation using 1 mm1 mm15 mm LYSO scintillator crystal. The SPM has many applications such as medical imaging, microscopy, high-energy physics, and homeland security.

Electron Momentum Density of Hexagonal Magnesium Studied by Compton Scattering

Directional Compton profiles of single crystal of hcp magnesium have been measured with scattering vectors along the [10 10], [1120] and [0001] directions in reciprocal space (special directions ΓΜ, ΓΚ, ΓΑ) using high-energy (662 keV) gamma radiation from a 137Cs isotope source. The experimental data were compared with corresponding theoretical Korringa-Kohn-Rostoker (KKR) calculations. The directional difference profiles, both experimental (of medium resolution) and theoretical ones, show very small anisotropy of the electron momentum density in magnesium, 2-3 times lower than in zinc and cadmium single crystals, significantly lower than observed in cubic metals. This small directional effect is in good agreement with Compton 60-keV energy experiments and positron annihilation data presented by other authors.

Phase composition at surface of Fe-3%Si alloy

The structure, phase and chemical compositions of surface layers in different depths of Fe-3%Si alloy were investigated. According to the X-ray Photoelectron Spectroscopy (XPS) spectrum (penetration depth of up to ∼ 1nm) of the as-prepared sample, a layer of SiO2 was present on the top. After the subsequent Ar+ sputtering (removing the SiO2 layer), a segregation of Si atoms and two other phases were observed. The phases were described as the cubic c-FeSi and Fe3Si. The emission57Fe Mossbauer spectra confirmed a presence of these phases. The α-Fe and solid solution of α-Fe + 1wt.%Si were recognized in the Conversion Electron Mossbauer spectra (penetration depth ∼ 300nm) while the Mossbauer spectra taken in scattering geometry with detection of 14.4 keV gamma radiation (scanning depth of ∼ 30 µm) indicate Fe-3wt.%Si solid solution as a main phase.

Electron densities in relation to magnetism: gamma-ray diffraction from transition-metal monoxides and difluorides.

In this article, results are described from an area of solid-state physics that heretofore has remained unexplored by Bragg charge-scattering experiments. It is shown that gamma-ray electron densities can provide detailed information on magnetic ground-state properties at a subatomic resolution. The use of 316 keV gamma radiation has allowed low-order structure factors at better than 0.1% accuracy to be determined and, at the same time, extended data sets to be collected up to high momentum transfer. Prototypic antiferromagnets such as the late 3d transition-metal monoxides and difluorides have been systematically investigated, in most cases both in the paramagnetic and in the fully ordered phase. At transitions with a lowering of symmetry, multidomain formation was suppressed by application of external mechanical stress or magnetic fields. The results are considered in the context of information provided by recent magnetic neutron and X-ray studies.

Electron momentum density of hexagonal cadmium studied by Compton scattering

AbstractThe directional electron momentum density distributions (Compton profiles) of single‐crystal cadmium have been measured in transmission and reflection experimental geometries using high‐energy (662 keV) gamma radiation from a 137Cs isotope source. Profiles along the [100] and [110] directions in reciprocal space were measured in both geometries, whereas only the transmission geometry was used for the measurements along the [001] direction. The experimental data have been compared with corresponding theoretical KKR semi‐relativistic calculations. The directional difference profiles, both experimental and theoretical, show, similarly to other hexagonal systems, very small anisotropy of the electron momentum density in hexagonal cadmium, about 0.3%, i.e. less than half of that presented in the literature for cubic systems. Minor discrepancies between KKR calculations and experiment probably occur due to the necessity to introduce an anisotropic electron–electron correlation correction. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Bremsstrahlung-induced highly penetrating probes for nondestructive assay and defect analysis

Nondestructive assay and defect analysis probes based on bremsstrahlung-induced processes have been developed to identify elements and probe defects in large volume samples. Bremsstrahlung beams from (electron accelerators) with end-point energies both above and below neutron emission threshold have been used. Below neutron emission threshold these beams (from 6 MeV small pulsed linacs), which exhibit high penetration, create positrons via pair production inside the material and produce X-ray fluorescence (XRF) radiation. Chemical assays of heavy elements in thick samples up to 10 g/cm 2 thick are provided by energy dispersive XRF measurements. The pair-produced positrons annihilate within the material, thereby emitting 511 keV gamma radiation . Doppler broadening spectroscopy of the 511 keV radiation can be performed to characterize the material and measure defects in samples of any desired thickness. This technique has successfully measured induced strain due to tensile stress in steel samples of 0.64 cm thick. Bremsstrahlung beams above neutron emission threshold, from a 20 MeV pulsed electron linac, have also been used to produce residual nuclei in excited states via photonuclear reactions allowing the detection of heavy elements via their characteristic γ-rays. This can be developed into a technique to trace some heavy metals in large rocks and soils for environmental applications.