Monoenergetic Gamma Research Articles

CeBr3 scintillators for 4He prompt gamma spectroscopy: Results from a Monte Carlo optimization study

Range uncertainties limit the potential of charged particle therapy. In vivo and online range verification techniques could increase the confidence in the dose delivery distribution and lead to more conformal treatments. Prompt gamma imaging and prompt gamma spectroscopy (PGS) have been demonstrated for such a purpose. The successful application of these techniques requires the development of a dedicated detector system optimized to the radiation energy ranges and the intensity. In this work, we investigated a detector system based on CeBr3 crystals capable of performing spectroscopy of the prompt gamma radiation induced by 4 He beams. We performed Monte Carlo simulations to optimize the detector system. The study was carried out both with the Geant4 toolkit and the FLUKA package. The simulated system consisted of a primary crystal for spectroscopy and secondary crystals for noise reduction in anticoincidence (AC). For comparison purposes, we considered a configuration without AC crystals. We first defined the dimensions of the primary cerium bromide (CeBr3 ) crystal and the secondary bismuth germanate (BGO) or CeBr3 crystals. We then evaluated their detection performance for monoenergetic gamma radiation up to 7MeV in such way that the probability of the photo-peak detection was maximized in comparison to the number of escape peak and Compton events. We simulated realistic prompt gamma radiation spectra induced by 4 He beams on homogeneous targets (water, graphite, and aluminum) and on implants (water with an aluminum insert). Finally, we tested the performances of the optimized systems in the detection of the realistic gamma spectra. The quantitative analysis was accomplished by comparing the signal-to-noise ratio between the different configurations and the ability to resolve the discrete reactions. We present the optimized dimensions for the primary CeBr3 crystals with and without AC shielding. The specific values are given over a wide range of crystal volumes. The results show an optimal primary CeBr3 crystal with an approximately diameter to length ratio of 1 without AC shielding and 0.5 with AC shielding. The secondary BGO and CeBr3 should have a transverse dimension of 3 and 4.56cm, respectively. The analysis of the prompt gamma spectra from 4 He beams highlighted the presence of specific discrete reactions not observed in 1 H studies, for example, 12 C transition 0+ (7.65MeV) →2+ (4.44MeV). This reaction is responsible for the generation of the 3.21MeV prompt gamma peak. The optimized primary crystal provides a significant increase in the signal-to-noise ratio together with an improved resolution of the discrete gamma lines, especially in the high-energy region. The detection configuration with an optimized anticoincidence crystal improved the signal-to-noise ratio up to a factor of 3.5. This work provides the optimal geometry for primary and secondary crystals to be used in range verification through PGS. The simulations show that such a PGS system may allow for the simultaneous detection of the discrete lines from a thin metal implant within a water phantom.

Calculation of the exposure buildup factors for x-ray photons with continuous energy spectrum using Monte Carlo code

Exposure buildup factors are very important for the calculation of radiation shielding and also applied radiation. We must distinguish the monoenergetic and continuous energy spectrum gamma source in order to calculate the exposure buildup factors. In this study, the exposure buildup factors for two x-ray continuous energy spectra (bremsstrahlung) with 5 and 10 MeV endpoint energies were calculated up to depths of 10 mfp of water. It was observed that there is a large difference between the obtained exposure buildup factors due to the monoenergetic and continuous energy spectrum gamma sources. The calculation results show that the relative differences in 5 MeV energy for 1 mfp to 10 mfp are 114% to 44%, respectively, and also the relative differences in 10 MeV energy for 1 mfp to 10 mfp are 87% to 38%, respectively. Actually, the main purpose of this paper is to illustrate the fact that there is a significant difference between the exposure buildup factors due to the continuous and monoenergetic gamma sources. Therefore, radiation staff must pay more attention to calculating the thickness of radiation shields for continuous energy gamma sources.

Cytogenetic Reconstruction of Gamma-Ray Doses Delivered to Atomic Bomb Survivors: Dealing with Wide Distributions of Photon Energies and Contributions from Hematopoietic Stem/Progenitor Cells.

Retrospective estimation of the doses received by atomic bomb (A-bomb) survivors by cytogenetic methods has been hindered by two factors: One is that the photon energies released from the bomb were widely distributed, and since the aberration yield varies depending on the energy, the use of monoenergetic 60Co gamma radiation to construct a calibration curve may bias the estimate. The second problem is the increasing proportion of newly formed lymphocytes entering into the lymphocyte pool with increasing time intervals since the exposures. These new cells are derived from irradiated precursor/stem cells whose radiosensitivity may differ from that of blood lymphocytes. To overcome these problems, radiation doses to tooth enamel were estimated using the electron spin resonance (ESR; or EPR, electron paramagnetic resonance) method and compared with the cytogenetically estimated doses from the same survivors. The ESR method is only weakly dependent on the photon energy and independent of the years elapsed since an exposure. Both ESR and cytogenetic doses were estimated from 107 survivors. The latter estimates were made by assuming that although a part of the cells examined could be lymphoid stem or precursor cells at the time of exposure, all the cells had the same radiosensitivity as blood lymphocytes, and that the A-bomb gamma-ray spectrum was the same as that of the 60Co gamma rays. Subsequently, ESR and cytogenetic endpoints were used to estimate the kerma doses using individual DS02R1 information on shielding conditions. The results showed that the two sets of kerma doses were in close agreement, indicating that perhaps no correction is needed in estimating atomic bomb gamma-ray doses from the cytogenetically estimated 60Co gamma-ray equivalent doses. The present results will make it possible to directly compare cytogenetic doses with the physically estimated doses of the survivors, which would pave the way for testing whether or not there are any systematic trends or factors affecting physically estimated doses.

Experimental study of the rigidity and transparency to ionizing radiation of composite materials used in the enclosure under pressure of the Micromegas detector

Innovation in the field of nuclear imaging is necessarily followed by a radical change in the detection principle. The gas detector Micromegas (Mesh Micro Structure Gaseous) could be an interesting option, thanks to the stability and robustness of such a detector. Thus, it was necessary to study the implementation of the detector enclosure in composite materials. The focus of the present study was the robustness and gamma rays transparency of a set of composites. The studied composites were reinforced with vegetable fibers (alfa), and synthetic fibers. The mechanical properties of all composites specimen were evaluated by three-point bending test, whereas, gamma ray transparency was evaluated by the exposition of composites specimen to a mono-energetic gamma ray beam emitted by a Technetium 99-m source. Findings revealed that the biocomposite materials using alfa fiber and Polymethyl Methacrylate matrix are very promising as long as they present good robustness and high gamma ray transparency in diagnostic range.

Simulation Study on Computer Tomography Imaging of Nuclear Distribution by Quasi Monoenergetic Gamma Rays with Nuclear Resonance Fluorescence: Case Study for ELI-NP Application

Non-destructive inspection carried out by using nuclear resonances excited by an MeV energy region gamma ray is a promising method. The high penetrability of MeV gamma ray of nuclear resonant energy makes possible the detection of nuclides surrounded by massive materials. As an application of this method, computed tomography imaging of nuclear distribution inside objects can be reconstructed from transmission factor of gamma rays. We have studied the image reconstruction of the nuclear distribution using Monte-Carlo simulations to estimate the gamma-ray transmission factor assuming the ELI-NP facility where about 3 order higher intensity of quasi-monoenergetic gamma rays will be available.

Initial results from a multiple monoenergetic gamma radiography system for nuclear security

The detection of assembled nuclear devices and concealed special nuclear materials (SNM) such as plutonium or uranium in commercial cargo traffic is a major challenge in mitigating the threat of nuclear terrorism. Currently available radiographic and active interrogation systems use ∼1–10MeV bremsstrahlung photon beams. Although simple to build and operate, bremsstrahlung-based systems deliver high radiation doses to the cargo and to potential stowaways. To eliminate problematic issues of high dose, we are developing a novel technique known as multiple monoenergetic gamma radiography (MMGR). MMGR uses ion-induced nuclear reactions to produce two monoenergetic gammas for dual-energy radiography. This allows us to image the areal density and effective atomic number (Zeff) of scanned cargo. We present initial results from the proof-of-concept experiment, which was conducted at the MIT Bates Research and Engineering Center. The purpose of the experiment was to assess the capabilities of MMGR to measure areal density and Zeff of container cargo mockups. The experiment used a 3.0MeV radiofrequency quadrupole accelerator to create sources of 4.44MeV and 15.11MeV gammas from the 11B(d,nγ)12C reaction in a thick natural boron target; the gammas are detected by an array of NaI(Tl) detectors after transmission through cargo mockups . The measured fluxes of transmitted 4.44MeV and 15.11MeV gammas were used to assess the areal density and Zeff. Initial results show that MMGR is capable of discriminating the presence of high-Z materials concealed in up to 30cm of iron shielding from low- and mid-Z materials present in the cargo mockup.

Spectroscopic neutron radiography for a cargo scanning system

Detection of cross-border smuggling of illicit materials and contraband is a challenge that requires rapid, low-dose, and efficient radiographic technology. The work we describe here is derived from a technique which uses monoenergetic gamma rays from low energy nuclear reactions, such as 11B(d,nγ)12C, to perform radiographic analysis of shipping containers. Transmission ratios of multiple monoenergetic gamma lines resulting from several gamma producing nuclear reactions can be employed to detect materials of high atomic number (Z), the details of which will be described in a separate paper. Inherent in this particular nuclear reaction is the production of fast neutrons which could enable neutron radiography and further characterization of the effective-Z of the cargo, especially within the range of lower Z. Previous research efforts focused on the use of total neutron counts in combination with X-ray radiography to characterize the hydrogenous content of the cargo. We present a technique of performing transmitted neutron spectral analysis to reconstruct the effective Z and potentially the density of the cargo. This is made possible by the large differences in the energy dependence of neutron scattering cross-sections between hydrogenous materials and those of higher Z. These dependencies result in harder transmission spectra for hydrogenous cargoes than those of non-hydrogenous cargoes. Such observed differences can then be used to classify the cargo based on its hydrogenous content. The studies presented in this paper demonstrate that such techniques are feasible and can provide a contribution to cargo security, especially when used in concert with gamma radiography.

Experimental response function of a 3 in×3 in NaI(Tl) detector by inverse matrix method and effective atomic number of composite materials by gamma backscattering technique

Response function of a widely used 3in×3in NaI(Tl) detector is constructed to correct the observed pulse height distribution. A 10×10 inverse matrix is constructed using 7 mono-energetic gamma sources (57Co, 203Hg, 133Ba, 22Na, 137Cs, 54Mn and 65Zn) which are evenly spaced in energy scale to unscramble the observed pulse height distribution. Bin widths (E)1/2 of 0.01 (MeV)1/2 are used to construct the matrix. Backscattered photons for an angle of 110° are obtained from a well-collimated 0.2146GBq (5.8mCi) 137Cs gamma source for carbon, aluminium, iron, copper, granite and Portland cement. For each observed spectrum, single scattered spectrum is constructed analytically using detector parameters like FWHM, photo-peak efficiency and peak counts. Response corrected multiple scattered photons are extracted from the observed pulse height distribution by dividing the spectrum into a 10 ×1 matrix. Saturation thicknesses of carbon, aluminium, iron, copper, granite and Portland cement are found out. Variation of multiple scattered photons as a function of target thickness are simulated using MCNP code. A relationship between experimental and simulated saturation thicknesses of carbon, aluminium, iron and copper is obtained as a function of atomic number. Using this relation, effective atomic numbers of granite and Portland cement are obtained from interpolation method. Effective atomic numbers of granite and Portland cement are also obtained by theoretical equation using their elemental composition and comparing with the experimental and simulated results.

Gamma Attenuation Coefficient of Carbonate Rocks Sampled from the North Western Coast of Egypt

Gamma attenuation coefficients of host rocks belonging to Moghra Formation of Eocene era in one of two candidate sites located at the North Western Coast of Egypt in Al-Dabaa locality were estimated using Monte-Carlo Code for Nuclear Power (MCNP). Carbonates rock samples were taken to represents several depth intervals. A virtual mono-energetic gamma source with increasing energies was used. The gamma attenuation properties were found to be totally independent on the lithology of rock type, provided that roch sample density remains constant. Ultimately it is found that, gamma attenuation coefficient showed an inverse exponential dependence on the gamma energy regardless rock type and their related depth.

Coincidence summing corrections for a clover detector

The true coincidence summing effect on the full energy peak efficiency calibration of a clover HPGe detector for point sources has been determined as a function of sample-to-detector distance using mono-energetic and multi-energetic gamma ray sources. The coincidence summing effect has been observed to increase at closer distances with the correction factors as high as 1.25 at closest distance studied. The correction factors for the total and the photopeak efficiencies have been obtained using the analytical method. The clover detector response has been simulated using MCNP code, taking care of the bevels and the flat surfaces of the clover detector. The geometry of the clover detector has been optimized to match the experimental and the theoretical efficiencies. The true coincidence summing correction factors (kTCS) have also been experimentally obtained by taking the ratio of corresponding mono-energetic extrapolated efficiencies to multi-energetic efficiencies. The kTCS obtained from analytical method has been found to match with the experimental kTCS with the simulated values within 1–5%.

Attenuation of bremsstrahlung from 90Sr–90Y, 147Pm and 204Tl in thick target compounds

The external bremsstrahlung (EB) produced by beta particles such as from 90Sr–90Y, 147Pm and 204Tl in PbCl2, PbF2, Pb(NO3)2 and CdO were measured using NaI(Tl) crystal. The beta stopper technique is employed to measure the integral intensities above 100keV energy in different absorber thicknesses. Attenuation of the external bremsstrahlung, excited by 90Sr–90Y, 147Pm and 204Tl beta-emitters in the same compounds has also been studied. The measured attenuation parameter is not constant with absorber thickness and it increases with increasing Zmod of the absorber. Whereas, the mass attenuation coefficient of gamma rays of equivalent energy is independent of the absorber thickness. This confirms that the attenuation of EB in an absorber does not conform to a single exponential law, unlike the absorption of monoenergetic gamma rays. Rather it may be a combination of a large number of exponential terms.

A new method for detecting hemoglobin directly in whole blood using photon attenuation techniques

The objective of the proposed work is focused on measuring iron concentration directly in whole blood as tool for estimating hemoglobin and anemic conditions in patients across the world. The investigated method depends on theory of photon attenuation through transmission of low energy in whole blood sample. The mathematical expressions for cal- culating hemoglobin and iron deficit on blood using photon attenuation are derived. Calculations are carried out for estimating concentration of iron in blood samples taken from children, adults and old patients and therefore measuring their hemoglobin and iron deficit from normal values. Theoretical mass attenuation coefficient values were obtained using the XCOM program. A high-resolution gamma-ray spectrometry based on high purity germanium detector was employed to measure attenuation of strongly collimated monoenergetic gamma beam through blood samples.

Reconstruction of distribution functions of fast ions and runaway electrons in fusion plasmas using gamma-ray spectrometry with applications to ITER

Gamma-ray spectrometry on ITER can provide information both on confined fusion alpha particles for optimization of plasma heating and runaway electrons, which is important for safe reactor operations. For the purpose of deconvolution of gamma-ray spectra recorded in fusion plasma experiments the DeGaSum code has been developed. The code can be applied for processing of both spectra of monoenergetic gamma rays, which are born in nuclear reactions produced by alpha particles and other fast ions, and continuous bremsstrahlung spectra generated by runaway electrons in the MeV range in the plasma and reactor structure materials. Gamma-ray spectrometer response functions and bremsstrahlung spectra generated by electrons in the MeV energy range are calculated and used in the DeGaSum code. The deconvolution of the discrete spectra allows the identification of nuclear reactions, which give rise to gamma rays, and the calculation of their intensities. By applying the code for continuous hard x-ray spectra, the runaway electron energy distribution can be inferred. It can provide the maximal energy of runaway electrons with accuracy, which satisfies the ITER project requirements. The code has been used for processing of spectra recorded in JET experiments. An application of the deconvolution technique for gamma-ray emission measurements on ITER is discussed.

Investigation Of Photon Shielding Property Changes in Curing High Density Concrete

High density concrete is usually used for radiation shielding around radiotherapy treatment rooms. Because the concrete is specified differently at the design, construction, and verification stages, the relationship between the intended performance and the actual performance of the shielding material might not be entirely clear. In this study, cylindrical samples of high density shielding concrete were taken as each section of a new radiotherapy bunker was poured. The shielding performance of each sample [measured by beam attenuation and tenth-value layers (TVL)] was evaluated for 15 MV and 6 MV x-ray beams and for the 1.25 MeV monoenergetic gamma beam from a Co source. Transmission curves to 3 TVL were mapped for a representative sample. The samples were also imaged and analyzed using Co Cone Beam Computed Tomography (CoCBCT). Results indicate no significant change in the TVL of high density concrete samples as they cure. The minor fluctuations in shielding properties observed are explained by the heterogeneous structure of the samples as indicated in the CoCBCT images.

Effective theories of gamma-ray lines from dark matter annihilation

Abstract We explore theories of dark matter in which dark matter annihilations produce mono-energetic gamma rays (“lines”) in the context of effective field theory, which captures the physics for cases in which the particles mediating the interaction are somewhat heavier than the dark matter particle itself. Building on earlier work, we explore the generic signature resulting from SU (2) × U (1) gauge invariance that two (or more) lines are generically expected, and determine the expected relative intensities, including the possibility of interference between operators.

Photoneutron spectroscopy using monoenergetic gamma rays for bulk explosives detection

To date, the most successful nuclear methods to confirm the presence of bulk explosives have been radiative thermal neutron capture (thermal neutron activation) and prompt radiative emission following inelastic fast neutron scattering (fast neutron analysis). This paper proposes an alternative: photoneutron spectroscopy using monoenergetic gamma rays. If monoenergetic gamma rays whose energies exceed the threshold for neutron production are incident on a given isotope, the emitted neutrons have a spectrum consisting of one or more discrete energies and the spectrum can be used as a fingerprint to identify the isotope. A prototype compact gamma-ray generator is proposed as a suitable source and a commercially available 3He ionization chamber is proposed as a suitable spectrometer. Advantages of the method with respect to the previously mentioned ones may include simpler spectra and low inherent natural neutron background. Its drawbacks include a present lack of suitable commercially available photon sources, induced neutron backgrounds and low detection rates. This paper describes the method, including kinematics, sources, detectors and geometries. Simulations using a modified Geant4 Monte Carlo modelling code are described and results are presented to support feasibility. Further experiments are recommended.

Gamma absorption technique in elemental analysis of composite materials

Expressions for calculating the elemental concentrations of composite materials based on a gamma absorption technique are derived. These expressions provide quantitative information about elemental concentrations of materials. Calculations are carried out for estimating the concentrations of copper and gold in some alloys of bronze and gold. The method was also applied for estimating the concentrations of some heavy elements in a water matrix highlighting the differences with photon attenuation measurements. Theoretical mass attenuation coefficient values were obtained using the WinXCom program. A high-resolution gamma-ray spectrometry based on high purity germanium detector (HPGe) was employed to measure the attenuation of a strongly collimated monoenergetic gamma beam through samples.

Monoenergetic gamma rays from nonminimal Kaluza-Klein dark matter annihilations

We investigate monoenergetic gamma-ray signatures from annihilations of dark matter comprised of Z^1, the first Kaluza-Klein excitation of the Z boson, in a non-minimal Universal Extra Dimensions model. The self-interactions of the non-Abelian Z^1 gauge boson give rise to a large number of contributing Feynman diagrams that do not exist for annihilations of the Abelian gauge boson B^1, which is the standard Kaluza-Klein dark matter candidate. We find that the annihilation rate is indeed considerably larger for the Z^1 than for the B^1. Even though relic density calculations indicate that the mass of the Z^1 should be larger than the mass of the B^1, the predicted monoenergetic gamma fluxes are of the same order of magnitude. We compare our results to existing experimental limits, as well as to future sensitivities, for image air Cherenkov telescopes, and we find that the limits are reached already with a moderately large boost factor. The realistic prospects for detection depend on the experimental energy resolution.

Application of gamma-ray transmission method for study the properties of cultivated soil

The objective of the proposed work was to apply gamma-ray transmission method for studying the properties of cultivated soil. In this study, mass attenuation coefficients, bulk density, moisture content, porosity, and field capacity are determined. Five soil samples are collected from different agriculture zones in Egypt. A high-resolution gamma-ray spectrometry based on HPGe (high purity germanium) detector was employed to measure attenuation of strongly collimated monoenergetic gamma beam through soil samples. The radioactive sources used in the experiment were 241Am, 133Ba, 137Cs and 60Co. The mass attenuation coefficients of soil samples were calculated from the transmission measurements. WinXCom program was used to calculate mass attenuation coefficients of soil samples. There is a satisfactory agreement between experimental and theoretical values. It was observed that gamma-ray transmission method is an efficient tool for studying soil parameters for agriculture purposes.

Determination of density and volumetric water content of soil at multiple photon energies

Gamma ray transmission methods have been used accurately for the study of the properties of soil for agricultural purposes. In this study, density and volumetric water content of soil are determined by using gamma ray transmission method. To this end, the soil sample was collected from Erzurum, Turkey. The attenuation of strongly collimated monoenergetic gamma beam through the soil sample was measured using a 3×3×1mm3 cadmium telluride (CdTe) detector. The radioactive sources used in the experiment were 241Am, 133Ba and 137Cs. The mass attenuation coefficients of dry soil sample were calculated from the transmission measurements. It was observed that gamma ray transmission method in measurement of the soil parameters with the portable CdTe detector has advantages such as practical, inexpensive, non-destructive and fast analysis.