Evaluating optimal quality assurance and quality control conditions of activation measurements at the accelerator-based boron neutron capture therapy system employing a lithium target.

Evaluating neutron output is important to ensure proper dose delivery for patients in boron neutron capture therapy (BNCT). It requires efficient quality assurance (QA) and quality control (QC) while maintaining measurement accuracy. This study investigated the optimal measurement conditions for QA/QC of activation measurements using a high-purity germanium (HP-Ge) detector in an accelerator-based boron neutron capture therapy (AB-BNCT) system employing a lithium target. The QA/QC uncertainty of the activation measurement was evaluated based on counts, reproducibility, and standard radiation source uncertainties. Measurements in a polymethyl methacrylate (PMMA) cylindrical phantom using aluminum-manganese (Al-Mn) foils and aluminum-gold (Al-Au) foils and measurements in a water phantom using gold wire with and without cadmium cover were performed to determine the optimal measurement conditions. The QA/QC uncertainties of the activation measurements were 4.5% for Au and 4.6% for Mn. The optimum irradiation proton charge and measurement time were determined to be 36 C and 900 s for measurements in a PMMA cylindrical phantom, 7.0 C and 900 s for gold wire measurements in a water phantom, and 54 C and 900 s at 0-2.2 cm depth and 3,600 s at deeper depths for gold wire measurements with cadmium cover. Our results serve as a reference for determining measurement conditions when performing QA/QC of activation measurements using HP-Ge detectors at an AB-BNCT employing a lithium target.

Dead layer estimation of an HPGe detector using MCNP6 and Geant4.

In this study, Monte Carlo simulations were used to calculate the full-energy peak efficiency of a p-type coaxial high-purity germanium (HPGe) detector. The HPGe detector was modeled using MCNP6 and Geant4, and the thickness of the dead layer of germanium crystals was estimated for an accurate simulation. The dead layer was divided into front and side components, where a point source and a Marinelli beaker source were used to estimate each dead layer thickness. The model was validated by comparing the simulated as well as experimental results for the standard sources of cylindrical and Marinelli beakers. The Geant4 results and experimental results matched up to 4% in the 59.54-1836.05 keV energy range, while MCNP6 matched up to 6% when adjusted for coincidence summing effects. HPGe detector modeled in Monte Carlo simulations can be utilized for experimental validation and experimental setup prior to using actual HPGe detectors.

Measured low-energy x-ray spectra of interest in diagnostic radiology and mammography.

Objective.In cities situated at high-altitude, the measured x-ray spectra are required to calculate the absorbed dose to water in radiobiology and medical dosimetry because of the air-density effect. This work aims to measure, in a high-altitude city, a set of x-ray spectra from an x-ray tube with tungsten anode generated at potentials of the M-series x-ray beams from NIST in the range of 20 and 150 kV as well as other beam qualities that have been characterized and used for dosimetry study in our group called W-series. To also measure some spectra of mammography interest in the energy range of 25 and 35 kV using additional filtration of rhodium (Rh), molybdenum (Mo) and silver (Ag).Approach.A tungsten anode x-ray tube with potential between 10 to and 160 kV was used. A high-purity germanium (HPGe) detector associated with a DSPEC Jr 2.0TMdigital signal processing module has been used for the spectra measurements. Prior the spectra measurements, the HPGe detector has been characterized and calibrated using several radioactive sources. Mainresults.The M80 spectrum was compared to a mathematically filtered beam from Physicalisch Technische Bundesanstalt corresponding to the same potential finding a difference of 0.7% in the average energy. So, the mathematically filtered beam from PTB matches very well our M80 beam. The beams M80, M100 and M120 were also compared with calculations for the corresponding kilovoltage from an executable that calculates x-ray spectra from tungsten anode x-ray tubes in the energy range between 40 to 300 kV called SpekCalc. The SpekCalc reproduces qualitatively the experimental spectra, but not quantitatively, mainly for M100 and M120 beams.Significance.These spectra can be used to simulate the patient dose as well as image quality using Monte Carlo (MC) codes or to evaluate the absorbed dose in dosimetry studies.

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.

Catalog of x-ray spectra of Mo-, Rh-, and W-anode-based x-ray tubes from 10 to 50 kV.

This work presents a comprehensive catalog of x-ray spectra measured from x-ray tubes with tungsten, molybdenum, and rhodium anodes generated at tube potentials between 10 and 50 kV in steps of 1 kV. They can serve as an input for dose calculations, image quality calculations, investigations of detector features, and validations of computational spectral models, among other things. The measurements are performed by means of a high-purity germanium detector-based spectrometer 1 m from the x-ray sources without any added filtration. The x-ray tubes are characterized by thin beryllium exit windows (0.15-4 mm); thus, for energies above 15 keV, the spectra recorded can be considered approximately unfiltered. This allows potential users of the catalog to computationally add any filter to the spectra in order to create special radiation qualities of their choice. To validate this option, a small number of spectra are recorded with filter materials in place whose purity and thickness are known with high precision. These spectra are compared to the corresponding spectra from the catalog obtained by means of computationally added filters. The two types of spectra agree extremely well. Several typical mammographic radiation qualities are selected to compare the spectra obtained from the catalog presented here with corresponding spectra obtained from other catalogs published by Booneet al(1997Med. Phys.241863-74) and Hernandezet al(2017Med. Phys.442148-60). In contrast to the work presented here, those spectra rely partly or fully on calculations. A quantitative comparison is made by means of typical x-ray quality descriptors such as the mean energy and the first and second half-value layer. The results obtained from the Boone catalog match those of the current catalog sufficiently well for the Mo- and Rh-anode-based spectra. However, significant differences up to 10 times the estimated uncertainties are found for the quality descriptors evaluated from the spectra of Hernandezet aland the W-anode based spectra of Booneet al.

Characterization of 252Cf sources using high-resolution gamma spectroscopy.

Californium-252 is used as a neutron calibration source for passive neutron correlation counting. Source age and isotopic information are needed to make decay corrections to the neutron emission rate due to the influence of 250Cf. Gamma-ray signatures present in the spectrum from spontaneous fission products and odd-numbered Cf isotopes can be used with high accuracy to confirm or query declared values on a technical data sheet. This method is good practice for independently verifying the content of 252Cf calibration sources.

Validation of TOPAS MC for modelling the efficiency of an extended-range coaxial p-type HPGe detector.

TOPAS MC software was used to model the efficiency of a coaxial p-type HPGe detector, type GX9023 from Canberra. The model was validated by comparing experimental efficiencies with efficiencies calculated by TOPAS MC simulations. Three different geometries of radionuclide sources, placed at different heights from the detector endcap, were used to validate the model. The imposed criteria of 5% relative difference was met for a range of radionuclides and gamma-ray energies. As a result, the created detector model with TOPAS MC was considered validated.

Verification of physical parameters of insity p-type HPGe detector by scan method using collimated low energy photon beam and MNCP simulation.

In this work, the physical dimensions and the actual position of germanium crystal within a detector housing, the homogeneity of the crystal surface and outer dead layer thickness for a p-type HPGe detector were confirmed by the scan method using the collimated low energy photon beams combined with Monte Carlo simulation. The length and the diameter of the crystal were found to match with the values supplied by the manufacturer in discrepancy of about 3%. Only one mounting strap (Typical) for holding the crystal inside the mounting cup instead of two which is indicated in the detector drawing supplied by manufacturer was revealed by scanning along the lateral face of detector. Scanning on the front surface and around the lateral face of detector by the collimated 59.5 keV photon beam verified the outer dead layer thicknesses at the front surface and lateral face of the crystal averagely increases about 6.5% and 12% respectively. Adjusting the detector parameters for MCNP simulation by these verified values, the simulated peak efficiencies for different photon energies become being in accordance with the experimental peak efficiencies.

Determination of the internal pair production branching ratio of 90Y.

The National Institute of Standards and Technology (NIST) measured the internal pair production branching ratio of 90Y using two sources and four high purity germanium (HPGe) detectors to detect the resulting annihilation radiation. The internal pair production branching ratio determined from these measurements, (32.0 ±â€¯1.5) × 10-6 (k = 1), agrees within 1 standard uncertainty with the recommended value of (32.6 ±â€¯0.7) × 10-6 (k = 1) from the DDEP database.

Uranium, Thorium, Potassium, and Cesium Radionuclides Concentrations in Desert Truffles from the Governorate of Samawah in Southern Iraq.

Studies have been conducted in some southern Iraqi governorates to measure the radioactive contamination in the soil and have revealed that these areas are contaminated with radioactive materials. In these test sites, where many military operations have been conducted and that may have been affected by the Chernobyl accident, pollution and its impact on the truffle crop have been examined. Truffles are fungi that grow in the ground and can be contaminated by radiation from polluted soil. Uranium, thorium, potassium, and cesium activities were analyzed in truffles collected from the desert of Samawah governorate in the southern part of Iraq, and the results were compared with global values. The radionuclide activities were measured with a high-purity germanium detector. The average activities of 238U, 232Th, 40K, and 137Cs were 3.9500, 2.5300, 260.36, and 1.7800 Bq kg-1 dry biomass, respectively. These results indicate that radionuclide activities are low and that desert truffles are suitable for human consumption.

Monte Carlo simulation of background characteristics of a HPGe detector operating underground in the Gran Sasso National Laboratory.

Monte Carlo (MC) simulation of background components of an ultra-low background high purity germanium (HPGe) detector operating in a deep underground laboratory was carried out. The results show that the background of the HPGe detector is about two orders of magnitude higher than the MC prediction when accounting only for cosmic-ray induced background. The difference is due to natural radioactivity in the parts surrounding the Ge detector. To get reasonable agreement between MC simulations and the experiment, a contamination in the parts surrounding the Ge crystal from 40K, 208Tl and 214Bi of 0.1mBqkg-1 was required to include in the simulations.

Equivalence of computer codes for calculation of coincidence summing correction factors - Part II.

The aim of this study was to check for equivalence of computer codes that are capable of performing calculations of true coincidence summing (TCS) correction factors. All calculations were performed for a set of well-defined detector parameters, sample parameters and decay scheme data. The studied geometry was a point source of (133)Ba positioned directly on the detector window of a low-energy (n-type) detector. Good agreement was established between the TCS correction factors computed by the different codes.

Natural and anthropogenic radioactivity levels and the associated radiation hazard in the soil of Oodalia Tea Estate in the hilly region of Fatickchari in Chittagong, Bangladesh.

Radioactivity in the soil of a tea garden in the Fatickchari area in Chittagong, Bangladesh, was measured using a high-resolution HPGe detector. The soil samples were collected from depths of up to 20 cm beneath the soil surface. The activity concentrations of naturally occurring (238)U and (232)Th were observed to be in the range of 27 ± 7 to 53 ± 8 Bq kg(-1) and 36 ± 11 to 72 ± 11 Bq kg(-1), respectively. The activity concentration of (40)K ranged from 201 ± 78 to 672 ± 81 Bq kg(-1), and the highest activity of fallout (137)Cs observed was 10 ± 1 Bq kg(-1). The average activity concentration observed for (238)U was 39 ± 8 Bq kg(-1), for (232)Th was 57 ± 11 Bq kg(-1), for (40)K was 384 ± 79 Bq kg(-1) and for (137)Cs was 5 ± 0.5 Bq kg(-1). The radiological hazard parameters (representative level index, radium equivalent activity, outdoor and indoor dose rates, outdoor and indoor annual effective dose equivalents, and radiation hazard index) were calculated from the radioactivity in the soil.

Equivalence of computer codes for calculation of coincidence summing correction factors.

The aim of the study was to check for equivalence of computer codes that can perform calculations of true coincidence summing correction factors. All calculations were performed for a set of well-defined detector and sample parameters, without any reference to empirical data. For a p-type detector model the application of different codes resulted in satisfactory agreement in the calculated correction factors. For high-efficiency geometries in combination with an n-type detector and a radionuclide emitting abundant X-rays the results were scattered.

Analytical approach for radioactivity correlation of disc sources with HPGe detector efficiency.

The HPGe detector efficiency is measured as a function of source to detector separation using disc sources of (131)I with diameter ranging from 10 to 400mm. Detector efficiencies are characterized using single photon point-like standard sources at different distances; the calculated efficiencies for disc sources were analyzed by utilizing the double point detector model (DPDM) and the efficiency transfer method. The developed approach provided satisfactory results. The axial variation and radial dependence for disc sources efficiency determination in gamma-ray spectrometry were described with both gamma ray standard sources and measured samples as their extended sources.

Simulation and measurement of diagnostic X-ray radiation qualities / 中华放射医学与防护杂志

Objective To validate the feasibility of the simulationmethod and the reliability of thesimulationresult through comparison between simulation and measurement of the energy spectrum from medical diagnostic X-ray (RQR-Radiation qualities in radiation beans emerging from the X-ray source assembly).Methods A simplified model of the medical diagnostic X-ray RQR radiation quality was established using code of BEAMnrc.The energy spectrum of the same RQR radiation quality were measured through a plane high-purity germanium spectrometer,and compared with the simulationresult.Results The difference of spectral distribution between measurement and simulation was less than 3％,in spite of the convolution processing not happened to the pulse height distribution measured by the spectrometer.And the spectral distribution,fluence,energy fluence,means energy distribution of the radiation was obtained using the code of BEAMDP.Conclusions As indicated above,it is possible to use the simulation of the energy distribution as a foundation for the establishment of X-ray RQR radiation quality.