Low Energy Germanium Detector Research Articles

β - and γ -spectroscopy study of Pd119 and Ag119

Neutron-rich $^{119}\mathrm{Pd}$ nuclei were produced in fission of natural uranium, induced by 25-MeV protons. Fission fragments swiftly extracted with the Ion Guide Isotope Separation On-Line method were mass separated using a dipole magnet and a Penning trap, providing mono-isotopic samples of $^{119}\mathrm{Pd}$. Their ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay was measured with $\ensuremath{\gamma}\ensuremath{\gamma}$- and $\ensuremath{\beta}\ensuremath{\gamma}$-spectroscopy methods using low-energy germanium detectors and a thin plastic scintillator. Two distinct nuclear-level structures were observed in $^{119}\mathrm{Ag}$, based on the $1/{2}^{\ensuremath{-}}$ and $7/{2}^{+}$ isomers reported previously. The ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay work was complemented by a prompt-$\ensuremath{\gamma}$ study of levels in $^{119}\mathrm{Ag}$ populated in spontaneous fission of $^{252}\mathrm{Cf}$, performed using the Gammasphere array of germanium detectors. Contrary to previous suggestions, our data show that the $1/{2}^{\ensuremath{-}}$ isomer is located below the $7/{2}^{+}$ isomer and is proposed as a new ground state of $^{119}\mathrm{Ag}$ with the $7/{2}^{+}$ isomer excitation energy determined to be 33.4 keV. Our data indicate that there are two $\ensuremath{\beta}$ unstable isomers in $^{119}\mathrm{Pd}$, a proposed ground state of $^{119}\mathrm{Pd}$ with tentative spin $1/{2}^{+}$ or $3/{2}^{+}$ and a half-life of 0.88 s and the other one about 350 keV above, having spin ($11/{2}^{\ensuremath{-}}$) and a half-life of 0.85 s. The higher-energy isomer probably decays to the $1/{2}^{+}$ or $3/{2}^{+}$ ground state via a $\ensuremath{\gamma}$ cascade comprising 18.7-219.8-$\mathrm{X}$-keV transitions. The unobserved isomeric transition with energy $X\ensuremath{\approx}100$ keV probably has an $E3$ multipolarity. Its hindrance factor is significantly lower than for analogous $E3$ isomeric transitions in lighter Pd isotopes, suggesting an oblate deformation of levels in $^{119}\mathrm{Pd}$. Oblate configurations in $^{119}\mathrm{Ag}$ are discussed also.

Experiment-based determination of the excitation function for the production of Ti44 in proton-irradiated vanadium samples

In this paper, the excitation function utilizing the nuclear reaction $^{\mathrm{nat}}\mathrm{V}(p,X)$ $^{44}\mathrm{Ti}$ was determined. The seven investigated metallic vanadium disks were proton irradiated within an energy range of 111--954 MeV between 1995 to 1996. The experiments' cross sections were validated using two independent measurements by combining $\ensuremath{\gamma}$ spectrometry with both a low-energy germanium detector and a high-purity germanium detector. The maximum cross section was observed for energies of 145 $\ifmmode\pm\else\textpm\fi{}$ 1.2 and 150.2 $\ifmmode\pm\else\textpm\fi{}$ 1.2 MeV with values of 803 $\ifmmode\pm\else\textpm\fi{}$ 28 and 805 $\ifmmode\pm\else\textpm\fi{}$ 27 $\ensuremath{\mu}\mathrm{b}$, respectively. In this regard, it was demonstrated that our data were in good agreement with the former, however, unpublished results which were investigated over a similar energy range. Thus, combined with these earlier measurements, a consistent data set for the $^{\mathrm{nat}}\mathrm{V}(p,X)$ $^{44}\mathrm{Ti}$ excitation function from 111 to 1350 MeV is provided. Model calculations using Li\`ege Intranuclear Cascade (INCL)/ABLA reproduce the shape of the excitation function correctly but overpredict the absolute values by factors of 2 to 3. Some considerations regarding this already earlier observed systematic overestimation of neutron-poor residues are given. The results will trigger new approaches in code development in order to improve the predictions.

Low-energy X-ray attenuation characteristics of Rhizophora spp. composites

Photon absorption parameters such as mass attenuation coefficients ( $${\mu }_{\mathrm{m}}$$ ), molar extinction coefficients ( $$\varepsilon$$ ), total molecular ( $${\sigma }_{\mathrm{t},\mathrm{m}}$$ ), atomic ( $${\sigma }_{\mathrm{t},\mathrm{a}}$$ ) and electronic ( $${\sigma }_{\mathrm{t},\mathrm{el}}$$ ) cross sections, half-value layers $$({X}_{1/2})$$ , tenth-value layers ( $${X}_{1/10}$$ ), mean free paths $$(\lambda )$$ , effective atomic numbers ( $${Z}_{\mathrm{eff}}$$ ), and effective electron densities ( $${N}_{\mathrm{el}}$$ ) were estimated for defatted soy flour (DSF), soy protein concentrate (SPC), and soy protein isolate (SPI)-based Rhizophora spp. particleboard composites substituted with 10 wt% sodium hydroxide (NaOH) and 0, 5, 10, and 15 wt% itaconic acid polyamidoamine-epichlorohydrin (IA-PAE) adhesives. Elemental composition was assessed using ultrahigh-resolution field emission scanning electron microscopy-energy dispersive X-ray spectrometry (UHR-FESEM-EDX). The interaction parameters were evaluated for $${\mathrm{K}}_{\mathrm{\alpha }1}$$ photons at 16.59, 17.46, 21.21, and 25.26 keV, employing a low-energy germanium (LEGe) detector system and an 241Am $$\gamma$$ -ray source. X-ray diffraction characterization revealed an amorphous phase in the developed particleboard composites. Samples DSF15′, SPC15′, and SPI15′ exhibited the highest values of $${\mu }_{\mathrm{m}}$$ , $$\varepsilon$$ , $${\sigma }_{\mathrm{t},\mathrm{m}}$$ , $${Z}_{\mathrm{eff}}$$ , and $${N}_{\mathrm{el}}$$ among all of the studied particleboard samples, within the range of measured photon energies. In addition, all of the modified samples exhibited lower $${X}_{1/2}$$ , $${X}_{1/10}$$ , $$\lambda$$ , $${\sigma }_{\mathrm{t},\mathrm{a}}$$ , and $${\sigma }_{\mathrm{t},\mathrm{el}}$$ than the unmodified samples, with DSF-, SPC-, and SPI/NaOH/Rhizophora spp./IA-PAE (15 wt%), indicating insignificant changes. The current results of the particleboard samples’ analysis can be useful for medical radiation applications and shielding research.

A research on the gamma ray attenuation characteristics for real bone and manganese substituted artificial bone dust

This research focalized on the gamma ray attenuation charesteristics of real bone and manganese substituted Nano hydroxyapatite artificial bone dusts. The current samples were excited with using 59.5 keV photons emitted from an 241Am annular radioisotope source with 50 mCi activity by using a narrow beam transmission geometry and detected with using Ultra Low Energy Germanium detector with a resolution 150 eV at 5,95 keV experimentally. The gamma-ray attenuation parameters such as linear attenuation coefficient, half value layer, tenth value layer and mean free path are also calculated experimentally and theoretically. The present results points out that the attenuation values of the manganese substituted hydroxyapatite artificial bone dust is very close to the value of the real bone.

A Comprehensive Research on Gamma-Ray Attenuation Characteristics of the Metal-Doped Hap and Natural Animal Bone

This investigation focuses on the gamma ray attenuation parameters of natural animal bone, iron, cobalt, copper and zinc doped Nano hydroxyapatite artificial bone powders and pure hydroxyapatite. The present specimens were excited by means of gamma ray photons with 59.5 keV energy radiated from a 241-Amercium annular radioactive source with 50 mCi activity by means of narrow beam transmission geometry. The transmitted gamma-rays were counted with using Ultra Low Energy Germanium (Ultra-LEGe) detector with a resolution 150 eV at 5.95 keV . The gamma-ray attenuation characteristics such as mass attenuation coefficient (MAC) ( µ/ρ ), linear attenuation coefficient (LAC) ( µ) , half value layer (HVL), tenth value layer (TVL) and mean free path (MFP), which has a significant role in the attenuation studies, are also calculated. The values obtained were checked with the predicted values from the XCOM NIST. The results show that the attenuation data of the metal-doped hydroxyapatite synthetic bone dust is very close to the value of the natural animal bone.

Optimization of HPGe detector response using fast and reliable method

Safeguards system with high effectiveness and efficiency must comprise a set of measurements with capabilities satisfactory for the verification of nuclear materials. In this paper, we present key parameter measurements of detector modeling in a commercial n-type low energy germanium detector of a planar crystal with a relative efficiency of nearly 15 %. The detector optimization will hold a significant function in measuring nuclear materials for safeguards application. Standard nuclear materials with diverse enrichment (depleted and low enriched) of uranium and point-like sources (137Cs, 60Co) and mixed radioactive source for Eu isotopes (152Eu, 154Eu, and 155Eu) were benefited to explore the energy resolution and detector efficiency. The energy resolution is measured over a wide range of rise time and flattop. In addition to the experimental work, the Monte Carlo simulation code is used for modeling the setup configuration to obtain the absolute efficiency at different energies. A fast and reliable method was applied in detector efficiency measurements. The data are discussed and interpreted.

Energy calibration and performance testing of LEGe detector

The low energy germanium detector (LEGe) is in all aspects optimised for performance at low and moderate energies. It has specific advantages over conventional planar or coaxial detectors. LEGe is a kind of semiconductor detector commonly used in X-ray detection. It can display the spectrum of X-ray and record photon counts. Photon fluence is used to describe the radiation field by recording the number of incident photons. In order to take full advantage of the low energy response of this intrinsically thin window detector, LEGe cryostats are usually equipped with a beryllium window, thin front and side contact allowing spectroscopy from 3 keV and above. The rear contact is of less than full area which gives a lower detector capacitance compared to a planar device of similar size. It is widely used in low energy gamma spectroscopy, X-ray absorption spectroscopy, nuclear safeguards or X-ray fluorescence spectrometer and X-ray diffraction. Spectrum is an intuitional and accurate description of X-ray radiation. In this work, experiment was carried out to calibrate the detector and test the spectrum, and then to calculate the energy resolution. The experiment results about energy resolution (full width at half maximum) are 222 eV (@5.9 keV) and 519 eV (@122 keV).

X-ray fluorescent (XRF) configuration for the measurement of mass attenuation coefficients at low energy photons

An X-ray fluorescent (XRF) configuration was used to measure the mass attenuation coefficient of materials at low energy photons. An Americium-241 (241Am) annular source was used in conjunction with niobium, palladium, molybdenum and tin plates that provided Kα1 photons with energies between 16.59 and 25.26 keV. The transmitted photons were measured by using a low energy Germanium (LEGe) detector and analyzed by using MAESTRO software. A calibration with 241Am showed good linearity between photon energies and peak channels with R2 value near to 1. The measurement of mass attenuation coefficient was carried out on Al plates and Perspex based on the transmitted photons on the samples. The measured mass attenuation coefficients were compared to the XCOM calculations. The results showed that the measured mass attenuation coefficients of aluminum and Perspex® were in good agreement to their XCOM values within 10% percentage of discrepancies at all experimented photon energies. The overall results indicated the suitability of the XRF configuration for the measurement of mass attenuation coefficients at low energy photons.

Assessment of the mass attenuation parameters with using gamma-rays for manganese substituted nano hydroxyapatite

Manganese substituted hydroxyapatite nanoparticles (nMnHAp) were produced using the ultrasonic wet chemical method. The elemental analysis was performed using Scanning Electron Microscopy (SEM) with integrated Energy Dispersive X-ray Spectrometry (EDX). The mass attenuation coefficients of manganese substituted hydroxyapatite nanoparticles have been measured at 59.5 keV gamma energy emitted from 241Am radioisotope annular source with 50 mCi activity by using Ultra Low Energy Germanium Detector. These values are found to be in good agreement with theoretical values based on calculated XCOM data. Electron densities and effective atomic numbers were calculated by using the mass attenuation coefficients. Also, the mass attenuation coefficient of the real bone was determined as experimentally. The obtained results may provide information on how much radiation is transmitted through the sample when they are exposed to gamma-rays at 59.5 keV by comparing real bone.

Analysis of the vertical distribution and size fractionation of natural and artificial radionuclides in soils in the vicinity of hot springs

ABSTRACTLead-210 is a naturally occurring radionuclide of great importance for environmental studies. Its vertical distribution in soil combined with that of Radium–226 may provide useful information on radon exhalation from the ground, or radon carried by ground water. Previous research has shown that natural radioactivity levels–in particular Lead–210 and Radium–226 activity in the ground–may be higher near hot springs. In this work two different locations near hot springs were selected for soil sampling: Kamena Vourla and Thermopylae, both in Greece. Depending on the special soil characteristics of each sampling location, it was decided to collect soil cores up to a depth of 20 cm from Kamena Vourla, and surface soil from Thermopylae. The soil cores were then sectioned into 1 cm slices, while the surface soil samples were separated into seven particle size fractions by dry sieving. All samples were analysed by high resolution gamma-ray spectrometry at the Nuclear Engineering Department of the National Technical University of Athens, using an XtRa germanium detector and a Low Energy germanium detector, to determine: (a) the terrestrial natural radionuclides Thorium–234, Radium–226, Lead–210, Radium–228, Thorium–228 and Potassium–40, (b) the cosmogenic radionuclide Beryllium–7, and (c) the artificial radionuclides Cesium–137 and Ruthenium–106. It is worth mentioning that, the Ruthenium–106 that was detected in samples collected from both sampling locations is the result of an accidental release over Europe, apparently originated in Russia, a few days before the sampling took place. The vertical profile of the radionuclides obtained from the core sample analysis indicated a disturbance in the first 7 cm of soil, while at greater depth the concentrations for all radionuclides were as expected. Lead-210 activity was higher than that of Radium–226, showing a disruption in the radioactive equilibrium, as expected. The analysis of the size-fractionated samples showed a higher activity concentration of Lead–210 and Cesium–137 in the finer fractions. The radioactive equilibrium between Thorium–234, Radium–226, and Lead–210 was found to be significantly disturbed in all size fractions.

Measurements of elastic scattering cross sections for 25.2, 28.5, 37.4, 36.8, and 42.2 keV X‐ray photons in elements with 22 ≤ Z ≤ 83

The differential elastic scattering cross sections were measured for 25.2 (Sn‐Kα), 28.5 (Sn‐Kβ1,3), 37.4 (Nd‐Kα1), 36.8 (Nd‐Kα2), and 42.2 (Nd‐Kα1,3) keV X‐ray photons at 139° scattering angle in elements with 22 ≤ Z ≤ 83. The measurement was done in reflection mode experimental setup involving 50Sn/60Nd secondary targets excited with 241Am radioisotope. The scattered X‐ray photons were detected using a high‐resolution low energy germanium detector (horizontal configuration, FWHM = 300 eV at 59.5 keV) coupled with computerized multichannel analyzer. The intensity of X‐ray photons along with geometrical factors were calculated from the theoretical knowledge of K X‐ray fluorescence cross sections and measured K X‐ray yields from excited targets. The measured values of differential cross sections were compared with the theoretical available values based on form factor and second‐order S‐matrix (SM) approaches. The experimental values of cross sections exhibit a large deviation from modified form (MF) values for the elements with BK/Ein ≈1, where BK is the K‐shell binding energy of electrons and Ein is the energy of incident photon. These deviations in experiment results were smooth out by the inclusion of anomalous scattering factors (ASFs) to the MF values. The measured elastic cross sections were found to be ~7% lower than MFASF values and agree with SM values for all elements under investigation.

Effect of the LEGe detector collimators on K-series peaks and Compton scattering in XRF analysis using gamma rays

The effect of a low-energy germanium detector collimator with different diameters on the measurement of the X-ray fluorescence of palladium (Pd) was studied experimentally. Changes in the Pd K-series and Compton scattering peaks were measured and analysed with and without a detector collimator, where for the former, collimators with different diameters were used. The signal-to-noise ratio increased when a shielding collimator was used with a narrow detector collimator. The Compton dispersion and fraction dead time were reduced considerably using a detector collimator by increasing the distance from the source to the detector, and the collimator length-to-diameter ratio. The full width at half maximum (FWHM) of the Pd Kα1 and Pd Kβ1 peaks decreased almost linearly with the collimator length-to-diameter ratio. The FWHM illustrated that the spectral resolution was improved when a collimator with a smaller diameter but unchanged length was used. The uncertainties at the Pd Kα1, Pd Kβ1, and Compton dispersion peaks were approximately correlated linearly with the collimator length-to-diameter ratio.

METHODOLOGY AT CIEMAT WHOLE BODY COUNTER FOR IN VIVO MONITORING OF RADIOIODINE IN THE THYROID OF EXPOSED POPULATION IN CASE OF NUCLEAR EMERGENCY.

Iodine-131 is one of the main concerns from the point of view of radiological protection in a short term after a nuclear accident. The WBC Laboratory of CIEMAT has developed a methodology for in vivo monitoring of radioiodine in the thyroid of exposed individuals in case of emergency. Thyroid-neck phantoms of different sizes are required for calibrating the detection systems in appropriate counting geometries for the measurement of exposed population. A Low-Energy Germanium (LEGe) detector and a Fastscan Counter were calibrated using a set of thyroid phantoms fabricated by CIEMAT. Each neck phantom consists of a Lucite cylinder with a vial source of 131I. Counting efficiencies depending on age and thyroid sizes were obtained to be used to determine the activity of 131I in internally contaminated people. DL of 131I varies with the age, being in the range of 5-8 Bq for the LEGe detector and 26-42 Bq for the Fastscan. Detection of intakes resulting in Committed Effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming a scenario of acute inhalation or ingestion of 131I by members of the public.

Measurement of large angle Rayleigh scattering cross sections for 39.5, 40.1 and 45.4 keV photons in elements with 26 ≤ Z ≤ 83

The present work reports Rayleigh scattering cross section measurements for the 39.5keV (Sm- Kα2), 40.1keV (Sm-Kα1) and 45.4keV (Sm-Kβ1,3) X-ray photons in 35 elements with 26 ≤ Z ≤ 83 at backward angle of 139°. The scattering measurements were performed in reflection mode geometrical set up involving a secondary photon source consisting of Samarium (62Sm) target excited by the 59.54keV γ-rays from the 241Am radioactive source. The scattered photons were detected using a low energy germanium (LEGe) detector. The product of detector efficiency, intensity of incident photons and other geometrical factors were determined by measuring the K X-ray yields from targets with 47 ≤ Z ≤ 59 and knowledge of the respective K X-ray fluorescence cross sections. The measured cross sections are compared with the theoretical cross sections based on the modified form factor (MF) formalisms and the second-order S-matrix approach. The experimental results demonstrate large deviations from the MF values for the elements with K shell binding energy (BK) in vicinity of the incident photon energy (Ein), which smooth out with inclusion of the anomalous scattering factors (ASFs). The S-matrix values, in general, agree with the measured cross sections for all the elements under investigation.

Comparison of low-energy and coaxial HPGe detectors for prompt gamma activation analysis of metallic samples

In the prompt-gamma activation analysis, the spectra of multi-element metallic samples contain low-energy regions with complicated multiplets that are difficult to evaluate by fitting. This has an impact on the accuracy and precision of the final results. To overcome this, parallel measurements with Compton-suppressed coaxial HPGe and high-resolution, low-energy germanium detectors, with and without Compton-suppression, were completed in order to assess the performances of the setups under controlled conditions. The selectivities, the signal-to-background ratios and other characteristic features of the setups are compared, and the results are discussed.

NUMERICAL ASSESSMENT OF 131I DEPOSITED IN THYROID FOR NON-STANDARD SITUATIONS.

At the CIEMAT whole-body counter, a low-energy germanium detector is used for the in vivo assessment of (131)I activity in thyroid, mainly for the individual monitoring programmes of workers. The detector is calibrated with a cylindrical neck phantom made of polymethyl methacrylate that mimics the neck of an adult, containing a vial with a radioactive solution. For an accurate activity assessment, it is necessary to perform the calibration of the detector with phantoms that closely reproduce the anatomy of a real person. Nevertheless, it is not affordable to count on a variety of physical phantoms covering the different anatomical characteristics that could be found over the whole population, including children. An alternative approach to face this situation is offered by the numerical calibration procedure based on Monte Carlo calculations in conjunction with realistic voxel phantoms. A series of computational voxel phantoms of different ages and dimensions have been used in this work to simulate an internal contamination of the thyroid and to estimate the response of the detector for measurements involving individuals whose anatomical characteristics differ from the reference adult man.

LEGe detector intrinsic efficiency calibration for parallel incident photons

A low energy germanium (LEGe) detector was calibrated by Monte Carlo simulation and experiment with radionuclides. At first, Monte Carlo simulations were carried out for calibrating the detector for parallel incident photons in the 1.5–180keV energy range. Then, a set of radionuclides emitting low-energy X- or γ-rays was used to calibrate the detector for quasi-parallel incident photons, which provided experimental values to compare with the simulated ones. The results show good agreement with a largest relative discrepancy of −1.8%.

EFFICIENCY STUDY OF A LEGe DETECTOR SYSTEM FOR THE ASSESSMENT OF 241Am IN SKULL AT CIEMAT WHOLE BODY COUNTER.

(241)Am incorporation due to an incident or chronic exposure causes an internal dose, which can be evaluated from the total activity of this isotope in the skeleton several months after the intake. For this purpose, it is necessary to perform in vivo measurements of this bone-seeker radionuclide in appropriate counting bone geometries with very low attenuation of surrounded tissue and to extrapolate to total activity in the skeleton (ICRP 89, Basic anatomical and physiological data for use in radiological protection: reference values. 2001. 265). The work here presented refers to direct measurements of americium in the Cohen skull phantom at the CIEMAT Whole Body Counter (WBC) using low-energy germanium (LEGe) detectors inside a shielding room. The main goal was to determinate the most adequate head counting geometry for the in vivo detection of americium in the bone. The calibration of the in vivo LEGe system was performed with four detectors with 2 cm of distance to Cohen phantom. Two geometries were measured, on junction of frontal to parietal bones and frontal bone. The efficiencies are very similar in both geometries, the preferred counting geometry is the most comfortable for the person, with the LEGe detectors in the highest part of the frontal bone, near the junction with the parietal bone, CIEMAT WBC participated in a skull intercomparison exercise organised by WG7 of EURADOS (European Radiation Dosimetry Group e.V.). Efficiencies using three different skull phantoms were obtained. Measurements were performed for different head counting positions, four of them in the plane of symmetry and others over the temporal bone. The detector was placed in parallel with the calibration phantom at a distance of 1 cm. The main gamma emission of (241)Am, 59.5 keV (36 %), was used for comparing efficiency values. The lower efficiency was obtained over the frontal and occipital bones. Measurement with one LEGe detector over the parietal bone is the most efficient. The activity of each skull phantom was calculated using CIEMAT head calibration. Results of the EURADOS intercomparison are presented here for discussion.

TU-AB-201-09: Calibration of An Element of a New Directional Pd-103 Planar Source Array

Purpose: The CivaSheet™ is a new directional Pd-103 planar source array, with a variable number of discrete source elements referred to as “dots”. Each dot consists of a polymer capsule containing 1⁰3Pd and a gold shield that attenuates radiation on one side of the device to define hot and cold dose regions. Fluorescence from the gold shield is observed in the dot spectrum. Since CivaSheet™ is a planar directional source, conventional methods used for calibration of azimuthally symmetric sources are not applicable. The purpose of this work is to establish an air-kerma-strength standard and a transfer to a well chamber for clinical calibration. Methods: Primary air-kerma strength measurement of the dots was performed using a variable-aperture free-air chamber (VAFAC). Charge measurements were recorded using a well chamber with a custom insert. Anisotropy measurements were performed using a Sodium-Iodide detector. Spectral measurements were performed using a low-energy germanium detector and compared to a source without gold. The dot geometry was modeled using the MCNP6 radiation transport code. Results: Air-kerma strength measurements of a batch of four dots performed with the VAFAC were within ±1.5% of the average measured value and the measurement precision was within ±0.5%. Anisotropy measurements indicated uniform emission within the measurement uncertainty for the solid angle defining the VAFAC aperture used. Charge measurements of each dot using the well chamber in four cardinal angle source orientations were within ±1.5% of the average measured values. The spectral study of a dot resulted in identification of fluorescence from the gold shield and primary spectral energies that were compared to MCNP6 simulations. Conclusion: Calibration procedures for the new directional Pd-103 source dot were established for future clinical use, based on the results of experimental and Monte Carlo investigations. This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.

Test spectra experimental construction for evaluating gamma-spectrometry computer codes for the 235U determination

The determination of 235U in environmental samples from its 185.72 keV photons may require the deconvolution of the multiplet photopeak at ~186 keV, due to the co-existence of the 186.25 keV photons of 226Ra in the spectrum. Successful deconvolution depends on many parameters, such as the detector characteristics, the activity concentration of the 235U and 226Ra in the sample, the background continuum in the 186 keV energy region and the gamma-spectrometry computer code used. In this work two sets of experimental test spectra were constructed for examining the deconvolution of the multiplet photopeak performed by different codes. For the construction of the test spectra, a high-resolution low energy germanium detector was used. The first series consists of 140 spectra and simulates environmental samples containing various activity concentration levels of 235U and 226Ra. The second series consists of 280 spectra and has been derived by adding 137Cs, corresponding to various activity concentration levels, to specific first series test spectra. As the 137Cs backscatter edge is detected in the energy region of the multiplet photopeak at ~186 keV, this second series of test spectra tests the analysis of the multiplet photopeak in high background continuum conditions. The analysis of the test spectra is performed by two different g-spectrometry analysis codes: (a) spectrum unix analysis code, a computer code developed in-house and (b) analysis of germanium detector spectra, a program freely available from the IAEA. The results obtained by the two programs are compared in terms of photopeak detection and photopeak area determination.