Efficiency HPGe Detector Research Articles

Recent developments in radiometric and mass spectrometry methods for marine radioactivity measurements

The most important recent developments in radiometric techniques have been the operation of high efficiency HPGe detectors with anticosmic or antiCompton shielding often placed underground, ship-board measurements of 234 Th using gamma-spectrometry or beta-counting and underwater gamma-spectrometry. In mass spectrometry techniques, the availability of high resolution ICP-MS and applications of AMS for the analysis of long-lived radionuclides have opened doors for investigations which previously required too large samples, or were not possible because of lack of sensitivity. These developments are illustrated by several examples of marine radioactivity studies, which include contaminated sites (e.g., Fangataufa Atoll) and open ocean studies (e.g., the Atlantic Ocean) as well as analyses of IAEA reference materials. A comparison of Pu results obtained by alpha-spectrometry, ICP-MS and AMS has shown that a reasonably good agreement has been obtained between all three methods.

Application of a low-background gamma-ray spectrometer to the determination of [formula omitted

A method for quantitative determination of 90Sr with a germanium γ-ray spectrometer is presented. The bremsstrahlung energy spectrum produced by high-energy beta particles from the 90Sr source encapsulated in a given absorbing material is measured. The idea was tested on various types of low-background germanium γ-ray spectrometers. The optimisation of absorber thickness for aluminium, iron, copper, cadmium, tantalum and lead is presented. The lowest achieved detection limit for a 10% efficiency HPGe detector was 0.38 Bq/sample which allows this method to be applied to some environmental studies.

Software for the Computation of Detection Efficiency and of Coincidence Summing Effects Including Neutron Self-Shielding

The GESPECOR software, initially developed for the computation of efficiency of HPGe detectors in environmental γ-ray spectrometry, was applied to NAA. The software is useful for the computation of efficiency and of self-attenuation and coincidence-summing corrections for common experimental conditions. A new source subroutine was implemented in GESPECOR for solving the more complex case of non-uniform sources. In this way neutron self-shielding in the activation of samples of large volume is taken into account. The dependence of the detection efficiency on the flux distribution is discussed.

A Rapid Method for the Determination of 137Cs in Seawater

A method is developed to measure 137CS in seawater. It entails the use of silica gel impregnated with hexacyanoferrates as an ion-exchanger to concentrate 137CS from large volumes of seawater, followed by gamma-ray spectrometry with a high efficiency HPGe detector. Both laboratory experiments and field operation resulted in satisfactory recovery of 137Cs. Compared with the traditional pre-concentration method using AMP as the scavenger, this method is more rapid, more cost-effective, and can be more easily performed aboard ships.

Correction equations of coincidence summing using75Se radionuclide in the efficiency of HpGe detector

Correction equations of the coincidence-summing effect for efficiencies of HpGe detector based on the decay scheme were developed by considering the summing up to triple coincidence. The correction equations which do not dependent on the kind of the Ge detector are very useful for efficiency calibrations of a Ge detector in the energy region from 60 to 400 keV by using75Se radionuclide even with very short source-to-detector distances.

Mixing activity-calibrated and uncalibrated gamma-ray sources in efficiency calibration

A method to calibrate the absolute efficiency of HPGe detectors in a large energy range using both activity-calibrated and uncalibrated multienergy gamma-ray radioactive sources is presented. The adopted efficiency calibration function ε( E) has the simple form ln ε(E)=a 0+a 1 ln(E/E B )+a 2 ln 2(E/E B ) . Different parameters a 0 are simultaneously fitted to the activity-calibrated and uncalibrated sources experimental efficiency data by the least-squares method. As an application example, the calibration of a HPGe detector in the 500 to 3500 keV energy range using a 207 Bi activity calibrated source and one uncalibrated 56 Co source is described.

Multielement analysis of human hair and kidney stones by instrumental neutron activation analysis with the k0-standardization method

This paper focuses on the evaluation of the k 0 method of instrumental neutron activation analysis in biological materials. The method has been applied in multielement analysis of human hair standard reference materials from IAEA, No. 085, No. 086 and from NIES (National Institute for Environmental Sciences) No. 5. Hair samples from people resident in different parts of Malaysia, in addition to a sample from Japan, were analyzed. In addition, human kidney stones from members of the Malaysian population have been analyzed for minor and trace elements. More than 25 elements have been determined. The samples were irradiated in the rotary rack (Lazy Susan) at the TRIGA Mark II reactor of the Malaysian Institute for Nuclear Technology and Research (MINT). The accuracy of the method was ascertained by analysis of other reference materials, including 1573 tomato leaves and 1572 citrus leaves. In this method the deviation of the 1/ E 1+ α epithermal neutron flux distribution from the 1/ E law ( P/ T ratio) for true coincidence effects of the γ-ray cascade and the HPGe detector efficiency were determined and corrected for.

232Th– 228Ra– 228Th disequilibrium in East China Sea sediments

Five sediment cores collected from the East China Sea have been analyzed for 228Ra and 228Th (via 228Ac and 208Tl, respectively) by γ-ray spectrometry with a 150% efficiency HPGe detector. In four cores, the 228Th/ 228Ra activity ratio decreases from >1 at the core top to a subsurface minimum around a depth of 5 cm and then increases towards unity at deeper layers. Such disequilibrium relationships between 228Th and 228Ra downcore manifest the decay with depth of 228Th scavenged from the water column and the ingrowth of 228Th towards equilibrium with 228Ra after burial. Profiles of 228Ra are characterized by an upward decrease to minimum values at core tops, indicating diffusion of 228Ra to seawater. From deficiencies of 228Ra relative to 232Th in the studied sediment cores, fluxes of 228Ra are estimated to be 1.2–3.1 dpm cm -2 (year) -1 at the steady state. Assuming the study area is representative of the East China Sea Shelf, it is estimated from the measured sedimentary 228Ra fluxes and water column 228Ra data that the residence time of the East China Sea shelf water with respect to the exchange with the open ocean water via Kuroshio is about 1–3 years.

Primary gamma-rays from 53 keV neutron capture reaction in23Na

The nucleus23Na has been investigated by studying the primary γ-rays emitted from 53 keV neutron capture in it using a high resolution and high efficiency (100%) HPGe detector and NaI(T1) detector for anti-Compton. 24 primary γ-rays were placed in the24Na, in which 3 primary γ-rays were new ones from a (n, γ) reaction, and reported for the first time. In order to obtain an exact energy calibration within 7 MeV,56Fe(n,γ)57Fe reaction was used at thermal neutron energy. Intensity calibration was obtained from the27Al(p,γ)28Si reaction atEp=2046 keV. The neutron binding energy of24Na was determined to be 6959.75 keV.

Gamma-spectrum of241Am

The γ-ray spectrum of241Am was reinvestigated by using intense sources. A purified solution source was used to make sure that the γ-lines presents in the spectrum come from the α-decay of241Am. The γ-spectrometer consists of 40% relative efficiency HPGe detector and 8192-channel ADC. Out of 137 γ-lines that are presents in the spectrum 46 are new.

Monte-Carlo calculation of the spatial dependence of the coaxial HPGe detector efficiency for point sources

It is shown that fine geometric modelling of the HPGe detector structure using the GEANT system leads to a good match between the calculated and measured spatial dependence of efficiency for point sources in the region of photon energies from 60 keV to 1115 keV.

The use of sources emitting coincident gamma-rays for the determination of photopeak and total efficiencies in non-point-source counting geometries

The validity of a previously published method for determination of full-energy peak as well as total efficiency curves and source activity from a 82Br spectrum is experimentally tested for the case of a thin slab counted on the end cap of a 20% relative efficiency HpGe detector, as well as for a Marinelli beaker geometry. It is concluded that, even though a full-energy and total efficiency curve can be found that reproduce the measured 82Br spectrum, the corresponding source activity is an underestimation of the true value, apparently depending on the degree of variation of the efficiencies over the source volume. The applicability of the curves found to other radionuclides is as yet unclear.

HPGe detector efficiency calibration for extended cylinder and marinelli-beaker sources using the ESOLAN program

A personal computer based program ESOLAN has been developed for HPGe detector absolute-peak-efficiency calibration for various source-detector arrangements. The applicability of the previously developed program is limited to sources with diameter smaller than that of the detector active crystal. In this work, the ESOLAN program is modified to extend its application to sources with dimensions larger than the detector crystal, including extended cylinder and Marinelli-beaker sources.

Environmental measurements at the Savannah River Site with underwater gamma detectors

Underwater NaI(T1) and HPGe detectors are used in the environmental measurements programs at the Savannah River Site (SRS). A 22.9 cm × 10.2 cm NaI(T1) detector on the Savannah River continuously monitors effluent releases from both SRS (DOE) and Plant Vogtle (Georgia Power). Correlations with known releases indicate a sensitivity of 4 mBq/l for58Co with 1500 min spectra; such levels are well below those of hazardous or legal concern. A 30%-efficient HPGe detector has appraised radionuclides in SRS cooling pond sediments; the dominant gamma-emitting radionuclide detected was137Cs, at levels ranging up to 2.0 MBq/m2. The pond activities were adequately quantified by 1 min counts with the HPGe detector; resulting contour maps of sediment137Cs provided guidance for partially draining the ponds for dam repairs.

Analysis of HPGe-detector relative photopeak efficiency

The dependence of the HPGe-detector efficiency on its intrinsic and geometrical properties such as energy resolution, electronic noise, charge production statistics and effect of the rise time is considered. This study also includes the detector's sensitive volume. Efficiencies of a 0.55 cm3 planar and 46.3, 56.4 and 62.3 cm3 active volume of coaxial HPGe-detectors have been estimated for γ-ray energies from 50 to 1000 keV only, for a point source. Agreement has been found between the present calculated and published experimental efficiencies.

HPGe detector efficiency calibration for extended sources in the 50–1400 keV energy range

A non-linear function is proposed to fit the experimental efficiency data for HPGe detector in the 50–1400 keV energy range for extended sources: 100 mL flask and 850 mL Marinelli beaker. The experimental data were corrected for coincidence summing effect. Covariances were taken into account. Simulation showed that the fitted data are Gaussian like distributed and the fit presents no appreciable bias.

Empirical relation between efficiency and volume of HPGe detectors by Monte Carlo calculation

The empirical relation between the detection efficiency and volume of Ge(Li) detectors obtained by Vaño et al. has been proved to be valid here by Monte Carlo simulation for HPGe detectors of active volume up to 175 cm 3. Simulations for the efficiency of the detectors with fixed active volume but different geometrical factors have also been made. It indicates that the slope of the HPGe detector efficiency curve depends only on the detector's active volume but not on its geometrical factor.

Single-to double-escape peak ratio of germanium detectors

Twenty-one HPGe detectors with a crystal volume of 60–256 cm 3 were used to explore the dependence of the single-to-double-escape peak ratio on the detector size. The variations of the escape peak ratio as functions of both relative efficiency and crystal volume of HPGe detectors are quantitatively described and the geometric influence on the ration is also discussed for the coaxial detectors with the D H ratio within the range of 0.85–1.44.

Empirical relation between efficiency and volume of HPGe detectors

Vaño et al.'s empirical relation has been proved to be valid for HPGe detectors with large active volume range. New values of a and b are 0.6246 and −2.136 respectively. The slope of the efficiency curve is characteristic of detectors and independent of the geometry conditions within 2% error. It can be calculated within an error less than 3% in a certain energy range.

Measurement of the efficiency of solid state detectors using atomic-field bremsstrahlung

We report on the current status of our efforts to use the atomic-field bremsstrahlung spectrum from the bombardment of thin-film targets by an electron beam to measure the photon energy dependence of the efficiency of HPGe and Si(Li) detectors. Results are presented for an HPGe detector from 15 to 100 keV and for an Si(Li) detector from 2 to 40 keV. Points on the efficiency curve are also obtained using calibrated radioactive sources for comparison and for absolute normalization. Problems associated with the background in bremsstrahlung measurements are also discussed.