Portable HPGe Detector Research Articles

IN VIVO public monitoring in emergency exposure scenarios by means of spectrometric and non-spetrometric devices.

In a nuclear or radiological accident scenario, when potentially members of the public can undergo internal contamination by anthropogenic radionuclides released in the atmosphere, effective methods that can be used directly in the field to perform a fast scan for internal contamination on a large number of individuals can play a major role to undertake appropriate countermeasures. Specific attention should be paid to the individual monitoring of children since they constitute the sensitive population group with the highest risk of developing cancer. At the ENEA Casaccia Research Center in Rome (Italy), monitoring procedures based on a portable HPGe detector and ratemeters were tested in the field. A total of 170 acquisitions of uncontaminated volunteers for the blank measurements were collected, 105 acquisitions on adult and 65 acquisitions on 10-y/o children. The detection limit calculation, in terms of activity taken up (Bq), was carried out according to the Standard ISO's 11929 and 28218, whereas the corresponding 'minimum effective dose' (mSv) was calculated based on international commission on radiological protection (ICRP) Publications 134, 137 and 141. Results and evaluations of the measurement campaign are presented and discussed in respect to the aspects reported in the current literature.

Monte Carlo techniques for in-situ specific activity estimation of radionuclides with a portable coaxial HPGe: preliminary results

In this work, gamma-ray spectrometry with HPGe detectors is used to measure radionuclides’ specific activity (Asp) in soils. The main purpose of the paper is to present a general procedure to assess Asp in soils from in-situ acquisitions. The soil from two experimental sites was analyzed both in the field, with a portable HPGe detector, and in the laboratory, with a BEGe detector. Sample analysis in the laboratory provided a benchmark for the values of soil’s Asp since it is easier to measure. Monte Carlo simulations were employed to obtain detectors’ efficiency at different gamma-ray energies and allowed to assess radionuclides’ Asp from in-situ acquisitions. Finally, the applicability and limitations of this procedure are discussed.

In situ gamma spectrometry using a portable HPGe detector. Radiological characterisation and environmental surveillance around an operating nuclear power plant. Possibilities and limits.

The in situ technique for measuring radionuclides in the soil using a portable Ge detector is a highly versatile tool for both the radiological characterisation and for the monitoring of operating nuclear power plants. The main disadvantage of this technique is related to the lack of knowledge of the geometry of the source whose activity concentration is to be determined. However, its greatest advantage is the high spatial representability of the samples and the reduced time and resource consumption compared to gamma spectrometry laboratory measurements. In this study, the possibilities and limits offered by in situ gamma spectrometry with a high-resolution gamma portable detector in two common uses are shown. First, the radiological background characterisation and its relationship with the geology of an area of 2700 km2 are assessed. Second, its potential for monitoring man-made activity concentration in soils located around an operating nuclear power plant in Spain for surveillance purposes is evaluated. Finally, high-accuracy radiation maps were prepared from the measurements that were carried out. These radiation maps are essential tools to know the radioactive background of an area, especially useful to assess artificial radioactive deposits produced after a nuclear accident or incident.

In vivo public monitoring in emergency exposure scenarios

In a nuclear or radiological accident scenario, where members of the public can potentially take up anthropogenic radionuclides released in atmosphere, verified methods to fast screen for internal contamination a large number of individuals directly on the field can play a major role to adopt appropriate countermeasures. At the ENEA Casaccia Research Centre (Rome, Italy), a spectrometric monitoring method, based on a portable HpGe detector Trans-Spec-DX-100, has been developed. In this work, the results of the 2019 measurement campaign, where the method sensitivity was tested, in terms of detection limits (DL) for common fission and (some) activation products by acquiring gamma spectra on 102 uncontaminated volunteers (57 adults, 45 children between 7 and 12 years of age) are presented. The spectra, collected with acquisition time of 180 s, have been analysed according to the Standard ISO 28218 for the activity detection limit (Bq) calculations and according to ICRP Publications 134, 137, and 141 for the related minimum measurable committed effective dose. The measurements were taken in open field on a paved surface, in the presence of an environmental radiation background, given in term of ambient dose equivalent rate, dot{H}*(10), equal to 0.230 ± 0.020 μSv/h, in order to study both the potentiality and the limitation of the technique with a significant statistic. The results are presented and discussed particularly focusing on the specific characteristics of the technique, in respect to features reported by the European Council Directive 2013/59/Euratom and the International Atomic Energy Agency (IAEA) document STI/PUB/1708 (2015), and to techniques described in the current literature.

PROCEDURES TO MEASURE MEAN AMBIENT DOSE EQUIVALENT RATES USING ELECTRET ION CHAMBERS.

The capabilities of electret ion chambers (EICs) to measure mean ambient dose equivalent rates were investigated by performing both laboratory and field studies of their properties. First, EICs were ‘calibrated’ to measure ambient gamma dose equivalent in the Ionizing Calibration Laboratory of the Greek Atomic Energy Commission. The EICs were irradiated with different gamma photon energies and from different angles. Calibration factors were deduced (electret’s voltage drop due to irradiation in terms of ambient dose equivalent). In the field studies, EICs were installed at eight locations belonging to the Greek Early Warning System Network (which is based on Reuter-Stokes ionization chambers) for three periods, averaging 5 months each. In the same locations, in situ gamma spectrometry measurements were performed with portable germanium detectors. Gamma ambient dose equivalent rates were deduced by the in situ gamma spectrometry measurements and by soil sample analysis. The mean daily electret potential drop (in Volts) was compared with the mean daily ambient dose equivalent, measured with a portable HPGe detector and Reuter-Stokes high-pressure ionization chambers. From these measurements, ‘field’ calibration factors (electret’s voltage drop due to gamma radiation in terms of ambient dose equivalent) were deduced and found in very good agreement with the values deduced in Laboratory. The influence of cosmic radiation and the intrinsic voltage loss when performing long-term environmental gamma measurements with EICs, was estimated.

Assessment of dose rate of detected gamma emitting nuclides using a carborne survey with a large volume NaI(Tl) detector

A carborne survey system based on a hexahedral 4″ × 4" × 16″ NaI(Tl) detector was developed to assess the dose rate from ground deposited radionuclides over a wide area. A concept based on dose rate spectroscopy was introduced to the carborne survey to simply and directly calculate the ambient dose rate and dose rates of detected gamma emitting nuclides. In addition, an attenuation correction to account for loading the survey system in a vehicle was established, by calculating the count rate of several ROIs and the dose rate of natural radionuclides at diverse sites with different dose rates levels. All of the results from the carborne survey were then corrected to a dose rate 1 m above the ground in the air, to provide data consistency between diverse survey platforms. An experimental verification was conducted by comparing the dose rates of nuclides measured at the same site from the carborne survey and from in situ gamma-ray spectrometry at a fixed position using a portable HPGe detector. Finally, the developed method of a carborne survey was successfully applied to the evaluation of dose rate around the construction site of a nuclear facility. It is anticipated this result can be used to make a baseline of background radiations in the site before operating the nuclear facility currently under construction.

Accuracy associated with the activity determination by in situ gamma spectrometry of naturally occurring radionuclides in soils

In situ gamma spectrometry (ISGS) is a technique mainly focused on the determination of man-made radionuclides deposited on soils. It is widely used for the radioactive characterization of soils in which there has been an incorporation of such radionuclides, especially 137Cs. Its use for the activity determination of naturally occurring radionuclides in soils has been more limited, and the accuracy associated with those measurements has yet to be treated extensively. There are numerous factors affecting the accuracy of the activity determination of naturally occurring radionuclides, such as the assumed soil geometry, the soil’s geological and mineral composition, its moisture content, etc. The present work studies the accuracy associated with the ISGS determination of the activity concentrations of natural radionuclides in soils using a portable HPGe detector. For 40K and 232Th activity determinations, the uncertainties associated with ISGS are generally of the order of 15%. However, 226Ra activity determined from its daughters 214Pb and 214Bi can be significantly overestimated when there is a major presence of 222Rn in the air around the detector. Finally, absorbed dose rate in air values were calculated from the naturally occurring radionuclide concentration in soils. The results showed good correspondence between the values obtained from ISGS and those obtained from laboratory determinations with the same soils.

Designing and producing large-volume liquid gamma-ray standard sources for low radioactive pollution measurements of seawater samples by comparison between experimental and simulation results

In order to in-situ measurement of large volume water samples, using of a portable HPGe detector was considered. Because of necessity of efficiency calibration of the detector for the geometry (100L), the large volume standard sources were prepared. Before making large volume standard sources (100L), the Monte Carlo method has been applied in order to optimizing the calibration procedures and in agreement with experiment results, has been caused reducing the amount of produced radioactive wastes. First, the efficiency of the portable coaxial P-type HPGe detector for 1L liquid standard sources in Marinelli beaker geometry was simulated. Then, the experimental efficiency calibration was carried out using the detector for those 1L liquid standard sources in Marinelli beaker geometry. The detector dead layer was determined by comparison of the simulation and experimental efficiency curve results. Then, a relation between simulation and experimental measurements, that is, between pulse-height per emitted particle, F8 tally, and estimated amount of spiked radioactive solution into the 1L distilled water in Marinelli beaker was found. Then, the efficiency calibration of the large volume liquid standard sources was simulated. The estimated amount of spiking radioactive solution into the large volume distilled water (100L) has been taken into account dividing experimental efficiencies (in Marinelli beaker) by the simulated efficiencies (in 100L). Finally, by spiking the large volume distilled water with the radioactive solution, efficiency calibration of the potable HPGe detector for 100L geometry was done.

Multivariate geostatistical analysis of fallout radionuclides activity measured by in-situ gamma-ray spectrometry

Cs-137 and other fallout radionuclides (FRNs) have been used worldwide for more than four decades as powerful techniques to assess the magnitude and spatial pattern of soil redistribution. Cs-137, 210Pbex, and 7Be have successfully been used as tracers of soil redistribution. Their coincident use can frequently provide worthwhile information for different time scales of soil redistribution. These radionuclides can either be measured in the laboratory or in-situ. In the present study in-situ measurements using a portable HPGe detector were carried out in two loessial paired sub-catchments with fairly similar characteristics in northeast Iran. Spatial sampling design based on a minimax approach was used to determine that 60 sites were sufficient for both areas of interest. Geostatistical analysis and the linear model of co-regionalization (LMC) were applied in this study for radionuclides. The spherical model for Sample and Testifier sub-catchments with ranges of 750 m and 500 m respectively was selected as the most suitable model. The highest and the lowest non-captured variability belonged to 210Pbex and 7Be for both studied areas. The patterns of spatial variation of 7Be and Cs-137 for Sample and the patterns of spatial variation of 7Be and 210Pbex for Testifier sub-catchment were very similar. For Cs-137, global uncertainty for both sub-catchments was nearly the same, but different for other radionuclides. The distribution of local uncertainty for all radionuclides in the Testifier sub-catchment was the same. The means of spatial distance between the grid cells with the highest and the lowest uncertainty for 7Be, Cs-137, and 210Pbex, are 0.4, 1, and 7 km, respectively.

SU‐E‐T‐543: Measurement of Neutron Activation From Different High Energy Varian Linear Accelerators

Purpose:Linear accelerators producing photons above 10 MeV may induce photonuclear reactions in high Z components of the accelerator. These liberated neutrons can then activate the structural components of the accelerator and other materials in the beam path through neutron capture reactions. The induced activity within the accelerator may contribute to additional dose to both patients and personnel. This project seeks to determine the total activity and activity per activated isotope following irradiation in different Varian accelerators at energies above 10 MeV.Methods:A Varian 21IX accelerator was used to irradiate a 30 cm × 30 cm × 20 cm solid water phantom with 15 MV x‐rays. The phantom was placed at an SSD of 100 cm and at the center of a 20 cm × 20 cm field. Activation induced gamma spectra were acquired over a 5 minute interval after 1 and 15 minutes from completion of the irradiation. All measurements were made using a CANBERRA Falcon 5000 Portable HPGe detector. The majority of measurements were made in scattering geometry with the detector situated at 90° to the incident beam, 30 cm from the side of the phantom and approximately 10 cm from the top. A 5 minute background count was acquired and automatically subtracted from all subsequent measurements. Photon spectra were acquired for both open and MLC fields.Results:Based on spectral signatures, nuclides have been identified and their activities calculated for both open and MLC fields. Preliminary analyses suggest that activities from the activation products in the microcurie range.Conclusion:Activation isotopes have been identified and their relative activities determined. These activities are only gross estimates since efficiencies have not been determined for this source‐detector geometry. Current efforts are focused on accurate determination of detector efficiencies using Monte Carlo calculations.

Measurement of Environmental Gamma Dose at AECD Campus of Bangladesh

A portable HPGe detector has been employed to assess environmental gamma-ray dose following in-situ technique from the primordial radionuclide 40K in the soil at 15 monitoring points (MPs) in the environment at the Atomic Energy Centre, Dhaka (AECD) campus, Bangladesh. The MPs were marked-out using Global Positioning System (GPS) navigation. The measured dose rate due to 40K range from 0.0428 µGy.h-1 to 0.1222 µGy.h-1 with an average of 0.0828 ± 0.0225 µGy.h-1. Keywords: Gamma; Environment; Dose rate.© 2014 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi: http://dx.doi.org/10.3329/jsr.v6i2.17146 J. Sci. Res. 6 (2), 285-291 (2014)

Development of the MCNPX model for the portable HPGe detector

The portable HPGe coaxial detector Canberra Big MAC is used in LVR-15 research reactor for spectrometric measurement of spent nuclear fuel. The fuel is measured in the dedicated system located in the spent fuel pool situated near the reactor. For the purpose of the spectrometric system calibration, the detector was precisely modeled with the MCNPX code. This model was constructed with the data acquired from the technical specification provided by the manufacturer and from the data obtained by the radiography of the crystal. The detector model was verified on the experimental data measured with available standard radionuclide sources and on-site prepared 110mAg source.

Photon Spectrum behind Biological Shielding of the LVR-15 Research Reactor

Abstract The LVR-15 reactor is a light water research reactor situated at the Research Centre Řež, near Prague. It operates as a multipurpose facility with a maximum thermal power of 10 MW. The reactor core usually contains from 28 to 32 fuel assemblies with a total mass of 235U of about 5 kg. Emitted radiation from the fuel caused by fission is shielded by moderating water, a steel reactor vessel, and heavy concrete. This paper deals with measurement and analysis of the gamma spectrum near the outer surface of the concrete wall, behind biological shielding, mainly in the 3- to 10-MeV energy range. A portable HPGe detector with a portable multichannel analyzer was used to measure gamma spectra. The origin of energy lines in gamma detector spectra was identified.

An intercomparison of Monte Carlo codes used for in-situ gamma-ray spectrometry

In-situ gamma-ray spectrometry is widely used for monitoring of natural as well as man-made radionuclides and corresponding gamma fields in the environment or working places. It finds effective application in the operational and accidental monitoring of nuclear facilities and their vicinity, waste depositories, radioactive contamination measurements and environmental mapping or geological prospecting. In order to determine accurate radionuclide concentrations in these research fields, Monte Carlo codes have recently been used to obtain the efficiency calibration of in-situ gamma-ray detectors. This work presents an inter-comparison between two Monte Carlo codes applied to in-situ gamma-ray spectrometry. On the commercial market, Canberra has its LABSOCS/ISOCS software which is relatively inexpensive. The ISOCS mathematical efficiency calibration software uses a combination of Monte Carlo calculations and discrete ordinate attenuation computations. Efficiencies can be generated in a few minutes in the field and can be modified easily if needed. However, it has been reported in the literature that ISOCS computation method is accurate on average only within 5%, and additionally in order to use LABSOCS/ISOCS it is necessary a previous characterization of the detector by Canberra, which is an expensive process. On the other hand, the multipurpose and open source GEANT4 takes significant computer time and presents a non-friendly but powerful toolkit, independent of the manufacturer of the detector. Different experimental measurements of calibrated sources were performed with a Canberra portable HPGe detector and compared to the results obtained using both Monte Carlo codes. Furthermore, a variety of efficiency calibrations for different radioactive source distributions were calculated and tested, like plane shapes or containers filled with different materials such as soil, water, etc. LabSOCS simulated efficiencies for medium and high energies were given within an accuracy of below 5% for point sources and 10% maximum accuracy for more complicated geometries. Accuracy for LabSOCS decreased for low energy emissions. Finally an analysis and discussion of the results and the main differences found between LabSOCS and GEANT4 were performed.

Calibration of a portable HPGe detector using MCNP code for the determination of 137Cs in soils

In situ gamma spectrometry provides a fast method to determine 137Cs inventories in soils. To improve the accuracy of the estimates, one can use not only the information on the photopeak count rates but also on the peak to forward-scatter ratios. Before applying this procedure to field measurements, a calibration including several experimental simulations must be carried out in the laboratory. In this paper it is shown that Monte Carlo methods are a valuable tool to minimize the number of experimental measurements needed for the calibration.

INVESTIGATION OF INDUCED RADIOACTIVITY IN THE LINAC-ADONE ACCELERATOR COMPLEX FOR THE MANAGEMENT OF THE DECOMMISSIONED MATERIAL

The LINAC-ADONE accelerator complex of the INFN-LNF Frascati National Laboratories, operating for 27 y prior to the commissioning of DAPhiNE, was dismantled in 1993. The scraps resulting from the decommissioning of LINAC-ADPhiNE have been temporarily stored in the same Frascati laboratory, waiting for definitive disposal. Relying on recommendations of the IAEA, European Commission and Italian committees, an experimental characterization study of the LNF repository was performed. The main objective was a classification of the scraps on the basis of internationally recognized "clearance levels," which are 0.1 Bq g(-1) for the isotopes of interest for this work. Secondly, a measurement of the materials suspected to be above 0.1 Bq g(-1) was planned. Activation isotopes were expected from the aluminum, copper, steel, and iron of the LINAC and the ADONE ring sections. For screening purposes, the repository area has been divided into zones, where in-situ measurements with a portable HP-Ge detector have been performed. In addition, small samples have been cut from a representative number of pieces, and accurate laboratory measurements have been made with a low background HP-Ge spectrometer. The experimental results are in good agreement with other studies and show that a large part of the material is below the mentioned specific activity level.

A combination study of indoor radon and in situ gamma spectrometry measurements in Greek dwellings.

The aim of the present study was to investigate of a possible correlation between indoor radon and indoor gamma dose rates deduced by in situ gamma spectrometry measurements by using a portable HPGe detector. Indoor radon and high resolution in situ gamma spectrometry measurements were performed in 60 apartments in Thessaloniki, the second largest city of Greece. Geometric mean radon concentration is 52 Bq m(-3). The mean total absorbed dose rate in air due to gamma radiation is 56 +/- 9 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 41% due to 40K, 36% due to the thorium series and 23% due to the uranium series. No correlation was found between indoor gamma dose rate due to the uranium series and indoor radon for ground and first floor apartments. For upper floor apartments (above the second floor) a weak correlation is observed. The mean annual effective dose due to radon is 1.15 mSv, i.e., more than four times higher compared to the effective dose due to gamma radiation (0.27 mSv).

A gamma monitoring technique for estimating plutonium contamination around nuclear weapons facilities

The objectives of this study were to establish a ratio for241Am to239Pu in soil at the Rocky Flats Plant and to compare241Am concentrations obtained using in-situ and laboratory gamma spectroscopy measurements to concentrations determined with radiochemical analysis and alpha spectroscopy. Soil samples were collected for radiochemical and laboratory gamma spectroscopy analysis from vertical profiles in 3 cm layers to a depth of 21 cm at predetermined locations along transects oriented in the direction of prevailing winds. The origin for the transects was the center of the 903 Pad at the Rocky Flats Plant, which is believed to be the source for most of the241Am and239Pu contamination. A 100 minute in-situ gamma spectroscopy measurement was made at each soil sample location with a portable HPGe detector. Soil samples were dried, passed through a 2 mm sieve, mixed, and split in two fractions. One fraction was analyzed radiochemically for241Am and239Pu and the second was analyzed using laboratory gamma spectroscopy. The median ratio of241Am to239Pu activities, which appears to be independent of soil depth and distance from suspected sources, was 0.17. There is a strong correlation between241Am and239Pu concentrations determined using radiochemical analysis with alpha spectroscopy and concentrations determined with laboratory gamma spectroscopy. Results from in-situ gamma spectroscopy measurements were also correlated with the radiochemical analyses but exhibited greater variability than laboratory measurements. This on-going investigation has demonstrated that it is possible to indirectly measure239Pu concentrations in soil if the ratio of241Am to239Pu can be established. The results indicate that judicious use of a combination of radiochemical analyses with laboratory and in-situ gamma spectroscopy measurements may provide a cost-effective approach for characterization of large sites where241Am and239Pu contamination occur.

Concentration of 90Sr and 137Cs in gaseous effluents

Concentration of 90Sr and 137Cs released in the gaseous effluents from a research reactor is evaluated from the measurement of their gaseous precursors namely 90Kr and 137Xe respectively. An on-line measuring system comprising of a sampling head and a portable HPGe detector coupled to a 4K MCA has been used for the measurement of concentration of these gases. A double filter method has been used to verify the measurement of 90Kr concentration. It is based on programmed counting of its daughter 90Rb. There is good agreement between the results of on-line and double filter methods.