BEGe Detector Research Articles

Calibration for in vivo monitoring of thyroid of exposed population at risk of intakes of radioiodine isotopes due to a nuclear or radiological emergency

This work presents an improvement of the calibration of a broad energy germanium detector (BEGe) using age dependent neck-thyroid phantoms for thyroid monitoring of exposed individuals (workers and members of the public), allowing the detection and quantification of incorporated radioiodine isotopes in a nuclear medicine frame or in case of accident of a nuclear reactor.A BEGe detector was calibrated using a family of age-dependent thyroid-neck phantoms that simulate thyroids of 1, 5, 10, 15 year-old children and (male and female) adults, based in ICRP Publication 8 (ICRP, 2002) and ANSI 13.44 Standard (ANSI, 2014).The calibration of the BEGe detector for all neck phantoms was performed with the same counting geometry, centered under the BE Ge detector and at the same distance of 15 cm. Using same counting parameters allows to compare efficiency curves of thyroid monitoring depending with age. The in vivo measurements with the BE Ge detector allow to identify X rays and gamma emissions between 10 and 1000 keV with a great resolution and to quantify activities of radioiodine isotopes in the thyroid of exposed population.Calibration curves have been obtained for different sizes of the thyroid, depending with age. This study of counting efficiency using the main energies of the most important radioiodine isotopes result in accurate activity calculations. Detection limits were obtained for each radioiodine isotope, using blank phantoms of each age.

True coincidence summing correction for a BEGe detector in close geometry measurements

The true coincidence summing correction factor for a Broad Energy Germanium detector has been calculated at far and close geometry set-up using radioactive γ-ray sources. The correction factors were calculated using both experimental and analytical methods. Geant4 simulation was done to calculate the full-energy peak and total efficiencies of the detector. Standard, as well as fabricated mono-energetic γ-ray sources, were used for the γ-ray efficiency measurements. The simulated efficiencies of mono-energetic γ-ray sources were matched to the experimental γ-ray efficiencies by optimizing the detector parameters. The same parameters were used to obtain the full-energy peak and total efficiencies for γ-rays of current interest. Analytical and experimental correction factors were found to agree well with each other. The coincidence summing effect is found to be significant for source-to-detector distances less than 5 cm.

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.

Recent developments in IBA analysis at CENTA, Bratislava

An experimental setup used at the CENTA (Centre for Nuclear and Accelerator Technologies) laboratory to carry out IBA (Ion Beam Analysis) techniques is described. PIXE (Particle Induced X-ray Emission) technique offers a unique way of non-destructive elemental analysis using accelerated ion beams. The calibration of instrumental constants (H-values) of SDD and BEGe detectors, used in the setup, is described in detail. The H-value was determined as a function of X-ray energy by using thin MicroMatter standards of chosen elements. The calibrated H-values were then used in GUPIXWIN for the determination of elemental concentrations in two IAEA reference materials, which were compared with reference values. A reasonable agreement was achieved between the measured and reference values, while the calibrated H-values will be used for further analyses.

Monte Carlo model of a BEGe detector to support γ-spectrometry in an emergency response

One of the problems of measuring high radioactivity in an emergency scenario is the fact that the detector can become saturated or reach a measuring dead time too high to give reliable results, which means repeating the measurement in different conditions with the associated delay in obtaining the results and the laboratory workers' risk of exposure. The counting rate can be controlled by varying the sample-to-detector distance as well as by using different source volumes. A Monte Carlo model of a BEGe detector was developed to analyse the system efficiency response for several measuring configurations (distances and volumes) using the MCNP6 code. The total efficiency curves were obtained for an energy range between 59.5 keV and 1836 keV. The simulations provided an estimation of the admissible γ-rate for different source volumes (in water matrix) and sample-to-detector distances to avoid detector saturation in given measurement conditions. The results were a compromise between geometry, distance and measuring time for certain emergency situations. Three case studies are provided to show the approach's effectiveness.

Low-background, digital gamma-ray spectrometer with BEGe detector and active shield: commissioning, optimisation and software development

This paper presents results of the development process of low-background, digital gamma-rays spectrometer equipped with Broad Energy Germanium detector (CANBERRA BE5030), multi-layer passive shield and cosmic veto system that consists of five plastic scintillators (SCIONIX EJ-200). Data acquisition is performed using digitizer CAEN DT5725 with CoMPASS software. Output data analysis is carried out with purposely written and developed code VETO. On the basis of conducted tests, acquisition parameters were set up and tuned as well as time delays between all detectors were established. As a result of the configuration process, the mean background counts reduction of 64% in the whole spectrum and 65% in annihilation peak were achieved. This procedure allowed diminishing detection limits of selected isotopes 37% on average.

GEANT4 investigation of 40K and 222Rn interference effects on actinide detection sensitivities of CEMRC BEGe lung detectors

Internal dosimetry measurements of trans-uranic (TRU) radionuclides within the human body can be accomplished by γ-ray spectroscopy using high-purity germanium detectors. While measurements are typically conducted inside shielded chambers in order to minimize the background detector signal, the presence of radioactive 40K within the body cannot be removed, which produces a high-energy γ ray at 1461 keV. The 40K, in addition to airborne 222Rn, contributes to the radiation field within the chamber that increases to the minimum detectable activity that can be achieved in practice.The objective of the present work is to estimate the contributions from 40K internal to the human body and airborne 222Rn to the background signal in a lung counter germanium detector array using GEANT4 simulations, with a focus on TRU isotope energy region (17–59 keV). The investigations consisted of three main simulations:1.Simulating the γ-ray flux at the geometric center of the CEMRC counting chamber arising from a 25 nCi source of 40K from (a) a point source, and (b) a source distributed throughout a BOMAB phantom.2.Simulating the response of the CEMRC BEGe detectors arising from a 25 nCi source of 40K from (a) a point source, and (b) a source distributed throughout a BOMAB phantom.3.Simulating the response of the CEMRC BEGe detectors to the environmental background in the counting chamber, consisting of airborne 222Rn (0–4 pCi/L) and 40K (0–160 nCi) internal to the human body.The results are used to investigate the 40K background contribution to a routine spectrum recorded by the lung detectors at the CEMRC Internal Dosimetry laboratory over a typical half hour counting interval used in the dosimetry of radiological workers. The minimum detectable activity was calculated for various 222Rn and 40K activities and compared to experimentally determined values. The contribution of cosmic rays was not included in this investigation.

Estimating natural radiation exposure from building materials used in Sri Lanka

In this work, the natural radioactivity levels of several building materials used in Sri Lanka, were determined in terms of Bq kg−1, and to calculate the radiological effects caused by this radioactivity. Activity concentrations of 226Ra, 232Th and 40K in eighteen samples of manufactured building materials were measured using gamma spectroscopy based on high purity germanium detector with an efficiency of 48% at 1332.5 keV. The measurement of the activity concentration in building materials is required to estimate the excess dose to public dwelling in such buildings. BEGe detector is a well-chosen equipment for this purpose. The activity concentrations for 226Ra, 232Th and 40K from the selected building materials ranged from (5.0 ± 0.5 to 45.2 ± 2.9 Bq kg−1), (7.1 ± 0.6 to 68 ± 5.9 Bq kg−1) and (42.8 ± 3.8 to 1773 ± 54 Bq kg−1) respectively. Radium equivalent activities, absorbed dose rate, the value of external hazard indexes and alpha indexes were calculated for the measured samples to assess the radiation hazards arising from using those materials in the construction of dwellings. The average value of indoor annual effective doses of Sri Lankan building materials was 0.22 mSv. Also the average value of outdoor annual effective doses of Sri Lankan building material was 0.05 mSv. It has been noted that the values of annual effective dose of Sri Lankan building materials were below the world average value of terrestrial annual radiation exposure which was 0.48 mSv. Therefore, the types used in the current study are quite safe to be used as building materials.

Detecting and quantifying uranium-series disequilibrium in natural samples for dosimetric dating applications

Isotopic fractionation is a process that may occur in natural aquatic environments. Samples originating from these open-system environments may contain radioisotopes with activity ratios between daughter and mother nuclide being not at unity. For the purpose of dosimetric dating, small deviations from unity may have negligible effect, but the mobility of 226Ra and 234U over longer time scales affects the accuracy of the dating result. Here we use the Canberra LabSOCS model in association with a standard 60 mm diameter BEGe detector in a 50 mm thick graded lead shield to carry out gamma spectroscopic measurements on the 238U decay series in a series of environmental samples. These samples were characterised in terms of density, filling height and chemical composition and peak interferences were corrected using the gf3 software. The model calculations have been shown to be in agreement with experimental transmission measurements taken with point sources and with results from standard IAEA materials and through a comparison with ICP-MS measurements. The results presented show excellent agreement between outputs from model and independent control measurements. This suggests that the method presented here is robust and allows quantifying and correcting isotopic fractionation using readily available gamma spectrometric setup and software.

Gamma spectrum and coincidence summation simulations with Geant4 in the analysis of radionuclide using BEGe detector

A Geant4 application has been developed to simulate the gamma spectrum of a BEGe detector. The summation effects were encompassed for both random and true coincidences through a time-based approach. The application well reproduces the typical spectral features such as full energy peaks, escape peaks, summation peaks and Compton/backscatter continuum. The simulated gamma response is consistent with empirical data within 3%, while simulations of the X-ray and baseline regions are valid within a 10% deviation.

Improved Limit on Neutrinoless Double-β Decay of ^{76}Ge from GERDA Phase II.

The GERDA experiment searches for the lepton-number-violating neutrinoless double-β decay of ^{76}Ge (^{76}Ge→^{76}Se+2e^{-}) operating bare Ge diodes with an enriched ^{76}Ge fraction in liquid argon. The exposure for broad-energy germanium type (BEGe) detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of 1.0_{-0.4}^{+0.6}×10^{-3} counts/(keV kg yr) has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any 0νββ experiment. No signal is observed and a new 90%C.L. lower limit for the half-life of 8.0×10^{25} yr is placed when combining with our previous data. The expected median sensitivity assuming no signal is 5.8×10^{25} yr.

Accurate efficiency characterization of a BEGe detector in the low-energy range using empirical and Monte Carlo simulation approaches

The efficiencies of a broad energy germanium detector were characterized down to energies below 10 keV. The K shell X-ray absorption in germanium was seen as a sharp drop in efficiency around 11 keV. This feature was used to determine the thickness of this detector’s dead layer. By comparing efficiency simulations with different dead layer thicknesses to those determined from empirical measurements, the best fit dead layer thickness was determined to be 5.7 ± 1.5 µm. Additional measurements, taken with a collimator, made analytical calculations of the efficiency possible and these results also supported the dead layer thickness determination.

Compton suppression in BEGe detectors by digital pulse shape analysis

A new method of pulse shape discrimination (PSD) for BEGe detectors is developed to suppress Compton-continuum by digital pulse shape analysis (PSA), which helps reduce the Compton background level in gamma ray spectrometry. A decision parameter related to the rise time of a pulse shape was presented. The method was verified by experiments using 60Co and 137Cs sources. The result indicated that the 60Co Peak to Compton ratio and the Cs-Peak to Co-Compton ratio could be improved by more than two and three times, respectively.

PIXE beam line at the CENTA facility of the Comenius University in Bratislava: first results

Optimization of the proton and helium beams from the alphatross ion source through the injection beam-line, the 3 MV Pelletron tandem accelerator, the high-energy analyzer and the PIXE chamber were carried out. Results obtained with the 4He ion beam showed better detection limits when compared with protons of the same energy and beam intensity. For detection of produced X-rays, a BEGe detector has been used, covering the energy range from 3 keV to 3 MeV. First measurements with 4He ions of 3.5 MeV energy included calibration runs with PIXE laboratory standards, as well as analyses of old silver coins.

LArGe: active background suppression using argon scintillation for the Gerda $$0\nu \beta \beta $$ 0 ν β β -experiment

LArGe is a Gerda low-background test facility to study novel background suppression methods in a low-background environment, for future application in the Gerda experiment. Similar to Gerda, LArGe operates bare germanium detectors submersed into liquid argon (1 m $$^3$$ , 1.4 tons), which in addition is instrumented with photomultipliers to detect argon scintillation light. The scintillation signals are used in anti-coincidence with the germanium detectors to effectively suppress background events that deposit energy in the liquid argon. The background suppression efficiency was studied in combination with a pulse shape discrimination (PSD) technique using a BEGe detector for various sources, which represent characteristic backgrounds to Gerda. Suppression factors of a few times $$10^3$$ have been achieved. First background data of LArGe with a coaxial HPGe detector (without PSD) yield a background index of (0.12 $$-$$ 4.6) $$\times 10^{-2}$$ cts/(keV kg year) (90 % C.L.), which is at the level of Gerda Phase I. Furthermore, for the first time we monitor the natural $$^{42}$$ Ar abundance (parallel to Gerda), and have indication for the $$2\nu \beta \beta $$ -decay in natural germanium. These results show the effectivity of an active liquid argon veto in an ultra-low background environment. As a consequence, the implementation of a liquid argon veto in Gerda Phase II is pursued.

Optimization of cylindrical sample geometry in determining the radioactive activity of environmental soil samples by using a Broad Energy Germanium detector

This paper describes the optimization of the geometric parameters of cylindrical geometry to maximize the detection efficiency for given sample volumes with a BEGe detector. A Monte Carlo model was developed and the detector efficiencies were studied for different sample geometries. The optimal sample dimensions that maximize the detection efficiencies have been determined by changing the sample dimensions through consecutive studies. The results show that the maximal detection efficiency depends on the appropriate selection of sample dimensions for a given sample volume. For the cylindrical geometry, the maximal detection efficiency can be obtained with the average sample radius/sample height value of about 1.75 (1.61 ∼ 1.91) for the corresponding given sample volume ranging from 150 to 400 cm3. Further studies show that the optimal sample height for a fixed cylindrical radius strongly depends on the measuring photon energy, and simply increasing the sample height does not generate higher full-energy peak net count rate. At last, optimal sample dimensions for the cylindrical geometry are recommended for a given detector specification with different sample volumes and photon energies.

Phase II Upgrade of the GERDA Experiment for the Search of Neutrinoless Double Beta Decay

Observation of neutrinoless double beta decay could answer the question regarding the Majorana or Dirac nature of neutrinos. The GERDA experiment utilizes HPGe detectors enriched with the isotope 76Ge to search for this process. Recently the GERDA collaboration has unblinded data of Phase I of the experiment. In order to further improve the sensitivity of the experiment, additionally to the coaxial detectors used, 30 BEGe detectors made from germanium enriched in 76Ge will be deployed in GERDA Phase II.BEGe detectors have superior PSD capability, thus the background can be further reduced. The liquid argon surrounding the detector array will be instrumented in order to reject background by detecting scintillation light induced in the liquid argon by radiation. After a short introduction the hardware preparations for GERDA Phase II as well as the processing and characterization of the 30 BEGe detectors are discussed.

GeFRO: A New Charge Sensitive Amplifier Design for Wide Bandwidth and Closed-Loop Stability Over Long Distances

A new approach was developed for the design of front-end circuits for semiconductor radiation detectors. The readout scheme is a charge sensitive amplifier, split between a very front-end stage (input transistor, feedback resistor and capacitor) located close to the detector and a remote second stage located far from the detector. The element of novelty, with respect to similar configurations, is the fact that the connecting links between the very front-end and the second stage are made with transmission lines. As a result, wide bandwidth and closed-loop stability are maintained even if the distance between the very front-end and the second stage is much larger than usual, up to tens of meters. The circuit was named GeFRO for Germanium front-end, and was tested with a BEGe detector from Canberra. Timing resolutions of 20 ns (open loop) and 185 ns (closed loop with 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> phase margin) were obtained with 10 m long cables between the very front-end and the second stage. The noise of the circuit after a 10 μs Gaussian shaping was close to 160 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> RMS with an input capacitance of 26 pF.

Monte Carlo characterisation of a Compton suppressed broad-energy HPGe detector

GEANT4 Monte Carlo simulations have been successfully utilised to characterise a Compton suppressed broad-energy HPGe detector. The detector setup has been fully recreated in the simulation, which has been optimised to consistently reproduce the detector response. The peak efficiencies for both the primary BEGe detector and NaI(Tl) guard detectors agree with the simulated values for multiple test sources within 3 %. Compton suppression has also been simulated, with good agreement seen between the simulated and actual CSF values (<10 %) for multiple radionuclides. A secondary reference source was also simulated, which contained up to 30 radionuclides in a different geometry to that of the previous source. This showed excellent agreement with experimental data in both unsuppressed and suppressed modes of operation.

The active area shadow-shielding effect on detection efficiency of collimated broad energy germanium detectors

The ISOCS calibration, when utilized for a BEGe detector with a small angled collimator, produces inaccuracies of about 19% for gamma rays with energies greater than 0.4MeV. Such a discrepancy is caused by the collimator algorithms currently utilized in the ISOCS software which, originally developed for HPGe detectors, are less suited for BEGe detectors. ISOCS's errors are due to the different crystal configurations of broad energy detectors compared to coaxial detectors, i.e. to a different importance of the active area portion obscured by the collimator. This work proposes some solutions for the problem, either using the ISOCS software or implementing a stochastic calibration procedure. In particular, the present work considers a virtual collimator that, maintaining its angular aperture, is capable of continuously enlarging its bottom collimator's aperture cone radius, to expose growing active area portions. In such a way two goals may be achieved: the mathematical characterization of ISOCS’ errors and the minimization of observed errors by means of the stochastic calibration procedure.Different reference set-ups are considered in order to test source geometry effects, source materials and different detectors. In particular, a 220L drum, a 2m3 box filled with uniformly contaminated cellulose or PVC, and small BE3825 and large BE5030 Canberra detectors are considered. Detection efficiencies calculated by ISOCS software are compared against a completely stochastic MCNPX simulation procedure, that is unaffected by any algorithmic correction. MCNPX simulations demonstrate, when widening collimators’ cone but maintaining the angular aperture unchanged, that ISOCS and MCNPX difference percentage between efficiency data points reduces, depending on energy, by more than 50%. This happens as far as the shadow-shielded portion of detector's active area reduces.