Coaxial Ge Research Articles

Modeling of N and P-Type of Coaxial Ge Detectors Using MCNPX and the Effect of Dead Layer Variation on Its Response Function

Abstract This study assessed the response function of a p-type and n-type coaxial high-purity germanium (HPGe) detector via Monte Carlo N-Particle eXtended (MCNPX). MCNPX was employed to model the Coaxial Ge detectors, and for a precise simulation, the dimensions of the dead layer of germanium crystals were added. The dead layer was separated into front and lateral surfaces, and the thickness of each dead layer was modeled. In this work, the simulated detectors have been performed at different energy lines using a radioactive source Eu-152 to study the response function of each with dead layer variations for the front dead layer and study the range of relative deviation of the Monte Carlo simulation outputs from the manufactured declared data. The results proved that the n-type coaxial HPGe detector is more sensitive to the dead layer change than the p-type with a thick change of 0.01 mm. This research has significant effects on the efficiencies of the radiation detection systems in the energy range ∼ (120–1410) keV.

A new efficiency calibration methodology for different atmospheric filter geometries by using coaxial Ge detectors

The study of the different pollutants present in atmospheric aerosols such as trace elements and radionuclides is essential to assess the air quality. To analyze the particulate matter (PM), atmospheric filters with different dimensions and geometries (rectangular, circular, slotted, and square filters) are usually employed. Regarding the pollutants existing in atmospheric aerosols, radionuclides are usually analyzed due to their multiple applications such as either in the environmental radiological control or as tracers of atmospheric processes. Therefore, this study aims to develop a new and general methodology to calibrate in efficiency coaxial Ge detectors to properly determine radionuclides present in the PM by gamma-ray spectrometry for several filter types. For this, granular certified reference materials (CRM) containing only natural radionuclides (238U-series, 232Th-series, and 40 K) were selected. Several granular solid CRMs were chosen allowing us to reproduce the same PM deposition geometry and to assure the homogeneity of the added CRMs. These are the main advantages in relation to the typical methods that use liquid CRMs. Furthermore, for filters whose surfaces are relatively large, they were cut in several pieces and placed one on top of the other, achieving the same geometry than the PM deposited onto the filter. Then, the experimental full-energy peak efficiencies (FEPEs) were obtained for each energy of interest (Eγ) and they were fitted versus Eγ, finding a general FEPE function for each filter type. Finally, this methodology was validated for both natural and artificial radionuclides (from 46 to 1332 keV) by using different filter types employed in proficiency test exercises, obtaining |zscore|< 2 for all cases.

Robustness of LabSOCS calculating Ge detector efficiency for the measurement of radionuclides

The LabSOCS software is one of the main simulation codes employed to calculate the full-energy peak efficiency (FEPE) for the measurements of radionuclides by gamma-ray spectrometry. The validity of LabSOCS has not previously been evaluated for a large variety of matrixes, geometry types, and energies. This study aims to analyze in depth the LabSOCS FEPE robustness comparing the LabSOCS and experimental FEPEs by using three coaxial Ge detectors for a wide range of samples, varying the matrix composition, counting geometry (thickness (h) for cylindrical geometry), gamma emission energy (Eγ), and bulk density (ρ). The FEPE averages and variances calculated for numerous matrix types prepared using gamma cocktails were statistically comparable for a wide Eγ range (from 46 keV (210Pb) to 1836 keV (88Y)). To test the accuracy of the LabSOCS FEPEs varying h (6–50 mm), four certified samples containing only natural radionuclides were used. The 234, 228Th, 228, 226Ra, 210Pb and 40K activities were determined for each h, obtaining |zscore| < 2 in general. This also proves the good reproducibility of LabSOCS calculating activity concentrations. The LabSOCS FEPE robustness was also tested for a wide ρ range (1.3–2.8 g cm−3) mixing a sediment sample with Pb(NO3)2 for h = 50 mm. The 210Pb and 234Th contained in each mixture were determined, achieving all |zscore| < 2. Furthermore, the ability of LabSOCS to correct self-attenuation effects was checked to be wider than when other correction models are applied.

A practical and general methodology for efficiency calibration of coaxial Ge detectors

The correct determination of artificial and natural radionuclides like 152Eu, 137, 134Cs, 60, 57Co, etc., and 234, 228Th, 228, 226Ra, 210Pb and 40K, respectively, is essential for many environmental science fields. For this, a general function was obtained for the full-energy peak efficiency (FEPE) by gamma-ray spectrometry using coaxial Ge detectors. Then, the experimental FEPE values, obtained fixing the energy, Eγ, were fitted varying the thickness, h, of cylindrical standards. The parameters resulted from these fittings were fitted, in turn, versus Eγ, obtaining a general efficiency function, εc (Eγ, h). εc (Eγ, h) was validated, obtaining very good zscore, except for Eγ affected by TCS effects. Consequently, a practical and general method was developed, recalibrating the detector by varying the sample-detector distance, d. εc (Eγ, h, d) was obtained, achieving very good zscore. Furthermore, this practical method was also employed to correct high self-absorptions and high dead times.

A general function for determining mass attenuation coefficients to correct self-absorption effects in samples measured by gamma spectrometry

This work is focused on obtaining a general function for calculating the mass attenuation coefficients of samples whose compositions are known such as waste, biota or NORM (Naturally Occurring Radioactive Materials) samples. After determining the general function, it is possible to assess the self-absorption effects by the self-absorption correction factor, which is really important to consider for samples measured by gamma spectrometry. In order to obtain a general function of the mass attenuation coefficients dependent on the gamma emission energy (Eγ) and the chemical elements (Zi) with their respective concentrations (xi), it was necessary to fit the tabulated values of the mass attenuation coefficients versus gamma energy in the range of 20 keV–2000 keV for each chemical element. This is the energy range for the majority of gamma emissions of natural radionuclides. Once those fittings for each chemical element, Z, from 1 (H) to 92 (U) were done, the parameters, that resulted from those fittings, were fitted versus the atomic number, Z. This provides a general function that allows to calculate the mass attenuation coefficient by knowing the gamma emission energy and the sample composition. Finally, both the general function for calculating the mass attenuation coefficient and the self-absorption correction factor, which is used in gamma spectrometry with coaxial Ge detectors, were validated by comparisons made with the values provided by databases for several samples with widely different known densities, compositions and activity concentrations.

Decay properties of 2.05-h [formula omitted]Am

Gamma rays following the β− decay of the 245Am radionuclide (T1/2 = 2.05 h) were measured in early 1970s with a co-axial Ge(Li) detector using a chemically and isotopically pure, mass-separated 245Am source. These data were analyzed in the present work where several weak γ rays in 245Cm were identified. The 245Am decay scheme was deduced and extended when compared to the previously known one.

Pulse shape discrimination performance of inverted coaxial Ge detectors

We report on the characterization of two inverted coaxial Ge detectors in the context of being employed in future 76Ge neutrinoless double beta (0νββ) decay experiments. It is an advantage that such detectors can be produced with bigger Ge mass as compared to the planar Broad Energy Ge (BEGe) or p-type Point Contact (PPC) detectors that are currently used in the Gerda and Majorana Demonstrator0νββ decay experiments respectively. This will result in a lower background for the search of 0νββ decay due to a reduction of detector surface to volume ratio, cables, electronics and holders which are dominating nearby radioactive sources. The measured resolution near the 76Ge Q-value at 2039 keV is 2.3 keV FWHM and their pulse-shape discrimination of background events are similar to BEGe and PPC detectors. It is concluded that this type of Ge-detector is suitable for usage in 76Ge 0νββ decay experiments.

Neutron-rich isotopes from 238U(n,f) and 232Th(n,f) studied with the ν-ball spectrometer coupled to the LICORNE neutron source

We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inversekinematic fast neutron source at the ALTO facility of the IPN Orsay, was coupled to the MINIBALL γ-ray spectrometer to study very neutron rich nuclei using the 238U(n,f) reaction. This reaction and 232Th(n,f), are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of ~16h. High selectivity in the experiment was achieved via triple γ-ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other reaction mechanisms such as spontaneous fission. The pulsing allows time correlations to be exploited to separate delayed γ rays from isomeric states and supresses unwanted γ-rays from beta decay. In Autumn 2017, the ν-ball array will be operational at the ALTO facility of the IPN Orsay. This high efficiency hybrid Ge-LaBr3 spectrometer based around 24 clover Ge detectors, 10 co-axial Ge detectors and 20 LaBr3 scintillators will help to further refine the technique and achieve a large increase in the current observational limit.

Development of a low-temperature germanium detector via mechanical cooling with a compact pulse-tube refrigerator

We have developed a new germanium (Ge) detector unit for hypernuclear γ-ray spectroscopy at J-PARC, which comprises a new Ge detector array Hyperball-J. A compact pulse-tube refrigerator is coupled to a coaxial Ge detector in order to achieve lower crystal temperatures as a means to increase radiation hardness. The obtained crystal temperature is 72K, while an energy resolution is maintained at (FWHM) 3.1(1)keV for 1.33MeV γ rays using a gate-integrated shaping amplifier (ORTEC 973U). Gain shifts with changing crystal temperature are also confirmed for the Ge detector.

Disintegration rate, gamma-ray emission probabilities and metastable half-life measurements of 67Ga

The procedure for determining the 67Ga disintegration rate by a primary method is described. The proposed triple 4πβ–γ coincidence system consists of a thin window gas-flow 4π proportional counter (PC) coupled to a NaI(Tl) scintillator and a HPGe crystal. Independent pulse height and occurrence time information is provided for the three detector outputs by means of a Software Coincidence System. Separate spectrometry measurements with a n-type reversed electrode coaxial Ge detector (REGe) were performed for obtaining gamma-ray emission probabilities per decay. Accurate values of disintegration rate, gamma-ray emission probabilities and the metastable half-life were achieved.

Gamma-ray emission probabilities in the decay of 177mLu

γ-Ray emission probabilities from the decay of the long-lived (T1/2=160.44d) isomeric state in 177mLu were measured with planar (LEPS) and coaxial Ge detectors. The isomer γ-ray and β−-decay branching intensities were also determined. Measurements were carried out at low absolute efficiencies in order to minimize coincidence summing losses. The results are compared with the previous measurements.

Synthesis and Magnetic Characterization of Coaxial Ge1–xMnx/a-Si Heterostructures

A method for synthesizing Ge1–xMnx/a-Si core–shell nanowires (x = 0.3(1)–1.0(2)) using a supercritical fluid deposition technique, with a homogeneous distribution of manganese along the entire lengths of the crystalline Ge cores but not in the a-Si shells, is reported. Investigations into the magnetic properties of the heterostructured nanowires revealed a significant influence of the amorphous Si shell covering the surface of the core Ge0.997Mn0.003 nanowires compared to pristine Ge0.997Mn0.003 nanowires with no a-Si coating. The magnetic data revealed diminished values of both the remanence and the saturation magnetization for pristine Mn-doped Ge nanowires at higher temperatures when compared to the Ge1–xMnx/a-Si core–shell nanowires, whereas both parameters increased as the temperature dropped down to 5 K. Differences in the temperature-dependent evolution of the coercivity were observed in the magnetically harder core–shell nanowires compared to the pristine Ge0.997Mn0.003 nanowires, showing a drop of 26% at 5 K vs room temperature compared to a drop of 66% for the pristine nanowires. The low dopant concentration (0.3(1)%) of Mn in the core–shell nanowires, combined with the observed ferromagnetic properties, suggests a combination of hole-mediated exchange and confinement processes are responsible for the observed properties. Our observations show the importance of a protective layer in covering the oxidation-sensitive dilute magnetic semiconductor nanowires.

Measurements of absolute gamma-ray emission probabilities in the decay of 233Pa

Abstract Gamma-ray emission probabilities from the β − decay of 233 Pa were measured with planar (LEPS) and coaxial Ge detectors. A 233 Pa source was produced after radiochemical separation from a 237 Np sample in which the parent ( 237 Np) and daughter ( 233 Pa) nuclides were in secular equilibrium. Absolute γ ‐ ray emission probabilities per 100 α decays of the parent nuclide 237 Np were also measured in conjunction with the α - and γ ‐ ray spectroscopy techniques.

Measurements of X- and γ-ray emission probabilities in the β− decay of 233Pa

X- and γ-ray emission probabilities from the β(-) decay of (233)Pa were measured with planar (LEPS) and coaxial Ge detectors. A (233)Pa source was produced after radiochemical separation from a (237)Np sample in which the parent ((237)Np) and daughter ((233)Pa) nuclides were in secular equilibrium. The results are compared with previous measurements and data evaluations.

Radioactive Contamination in Lichens Collected from Trabzon and Rize in the Eastern Black Sea Region, Turkey, and a Comparison with that of 1995

After the Chernobyl nuclear accident in 1986, 14 lichen specimens collected from Trabzon and Rize in 1995 were used to detect the amount of the fallout radionuclides. In this paper, radioactivity levels in the same species from the same localities were re-detected to compare with those of 1995. According to the results of the two studies, the radioactivity levels that this paper found for 137Cs and 40K are significantly lower than those of 1995 (about 5.5-127 folds for 137Cs, 5-17 folds for 40K). The level of 212Pb was acceptably small. The highest activities of the lichen species are seen in the locality of Helvaci (Trabzon, 100 m) and Camlihemşin (Rize, 1850 m) while the activities are medium in Bozdoğan (Trabzon, 150 m), Kemaliye (Trabzon, 750 m) and Camlihemşin (Rize, 900 m). The activity values generally increase significantly depending on the altitudes. Since the measurements were performed 20 years after the Chernobyl accident in 1986, radionuclides of 134Cs having short half-life (2.062 y) have not been detected. All data was obtained with a coaxial high purity Ge detector of 15% relative efficiency and resolution 1.9 keV at the 1332 keV gamma of 60Co (Canberra, GC 1519 model).

Investigation of Absolute Counting of Radioactivity by Gamma-gamma Coincidence Counting Method Using Ge Detectors

The gamma-gamma coincidence counting method with two coaxial Ge detectors was applied to the absolute measurement of radioactivity. To investigate the dependence of the calculated activity on the coincidence time, a 60Co standard point source was measured by a gamma-gamma coincidence counting system. As a result, it was confirmed that the coincidence time did not influence the calculated activity, which agreed with the calibrated value within 10%. To estimate measurable range of source disposition, two or nine 60Co sources were measured by this system. As a result, the measurable range was 3cm × 10cm × 10cm(thickness × width × height), when the detector-detector distance was 10cm.

An assessment of radiation damage in space-based germanium detectors due to solar proton events

Radiation effects caused by solar proton events will be a common problem for many types of sensors on missions to the inner solar system because of the long cruise phases coupled with the inverse square scaling of solar particle events. As part of a study in support of the BepiColombo mission to Mercury we have undertaken a comprehensive series of tests to assess these effects on a wide range of sensors. In this paper, we report on the measurements on a large volume coaxial Ge detector which was exposed to simulated solar proton spectra of integrated fluences 8 × 10 8 , 6 × 10 9 and 6 × 10 10 protons cm - 2 . After each irradiation the detectors performance was accessed in terms of energy resolution, efficiency and activation. The detector was then annealed and the measurements repeated before the next irradiation. The minimum operational performance criteria were based on the resolution and efficiency requirements necessary to detect and separate specific radioisotope emission lines from a planetary regolith. Specifically that the energy resolution be restored to 5 keV FWHM at 1332 keV and the detection efficiency be degraded to no more than 10% of its pre-irradiation value. The key conclusion of this study is that even after a modest solar proton event the detector requires extensive annealing. After exposure to an event of integral fluence ∼ 8 × 10 8 protons cm - 2 this amounts to ∼ 1 week duration at 100 ∘ C , whereas for a fluence of ∼ 6 × 10 10 protons cm - 2 , the detector requires 3.5 months of annealing to satisfy the minimum operational performance requirements and 4.5 months to return the energy resolution to < 3 keV FWHM at 1332 keV. As a consequence such an instrument will require constant, planned and active management throughout its operational lifetime. The impact on spacecraft operations including resource management therefore needs careful consideration.

The applicability of MGA method for depleted and natural uranium isotopic analysis in the presence of actinides ( 232Th, 237Np, 233Pa and 241Am)

The multi-group analysis (MGA) method for the determination of uranium isotopic abundances in depleted uranium (DU) and natural uranium (NU) samples is applied in this study. A set of non-destructive γ-ray measurements of DU and NU samples were performed using a planar Ge detector. The relative abundances of 235U and 238U isotopes were compared with the declared values of the standards. The relative abundance for 235U obtained by MGA for a “clean” DU or NU sample with a content of uranium >1 wt% is determined with an accuracy of about ±5%. However, when several actinides such as 232Th, 237Np, 233Pa and 241Am are present along with uranium isotopes simulating “dirty” DU or NU, it has been observed that MGA method gives erroneous results. The 235U abundance results for the samples were 6–25 times higher than the declared values in the presence of above-mentioned actinides, since MGA is utilized the X-ray and γ-ray peaks in the 80–130 keV energy region, covering XK α and XK β regions. After the least-squares fitting of the spectra, it is found that the increases in the intensities of the X-ray and γ-ray peaks of uranium are remarkably larger in the complex 80–130 keV region. On the other hand, it is observed that the interferences of the actinide peaks are relatively less dominant in the higher γ-ray region of 130–300 keV. The results imply the need for dirty DU and NU samples that the MGA method should utilize the higher energy γ-rays (up to 1001 keV of 234mPa) combined with lower energies of the spectra, which may be collected in a two detector mode (a planar Ge and a high efficient coaxial Ge).

A γ-ray background model for Monte Carlo simulations

We present here a γ-ray background model for a typical urban environment. Such models are crucial for realistic evaluations of the sensitivity of nuclear detection systems. The model spectrum consists of a collection of lines and a continuum component. The details of the iterative approach used in the creation of the model are discussed. When the final model is used as the source spectrum emitted by the ground or the concrete walls surrounding a typical coaxial Ge detector, the simulated response of the detector matches the data observed in the field extremely well. The final emission spectrum is very precise, and contains features crucial in nuclear detection applications. The prominent 40K line (1460.8 keV) is clearly seen, as well as the 2615 keV peak due to Tl-208 (thorium natural decay series). The lines of 238U (1001.2 keV) and 235U (185.7 keV) are also present. We find this spectrum to be a useful tool for estimating sensitivities in our Monte Carlo modeling of several nuclear detector setups. We offer this model to the community for unlimited use, in the form of a Geant4 class or as a table of ‘intensity vs. energy’ for use with other Monte Carlo packages. We also note that the iterative procedure described here can be used for the creation of other background spectra.

機器中性子放射化分析法による認証鉄鋼標準物質中の微量元素の定量

Trace elements in certified iron and steel reference standard materials of NIST, SRM1763 and SRM1765 were determined by an instrumental neutron activation analysis (INAA). Three aliquot samples of each certified standard reference material (ca. 85-210 mg) were irradiated for 6 h at thermal power of 100 kW (thermal neutron flux of 4.3×1014 n m-2s-1) and at thermal power 3.5 MW (thermal neutron flux of 5.3×1017 n cm-2s-1) in JRR-4 (Japan Atomic energy Agency). The irradiated samples were measured by γ-ray spectrometry using a coaxial Ge detector. The concentration of 11 elements (Al, Ti, V, Cr, Mn, Co, Ni, Cu, As, Mo, Sb) in the SRM1763 and 9 elements in the SRM1765 were determined by INAA. The determined values were in good or nearly good agreement with the certified values and reference value.