Ge Gamma-ray Detectors Research Articles

Investigation of 252Cf sources with a Ge gamma-ray detector.

This study investigated the feasibility of combining high-resolution gamma-ray spectroscopy with the simulation capabilities of the Nucleonica Nuclear Science Portal with the aim to determine the properties of Cf sources. In this contribution, we present the results for a 20-month-old and a 49-year-old Cf source. In particular, the question arises whether the neutron emission rate can be determined using gamma-ray spectroscopy.

Internal dosimetry of 210Pb in the human cranium: preliminary results from instrumentation needs for in vivo counting in a low-background underground counting facility

Internal dosimetry of (210)Pb in the cranium deals with the determination of the amount of energy deposited in tissue by (210)Pb radiations within the cranium. (210)Pb in the human cranium was monitored by in vivo counting in a low background facility 640 m (2100 ft) underground with a germanium (Ge) gamma-ray detector having a beryllium window. The minimum detectable activity (MDA) was established with this system to be 0.2 Bq (5 pCi) in 25-h counting time with a 15-mm diameter and 7-mm thick Ge detector, having a beryllium window of thickness of 0.08 mm, in contact with the cranium just above the ear adjacent to the temple region. To establish an MDA of 0.004 Bq (0.1 pCi) with this system, the limitation arising from the ambient radon level at 10 Bq m(-3) was investigated.

Computational models of germanium point contact detectors

Abstract In the crystal bulk of group IV covalent semiconductors such as germanium (Ge), simple analytic models for the valence band structure can provide fast, accurate computations of hole mobility for moderate energy ranges up to a few eV. On the surfaces of these materials, such as on Ge-vacuum or Ge–GeO2 interfaces, the transport rates differ significantly from the bulk. This can be problematic for both point contact and segmented Ge gamma ray detectors, that require accurate carrier drift rates for computing signal basis sets, which themselves are necessary for the precise determination of gamma-ray induced compton scattering events. While several techniques exist for computing surface hole mobilities, more often than not, these methods are complex to implement, require significant computational resources, and lack the simplicity of bulk models for interpreting results. This paper presents a new technique for computing Ge surface hole mobility that can give a first estimate for the surface transport rates after tuning a physically based computational parameter. This model is used in conjunction with particle-in-cell (PIC) simulations for modeling hole-dynamics inside a Ge p-type point contact detector. The results of our calculations agree with experimental data gathered from Ge p-type point contact detectors at Oak Ridge National Laboratory.

Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors

The effects of prolonged annealing at elevated temperatures have been investigated in a 53cm3 closed-end coaxial high purity germanium detector in the reverse electrode configuration. The detector was multiply annealed at 100°C in block periods of 7 days. After each anneal cycle it was cooled to 77 K and the relative efficiency, peak channel location and FWHM energy resolution measured at 6 gamma-ray energies. At the present time, the detector has completed 16 anneal cycles. It was found that above ∼ 662 keV the photopeak efficiency decreased almost linearly at a rate of ∼ 1.5% per anneal cycle, although the energy resolution and centroid (and therefore charge collection efficiency) remained unchanged. The change in detection efficiency is attributed to the expansion of the inner n+ contact due to the thermal drive-in of Li ions into the bulk. The rate is found to follow a power-law dependence in agreement with that expected from Fick's diffusion laws. Using these data, we have derived a simple 1-D phenomenological model in which the n+ contact thickness is simply related to the Li diffusion length. For annealing at 100°C, the thickness of the n+ contact, d, as a function of the annealing time, t, can be described semi-empirically by d(mm) = 0.231 × t(days)1/2.

Spline and polynomial models of the efficiency function for Ge gamma-ray detectors in a wide energy range

In one of our recent papers, the applicability of linear parameter functions for fitting the full-energy peak efficiency of n-type Ge gamma-ray detectors has been examined over a wide energy range of 50-8500 keV. In that paper we compared six different analytical functions and showed that higher-order polynomial functions on a log-log scale gave the best performance. However, there is a drawback to using the log-log scale when an additive function of efficiency at different energies or of the inverse efficiency has to be used in a fitting procedure. In the present study, the applicability of higher-order polynomial and spline functions to linear and inverse efficiency, but logarithmic energy scales, is examined.

Comparison of NAA and ICP-MS for the determination of major and trace elements in environmental sample

Major and trace elements in soil and plant samples, including standard reference materials were determined by means of neutron activation analysis (NAA) and inductively coupled plasma-mass spectrometry (ICP-MS). The analytical procedure for NAA utilized dried powder samples. The concentration of iodine in soil samples was determined by radiochemical NAA. The irradiated samples were cooled and then counted with a Ge gamma-ray detector connected to a multi-channel analyzer. For ICP-MS analysis, the samples were decomposed by microwave digestion with an acid mixture. The concentration of I in the soil samples was measured by ICP-MS after separation by ignition. The analytical values for most elements in the environmental samples by both methods were in good agreement, whereas sample treatments were different. Measured value of Zr in the soil samples by ICP-MS was about 50% lower than that by NAA. It should be assumed that some minerals of Zr in soil particles were not entirely dissolved by the acid mixture. Analytical results of Cd for three different Cd levels in unpolished rice flour samples (NIES 10-a, b and c) determined by ICP-MS were in agreement with certified values. The concentration of Cd in the sample with the lowest Cd level, as determined by NAA with 57% counting error, was 3 times higher than the certified value.

Performance comparison of a new approach to nuclear spectral analysis with commercial codes

The performance of a new approach to nuclear spectral analysis was compared with two widely accepted commercial codes. The comparison measured the new approach's ability to determine the presence and activity of multiple nuclides in spectra dominated by natural background. The new approach is implemented in the spectral analysis software, RobWin/sup TM/. Ten calibration sources ranging in activity from 25 to 450 kBq were placed 20.5 meters from a bare, 100% relative-efficient high purity Ge gamma-ray detector, thus assuring dominance of the natural background radiation over the test nuclides. Accumulated spectra were recorded at ever-doubling time intervals from 225 seconds to 128 hours. All spectra were analyzed by each code according to a defined procedure designed to achieve the best results from the comparator codes. The results from all codes were in general agreement for most nuclides where acquisition times were long, but RobWin's performance was significantly superior for short counting times.

High accuracy measurement of the relative efficiency curve and determination of gamma-ray relative intensity for 38Cl

Relative efficiency curves were accurately determined for Ge gamma-ray detectors from measurements for radionuclides which emit two gamma-rays with essentially the same emission probabilities. The relative intensity of the 1643 and 2167 keV gamma-rays from 38Cl was determined to be 0.7496 (11) by using these highly accurate efficiency curves.

Comparison of efficiency functions for Ge gamma-ray detectors in a wide energy range

The applicability of linear parameter functions for fitting the full-energy peak efficiency of Ge gamma-ray detectors has been examined in a wide energy range of 50–8500 keV, typical for prompt gamma activation analysis, by using efficiency data measured with the Budapest capture gamma-ray spectrometer. In a least-squares fitting procedure involving correlation and singular value decomposition the performance of six different analytical functions has been compared. It turns out that a high-order polynomial function on a log–log scale gives the best performance if a proper fitting procedure is used, as in the program Hypermet-PC.

Low level gamma-spectrometry by beta coincidence

Backgrounds of gamma-ray detectors can be drastically reduced using a gas flow proportional beta counter in coincidence. The NaI(Tl) and Ge(Li) gamma-ray detectors were non-selected, usually shielded. The beta efficiencies of the samples must be high, reproducible and measurable which is the main difficulty of the method. However for small mass samples such as residues from evaporated liquids, ashes from incinerated organic samples, samples used in neutron activation analysis, the method can be used advantageously.

Natural radioactivity mapping of Greek surface soils

A total of 1440 samples of soil, collected across Greece from the 1 cm surface layer, were analysed for natural radioactivity ( 226Ra, 232Th, and 40K). The samples were air-dried and then hermetically sealed in 0.282 L plastic boxes covered with a film of epoxy resin to ensure that no gases escaped from them. Secular equilibrium of 226Ra and 232Th with their decay products was obtained before the samples were analysed using high resolution Ge gamma-ray detectors. A Unix-based in-house built complex Data Base/Geographical Information System (DBGIS) was used to analyze the data and present them in map form. The analysis of a second 1 cm thick sample, collected at several sites at a depth of 10 cm, led to the statistically justified conclusion that the natural radioactivity content of the surface and of 10 cm deep soil layers do not significantly differ. According to these results, the natural radioactivity content of Greek surface soils is rather low and is for 226Ra: 25 ± 19 Bqkg −1, for 228Ra: 21 ± 16 Bqkg −1, and for 40K: 355 ± 220 Bqkg −1. They entail a gamma-ray dose rate outdoors of 40 nGyh −1. A statistical analysis showed that only 90 samples, collected at 67 locations, have 226Ra content exceeding their mean value by more than 1.65σ. The 226 Ra 232 Th and 226 Ra 40 K concentration ratios were 1.10 ± 0.48 and 0.06 ± 0.03, respectively.

Study of the beta-delayed alpha-particle emission ofN16

The beta-delayed alpha-particle emission of $^{16}\mathrm{N}$ has been studied, with $^{16}\mathrm{N}$ nuclei produced using 80 MeV/nucleon $^{18}\mathrm{O}$ beams on $^{9}\mathrm{Be}$ targets. The $^{16}\mathrm{N}$ secondary nuclei were mass analyzed and separated from the reaction products using the Michigan State University A1200 isotope separator. A detector array, including four thin surface barrier detectors, a p-i-n diode, a Ge gamma-ray detector, and a two-dimensional position sensitive parallel plate avalanche counter, was used for implantation and study of the separated nuclei. A beta-decay branching ratio of (1.3\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ to the ${1}^{\mathrm{\ensuremath{-}}}$ state at 9.6 MeV and a centroid of 2.35\ifmmode\pm\else\textpm\fi{}0.05 MeV for the beta-delayed alpha-particle emission were measured. These results are essential for the analysis of a high sensitivity measurement at Yale University of the low-energy beta-delayed alpha-particle emission of $^{16}\mathrm{N}$, and for understanding the $^{12}\mathrm{C}$(\ensuremath{\alpha},\ensuremath{\gamma}${)}^{16}$O reaction in the helium burning process in massive stars.

Absolute calibration of a total yield indium activation detector for DD and DT neutrons

Progress in Z-pinch experiments at Sandia’s Saturn facility have underscored a need for an absolute yield measurement for DD fusion neutrons. The technique chosen for making this absolute yield measurement was neutron activation of indium metal samples. To calibrate the technique, a 175-keV deuteron beam was allowed to impinge on a 3.0-μm-thick erbium deuteride target, producing neutrons through the 2H(d,n)3He fusion reaction. The neutron flux produced at 0° and incident on nominal 5-g indium samples was determined by the associated particle method. This method employed protons measured from the 2H(d,p)3H reaction to infer the neutron flux produced. After neutron irradiation, the activity of the indium samples was measured with a Ge gamma-ray detector. The total activity of the metastable state 115mIn (336.23 keV) was measured, compared with the total incident flux, and a calibration factor (indium counts/neutron/gram of indium) determined. For completeness, a calibration factor for DT neutrons from the 3H(d,n)4He fusion reaction was also obtained through the measured activity of the metastable state 114mIn(190.29 keV). The experiment and the measured calibration factors for both reactions are described in the paper.

Level structures of 119Te and 121Te populated in the decay of 119I and 121I.

The structures of the odd-neutron nuclides $^{119,121}\mathrm{Te}$ have been investigated following beta decay of $^{119,121}\mathrm{I}$. Gamma-ray and conversion-electron singles and coincidence measurements have been performed on mass separated sources using Ge gamma-ray detectors and Si(Li) electron detectors and a mini-orange positron filter. New levels and branching ratios have been determined for both nuclides. E0 components have been identified on M1 and M1/E2 transitions in $^{119}\mathrm{Te}$ and interpreted as arising from coupling of particle-hole intruder states with the odd neutron.

A search for neutrons, protons, tritons, 3He ions, gamma- and x-rays from deuterium-deuterium nuclear reaction in electrochemically charged palladium

A search for neutrons, protons, tritons, 3 He ions, γ- and X-rays emitted from D + D fusion in a Pd tube charged electrochemically with deuterium was carried out with a radiation detection system using mainly passive detectors. The system was composed of: (i) an array of six 3 He neutron detectors (total efficiency 0.14%); (ii) a bubble damage polymer neutron detector (1.2 × 10 −4 %); (iii) CR-39/BN-1 neutron detector/radiator (3.2 × 10 −4 %); (iv) CR-39/polyethylene neutron detector/radiator (8.5 × 10 −3 %); (v) CR-39 proton detector (0.17%); (vi) a Ge gamma-ray detector (2.1 × 10 −3 %); (vii) a CaF 2 thermoluminescent detector (8.9 × 10 −3 %). It is shown that the advantage of passive detectors (track-etch, bubble damage) is their ability to integrate fluxes during long exposure without an appreciable increase in the background. The lowest detectable fusion rate in a similar but longer experiment was estimated to be near 10 −25 fusions per DD pair s −1 . Using these detectors we found that the rate of “cold fusion” is < 1.1 × 10 −23 (DDp) fusions per DD pair s −1 and <2.3 × 10 −22 (DDn) fusions per DD pair s −1 .

Calibration of a portable intrinsic Ge gamma-ray detector using point sources and testing for field applications.

A simple procedure using point sources is described for the calibration of portable high-resolution gamma-ray detectors used in field surveys. The point source data are fitted by empirical equations that are used to calculate efficiency for field applications. Two models for the distribution of radionuclides are treated: a thin surface-film model and a vertically homogeneous model. The success of the procedure has been demonstrated by field applications in plots where the levels of contamination are known.

Measurement of pair production cross sections in Ge for the 1.238-3.548 MeV energy range

Pair production cross sections have been determined for the 1.238-3.548 MeV energy range in germanium (Z=32) using a Ge(Li) gamma ray detector. The experimental results have been compared with the theoretical cross sections of Bethe and Heitler (1934), Tseng and Pratt (1981) and Overbo (1970) and experimental results of En'yo et al. (1980). The results of the present measurements agree with the Bethe-Heitler results down to 1.771 MeV. However, at 1.238 MeV the experimental results are higher than all the theories.

Experimental determination of absolute efficiency and energy resolution for NaI(Tl) and germanium gamma ray detectors at energies from 2.6 to 16.1 MeV

Measurements have been made to characterize the response of NaI(Tl) and Ge(Li) gamma ray detectors to gamma rays in the energy range of 2.6 to 16.1 MeV. Both absolute efficiency and energy resolution are reported. At 16.1 MeV the absolute full energy efficiency of a 10 cm × 10 cm NaI(Tl) detector is about 2% and the energy resolution is also about 2%. For a 65 cm 3 Ge(Li) detector, the full energy peak absolute efficiency at 16.1 MeV is 0.2% (the escape peak efficiencies are 5 times larger), and the fwhm energy resolution is about 0.1%.

Blood volume measurement of newborn using stable isotope 50Cr

A technique for the blood volume measurement of newborns was established in which nonradioactive 50Cr was used in patients for whom radioactive labels were not advisable. The red blood cells (RBC) in the newborn's blood withdrawn from umbilical cord after birth were tagged with enriched stable isotope 50Cr (96%, normal abundance 4.3%) and reinjected into the newborn. Blood samples (0.5 ml) were withdrawn at 30 min and thereafter at 6, 12, 24, 48, 72 and 120 hours old. Samples were centrifugalized and portion of RBC was then freeze-dried, weighed and sealed into polyethylene sheet bag together with 50Cr standard. Neutron irradiation was performed in the reactors of the JAERI with thermal neutron flux 5 X 10(13), 2 X 10(13), 8 X 10(13) cm-2s-1 at JRR-2, -3 and -4 respectively for 20 min and samples were left for about two weeks after irradiation. Induced radioactivity (51Cr, 59Fe) of the sample was measured with a Ge(Li) gamma-ray detector system and 4096 channels pulse height analyzer. Analysis of activity data was carried out by BOB-76 code. The RBC and total blood volume of the newborn was calculated using an isotopic dilution technique. We have investigated on tagging efficiency of 50Cr to RBC, washing effect and dilution rate by 50Cr content or 51Cr/59Fe ratio. Significant difference was observed in the total blood volume of newborns depending on the delivery style and in addition, it changed dynamically along the time elapsed after birth.

Evaluation of Compton contamination events in an actively shielded Ge gamma-ray detector

An expression has been developed which gives the flux of unvetoed Compton-contamination events for a particular source measurement using an actively shielded gamma-ray telescope. By use of suitable approximations, this expression reduces to simpler functions which have been evaluated for some recent measurements of the Crab nebula. It has been shown that for the exposures typical of balloon-borne observations, and a reasonably efficient anti-coincidence system (>50%), the non-photopeak component of the detected source energy-loss spectrum can be neglected.