High-purity Ge Research Articles

Absolute-scale measurement of compton backscattering in germanium at 105.3 keV

The differential cross section d 2σ/ dE d Ω was measured at an incident photon energy of 105.3 keV in germanium on absolute scale. The measurements were made using two high purity Ge detectors that operated in a coincidence mode. One detector served as the target and detector of ejected electrons, and another as the detector of Compton-scattered photons. It was found that fast (multiple) cascades have little influence on the data of the 105.3 keV crossover transition. An improved determination of the detector efficiency was made. The calculated values of the cross-section d 2σ/ dE d Ω using the impulse approximation (IA) with Hatree–Fock (HF) wave functions are in excellent agreement with the experimental cross-sections, while the IA with hydrogen like (HL) wave functions give fair agreement. A comparison of the calculated values of the cross-sections obtained with HF and HL wave functions for each subshell in germanium gives new values for effective charges, which improve agreement between the results of IA with HL and experimental values.

High Spin States in 70 Ge [Erratum: APH N.S., Heavy Ion Physics 11 (2000) 189

High spin states in70Ge nucleus have been studied in two different experiments using heavy ion fusion evaporation reaction. The Gamma Detector Array comprising of eight Compton-suppressed High Purity Ge detectors, was used in conjunction with a Recoil Mass Spectrometer — the HIRA — in order to identify and measure the transitions of this weakly populated nucleus. The level scheme is extended up to an excitation energy of13MeV for spin-parity 21- with several newly observed transitions placed in it. A rotational like band is also observed in this nucleus for the first time.

On the glass transition temperature and related parameters in the glassy Ge xSe 1− x system

High-purity Ge x Se 1− x amorphous samples of different composition (0.05⩽ x⩽0.30) were prepared. An empirical relation between the glass transition temperature ( T g) and the coordination number N c is proposed by modifying the Gibbs–Di Marzio equation for glass transition temperature of a cross-linked polymer as a function of cross-linked density. The utility of the Gibbs-Di Marzio relation was achieved by estimating T g theoretically. The T g results were also compared with an arbitrary defined optical gap ( E o) where T g provided an index of atomic mobility, and E o an index of covalent bond strength. From the previous calculations the T g– E o correlation is interpreted in terms of a proposed fluidity equation for covalent liquids with 2.1⩽ N c⩽2.7. The relationship between E o and the chemical composition in the vacuum prepared Ge x Se 1− x is discussed in terms of the average heat of atomization ( H s) and the average coordination number ( N c). The effect of both the chemical composition and the nature of the chemical bonding on the efficiency of the structural modification (Δ Φ) of the Ge x Se 1− x system is also analyzed.

NIF total neutron yield diagnostic

We have designed a total neutron yield diagnostic for the National Ignition Facility (NIF) which is based on the activation of In and Cu samples. The particular approach that we have chosen is one in which we calibrate the entire counting system and which we call the “F factor” method. In this method, In and/or Cu samples are exposed to known sources of DD and DT neutrons. The activated samples are then counted with an appropriate system: a high purity Ge detector for In and a NaI coincidence system for Cu. We can then calculate a calibration factor, which relates measured activity to total neutron yield. The advantage of this approach is that specific knowledge of such quantities as cross sections and detector efficiencies is not needed. Unless the actual scattering environment of the NIF can be mocked up in the calibration experiment, the F factor will have to be modified using the results of a numerical simulation of the NIF scattering environment. In this article, the calibration factor methodology will be discussed and experimental results for the calibration factors will be presented. Total NIF neutron yields of 109–1019 can be measured with this method assuming a 50 cm stand-off distance can be employed for the lower yields.

Decay of 1.643-hr 95Ru to 95Tc

The decay of 95Ru has been investigated by means of γ-ray spectroscopy. The 95Ru nuclei were produced by the reaction 92Mo(α,n)95Ru at the beam energy of 17 MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of 95Ru to 95Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of 95Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated logft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus 95Tc.

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.

Determination of 75Se, 95Zr, 237Np and 241Am activities in Boom Clay samples from laboratory migration experiments using γ-ray spectrometry

Percolation tests (i.e. routine laboratory migration experiments) have been performed to evaluate the diffusion behaviour of a number of long-lived radionuclides in Boom Clay, a candidate geological host formation for high level radioactive waste (HLW) in Belgium. Among the many potentially hazardous radionuclides under investigation are 79Se, 93Zr, 237Np, 241Am and 243Am. Actinide migration experiments have been carried out with 237Np and 241Am, while for the studies with Se and Zr the radioisotopes 75Se and 95Zr were used. Their transport patterns in the Boom Clay were examined using a combination of a NaI(Tl) detector and High-Purity Ge detectors either on the dissolved matrix (237Np, 241Am) or directly on the clay (75Se, 95Zr).

Measurement of Induced Radioactivity in Copper Exposed to High Energy Heavy Ion Beam

The residual radioactivities produced by high energy heavy ions have been measured using the 290MeV/u and 400MeV/u 12C ions and 400MeV/u 20Ne ion beams of the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences. During the irradiation experiment, the beam intensities were measured with a transmission-type ionization chamber. We used the natural copper target of 100mm x 100mm size and 5mm thickness which had total thickness of 3.5cm, 5.5cm and 10cm to stop the projectile heavy ion beams, 290 and 400MeV/u-C ion beams and 400MeV/u-Ne ion beam, respectively. Additional activation foils of copper, aluminum, iron and stainless steel were inserted at every 5mm to 20mm interval in the copper target to measure the spatial distribution of residual nuclei in the copper target. The spatial distribution of residual nuclei was obtained by measuring the gamma-ray activities of 0.5mm thick copper, aluminum, iron and stainless steel foils inserted in the target with a high purity Ge detector after about lhr to 6 hrs irradiation. From the irradiation experiments, we identified the residual nuclei induced in these activation foils and obtained the spatial distributions of 61Cu, 60Cu, 62mCo, 61Co, 56Mn, 49Cr, 44Sc and 38Cl in the copper target.

Systematic Comparisons of Measurements and EGS4 Regarding 20-40 keV Photons

To investigate the validity of the EGS4 code regarding photon transport in the keV region, we performed systematic comparisons of measurements and EGS4. The scattered-energy spectra of monochronized synchrotron-radiation photons toward 90° by samples (C, Cu, Pb) were measured using high-purity Ge detectors. The incident photons were in a linearly polarized beam of 20, 30 and 40 keV. EGS4 calculations were performed in default status and with improvements of low-energy photon transport (linearly polarized photon scattering, Doppler broadening, L-X and K-X). The measurement and calculations were compared in absolute values. Both the intensity and the shape of the peaks were compared. EGS4 calculations with improvements in low-energy photon transport agreed well with the measurements.

Radiation Dose Estimation from the Analysis of Radionuclides in Marine Fish of the Bay of Bengal

The concentrations of some natural radionuclides and fallout radionuclides in fifteen species of marine fish samples from the Bay of Bengal were determined using a p-type coaxial high purity Ge detector with 23% relative efficiency. In some body parts of the fish samples contamination by 137Cs radionuclide was observed, 134Cs was below detection level of 0.07 Bq.kg-1. The 137Cs concentrations in fish samples varied from 0.04 ± 0.03 to 1.50 ± 0.33 Bq.kg-1. The potassium concentration was calculated from the observed 40K activity concentration: these values ranged from 0.54 to 2.6 g.kg-1. 226Ra and 228Ra concentrations of 0.10 to 1.66 Bq.kg-1 and 0.39 to 1.35 Bq.kg-1 were found, respectively. The annual effective doses due to ingestion of radionuclides from fish have been estimated to be 0.36 µSv for the natural 226Ra and 228Ra isotopes and only 3.5 nSv (0.0035 µSv) for the fallout radionuclide 137Cs. The contribution of 137Cs amounts to less than 2% of the effective dose caused by the naturally occurring 40K.

Deep defects in n-type high-purity germanium: quantification of optical variants of deep level transient spectroscopy

The characterization of high-purity (HP) Ge for the fabrication of γ-ray detectors poses very specific demands due to the high degree of purity of the material (shallow concentration of the order 109–1010cm−3). Deep level transient spectroscopy (DLTS) may still be applied to this kind of material since the sensitivity is relative to the shallow doping concentration. In contrast with p-type HP Ge which was characterized extensively in the 1980s, very little is known about deep defects in n-type HP Ge. Two optical variants of DLTS have been applied to n-type HP Ge and quantified for the first time. Several deep minority carrier traps are detected and identified as mainly Cu-related traps with concentrations in the 106–108cm−3 range. These Cu-related traps, which are well known as the majority carrier traps appearing in typical p-type HP Ge, are thus present as minority carrier traps in typical n-type HP Ge. The conclusion that deep-level defects in n- and p-type HP Ge are very similar could be expected from the similarity in growing conditions for the two types of materials. In the first DLTS variant, known as optical DLTS or ODLTS the deep levels are filled by optical injection (with light of above bandgap energy) at the back ohmic contact of a reverse biased diode. The spectrum is generated by the capacitance transients following the optical excitation. In the second variant, known as photo induced (Current) transient spectroscopy or PI(C)TS the deep levels are also filled optically with intrinsic light, but here a neutral structure is used with two ohmic contacts in sandwich configuration. The spectrum is generated by current transients instead of capacitance transients. This method is especially suited for high-resistivity or semi-insulating materials which cannot be measured with capacitance-based DLTS. PICTS was applied to n-type Ge with a shallow concentration as low as 109cm−3.

Concentrations of [formula omitted], [formula omitted] and [formula omitted] in surface sea water of the Bay of Bengal

Concentrations of 222 Rn , 226 Ra and 228 Ra in surface sea water of the Karnaphuli river estuary, near-shore and off-shore regions of the Bay of Bengal were measured using a p-type coaxial high purity Ge detector along with in situ measurement of air and water temperature, salinity, pH and tides of the water. The activities of 226 Ra and 228 Ra were in a range of 5.4±2.4–29.0±8.3 mBq l −1 and 3.0±2.0–7.6±3.7 mBq l −1, respectively. These values are compared with concentrations reported for other countries of the world.

Measurement of the Effective Neutron Capture Cross Section of Cesium-134 by Triple Neutron Capture Reaction Method

The measurement of effective neutron capture cross section() of 134Cs was carried out with a method using a triple neutron capture reaction,133Cs(n, γ)134Cs(n,γ)135Cs(n, γ)136Cs. The target used for the experiment was natural cesium(133Cs), and was irradiated for 23 days and 17 hours in the reactor JRR-3 at Japan Atomic Energy Research fnstitute(JAERI). The neutron field of the reactor was monitored by Au/Al and Co/Al alloy wires. A high purity Ge detector was employed for the measurement of γ-rays from the irradiated target and monitor wires. Gamma-rays emitted in the decay of 134Cs and 136Cs nuclides induced by single and triple neutron capture reactions of 133Cs were seen at the energies of 563, 569. 605, 796, 802, 819, 1,039, 1,048, 1,168 and 1,235 keV. Decays of the 819 and the 1,048 keV γ-ray intensities were followed; it was confirmed that these γ-rays originated in the 136Ba, the decay product of 136Cs. Data obtained were analyzed with values of neutron capture cross sections of 133Cs and 135Cs. The of 134Cs obtained is 140.6±8.5 barns and agrees with the value measured by Bayly et al.with a mass analysis method within the limits of error.

Vacancies and interstitial atoms in e−-irradiated germanium

High purity Ge wafers have been irradiated at low temperatures with MeV electrons and have subsequently been investigated by x-ray diffraction methods. The intensity of the Huang diffuse scattering shows that a high concentration of defects (>1019 cm−3) can be frozen in at 4 K. A large fraction of the defects is stabilized in the form of close Frenkel pairs which are characterized by the nearly perfect cancellation of the long range displacement fields of the interstitial atom and the vacancy. We discuss the absolute size of these displacements as well as the introduction rate of the defects, which is of the order of ∑=3 cm−1. The high defect introduction rates are at variance to the results of electrical and optical investigations and indicate that these methods detect only a few percent of the total defect concentration which is produced and frozen in at 4 K. The consequences for the understanding of the defect production in Ge and for the assumption of an athermal migration of interstitial atoms are discussed in close relation to similar results for Si. In addition, we discuss the differences between the defect patterns observed after 4 K irradiation to those observed after room-temperature irradiations and the thermally activated defect reactions up to the final annealing at 600 K.

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the Reaction 127I(n, γ)128I

The thermal neutron (2,200 m/s neutron) capture cross section (σ0) and the resonance integral (I 0) of the reaction 127I(n, γ)128I were obtained. The targets of the iodine were irradiated within and without a cadmium capsule at Rikkyo University Research Reactor. Characteristic features of neutron field were monitored by Co/Al and Au/Al wires. Gamma-rays from the irradiated targets were measured by a high purity Ge detector. The γ-ray spectra were taken successively and the decay of peak-area counts of the 443 keV γ-ray of 128I was followed. A half-life of 128I obtained was 24.72±0.03 min. The σ0 and I 0 of the reaction 127I(n, γ)128I were deduced from the analysis of obtained γ-ray spectra according to the Westcott's convention and were 6.40±0.29 barns and 162±8 barns, respectively. The previous measurements of the σ0 and I 0 of the reaction 127I(n, γ)128I were reviewed and differences between the present values and the previous results were discussed with special emphasis on the experimental results by Friedmann et al., whose experiment was the same as the present simultaneous measurement of the σ0 and I 0.

Accelerated Emission of Gamma Rays from the 31-yr Isomer of178HfInduced by X-Ray Irradiation

A sample of $6.3\ifmmode\times\else\texttimes\fi{}{10}^{14}$ nuclei of the 4-quasiparticle isomer of ${}^{178}\mathrm{Hf}$ having a half-life of 31 yr and excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device typically used in dental medicine. It was operated at 15 mA to produce bremsstrahlung radiation with an end point energy set to be 70 or 90 keV. Spectra of the isomeric target were taken with a high purity Ge detector. Intensities of selected transitions in the normal decay cascade of the ${}^{178}\mathrm{Hf}$ isomer were found to increase by about $4%$. Such an accelerated decay is consistent with an integrated cross section of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\mathrm{cm}{}^{2}\mathrm{keV}$ for the resonant absorption of x rays to induce gamma decay.

Gamma-ray spectrometer for Japanese lunar polar orbiter

We review the current status of the development of Gamma-Ray Spectrometer (GRS) for the Lunar mission SELENE. The GRS instrument will measure gamma-rays in the energy range from 100 keV to 9 MeV. The instrument is a high-purity Ge detector surrounded by BGO and plastic scintillators which are operated as an anticoincidence shield, and is cooled by a Stirling cycle cryocooler. The primary objective is to provide global maps of the lunar composition. Measurements are anticipated for Fe, Ti, U, Th, K, Si, Mg, Al, O, Ca and Na over the entire lunar surface. The abundance of water ice in the permanently shaded craters at both the lunar poles will be measured with this instrument.

Status of the EDELWEISS experiment

The status of the EDELWEISS experiment, installed in the Fréjus tunnel, is presented. In its first stage, the experiment uses a 70 g high purity Ge bolometer with heat-ionization discrimination. Based on physics data, gamma and neutron calibrations, the influence of inverse bias voltage (−2 and −6 V) on incomplete surface charge collection, which limits at present the performances of these detectors, is presented. Analysing runs with a total exposure of 1.17 kg×day after cuts, an upper limit of 0.6 event day kg keV at 90% confidence level in the 12–70 keV recoil energy interval is obtained. Planned upgrades are summarized.

Compositional trends of the compactness in ternary chalcogenide glasses of the Ge–In–Se system

Chalcogenide glasses, from the Ge x In y Se 100− x− y system with y=6 and 12 at%, have been prepared from high purity Ge, In and Se. The compactness, δ, of the structure of the glasses is determined from the measured densities of the glasses. The peculiarities observed in the δ-composition dependence are interpreted by using the ordered bond network model and the topological models proposed to describe the atomic arrangements in these solids.

Half-life measurements of Europium radionuclides and the long-term stability of detectors

Consideration of the long-term stability of detectors has proved to be very important in half-life measurements. For example, studies of a 226Ra reference source with a pressurised 4 πγ ionization chamber for stability checks showed an average decrease in efficiency of 0.005% per year. Taking this effect into account, half-lives of T 1/2( 152Eu)=4936.6(20) d and T 1/2( 154Eu)=3138.1(16) d were determined. Using the half-life value of 152Eu as a reference, the time-dependent decrease of the efficiency of semiconductor detectors at different photon energies was determined for periods of the order of twenty years. Values decreased by an average of less than 0.01% per year for a high-purity Ge detector, by about 0.03% per year for a Ge(Li) detector and by about 0.07% per year for a Si(Li) detector. Half-life values of T 1/2( 154Eu)=3146(11) d and T 1/2( 155Eu)=1739(8) d were determined. The uncertainty of the 155Eu half-life value was reduced by a factor of three in comparison to an earlier PTB measurement to which this correction had not been applied.