High-purity Ge Research Articles

γ-ray production by proton and α-particle induced reactions onC12,O16,Mg24, and Fe

{gamma}-ray production cross sections for proton and {alpha}-particle interactions with {sup 12}C, {sup 16}O, {sup 24}Mg, and Fe have been measured in the energy range 5-25 MeV with proton beams and 5-40 MeV with {alpha}-particle beams. Isotopically pure foils of {sup 24}Mg and foils of natural isotopical composition of C, MgO, and Fe have been used. {gamma}-ray angular distributions were obtained with five high-purity Ge detectors with bismuth germanate Compton shields placed at angles of 45 deg. to 157.5 deg. Cross sections for more than 50 different {gamma}-ray transitions were extracted, and for many of them no data have been published before. Comparison of present data with data available in the literature shows mostly good to excellent agreement. In addition to the production cross sections, high-statistics, low-background line shapes of the 4.438 MeV {sup 12}C {gamma} ray from inelastic scattering off {sup 12}C and spallation of {sup 16}O were obtained. Comparison with nuclear reaction calculations shows that these data place interesting constraints on nuclear reaction models.

Near and mid-infrared luminescence of new chalcohalide glasses doped with Pr 3+ ions

Chalcohalide glasses of the system 100 − y((GeS 2) 80(Sb 2S 3) 20− x (PbHal 2) x )· yPr 2S 3, where Hal is I or Cl, x = 2 or 5, y = 0.01 or 0.1, were prepared by direct synthesis from high purity Ge, Sb, S, Pr and PbCl 2 or PbI 2. The prepared glasses were stable and homogeneous. Absorption spectra were measured in the interval from 500 nm to 2.5 μm. Room temperature luminescence was observed in the near and middle infrared regions with maxima at ∼1.3, ∼1.6, ∼2.2, ∼2.4, ∼4 and ∼5 μm. The luminescence bands were ascribed to f–f electron transitions in Pr 3+ ions.

Luminescence dating of a geological sample from Denizli, Turkey

Recent advances in luminescence dating have led to increasing application of the optically stimulated luminescence (OSL) technique to investigate the sedimentation of the depositional environmental samples. In this study, a geological sample was dated by using OSL technique. The sample was collected from a main fault line located in Denizli, Turkey. It was prepared using the fine grain method. The optimum preheat temperature of 205 °C and duration value of 3 min are determined through a sequence of experiments. For the calculation of the age of the samples the equivalent dose (ED) was measured using both the multiple-aliquot and single-aliquot techniques. The annual dose (AD) was obtained by measuring the concentration of the major radioactive isotopes in the samples by using a high purity Ge detector. The age of the sample was found to be between 5490±300 years and 6000±320 years.

Decay of 1.643 h 95Ru and its daughter's level structure

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 a beam energy of 17MeV. 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 log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus 95Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of 95Tc is discussed in the framework of the projected shell model.

Detection of explosive substances by tomographic inspection using neutron and gamma-ray spectroscopy

In recent years the detection and identification of hazardous materials has become increasingly important. This work discusses research and development of a technique which is capable of detecting and imaging hidden explosives. It is proposed to utilise neutron interrogation of the substances under investigation facilitating the detection of emitted gamma radiation and scattered neutrons. Pulsed fast neutron techniques are attractive because they can be used to determine the concentrations of the light elements (hydrogen, carbon, nitrogen, and oxygen) which can be the primary components of explosive materials. Using segmented High Purity Ge (HPGe) detectors and digital pulse processing [R.J. Cooper, G. Turk, A.J. Boston, H.C. Boston, J.R. Cresswell, A.R. Mather, P.J. Nolan, C.J. Hall, I. Lazarus, J. Simpson, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 7th International Conference on Position Sensitive Detectors, Nuclear Instruments and Methods A, in press; I. Lazarus, D.E. Appelbe, A. J. Boston, P.J. Coleman-Smith, J.R. Cresswell, M. Descovich, S.A.A. Gros, M. Lauer, J. Norman, C.J. Pearson, V.F.E. Pucknell, J.A. Sampson, G. Turk, J.J. Valiente-Dobón, IEEE Trans. Nucl. Sci., 51 (2004) 1353; R.J. Cooper, A.J. Boston, H.C. Boston, J.R. Cresswell, A.N. Grint, A.R. Mather, P.J. Nolan, D.P. Scraggs, G. Turk, C.J. Hall, I. Lazarus, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 11th International Symposium on Radiation Measurements and Application, 2006. [1–3]] the scatter path of incident photons can be reconstructed to determine the origin of the gamma-rays without the need for mechanical collimation by applying the Compton camera principle [V. Schonfelder, A. Hirner, K. Schneider, Nucl. Instr. and Meth. 107 (1973) 385; R.W. Todd, J.M. Nightingale, D.B. Everett, Nature 251 (1974) 132. [4,5]]. In addition, it is proposed to utilise the scattered neutrons which recoil from the materials being assayed, detecting them with a fast neutron detector providing data for inversion to tomographic images.In this paper, we present our approach to the design and implementation of a system for the efficient screening of goods in luggage and cargo containers. The simulation in a Monte Carlo framework using GEANT4 has been carried out for the imaging of gamma-ray events using the Compton camera design which will be discussed. The results of Compton camera measurements using HPGe detectors and the subsequent reconstructed images will also be presented.

Clock and trigger synchronization between several chassis of digital data acquisition modules

In applications with segmented high purity Ge detectors or other detector arrays with tens or hundreds of channels, the high development cost and limited flexibility of application specific integrated circuits outweigh their benefits of low power and small size. The readout electronics typically consist of multi-channel data acquisition modules in a common chassis for power, clock and trigger distribution, and data readout. As arrays become larger and reach several hundred channels, the readout electronics have to be divided over several chassis, but still must maintain precise synchronization of clocks and trigger signals across all channels. This division becomes necessary not only because of limits given by the instrumentation standards on module size and chassis slot numbers, but also because data readout times increase when more modules share the same data bus and because power requirements approach the limits of readily available power supplies. In this paper, we present a method for distributing clocks and triggers between 4 PXI chassis containing DGF Pixie-16 modules with up to 226 acquisition channels per chassis. The data acquisition system is intended to instrument the over 600 channels of the SeGA detector array at the National Superconducting Cyclotron Laboratory. Our solution is designed to achieve synchronous acquisition of detector waveforms from all channels with a jitter of less than 1ns, and can be extended to a larger number of chassis if desired.

Safer alternative liquid germanium precursors for relaxed graded SiGe layers and strained silicon by MOVPE

Commercial strategy to graded SiGe buffer layers and “strained silicon” involves passing germane (GeH 4) gas or germanium tetrachloride (GeCl 4) vapors as the preferred germanium sources, along with a silicon source over a heated substrate. Today, one of the major limitations impacting the commercialization of SiGe technology is the lack of a commercially viable and safer process that eliminates hazards associated with GeH 4 and the excessively higher thermal budget associated with GeCl 4. The key to growing successful SiGe structures is thus a strategic deposition process that employs safer alternative germanium sources, and allows a wide growth temperature window without degrading the film properties and jeopardizing the environment, health and safety (EHS) aspects of overall operation. In this paper, we report on the development of safer alternative liquid germanium precursors along with the first successful use of a new organo germanium precursor, iso-butyl germane (IBGe) for the growth of high purity Ge and SiGe films. We also detail our strategy to identify the most appropriate candidates from a large number of organo germanium compounds along with initial results on SiGe films and high-quality epitaxial Ge films deposited using IBGe.

Application of voxel phantoms and Monte Carlo method to whole-body counter calibration

Voxel phantoms and Monte Carlo methods are of considerable interest in calibrating in vivo counting applications for radioactive body burden such as whole-body counters. At the Japan Atomic Energy Research Institute (JAERI), a calculation code--UCWBC code--for whole-body counter calibrations using voxel phantoms has been developed as an EGS4 Monte Carlo user code. To validate the UCWBC code for calibrating whole-body counters at JAERI, response functions and counting efficiencies of a p-type high-purity Ge (HPGe) semiconductor detector used for the whole-body counter were evaluated for a water-filled block-shape phantom by use of UCWBC code and were measured by experiments. The voxel version of the water-filled block-shape phantom based on an actual phantom was used for the calculations. Furthermore, counting efficiencies of the Ge semiconductor detector for the male and female voxel phantoms developed at JAERI were evaluated in the photon energy range from 60 to 1836 keV by the UCWBC code in order to examine the differences between the counting efficiencies for voxel phantoms. In conclusion, it was found that the response functions and counting efficiencies of the Ge semiconductor detector found by the UCWBC code for the water-filled block-shape phantom are in good agreement with measured data. The UCWBC code was validated by those comparisons. It was also found that the counting efficiencies of the Ge semiconductor detector depend on the size of the phantoms and the effective distance between phantom and detector. The calibration of whole-body counters using voxel phantoms and Monte Carlo methods would be quite useful for the improvement in the accuracy of measurement results.

Development of Novel Germanium Compounds for Use in SiGe Epitaxy

Today, one of the major limitations impacting the commercialization of SiGe technology is the lack of a commercially viable and safer process that eliminates hazards associated with GeH4 and higher thermal budget associated with GeCl4. The key to growing successful SiGe structures is thus a strategic deposition process that (a) employs safer germanium sources, and (b) offers a wide growth temperature window without degrading the film properties and jeopardizing the environment, health and safety (EHS) aspects of overall operation. In this paper, we report on the development of novel germanium precursors along with the first successful use of an enabling germanium precursor, isobutyl germane (IBGe) for the growth of high purity Ge and SiGe films. We also elucidate our strategy to identify the most appropriate candidates from a large number of promising organogermanium compounds along with initial results on SiGe films and high quality epitaxial Ge films deposited using IBGe.

Improvements of 60 keV [formula omitted]-ray spectrum by reducing scattering effects

A considerable reduction of background and an improvement of spectra of low-energy γ -rays, measured with a planar high-purity Ge detector, has been achieved using a small source and a careful design of collimators and shielding. The aim of the design was to reduce strongly the detection of scattered radiation. The design of the shielding was based on previous studies by the present authors of effects of near-source scattering on photon spectra. That work has shown the effects of different distribution of mass around the γ -ray emitting atoms, seen as continuous distributions adjacent to the full-energy peaks (the “shoulders”). In the present measurement, reduction of intensity of the shoulders by as much as a factor of 10 has been achieved. The calculated shoulder spectra reproduce well the measured ones. Since a much lower background was achieved (peak-to-shoulder height ratio of about 2500), the shape of the full-energy peak could be analysed in a broader range. Deviations from the Gaussian shape have not been observed in the range ± 3.4 σ about the midpoint of the peak. The calculated shoulder spectrum, which is dominated by scattering in the source, and the Gaussian peak represent the measured spectrum in their energy range very well, so that less than 0.1% of counts are not accounted for. Present arrangements offer improved searches for lines of weak intensity and more accurate determination of peak intensities in X-ray and low-energy γ -ray spectra.

GERmanium detector array, GERDA

The GERmanium Detector Array, GERDA, is designed to search for ‘neutrinoless double beta decay’ (0ν2β) in 76Ge. The high-purity segmented Ge detectors will be directly submerged and operated in liquid N2 or Ar. The measurement of the half-life time of 0ν2β decay will provide information about the absolute neutrino mass scale and indirectly, the hierarchy. The design goal of GERDA is to reach a sensitivity of 0.2 eV on the effective Majorana neutrino mass (mββ). The GERDA experiment is located in hall A of the Grand Sasso national lab (LNGS) and the construction will start in 2006.

Activation experiment with D–T neutrons on materials relevant to liquid blankets

In order to evaluate neutron activation of materials relevant to the liquid blankets such as Lithium/vanadium-alloy and Flibe/vanadium-alloy blankets, irradiation experiments have been performed using the fusion neutronics source (FNS) at JAEA. Specimens of Er, Teflon (CF 2 CF 2) and NIFS-HEAT-2 (V–4Cr–4Ti) were selected in the experiments for the evaluations of the activation of Er in the MHD coating (Er 2O 3) , F in Flibe (LiF–BeF 2) and V, Cr, Ti in the structural materials, respectively. The irradiation experiments were performed with two kinds of neutron field: D–T neutrons and Be moderated neutrons for the purpose of reaction with high and low energy neutrons, respectively. The neutron spectra calculations were carried out using Monte Carlo transport codes MCNP-4C and JENDL3.3 files. The neutron-induced activity measured with a high purity Ge detector was compared with calculations carried out by the FISPACT-2001 codes and EAF-2001 files. The results showed that the calculated activities of most of products through reaction with high energy neutrons are in agreement with the experiments within 20% uncertainty.

Status of GENIUS-TF-II and TF-III—The long-term stability of naked detectors in liquid nitrogen

GENIUS-TF-II is a setup of six naked high purity Ge detectors (15 kg) in liquid nitrogen in Gran Sasso. It has been installed in October, 2004—after the first four naked Ge detectors had been installed on May 5, 2003 (GENIUS-TF-I). The GENIUS-Test-Facility (GENIUS-TF) is the first and up to now only setup ever testing the novel technique aiming at extreme background reduction in search for rare decays in particular underground. The goal of GENIUS-TF was to test some key operational parameters of the full GENIUS project proposal in 1997 [H.V. Klapdor-Kleingrothaus, Int. J. Mod. Phys. A 13 (1998) 3953; H.V. Klapdor-Kleingrothaus, J. Hellmig, M. Hirsch, GENIUS-Proposal, 20 November 1997; J. Hellmig and H.V. Klapdor-Kleingrothaus, Z. Phys. A 359 ( 1997) 351 and nucl-ex/9801004; H.V. Klapdor-Kleingrothaus, M. Hirsch, Z. Phys. A 359 (1997) 361; H.V. Klapdor-Kleingrothaus, J. Hellmig, M. Hirsch, J. Phys. G 24 (1998) 483; H.V. Klapdor-Kleingrothaus, CERN Courier, November 1997, pp. 16–18]. Simultaneous physical goal is to search for the annual modulation of the Dark Matter signal [H.V. Klapdor-Kleingrothaus, et al., Nucl. Instr. and Meth. A 481 (2002) 149; C. Tomei, A. Dietz, I. Krivosheina, H.V. Klapdor-Kleingrothaus, Nucl. Instr. and Meth. 508 (2003) 343]. After operation of GENIUS-TF over three years with finally six naked Ge detectors (15 kg) in liquid nitrogen in Gran Sasso we realize serious problems for realization of a full-size GENIUS-like experiment: (1) Background from Rn 222 diffusing into the setup, on a level far beyond the expectation. (2) Limited long-term stability of naked detectors in liquid nitrogen as result of increasing leakage current. None of the six detectors is running after three years with the nominal leakage current. Three of the six detectors do not work any more at all. The results of our three years of investigation of the long-term stability may cast doubt on the possibility to perform full GENIUS-like projects.

Hydrogen in germanium

A brief review is presented on the properties of hydrogen in germanium. We will discuss the early work which was driven by the quest for high-purity Ge. Emphasis is given to recent work on isolated hydrogen and hydrogen dimers.

Preparation and Characterization of Ba8Ga16Ge30/Sr8Ga16Ge30 Core−Shell Single Crystals

Ba- and Sr-filled type I Ge clathrate single crystals were synthesized by the Ga flux method, using high purity elemental Ba, Sr, Ga, and Ge as starting materials. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and Raman spectroscopy were used to characterize the cross-section of a single crystal. The results indicate an inhomogeneous composition distribution of the crystal: the core of the crystal is composed of Ba 8 Ga 16 Ge 30 and the shell is composed of Sr 8 Ga 16 -Ge 30 with a transition layer in between. This inhomogeneous composition of the crystal is confirmed by a locally resolving Seebeck coefficient measurement and thermal analysis by differential scanning calorimeter.

Cross sections and isomeric cross-section ratios in the interactions of fast neutrons with isotopes of mercury

Excitation functions were measured for the reactions $^{196}\mathrm{Hg}$($n$, $2n)$$^{195}\mathrm{Hg}$${}^{m,g},$$^{198}\mathrm{Hg}$($n$, $2n)$$^{197}\mathrm{Hg}$${}^{m,g},$$^{204}\mathrm{Hg}$($n$, $2n)$$^{203}\mathrm{Hg}$,$^{198}\mathrm{Hg}$($n,p)$$^{198}\mathrm{Au}$${}^{g}$, and $^{199}\mathrm{Hg}$($n,p)$$^{199}\mathrm{Au}$ over the neutron energy range of 7.6--12.5 MeV. Quasimonoenergetic neutrons were produced via the $^{2}\mathrm{H}$($d,n)$$^{3}\mathrm{He}$ reaction using a deuterium gas target at the J\"ulich variable energy compact cyclotron CV 28. Use was made of the activation technique in combination with high-resolution, high-purity Ge detector $\ensuremath{\gamma}$-ray spectroscopy. All the data were measured for the first time over the investigated energy range. The transition from the present low-energy data to the literature data around 14 MeV is generally good. Nuclear model calculations using the codes STAPRE and EMPIRE-2.19, which employ the statistical and precompound model formalisms, were undertaken to describe the formation of both the isomeric and ground states of the products. The total reaction cross section of a particular channel is reproduced fairly well by the model calculations, with STAPRE giving slightly better results. Regarding the isomeric cross sections, the agreement between the experiment and theory is only in approximate terms. A description of the isomeric cross-section ratio by the model was possible only with a very low value of \ensuremath{\eta}, i.e., the ${\ensuremath{\Theta}}_{\text{eff}}$/${\ensuremath{\Theta}}_{\text{rig}}$ ratio.

Energy Spectra of Prompt Gamma Rays from Al and Fe Thick Targets Irradiated by Helium and Proton Beams: Concerning Planetary Gamma-Ray Spectroscopy

Bombardment experiments with thick targets made of each of Al and Fe were performed using 230 MeV/nucleon helium and 210 MeV proton beams. The energies and intensities of prompt gamma rays emitted by inelastic nuclear scattering of energetic neutrons were measured by a high-purity Ge detector. This work presents the first experimental results concerning the emission of prompt gamma rays from thick targets anticipated by helium component in galactic cosmic rays, since no foregoing work related to this one has been done. It is concluded that helium has the capability of prompt gamma ray line emission through the inelastic nuclear reaction of neutrons with target material by a factor of 3.5 on average in comparison with proton. As regards the lunar and planetary nuclear spectroscopy, a consideration is given on the role of helium particles to the total production of gamma rays emitted from a planetary surface.

E1andE2Sfactors ofC12(α,γ0)O16fromγ-ray angular distributions with a 4π-detector array

A new experiment to determine the thermonuclear cross section of the C-12(alpha,gamma)O-16 reaction has been performed in regular kinematics using an intense alpha-particle beam of up to 340 mu A from the Stuttgart DYNAMITRON. For the first time, a 4 pi-germanium-detector setup has been used to measure the angular distribution of the gamma rays at all angles simultaneously. It consisted of an array of nine EUROGAM high-purity Ge detectors in close geometry, actively shielded individually with bismuth germanate crystals. The C-12 targets were isotopically enriched by magnetic separation during implantation. The depth profiles of the implanted carbon in the C-12 targets were determined by Rutherford backscattering for purposes of cross-section normalization and absolute determination of the E1 and E2 S factors. Angular distributions of the gamma decay to the O-16 ground state were measured in the energy range E-c.m.=1.30-2.78 MeV and in the angular range (lab.) 30 degrees-130 degrees. From these distributions, astrophysical E1 and E2 S-factor functions vs energy were calculated, both of which are indispensable to the modeling of this reaction and the extrapolation toward lower energies. The separation of the E1 and E2 capture channels was done both by taking the phase value phi(12) as a free parameter and by fixing it using the results of elastic alpha-particle scattering on C-12 in the same energy range.

Measurement ofK-shell photoelectric absorption parameters of Hf, Ta, Au, and Pb by an alternative method using a weakβ-particle source

Both the $K$ absorption edge and the $K$-shell photoelectric cross section have been determined for Hf, Ta, Au, and Pb by using a continuous external bremsstrahlung (EB) radiation from a weak $\ensuremath{\beta}$ source. In this method the EB photons produced in a nickel foil by the $\ensuremath{\beta}$ particles from a weak $^{90}\mathrm{Sr}\text{\ensuremath{-}}^{90}\mathrm{Y}$ $\ensuremath{\beta}$ source are incident on a target and the spectrum of the transmitted photons is recorded with a high-purity Ge detector coupled to an 8000 multichannel analyzer. The transmitted spectrum exhibits a sharp fall in intensity at the $K$-shell binding energy; and such a fall is used to determine both the $K$-absorption edge and the photoelectric cross section of the target.

Simultaneous measurements of indoor radon, radon–thoron progeny and high-resolution gamma spectrometry in Greek dwellings

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.