High-purity Ge Detector Research Articles

AstrophysicalSfactor forαcapture onSn117

The cross sections of the $^{117}\mathrm{Sn}$($\ensuremath{\alpha},\ensuremath{\gamma}$) $^{121}\mathrm{Te}$ and $^{117}\mathrm{Sn}$($\ensuremath{\alpha},p$) $^{120}\mathrm{Sb}$ reactions have been measured in the effective center of mass energy from 11.5 to 14.6 MeV. Highly enriched self-supporting $^{117}\mathrm{Sn}$ (90%) foils were bombarded with an $\ensuremath{\alpha}$ beam delivered by the Bucharest IFIN-HH tandem accelerator. The induced activity of $^{121}\mathrm{Te}$ and $^{120}\mathrm{Sb}$ was measured with two large-volume high-purity Ge detectors in close geometry to maximize the detector efficiency. The experimental cross section and astrophysical $S$ factor are compared with statistical model predictions for different global $\ensuremath{\alpha}$-nucleus optical potentials.

Azimuthal-angle dependence ofLx-ray intensity following photoionization of Pb, Au, and W atoms by a linearly polarized photon

We measured the $L$ x-ray intensities of Pb, Au, and W for several different azimuthal angles and partially polarized photon beams by using high-purity low-energy Ge detectors. We utilized a monochromatized synchrotron beam as the source. It had an energy of $10.88--40\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$, and its degree of linear polarization $P$ ranged from 0.84 to 0.89. The scattering polar angle $(\ensuremath{\theta})$ was 90\ifmmode^\circ\else\textdegree\fi{}, and the azimuthal angle $({\ensuremath{\phi}}_{1})$ was 0\ifmmode^\circ\else\textdegree\fi{} or 90\ifmmode^\circ\else\textdegree\fi{}, relative to the polarization direction. We obtained the x-ray intensity ratio $R\phantom{\rule{0.2em}{0ex}}[=I({\ensuremath{\phi}}_{1}=0\ifmmode^\circ\else\textdegree\fi{})∕I({\ensuremath{\phi}}_{1}=90\ifmmode^\circ\else\textdegree\fi{})]$. We observed that the $Ll$ intensities depended on the azimuthal scattering angle ${\ensuremath{\phi}}_{1}$, i.e., $R=0.92--0.94$, 0.91--0.94, and 0.90--0.93 for Pb, Au, and W, respectively. On the other hand, the dependence of $L\ensuremath{\alpha}$ on the azimuthal scattering angle was not clear due to experimental uncertainty. The anisotropy of $L\ensuremath{\gamma}$ was not observed. These results agreed with the theoretical calculations based on Scofield's theory.

NEW LEVELS AND TRANSITIONS IN 72Ge OBSERVED IN THE 72As(β++EC)72Ge DECAY

The decay of 72 As has been investigated by means of γ-ray spectroscopy. The 72 As nuclei were produced through the 72 Ge (p, n)72 As reaction. The Compton-suppressed spectrometer and high-purity Ge detectors have been used in singles and in coincidence modes respectively to study γ-rays in the β++ EC decay of 72 As to 72 Ge . 79 γ-rays, among which 3 were observed for the first time, were reported. A decay scheme of 72 As including 1 new level is proposed that accommodates 77 of these transitions. Tentative spin and parity assignments are suggested for a number of levels according to the log ft values and γ-branching ratios.

Neutron Emission Profile of d-Be Reaction with Low-energy Deuteron Beam for Accelerator Neutron Source

The neutron emission profile of the 9Be(d,n)10B nuclear reaction using a low-energy deuteron beam (300 keV) was examined to develop an accelerator neutron source for boron neutron capture therapy (BNCT). The gamma rays corresponding to the transition from excited levels of 10B were measured using a high-purity Ge detector. By analyzing the gamma-ray yields, the transition probability to each excited state of 10B was determined and the neutron yields for the individual energies were evaluated. The emission of the 3.8 MeV neutron was approximately 42% of the total emission, and other neutron emissions from 1.1 to 4.5 MeV were clearly specified. A neutron moderator assembly using heavy water (D2O) or Be metal was designed in order to obtain thermal neutrons from the d-Be reaction with high efficiency. The simulations of neutron transport in the assembly were performed using the Monte Carlo code MCNP4C. Thermal, epithermal, and fast neutron fluxes were calculated as a function of the moderator thickness. The experimentally evaluated neutron emission property was reflected in the simulation. The results indicate that the use of the D2O moderator is suitable for thermal neutron production and shielding of fast neutrons rather than that of Be.

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).

Measurement of thermal neutron cross-section and resonance integral for the 174Yb(n,γ)175Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the 174Yb(n,γ)175Yb reaction were measured by the activation method using a 55Mn monitor as single comparator. Analytical grade MnO2 and Yb2O3 powder samples with and without a cylindrical 1mm Cd shield box were irradiated in an isotropic neutron field obtained from three 241Am–Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the 174Yb(n,γ)175Yb reaction is found to be 126.5±6.6b, relative to that of the 55Mn monitor. The resonance integral value for the 174Yb(n,γ)175Yb reaction is found to be 59.6±8.5b, at cadmium cut-off energy of a 0.55eV. Using the measured cadmium ratios of 55Mn and 174Yb, the result for resonance integral of the 174Yb(n,γ)175Yb reaction has also been obtained relative to the reference value of the 55Mn monitor. The present results for the 174Yb(n,γ)175Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30–69b.

Thermal neutron cross-section and resonance integral of the 186W(n, γ)187W reaction

We measured the thermal neutron cross-section and the resonance integral of the reaction 186W(n,γ)187W by the activation method using a 197Au(n,γ)198Au monitor reaction as single comparator. The high-purity natural W and Au metallic foils with and without a cadmium shield case of 0.5mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the samples were measured by high-resolution γ-ray spectrometry with a calibrated p-type high-purity Ge detector. The necessary correction factors for γ-ray attenuation (Fg), thermal neutron self-shielding (Gth), and resonance neutron self-shielding (Gepi) effects, and the epithermal neutron spectrum shape factor (α) were taken into account. The thermal neutron cross-section for the 186W(n,γ)187W reaction has been determined to be 37.2±2.1barn, relative to the reference value of 98.65±0.09barn for the 197Au(n,γ)198Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated value of ENDF/B-VII.0 by 5.7%. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral obtained is 461±39barn, which is determined relative to the reference values of 1550±28barn for the 197Au(n,γ)198Au reaction. The present resonance integral value is in general good agreement with the recently measured values by 9%. The present result is lower than the evaluated ones by 10–13%.

Thermal-Neutron Capture Cross Sections and Resonance Integrals of the 80Se(n,γ)81m,81gSe Reactions

The thermal-neutron capture cross sections (σ0,m and σ0,g) and resonance integrals (I 0,m and I 0,g) leading to the isomeric and ground states of 81Se were measured by the activation method. Samples of high-purity (99.99%) selenium oxide were irradiated in a rotary specimen rack of the research reactor of Rikkyo University. Wires of Co/Al and Au/Al alloys, which have different sensitivities to neutrons in the thermal and epithermal energy regions, were irradiated to monitor the thermal neutron fluxes and the epithermal components at the same position of the rotary specimen rack. The cadmium-shielded samples were also irradiated to obtain the cadmium ratio and the resonance integrals (I 0,m and I 0,g). A high-purity Ge detector was used to measure the γ-rays emitted from the irradiated samples and wires, and reaction rates were calculated from γ-ray yields. On the basis of Westcott's convention, the cross sections were obtained as follows: σ0,m = 0.057 ± 0.003 b and I 0,m = 0.186 ± 0.014 b leading to 81mSe, and σ0,g = 0.536 ± 0.046 b and I 0,g = 0.867 ± 0.102 b leading to 81gSe.

Global Trigger and Readout System for the AGATA Experiment

AGATA is a 4-pi array of high purity Ge detectors for in-beam gamma-ray spectroscopy based on the novel concepts of pulse shape analysis (PSA) and gamma-ray tracking. Tracking and PSA require the concurrent digitization-at a sampling rate of 100 Msamples/s-of preamplifier signals of the 36-fold segmented Ge crystals composing the array. Locally digitized data are optically transferred to remote pre-processing nodes for pulse energy computation. The design of the front-end readout and level-1 (L1) trigger in AGATA follows a synchronous pipeline model: the detector data are stored in pipeline buffers at the global AGATA frequency, waiting the global L1 decision. A global timing system provides a reference clock and time tag to the digitizers and the pre-processing units by means of a tree of optically connected timing units. Pre-processing nodes are integrated in advanced TCA-based carrier cards with full mesh connectivity in the backplane and read-out through pci-express based optical links. The front-end data readout and its integration in the global trigger and synchronization system will be described.

Spectral Effects of Activation for Liquid Blanket Relevant Materials Induced by D-T Neutron Irradiation

A series of irradiation experiments were performed using Fusion Neutronics Source (FNS) at JAEA for the investigation of activation of materials relevant to Lithium/vanadium-alloy and Flibe/vanadium-alloy blankets. The specimens of V-4Cr-4Ti, Er and Teflon in 10 mm×10 mm×0.03-0.1 mm were prepared for studying the activation of V-alloy structure, MHD coating of Er2O3, and F in molten salt Flibe, respectively. Be, Li and Li/Be mock-ups were assembled with Be and solid Li blocks in addition to the assembly for direct D-T neutron irradiation to examine the dependence of the activation on neutron spectrum. The neutron spectra in all irradiation locations were calculated using MCNP code and JENDL-3.3 file. The activities of the specimens induced in various neutron fields were measured with a high purity Ge detector (HP-Ge). Experimental analyses were carried out using FISPACT-2001 codes with both EAF-2001 file and FENDL/A-2.0 & FENDL/D-2.0 libraries. The typical calculation/experiment (C/E) values lay in the range of 0.8-1.2. Coarse group treat for (n,σ) reactions, especially in resonance range, could result in overestimation. Use of continuous cross section improves consistency of the calculation with the experiment. However, accurate estimate of spectra is necessary when the flux changes largely with energy around the threshold or the resonance peak.

Measurement of thermal neutron cross-sections and resonance integrals for 179Hf(n,γ) 180mHf and 180Hf(n,γ) 181Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the 179Hf(n,γ) 180mHf and the 180Hf(n,γ) 181Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector. In the experimental procedure, the thermal neutron cross-sections, σ 0, and resonance integrals, I 0, for the 179Hf(n,γ) 180mHf and the 180Hf(n,γ) 181Hf reactions have been determined relative to the reference values of the 197Au(n,γ) 198Au reaction, with σ 0 = 98.65 ± 0.09 barn and I 0 = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ 0 = 0.424 ± 0.018 barn and I 0 = 6.35 ± 0.45 barn for the 179Hf(n,γ) 180mHf reaction, and σ 0 = 12.87 ± 0.52 barn and I 0 = 32.91 ± 2.38 barn for the 180Hf(n,γ) 181Hf reaction. The present results are in good agreement with recent measurements.

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.

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.

Determination of the soil-to-grass transfer of 137Cs and its relation to several soil properties at various locations in Serbia

Transfer coefficients of 137Cs from soil to grass were determined for the terrain around the city of Kragujevac in central Serbia. Mass activity concentrations of 137Cs in soil and grass samples were determined with a high-purity Ge-detector (HPGe). The activity concentration at the depth of 20 cm was found to be in the range of 14.92–124.05 Bq kg−1, whereas the activity in grass for the same location was in the range of 4.60–84.95 Bq kg−1. Transfer factors (TFs) were in the range of 0.07 up to 1.94. Dependences of TFs on different soil characteristics were presented graphically. Weak dependences were determined between them. Absalom's model was used to predict TFs based on soil characteristics: pH value, contents of clay, exchangeable potassium and humus. A comparison of measured and predicted values from Absalom's model is shown graphically. It has been found that Absalom's model might be carefully used for the prediction of 137Cs in grass for specific regions.

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.