Planar Ge Detector Research Articles

Investigation of the electrical conduction mechanisms in P-type amorphous germanium electrical contacts for germanium detectors in searching for rare-event physics

For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of 2.13^{-0.05}_{+0.07}mathrm{{A}}^circ to 5.07^{-0.83}_{+2.58}mathrm{{A}}^circ , depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches.

Determination of 242Pu abundance in plutonium samples using self-fluorescent X-ray emission

Non-destructive gamma spectrometric measurements of the isotopic composition of plutonium are routinely carried out in the framework of nuclear safeguards inspections. High-resolution spectra of Pu obtained from planar Ge detectors are de-convoluted by means of special codes such as MGA or FRAM and these results are then applied when determining the total plutonium mass using neutron coincidence measurement techniques. The radiation emission of 242Pu is so weak that its abundance cannot be measured directly; hence isotopic correlations are utilized to estimate it in low and medium burn-up Pu material. The present work investigates the feasibility of determining the total Pu/Am ratio, exploiting X-ray fluorescence lines present in the plutonium spectrum. Combining the total Pu/Am ratio with individual Pu isotopic ratios to 241Am then allows an estimate of the 242Pu to be made. To this end, reference samples of plutonium, with an 241Am content comprised between 5 and 7 %, were measured using a planar germanium detector. The spectra were processed using MGA followed by quantification of the X-ray fluorescence peak of Americium, and then further calculations, including MCNP simulations. The conclusion of the present work is that, when the americium content of the sample is high enough to produce an Am Kα1 line which can be exploited, it is possible to indirectly determine the 242Pu abundance by analysing the X-ray fluorescent lines present in the plutonium gamma spectrum, thus raising the prospect to apply this method to cases for which the algorithms based on empirical correlations cannot be applied.

Pulse shape discrimination performance of inverted coaxial Ge detectors

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

Nondestructive Determination of 235U Enrichment of Uranium Samples in the Presence of Actinides (232Th, 236U, 237Np)

The measurements were performed using a planar Ge detector. The multi-group analysis (MGA) for the determination isotopic abundances in low enriched uranium samples is applied in this study. In order to perform the analysis of complex gamma-spectrums, were taken a number of gamma-spectrums of single reference samples, containing 235U, 238U, 232Th, 236U, 237Np with declared isotopic abundance. The gamma-ray spectrums in the range of low energy X-ray and gamma-ray peaks of these samples were obtained and analyzed.

Observation of Doppler broadening inβ-delayed proton-γdecay

Background: The Doppler broadening of $\gamma$-ray peaks due to nuclear recoil from $\beta$-delayed nucleon emission can be used to measure the energies of the nucleons. This method has never been tested using $\beta$-delayed proton emission or applied to a recoil heavier than $A=10$. Purpose: To test and apply this Doppler broadening method using $\gamma$-ray peaks from the $^{26}$P($\beta p\gamma$)$^{25}$Al decay sequence. Methods: A fast beam of $^{26}$P was implanted into a planar Ge detector, which was used as a $^{26}$P $\beta$-decay trigger. The SeGA array of high-purity Ge detectors was used to detect $\gamma$ rays from the $^{26}$P($\beta p\gamma$)$^{25}$Al decay sequence. Results: Radiative Doppler broadening in $\beta$-delayed proton-$\gamma$ decay was observed for the first time. The Doppler broadening analysis method was verified using the 1613 keV $\gamma$-ray line for which the proton energies were previously known. The 1776 keV $\gamma$ ray de-exciting the 2720 keV $^{25}$Al level was observed in $^{26}$P($\beta p\gamma$)$^{25}$Al decay for the first time and used to determine that the center-of-mass energy of the proton emission feeding the 2720-keV level is 5.1 $\pm$ 1.0 (stat.) $\pm$ 0.6 (syst.) MeV, corresponding to a $^{26}$Si excitation energy of 13.3 $\pm$ 1.0 (stat.) $\pm$ 0.6 (syst.) MeV for the proton-emitting level. Conclusions: The Doppler broadening method has been demonstrated to provide practical measurements of the energies for $\beta$-delayed nucleon emissions populating excited states of nuclear recoils at least as heavy as $A=25$.

Lifetime measurements and decay spectroscopy of132I

The low-lying states of odd-odd 132 I, the 3p-3h nucleus with respect to the doubly magic 132 Sn, have been characterized from decay spectroscopy. The neutron rich Iodine and Tellurium isotopes have been produced as fission product of alpha-induced fission of 235 U and radiochemically separated. The life-time of the first excited state of 132 I have been precisely measured using LaBr3(Ce) scintillators from the decay of 132 Te. The IT decay of the high spin isomer (8 - ) in 132 I has been measured with a Low Energy Photon Spectrometer (LEPS) of segmented planar Ge detector.

Gamma-ray emission probabilities in the decay of 177mLu

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

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

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

Background rejection capabilities of a Compton imaging telescope setup with a DSSD Ge planar detector and AGATA

In this work, we show the first Monte Carlo results about the performance of the Ge array which we propose for the DESPEC experiment at FAIR , when the background algorithm developed for AGATA is applied. The main objective of our study is to characterize the capabilities of the γ -spectroscopy system, made up of AGATA detectors in a semi-spherical distribution covering a 1 π solid angle and a set of planar Ge detectors in a daisy configuration, to discriminate between γ sources placed at different locations.

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

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

A versatile Monte Carlo package for computation of efficiencies of Si(Li), SDD and Ge detectors

AbstractCurrently, most detector efficiency calculations for X‐ray detectors assume that the source is a point source on the axis of symmetry of the detector, but this is not always accurate. We have devised a Monte Carlo program to simulate photon transport in Si(Li), SDD and planar Ge detectors that natively handles finite, tilted and off‐axis sources. Although electron transport is not handled at this stage, photon transport is completely handled, including absorption from filters and multiple scattering in the detector crystal. The K escape peak is handled for both silicon and germanium detectors, and the L escape peak is also handled for germanium detectors. Our efficiency results compare very well with previous work when idealized systems are simulated, and the effect of a non‐idealized system is presented. Escape peak intensity ratios are given for both silicon detectors (K peak only) and germanium detectors (K and L peaks), and the results for the K escape peaks agree well with previous work. Results are presented for a recent annular detector system, which is a good example of systems that are poorly handled under previous efficiency calculations. Copyright © 2010 John Wiley & Sons, Ltd.

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

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

SPEIR: A Ge Compton camera

The SPEctroscopic Imager for γ - Rays (SPEIR) is a Compton scatter γ -ray imaging system of high efficiency and spectroscopic resolution with a 4- π field-of-view. The imaging system consists of double-sided segmented (DSSD) planar Ge detectors, an acquisition system instrumenting the detectors, and a set of data analysis methods. The analysis methods employ event reconstruction algorithms that increase the intrinsic position resolution and granularity of the detectors, and provide photon scattering information relevant for Compton imaging.

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.

Position sensitivity of a segmented planar Ge detector

A method to extract depth of interaction information for gamma-rays in a segmented planar Ge detector is presented. The method is demonstrated on signals from a segmented detector which were stored ...

Partial γ-Ray Cross Sections for the Reaction 239Pu(n,2nγi) and the 239Pu(n,2n) Cross Section

Absolute partial γ-ray cross sections for discrete γ-ray production in the 239Pu(n,2nγi)238Pu reaction have been measured. The experiments were performed at LANSCE/WNR on the 60R neutron flight path. Reaction γ-rays were measured using the large-scale Compton-suppressed array of Ge detectors, GEANIE. The motivation for this experiment, an overview of the partial γ-ray cross-section measurement, and an introduction to the main experimental issues will be presented. The energy resolution of the Ge detectors allowed identification of reaction γ rays above the background of sample radioactivity and fission γ rays. The use of planar Ge detectors with their reduced sensitivity to neutron interactions and improved line shape was also important to the success of this experiment. Absolute partial γ-ray cross sections are presented for the 61+ → 41+ member of the ground state rotational band in 238Pu, together with miscellaneous other γ-ray partial cross sections. The n,2n reaction cross section shape and magnitude as a function of neutron energy were extracted from these partial cross sections using nuclear modeling (enhanced Hauser-Feshbach) to relate partial γ-ray cross sections to the n,2n cross section. The critical nuclear modeling issue is the ratio of a partial cross section to the reaction channel cross section, and not the prediction of the absolute magnitude.

Measurements of photon emission probabilities from the decay of 226Ra and daughters

X- and γ-rays spectrometric techniques have been used to determine and improve the photon emission probability data of 226Ra. These values were obtained from 226Ra spectra in radioactive equilibrium with daughters such as 222Rn, 214Bi and 214Pb in the 50–2500 keV energy range. The efficiency calibration of the coaxial and planar Ge detectors took into account correction factors for pile-up losses, attenuation and source geometry effects, and γ–γ and γ–X summation losses. XK emission probabilities were successfully resolved and determined more precisely because of the ability to de-convolute complex regions of the spectrum below 90 keV combined with spectral knowledge of the interferring Pb-XK-rays. The resulting absolute intensities of the main photon emissions of 226Ra and daughters exhibit improvements (±0.7% for the smallest uncertainty estimated to one standard deviation) or agree with published data.

Photoexcitation of 180Ta by 60Co and 137Cs gamma rays

The depopulation of the quasistable 180Ta m was studied by irradiating natural Ta samples with strong 60Co and 137Cs sources. Decay of the ground state ( t 1/2=8.1 h) was observed by taking gamma-spectra using a large planar Ge detector in a NaI(Tl) anticoincidence shielding. Clear evidence was found for activation levels lying below 1.4 MeV, and their presence seems to be possible below 0.737 MeV as well, which couple effectively the quasistable isomer and the ground state. Integral cross sections and effective half-lives relevant in stellar environment have been inferred for depopulation of the isomer through mediating levels assumed at various energies. Implications for 180Ta m production in the s-process nucleosynthesis are discussed.

X-ray diagnostic systems for the TJ–II flexible heliac

The set of diagnostics that are being installed in TJ–II are meant to cover the full photon energy range expected in TJ–II during the electron cyclotron resonance heating phase. The obtained information will be used to evaluate the energy contained in the superthermal electron populations and its possible relevance in the global power balance as well as for standard electron temperature estimations. Two NaI(Tl) detectors located at the equatorial plane of the machine will be used to analyze the highest energy photons (over 50 keV). One Si(Li) and a planar Ge detector will be used to obtain the emission spectra between 1 and 100 keV. Tomographic reconstruction of plasma emissivity (up to 10 keV) will be carried out using four p-n silicon photodiodes arrays of 16 detectors, located at the same poloidal section. An additional camera will be used to detect toroidal asymmetries.

Search for a 17 keV neutrino in the internal bremsstrahlung spectrum of 125I.

We have searched for evidence of the emission of a 17 keV neutrino in the internal bremsstrahlung (IB) spectrum accompanying the electron capture decay of $^{125}\mathrm{I}$. The IB spectrum, recorded in a planar Ge detector, has 1.2\ifmmode\times\else\texttimes\fi{}${10}^{6}$ counts per keV at 17 keV below the 2p end point. We set an upper limit of 0.4% for the admixture of a 17 keV neutrino, at the 90% confidence level, and exclude a 0.8% admixture at the 99.6% confidence level. The ${\mathit{Q}}_{\mathrm{EC}}$ value is found to be 185.77\ifmmode\pm\else\textpm\fi{}0.06 keV. We also find that the recent calculations of Suri\ifmmode \acute{c}\else \'{c}\fi{} et al., which employ relativistic self-consistent-field atomic wave functions, reproduce the shape and relative intensity of IB partial spectra within a few percent.