Intrinsic Ge Detector Research Articles

Preliminary characterization of an intrinsic germanium detector on a 400‐keV microscope

SUMMARYAn evaluation was made of an intrinsic germanium X‐ray detector fitted to a 400‐keV electron microscope. Its characteristics as a function of accelerating voltage, pulse processor settings and count rate were investigated. Comparisons are drawn between intrinsic Ge and Si(Li) detectors at both an experimental and theoretical level. The software requirements for the successful collection of spectra are discussed.

Double K-shell vacancy production in the electron capture decay of 139Ce.

The probability of double K-shell vacancy production in the electron capture decay of $^{139}\mathrm{Ce}$ to the 166-keV level of $^{139}\mathrm{La}$ has been investigated. Triple coincidences between the 166-keV gamma ray, the La satellite K\ensuremath{\alpha} x ray, and the La hypersatellite K\ensuremath{\alpha} x ray were measured using two intrinsic Ge detectors. We looked for the sum of two of the three radiations in one detector in coincidence with the third radiation in the other detector. The probability of double K-shell vacancy production per K-shell electron capture (${\mathit{P}}_{\mathit{K}\mathit{K}}$) was found to be (2.0\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$. From this and the known ${\mathit{P}}_{\mathit{K}\mathit{K}}$ for $^{131}\mathrm{Cs}$ we estimate a probability for zero K-shell vacancy production (shakedown) per K-shell electron capture of \ensuremath{\lesssim}2.4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ for $^{139}\mathrm{Ce}$.

Micro-X-Ray Fluorescence Analysis on a Synchrotron Radiation Wiggler Beam Line

AbstractIt has been well established over recent years that synchrotron radiation possesses some unique features as a source of primary x-rays for x-ray fluorescence analysis. Advantage has been taken of the high intensity emanating from the bending magnets of storage rings to develop x-ray microprobes utilizing apertures or focussing optics, or both, to provide a beam spot at the specimen of the order of micrometers. The use of insertion devices wigglers and undulatora, can further increase the available intensity, especially for the high energy photons. Beam Line X-17C at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, accepts the unmodified continuum radiation from a superconducting wiggler in the storage ring. Some initial XRF measurements have been made on this beam line using apertures in the 10 to 100 micrometer range. The fluorescent radiation was measured by an intrinsic Ge detector having an energy resolution of 300 eV at 15 kev, and located at 90° to the incident beam in the plane of the electron orbit. In samples containing many elements, detection limits of a few ppm were achieved with 100 μm beams.

Microanalysis At Intermediate Voltages

Microanalysis using x-ray emission spectrometry (XES) or electron energy-loss spectrometry (EELS) at intermediate voltages should offer advantages over 100kV instruments. Brightness increases linearly with kV (for thermionic sources), but the inelastic scattering cross section decreases. Potential improvements in detectability limit and spatial resolution in both XES and EELS have been major factors spurring the development of intermediate voltage AEMs.The x-ray peak to background ratio increases with kV (Figure 1), and improvements in detectability limits have been reported at 300kV. The variation of detectability with spatial resolution is discussed elsewhere in these proceedings. Beam spreading should decrease linearly with kV, but experimentally the spatial resolution (Figure 2a,2b) does not show the expected improvement. This may be due to increased beam broadening from fast secondary electrons. The smallest probe size consistent with generating sufficient signal (i.e. an FEG) is better than increased kV for improved spatial resolution3. Increased kV has seen the return of the ‘hole count’ problem in XES. Higher voltage electrons generate harder x-rays at the C aperture, and current aperture design cannot sufficiently restrict the xray flux. The flux at 300kV can contribute up to 10% of the characteristic x-ray signal, which severely compromises the microanalysis quality. An FEG with reduced source size may help. At intermediate voltages, intrinsic Ge (IG) detectors can be used for analysis of Kα, lines from high atomic number elements. K line analysis gives improved accuracy compared with L and M line analysis for which Cliff- Lorimer k factors, (both experimental and theoretical) are extremely variable, possibly due to fast secondaries also. IG detectors can detect Au K lines, resolve Kα1Kα2 lines, (see Figure 3) offer improved energy resolution (~120eV) over Si(Li) detectors, and may be more stable under electron irradiation. Continued improvement in IG detectors may result in their displacing Si(Li) detectors from most AEMs.

High-resolution spectroscopy of 32P : (II). Level density and primary transition strengths observed after thermal neutron capture in 31P

The -γ-ray spectrum emitted after thermal neutron capture in 31P was studied at the ILL high flux reactor with a pair spectrometer and an intrinsic Ge detector. A total of 212 transitions were assigned to the decay of 32P and 155 of these, representing 96.7% of the observed flux, were placed in a level scheme of 38 states. The neutron binding energy was determined as 7935.74 (16) keV. The densities of states observed in this reaction and in a recent (d, p) study are analyzed in the constant temperature Fermi-gas model. The primary E1 and M1 transition strengths in 32P are discussed and are compared to other sd-shell nuclei.

Decay of 50V.

The decay of /sup 50/V has been studied with a low-background, three-crystal intrinsic Ge detector operating in a salt mine. The partial half-life for electron-capture decay to the first excited state of /sup 50/Ti has been estimated to be (2.05+-0.49)/times/10/sup 17/ yr, and the partial half-life for ..beta../sup /minus// decay to the first excited state of /sup 50/Cr has been estimated to be (8.2/sub /minus/3.1//sup +13.1/)/times/10/sup 17/ yr.

Level structure of 89Sr investigated with thermal and fast neutron capture and the (d, p) reaction

Abstract The γ-ray spectrum emitted after thermal neutron capture in 88Sr was studied at the ILL high flux reactor with a pair-spectrometer and an intrinsic Ge detector. A total of 221 transitions were assigned to the decay 89Sr, and 55 of these, representing 55% of the observed flux, were placed in a level scheme of 19 states. The neutron binding energy was determined as 6358.73 (13) keV. Neutron capture in the 23.6 keV 3 2 − resonance was studied at the BNL filtered beam facility. Only seven transitions were attributed to 89Sr, and the decay of the capture state was found to be dominated by the valence process. High resolution (d, p) spectra were recorded at 20 MeV beam energy at the Munich Q3D spectrometer, and 55 states up to 4.5 MeV excitation energy in 89Sr were populated. The density of states observed in (n, γ) and (d, p) is analyzed in the Fermi-gas model, and the distribution of single-particle strengths is discussed from a statistical point of view.

K-Capture Probabilities in the Decay of175Hf

The K-capture probabilities in the decay of 175 Hf to 433 and 343 keV levels have been determined by the KX-ray-gamma ray sum peaks observed with a high resolution single intrinsic Ge detector.

Absorption edge technique for determination of intrinsic Ge detector parameters

A systematic study of the intrinsic Ge detector efficiency in the energy region 2–20 keV is presented. The definition of the efficiency is discussed and auxiliary quantities introduced. The most influential construction parameters of the detector — the dead layer width and the thickness of the gold contact — are determined in separate measurements employing the differential counting technique in the vicinity of respective absorption edges. A simple analytical aproximation to the efficiency is proposed.

K capture in the decay of 131Ba.

A single high resolution intrinsic Ge detector was used to measure the gamma--K-x-ray sum coincidences in the electron capture decay of $^{131}\mathrm{Ba}$. The sum spectrum was then analyzed in order to determine the relative K-capture probabilities to different levels in $^{131}\mathrm{Cs}$. The measured ${P}_{K}$ ratios compare well with the theoretical results.

A 13-element Ge detector for fluorescence EXAFS

At low concentrations, recording X-ray absorption spectra in fluorescence excitation mode is more sensitive than transmission mode. For dilute samples, the fluorescence signal is often obscured by scattered X-rays, and matrix and filter fluorescence. To discriminate against this background, while maintaining a large angular acceptance and high count rate capability, we have constructed a new detection system based on an array of intrinsic Ge detectors. The device uses 13 individual 11 mm diameter Ge detectors, clustered in a 1:3:5:3:1 pattern on a common cryostat, combined with Soller slits and filters to reduce the background signals. Pulsed optical feedback preamplifiers are followed by Gaussian-shaping amplifiers having fast discriminators to register the incoming count rate (ICR). Correction for dead time using the ICR signal allowed operation in the vicinity of 75 kHz per channel, with a 1 μs shaping time at 6 keV. For lower count rate applications, an average resolution of 160 eV at 5.9 keV was obtained with 8 μs shaping. Recent experience with this detector at the Stanford Synchrotron Radiation Laboratory is presented. The performance is illustrated using spectra obtained from phosphorus compounds and a thin iridium foil. The performance of this device is compared with previous fluorescence detection schemes, such as those using filter/slit combinations or barrel monochromators.

Exotic-atom measurement of the magnetic dipole moment of theΣ−hyperon

The magnetic dipole moment of the ..sigma../sup -/ hyperon has been determined from ..sigma../sup -/-atom x-ray transitions in natural lead and tungsten. Negative kaons were stopped in a target which consisted of sheets of W or Pb immersed in liquid hydrogen. The ..sigma../sup -/ resulting from the reaction K/sup -/p..--> sigma../sup -/..pi../sup +/ were tagged by observing the monoenergetic ..pi../sup +/. X rays from ..sigma../sup -/ atoms were detected by intrinsic Ge detectors. The x-ray lines were analyzed for fine-structure splitting and the magnetic moment was determined from the measured splitting. The value obtained for the magnetic moment is ..mu..(..sigma../sup -/) = (-1.105 +- 0.029 +- 0.010)..mu../sub N/ where the first error is statistical and the second systematic. This value is in reasonable agreement with measurements that used precession techniques and with the theoretical predictions of simple quark models.

In-Vivo Counting of 241Am in Human Lungs and Tracheobronchial Lymph Nodes

A study was conducted of a human male who had inhaled a mixture of 241Am and Pu. To distinguish 241Am deposited in the subject's lungs from translocated activity deposited in the tracheobronchial lymph nodes (TBLN), two intrinsic Ge detectors were collimated with 0.3-cm Pb sheeting. A tissue-equivalent phantom containing either 22.9 kBq (620 nCi) of 241Am in the lungs or a 81.4 kBq (2200 nCi) 241Am point source in the TBLN was measured. Calibration curves observed from lateral differential scans on the phantom were compared to data obtained by the same detection system for a human male with a measured lung deposition of 89 Bq (2.4 nCi) of 241Am. Comparison of the human data to the calibration curves indicated the activity was restricted primarily to the lungs. The calibration curves demonstrate that this method is useful in determining the distribution of inhaled radioactivity between the lungs and TBLN. The measured activity from the male subject generally supported the ICRP Publication 30 model translocation prediction for class Y compounds.

K-Capture Probabilities in the Decay of169Yb to169Tm

Relative K-capture probabilities in the decay of 169 Yb to 472 keV, long lived 379 keV (52 nsec.), and 316 keV (660 nsec.) levels of 169 Tm are measured using the technique of gamma-K X-ray sum coincidence in a single intrinsic Ge detector. The results agree with the theoretical values.

Pionic carbon/oxygen capture ratios in blood and muscle tissue of pig

The pionic carbon/oxygen capture ratio for the blood and muscle tissue of a pig was measured using an intrinsic Ge detector in order to investigate possible explanations for an enhanced lesion observed in the autopsy of pion-irradiated patients. Pure iron was also irradiated in order to determine the energies and intensities of pionic X-rays from iron. It was expected that some of them originated from haemoglobin and could be observed in the spectrum for a blood sample. TE plastic (Shonka A-150) and Lucite were also investigated for comparison with other work.

A new method for measuring the neutron-induced background in BGO Compton-suppressed Ge detectors applied to in-beam γ-ray studies

A method for measuring the response of intrinsic Ge detectors equipped with bismuth germanate (BGO) anti-Compton shields to evaporation neutrons is presented.

Self-absorption correction for low energy gamma rays: Application to 210Pb determination in marine sediments

A series of nondestructive, low energy gamma-ray spectrometric measurements by means of intrinsic Ge detectors was carried out for the activity determinations of several naturally occurring radionuclides in marine sediments. The system was calibrated for efficiency using a radioactive sample obtained by combining standard radioactive solutions with a suitable matrix. This procedure is strictly only correct for the analysis of samples of similar composition with the same mass absorption coefficients at the investigated energies. Nevertheless, the efficiency calibration can be extended to different matrix samples if the variation in self-absorption is accurately taken into account. A method for calculating the self-absorption correction at any energy of interest is proposed and verified for the determination of 210Pb activity at an energy of 46.5 keV. The direct gamma method and the conventional, accurate, but tedious, alpha technique via 210Po, which can be alternatively applied to the determination of 210Pb, agreed mostly within 8%.

Thorium in man and environment uptake and clearance

The intake and tissue distribution of thorium (2 3 2Th) was studied in an urban (Bombay) population in India. From the analysis of 16 whole diet samples, the average daily intake through food was found to be 2 μg (range 0.8–4.3 μg·d−1). The estimated intake through drinking water and inhalation comes out to be 0.03 and 0.02 μg per day. From the analysis of human autopsy tissue samples it is observed that the concentration ranges in lungs and bone are 1.5–16 μg/kg and 0.2–9.0 μg/kg fresh weight respectively. The average urinary concentration is 12 ng/1 (range 7–22 ng/l for 10 samples). Among the different body tissues, pulmonary lymph nodes were found to contain the highest concentration (geometric mean 53.4 μg/kg, range 31.4–85.5 μg/kg for 6 samples). Analysis of the samples was done by the neutron activation technique. 311.8 keV gamma photons of2 3 3Pa which is the activation product of2 3 2Th, were counted after chemical separation. A 54 cm3 intrinsic Ge detector coupled to 1024-channel analyser was used. Using the average lung content and the daily average intake values of thorium through inhalation, the clearance half-time from lung was estimated.

Gamma-spectrometric determination of uranium isotopes in biofuel ash

Gamma-ray measurements have been performed on biofuel samples using a planar intrinsic Ge detector. The samples were first homogenized and then packed into 90 ml plastic tubs. The radiation from each sample was usually measured for 1 to 2 days. The intensity of the 63.3 keV γ-ray in234Th was used to determine the amount of238U present. The amount of235U can be determined from the intensity of the 143.8 keV γ-ray.

An ultralow background germanium gamma-ray spectrometer

An ultralow background 135 cm 3 intrinsic Ge detector has been developed providing a new benchmark in low background gamma-ray spectroscopy. The radioactive background from construction materials has been reduced by more than two orders of magnitude over conventional low background gamma-ray spectrometers. The sources of background in standard commercial cryostats have been identified and eliminated. Data taken with this prototype after elimination of most cosmic ray induced background are presented. The first application of the prototype as well as a large, second generation, multicrystal (∼ 1440 cm 3) germanium detector will be an ultrasensitive search for neutrinoless and two-neutrino double beta decay of 76Ge.