Intrinsic Germanium Detector Research Articles

PIXE analysis of toxic mussels

In connection with an outbreak of atypical shellfish poisoning in Canada due to consumption of mussels from Prince Edward Island in late 1987 and early 1988, an elemental analysis of domoic acid-contaminated mussels harvested during the epidemic was undertaken using the proton induced X-ray emission technique. For this analysis, 30 MeV protons were used to induce K X-ray emission from all elements present above chlorine in the periodic table. A Si(Li) detector was used to detect the lower energy K X-rays and an intrinsic germanium detector to measure As and above. Observed concentrations of several elements were much higher than normal and at a level known to induce toxicity in other bivalved mollusks. Traces of certain heavy elements were also detected. The influence of trace metals on domoic acid toxicity is currently being investigated in our laboratories.

Simultaneous determination of noble metals, Re, Se, As and Sb by radiochemical neutron activation analysis

A sensitive radiochemical technique is described, which allows the simultaneous analytical determination of the platinum-group elements Pd, Pt, Ir, Os and Ru, as well as Au, Se, As, Re and Sb, in common silicate rocks. About 100 mg of finely ground powder is irradiated with different neutron fluxes, either at the SLOWPOKE reactor (University of Toronto) or at the reactor of the McMaster University, Hamilton, Ontario. After adding powdered FeNi alloy and the carrier-spike solution, the irradiated samples are fused at 1600°C in a reducing atmosphere of N 2, CO and CO 2. These conditions result in the formation of an immiscible metal liquid which separates the siderophile elements from the lithophile elements. The metal phase is dissolved in HCl and the solution is put on an ion exchange column of Srafion NMRR, which selectively absorbs the noble metals. The resin itself is counted on a sensitive intrinsic germanium detector. After a suitable delay, the resin from each sample is reirradiated and recounted to obtain the yield of the separation, which averaged 65–75% for the precious metals, Re and Sb. Recovery rates for Se and as are significantly lower, at 55% and 30%, respectively. Under optimum conditions, detection limits of 0.004 ppb for Au, 0.03 ppb for Ir and Re, 0.05 ppb for Sb, 0.2 ppb for As, 3 ppb for Pd, 1 ppb for Os, 1.5 ppb for Pt, 2 ppb for Ru and 5 ppb for Se in the silicate sample can be achieved. Precision is best for Au, followed by Ir and Re, Sb, As, Os, Pt, Pd, Ru, and Se. Accuracy, as determined by the analysis of in-house and international rock standards, is usually better than 10%. Thus, this method allows reasonably precise determinations of precious metals and associated chalcophile elements at concentration levels in the low-ppb range.

Analytical Sensitivities for Thirty-Six Elements in Cellulose Matrix by Means of High-Energy Photon Activation and Low-Energy Photon Detection

The analytical potentiality of the combined use of high-energy photon activation and low-energy photon detection has been investigated by irradiating 36 elements with 30-MeV bremsstrahlung. The characteristic X-rays and low-energy gamma-rays from the activation products were measured with an intrinsic high-purity germanium detector, and the experimental sensitivities have been estimated. A comparison was applied to the results with the conventional gamma-ray measurements with a lithium-drifted germanium detector. The attenuation of the low-energy photons due to a sample matrix was also considered. Practical detection limits for several elements were evaluated by analyzing a biological standard reference material, NIST Orchard Leaves. For Ba, Br, I, Ni, Mo, Pb, Sb and Zn, detection limits were lowered by low low-energy photon spectroscopy. From the results, applicability and versatility of this method have been demonstrated.

Optimization of neutron activation analyses of 129I in low-level radioactive waste samples

Determination of 129I in low-level radioactive waste (LLW) samples from reactors can be a tedious and time consuming procedure often leading to results with large margins of error. This study used an efficient (approx. 2–3 h per sample) and reliable procedure, which could be used for LLW waste samples in various physical forms (solid, liquid, resin). Samples were processed without pretreatment by distillation of the LLW samples, followed by separation using chemical extraction. The extracted 129I solution was then irradiated for 5 min in a 2 MW research reactor (neutron flux of about 10 13 n/cm 2-s), and the activation product, 130I, was analyzed with a high-purity intrinsic germanium detector. A tracer of 127I was also activated to 128I to determine radiochemical yield, which was 29 ± 7%. The lower limit of detection of the procedure was about 30 pCi/g for 4 g samples, 29% recovery, and a 1000 s counting time.

Measurement of 55Fe in reactor samples by an intrinsic Germanium detector

Determination of 55Fe in reactor samples requires some care because of the low-energy x-rays emitted following decay by electron capture and the presence of 59Fe and other possible γ-ray emitting contaminants in radiochemical separations. This problem was dealt with by radiochemical separation of Fe followed by use of an intrinsic germanium detector operated at high amplifier gain to count the low-energy x-ray emissions to quantitate 55Fe. Separation of this important nuclide in reactor samples was by solvent extraction using triisooctylamine in xylene. Low-energy photon counting was done with a high gain setting and a 3 μs shaping time, which provided accurate quantitation without interference of 59Fe and other potential contaminants, which were either removed by separation or discriminated against by the counting procedure. Iron-59, either present in the sample or added as a spike, was used as a tracer for determining radiochemical yield, which was about 70%. The lower limit of detection was found to be 80 pCi/g based on a 10 g sample and a 5 min counting time.

Large angle elastic scattering of 59.5 keV photons

The work reported has been carried out using an intrinsic germanium detector in order to extend to a lower energy region previous investigation on Rayleigh scattering between 0.1 and 1 MeV. Differential cross sections for Rayleigh scattering of 59.5 keV photons from Sn, Mo, Ta, Er, Cd, Nb and Yb, measured for angles ranging from 60 to 165', are presented. The results are discussed in comparison with theoretical calculations.

Use of indirectly measured spectra in fundamental parameters X-ray fluorescence analysis

X-ray fluorescence spectrometry by recourse to computations with fundamental physical parameters, requires one to determine the irradiation spectra with precision and as frequently as possible, since changes with anode material, high voltage conditions, age, contaminants, etc. are known to alter its shape. Knowledge of a spectrum before an experimental run, allows one to carry out computations of fluorescet intensities with better accuracy In order to do this, we have implemented a procedure of indirect determination of spectral shape through a parametric fitting of a mathematical model, containing the X-ray excitation spectra and detector characteristics convoluted with the attenuation factor. As shown elsewhere, this is a Laplace transform and it is proportional to the absorbed dose as measured with an ionisation chamber. Direct measurements were also performed on the collimated beam with an intrinsic germanium detector, for test purpose, with good results. Elemental concentrations for a sample of interest, were finally calculated by means of the Lachance-Traill method as modified by Claisse and Quintin, but with binary and multicomponent standards calculated with theoretical equations instead of using measurements on real standards. The final test of this proposal is given by measurements on standards from the National Bureau of Standards.

Performance of a HPGe-NaI(Tl) Compton suppression spectrometer in high-level radioenvironmental studies

A Compton suppression spectrometer used for gamma-ray spectroscopy in high level radioenvironmental studies is described. A 113 cm 3 intrinsic germanium detector is inserted into a 22.9×25.4 cm annular NaI(Tl) detector and coupled to an anticoincidence gating system. The performance of suppression of the Compton continuum is studied as a function of various source-to-detector distances, incident gamma-ray energies, as well as the intensity of activities. The optimum suppression factor is 5.2 at a photon energy of 662 keV. Examples are given for use at medium and high level radioenvironmental measurements on the nuclear reactor experimental floor before and during reactor operation. Characteristics of this spectrometer are compared with other representative systems and special features are discussed.

Comparison between the experimental Compton profiles of Ti and TiH1.98

Compton profiles for the polycrystalline Ti and TiH1.98 have been measured at room temperature using 59.54 keV γ-radiation from a 0.5-Ci241 Am annular source and an intrinsic germanium detector. The difference of the profiles before and after hydrogen loading are compared with different theoretical models for the electronic structure of TiH1.98. It is shown that the Compton profile is a sensitive test of the accuracy of various model wavefunctions for the hydrides. The best fit to our experimental data is given by a model based on self-consistent band structure calculations. In this model the Compton profile is completely defined through the wavefunctions of the system.

Electronics Package for Rugged HPGE Detectors

A prototype electronics package of amplifier, ADC, pulser, data-bus interface, bias supply and low voltage supply has been developed to process high resolution data from rugged intrinsic germanium detectors with high reliability in a harsh environment. This sturdy modular package attachable to the dewar of a rugged detector oriented horizontally or downward degrades detector energy resolution at 1332 KeV less than 0.25 KeV.

Applications of emission tomography in the nuclear industry

An emission tomography system has been used to carry out experiments to simulate the scanning of irradiated nuclear fuel. A phantom made of titanium containing a multi-energetic radionuclide, 182Ta, has been used in conjunction with a high resolution intrinsic germanium detector to study the effects of scattering and attenuation on the image obtained. Reconstructed images produced from data in two energy regions, one a “photopeak window” and the other a “scattering window” show the importance of these effects with multi-energetic spectra. 182Ta sources separated by 0.5 mm of titanium could be resolved.

Background events in the energy region below 4 MeV detected with a 208 cm 3 intrinsic germanium detector : I. Characteristic γ-radiation

A detailed study of the events recorded with a 208 cm 3 intrinsic germanium γ-ray detector produced by interactions of natural environmental radiation was undertaken. In the first part of this work, the data on events from characteristic radioactivity are analysed to optimise the shielding requirements for reducing the γ-ray background as seen by the detector. A thickness of 15 cm of Pb all around the detector in the laboratory location, or only 5 cm in the underground location at the mine, is found to be sufficient to attenuate the event rates from environmental characteristic γ-rays to less than the event rates from intrinsic contamination of the detector components in the detector assembly. The salt mine is found to be a natural environment low in γ-ray background.

Side effects of the use of cylindrical grooves in planar intrinsic germanium detectors

One technique for producing planar intrinsic germanium detectors involves machining a deep groove in the detector crystal just inside the outer cylindrical surface and running from one plane face almost to the other. Weak collection fields near the base of the groove can then be expected to lead to the appearance of some output pulses having very long rise times. Two detectors of this type have been examined. It was found that at low counting rates and in the absence of pulse shape discrimination slowly rising pulses were processed as if they formed a continuum of low energy pulses extending into regions where with a mono-energetic gamma source pulses would not normally be present. At high counting rates the smallest slow pulses, which escape the attention of the pile-up detection circuits, were found to give rise to lines with high energy tails, and to excess rate dependent line broadening.

A Comparison of Theoretical and Experimental Calibration of a Highly Collimated Mobile Gamma-Ray Spectrometer

A highly collimated mobile gamma-ray spectrometer constructed by EGandG Idaho has been calibrated for full-energy peak efficiency. This spectrometer contains a high resolution intrinsic germanium detector, and it is designed for making activity measurements inside reactor containment buildings in high radiation fields. Peak efficiencies were determined for point sources positioned on and off the detector-collimator axis over an energy range from 80 to 2800 keV. The off-axis distributions were integrated to give the isotropic disk source efficiencies. These results were compared to those obtained from directly measuring a /sup 24/Na-doped aluminum foil ''disk.'' Theoretical disk source efficiencies were calculated using the point kernel approach. These results were normalized to the on-axis point source efficiencies. The procedure is selfconsistent but it requires more detailed measurements in the future in order to provide accurate results. Once the measurements are made, however, the spectrometer system can then be used to accurately assay arbitrary distributions of surface activities. The method is also well suited for use in collimator design because leakage effects can be directly calculated.

Compton line profile component of atomic hydrogen in the profile of NbH1.2

The Compton profile of polycrystalline NbH1.2 has been measured at room temperature using a ψ-ray Compton spectrometer with a 1.85×1010 Bq(0.5 Ci)241 Am annular source and an intrinsic Germanium detector. This is compared to the spherical average profile of NbH0.3 single crystals oriented along [100], [110] and [111]. The difference between these profiles\(J(q)_{NbH_{1.2} } - J(q)_{NbH_{0.3} }\) bears a striking similarity to the Compton profile of atomic hydrogen. This can be understood assuming that a large part of the dilute hydrogen forms atomic clusters at the grain boundaries.

Some experimental evidence of critical γ-ray Compton scattering by binary mixtures at the demixing temperature

Using a gamma ray Compton spectrometer with a 1.85 × 10 10 Bq (0.5 Ci) 241 Am annular source and an intrinsic germanium detector the total Compton cross section of nitrobenzene- n-heptane (63.4 ± 0.1 vol%) binary liquid system was measured at different temperatures near the critical one of 19.03 ± 0.01 °C. At the demixing temperature the total Compton cross section shows a sharp increase of no less than 20%. This increase is attributed to the enormous increase of the correlation range near the critical temperature.

The study of short-lived nuclei in the regionZ=59?68

β + -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. QEC values have been obtained and new isomeric states have been identified for the first time.

Characterization of tissue via coherent-to-Compton scattering ratio: sensitivity considerations.

It is known that the ratio (R) of the detected coherent and Compton scattered photons from bone can be used in order to determine its mineral density. This technique utilizes the dependence of the coherent scattering on the effective atomic number (Z) of the scattering medium. It is generally accepted that a small scatter angle is preferred in order to ensure adequate counting statistics by favoring the detection of more coherent photons. Moreover, it has been assumed that a change in the scatter angle does not affect the sensitivity of the measurement. Our theoretical calculations for 60-keV photons and for the range of Z that corresponds to trabecular bone, indicate that increasing the scatter angle results in a stronger power dependence of the measured ratio on Z. This implies that by increasing the scatter angle, smaller changes in the mineral density can be detected, thus improving the sensitivity of the measurement. This effect was investigated experimentally by using a collimated beam of 59.54-keV photons from Am-241 (44.4 GBq) and a collimated intrinsic germanium detector. Solutions of K2HPO4 with different concentrations were used in order to simulate trabecular bone. The scatter spectra were recorded for all solutions at six scatter angles between 37 degrees and 98 degrees and the value of R was computed for each spectrum. The sensitivity of the measurement, evaluated from these experiments increased, with the increase of the scatter angle.

A Monte Carlo study of the response of a germanium detector to electrons and positrons

A Monte Carlo code has been developed which predicts electron and positron response functions of a planar intrinsic germanium (Ge) detector. The operational flow chart for the main program is given and the function of each subroutine is discussed. The characteristics of the response functions are studied by considering effects due to bremsstrahlung, annihilation radiation and the total electron transit distance. It is found that electron spectra are distorted primarily near the full energy peak by bremsstrahlung while positron spectra are seriously distorted by both annihilation radiation and bremsstrahlung. Total transit distances calculated here are found to be in good agreement with those calculated using the Bethe-Bloch formula. The effects of bremsstrahlung, annihilation radiation and total stopping distance, calculated independently in the complete code, are then used to construct an abbreviated version which reduces the computer time by a factor of 16. Sample computations are presented for a 16 mm diameter by 7 mm thick, planar detector. The calculated response functions reproduce experimental spectra accurately; they are also used to analyze positron spectra and obtain endpoint energies.

Evaluation of an Automated Assay System to Measure Soil Radionuclides by L X‐Ray and Gamma‐Ray Spectrometry

AbstractAn automated radionuclide assay system was evaluated for performing soil radioassays using L x‐ray and gamma‐ray spectrometry. Wet chemistry assay procedures were shown to be considerably more time consuming than similar analyses of soils on this radionuclide assay system. The detection limits of 241Am and Pu were determined, as well as the reproducibility of radionuclide assay results. The L x‐ray spectrometric measurements were compared with radiochemical analysis on several tuff samples. The assay system's intrinsic germanium detector was found to respond linearly to varying low concentrations of 241Am and Pu, both of which were easily detected in the presence of elevated concentrations of 137Cs.