HPGe X-ray Detector Research Articles

K β to K α X-ray intensity ratios and K to L shell vacancy transfer probabilities of Co, Ni, Cu, and Zn

The K to L shell total vacancy transfer probabilities of low Z elements Co, Ni, Cu, and Zn are estimated by measuring the Kβ to Kα intensity ratio adopting the 2π-geometry. The target elements were excited by 32.86 keV barium K-shell X-rays from a weak 137Cs γ-ray source. The emitted K-shell X-rays were detected using a low energy HPGe X-ray detector coupled to a 16 k MCA. The measured intensity ratios and the total vacancy transfer probabilities are compared with theoretical results and others’ work, establishing a good agreement.

K-shell X-ray intensity ratios and vacancy transfer probabilities of Pt, Au, and Pb by a simple method

The K-shell X-ray intensity ratios, radiative and total vacancy transfer probablities of platinum, gold, and lead are measured by employing the 2π-geometrical configuration and a weak gamma source, a simple method proposed previously by our group. The targets of Pt, Au, and Pb were excited using γ-rays of weighted energy 123.6 keV from a weak 57Co source and the emitted K-shell X-rays were detected using an HPGe X-ray detector spectrometer coupled to a 16k multichannel analyzer. The measured values of these parameters are compared with the theoretical values and experimental data of other researchers, finding a good agreement. Thus, the 2π-geometrical configuration method with a weak gamma source can be alternative simple method to measure various atomic parameters in the field of X-ray spectroscopy.

Efficiency calibration of an HPGe X-ray detector for quantitative PIXE analysis

Particle Induced X-ray Emission (PIXE) is an analytical technique, which provides reliably and accurately quantitative results without the need of standards when the efficiency of the X-ray detection system is calibrated. The ion beam microprobe of the Ion Beam Modification and Analysis Laboratory at the University of North Texas is equipped with a 100mm2 high purity germanium X-ray detector (Canberra GUL0110 Ultra-LEGe). In order to calibrate the efficiency of the detector for standard less PIXE analysis we have measured the X-ray yield of a set of commercially available X-ray fluorescence standards. The set contained elements from low atomic number Z=11 (sodium) to higher atomic numbers to cover the X-ray energy region from 1.25keV to about 20keV where the detector is most efficient. The effective charge was obtained from the proton backscattering yield of a calibrated particle detector.

Efficiency calibration of x-ray HPGe detectors for photons with energies above the Ge K binding energy

We report on the efficiency calibration of a HPGe x-ray detector using radioactive sources and an analytical expression taken from the literature, in two different arrangements, with and without a broad-angle collimator. The frontal surface of the Ge crystal was scanned with pencil beams of photons. The Ge dead layer was found to be nonuniform, with central and intermediate regions that have thin (μm range) and thick (mm range) dead layers, respectively, surrounded by an insensitive ring. We discuss how this fact explains the observed efficiency curves and generalize the adopted model. We show that changes in the thickness of the Ge-crystal dead layer affect the efficiency of x-ray detectors, but the use of an appropriate broad-beam external collimator limiting the photon flux to the thin dead layer in the central region leads to the expected efficiency dependence with energy and renders the calibration simpler.

Study of non-validity of mixture rule near K-absorption edges by X-ray spectrometric technique

X-ray spectrometric technique has been described to determine the X-ray mass attenuation coeffi- cient, l/q, of X-rays employing HPGe X-ray detector and radioactive sources. The photon intensity is measured by gating the channel of the spectrometer at FWHM/photo peak. Using the technique the ''best value'' values of l/q were obtained for those thicknesses which lie in the transmission (T) range 0.5 C T C 0.02. Total attenuation cross sections for other elements and lead compounds were measured at photon energies from 17 to 88 keV to study the Bragg's additivity law near the absorption edge of the lead. The measured values of mass attenuation coefficient values are compared with theoretical values obtained using Winxcom (programme). This study suggests that measured mass attenuation coefficient values at and near absorption edges differ from the theoretical value by about 17-23%.

Determination of X-ray mass attenuation coefficients using HPGe detector

A detail analysis of a method to determine the mass attenuation coefficient, μ m, of low energy X-rays employing HPGe X-ray detector and radioactive sources is described. This method incorporates all the suggestions made by Creagh and Hubbell. An optimum distance is set under the broad beam as well as good geometry arrangement. The photon intensity is measured by gating the channel of the spectrometer at FWHM/photo peak. The selection of the absorber foils, optimum counting times are all done after detailed investigations for the μ m value. The method is studied in detail using aluminum/nickel as an absorber since these are standard reference materials. From these results, we conclude that the “best value” for μ m can be obtained for those thicknesses which lie in the transmission ( T) range 0.5≥ T≥0.02. The measured values of μ m for Magnesium, Nickel, Copper, Molybdenum and Tantalum and three biological equivalent materials are compared with standard theoretical values.

Development of a microtomography system at the Lund sub-micron beamline

A system for ion beam tomography has been implemented in conjunction with the new sub-micron beamline at the Lund Nuclear Microprobe laboratory. The first version of the system is dedicated to STIM (scanning transmission ion microscopy) tomography for three-dimensional mass density analysis, but future development will allow also PIXE (particle induced X-ray emission) tomography for elemental analysis of micrometer-sized samples. The PIXE tomography will gain from the 8-element large area HPGe X-ray detector (100mm2 for each element) at the low beam currents inherited with a sub-micrometer beam spot size.In this work, the first results are presented together with a detailed description of the developed system, including computer control of the sample rotation. The reconstruction technique, as well as potential tomography applications is briefly discussed.

DEVELOPMENT OF REGIONAL PIXE FACILITY AT PANJAB UNIVERSITY CYCLOTRON, CHANDIGARH (INDIA)

A description of modifications in the variable energy cyclotron (VEC) Chandigarh along with the installation of Proton Induced X-ray Emission (PIXE) setup is presented. A new main magnet power supply of 400A/125V out put with ±10 ppm stability and a new stabilized solid state power supply for RF oscillator has improved the beam characteristics substantially. A new chamber has been designed to cater for Proton Induced Gamma Emission (PIGE) and Rutherford Back Scattering (RBS) along with PIXE measurements. The HPGe x-ray detector, the Ge(Li) γ-ray detector and a silicon surface barrier (SSB) detector can be mounted simultaneously in the chamber for this purpose. A Turbo-Molecular vacuum pump is provided to produce a clean vacuum of the order of 10-8mbar in the PIXE chamber. A remotely controlled stepper motor is provided to move the wheel having 12/24-position target holder. Beam size optimization along with the minimization of background has been done with the help of graphite collimators, thus making the setup suitable for practical applications. Preliminary experiments for the PIXE analysis of aerosol, gunshot residues and kidney stone samples are presented.

K-shell X-ray production of In and Sn by proton, helium, and lithium ions

K-shell X-ray production cross sections for 1–5MeV 1H+ ions, 3–7MeV 4He2+ ions, 3–10MeV 7Li2+,3+ ions in In and Sn have been measured using a HpGe X-ray detector with a resolution of 145eV at 5.9keV, they were obtained by a comparison with the simultaneously measured Rutherford scattering cross section. The efficiency of the X-ray detector was determined using standard calibrated radioactive sources. Uncertainties inherent in this method are minimized to ∼8%. The experimental results are compared to the predictions of the ECPSSR theory and the K-shell empirical databases of Paul. Comparisons of our data with those from other measurements in earlier works are discussed.

Characterization of a new large area HPGe X-ray detector for low beam current application

In the new sub-micron beamline at the Lund Nuclear Microprobe facility a special large area HPGe X-ray detector has been installed. It consists of eight 100-mm 2-size detector elements arranged in an annular formation around the beam entrance hole. Different parameters like FWHM, FWTM, peak-to-background ratio and peak-to-valley ratio for each individual detector element as well as their sum spectra have been investigated. The data handling, i.e. how eight parallel signals are individually stored and summed together, has been discussed. The possibility to use the detector for simultaneous measurement of high and low energy photons, i.e. PIXE combined with PIGE has been demonstrated.

Evaluation of low-energy tailing parameters of a HPGe X-ray detector to be used in GUPIX software library for PIXE analysis

Accurate description of the response function of X-ray detectors is important for quantitative PIXE analysis. For analytical description of low-energy tailing in PIXE spectra, the GUPIX approach was used, i.e. a combination of Hypermate type functions. The low-energy tailing parameters of a low-energy high purity germanium X-ray detector in the region 1.3–9.2 keV was determined by systematic fitting of X-ray spectra from thin MicroMatter standards. Except for the main Gaussian peak and germanium escape peaks, one shelf, one truncated shelf, one exponential function and KMM radiative Auger feature was applied to fit the spectral data collected with this low-energy Ge X-ray detector. The overall trend of different tail parameters shows similar characteristic as those for Si(Li) X-ray detectors used in this energy range, i.e. very strong tailing at low X-ray energies and a rapid fall off with increasing X-ray energy. The fitted parameters, as a function of X-ray energy, were then incorporated into the GUPIX library for PIXE analysis.

Measurement ofK-electron capture probability (P k ) in the decay of197Hg (64.1 h)

TheK-electron capture probability (P K ) for the 268.7 and 77.3 keV states of197Au in the decay of197Hg (64.1h) have been determined from theKX-ray gamma ray summing in a HPGe X-ray detector. The measured values,P k (268.7)=0.746±0.033 andP k (77.3)=0.774±0.036 are found to be in good agreement with the theoretical results.

Charge determination of fission fragments via energy loss and X-ray measurements

Energy loss of fission fragments of specified charges and kinetic energies have been measured with a gas detector telescope. The singles data from the telescope (DE-E R) and coincidence data with a HP Ge X-ray detector (DE-E R-X) were taken using a 252Cf fission source. An empirical expression for the dependence of Z eff on charge and energy of fragments has been determined by fitting the observed energy loss behaviour of the fission fragments. The resolution in the measurement of charge from event by event analysis of DE-E R data for the light fragment mass group was found to be about 1.8 charge units (FWHM). The present data were analysed to determine the fragment charge distribution as well as the X-ray yield per fragment in 252Cf fission.