Determination of selenium in animal tissue samples using radioisotope induced X-ray fluorescence

A summary of sources of background affecting gamma-ray spectrometers and methods for eliminating each are discussed, along with practical cost/benefit ratios. Background contributed by samples generally defines practical levels for system background. The practical bottom line can be obtained for relatively modest costs. A realistic bottom line is attained in underground systems when the major contributions to the background come from cosmogenically produced⁶⁸Ge and double-beta decay of⁷⁶Ge in the detector. The true bottom line is reached with isotopically enriched detectors that eliminate these two chemically inseparable radioactive impurities. Data from isotopically enriched detectors are presented.     

Use of electrodeposition for sample preparation and rejection rate prediction for assay of electroformed ultra high purity copper for 232Th and 238U prior to inductively coupled plasma mass spectrometry (ICP/MS)

The search for neutrinoless double beta decay in ⁷⁶Ge has driven the need for ultra-low background Ge detectors shielded by electroformed copper of ultra-high radiopurity (<0.1 μBq/kg). Although electrodeposition processes are almost sophisticated enough to produce copper of this purity, to date there are no methods sensitive enough to assay it. Inductively coupled plasma mass spectrometry (ICP/MS) can detect thorium and uranium at femtogram levels, however, this assay is hindered by high copper concentrations in the sample. Electrodeposition of copper samples removes copper from the solution while selectively concentrating thorium and uranium contaminants to be assayed by ICP/MS. Spiking ²³²Th and ²³⁸U into the plating bath simulates low purity copper and allows for the calculation of the electrochemical rejection rate of thorium and uranium in the electroplating system. This rejection value will help to model plating bath chemistry.     

Pulse shape analysis to reduce the background of BEGe detectors

A simple technique for pulse shape discrimination in HPGe-detectors of the so-called BEGe type, based on just one parameter obtained from one signal read out, is presented here. This technique allows discriminating between pulses generated when the deposited energy is located within a small region of about 1 mm³ from the pulses generated when the energy is deposited at different locations several mm or cm apart. Two possible applications using this technique are: (i) experiments that look for neutrinoless double β decay in ⁷⁶Ge, such as GERDA; (ii) γ spectrometry measurements where the Compton continuum can be reduced and the efficiency for cascading γ-rays can remain high. With this active background reduction technique a Compton suppression factor of about 3 was obtained. The detector response may be influenced by the detector size. The detector used for this study had a diameter of 6 cm, a thickness of 2.6 cm and a relative efficiency of 19%. The results obtained with this detector were consistent with the results obtained by Budjá? et al. [J Instrum 4:10, 2009] with a 50% relative efficiency BEGe detector.     

Correction equations of coincidence summing using75Se radionuclide in the efficiency of HpGe detector

Correction equations of the coincidence-summing effect for efficiencies of HpGe detector based on the decay scheme were developed by considering the summing up to triple coincidence. The correction equations which do not dependent on the kind of the Ge detector are very useful for efficiency calibrations of a Ge detector in the energy region from 60 to 400 keV by using⁷⁵Se radionuclide even with very short source-to-detector distances.     

Thick silver electrodeposition on copper substrate for <Superscript>109</Superscript>Cd production

Spectrometers for the lowest-level radiometric measurements require materials of extreme radiopurity. Measurements of rare nuclear decays, e.g., neutrinoless double-beta decay, can require construction and shielding materials with bulk radiopurity reaching one micro-Becquerel per kilogram or less. When such extreme material purity is achieved, surface contamination, particularly solid daughters in the natural radon decay chains, can become the limiting background. High-purity copper is an important material for ultra-low-background spectrometers and thus is the focus of this work. A method for removing surface contamination at very low levels without attacking the bulk material is described. An assay method using a low-background proportional counter made of the material under examination is employed, and the preliminary result of achievable surface contamination levels is presented.     

Non-destructive determination of rhodium in platinum by epithermal reactor neutron activation analysis

Activation in connection with Ge(Li) γ-spectrometry proves profitable in determining traces of rhodium (and silver) in pure platinum. As the 556 keV photopeak of¹⁰⁴Rh was chosen for evaluation, its decay behaviour had to be considered. Moreover, a special automatic correction of dead-time and decay was applied. The limit of detection in a single run was 5 ppm.     

Relative efficiency calibration of Ge(Li) detector in low energy region

The relative gamma-ray intensities in the energy region between 122 and 411 keV in the decay of¹⁵²Eu were measured by using a Ge(Li) detector. Its efficiency calibration was carried out with the radioactive sources of²⁴¹Am,⁵⁷Co,²⁰³Hg,¹³⁷Cs,¹³³Ba,⁷⁵Se,¹⁶⁹Yb and¹⁹²Ir.     

The decay of188Re

The -ray spectra of¹⁸⁸Re decay have been studied by using two Ge/Li/ spectrometers and a three parameters /E-E-T/ List coincidence system. The energies and relative intensities of 52 -rays and cascade relations of 14 -rays are determined. Ten new -rays: 155 /633–478/, 984, 1096, 1463, 1332, 1530, 1574, 1810, 1867, and 1937 keV have been identified. The 155 /633–478/ transition is confirmed and its relative intensity is estimated by means of coincidence experiment. 24 levels of¹⁸⁸Re are assigned. Among those, 6 levels are first put into the decay scheme of¹⁸⁸Re. In addition to 1443 keV and 1937 keV levels, 1685, 1729 and 1965 keV levels are also observed in the decay of¹⁸⁸Ir and other reaction studies. The 1948 level is recently suggested in the¹⁹⁰Os/p, t/¹⁸⁸Os reaction. The 486 keV and 811 keV -transitions are also put into the level scheme of¹⁸⁸Re. The ^– decay branching ratio is deduced.     

On the γ-spectrum following225Ac α-decay

The decay of a²²⁵Ac source in equilibrium mixture with its decay products was investigated using high-resolution HP/Ge/ detectors. Energies and intensities of more than 78 -photons were measured with an improved accuracy; 44 of them are reported for the first time. A tentative²²¹Fr level scheme was built on the basis of good energy sum relationships; seven new²²¹Fr excited levels are proposed at 496.9, 570.9, 603.5, 630.7, 637.7, 649.0 and 758.9 keV.     

Bremsstrahlung emission in α-decay of210Po

Bremsstrahlung photons associated with the α-decay of²¹⁰Po were measured in α-γ coincidence measurements with Si and Ge detectors. Emission probabilities of the bremsstrahlung deduced for²¹⁰Po were 10⁻¹¹∼10⁻¹²/keV/sr/decay for 100≤E _γ≤600 keV. It was found that the bremsstrahlung yields are much smaller than those predicted by a Coulomb acceleration model. This suggests that α-particles also emit photons inside the barrier. The bremsstrahlung spectrum was compared with a quasi-classical calculation in which the bremsstrahlung emission in tunneling motion of α-particles is taken into account. It is shown that the data can be interpreted as a consequence of destructive interference of radiative amplitudes outside the Coulomb barrier with those in tunneling.     

Analysis of low energy X-ray and excitation spectra of Ba 35+

We present a theoretical analysis of the low energy X-ray spectra of the Ba³⁵⁺ + e ^- system, in the energy region below 2 keV, for comparison with future experiments. In a recent study carried out at the National Institute of Standards and Technology, scandium-like Ba³⁵⁺ ions were created, trapped and excited using an Electron Beam Ion Trap and an electron beam with kinetic energy of 2.35 keV. The theory agrees well with experiment for X-ray energies in the region 2–5 keV. The experiment also gives evidence suggestive of a large cross section for X-ray production in the region below 2.0 keV. We include the contribution to the X-ray spectra of collisional excitation followed by fluorescence decay, radiative cascade processes, M-shell dielectronic recombination, Bremsstrahlung, and a new off-shell, quasi-resonant continuum dielectronic recombination process. We find that excitation fluorescence is the dominant process, with smaller contributions from the other radiative cascade processes as well as a continuous Bremsstrahlung background.     

The determination of bromine in dry biological material by instrumental neutron activation analysis

Procedures for the determination of bromine by the reactions⁸¹Br(n, γ)⁸²Br (T=35.4 h) and⁷⁹Br(n, γ)^80mBr (T=4.4 h). In the case of⁸²Br a flat coaxial Ge(Li) crystal is used to measure the 619 keV photopeak. For^80mBr a planar Ge(Li) detector is applied to measure the 39 keV γ-ray. The agreement between the data obtained with both techniques for some Standard Reference Materials is satisfactory.     

The half-life of 76As

In the course of making high-accuracy measurements of arsenic, we found that the most recently published and compiled half-life of ⁷⁶As did not agree with our data as well as the earlier accepted value. To redetermine this parameter, ⁷⁶As sources were measured on four Ge gamma detector systems, and an exponential function was fitted to the decay data by two different nonlinear least-squares methods. We obtained T _1/2 = 1.09379 days with a standard uncertainty of 0.00045 days. This result is 1.5% higher than the most recent value, but is in agreement with the older, less precise, consensus value.     

Using the 186-keV peak for 226Ra activity concentration determination in Hungarian coal-slag samples by gamma-ray spectroscopy

The uranium isotopic abundance and the ²³⁸U–²²⁶Ra secular equilibrium were determined in nine Hungarian coal slag samples. The ²²⁶Ra activity concentration was measured based on the radon decay products and also the ²²⁶Ra peak at 186 keV. Secular equilibrium existed in eight samples, whereas one sample showed a slight disequilibrium. The direct and fast measurement using only the 186 keV peak was validated which can be used after measuring the uranium isotopic ratio and verifying the ²³⁸U–²²⁶Ra secular equilibrium. This method can be used to measure the ²²⁶Ra content of high number of samples from the same geochemical background.     

Uranium assay of fuel rods by passive gamma-ray spectrometry

The spontaneous gamma-rays characteristic of uranium isotopes can be detected and measured in order to identify the isotopic composition of uranium and to assay its total amount in various objects and materials. In order to test these methods of passive gammaray spectrometry in practice, the²³⁵U-enrichment of a known fuel rod was determined by counting 186 keV gammas from²³⁵U with Ge(Li) detectors of different volumes. The 1001 keV gammas characteristic to²³⁸U were counted too. Expected counting rates of 186 keV and 1001 keV gammas for WWER fuels are given and the suitability of passive gamma-ray spectrometry for the determination of²³⁵U-enrichment and for the assay of total uranium in reactor fuels are discussed based on these measurements.     

Polonium–lead extractions to determine the best method for the quantification of clean lead used in low-background radiation detectors

Radiation detectors used to search for the existence of exceptionally rare phenomena, such as double-beta decay and dark matter interactions, as well as tiny traces of environmental radioactivity, require the elimination of background signals. Modern detection systems created from ultra pure materials and operated deep underground may be sensitive enough to “see” these rare phenomena, but background activity in Pb gamma-ray shielding could still be a critical stumbling block owing to alpha and beta emissions of Pb, Bi, and Po in the mass 210 chain. To minimize the probability of overwhelming activity from Pb, the alpha activity of ²¹⁰Pb is quantified. However, a reliable quantification procedure that does not require large volumes of chemicals has not yet been established. Two procedures created for this purpose have been tested for the quantification of alpha activity in lead. Both procedures were designed to start with less than 10 g Pb samples to reduce reagents needed and combined precipitation with column separation to isolate ²¹⁰Pb, followed by alpha spectrometry. One procedure shows promise for obtaining high recoveries and good separation.     

Bismuth radionuclides in the natural background gamma radiation spectrum

The natural background gamma (NBG) spectrum was accumulated inside the laboratory, with 102.88 cm³ Ge(Li) detector, to investigate bismuth natural radionuclides in the energy range of 500–1700 keV. The relative intensities of identified²¹⁴Bi gamma lines were obtained from the spectrum. The results were in good agreement with that obtained from a source of a precise strength. Out of the 25 gamma lines of²¹⁴Bi, 19 lines were established including 6 lines observed for the first time in the NBG spectrum. Most of the gamma lines of²¹¹Bi and²¹²Bi were observed. Some of these lines are new.     

Molekulares S=GeCl2 Matrix-IR-Untersuchungen und ab initio SCF-Rechnungen

The Molecule S?GeCl₂. Matrix IR Investigation and Ab initio SCF Calculation Molecular S?GeCl₂ is found in a matrix reaction between the high-temperature molecule Ge?S and Cl₂. A structure analog to that of phosgene can be derived from the isotopical shifts (⁷⁰Ge/⁷²Ge/⁷³Ge/⁷⁴Ge/⁷⁶Ge and ³⁵Cl/³⁷Cl) within the IR spectra. The normal coordinate analysis results for the Ge?S force constant a value of 4.21 mdyn/Å. The spectroscopic results are confirmed by ab initio SCF calculations.     

Microcalorimeter arrays for ultra-high energy resolution X- and gamma-ray detection

Microcalorimeter detectors provide superior energy resolution for the detection of X-rays and gamma-rays. The technology utilizes a cryogenic transition-edge sensor (TES) coupled to a tin bulk absorber. We are working on fabrication methods for the production of arrays with many sensors. In this paper, we present data collected with an array of microcalorimeters using as many as 26 sensor elements simultaneously. Advances in sensor design have extended the useful dynamic range to photon energies up to ～200 keV, while providing resolution performance in the 80–90 eV FWHM range, significantly better than planar high-purity germanium. These sensor arrays have applications in the measurement of nuclear materials. We present data collected from ¹⁵³Gd, a highly-enriched uranium sample, and a plutonium isotopic standard source. We also demonstrate clean separation of the ²³⁵U 185.715 keV peak from the ubiquitous ²²⁶Ra 186.211 keV background peak interference.     

Medium energy ion irradiation of Ge surface – search for a better understanding of the surface nano‐patterning

We report the morphological changes on Ge surfaces upon 50 keV Ar⁺ and 100 keV Kr⁺ beam irradiation at 60° angle of incidence. The Ge surfaces having three different amorphous–crystalline (a/c) interfaces achieved by the pre‐irradiation of 50 keV Ar⁺ beam at 0°, 30° and 60° with a constant fluence of 5 × 10¹⁶ ions/cm² were further processed by the same beam at higher fluences viz. 3 × 10¹⁷, 5 × 10¹⁷, 7 × 10¹⁷ and 9 × 10¹⁷ ions/cm² to understand the mechanism of nano‐scale surface patterning. The Kr⁺ beam irradiation was carried out only on three fresh Ge surfaces with ion fluences of 3 × 10¹⁷, 5 × 10¹⁷ and 9 × 10¹⁷ ions/cm² to compare the influence of projectile mass on surface patterning. Irrespective of the depth of a/c interface, the nanoscale surface patterning was completely missing on Ge surface with Ar⁺ beam irradiation. However, the surface patterning was evidenced upon Kr⁺ beam irradiation with similar ion fluences. The wavelength and the amplitude of the ripples were found to increase with increasing ion fluence. In the paper, the mass redistribution at a/c interface, the incompressible solid flow through amorphous layer, the angular distribution of sputtering/backscattering yields and the generation of non‐uniform stress across the amorphous layer are discussed, particularly in analogy with low energy experiments, to get better understanding of the mechanism of nanoscale surface patterning by the ion beams. Copyright © 2016 John Wiley & Sons, Ltd.