Ge Li Detector Research Articles

Prompt gamma-ray emission from fission of239Pu by resonance neutrons I

Gamma-ray spectra from239Pu(n,f) reaction were measured with the gamma spectrometer on the pulsed reactor IBR-30. The fast 19-section ionization chamber with 1.6 g of239Pu targets was used. The fission gamma-rays within the 32 ns time window were measured using a Ge(Li) detector. Based on the measured gamma-ray spectrum in the (0.1–1.8) MeV interval, the total number of emittedγ-quanta-multiplicity 〈N γ tot 〉 and total energy of γ-quanta per fission event, 〈E γ tot 〉, were calculated. The results were 7.0±0.6γ/fission and 6.8±0.5 MeV/fission respectively.

L-shell x-ray intensity ratios for Au and Pb at excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV

The L-shell x-ray intensity ratios I(L1)/I(Lα), I(Lβ)/I(Lα) and I(Lγ)/I(Lα) for Au and Pb have been measured at the excitation energies 36.82, 43.95, 48.60, 50.20 and 53.50 keV with a HP Ge(Li) detector. Measurements have been performed using an x-ray tube with a secondary exciter system as the excitation source. The x-ray tube with a secondary target arrangement was used to obtain high intensity with high degree of monochromatisation. A comparison is made of the experimental results with the calculated values obtained by using theoretical x-ray emission rates, sub shell ionisation cross-sections sub shell fluorescence yields and Coster-Kronig transition probabilities. A fairly good agreement is observed between experimental and theoretical values. The intensity ratios for intense transitions ILβ/ILα are in good agreement with the theoretical values.

Empirical relation between efficiency and volume of HPGe detectors by Monte Carlo calculation

The empirical relation between the detection efficiency and volume of Ge(Li) detectors obtained by Vaño et al. has been proved to be valid here by Monte Carlo simulation for HPGe detectors of active volume up to 175 cm 3. Simulations for the efficiency of the detectors with fixed active volume but different geometrical factors have also been made. It indicates that the slope of the HPGe detector efficiency curve depends only on the detector's active volume but not on its geometrical factor.

The gamma-ray detection efficiency of a 118 cm 3 Ge(Li) detector for disc-sources of 7Be

The full energy peak detection efficiency of a 118 cm 3, closed end, coaxial Ge(Li) detector has been measured as a function of source to detector separation using disc-sources of 7Be with diameters ranging from 5 to 80 mm. The detector was characterized using a number of point-like sources of different energy placed on axis at different distances from the detector. The combined results were analysed in terms of the point-detector model and the Gaussian radial dependence model. The point-detector-model was found to provide a satisfactory parameterization of the axial variation of efficiency for point-sources. However the method did not predict the radius dependence of the efficiency for disc-sources. The Gaussian model provided much better fits in this case.

Analytical study of amplitude rise time compensated timing with coaxial Ge(Li) detectors

The performance of a system for zero-cross-over, amplitude- and risetime-compensated (ARC) timing of coaxial Ge(Li) detectors is analyzed using an average-pulse-shape method. The standard deviation of walk and noise jitter as a function of energy deposited in the detector are computed, and the FWHM of amplitude- and risetime-compensated (ARC) timing spectra are verified by comparing them with experimental results published elsewhere. Deviations of the centroid of ARC prompt time distributions from the corresponding pack positions are studied through mathematical expressions. >

Dependence of the Kβ/Kα intensity ratio on the oxidation state

The Kβ/Kα X-ray intensity ratios were measured for pure Cr, Mn, Co and Cu belonging to the 3 d shell as well as in their compounds, to look for the influence of the chemical environment on the fluorescence yield ratios. The vacancies in the K shell created by 59.5 keV γ-rays from an241Am source and the X-rays were measured using a Ge(Li) detector. A steady increase of the Kβ/Kα intensity ratio was observed with increasing oxidation. The present results agree with previously published experimental data.

Excitation function for α-particle-induced reactions in light-mass nuclei

The excitation functions of 51V [(α, xn), x = 1.3; (α, p3n); (α, α3n) (α, 2α)] and 59Co[(α, 2n); (α, αxn); x = 1, 2] reactions were measured up to 50 MeV by the stacked-foil activation technique and high-resolution Ce(Li)–HPGe spectroscopy method. Of these 51V(α, xnypzα) reactions were studied for the first time with better accuracy than earlier measurements, which were done with a poor resolution scintillation–Ge(Li) detectors some 20 years ago. In the case of 59Co, existing data show large discrepancies at low energy. Comparisons are presented with the prediction of hybrid and exciton models. While for the (α, xn) type of reactions, reasonably explainable pre-equilibrium contributions are found, there seem to be indications of direct inelastic scattering effects in the (α, αxn) type of reactions.

Chemical effects on K beta /K alpha X-ray intensity ratios in coordination compounds of some 3d elements

The effects of changes in coordination number on K beta /K alpha X-ray intensity ratio have been studied experimentally. The K beta /K alpha X-ray intensity ratios for both pure Cr, Mn and Cu and their various chemical compounds with tetrahedral and octahedral symmetry are investigated using a Ge(Li) detector. The measured results indicate that the K beta /K alpha ratios for compounds with tetrahedral symmetry are in general larger than those with octahedral symmetry. The obtained K beta /K alpha X-ray intensity ratios are comparable with both previous published experimental and theoretical results.

Recent studies on radon—A measure of living standard

Following the work reported elsewhere, we studied the effect of temperature on the radon concentration levels. A radon source was made by depositing 226Ra standard solution on a plastic disk and radon emanation rate was studied as a function of temperature using a Ge(Li) detector. In order to determine the radon and its daughters' concentration levels with CR-39 detectors, small and equal volumes of 226Ra solution were taken in unsealed tubes and then placed carefully in bottles and radon concentration levels were studied as a function of temperature. To obtain the desired temperature, refrigerator and temperature controlled water bath were used. This study indicated that temperature significantly affects the radon concentration levels and together with the ventilation data, one may be able to guess about the living standards of the residents from the measured values of radon and its daughter products' concentration levels.

Isomeric yields of130Sb,132Sb,134I, and136I in the thermal neutron fission of235U

Isomer yield ratios of130Sb,132Sb,134I and136I isomers formed in the thermal neutron fission of235U have been calculated from our previous experimental studies that led to the identification of these species. In those studies the iodine and antimony fractions formed in fission were rapidly separated and the decay of γ-rays belonging to each isomer pair were followed using Ge(Li) detectors and a multichannel analyzer. The isomer ratios were calculated from growth and decay considerations of these γ-rays. The results are compared with the recently published values obtained with an on-line isotope separator, those from LOHENGRIN, and those from model calculations. Angular momenta of fission fragments corresponding to the measured isomer yields have also been calculated.

Directional correlations of γ-rays in149Gd

Theγ-γ directional correlations for cascades observed in the 4.1 hour149Tb decay were measured on the multidetector system consisting of 7 Ge (Li) detectors. The results together with the experimental data on the internal electron conversion allowed a model-independent assignment of the spin values at a confidence level higher than 95% for three levels in149Gd: 325 keV 3/2−, 817 keV 3/2− and 1206 keV 1/2−. Multipole mixing ratios for sixγ-transitions were also derived.

The development of a rectilinear scanner utilizing high resolution gamma-ray detection

A rectilinear scanner has been constructed which incorporates high resolution gamma-ray spectroscopy. This scanner was built to simultaneously image the distributions of multiple gamma-emitting radionuclides in small animals, such as rabbits and rats. The instrument design is described, followed by studies of the Ge(Li) detector response and calibration tests of a single straight-hole collimator. Based on these results, two new collimators were designed and constructed; (1) a six tapered-hole focusing collimator and (2) a nine straight-hole focusing collimator. These new collimators are advantageous because they offer an increased efficiency of gamma-ray detection during scanning. They also give better image resolution in the differentiation of two points (or organs) on a plane. The results of the calibration tests and comparisons of the resolution and efficiency among collimators are illustrated and discussed.

Measurement of the photon emission probabilities in the decay of 182Ta and 185W

The K X-ray and gamma-ray spectra of 182Ta have been measured with a 72 cm3 HPGe detector in the energy range up to 2.0 MeV and a planar HPGe detector (3.0 cm2 × 1.0 cm) in the range up to 300 keV. The detector efficiencies versus energy were determined by means of standard sources manufactured in our Laboratory of Radionuclide Metrology. The K X- and gamma-ray relative emission probabilities were determined on the basis of the spectra analysis. A discrepancy between the intensity values of doublet lines in 182Ta at energy about 67.7 keV may be seen when compared with papers which have not taken into considerationIn the case of 185W the 123.3 keV gamma-ray absolute emission probability was determined from the activities and the gamma-emission rates of measured sources. The spectrometric measurements of 185W were performed with a 20 cm3 Ge(Li) detector and a HPGe detector (0.8 cm2 × 0.7 cm). The activity of 185W was measured by the triple-to-double coincidence ratio (TDCR) method [12].

Efficiency calibration of Ge(Li) detectors, and the effects of geometry and physical properties of samples on the efficiency of detectors

To perform quantitative analysis of Ge(Li) spectra, not only energy calibration but also efficiency calibration procedures are done. Although the use of standard sample volume, mass, density and geometry is preferable, this optimum is not always possible. So to achieve an optimization is the main objective of the work reported here. Efficiencies have to be determined as a function of energy, density, thickness, mass of sample, intensity, and source-to-detector distance.

Precise Radiation Energy and Core Electron Contribution of Positron Annihilation in Al Studied with Two Ge(Li) Detectors

The average energy of positron annihilation radiation from Al has been determined by the Doppler-broadening summing technique with two detectors. Energy differences of annihilation radiation from the electron rest mass are 8.2±3.1 eV and 8.9±3.3 eV for the single and coincidence measurements, respectively. According to the analysis by using the electron binding energy, half of the intensity of the momentum distribution outside the Fermi momentum is due to high-momentum components of the conduction electrons. The contribution of the core electrons to the total annihilation is estimated to be 5∼6%, and the core enhancement factor is 1.2∼1.5. The average energy of annihilation radiation estimated with this contribution is consistent with the above measured values within the experimental accuracy.

Measurements of the half-life of the 2 nu beta beta -decay of 76Ge

Two measurements of the half-life of the 2 nu beta beta -decay of 76Ge are reported. One was made with the PNL-USC natural isotopic abundance germanium twin detectors. T12/2 nu =(1.12+-0.26+0.48)*1021 y (2 sigma ), and one with a Soviet-manufactured 0.25-kg Ge (Li) detector isotopically enriched to 85% in 76Ge, T12/2 nu (9.2+-0.4+0.7)*1020 y (2 sigma ). Both were measured in the same facility. These values are in good agreement with nuclear structure calculations and with an independent measurement by the ITEP-YPI collaboration.

Experimental solid-angle correction for gamma angular correlations

A new method is described for performing solid-angle corrections on gamma angular correlation data. The gamma scanning technique was applied to two wrap-around Ge(Li) detectors in order to map their intrinsic photopeak efficiencies as functions of the energy and direction of incidence. A collimated 152Eu radioactive source of 1 mCi was used in the mapping procedure. Concerning directional correlations, no numerical integration is necessary for each gamma cascade measured, because a different correlation function is proposed for the fitting, where the angle-dependent effects to be corrected have been factorized. Only few energy interpolations are needed, in order to obtain the correction coefficients present in the new function. Tests were performed with the 4 → 2 → 0 cascade of 60Ni, and 0′ → 2 → 0 and 2′ → 2 → 0 of 100Ru, showing good agreement with previous results.

Systematic treatment of the photopeak efficiency

The method introducing the effective interaction depth for the photopeak efficiency proposed for small detectors was applied to three large germanium detectors and found feasible for large detectors too, except for soft γ-rays measured at small source-to-detector distances. These exceptional cases, are caused by attenuation by the absorption layer, or by ineffective core in the case of coaxial Ge(Li) detectors. Coincidence summing effects are also discussed in order to extract a simple relationship between the magnitude of the coincidence summing and the source-to-effective-volume distance regardless the details of individual cascade relations. This enabled us to devise a correction method for the coincidence summing even when the decay scheme is unknown for the relevant γ-ray.

Applicability of the analytical functions and semi-empirical formulae to the full energy peak efficiency of large volume HPGe gamma detectors

The applicability of various analytical functions and semi-empirical formulae proposed for representing the full energy peak efficiency (FEPE) curves of Ge(Li) and HPGe detectors has been studied for 114 cm3 and 157 cm3 HPGe coaxial detectors for gamma ray energies ranging from 244.66 to 1408.03 keV and from 80.997 to 1408.03 keV respectively. One of the functions proposed provides by far the best description of the present data. The most recent function, employed above approximately=110 keV, also gives more or less the same quality of fit. The low-energy (below approximately=110 keV) version of this function reproduces the trend of the 157 cm3 detector data very well below 122.06 keV. This particular function also describes the efficiency of a 38 cm3 Ge(Li) coaxial detector from 319.80 to 2598.80 keV exceedingly well. The semi-empirical formulae of Freeman and Jenkin (1966), Mowatt (1969) and of Vano and co-workers (1975) provide (above 244.66 keV) a very good representation of the present data. In general, the analytical functions describe the data better than the semi-empirical formulae. The present investigation shows that the analytical functions and semi-empirical formulae which represent the FEPE of moderate volume Ge(Li) detectors quite satisfactorily, can also be used for large volume HPGe detectors quite fruitfully, particularly in the energy range 244.66 to 1408.03 keV. This is also true the other way round for a 38 cm3 Ge(Li) detector from 319.80 to 2598.80 keV.

A new improved expression for gamma-ray detection efficiency of Ge(Li) detectors

In the present paper, a new improved expression for γ-ray detection efficiency of Ge(Li) detectors, ∈ γ 0 , is given. It is represented as a continuous function of x (viz. Eγ−1) with a maximum and decreases very rapidly to a small positive value as γ-ray energy, Eγ, drops to 40 keV or lower, but slowly as Eγ rises to 1.7 MeV or higher. Since it can well represent the whole physical process of the γ-ray detection, this expression may be one of the simplest and most precise representations, for ∈ γ 0 at the present time.