Paulo R. Pascholati

An experimental method for a precise determination of gamma-ray energies with semiconductor detectors

Abstract This paper presents a method for determining gamma-ray energies with a precision similar to that of the primary standards. The method consists of both an experimental procedure which employs Ge detectors, and the statistical treatment of data. An actual example with 159 Gd β − decay illustrates its use.

Decay of 159Gd

Abstract The γ-ray spectrum of 159 Tb following the β − -decay of 159 Gd has been studied through γ spectroscopy. A new branch in the 159 Gd decay has been evidenced through the observation of two new γ transitions with 273.6 and 753.7 keV attributed to 159 Tb. A level with 891.3 keV belonging to 159 Tb has been observed for the first time by following the 159 Gd decay. Four γ transitions previously attributed to this decay were not confirmed.

Covariances between gamma-ray energies

Abstract Covariances between experimental data are as significant as variances both in the evaluation of uncertainties and to perform statistical tests. If standard data are used in calibrations, covariances must be taken into account. Covariances are also necessary in order to update values every time when new data are obtained. In this paper we determined covariances between the most important gamma-ray energies for use in Ge-semiconductor detectors calibration recently published by Helmer and van der Leun (Nucl. Instr. Meth. A 450 (2000) 35).

A Method for Evaluating Electron Transport Parameters on a Pulsed Townsend Experiment

In this work, we present a physical model that links fundamental theory of electron kinetics on weakly ionized gases to direct measurements of induced pulsed signals in a Resistive Plate Chamber. It is also presented preliminary measurements of electron transport parameters in nitrogen obtained for reduced electric fields ranging from 129 Td up to 216 Td. These parameters were indirectly determined by fitting the proposed model to the time dependent pulse current induced on the parallel plate chamber electrodes by an electron avalanche triggered near the cathode by a N2 laser pulse. Experimental results are compared with previous measurements, Monte Carlo simulation results from Magboltz and results from classical two‐term expansion Boltzmann equation solution from Bolsig+.

Determination of the First Townsend Coefficient in Pure Isobutane

In this work studies of the first Townsend coefficient (α) behavior in isobutane for reduced electric fields ranging from l39Td up to 2O8Td are presented. Pure isobutane has been widely used in Resistive Plate Chambers (RPCs) and other gaseous detectors because of its excellent timing properties. Regardless of these characteristics, there is a lack of swarm parameters data in the literature for this gas. The measurements were based on the Pulsed Townsend technique. Considering the ratio between the current, measured in avalanche mode, and the primary ionization current, the first Townsend coefficient can be determined. In order to validate the technique, results for nitrogen are also presented.

Studies of Gaseous Multiplication Coefficient in Isobutane

This work presents the studies of gaseous multiplication coefficient behavior for isobutane, as function of the reduced electric field, by means of signal amplitude analysis. The experimental method used is based on the Pulsed Townsend technique, which follows from Townsend equation solution for a uniform electric field. In our configuration, the anode is made of a high resistivity (2.1012 Ω.cm) glass, while the cathode is of aluminium. In order to validate the technique and to analyze effects of non‐uniformity, results for nitrogen, which has well‐established data available in literature, are also presented.

Level and Gamma-Ray Energies of 229Th

Gamma‐ray and level energies of 229Th were reinvestigated using available experimental information and different assumptions regarding the decay scheme. We used in the fitting a statistical approach that takes into account both variances and covariances. The unusually low excitation energy of the 32+ level of 229Th was calculated.

Efficiency loss in HPGe detectors due to beta and gamma sum coincidence

Among the secondary detection effects in gamma-ray spectroscopy with HPGe detectors that reduce the peak area and must be properly taken into account in accurate measurements, the less well known is counting loss by beta and gamma-ray sum coincidence. The fraction of lost counts was estimated assuming that a photon detection event can sum either with the coincident beta-ray or its bremsstrahlung in the detector capsule or surrounding materials. The beta-ray was tracked through all the materials between source and detector. The result was calculated as a sequence of integral expressions evaluated numerically, without resorting to simulation. It is shown that the counting losses due to this effect are negligible for most calibration sources in typical detector arrangements.

The Correlations between the Emission Probabilities of the More Intense Gamma Rays in 152Gd and 152Sm Following 152Eu Decay

The variance matrix between the emission probabilities of the strong gamma-rays following the β decay of 152Eu were determined in a specially designed experiment. The emission probabilities are deduced from the decay scheme, whose branching-ratios and beta feeding fractions were fitted to the observed peak areas.

Experiment Planning of Subcritical Reactivity Measurements Using High Order Statistics of Neutron Counting

The reactivity measurement of subcritical fissile arrangements (subcriticality) is a featured subject among those in reactor physics, because it is necessary to handle, process, and transport fissile material from nuclear installations safely. None of the many available experimental methods of subcriticality measurements used nowadays allows its direct determination; however, the third order correlation of neutron counting allows subcriticality estimation from a fissile material without any previous knowledge of its kinetic parameters or any pulsed neutron source. Despite of its intrinsic advantages, high order statistics requires a careful planning and an optimized procedure because this type of experiment demands a long acquisition time when compared to the usual methods. It is estimated that such procedure could ask for acquisition times a few orders of magnitude longer than those required by the usual methods of subcriticality estimation (for similar uncertainties). The main experimental results of th...