Vito R. Vanin

Analysis of discrepant data using a bootstrap procedure

Abstract We present in this paper a statistical procedure to deduce a best value and its standard deviation for a discrepant set of data. This method, rather than using the conventional average, uses a Bootstrap Method to estimate these quantities. The usual weighted average may be used to combine this estimate with additional data, thus avoiding a more complex calculation required by other methods, which would include all of the original experimental values. The current application of this procedure to the half-lives of 137Cs, 90Sr, and Tritium illustrates its usefulness.

Gamma-ray calibration energies: a review of the 192Ir data

Abstract In order to perform evaluations by the least-squares method, the complete covariance matrix for the gamma-ray energy standards is needed. Some errors due to excluding the covariances from the statistical analysis are pointed out. The gamma-ray energies of 192 Ir and 198 Au, measured with curved-crystal spectrometers, were reanalyzed and the covariances between results determined. The gamma-ray energies were updated by including the latest values of the fundamental constants. The covariance matrix between gamma-ray energy data and the fundamental constants is deduced, so that the energy values can be updated correctly if new measurements are performed or if the fundamental constants are reevaluated.

Transfer coefficient measurements of uranium to the organs of Wistar rats, as a function of the uranium content in the food.

Groups of animals (Wistar rats) were fed with rations doped with uranyl nitrate at concentrations ranging from 0.5 to 100 ppm. The uranium content in the ashes of the organs was measured by the neutron-fission track counting technique. The most striking result is that the transfer coefficients, as a function of the uranium concentration, exhibit a concave shape with a minimum around 20 ppm-U for all organs. Explanations to interpret this finding are tentatively given.

Ionization cross sections of the L subshells of Au by 50 to 100 keV electron impact

We have measured the Lα, Lβ, , , L, and Lη x-ray production cross sections of Au by 50–100 keV electron impact. From this experimental information we derived the L1, L2 and L3 subshell ionization cross sections with a novel analysis procedure that is based on an overdetermined system of equations and achieve the estimates by the least-squares method. The uncertainties in the atomic relaxation parameters needed to transform the x-ray intensities to ionization cross sections impose a lower limit to the relative standard deviations of the L subshell ionization cross sections, which is found to be 5–10% depending on the selected set of relaxation parameters. Our experimental results are in reasonable accord with most of the measurements carried out by other authors, and they agree with the predictions of the semi-relativistic distorted-wave Born approximation.

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.

Measurement of thermal neutron cross section and resonance integral for the 165Ho(n, γ)166gHo reaction

Abstract The ground state thermal neutron cross section and the resonance integral for the 165Ho(n, γ) 166Ho reaction in thermal and 1/E regions, respectively, of a thermal reactor neutron spectrum have been measured experimentally by activation technique. The reaction product, 166Ho in the ground state, is gaining considerable importance as a therapeutic radionuclide and precisely measured data of the reaction are of significance from the fundamental point of view as well as for application. In this work, the spectrographically pure holmium oxide (Ho2O3) powder samples were irradiated with and without cadmium covers at the IEA-R1 reactor (IPEN, São Paulo), Brazil. The deviation of the neutron spectrum shape from 1/E law was measured by co-irradiating Co, Zn, Zr and Au activation detectors with thermal and epithermal neutrons followed by regression and iterative procedures. The magnitudes of the discrepancies that can occur in measurements made with the ideal 1/E law considerations in the epithermal range were studied. The measured thermal neutron cross section at the Maxwellian averaged thermal energy of 0.0253 eV is 59.0±2.1 b and for the resonance integral 657±36 b. The results are measured with good precision and indicated a consistency trend to resolve the discrepant status of the literature data. The results are compared with the values in main libraries such as ENDF/B-VII, JEF-2.2 and JENDL-3.2, and with other measurements in the literature.

Cross sections of K-shell ionization by electron impact, measured from threshold to 100 keV, for Au and Bi

We have measured cross sections for the ionization of the K shell by electrons with energies from the respective thresholds up to 100 keV, for Au and Bi. The experimental values are obtained by dividing the number of counts in the K? peak by the number of counts in an energy interval near the tip of the bremsstrahlung continuum, and multiplying this ratio by the theoretical estimate of bremsstrahlung emission towards the detector in this energy interval. Although such a procedure has already been described in the literature, here it is implemented avoiding some of the simplifications made in earlier works. Our experimental cross sections, which are the first ones to be reported for atoms with 47

Decay of 159Gd

SRC=http://ej.iop.org/images/0953-4075/47/15/155201/jpb497279ieqn1.gif/> close to the threshold, are in reasonable agreement with the theoretical predictions of the semirelativistic distorted-wave Born approximation. Hippler?s plane-wave Born approximation with corrections for Coulomb and exchange effects yields cross sections that are closer to the experimental data than those evaluated from the relativistic binary-encounter-Bethe model.

First Experiments with the IFUSP Microtron Injector

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.

IMPROVEMENT OF 192IR AND 152EU GAMMA-RAY CALIBRATION ENERGIES BY USING A SELF-CALIBRATION PROCEDURE

The first accelerating structures of the Sao Paulo microtron accelerator presently deliver a continuous‐wave 1.9 MeV electron beam, which can be used in atomic physics studies. An energy‐analyzed beam line with focalization magnets, irradiation chamber, movable target system and Faraday cup was built. Here, we will describe the preliminary results of two experiments. In the first one, upper limits on K‐shell ionization cross sections of Pd and Au atoms by electron impact were obtained. To this end, thin targets of these elements were irradiated with the beam impinging at 45° while the emitted Kα x‐rays were recorded with an HPGe x‐ray detector positioned at 90° with respect to the beam direction. The other experiment was the measurement of the bremsstrahlung energy spectra produced by the aforementioned targets in the same geometrical configuration but using an HPGe γ‐ray detector instead. The latter experiment enabled the determination of the electron‐beam energy as 1.909(5) MeV.