Page 21 - PR 2014 2016 07 Nuclear Science and Technology

Nuclear Science and Technology | Progress Report 163

analytical technique in IPEN at the Neutron NAA data analysis procedures, a simple soft-
Activation Laboratory (LAN). Nevertheless, sev- ware that automatically analyses spectra in
eral tasks have been undertaken in the last different formats (CHN, CNF and MCA) and ex-
years aiming to improve IPEN’s NAA results, ports the results to an Excel-compatible spread-
either by focusing in the technique itself or sheet was developed. The software, written
in the data analysis. in the Pascal computer language, makes use
of several tools shipped with Canberra’s Ge-
In this sense, Sm determination in urani- nie-2000 to import all the spectra found in a
um-rich samples was studied, focusing not given folder, import energy and FWHM calibra-
only in the interference of fission-produced tions from a saved reference spectrum (chosen
Sm, but also in the spectral interference in the by the operator according to the detector sys-
103keV gamma-ray line that arises from the tem from which the spectra came) and analyze
x-rays of Pu, which is produced by sequential the resulting spectra; an in-house procedure
238
239
neutron captures on U and Np. The result- then reads Genie’s output file and produces a
ing time-depending correction factor, a novel Comma-Separated Values (CSV) file converted
concept that arose from this work, proved to the Brazilian language standards (commas
to properly address the problem, rendering as decimal separators and semicolons sepa-
reliable results for Sm even in the presence of rating fields) that can be opened in a typical
high amounts of uranium. installation of Microsoft Excel.

A thorough investigation on sources of uncer- Preliminary studies aiming to implement coin-
tainty in comparative NAA measurements cidence comparative NAA in IPEN were started,
has also been made, focusing not only in the in collaboration with NIST and UTexas-Aus-
explicit uncertainty factors, but also in factors tin (USA), and a fully-digital gamma-gamma
that are hidden in the simplification made coincidence system is under development at
in the comparative method. In this work, the IPEN’s Applied Nuclear Physics Laboratory.
possible variation in the HPGe detector effi- This technique aims to provide an extra tool
ciency between measurements was studied in for NAA analyses when regular NAA can’t give
great detail, and it was shown that for dead- good results because of strong spectral inter-
times below 10%, the efficiency variation won’t ferences, either from very similar gamma-ray
contribute with more than 0.05% to the final peaks or from strong Compton or bremsstrah-
uncertainty. A study on the explicit sources lung continua.
of uncertainty has shown that, for long-lived
isotopes (half-lives greater than one day), the Basic Nuclear Physics
time-related parameters (decay constant and
time) contribute with no more than 0.5% of The half-life of short-lived Mg was studied
27
the final uncertainty; the counting statistics by following the activity of samples after they
and comparator concentration contribute with were irradiated in the IEA-R1 reactor. The re-
most of the uncertainty (usually around 80- sulting value of 564.5(7) s is compatible with
90% of the total), while the uncertainties in most of the literature values, but not with the
the masses typically contribute with less than ENSDF compilation value, accepted as a refer-
20% of the final uncertainty value. ence value for most experiments, suggesting
that further precise measurements of this
In an attempt to promote automation of the half-life should be made, and that the ENSDF