A variety of unique radioactive samples have been measured recently at Los Alamos National Laboratory (LANL) using an electrically-cooled
high-purity germanium detector. In each case the purpose of the measurements included one or more of the following objectives:
(1) an accurate determination of the isotopic weight fractions of different plutonium or uranium materials; (2) an accurate
determination of the isotopic quantity in the absence of relevant calibration standards; and (3) a qualitative determination
of various sample impurities for additional forensic information. This paper discusses how simple modifications to the PC-FRAM
parameter sets enabled a better determination of the isotopic content of the following samples: (1) high-purity plutonium
metal, (2) plutonium-beryllium (PuBe) neutron sources, (3) neutron-irradiated natural uranium, and (4) re-processed HEU fuel
with elevated 236U content. The isotopic quantity in a variety of samples was determined using a combination of the Spectral Nondestructive
Assay Platform (SNAP™) routine from Eberline Services and the Monte Carlo Neutral Particle (MCNP) code developed at LANL.
The non-traditional sources that were quantified with these gamma ray modeling codes included dozens of neutron-irradiated
targets of natural uranium, several plutonium-beryllium neutron sources, and three high-purity samples of plutonium metal.
An activity predictor software was previously developed to foresee activities, exposure rates and gamma spectra of activated
samples for Radiation Science and Engineering Center (RSEC), Penn State Breazeale Reactor (PSBR), Neutron Activation Analysis
(NAA) measurements. With Activity Predictor it has been demonstrated that the predicted spectra were less than satisfactory.
In order to obtain better predicted spectra, a new detailed model for the RSEC NAA spectroscopy system with High Purity Germanium
(HPGe) detector is developed using Geant-4. The model was validated with a National Bureau of Standards certified 60Co source and tree activated high purity samples at PSBR. The predicted spectra agreed well with measured spectra. Error in
net photo peak area values were 8.6–33.6%. Along with the previously developed activity predictor software, this new model
in Geant-4 provided realistic spectra prediction for NAA experiments at RSEC PSBR.
For the analysis of pottery fragments from ancient Lefkanti, instrumental neutron activation analysis was used. To have a good throughput of samples, a detectable series of short-lived isotopes was selected for the investigation. The problem of the initial high radioactivity, which normally hinders a fast -spectroscopic analysis, was eluded by using loss-free counting technology. This technology allows the measurement of pottery samples of about 100 mg size 1 day after a 30 min epithermal irradiation. Up to 15 samples could be analyzed in one day under these working conditions, having the possibility to analyze the elements As, Eu, Ga, Gd, La, Mn, Sb, Sm, Th, U, W and Zn, which are enough to perform statistical characterizations of potteries.
Authors:K. Ochsenkühn, P. Fafouteli, and M. Ochsenkühn-Petropoulou
For the determination of gold in Greek bauxites from the Parnassos-Ghiona area, an analytical technique was used based on the selective adsorption of gold on SRAFION NMRR chelating anion exchanger resin, after leaching the bauxites with aqua regia in a teflon-autoclave at 120 °C, and the determination of the retained gold directly on the resin by instrumental neutron activation analysis (INAA), using the 411.8 keV line of the 198Au isotope. The procedure allowed to determine Au in concentrations down to ng/g. The obtained data were used to examine the distribution of Au in the profiles of a group of different bauxites from the upper or the called third bauxitic horizon of the Parnassos-Ghiona area in Greece. Especially in the basement of some bauxite deposits unexpected high concentrations of Au up to 2 mg/g have been found. Furthermore, the correlation of Au with other trace elements, found in the bauxitic samples, was investigated.
Authors:Owen Drury, Miguel Velazquez, Jonathan Dreyer, and Stephan Friedrich
We are developing superconducting ultrahigh resolution gamma-detectors for non-destructive analysis (NDA) of nuclear materials,
and specifically for spent fuel characterization in nuclear safeguards. The detectors offer an energy resolution below 100 eV
FWHM at 100 keV, and can therefore significantly increase the precision of NDA at low energies where line overlap affects
the errors of the measurement when using germanium detectors. They also increase the peak-to-background ratio and thus improve
the detection limits for weak gamma emissions from the fissile Pu and U isotopes at low energy in the presence of an intense
Compton background from the fission products in spent fuel. Here we demonstrate high energy resolution and high peak-to-background
ratio of our superconducting Gamma detectors, and discuss their relevance for measuring actinides in spent nuclear fuel.
Total oxygen, in fourteen rock standards and three ores, was determined with an experimental set up employing cyclic activation analysis using a 14 MeV neutron generator gamma-spectroscopy and NaI(T1) detectors.
Authors:S. Ibrahim, M. Schierman, S. Hulse, and F. Whicker
The objectives of this study were to establish a ratio for241Am to239Pu in soil at the Rocky Flats Plant and to compare241Am concentrations obtained using in-situ and laboratory gamma spectroscopy measurements to concentrations determined with radiochemical analysis and alpha spectroscopy. Soil samples were collected for radiochemical and laboratory gamma spectroscopy analysis from vertical profiles in 3 cm layers to a depth of 21 cm at predetermined locations along transects oriented in the direction of prevailing winds. The origin for the transects was the center of the 903 Pad at the Rocky Flats Plant, which is believed to be the source for most of the241Am and239Pu contamination. A 100 minute in-situ gamma spectroscopy measurement was made at each soil sample location with a portable HPGe detector. Soil samples were dried, passed through a 2 mm sieve, mixed, and split in two fractions. One fraction was analyzed radiochemically for241Am and239Pu and the second was analyzed using laboratory gamma spectroscopy. The median ratio of241Am to239Pu activities, which appears to be independent of soil depth and distance from suspected sources, was 0.17. There is a strong correlation between241Am and239Pu concentrations determined using radiochemical analysis with alpha spectroscopy and concentrations determined with laboratory gamma spectroscopy. Results from in-situ gamma spectroscopy measurements were also correlated with the radiochemical analyses but exhibited greater variability than laboratory measurements. This on-going investigation has demonstrated that it is possible to indirectly measure239Pu concentrations in soil if the ratio of241Am to239Pu can be established. The results indicate that judicious use of a combination of radiochemical analyses with laboratory and in-situ gamma spectroscopy measurements may provide a cost-effective approach for characterization of large sites where241Am and239Pu contamination occur.
Sensitivity data for low energy photon spectroscopy used in photon activation analysis are compiled and compared with those
for classical gamma-spectroscopy. All elements of the periodic table with a few exceptions were irradiated with 30 MeV-bremsstrahlung
of a linear electron accelerator. Low energy photon spectra were taken with a LEP-detector as well as with a coaxial Ge(Li)-detector.
Resulting data were processed by computer. The results show that in some cases low energy photon spectroscopy used in photon
activation analysis provides higher sensitivity than can be achieved by classical gamma-spectroscopy.
Indium (10–15,000 ppm) and tin (20–90%) are quantitatively determined in cassiterite samples by instrumental (thermal) neutron activation analysis, using semiconductor detectors and gamma spectroscopy. Precision is 7% or better for In and 5% or better for Sn. The detection limit is 2 ppm for In and 0.4% for Sn in Mexican cassiterites.