Measurement of the 241Am(n,2n) Reaction Cross Section, by the Activation Method

The measurement of the cross section of the reaction 241Am(n,2n)240Am, has been performed, for the first time at neutron energies of 8.8, 9.6, 10.6 and 11.4 MeV, by the activation method. The monoenergetic neutron beam was produced at the 5.5MV TANDEM accelerator of NCSR "Demokritos", using the H{d,n) He reaction. During the 5-day long irradiation, the neutron flux was monitored by a BF3, counter. The neutron yield as well as the beam current, were recorded in 100 sec intervals by two multiscaling units. The radioactive target consisted of a 37GBq 241Am source enclosed in a Pb container. A natural Au foil, 27Al foil and a 93Nb foil were used as reference materials for the neutron flux determination. The activity of the irradiated targets, was measured off-line by a 56% relative efficiency, HPGe detector. The first preliminary results are presented and compared with evaluated libraries and existing data.

Alpha-particle fluence in radiobiological experiments

Two methods were proposed for determining alpha-particle fluence for radiobiological experiments. The first involved calculating the probabilities of hitting the target for alpha particles emitted from a source through Monte Carlo simulations, which when multiplied by the activity of the source gave the fluence at the target. The second relied on the number of chemically etched alpha-particle tracks developed on a solid-state nuclear track detector (SSNTD) that was irradiated by an alpha-particle source. The etching efficiencies (defined as percentages of latent tracks created by alpha particles from the source that could develop to become visible tracks upon chemical etching) were computed through Monte Carlo simulations, which when multiplied by the experimentally counted number of visible tracks would also give the fluence at the target. We studied alpha particles with an energy of 5.486 MeV emitted from an 241Am source, and considered the alpha-particle tracks developed on polyallyldiglycol carbonate film, which is a common SSNTD. Our results showed that the etching efficiencies were equal to one for source–film distances of from 0.6 to 3.5 cm for a circular film of radius of 1 cm, and for source–film distances of from 1 to 3 cm for circular film of radius of 2 cm. For circular film with a radius of 3 cm, the etching efficiencies never reached 1. On the other hand, the hit probability decreased monotonically with increase in the source–target distance, and fell to zero when the source–target distance was larger than the particle range in air.

Damage to soil physical properties caused by soil sampler devices as assessed by gamma ray computed tomography

Soil sample physical properties can be greatly affected during soil sampling procedures. Improper procedures can impose modifications on soil sample structure and consequently lead to wrong measurements of soil properties. The objective of this work was to evaluate the damage caused by soil samplers to soil structure through the analysis of computed tomography (CT) images. A first generation tomograph was used, having a 241Am source and a 7.62 × 7.62 cm NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Results confirm the effect of soil sampler devices on the structure of soil samples, and that the compaction caused during sampling causes significant alterations to soil bulk density. Through the use of CT it was possible to determine the level of compaction and to make a detailed analysis of the soil bulk density distribution within the soil sample.

Planosol soil sample size for computerized tomography measurement of physical parameters

Computerized tomography (CT) is an important tool in Soil Science for noninvasive measurement of density and water content of soil samples. This work aims to describe the aspects of sample size adequacy for Planosol (Albaqualf) and to evaluate procedures for statistical analysis, using a CT scanner with a 241Am source. Density errors attributed to the equipment are 0.051 and 0.046 Mg m-3 for horizons A and B, respectively. The theoretical value for sample thickness for the Planosol, using this equipment, is 4.0 cm for the horizons A and B. The ideal thickness of samples is approximately 6.0 cm, being smaller for samples of the horizon B in relation to A. Alternatives for the improvement of the efficiency analysis and the reliability of the results obtained by CT are also discussed, and indicate good precision and adaptability of the application of this technology in Planosol (Albaqualf) studies.