Evaluation of the /sup 63/Cu activation foil for determining the neutron dose in the energy range of 1 eV to 1 MeV

The appropriateness of the /sup 63/Cu activation foil for determining the neutron dose in the energy region from 1 eV to 1 MeV has been investigated for spectra of seven different criticality accident configurations. A program was written for folding the published spectra with the /sup 63/Cu activation cross sections and with the fluence-to-dose or kerma conversion factors. It is shown that for these spectra the neutron dose and kerma result primarily from the energy region above 15 keV whereas the measured /sup 64/Cu activity is mainly determined by the fluence in the region between 1 eV and 15 keV. Uncertainties in the fluence spectrum in the low-energy region between 1 eV and 15 keV, which in reality do not affect the dose contribution, might lead to large deviations in the measured /sup 64/Cu activity and hence to the derived dose in the 1 eV to 1 MeV range. Use of /sup 10/B shielding for attenuating the fluence in the 1-eV to 15-keV region was evaluated, leading to the conclusion that the necessary amount of boron material is unacceptably large and would appreciably increase the cost of the dosimeter currently used at Los Alamos. The lower limit of neutron detectability would also be increased

Validating Gene Clusterings by Selecting Informative Gene Ontology Terms with Mutual Information

We propose a method for global validation of gene clusterings. The method selects a set of informative and non-redundant GO terms through an exploration of the Gene Ontology structure guided by mutual information. Our approach yields a global assessment of the clustering quality, and a higher level interpretation for the clusters, as it relates GO terms with specific clusters. We show that in two gene expression data sets our method offers an improvement over previous approaches

Performance of low pressure tissue equivalent chambers and a new method for parameterizing the dose equivalent

The performance of spherical tissue equivalent chambers with equivalent diameters between 0.5 and 2..mu.. was tested experimentally using monoenergetic and polyenergetic neutron sources in the energy region of 10 keV to 14.5 MeV. Theoretical calculations were performed in order to obtain a simple algorithm for deriving the dose equivalent from the measured data. The algorithm relates the number of recoil particles to the dose equivalent, rather than having a one-to-one correspondence between the lineal energy and the linear energy transfer of the recoil particles. The calculations took into account neutron interactions with hydrogen atoms in the chamber wall as well as in the gas, and also the finite energy resolution determined by both the detector and the electronic system. Qualitatively, the calculations well dscribe the experimental results. The algorithm that was developed determines the neutron dose equivalent, from the data of the 0.5..mu.. chamber, to better than +-20% over the energy range of 30 keV to 14.5 MeV. The same algorithm also determines the dose equivalent from the data of the 2..mu.. chamber to better than +-20% over the energy of 70 keV to 14.5 MeV. The efficiency of the chambers is low and has an average value of 330 counts per mrem, or equivalently about 0.2 c/s per mrem/h. This efficiency enables the measurement of dose equivalent rates only above 100 mrem/h for an integration period of 3 seconds. However, integrated dose equivalents can be mesured as low as 0.1 mrem