Unexpected 13N concentrations in ISIS synchrotron room air.

The specific activity of air in the large open room housing the 800-MeV proton synchrotron of the ISIS Spallation Neutron and Muon Source has been measured. Air from several positions within the ISIS synchrotron room was sucked through a long flexible tube, and run past a shielded HPGe gamma-ray detector outside the synchrotron room. In spite of an expectation that 13N should be the largest component of the overall activity in the air, the results of the measurements are consistent with the presence in the air of 11C and 41Ar only, and suggest that the activity in the air is mostly created not in the synchrotron room itself but in the massive shielding monoliths around the neutron-producing targets, monoliths through which ventilation air is drawn into the synchrotron room. Typical specific activities of 11C and 41Ar in the air in the synchrotron room are ∼0.10 and ∼0.03 Bq cm-3 respectively, the upper limit for 13N being at most ∼0.01 Bq cm-3.

Measurement of single- and double-escape HPGe efficiency ratios for 60Co.

As a by-product of another measurement, ratios of the single-escape (SE) and double-escape (DE) efficiencies relative to the full-energy-peak efficiency (FE) have been measured for two HPGe detectors for 60Co. For a 2.5-cm-thick 95 cm3 crystal the results were SE/FE = 0.000 48 ± 0.000 20 and 0.003 25 ± 0.000 24 for 1173 and 1332 keV gamma-rays, respectively, and DE/FE = 0.000 90 ± 0.000 17 and 0.003 41 ± 0.000 11 for 1173 and 1332 keV, respectively. For a 3.0-cm-thick 84 cm3 crystal the results were SE/FE = 0.000 67 ± 0.000 32 and 0.003 79 ± 0.000 27 for 1173 and 1332 keV respectively, and DE/FE = 0.001 05 ± 0.000 28 and 0.004 29 ± 0.000 16 for 1173 and 1332 keV, respectively. These measurements may be of relevance in connection with Monte Carlo calculations of HPGe detector efficiencies, and may also suggest a path towards improved atomic cross-section measurements.

Gamma-ray spectroscopy for probing highly radioactive items behind thick shields?

In favourable circumstances, including the availability of prior knowledge, a potential use of gamma-ray spectroscopy with an HPGe detector for probing highly radioactive items behind thick shields is described.

Experimental verification of spallation inventory calculations.

Monte Carlo calculations and gamma-ray spectrometry measurements have been made for a highly irradiated tungsten target from a proton-driven spallation neutron source. A comparison of the calculated and measured activities of 60Co and 172Lu in the radionuclide inventory shows surprisingly good agreement.

Adherence of Staphylococcus epidermidis to fibrin-platelet clots in vitro mediated by lipoteichoic acid.

The adherence of two strains of Staphylococcus epidermidis to human fibrin-platelet clots in vitro was investigated. Both strains were noncapsulated, nonhemagglutinating, and nonslime producers. Binding was not related to surface charge, carbohydrate profile, or hydrophobicity of the bacteria. Adherence was reduced four- to sixfold (P less than 0.001) on pretreatment of bacteria with lipase, while neuraminidase, trypsin, phospholipase C, and sodium periodate did not alter their binding. Pretreatment of bacteria with substances known to bind lipoteichoic acid (LTA), such as human albumin and anti-LTA antibodies, also resulted in a fourfold (P less than 0.001) reduction in adherence. Prior incubation of clots with free LTA, but not with deacylated LTA, produced a fourfold (P less than 0.001) decrease in the adherence of homologous and heterologous strains of S. epidermidis. A similar reduction was also observed when LTAs derived from Staphylococcus aureus and Streptococcus pyogenes were used. These data provide evidence that the lipid moiety of LTA has a central role in the adherence of S. epidermidis to fibrin-platelet clots in vitro.