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  • Author or Editor: E. A. Smith x
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Abstract  

Nearly all natural materials contain trace quantities of uranium (U) and thorium (Th) and their daughter nuclides, many of which emit α-particles in their decay. Lead, at the end of the U-decay chain, typically contains some radioactive210Pb which is chemically inseparable from the other Pb isotopes. α-particle emission from these decays can affect sensitive electronic components, such as memory chips or processors. Measurement of α-particle emitters can be accomplished by direct detection of the α-particles (which typically provides no positive identification of the emitting isotope because of energy loss in the sample) or by low-background γ-ray spectroscopy (which does provide positive identification via characteristic γ-rays.) The latter is by far the best method for screening kg-sized samples of materials like ceramics, aluminum, iron or copper. The difference between α counting and γ-ray spectroscopy is less for measuring210Pb in Pb since the 46.5 keV characteristic γ-rays directly following the210Pb decay are strongly absorbed and both methods are limited to thin layers. This paper discusses these two cases and concludes that a large n-type germanium γ-ray spectrometer is probably the best overall system for both measurements.

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Abstract  

Following many years of productive research, the 184-inch Cyclotron, the SuperHILAC, and the BEVALAC accelerators at the Berkeley Laboratory were closed, leaving thousands of concrete shielding blocks available for reuse, recycling, or disposal. The process history of these blocks precludes free release pending radiological characterization. This paper describes a procedure whereby a high efficiency shielded germanium spectrometer is used to rapidly characterize natural and man-made activity within the blocks. The spectrometer is moved up to the block and 5 minutes of data are collected at the point on the block that registers highest on a micro-R meter. Sensitivity is better than 1 pCi/g (0.037 Bq/g) for Co-60 and Eu-152, the prominent man-made activities observed. One-time calibration of the detector system is obtained from a sample of concrete, drilled with a hammer drill, counted in our low-background facility, and compared to crushed rock with known U, Th, and K activity. A simple relationship exists between the counts/minute observed in a characteristic gamma-ray peak and the activity in the block.

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Abstract  

Instrumental Neutron Activation Analysis (INAA) is a common method of trace element analysis whose sensitivity is limited either by interference from other trace elements in the sample or by interference from ambient background radiation in the detection system. In at least two cases, a true low-background facility, such as that at Lawrence Berkeley National Laboratory, substantially enhances senitivity: (1) Ultra-pure silicon, such as that used in semiconductor fabrication. Even after prolonged exposure within a nuclear reactor, minimal observable gamma-ray emitting activities are produced in the silicon. Extrapolated from our 7 gram sample size experiments, parts-per-quadrillion (1.E-15) sensitivity to 23 elements should be obtainable for 400 gram sample sizes. (2) Similarly, the life elements H, C, N, O are effectively inert within the reactor, and this enhances sensitivity to trace elements in, for example, bacteria. Data will be presented for these two cases.

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Authors: H. F. Lyle III, E. A. Smith and R. J. Sullivan

Abstract

This is the first empirical investigation of blood donations in evolutionary perspective. We examine blood donor and non-donor attitudes about health and injury risks, donor characteristics, and the social value of donor participation. We propose that blood donations may communicate qualities about donors to third parties. Observers may benefit from information about the donor's health, value as a reciprocal partner, and/or ability to endure what is perceived as an anxiety-provoking and risky experience. Donors may benefit from an enhanced reputation, which can lead to greater access to cooperative networks and high-quality partners. We found that participants recognized the need for blood and perceived blood donors as generous and healthy. Study results indicated that anxiety and the perceived risk of a negative health consequence dramatically affected the willingness of donors and non-donors to donate blood in the future. These findings support our hypothesis that the act of blood donation may signal adaptive information about donor quality to third parties.

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Authors: A. Aarkrog, S. Boelskifte, H. Dahlgaard, S. Duniec, E. Holm and J. Smith

Abstract  

Since the accidental loss of four nuclear weapons by a B-52 at Thule Airbase, Greenland in 1968, the marine environment at Thule has showed enhanced levels of Pu and Am. Most of the activity is confined to the benthic environment within a distance of 50 km from the crash site of the B-52. Samplings of sediments, benthos, seaplants, fish, and water have been carried out in 1968, 1970, 1974, 1979, and in 1984. The study presented herein intends to answer the following questions: What is the mean residence time of these transuranics in the benthic communities? Do Pu and Am behave differently in the environment?

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