Richard W. Perkins

Radionuclide composition of the allende meteorite from nondestructive gamma-ray spectrometric analysis.

The concentrations of beryllium-7, sodium-22, aluminum-26, potassium-40, scandium-46, vanadium-48, chromium-51, manganese-54, cobalt-57, cobalt-60, and thorium-232 (thallium-208) have been measured in the Allende meteorite by nondestructive gamma-ray spectrometry. The high cobalt-60 content of the meteorite is indicative of a preatmospheric body with a minimum effective radius of 50 centimeters and a weight of 1650 kilograms; the aluminum-26 activity indicates a minimum exposure age of 3 million years.

Glass-fiber-based neutron detectors for high- and low-flux environments

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers typically have a operational transmission length (e-1 length) of greater than 2 meters. This permits the fabrication of devices which were not possible to consider. Scintillating fibers permit conformable devices, large-area devices, and extremely small devices; in addition, as the thermal-neutron sensitive elements in a fast neutron detection system, scintillating fibers can be dispersed within moderator, improving neutron economy, over that possible with commercially available 3He or BF3 proportional counters. These fibers can be used for national-security applications, in medical applications, in the nuclear-power industry, and for personnel protection at experimental facilities. Data are presented for devices based on single fibers and devices made up of ribbons containing many fibers under high-and low-flux conditions.

An anticoincidence-shielded Ge(Li) gamma-ray spectrometer and its application to radioanalytical chemistry problems

An anticoincidence-shielded Ge(Li) γ-ray spectrometer incorporating a largevolume, high-resolution coaxial diode inside a large plastic phosphor shield is described. It provides a peak-to-Compton ratio of 245: 1 for137Cs and a significantly improved sensitivity for both low- and high-level radionuclide measurements. Examples of its application to neutron activation analysis, analysis of proton activated sources, and environmental radionuclide analysis are illustrated.

In situ activation analysis of marine sediments with252Cf

A seabed nuclear probe has been developed which permits the measurement of up to 33 elements at the parts per thousand to parts per million levels in continental shelf areas. The probe consists of a neutron irradiation source,252Cf, which neutron activates the elements in the minerals of interest. These resulting radioactive elements emit characteristic gamma radiation which is analyzed in situ in 2- to 10 min counting intervals with a Ge(Li) detector system. Details of the irradiation source, the Ge(Li) detector, and spectra taken in situ in a marine environment are discussed with respect to the detection of the minerals at concentrations of economic interest.

COSMOGENIC AND PRIMORDIAL RADIONUCLIDES IN LUNAR SAMPLES BY NONDESTRUCTIVE GAMMA-RAY SPECTROMETRY.

The 7Be, 22Na, 26Al, 44Ti, 46SC, 48V 51Cr, 54Mn, 56Co, 57Co, 57CO, 40K, 238U, and 232Th were measured in lunar fines and portions of three rocks. Major production of cosmogenic radionuclides is due to solar protons, thus their concentrations are far different than those in meteorites. Surface exposures of the rocks and fines are long compared with the 0.74 million year half-life of 26Al. Lunar fines show substantially higher concentrations of low energy reaction products. The ratios of thorium to uranium are extremely constant at 3.8, which indicates very little geochemical differentiation and are in good agreement with a common nucleosynthesis for lunar and earth materials.

Radium Isotope Accumulation in Animal Thyroids

Uranium and thorium daughters are ten times more concentrated in thyroids from some bovine animals than in the teeth of the same animals. These radioactive isotopes are believed to be from natural sources, but their resulting annual dosage of thyroid radiation has exceeded that from iodine-131 fallout.

Cosmic-ray induced radioactivity in astronauts as a measure of radiation dose.

The activity-dose-energy relationships for7Be,13N,22Na, and24Na activities induced in muscle tissue by proton bombardment have been measured through the energy range up to 580 MeV. The relationship between radiation dose and induced activity for any given proton bombarding energy is defined. The determination of the radiation dose received by an astronaut from cosmic radiation of unknown energy by measuring the concentrations of the radioactive isotopes induced in his body is discussed.