Elemental compositions and ages of lunar samples by nondestructive gamma-ray spectrometry.

A gamma-ray spectrometry system with low background was used to determine the radioactivity of crystalline rocks, breccias, and fine material. Nuclides identified were (40)K, (232)Th, (238)U, (7)Be, (22)Na (26)A1, (44)Ti, (46)Sc, (48)V, (52)Mn, (54)Mn, and (56)Co. Concentrations of K, Th, and U ranged between 480 and 2550, 1.01 and 3.30, and 0.26 and 0.83 parts per million, respectively. Concentrations of thorium and uranium were those of terrestrial basalts, while the potassium concentrations were near values for chondrites. Products of low-energy nuclear reactions showed pronounced concentration gradients at rock surfaces. Concentrations of K and of (22)Na determined here were combined with concentrations of rare gases to estimate gas-retention ages and cosmic-ray exposure ages with ranges of 2200 to 3200 and 34 to 340 million years, respectively, for three rocks.

Primordial radioelements and cosmogenic radionuclides in lunar samples from apollo 15.

Two basalts, two breccias, and two soils from Apollo 15 were analyzed by nondestructive gamma-ray spectrometry. The concentrations of potassium, thorium, and uranium in the basalts were similar to those in the Apollo 12 basalts, but the potassium: uranium ratios were somewhat higher. Primordial radioelements were enriched in the soils and breccia, consistent with a two-component mixture of mare basalt and up to 20 percent foreign component (KREEP). The abundance patterns for cosmogenic radionuclides implied surface sampling for all specimens. The galactic cosmic-ray production rate of vanadium-48 was determined as 57 +/- 11 disintegrations per minute per kilogram of iron. Cobalt-56 concentrations were used to estimate the intensity of the solar flare of 25 January 1971.

Meteorite fail at pueblito de allende, chihuahua, Mexico: preliminary information.

Specimens from the meteorite fall at 1:05 a. m., on 8 February 1969 at Pueblito de Allende, Chihuahua, Mexico, have been recovered. The meteorite is a chondrite (C3 and C4) with both opaque and microcrystalline matrices. Specimens were brought to a low background gamma counter less than 4 (1/2) days after the fall, and gamma rays from short-lived isotopes have been observed.

Relaxation times of normal and atrophied muscle.

Magnetic resonance imaging is being used to investigate physiological changes induced by microgravity. Using human (bed rest) and animal (tail suspension) models simulating zero gravity, muscle atrophy was studied. Despite significant physiological changes in muscle mass, distribution of blood flow, and muscle water, no changes in muscle proton relaxation times were found at several different resonant frequencies (6, 10, 20, and 200 MHz). These results suggest that observed changes in relaxation times as reported in pathologic studies are likely due to the pathological changes and not the accompanying muscle atrophy.

Calf muscle area and strength changes after five weeks of horizontal bed rest.

Nine male volunteers participated in a 10 week metabolic study in which subjects underwent 5 weeks of ambulatory control and 5 weeks of complete horizontal bed rest. Bed rest is a model commonly used to simulate space flight. The changes in muscle area and strength of the calf dorsiflexors and plantar flexors were measured before and after bed rest using magnetic resonance imaging (MRI) and a Cybex II dynamometer. The muscle area of the plantar flexors (gastrocnemius and soleus) decreased 12%, whereas the muscle area of the dorsiflexors was not significantly decreased. The maximal muscle strength of the plantar flexors decreased 26%; the muscle strength of the dorsiflexors was not significantly decreased. These results, which demonstrate differential muscle atrophy and a larger loss in strength relative to muscle area, have important implications in the development of exercise counter-measures to be implemented during space flight. The results also have implications for patients who have severe orthopaedic disorders and must be bed rested for long periods of time, and for persons who are voluntarily inactive (a large number of the elderly).

Comparison of measured and calculated emission probabilities for K and L X-rays following radioactive disintegration processes.

The program EMISSION has been developed at the Physikalisch-Technische Bundesanstalt (PTB). It allows emission probabilities to be calculated for K and L X-rays following radioactive disintegration processes. This program was already applied to the calculation of total K X-ray emission probabilities for six radionuclides. The results are found to be in reasonable agreement with measured values. In order to check the validity of this program also for the individual components of K and L X-rays, calculated emission probabilities of K X-ray components (139Ce, 203Hg) and L X-ray components (139Ce, 203Hg, 241Am) were compared with remeasured (139Ce, 203Hg) and already available (241Am) emission probabilities, measured earlier at the PTB. In most cases there is an agreement within the standard uncertainties of the measured and calculated values, usually within 1-5%. Larger deviations, not covered by three times the standard uncertainty have been found for some weak lines.

Standardisation and decay data of 177Lu and 188Re.

The activity values of 177Lu and 188Re standard sources were measured using the 4pibeta-gamma-coincidence method and by liquid scintillation counting. The X- and gamma-ray emission probabilities per disintegration were determined by means of photon spectrometry with calibrated Ge and Si(Li) detectors and using the pertinent activity values. The half-lives were measured with ionization chambers, yielding T(1/2)(177Lu) = 6.646(5) d and T(1/2)(188Re) = 0.70848(9) d.

Production of Co-60 sources for high-accuracy efficiency calibrations of gamma-ray spectrometers.

Activity determination by gamma-ray spectrometry is a valuable aid which is widely used where radioactive sources are applied. For the construction of an efficiency curve vs. energy in a standard geometry, the accuracy is limited not only by the uncertainty of peak area determination and the knowledge of the relevant emission probabilities but also by the uncertainties of the activity values applied to efficiency calibration with standard sources. Recently, a method to determine a relative efficiency function using selected radionuclides with gamma cascades of well known emission probabilities has been developed which yields very accurate efficiency values. Such a curve has to be converted into an absolute efficiency curve by calibration of the detector system with at least one source of very well known activity. Especially for this purpose, a set of Co-60 gamma-ray spectrometer sources was produced at the PTB. The activity values (10-45 kBq) were measured by the 4pi beta-gamma coincidence technique with a standard uncertainty of less than 0.1%. Production and measurement of these sources are described in the present paper. Special care was taken to include all contributions to the standard uncertainty of the activity value when establishing the uncertainty budget for the activity of each of these sources. The activity ratio of two of these sources, as obtained by the absolute measurements, was checked by independent gamma-ray counting at two other laboratories, where the precision achieved was less than 0.2%. The procedure described is considered to be a step towards more accurately determined efficiency functions in gamma-ray spectrometry.

Standardization and decay data of 237Np.

This paper reports contributions from participants in the EUROMET project (No. 416) which was entitled "237Np research into problems relating to purification, characterization and standardization". Primary standardizations were made by the defined low solid angle, coincidence, 4pi alpha, 2pi alpha and liquid scintillation counting methods. Secondary standardizations were made with calibrated gamma-ray spectrometers. Absolute X-ray, gamma-ray and alpha-particle emission probabilities were also determined. The results for the successful conclusion of both primary and secondary standardization are presented together with the values for alpha-particle and gamma-ray emission probabilities determined in this exercise. Several significant inconsistencies remain with the gamma-ray emission probabilities, and these are highlighted.

Calculation of emission probabilities of X-rays and Auger electrons emitted in radioactive disintegration processes

A complete set of data for the decay scheme of a radionuclide requires knowledge of the emission probabilities of X-rays and Auger electrons. If adopted sets of transition probabilities for the transitions of the decay scheme and atomic shell data (such as fluorescence yields and relative emission probabilities) are available, the emission probabilities of the X-rays and Auger electrons can be calculated from these data. Only data calculated in this way are consistent with the adopted input data and can be compared with measured data. Conclusions can be drawn with respect to the internal consistency of the data sets by comparing the measured and calculated data. Hence, the EMISSION program has been developed and tested to calculate X-ray and Auger electron emission probabilities along with their error propagation.

Standardization and photon emission probabilities in the decay of 237Np/233Pa

The activity concentration of a 237Np solution was determined by 4pialpha counting, by alpha particle spectroscopy with defined solid angle and by liquid scintillation counting (LSC). These methods yielded results which differ by less than 0.1% from the mean, the relative standard uncertainties being 0.23% (4pialpha), 0.27% (LSC) and 0.5% (solid angle). X-ray and gamma-ray emission probabilities of several transitions were measured using semiconductor detectors.

Redetermination of the total internal conversion coefficient of the 279 keV transition following the decay of 203Hg

A new measurement of the total internal conversion coefficient of the 279 keV transition following the decay of 203Hg resulted in alpha = 0.2250(12).

The spine: changes in T2 relaxation times from disuse.

Magnetic resonance imaging of the spine was performed in six healthy male volunteers before and after 5 weeks of continuous bed rest. Imaging studies consisted of a single 1-cm sagittal section obtained with a spin-echo technique through the center of the spinal column. The T2s of the lumbar vertebral body and nucleus pulposus and the area of the latter were measured. In both vertebrae and disks, there was a significant decrease in T2 after bed rest. The nucleus pulposus also decreased in size with bed rest. The decrease in relaxation time of the lumbar vertebrae could be explained by the replacement of hematopoietic marrow by fatty marrow, a known consequence of paralytic immobilization. The decreases in size and T2 of the disks probably represent loss of water. The significance of these changes to the mechanical integrity of these structures after immobilization or space flight is not known but will depend in part on whether changes are progressive with increasing length of immobilization and on the rate and extent that they are reversed after reambulation. These results indicate that relaxation times can be altered by simple disuse, which often accompanies the underlying disease.