Nuclear Track Detection最新文献

Observations of cosmic-ray tracks in silicate grains in chondrites and in stony-iron meteorites have long been recognized to be useful for the study of effective shielding depths in a preatmospheric body. In this paper we discuss ways of estimating the preatmospheric radius or mass of the original body from such observations. We consider various cases of ablation and methods to determine the magnitude of ablation in each case. In cases where a single stone survives, a determination of shielding depths in several representative samples from the surface of the stone allows a fairly accurate reconstruction of the preatmospheric shape, provided ablation is not too asymmetric. In the case of asymmetric ablation the preatmospheric radius and the magnitude of ablation can be determined from the frequency distribution of shielding depths of samples from the surface and/or from a study of shielding depths along a slice cut from the recovered stone. If, instead, the ablationary processes lead to production of a large number of stones, an estimation of the lowest track density should in most cases allow a fairly precise value of the preatmospheric radius. We also discuss a method for the estimation of mass wastage from concentric shells in the preatmospheric body based on a representative study of the distribution of surviving mass in suitably chosen track-density intervals.

In recent years the term ‘archaeometry’ has been introduced into scientific literature to denote the many interdisciplinary studies which have resulted from the application and development of methods of the natural sciences in archaeology. Apart from material analyses, radiometric dating is most important among archaeometric activities. It is fission-track dating that is of special value and promise for archaeological objects in view of its demonstrated success in dating geologically young rocks (a few million years old).

The diffusion of ²⁴¹Am³⁺ ions in a sulphonic acid polystyrene type ion-exchange membrane has been studied. Ion diffusion-concentration profiles within the membrane is determined using quantitative microautoradiography performed with Agfa-Gevaert photoemulsions and plastic nuclear track detectors. The diffusion coefficients derived from the radiograms of the ion-concentration profiles and the results obtained by the two different methods are compared.

A brief review of the application of solid state nuclear track detectors (SSNTDs) in neutron dosimetry is given. The present state and the most important properties of the SSNTD neutron dosimeters are discussed and their advantages in comparison with other possible detectors are listed. Particular attention is devoted to the applications in personnel neutron dosimetry and here the authors' original work is also described. Possible future applications of SSNTDs in neutron dosimetry are discussed. Both technical improvements and new fundamental approaches are analysed.

Systematic annealing experiments have been carried out in order to obtain correction factors for the ages of chlorite, which may have undergone geological annealing. All the tracks in the mineral are annealed by heating for one hour at 500°. Extrapolation of experimental data suggests that a temperature of 160° would be required for 10⁶ years to remove all the tracks in chlorite. Ages of 6 samples have been determined. The corrected age of 606 ± 17 × 10⁶ y obtained for Nellore, Andhra Pradesh, India, agrees well with the ages of coexisting minerals, determined by the fission-track method. The activation energy for chlorite ranges from 1.2 to 2.0eV, with a mean value of 1.5 eV.

By using a selective etching technique in olivines from the Marjalahti meteorite, more than 2000 tracks longer than 150 μm have been found to be due to galactic cosmic-ray nuclei of Z > 50. The olivines examined were taken from locations ∼ 5 cm and 8–9 cm below the preatmospheric surfaces of the meteorites, respectively. The data on the track distribution are compared with the known values of the relative abundances of the 50<Z≦92 elements of the solar system. A satisfactory agreement (within a factor of 0.5–2) between the abundances of the nuclei of Z≧70,Z≧90 in galactic cosmic rays and in the solar system is obtained by assuming the group of the longest tracks (720–900 μm) to correspond to the region of thorium to uranium.

Although radon and its airborne daughter products are prevalent in our natural environment, they constitute a significant hazard only when concentrated in some enclosure such as a mine, cave, cellar, or house. This paper describes the nature of radon/daughter concentrations occurring in a variety of situations, the resultant biological hazard, and present methods used in the attempt to reduce man's exposure to harmful radiation. Many attempts to perfect environmental and occupational dosimetry have been made. Area monitoring methods are presently used, but can give only approximations of personal exposures. Several personal dosimeters employing track-etch, TLD, and photographic film detectors have been developed and are evaluated here on the basis of tests performed in working uranium-mine conditions. An improved passive track-etch dosimeter for personal use is proposed which has a measurement range of about 30–400 WLH with a 95% confidence interval of ∼25% for the accuracy of individual measurements in relatively stable mine air. The cellulose nitrate plastic used in these measurements is only moderately sensitive (E_c3.5. MeV) and performance can be improved by using a more sensitive detector. Some measurements of these dosimeters adapted to environmental use are also presented.