Nuclear Track Detection最新文献

Accelerated argon and neon particles of 280 MeV/nucleon were stopped in stacks of 250 μm Daicel cellulose nitrate visual track detector sheets. The nuclear charge and mass of 172 particles from the neon exposure and of 23 particles from the argon exposure was determined by means of the cone-length vs residual-range method using the REL criterion. A mass resolution of 0·41 amu for ²⁰Ne and 0·25 amu for ⁴⁰Ar was obtained. The influence of fragmentations within the registration range on the particle identification is discussed.

Nuclear emulsions may be desensitized in manufacture and/or may be so processed as to discriminate against small latent image sites; to yield supralinear sensitometric response after x-irradiation; and to discriminate against lightly ionizing radiations in favor of heavily ionizing particles. In a circumstance where one electron passing through an emulsion grain is unlikely to generate a latent image sufficiently large to yield a visible grain after development, some larger number of electrons is required, resulting in “many-hit” statistics, supralinearity, and particle discrimination: for lightly ionizing particles are not likely to generate more than one δ-ray (secondary electron) in their passage through or near a grain. Since these properties are analagous to the response of many biological cells to ionizing radiations, such emulsion-developer combinations have the potential to mimic the response of biological systems to particulate radiations of different charge and speed.

A survey of some actual problems of the track processing methods available at this time for plastics is presented. In the case of the conventional chemical track-etching technique, mainly the etching situations related to detector geometry, and the relationship between registration sensitivity and the etching parameters are considered. Special attention is paid to the behaviour of track-revealing by means of electrochemical etching. Finally, some properties of a promising new track processing method based on graft polymerization are discussed.

High-LET particle radiation-measurements taken inside manned spacecraft are presented for the Apollo, Skylab, and ASTP space missions. The measurements include particle flux, integral LET spectrum, and stopping-density charge-distribution registered in plastic nuclear track detectors worn by astronauts and located at various positions inside the spacecraft. They reflect a wide range of shielding depth and mission type.

The influence of crystallographic structure of the annealing of fission-fragment tracks in muscovite has been reported in the past, but the possibility of such an effect in other minerals has received little attention. We have investigated the annealing behaviour of tracks in bronzite, using collimated beams of ²⁵²Cf fission fragments, and heavy ions (Fe and Kr of 9·6 MeV/nucleon) employing the ‘L-R plot’ technique. No influence of structure on the annealing of these tracks is found. The annealing behaviour of fossil-fission tracks in apatite is also studied from this aspect, and here significant crystallographic effects are found. After reduction of track density to 0·25 of the original unannealed value, the great majority of tracks are aligned with the c-axis of the crystal prism. However, the overall significance of this effect, in terms of track densities, seems to be small.

Heavy-ion detection by solid dielectrics has been so far obtained by chemical etching. In this paper the detection of fission fragments is based on the counting of breakdowns in thin films of solid dielectrics. These films are used as dielectric materials in capacitors with one electrode usually less than 1000 A thick. Breakdowns in such capacitors are non-shorting and can be repeated up to millions of times/cm² of the capacitor area. The property that makes these capacitors suitable for detection is that fission fragments induce breakdowns at electric fields distinctly lower than those due to the application of field alone. The characteristics of these new detecting systems are described and compared with those of the damage-track detectors.

Fission fragments produce measurable current pulses in thin film capacitors at electric fields which are high, but still below the breakdown range for fragments. This paper describes the use of silicon dioxide capacitors for the detection of fission fragments by such current pulses. With capacitor areas of 2 x 10^-2 cm², the pulses were insignificant when the oxide was relatively thin, but with 3800 Å thick oxide, fission fragments produce detectable pulses of about 10^-15C. The mechanisms producing the current pulses by fission fragments are discussed.