Klaus Becker

Automatic spark counting of fast-neutron-induced recoil-particle tracks in polymer foils☆

Abstract It is shown that not only fission-fragment and alpha-particle tracks, but also heavy-recoil-particle tracks which are produced by direct fast-neutron interaction with organic foil (or foil cover) constituents can be counted automatically with the well-known automatic “spark-counting” technique. Extended etching of cellulose-nitrate and polycarbonate foils of 10 μm thickness to a point close to that at which electrical breakdown would occur in unexposed foils resulted in good counting efficiency for the recoil tracks. There is a pronounced increase in sensitivity with increasing neutron energy.

Nonphotographic Alpha Autoradiography and Neutron-Induced Autoradiography

With a new combination of two techniques, (i) alpha-particle or fission fragment registration in thin polymer foils by etching and (ii) automatic counting and magnification of the etched perforations by local evaporation of a thin metal layer with an electric spark, the sensitivity of conventional photographic methods for determining quantity and spatial distribution of alpha emitters, fissile materials, and of elements undergoing (n, α) reactions can be drastically improved, without need for darkroom processing and microscopic evaluation.

Fast neutron personnel monitoring by fission fragment registration from 237Np

Abstract A combination of 237 Np (≈3 mg / cm 2 ) and a polycarbonate foil, to be spark-counted after etching, is used for fast neutron dosimetry between ≈10 −3 and > 10 rad.

ENVIRONMENTAL MONITORING WITH TLD.

Abstract CaSO 4 :Dy has advantages for environmental TLD: It can easily be prepared, is ≈30 times as sensitive as LiF:Mg,Ti, and exhibits considerably less fading than previously used CaF 2 :Dy.

STIMULATED EXOELECTRON EMISSION FROM THE SURFACE OF INSULATING SOLIDS.

Abstract The term “exoelectrons” cannot be found in any encyclopedia, dictionary, textbook, or handbook of physics, solid state science or surface phenomena. Yet, the effect of structure dependent emission of low energy electrons that occurs from surfaces of many insulating solids at temperatures well below those at which thermionic emission occurs has been the subject of more than 300 publications and several international conferences, most recently in Sverdlovsk, 1969′ and Braunschweig, 1970. So far, only one recent review of a particular application of this effect, namely in radiation dosimetry, is available in Englih. It is the purpose of this review to provide an introduction to the field in general and its many applications for the increasing number of scientists who have become interested in exoelectron emission.

A sensitive integrating fast neutron dosimeter based on TSEE

Abstract A new method for integrating fast neutron dosimetry using thermally stimulated exoelectron emission from pairs of ceramic beryllium oxide discs, of which one has been covered with a non-hydrogenous material (graphite), and the other with a hydrogenous material (polyethylene), is described. The difference in the radiation effect recorded in the detectors due to the contribution of recoil protons permits to detect low fast neutron doses with a sensitivity increasing from 18 to 28% of the gamma radiation sensitivity in the 0.1 to 16 MeV neutron energy range.

On the LET dependence of thermally stimulated exoelectron emission

Abstract If the emission rate of low-energy electrons from the surface of irradiated ionic crystals is plotted as a function of temperature, a characteristic curve with one or several peaks which are related to the surface trap distribution, is obtained. It has been observed that the peak ratio in some materials such as CaSO 4 , SrSO 4 and BaSO 4 is different after exposure to alpha and to gamma radiation. The fading kinetics also depend on LET. This effect is of interest for several dosimetric applications of thermally stimulated exoelectron emission.

A quick method for authentication of ceramic art objects

Abstract Thermoluminescence (TL) readout equipment is now in wide use for dosimetric purposes, and the principle of TL dating of ancient pottery generally known. On the other hand, the well-known difficulties in establishing ages by this method with reasonable accuracy discouraged investigators to apply commercial or self-developed TL equipment to the much more frequent and simpler problem of distinguishing between old (=original) and new (=faked) ceramic art objects. The paper describes how, with little additional eqipment and modifications of TL readers, authentication tests can be carried out based on the measurement of the TL from large (∼0.1-0.25 mm) quartz grains which have been isolated from the pottery.

A simple method for the automatic evaluation of particle tracks in mica

Abstract It is shown that the perforation created at the impact location of high-LET charged particles, such as fission fragments in thin (∼5–15 μ m) sheets of etched muscovite mica, can be counted conveniently by an automatic “spark counter” as used previously for track-counting in organic polymer foils. Ancient fission tracks in the mica are annealed by an 800°C treatment. Mica offers advantages in certain applications as an inorganic detector which can be scanned easily by non-optical means, because of the high thermal stability of the latent tracks (>500°C) and excellent discrimination against low-LET particles.

Search for exoelectrons in Apollo 12 materials.

Abstract The search for exoelectron emission from Apollo 12 materials usually produced negative results, suggesting that the concentration of naturally occurring traps is very low. Weak exoelectron activity was found scattered inhomogeneously within a pigeonite basalt rock and in a deep core tube sample. Its erratic appearance and intensity makes any interpretation of radiation history most difficult and is attributed to the activity being carried by only a few scattered crystals. The thermally stimulated emission of exoelectrons is judged an unsuitable technique for tracing the radiation histories of these samples.