G. Somogyi

Measurement of radon, radon daughters and thoron concentrations by multi-detector devices

Abstract There is a growing interest in collection of data concerning human exposures to naturally occurring alpha-emitting radionuclides (e.g. in mines, dwellings, building materials, industrial wastes, coal fuel cycle, water supply, soil, plants, etc). Most of such studies is incomplete for the following reasons: 1) In radon measurements the contribution of thoron is generally neglected. 2) The determination of equilibrium factor is complicated or not possible at all. 3) Short- and long-term concentration fluctuations cause difficulties in obtaining representative mean values. 4) The plate-out effect is generally not taken into account. We have studied a variety of simple methods that could be used to overcome some of these difficulties by using cups equipped with two or more alpha-sensitive nuclear track detectors. A theoretical foundation of the quantitative measurements with such devices is presented. Experimental data are reported on radon, radon daughters and thoron concentrations measured by multi-detector devices in cave soil gas and in air of Hungarian dwellings.

Spark counting of α-radiograms recorded on LR-115 strippable cellulose nitrate film

Abstract In this paper a study on the spark counting of etch-holes of α-particle tracks recorded on 13 μm strippable cellulose nitrate track detectors (Kodak-Pathe LR-115 films) is described. Results for the counting characteristics as a function of etching and irradiation parameters are given. Applications of the spark counting technique to α-radiograms obtained by the ( p , α) nuclear reaction and soil-radon exhalation measurements are presented.

A new possibility for high-resolution spectroscopy of nuclear particles entering CR-39 at selected dip angles

Abstract In nuclear reaction studies a differentiation of the reaction products according to their type and energy is generally required. At right angle of incidence a particle identification method based on the relation netween the track diameter and particle energy can be well applied to plastic track detectors of low registration sensitivity. We have tried to extend this “track-diameter method” to the high-sensitivity CR-39 sheets by selecting special incident angles for particle detection. The utility of such a measuring procedure, called “track-size method”, is presented for alpha and proton spectroscopy. A theory is developed to calculate at arbitrary angles the main parameters affecting the energy resolving power of the “track-size method”, namely the critical layer thickness (which has to be removed from the detector surface for track-induction) and the depth and minor axis of etch-pits.

AUTOMATIC SPARK COUNTING OF ALPHA-TRACKS IN PLASTIC FOILS

Abstract The possibility of α-track counting by jumping-spark counter in cellulose acetate and polycarbonate nuclear track detectors was studied. A theoretical treatment is presented which predicts the optimum residual thickness of the etched foils in which completely through-etched tracks (i.e., holes) can be obtained for α-particles of various energies and angles of incidence. In agreement with the theoretical prediction, it is shown that a successful spark counting of α-tracks can be performed even in polycarbonate foils. Some counting characteristics, such as counting efficiency vs particle energy at various etched-foil thicknesses, surface spark density produced by electric breakdown in unexposed foils thickness, etc., have been determined. Special attention is given to the spark counting of α-tracks entering thin detectors at right angle. The applicability of the spark-counting technique is demonstrated in angular-distribution measurements of the 27 A1 ( p ,α 0 ) 24 Mg nuclear reaction at E p =1899 keV resonance energy. For this study 15 μm thick Makrofol-G foils and a jumping-spark counter of improved construction have been used.

Vacuum effect on the etch induction time and registration sensitivity of polymer track detectors

Abstract The vacuum effect on etch induction time and track etch rate ratio of some polymeric track detectors were studied systematically with alpha particles of different energies. It is found that the etch induction time increases and the track etch rate ratio decreases drastically when the detectors were irradiated in vacuum and also kept in vacuum for a few hours before and for a new minutes after the irradiation. These times proved to be characteristic for the outgassing of oxygen from the sheets and the stabilization of latent track, respectively. The role of oxygen in latent track formation is discussed. We have found that the vacuum effect is most significant near the surface and its diminution with depth depends on the time of outgassing in accordance with the time variation of dissolved oxygen concentration profile inside the sheets.

Neutron radiographic characteristics of MA-ND type (allyl-diglycol-carbonate) nuclear track detectors

Abstract Neutron radiographic properties of recently developed new nuclear track detectors (MA-ND/α, MA-ND/p and MA-ND/p1), manufactured from allyl diglycol carbonate, were studied. It was found that the quality of radiographic image has an optimum at a removed layer thickness of about 0.8μm. The image obtained under this condition is characterized by high detection sensitivity to neutrons (∼8·10 -3 tracks/n th when using B converter) and by excellent inherent unsharpness (∼5μm) as well as high image contrast (maximum value of net optical density is ∼1.4).

Boron determination using PC nuclear track detector and252Cf neutron source

The possibility of quantitative boron determination via (n,α) reaction in silicon and B2O3+PVA samples has been studied. As alpha-sensitive track detector Makrofol-E polycarbonate foil and as neutron source lmg252Cf with a cadmium ratio of 8 were applied. It was shown that, if the lowest acceptable track density was 103 tracks cm−2 the method could be used to measure B concentrations down to 1 ppm.

Study of transport processes in plants by radioabsorption and microradiographic methods

The passive transport processes in plants of22Na+,137Cs+,45Ca2+,65Zn2+,59Fe3+ and32PO43− ions and the plant-protecting agent “Saphidon (14C)” were studied by a radioabsorption method. The parameters of the passive transport processes of212Pb2+, borate and tetraborate ions in plants were measured by quantitative microradiographic methods, using photoemulsion and solid state nuclear track detectors. Ion diffusion concentration profiles within the plants were determined at various diffusion times and temperatures. The equation of linear diffusion combined with convection was used to determine the diffusion coefficients characteristic of the transport processes.

Studies on nitrogen mapping by various CR-39 track detectors

The possibility of using CR-39 track detectors for nitrogen distribution measurements via 14N(n,p) 14C reaction is studied. In this respect the proton detection properties of different CR-39 products have been analyzed. By PIXE and neutron activation methods the possible disturbing impurity content of the detector sheets is determined. It is found that the main contaminant is chlorine which remains in the CR-39 monomer during its manufacture. The variation of background track density induced in the bulk of detectors is examined under different conditions of neutron irradiation. The analysis of our experimental data has led to the conclusion that the sources of proton background tracks are the fast neutron component of neutron source, chlorine in detector and nitrogen diffused from air into the upper layer of detector. Efforts have been made to decrease the nitrogen content of diffusion origin by removing the upper detector layer and by outgassing the CR-39 sheet in vacuum before irradiation. Finally the “signal/noise” ratio for steel specimen and the sensitivity of nitrogen determination are given.

Formation of ion-beam images in gelatine and various polymers

Abstract It has recently been reported by Najzer, Humar and Ilic (1982) that the pure gelatine can be used for producing relief images of high-fluence ion-beams after a treatment in water at room temperature for few minutes. The new method is proposed for high-resolution microradiography of boron in metals via 10B(n,α)7Li reaction. In our present work studies are performed to understand the phenomenon observed. We have simulated the image formation by accelerated electron, proton and alpha-particle beams at different fluences. A narrow fluence region is found in which a highly enhanced dissolution rate of the irradiated gelatine is induced. We assume that when the fluence exceeds a critical value (tipically 1012–1013 ions·cm-2) the damage zones of individual tracks cover almost completely the irradiated area, transforming the irradiated layer into a huge damage zone. In this case the effective diameter of damage zone around a single track has to be d eff= =φ c -1 2 ≅(3–10) nm . We have found that the ion-induced image formation phenomenon observed in gelatine is a more general one and the method may be extended to almost all the etch-track and non-etch-track forming polymers and perhaps to insulating silicates. For example high-resolution α- microradiographs have been obtained with CR-39, CN-85, PC and PET sheets and even with hydrate-cellulose known as a non-track-forming material.