Nuclear Tracks

The proton response of the TS-16 type of CR-39 plastic nuclear track detector has been studied with accelerated and fast neutron induced protons in vacuum and in air. The diameters of etched tracks were measured as a function of etching time and the etch rate ratio and the etch induction layer were determined from the growth curve of the diameter using a variable etch rate ratio model. In the case of the accelerated protons in vacuum an anomalous incident angle dependence of the response is observed.

The CR-39 track detectors have been applied to irradiate the Chinese hamster V79-753B cells for survival studies. The survival curves have given satisfactory results. Energies of the incoming as well as outgoing proton beams evaluated from the track diameters are found to be close to the values found separately by surface barrier detector (SSBD).

During IML-1 mission, we carried out space experiments on radiobiological effect of a single HZE cosmic particle. In the experiment, the precise determination of the distance between the center of the particle trajectory and the individual biological objects around it is an indispensable condition. For the detection of HZE particles CR-39 track detectors were used and analyzed by the video image processing. The positions of biological objects in relation to a particle trajectory were measured by referring to the laser grid marks which were printed on the surface of CR-39 detector. We describe such an experimental method and report the applicability of this method.

ABSTRACT In order to get significant results in momentum and angular correlation analysis of particles inside jets at very high energy a new charged particles detector has been developped and tested. Preliminary comments and results are presented.

The ENEA fast neutron dosemeter is based on a planar poly allyl diglicol carbonate (PADC) placed in a polyethylene holder. The present paper reports the results of an experimental study of a CR-39® material with the addition of 0.1% of dioctylphthalate (DOP) produced by the Italian company Intercast Europe S.p.A.The etching procedure is: pre-etching with 40% KOH water solution 6.25N and 60% ethyl alcohol at 70°C followed by 12h of etching in 6.25N KOH water solution. For the energy dependence of response, dosemeters have been irradiated with neutron sources (241Am–Be, 252Cf, Pu–Li) and 14.9MeV monoenergetic neutrons. The dosimetric performance of the material for fast neutrons is expressed in terms of sensitivity, background value, lowest detectable dose and energy dependence of response. Moreover, the results of a quality acceptance test of the material, performed on 11 sheets (980×980mm2, 1.4mm thick) of the same production batch, are given. Therefore, the homogeneity of the neutron sensitivity and of the background signal within a sheet and the whole batch is considered. The results are compared with the acceptance test outcome for a CR39 standard material batch.

ABSTRACT Batches of CR-39 polymer have been produced using a temperature-time polymerisation cycle designed to minimise temperature gradients during curing. Track detector evaluation tests of these batches were carried out using Argon and Iron beams at the LBL Bevalac. The results indicate a significant improvement in the uniformity of track response compared with commercially available CR-39 sheet. This improvement is particularly relevant to the use of CR-39 for cosmic ray composition studies.

Sheets of CR 39 have been irradiated with 20Ne, 32S, 40Ar, 56Fe and 63Cu ions at normal incidence to the surface of the sheets and at normal incidence to the edges. The profiles of the etched tracks have been observed side-on and measurements made of the variation of V (the ratio of track to bulk etching velocities) along the tracks and of the fully etched range of the tracks. Heating the plastic at 100 °C prior to etching produces zones within the plastic having different bulk etching rates VB. An outer zone of low VB is followed by a zone of much higher VB. This allows tracks to be readily etched to very large diameters, comparable in size to the breakdown spots produced by electrochemical etching.

ABSTRACT The application of CR-39 polycarbonate plastic to quantitative B mapping in mineral assemblages has been investigated. The investigation included the calibration of the detector material using standards prepared from spectrographic grade carbon powder and boric acid, and the determination of correction factors for the potentially interfering reactions 6Li(n,α) 3H and 14N(n,p) 14C. Samples and standards were irradiated with thermal neutrons for between 0.5 and 8 hours. The method is being applied to a suite of minerals from the Mendip Hills in southwest England.

Following G. Tarié's discovery of the remarkable effect of a 1% addition of dioctyl phthalate to CR-39 monomer, we have cast sheets of CR-39 with no additive and with 1% of dioctyl phthalate, dioctyl teraphthalate, and diisodecyl phthalate. Sheets made from any of the additives are much more transparent after etching and the etched cones are more uniform than is the case with pure CR-39. In irradiations with Ar, Ne, C, and He, we find that the dependence of reduced etch rate, VT/VB-1, on Z/β is significantly different for the pure CR-39 and for each kind of additive. One can thus choose an additive that gives the optimal response for a particular application. All of our sheets with additives are more sensitive than those with dioctyl phthalate made for us by Pershore; our pure CR-39 is more sensitive than Pershore's pure CR-39.

ABSTRACT Selection of optimum etching conditions for plastic track detectors is essential if they are to be used to best advantage. We present results of a study of the influence of etchant type, temperature and concentration, on the etching response of CR39. We conclude that 6N NaOH at 70°C gives the steepest response curve for CR39, within the range of temperatures (40 – 70 °C) and concentrations (1N-12N) studied. Other plastics are briefly discussed.

Plastic nuclear track detectors in conjunction with computerized image analysis are being utilized for the study of fragmentation of high-energy heavy accelerated beams. This paper reports the findings of an experiment involving a 570 MeV/nuc argon beam which is degraded in water and stopped in a stack of Lexan detectors. Tracks of beam fragments were measured between 18 and 22 g/cm2 which is downstream of the original particle stopping point (17.6 g/cm2). The charge distribution of fragments, and the distribution of stopping points in the plastic stack for individual fragments, were measured. The stopping point distributions are compared with the results of a Monte Carlo calculation.

Generally the track formation in plastics is associated with chemical damage. In order to investigate the latter, three analytical techniques have been utilised: I.R. and U.V. optical absorption spectroscopy and for all the plastics (including CR 39) E.S.R. spectroscopy. As an electron bombardment does not give rise to such etchable tracks, we have compared the effects of two types of radiation: Ar or Kr ions and 1,6 MeV electrons. On the other hand, as a thermal treatment anneals the latent tracks, the E.S.R. signal is followed versus annealing temperature up to total annealing. The dose effect is also widely investigated. We conclude that, a track effect can be a mere dose effect in most cases (e.g. polyethylene, polypropylene,…); in other cases, the formation of etchable tracks requires a time correlation in addition to the spatial correlation. We suggest that the existence of heavy ion latent tracks might be correlated with the formation of carbon-like radicals such as are produced in polymer pyrolysis. In the special case of teflon, the carbon like radicals are converted so quickly to RO2 radicals that subsequent etching of the tracks is not possible.

Current analyses of the annealing process in Solid State Track Recorders (SSTR) reveal fundamental misconceptions. The use of the Arrhenius equation to describe the decrease in track density resulting from annealing is shown to be incorrect. To overcome these deficiencies, generalized reaction rate theory is used to describe the annealing process in SSTR. Results of annealing experiments are used to guide this theoretical formulation. Within this framework, the concept of energy per etchable defect for SSTR is introduced. A general correlation between sensitivity and annealing susceptibility in SSTR is deduced. In terms of this general theory, the apparent correlation between fission track size and fission track density observed under annealing is readily explained. Based on this theoretical treatment of annealing phenomena, qualitative explanations are advanced for current enigmas in SSTR cosmic ray work.

ABSTRACT In our track developing model two processes are regarded to create the latent track: first the well-known process of the energy deposit along the path of the ion and second the newly proposed process of additional track formation in the region of the already existent latent track through NaOH which has diffused into the detector material before the real etching process had started. A first order mathematical description of the model and a discussion of the experimental implications will be given.

A method of particle tracks enlargement through a sequential electrical and chemical treatment was tested on fission fragment tracks in PETP-foils down to a thickness of 23 μm. The influence of the experimental conditions on the spot diameter was investigated. The shape and behaviour of the spots and the bubbles give evidence that electroosmotic pressure is responsible for the effect.

Accepted descriptions of the annealing process in Solid State Track Recorders (SSTR) are reviewed with emphasis on current misconceptions. In particular, it is shown that the Arrhenius equation should not be used to describe the decrease in observable track density induced by annealing. Results of annealing experiments in different SSTR media are examined. On this basis, a general reaction rate theory of the annealing process in SSTR is advanced. This formalism is used to introduce the new concept of the energy per etchable detect for SSTR. An important qualitative outgrowth of this work is the establishment of a general sensitivity-annealing correlation for SSTR. Observed annealing induced correlations between track size and track density for fission fragments are readily understood in terms of this general theory. Qualitative explanations of current enigmas in SSTR cosmic ray work are also advanced.

In order to further the understanding of the chemical nature of the damage along nuclear tracks in polycarbonates and of the enhancement of this damage by photo-oxidation, the following study is undertaken. Available data on the radiolytic products of polycarbonate and model compounds are assembled together with the known photolytic behavior behavior of these materials in the presence and absence of oxygen. These properties are then used to interpret preferential track etching and the increase in track etch rate observed for polycarbonate upon exposure to UV radiation in the presence of oxygen. Studies such as this may lead to the ability to design molecular structures specifically for the task of nuclear track detection.

Fission-track analyses using both the track-size and the plateau-annealing age-correction techniques have been applied to a collection of obsidian artifacts and obsidian glasses from South America. Both archaeological and geological ages have been obtained in some cases. Several cases illustrating both correction techniques used in fission-track analysis are presented. A study of a suite of obsidian artifacts from one geological site, Palmar, Ecuador, indicates two obsidian sources. The results show a potential for correlating obsidian artifacts to the obsidian glass used to produce the artifacts based on the geological age and uranium concentration determined by using fission-track analysis.

The present work was attempts to develop rapid and accurate alternative analytical method for measuring naturally occurring radioactivity in the crude phosphoric acid (CPA). The measurements were achieved using nuclear method based on the non-destructive γ-ray measurements; and non-nuclear methods, including the ICP-OES and UV–vis colorimetric method. The results showed that, radionuclides of Th-234, Pa-234m (daughters of U-238) and U-235 were identified and quantified. The activity ratio of Th-234:U-235 was 21.0 ± 0.86. This value is significant because it is close and agrees with the reference naturally occurring activity ratio of 21.7 between U-238 and U-235. Total U in four different brands of the CPA (I–IV) was quantified using γ-emissions of its progeny (Th-234) for the aged samples only, or its natural isotope (U-235) for both fresh and aged samples. It was found that, the total U concentration in different four brands CPA (I–IV) of CPA using γ-emissions of Th-234 was 100.2, 68.7, 67.9 and 87.6 ppm for the brands I, II, III and IV, respectively with small coefficient of variance (CV,%) does not exceed 4%. For the same brands (I–IV) using γ-emissions of U-235 isotope, the total U concentration was 98.3, 75.5, 70.2 and 89.6 ppm, respectively with CV(%) below 5.3%. By ICP-OES method, U determination is negatively interfered with the phosphorous in all brands of CPA(I-IV). Alternative UV–vis spectrophotometry analytical method has been developed to detect the total U concentration using 10% oxalic acid as an efficient masking agent for Fe. By UV–vis method, the total U concentration in CPA brands was 102.3, 58, 56 and 73 ppm for I, II, III and IV brands, respectively with CV (%) less than 3.3%. Finally, it is concluded that the nondestructive γ-ray spectrometry may be the best choice for uranium measurement, especially in crude phosphoric acid (CPA) with relatively high P and Fe concentration.

A computer program called TRACK_TEST for calculating parameters (lengths of the major and minor axes) and plotting profiles in nuclear track materials resulted from light-ion irradiation and subsequent chemical etching is described. The programming steps are outlined, including calculations of alpha-particle ranges, determination of the distance along the particle trajectory penetrated by the chemical etchant, calculations of track coordinates, determination of the lengths of the major and minor axes and determination of the contour of the track opening. Descriptions of the program are given, including the built-in V functions for the two commonly employed nuclear track materials commercially known as LR 115 (cellulose nitrate) and CR-39 (poly allyl diglycol carbonate) irradiated by alpha particles.Title of the program:TRACK_TESTCatalogue identifier:ADWTProgram obtainable from:CPC Program Library, Queen's University of Belfast, N. IrelandProgram summary URL: http://cpc.cs.qub.ac.uk/summaries/ADWTComputer:Pentium PCOperating systems:Windows 95+Programming language:Fortran 90Memory required to execute with typical data:256 MBNo. of lines in distributed program, including test data, etc.: 2739No. of bytes in distributed program, including test data, etc.:204 526Distribution format:tar.gzExternal subprograms used:The entire code must be linked with the MSFLIB libraryNature of problem: Fast heavy charged particles (like alpha particles and other light ions etc.) create latent tracks in some dielectric materials. After chemical etching in aqueous NaOH or KOH solutions, these tracks become visible under an optical microscope. The growth of a track is based on the simultaneous actions of the etchant on undamaged regions (with the bulk etch rate Vb) and along the particle track (with the track etch rate Vt). Growth of the track is described satisfactorily by these two parameters (Vb and Vt). Several models have been presented in the past describing the track development, one of which is the model of Nikezic and Yu (2003) [D. Nikezic, K.N. Yu, Three-dimensional analytical determination of the track parameters. Over-etched tracks, Radiat. Meas. 37 (2003) 39–45] used in the present program. The present computer program has been written to calculate coordinates of points on the track wall and to determine other relevant track parameters.Solution method:Coordinates of points on the track wall assuming normal incidence were calculated by using the method as described by Fromm et al. (1988) [M. Fromm, A. Chambaudet, F. Membrey, Data bank for alpha particle tracks in CR39 with energies ranging from 0.5 to 5 MeV recording for various incident angles, Nucl. Tracks Radiat. Meas. 15 (1988) 115–118]. The track is then rotated through the incident angle in order to obtain the coordinates of the oblique track [D. Nikezic, K.N. Yu, Three-dimensional analytical determination of the track parameters. Over-etched tracks, Radiat. Meas. 37 (2003) 39–45; D. Nikezic, Three dimensional analytical determination of the track parameters, Radiat. Meas. 32 (2000) 277–282]. In this way, the track profile in two dimensions (2D) was obtained. In the next step, points in the track wall profile are rotated around the particle trajectory. In this way, circles that outline the track in three dimensions (3D) are obtained. The intersection between the post-etching surface of the detector and the 3D track is the track opening (or the track contour). Coordinates of the track 2D and 3D profiles and the track opening are saved in separate output data files.Restrictions: The program cannot calculate track parameters for the incident angle of exactly 90°. The alpha-particle energy should be smaller than 10 MeV. Furthermore, the program cannot perform calculations for tracks in some extreme cases, such as for very low incident energies or very small incident angles.Additional comments: This is a freeware, but publications arising from using this program should cite the present paper and the paper describing the track growth model [D. Nikezic, K.N. Yu, Three-dimensional analytical determination of the track parameters. Over-etched tracks, Radiat. Meas. 37 (2003) 39–45]. Moreover, the references for the V functions used should also be cited. For the CR-39 detector: Function (1): S.A. Durrani, R.K. Bull, Solid State Nuclear Track Detection. Principles, Methods and Applications, Pergamon Press, 1987. Function (2): C. Brun, M. Fromm, M. Jouffroy, P. Meyer, J.E. Groetz, F. Abel, A. Chambaudet, B. Dorschel, D. Hermsdorf, R. Bretschneider, K. Kadner, H. Kuhne, Intercomparative study of the detection characteristics of the CR-39 SSNTD for light ions: Present status of the Besancon–Dresden approaches, Radiat. Meas. 31 (1999) 89–98. Function (3): K.N. Yu, F.M.F. Ng, D. Nikezic, Measuring depths of sub-micron tracks in a CR-39 detector from replicas using atomic force microscopy, Radiat. Meas. 40 (2005) 380–383. For the LR 115 detector: Function (1): S.A. Durrani, P.F. Green, The effect of etching conditions on the response of LR 115, Nucl. Tracks 8 (1984) 21–24. Function (2): C.W.Y. Yip, D. Nikezic, J.P.Y Ho, K.N. Yu, Chemical etching characteristics for cellulose nitrate, Mat. Chem. Phys. 95 (2005) 307–312.Running time: Order of several minutes, dependent on input parameters and the resolution requested by the user.