Study of the neutron field with etched track detectors in radiobiological experiments

Low dose cell culture irradiation experiments have been carried out at the filtered beam of Budapest Research Reactor for several years. The aim of the present study is to provide along with the macroscopically determinable “dose”, more detailed information on the components of the radiation affecting the cells. For this purpose CR-39 detectors with several types of radiator and absorber materials were mounted in different geometrical arrangements on the walls of the cell holder flasks and irradiated under the same conditions as those of the cells. With these detectors individual particles can be investigated using an image analyser and the effect of thermal, intermediate and fast neutrons hitting the cells, the protons induced by neutrons in the wall of the flasks, backscattered by the medium and by the surroundings can be studied. The methods, results of the measurements and dose calculations will be presented.     

Operational and dosimetric characteristics of etched-track neutron detectors in routine neutron radiation protection dosimetry

There are a number of etched-track neutron dosimetry systems in routine use for personal monitoring. In this paper, the operational and dosimetric characteristics of these systems are summarized. Brief details are given of the dosemeter design, the material used, its quality control procedures, background, processing and read methods, neutron energy range, energy and angle dependence of response, decision threshold, linearity, signal storage stability, calibration methods including normalization, effect of influence quantities, and the advantages and disadvantages of the systems in routine application.     

Neutron response study of two CR-39 personal dosemeters with air and Nylon converters

A neutron personal dosemeter using CR-39 as a detector and hydrogenated materials as proton converters for fast neutron detection plus an air layer for thermal neutron detection is being developed in our laboratory. To increase the CR-39 response to thermal neutrons, the air converter was substituted with Nylon in some dosemeters. Several dosemeters with these two configurations were mounted on a water-filled phantom and exposed under different incidence angles (0, 30 and 60) to: (i) Three ISO neutron sources (²⁴¹Am–Be, bare ²⁵²Cf and moderated ²⁵²Cf with Cd shielding), and (ii) two realistic neutron sources (SIGMA and moderated ²⁵²Cf) at the IRSN (Cadarache) facilities. The irradiated detectors were electrochemically etched and evaluated in order to determine their dose equivalent response in terms of H_p(10,α). The results obtained are compared to those obtained from Monte Carlo simulations using the MCNPX code.     

Uranium analysis by neutron induced fissionography method using solid state nuclear track detectors

In this study total twenty samples (eight reference materials and twelve sediment samples) were analysed for their uranium content which is in the range of 1–17 μg/g, by neutron induced fissionography (NIF) method using solid state nuclear track detectors (SSNTDs) in comparison with the results of neutron activation analysis (NAA), delayed neutron counting (DNC) technique or fluorometric method. It is found that NIF method using SSNTDs is very sensitive for analysis of uranium.     

Calibration of PM-355 nuclear track detectors; comparison of track diameter diagrams with track depth characteristics

The calibration diagrams, i.e. track diameters and track depths versus ion energy and etching time, as obtained for PM-355 track detector irradiated with He-ions are presented. The both detector characteristics are compared. The track etch rate is determined by two methods, as a function of the etch pit depth and the ion energy loss.     

Radon epidemiology and nuclear track detectors: Methods, results and perspectives

An important achievement of nuclear track detectors is that they render it possible to measure a large number of radon concentrations. These are necessary for epidemiological studies aimed to estimate the lung cancer risk due to exposure to radon and its decay products in dwellings. Many case–control studies were conducted in the last 15 years in Europe, North America and China, in order to avoid the uncertainties associated with the risk extrapolation from epidemiological studies on miners exposed in underground mines. In this review paper, the main methodological issues of these studies are introduced: confounding factors, the impact of radon exposure uncertainties on the estimated risk, the retrospective assessment of radon exposure through the measurement of surface concentration on glass objects, the interaction between radon and smoking, statistical methods to analyze data and combine studies, etc. As regards the estimated risk of lung cancer, the main characteristics and results of each study are reported and discussed, together with the results of meta-analyses and, most importantly, of the three recently published analyses that pool 2 Chinese, 7 North American, and 13 European studies. Finally, some conclusions are given and a brief reference is made to ongoing studies.     

Single-sheet identification method of heavy charged particles using solid state nuclear track detectors

The theoretical and experimental investigations of the penetration of charged particles in matter played a very important role in the development of modern physics. Solid state nuclear track detectors have become one of the most important tools for many branches of science and technology. An attempt has been made to examine the suitability of the single-sheet particle identification technique in CR-39 and CN-85 polycarbonate by plotting track cone length vs. residual range for different heavy ions in these detectors. So, the maximum etchable ranges of heavy ions such as ⁹³Nb, ⁸⁶Kr and ⁴He in CR-39 and ⁴He and ¹³²Xe in CN-85 polycarbonate have been determined. The ranges of these ions in these detectors have also been computed theoretically using the Henke-Benton program. A reasonably good agreement has been observed between the experimentally and theoretically computed values.      

Effect of environmental conditions on radon concentration-track density calibration factor of solid-state nuclear track detectors

In this work, the effect of environmental conditions viz., temperature (T) and relative humidity (RH) on the track density-radon concentrations calibration factor (K) has been studied for CR-39 and LR-115 track detectors. The factorK was determined using a reference radon chamber in the National Institute for Standards (NIS) in Egypt. Track detectors were etched at the recommended optimum etching conditions. It is found that, the calibration factorK varies with bothT and RH, so they should be considered for the sake of uncertainty reduction. Good agreement is found between the calculated and measured values ofK and the compatibility between them is in the range of experimental uncertainty.     

Counting recoil proton tracks on PADC without a pre-etching step. A novel approach for neutron dosimeter application

At many laboratories involving in routine, individual neutron dosimetry, poly allyl diglycol carbonate (PADC) is utilized for particle registration. A pre-etching step is commonly applied in order to remove the alpha tracks of the environmental radon, so achieving the required lower limit of detection (LLD) performance. A novel approach is presented, which makes this pre-etching step unnecessary, but ensuring an excellent LLD performance, also providing a good throughput for a routine service. Exposing the PADC material to carbon dioxide atmosphere before the main etching step enhances the visibility of the microscopic track image. The enhancement is so efficient that the track size and image contrast between the alpha and the proton tracks are well distinctive. Customized image analyzer software is able to distinguish alpha and proton tracks, so providing the proton track density separately. A pilot study about the performance and potentials of this novel approach is presented. A complete application working with this approach was introduced to routine neutron dosimeter service 2 years ago and its good performance has been verified.     

Inter-comparison among fast neutron dosimetric services using PADC material of different composition

A trial inter-comparison has been performed among four fast neutron dosimetric services: PSI(CH), ENEA (I), DRPS (UK), LANL (US). The PADC used for the tests has been produced by Intercast Europe S.p.A. Three sets of detectors have been employed: two of PADC standard material from two different batches, and one of PADC with the addition of 0.1% dioctylphthalate. Each set consisted of 50 detectors.

For each set of detectors, 20 have been irradiated free-in-air at 1 mSv of H^*(10) with an ²⁴¹Am–Be source at ENEA-IRP, whilst the other detectors have been used as background samples. For each batch the value of the average background signal, B, the average neutron sensitivity, S, and minimum detectable dose equivalent, MDDE, have been determined. Two identical tests have been completed and separated with a time of 4 months in order to evaluate the ageing effect on the material stored in different conditions. Each dosimetric service processed the detectors according to local routine procedures. Three laboratories used an Autoscan60 reader, whilst one laboratory has an in-house reading system. Therefore, the results of the tests allowed a comparison of either the performance PADC materials, of different batches and of different compositions, or to evaluate how different etching, reading and storage conditions affect the results.     

Application of solid-state nuclear track detectors for studies of fast ion beams within PF-1000 and other plasma-focus facilities

The paper presents results of studies of the fast ion emission from two plasma facilities: PF-1000 and PF-II. The measurements were carried out mainly with solid-state nuclear track detectors (SSNTDs). To register ion mass- and energy-spectra, obtained when primary ion beams are deflected by magnetic and electric fields of a Thomson-type spectrometer, the SSNTDs plates were installed inside the analyzer. To measure ion angular distributions the SSNTDs were located within the main discharge chamber, at different angles to the electrode axis. The SSNTDs were also applied to register ion beam images formed within an ion pinhole camera, and to determine a spatial location of the fast ion sources.     

Ageing of AgCl/Cd nuclear track detectors monitored by luminescence spectroscopy

Abstract

Solid-state nuclear track detectors, made of Cd doped AgCl crystals, are commonly prepared by rolling into the form of thin foils. Subsequent long-term relaxation is however needed to obtain good quality tracks. The present communication shows for the first time that this detector “ageing” is reflected in lowtemperature (77 K) luminescence spectra. Maximum of the emission band shows a slow (lasting for ～ 100 hours) blue shift, the magnitude of which (as much as 25 nm) depends on the compression ratio caused by the rolling. The shift is believed to be due to the rearrangement of Cd⁺⁺ ions around freshly introduced dislocations. This finding opens the possibility of monitoring non-destructively the process of detector ageing and to determine the minimum time required for saturation.     

Damage track detectors in radioprotection dosimetry: a novel approach

Limited sensitivity and unpredictable background are the major drawbacks of damage track detectors in the assessment of low neutron doses and low concentrations of alpha emitters in biological and environmental samples. The simplest way to increase the sensitivity of the damage track detectors is to increase both the exposure time and the detector area. However, the strong variability of the background may make this task often impossible. This background problem has been finally solved by a new registration method based on counting coincidence spots in geometrically matched pair of detectors. By using spark counting and electrochemical etching, both of which produce spots visible at low magnification, coincidences induced in two matched detector-surfaces by a few-microns-long tracks can be easily seen. This novel counting approach can be considered just the converse of those used in the past with Bi-fission detectors and cosmic ray stacks.     

Annealing of 54 132 Xe-ion tracks in Lexan and Makrofol plastic track detectors

Samples of Lexan and Makrofol-E polycarbonate plastic track detectors were exposed to 1·1 MeV/N ₅₄ ¹³² Xe-ions to investigate the thermal track fading properties of these plastics. The experimental results show that there is no effect of annealing on the bulk etch rate while the track etch rate decreases with annealing. The track diameter decreases with increase in annealing time and temperature. It is also observed that the track density is reduced as a result of annealing. The experiments reveal that the track lengths are, in general, decreased by the application of heat and that the oblique tracks are less stable than the vertical tracks. The decrease in diameter of ₅₄ ¹³² Xe-ion tracks in Makrofol-E due to heat treatment is faster than that of ₅₄ ¹³² Xe-ion tracks in Lexan.     

Annealing of heavy ion tracks in cellulose nitrate plastic track detectors

The effect of heat treatment on the latent tracks in cellulose nitrate plastic track detectors has been studied. The bulk etch rate increases with annealing temperature while the track diameters of different ions in cellulose nitrate decrease with increase in annealing time and temperature. Experimental results show that for heavier ions higher temperatures are needed for their complete erasure. The track length and track etch rate are decreased by the application of heat. Experiments reveal that annealing reduces track density. The vertical tracks are more stable than the oblique tracks and require higher temperature for their complete erasure.     

Neutron-induced complex reaction analysis with 3D nuclear track simulation

Complex (multiple) etched tracks are analysed through digitised images and 3D simulation by a purpose-built algorithm. From a binary track image an unfolding procedure is followed to generate a 3D track model, from which several track parameters are estimated. The method presented here allows the deposited energy, that originated from particle fragmentation or carbon spallation by means of induced tracks in commercially available PADC detectors, to be estimated. Results of evaluated nuclear tracks related to ¹²C () reaction are presented here. The detectors were exposed on the ISS in 2001.     

Measurement of target fragments produced by 160 MeV proton beam in aluminum and polyethylene with CR-39 plastic nuclear track detectors

Production of target fragments from reactions of 160 MeV proton beams in aluminum and polyethylene was measured with CR-39 plastic nuclear track detectors (PNTD). Due to the detection limit of PNTD, primary protons cannot be detected; only low-energy short-range target fragments are registered. As a feasibility study, a so called “two step etching method” was employed to get the linear energy transfer (LET) spectra, absorbed dose, and dose equivalent. This method is discussed in this paper, together with the measured results.     

Calibration of different plastic track detectors using accelerated heavy ions

Measurements of the dependence of track etch rate on the energy-loss of different ions have been presented. In this method, ₁₈ ⁴⁰ Ar, ₁₀ ²² Ne, ₈ ¹⁶ O and ₆ ¹² C-ions of different energies are used as energetic heavy ions for track formation in the detectors. The bulk etch rate and track etch rate are measured for different temperatures and hence the activation energies are determined. The variation ofV =V _t /V _b along the trajectory of the track has been shown for different temperatures. The maximum etched track length is compared with the theoretical range as well as with the range reported earlier. The experimental results indicate the absence of a well-defined threshold in the plastics studied.     

Cosmic-ray neutron spectrometry by solid state detectors

Extensive data have been gathered since the early 1990s on the response of different detectors based on the registration of neutron-induced fission in bismuth, gold, tantalum by the spark replica counter and the thin film breakdown counter. These detectors make it possible to exploit the excellent characteristics of the fission reactions in bismuth, gold and tantalum for the measurements of high-energy neutrons.

Most of the investigations have been carried out at the quasi-monoenergetic neutron beam facility at The Svedberg Laboratory-TSL of the Uppsala University in cooperation with the Khlopin Radium Institute (KRI).

The responses of different fission detectors in the intermediate range of neutron energy (35–180 MeV) have been evaluated: a region where the predictive power of available nuclear reaction models and codes is not reliable yet. For neutron energy greater than 200 MeV, the fission-detector responses have been derived from the data of the proton fission cross-sections.

Finally, by using the ratio of the responses of these detectors, a simple and accurate way to evaluate the spectrum hardness can be obtained, thus providing a tool to obtain spectral information needed for neutron dosimetry without the need to know the entire spectrum.

The experimentally measured spectra obtained to-date have different shapes and they are also different from those calculated.

In this paper, a new approach will be reported to analyse the existing spectra by using response ratios of different detectors. Preliminary data have been already obtained for the high-energy neutron spectrum from the CERN concrete facility.     

Low-energy ion measurements by means of CR-39 nuclear track detectors

The paper presents an additional acceleration system, used to shift up an ion energy spectrum by 20 keV, and some examples of the ion parabolas registered by means of a Thomson-type spectrometer within the rod plasma injector (RPI-60) facility, designed for plasma physics and application studies. The use of the described acceleration system and CR-39 track detectors has enabled the registration of ions of energy above 20 keV to be performed. It made possible to measure the ion (e.g. deuteron) energy spectrum more exactly in the low-energy range, what is important for the determination of ion emission characteristics.