Fission Track Detectors Research Articles

EURADOS intercomparison for whole-body neutron dosemeters from 2012 to 2022

Within the EURADOS (European Radiation Dosimetry Group) self-sustained programme of regular intercomparisons (ICs) for individual monitoring, three campaigns had been performed in 2012, 2017 and 2022 to assess the performance of neutron personal dosemeters routinely used to measure personal dose equivalent, Hp(10). The irradiation schemes were established to provide participants with useful information regarding linearity, reproducibility and response of their dosimetry systems at different energies and angles of incidence. Small alterations were made in irradiation plans for subsequent exercises. Combinations of standard calibration fields and simulated workplace fields were employed, using bare and moderated neutron sources as well as monoenergetic and thermal neutron fields. Neutron energies used to evaluate dosemeter performance ranged from thermal to several MeV. Dose values varied between 0.3 mSv and 15 mSv. The number of participating laboratories in the three campaigns was stable: 31 in IC2012n, 32 in IC2017n and 29 in IC2022n. The dosimetry systems could have been categorized according to their detection principle into albedo and track dosemeters, or a combination of both. In 2012, a category ‘other’ had to be introduced to consider active personal dosemeters and fission track detectors. In 2012, participants were asked to provided results in a two-step procedure: (i) with no information on the radiation fields, and (ii) after receiving additional simplified a priori information on the energy distribution of the neutron fields to enable correction for dosemeter response. In 2017 and 2022, based on a one-step procedure, however, participants might have requested a priori information upon registration, which was reported in the certificate of participation. Intercomparison results were analysed against the acceptance criteria of the ISO 14146:2018 standard, although there were no standardized performance requirements for neutron personal dosemeters at the time of IC2012n. The paper compares the results of the three exercises, identifies major problems for individual monitoring services and shows trends in dosimetric performance. In all three intercomparisons, a few systems had shown problems related to calibration. Data do not allow to draw a universally applicable conclusion with regard to potentially superior performance of one particular dosimetry system.

Advances in fission-track detection and analysis for nuclear forensics and safeguards investigations

Advances in fission-track detection and analysis for nuclear forensics and safeguards investigations

Fission Track Detection Using Automated Microscopy

Detection of microscopic fission track (FT) star-shaped clusters, developed in a solid state nuclear track detector (SSNTD) by etching, created by fission fragments emitted from particles of fissile materials irradiated by neutrons, is a key technique in nuclear forensics and safeguards investigation. It involves scanning and imaging of a large area, typically 100–400 mm2, of a translucent SSNTD (e.g., polycarbonate sheet, mica, etc.) to identify the FT clusters, sparse as they may be, that must be distinguished from dirt and other artifacts present in the image. This task, if done manually, is time consuming, operator dependent, and prone to human errors. To solve this problem, an automated workflow has been developed for (a) scanning large area detectors, in order to acquire large images with adequate high resolution, and (b) processing the images with a scheme, implemented in ImageJ, to automatically detect the FT clusters. The scheme combines intensity-based segmentation approaches with a morphological algorithm capable of detecting and counting endpoints in putative FT clusters in order to reject non-FT artifacts. In this paper, the workflow is described, and very promising preliminary results are shown.

Identification of uranium-bearing particles in swipe samples with fission track method

In this study, an advanced method has been developed to identify uranium-bearing particles through fission track and make the particles and fission track detector form a whole. This method can result in the one-to-one correspondence between the fission track and uranium-bearing particles. It is unnecessary to separate the particles from the detector and relocate the particles when they are picked up under microscope. This simple identification is helpful in reducing the loss of particles, which would be picked up and transferred to mass spectrometer for analysis.

EURADOS IC2012N: EURADOS 2012 intercomparison for whole-body neutron dosimetry

The European Radiation Dosimetry Group (EURADOS) IC2012n intercomparison for neutron dosemeters intended to measure personal dose equivalent, Hp(10), was performed in 2012. A total of 31 participants (27 individual monitoring services from Europe, 2 from Japan, 1 from Israel and 1 from USA) registered with 34 dosimetry systems. Participation was restricted to passive or active neutron dosemeters routinely used in individual monitoring of radiation workers. The dosimetry systems were based on thermoluminescence, polyallyldiglycol carbonate, optically stimulated luminescence, fission track detection and silicon diodes (electronic devices). The irradiation tests were chosen to provide the participants with useful information on their dosimetry systems, i.e. linearity, reproducibility, responses for different energies and angles and to simulated workplace fields. The paper will report and discuss the first analysis of the results of the EURADOS IC2012n intercomparison.

Fission of 209Bi, natPb and 197Au in the particle field of a fast accelerator driven system

Accelerator driven systems (ADS) are expected to have particle spectra of significantly greater energy range than that of current power reactors. The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research, Dubna, Russia, is designed to emulate the neutron spectrum in a fast ADS through the use of a spallation target surrounded by a blanket of natural uranium. The spectrum is further modified by a reflective layer of polyethylene and an internal absorbing layer of cadmium. The spallation target of EpT was irradiated with a beam of 4GeV deuterons, and the fission rates of bismuth, lead and gold samples, placed in the target-blanket region were recorded using a fission track detector technique. The fission rates were also calculated using the MCNPX Monte Carlo code with the INCL4 cascade model and cross sections for nucleon induced fission obtained from literature. Agreement between the measured and calculated results indicates the model’s ability to predict the particle spectra and spatial distribution.

Spatial distribution of thorium fission rate in a fast spallation and fission neutron field: An experimental and Monte Carlo study

The Energy plus Transmutation (EpT) set-up of the Joint Institute for Nuclear Research (JINR), Dubna, Russia is composed of a lead spallation target surrounded by a blanket of natural uranium. The resultant neutron spectrum is a combination of spallation and fission spectra, modified by a reflective external layer of polyethylene and an internal absorbing layer of cadmium. The EpT set-up was irradiated with a beam of 4 GeV deuterons from the Nuclotron Accelerator at JINR. The spatial distribution of thorium fission rate within the assembly was determined experimentally, using a fission track detector technique, and compared with Monte Carlo predictions of the MCNPX code. Contributions of neutrons, protons, deuterons, photons and pions to total fission were taken into account. Close agreement between the experimental and calculated results was found.

Response studies of fission track detectors within moderators in CAVE A at GSI

Abstract At the Paul Scherrer Institut (PSI) fission track detectors are routinely used in moderators for determining the ambient dose equivalent in stray radiation fields due to neutrons. At the high-energy field CERF (CERN EU high-energy reference field) at CERN, the response of fission track detectors within two different moderators, where one moderator has an inlay of Pb to increase the response of the detector to high-energy neutrons, was surprisingly similar. To confirm this unexpected behaviour, a measurement campaign in another high-energy field, i.e. CAVE A at the Helmholtzzentrum fur Schwerionenforschung (GSI) was carried out. CAVE A at GSI is one of few facilities where a stray radiation field with neutrons above 20 MeV can be generated under controlled conditions. Reference doses were obtained by simulating the stray radiation field in the measurement positions. These simulations were carried out independently by GSI and PSI using two different Monte Carlo codes, i.e. Fluka and MCNPX, respectively. In this paper the measurements at GSI are described in detail. The results are then compared to previous measurement campaigns in the radiation field of CERF as well as 241 Am-Be and 252 Cf radionuclide sources, which all feature different neutron spectra. None of these campaigns confirm the improvement in sensitivity of the Pb enhanced moderator compared to the PSI standard moderator in combination with fission track detectors.

Selective Detection of Particles Containing Highly Enriched Uranium for Nuclear Safeguards Environmental Samples

A method to selectively detect uranium particles with high 235U enrichment has been developed; this method can contribute to improving particle analysis on nuclear safeguards environmental samples. The newly developed method involves three key components: (1) a two-step filtration system for particle recovery from swipe samples, (2) a system for controlling the etching time of fission track (FT) detector, and (3) a system for comparing the FT morphologies and particle sizes. The method to screen uranium particles according to their enrichment is focused on detecting highly enriched uranium particles preferentially in various particles recovered from swipe sample; this is one of the most important tasks involved in nuclear safeguards. In order to verify the effectiveness of the screening method developed, a mixture sample containing uranium particles with natural composition and those with 10% enrichment is used. It was shown that enrichment-based screening of uranium particles is possible by comparing the FT morphologies and particle sizes, in addition to controlling the etching time. The developed method uses the etching behaviors of the FT detector mainly; thus, it can be applied to real swipe samples easily.

Determination of uranium fission rate in an arbitrary neutron field using fission track detectors

In accelerator driven systems, particularly near the spallation target, the neutron spectrum covers a very wide range of energies and has a complex angular distribution. It is possible to determine the fission rate of fissionable nuclei in such neutron fields using fission track technique. We use the mean density of fission tracks in the two track detectors in contact with two faces of a fission foil (radiator). A calibration factor, w , relating the number of fission events to the track density is needed and was determined in a very well-known neutron field. It was used to estimate the fission rate in a uranium–lead assembly when the lead target was irradiated with protons of energy 1 GeV. Experimental results are compared with Monte Carlo predictions using MCNPX code.

Response study of fission track detectors using two different moderator designs in a high-energy radiation field

Fission track detectors in the center of moderating spheres are routinely used to measure the ambient dose equivalent due to neutrons in the environmental dosimetry at Paul Scherrer Institut (PSI). Originally, the system was designed to cope with neutrons from skyshine effects. Later, the system was also adapted behind the shielding of PSI's accelerators. Nowadays, as a consequence of continuously upgrading accelerator energies and intensities, the neutron energy behind thick shielding can range from fractions of eV to about 1 GeV (e.g. at CERN). For this reason a measurement campaign in a high-energy stray radiation field at CERN's High-Energy Reference Field Facility (CERF) was initiated to study and compare the response of the already existing detector-moderator configuration and a new design, the “GSI ball”. Employing an additional lead layer in a moderator sphere of 32.5 cm diameter, the GSI ball was primarily designed for the use with thermoluminescent based dosimeters in its center in order to optimize the response for the measurement of H * ( 10 ) to higher neutron energies. In this work, the measurement results for fission track detectors using two different radiator materials in the PSI and the GSI moderator are presented. Based on these studies, on the one hand, field calibration factors for the use in presumably similar high-energy fields around accelerators could be deduced. On the other hand, it could be shown that there is no need to replace the established PSI moderator by the GSI moderator since the combination of fission track detector and GSI moderator does not result in a significant sensitivity improvement.

Track etching characteristics of polyester track detector and its application to uranium estimation in seawater samples

Garware Polyester Film, an indigenously available material has been evaluated systematically as a nuclear track detector for the detection of fission fragments. The relative fission track detection efficiency of this film was found to be (86.0±4.0)%. The bulk etch rate, determined by the gravimetric method, was found to be 0.75±0.05 μm/h. The track etch rate was determined as 15.0±1.5 μm/h. This detector was employed for the estimation of uranium in seawater samples and the results obtained were compared with the results obtained by using the commonly used Lexan detector. Uranium fractions after chemical separation from seawater samples were also analyzed by alpha-spectrometry and neutron activation analysis techniques and the results were compared with that obtained by the fission track method. Fission track method has the advantage, as it does not require any chemical separation. The indigenously available polyester film (polyethylene terphthalate) appears to be a good substitute of Lexan as nuclear track detector.

Search for β-delayed fission ofAc228

Radium was radiochemically separated from natural thorium. Thin $^{228}\mathrm{Ra}$$\stackrel{{\ensuremath{\beta}}^{\ensuremath{-}}}{\ensuremath{\rightarrow}}$$^{228}\mathrm{Ac}$ sources were prepared and exposed to mica fission track detectors, and measured by an HPGe $\ensuremath{\gamma}$-ray detector. The $\ensuremath{\beta}$-delayed fission events of $^{228}\mathrm{Ac}$ were observed and its \ensuremath{\beta}-delayed fission probability was found to be ($5\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$.

Influence of uranium enrichment on the etching rate of polycarbonate fission track detector containing uranium particles

The etching rates of fission track detectors made of polycarbonate containing uranium particles were measured after thermal neutron irradiation with fluence of 8 × 10 14 n/cm 2, in order to study the influence of uranium enrichment on the etching rate that was calculated from the weight loss by etching. There is a strong correlation between the etching rate of detector and the enrichment E of uranium particle: the former increases as the latter increases. Particularly, the etching rate per particle was proportional to E 2/3 rather than E 1, which is probably due to the overlapping of fission tracks. The etching behaviors of detector revealed that the existence of two different etching rate regions, a nonlinear region in the beginning of etching process and a subsequent constant region, which was explained as the opening of fission tracks and the broadening of opened tracks, respectively. The enrichment dependence of bulk etch of a detector was qualitatively the same in two different etching rate regions.

Detection of fission tracks on resin plates formed from three kinds of DAP monomers

This work compares the response properties of ortho, meta and para diallyl phthalate (DAP) resin plates and their copolymer plates cast under the same curing conditions. The plates were irradiated with fission fragments and alpha-particles. After irradiation, the plates were etched with a potassium hydroxide, ethanol and water (PEW) solution or an aqueous solution of potassium hydroxide. Enlarged nuclear tracks were observed and counted using an optical microscope. All plates were found to have a detection efficiency of almost 100% for fission fragments, and yet were found to be insensitive to alpha-particles. From the experimental results of finish in curing, ease in cutting, etching speed and heat resistance, the ortho-based plates have been found to be superior to the meta- or para-based plates as a fission track detector.

Study on the etching conditions of polycarbonate detectors for particle analysis of safeguards environmental samples

The fission track technique was applied to the particle analysis for safeguards environmental samples to obtain information about the isotope ratio of nuclear materials in individual particles. To detect the particles containing nuclear material with high detection efficiency and less particle loss, the influence of uranium enrichments on etching conditions of a fission track detector made of polycarbonate was investigated. It was shown that the increase in uranium enrichment shortened the suitable etching time both for particle detection and for less particle loss. From the results obtained, it was suggested that the screening of the uranium particles according to the enrichment is possible by controlling the etching time of the detector.

Absolute measurements of the uranium concentration in thick samples using fission-track detectors

We propose an improved equation for calculating the uranium concentration in thick samples based on induced fission-track counts in an external detector that takes into consideration (1) the fission-fragment ranges in the sample and external detector, (2) the etchable track length and (3) the track counting efficiency in the external detector. The values of these parameters have been determined by calculation and experiment and are shown to have a significant effect on the calculated uranium concentrations. The new equation was tested by calculating the uranium concentrations in standard uranium glasses (CN-5; IRMM-540R) and apatite samples (Durango; horse tooth) in which the uranium content was also determined with independent methods (INAA; ENAA; TIMS). The results show that: (1) accurate measurements with the fission-track method are feasible within a broad range of uranium concentrations and (2) uranium determinations based on standards are only accurate if the standard and sample are made of the same material. Because the absolute fission-tack dating method is also based on accurate thermal neutron fluence measurements and similar correction factors for the track registration and counting efficiencies, this study provides a strong endorsement for the fact that absolute fission-track ages are accurate.

Detectors/Dosemeters of galactic and solar cosmic rays.

Different passive multidetector stacks have been developed at the Italian National Agency for Environmental Protection (ANPA-stack), which makes it possible to measure directly ionising radiations, low-energy and high-energy neutrons, and high-energy charged (HZE) particles. The stack consists of several types of passive devices, namely recoil-track and fission-track detectors, bubble detectors, thermoluminescence dosemeters and an electronic personal dosemeter. Most of these detectors have been used on earth for the assessment of the occupational exposure, or in outer space for cosmic ray physics and/or for the assessment of the dose received by astronauts. A great deal of efforts and new developments have been required to make these detectors useful for in-flight measurements. As outcome of these extensive efforts, different new detectors have been developed, which exploit some of the most successful principles of radiation detection, such as the use of avalanche processes to facilitate the registration of nuclear tracks and the use of coincidence-counting to increase the signal-to-noise ratio. On the basis of these new detectors, different systems (generally referred to as ANPA-stack) have been obtained, which have been successfully applied for a variety of different measurements of cosmic ray radiation fields and doses.

Determination for β -delayed fission probability of230Ac

The230Ra has been produced via232Th-2p reaction induced by 60 MeV/u18O ion irradiation of natural thorium. The radium was radiochemically separated from the mixture of thorium and reaction products. Thin Ra sources in which230Ac was got through\(^{230} Ra\xrightarrow{{\beta ^ - }}^{230} \)Ac were prepared for observing fission fragments from β-delayed fission of230Ac. The sources were exposed to the mica fission track detectors and measured by the HPGe γ detector. The precursor230Ac was identified by means of observed two fission events as well as γ spectra, and the β-delayed fission probability of230Ac was obtained to be (1.19 ± 0.85) × 10-8.

Polymerizing condition of DAP resin as fission track detector

Three kinds of diallyl phthalate resin plates were cast under different polymerizing conditions. The plates were irradiated with fission fragments, α-particles, fast and thermal neutrons. After irradiation, the plates were etched with an aqueous solution or a PEW solution. After etching, enlarged nuclear tracks on the plates were observed and counted using an optical microscope. All plates were found to have high detection efficiency for fission fragments, but to be insensitive to α-particles, fast and thermal neutrons. The etching speed of fission tracks on under-cured plates was faster than that on full- and over-cured plates whichever etching solution was used. In the case of adopting the aqueous solution, surface roughness occurs remarkably on the full- and over-cured plates in comparison with the under-cured plates. From these experimental results the conclusion was drawn that the under-cured plate was superior to the full- and over-cured plates as fission track detector.