Track Size Distribution Research Articles

PADC-NTM Applied in 7Li+Pb at 31 MeV Reaction Products Study

Passive nuclear track methodology (NTM) is applied to study charged particles products of the reaction 7Li+Pb at ~ 31 MeV. It is a contribution to the 8pLP Project (LNL-INFN-Italy) in where we show an alternative approach to register charged particle from reaction fragments by PADC detection. The main advantage is that the passive system integrates data over the whole experiment and has its importance for low rate reaction processes. Reaction products as well as scattered beam particles are determined from track shape analysis. Some limitations are inherent to NTM since a priori knowledge is required to correlate track size distribution given by each type of particle emerging from the target. Results show that the passive technique gives useful information when applied in reaction data interpretation for a relatively large range of particle types.

Sensitization effects on the tracks of neutron irradiated CR-39 detectors treated with CO2 under pressures greater than 0.6 MPa

An extensive investigation was done of the sensitization effects of carbon dioxide pre-etching treatments on the tracks of CR-39 detectors exposed to fast neutrons. The detectors were irradiated with an 241AmBe neutron source in a low-scatter laboratory, delivering a personal dose equivalent Hp(10) of 1 mSv. Prior to the chemical etching, the detectors were treated in carbon dioxide at partial pressures ranging from 0.6 to 2.4 MPa for times ranging from 6 to 144 h. By examining treatments under pressures greater than 0.6 MPa, our goal was understanding the correlation between detector response and treatment time and optimizing the conditions for practical applications of CR-39 detectors in neutron dosimetry and spectrometry. From the analysis of the track size distribution for each treatment condition, we found a consistent trend regarding the increasing number of detected tracks. Moreover, by correlating the integral of these track distribution curves with the treatment time, we found a linear increase in detector sensitivity for all the investigated pressures, the first time such behavior is reported. This could help a dosimetry laboratory optimizing and adjusting the treatment time, while also improving the detector sensitivity.

A new sensitization technique combining CO2 and UV treatments for improved neutron dosimetry of CR-39 track detectors

A new sensitization technique combining carbon dioxide and UV treatments was investigated for improved neutron dosimetry of CR-39 track detectors. The detectors were irradiated with an 241Am–Be neutron source in a low-scatter laboratory facility, delivering a personal dose equivalent Hp(10) of 1 mSv. Prior to their chemical etching, the detectors were treated in carbon dioxide at a pressure of 0.6 MPa for 6 days followed by a UV (254 nm) treatment at a distance of 5 cm from the lamp, for 20 h. The opposite, UV followed by carbon dioxide treatment, was also investigated. The qualitative impact of these treatments on the background noise of the detectors, and their track size distributions compared to only carbon dioxide, only UV treated detectors, and untreated ones was analysed. Overall, the technique combining CO2 and UV treatments, independently of their order, increased the sensitivity by about 40% and 120% compared to the UV treatment alone and the untreated detectors, respectively, and reduced approximately 15% compared to the CO2 treatment alone. It also significantly enhanced the average diameter of the tracks compared to both treatments separated, allowing a better distinction between real tracks and the noisy background.

Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago

Abstract. Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the “NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments” (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5∘ N, 62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 µgm-2day-1, north of 50∘ N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model–observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %–50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90 % of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semi-volatile species: the model–observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climate-relevant simulated summertime pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and cloud-albedo indirect (−0.4 W m−2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA.

Track size distributions in CR-39 neutron dosimeters treated with carbon dioxide

A parametric study was performed examining the effect on CR-39 neutron dosimeters of pre-etching treatments with carbon dioxide at different pressures and durations. The detectors were irradiated with an 241Am-Be neutron source in our low-scatter laboratory, delivering a personal dose equivalent Hp(10) of 1 mSv. Prior to their chemical etching, the detectors were treated for times ranging from 1 to 5 days in carbon dioxide at pressures ranging from 0.1 to 0.5 MPa. In agreement with previous studies, track densities were found to increase following treatments of increasing duration and pressures. Our particular interest was examining the differential track size distributions produced by the treatments. In particular, we analyzed the track size distributions for untreated detectors versus detectors treated with a CO2 partial pressure of 0.5 MPa for 1, 3 and 5 days. Overall, the track size distribution appears to shift to higher diameters with increasing treatment time, while the overall pattern appears largely preserved. This “signature” may be associated with the energy distribution of the neutrons. In turn, this may allow establishing “adaptive” track-to-dose conversion coefficients accounting for the energy dependence of the CR-39 dose equivalent response.

The densities and dimensions of recoil-track etch pits in mica

Measurements of alpha-recoil-track densities in mica as a basis for geological dating depend on an etch model relating the number of tracks per unit volume (NRT) to the counted number of etched tracks per unit area (ρRT). The model of Gögen and Wagner (2000) implies that ρRT increases linearly with etch time (tE), so that NRT can be calculated from the slopes or intercepts of step-etch functions ρRT(tE). This model rests on the assumption that the etch rate of the mica surface (vV) and the horizontal etch pit growth rate (vH) are both constant, in contradiction with experimental results and computer simulations of mineral dissolution. We present results of four different experiments aimed at relating etch pit densities to volumetric track densities. Step-etch data are vulnerable to observation-related artefacts at increasing tE and lack the resolution to confirm or refute the supposed linear increase of ρRT with tE. The intercepts of regression lines fitted to step-etch data are imprecise and perhaps inaccurate. Intercept estimates based on mirror-image counts and (etch)–anneal–etch experiments indicate that vV increases during the initial etching stages. The (etch)–anneal–etch results show that no pre-etch is in fact required, implying that surface tracks are more resistant to annealing than tracks in the bulk of the mineral. Track-size measurements confirm that vH is also not constant but decreases with increasing etch-pit size. The results show that no recoil-track etch pit in phlogopite etched in 40% HF grows larger than ca. 7μm and that the track-size distribution becomes quasi-invariant at >6min etching. This signifies that there exist accessible etching conditions at which the etch-pit size distribution becomes a fixed, distorted reflection of the size distribution of latent recoil tracks. It is not improbable that track addition and loss also cancel each other out in this equilibrium state, in which case both the etch-pit size distributions and densities ρRT become independent of etch time.

Comparison of different PADC materials for neutron dosimetry

Investigations on track density and track size distributions of different PADC (poly allyl diglycol carbonate) materials have been performed. The PADC used for the tests has been produced by Thermo Electron (USA), Track Analysis System Limited (UK), Chiyoda Technol Corporation (Japan) and Intercast srl (Italy). For each PADC material 120 detectors were randomly selected out of 2 sheets: 60 detectors from one sheet have been irradiated with a personal dose equivalent of 3 mSv in the field of a (241)Am-Be source at the calibration laboratory of PSI, whilst the other 60 detectors from the other sheet have been used as background samples. All detectors have been processed according to an identical etching procedure and have been analysed with TASLImage scanning system. For each set of detectors the value of the average background signal, the average neutron sensitivity and the detection limit with respect to a personal dose equivalent measured with a dosemeter based on PADC have been determined. The results of the investigations allowed a comparison of the neutron sensitivity and background signal behaviours of PADC materials from different manufacturers and the assessment of the variation of neutron sensitivity and background signal over a single sheet.

Design of an alpha spectrometry system for separated measurement of radon/thoron daughters’ concentration by lexan PC SSNTD

A special system has been designed to measure separately the concentration of radon and thoron alpha emitter's daughters in air. The system components consist of collimators, energy degraders, a filter and a lexan PC (polycarbonate) film, which are integrated and connected to a small portable pump. In this spectrometry method, alpha peaks are resulted from registered track size distribution in a wide energy range of 0.9–5.2 MeV under new electrochemical etching (ECE) conditions. Geometric characteristics of the system components are determined based on the optimization between desirable FWHM and detection efficiency by means of the Monte Carlo simulation method using the Fluka code. The results show that 218Po and 214Po from radon chain and 216Po (which is the representative of thoron concentration), 212Bi and 212Po from thoron chain can be measured separately in a mixed field with the FWHM of less than 0.2 MeV. The sensitivity was calculated to be 8.5 and 0.018 (Track cm −2 kBq −1 m 3 h −1) for radon and thoron, respectively. The radon level can be measured via 218Po concentration using a special measurement setting so that a short-term measurement of equilibrium factor can be performed by this spectrometry method.

Passive α-particles spectrometry by polycarbonate SSNTD using new etching conditions

By adding ethylenediamine to the common etchant composition (potassium hydroxide, water, methanol and/or ethanol) in electrochemical etching of lexan polycarbonate detectors, a passive α-particle spectrometry is resulted in the energy range of 0.8–5.2 MeV. This spectrometry is based on the track size distributions, which have a tailed normal shape and FWHM of less than 0.5 MeV. Also the energies of α-particles emitted by a 226Ra micro-precipitated source and its α-emitter daughters, which were detected by this method, were in accord with that of a surface barrier detector. Consequently, this method can be developed for alpha spectrometry such as radon/thoron and their α emitter daughters’ detection, separation and measurements.

Neutron spectrometry using CR-39 track etch detectors

Track-size distributions were measured for chemically etched CR-39 foils exposed to monoenergetic neutrons with energies ranging from 0.144 to 19 MeV and to various broad-spectrum neutron sources including spontaneous fission neutrons from (238)Pu. These tracks are due to energetic charged particles resulting from interactions of the neutrons with the CR-39. The tracks are visible with an optical microscope after chemical etching and vary in size and configuration depending on the particle, energy and angle of incidence. The foils were analysed using an automatic analysis system that scans the foils, identifies valid tracks and records the track-size parameters. The track-size distributions vary with neutron energy for the monoenergetic sources and with the hardness of the broad-spectrum sources. The distribution from the (238)Pu fission source is readily distinguishable from the other sources measured and from distributions owing to the background.

A Monte-Carlo calculation of the size distribution of latent alpha-recoil tracks in phlogopite: Implications for the recoil-track dating method

We used a Monte-Carlo method to calculate the size distribution of alpha-recoil tracks in phlogopite. The calculations span the age range 0–1 Ma and the range of Th/U-ratios encountered in phlogopites of different origin. The track-size distribution is bimodal, with a narrow maximum centred on ∼ 30 nm and a broader maximum centred on ∼ 110 nm . The bimodal distribution is a consequence of the long half-lives of the daughters of 238U and, to a lesser extent, 234U, and the fraction of small-sized tracks, therefore, decreases with increasing age and Th/U-ratio. The fact that the recoil-track population cannot be characterised by a single average size complicates the relationship between the number of tracks intersecting a unit area of mineral surface, ρ ART , and the number of recoil tracks per unit volume of the mineral, N ART . On the other hand, the present results offer the prospect of an alternative recoil-track dating method, based on the ratio r of small-sized tracks to that of larger-sized tracks. It is shown that, if r can be measured and the Th/U-ratio of the sample is known, then its recoil-track age can be calculated. There exists a less than straightforward relationship between the size distribution of latent and the maximum-diameter distribution of etched recoil tracks, so that r can, in principle, be calculated after deconvolution of the etched-track diameter distribution. The Monte-Carlo calculation can be extended to minerals doped with known amounts of other radioactive isotopes.

Nitrogen distribution measurements by neutron induced autoradiography

A method utilizing plastic track detectors was developed to determine the nitrogen distribution and concentration in the presence of boron in metals. Experiments were performed at the UVAR (cadmium ratio ≈25) and the NIST Reactor (cadmium ratio ≈3000). The minimum detectable concentration of nitrogen at a given concentration of boron has been estimated using the detector’s response to10B(n,α)7 Li reaction products in terms of track size distribution. The capability of the technique to detect nitrogen in the presence of boron has been demonstrated using 316L stainless steel with a nitrogen concentration of ≈560 ppm and a boron concentration of ≈0.86 ppm.

Etched Track Size Distributions Induced by Broad Neutron Spectra in PADC

Detectors based on the PADC plastic, made by Pershore and TASL, were irradiated with protons, alpha particles, and monoenergetic neutrons from an accelerator, and with broad-spectra neutrons from Am-Be and 252 Cf neutron sources. Latent tracks were etched in a two-step electrochemical procedure and measured using an image analysis system. Track size distributions were determined showing systematic changes with the quality of charged particle spectra.

Characteristics of the CRS fast neutron personal dosemeter

A fast neutron personal dosemeter based on the two-step electrochemcially etched CR-39 detectors has been developed by the “Centre de Radioprotection et de Sûreté” (CRS), in as simple a form as possible to be used in routine monitoring of neutron irradiated workers in Algeria. This paper presents the dosimetric characteristics of the developed dosemeter such as energy and angle dependence, dose equivalent response and low limit of detection which are much improved compared to our previous work. The obtained energy response is both flatter (±25%) and extended to lower energy (≈25 keV). Also, a lower detection limit of about 90 μSv has been achieved. In addition, the evaluation of the energy response in term of track size distributions has been performed.

Time-development of proton-induced track-size distributions in PADC

This paper presents results obtained from an organic polymer polyallyl diglycol carbonate (PADC) irradiated with protons of different energies. Samples, made of PADC foils 600 μm thick, were irradiated at normal incidence with monoenergetic protons from a linear accelerator. Latent tracks induced by protons in the surface layer of the samples were etched using a chemical (CE) and an electrochemical (ECE) etching, respectively. The etching time was varied. Diameters of CE and ECE tracks were measured under specific magnifying and viewing conditions, and frequency distributions were determined by means of an image analysis system.

Evaluation of the CR-39 response on the basis of track-size distributions

Track size distributions obtained in the CR-39 detectors exposed to the natural background, to alpha radiation from radon and its progeny, irradiated with neutrons from the Am-Be source and with monoenergetic neutrons at energies of 1.2, 5.3, and 15.1 MeV were investigated. The two-step etching regime was applied consisting of a low and high frequency electrochemical etching. Track size distributions were measured by the aid of a fully-automated image analysis system. The results show systematic differences between background and neutron-induced distributions giving thus additional information on the integral quantities.

The effect of processing conditions on the track-size distributions in CR-39 detectors

The effects of selected parameters of a two-stage electrochemical etch upon frequency distributions of track diameters in Cr-39 plastic detectors irradiated with AmBe neutrons were studied. Changes in the mean track diameter with a varying etching temperature, the first stage and the second stage duration are presented.

Hydrodynamic studies of an advanced fluidized-bed bioreactor for direct interaction with coal

Fine coal particles fluidized by the upflow of a liquid medium containing a dissolved biocatalyst undergo size reduction as the reaction progresses. Three aspects of the design of such a reactor were examined: 1. (1)the use of force balances to describe pressure drop for the segregated bed; 2. (2) measurement of liquid-phase dispersion coefficients; and 3. (3) fluorescent tagging of particles to track size distribution. Hydrodynamic data were obtained for a liquid-solid fluidized bed of coal particles in the size range 30–150 μm. Illinois No. 6 coal was ball-milled, sieved into four fractions, and suspended in a 0.1% aqueous solution of Tween 80. A sample with a bimodal particle size distribution centred on 49 and 63 μm was placed in a glass column and fluidization and pressure-drop data were compared with a new model developed to describe particle segregation. Measured liquid-phase dispersion coefficients varied from 0.034 to 0.283 cm 2 s −1 as the flow varied from 0.005 to 0.0159 cm s −1. A technique was also developed for coating coal particles with a fluorescent paint which may allow direct measurement of the change in the fraction of marked particles of known size along the axis of a fluidized bed.

New Etching Conditions for CR-39 for Neutron Dosimetry

The results of investigations on track density and track size distributions of the PADC/CR-39 track detectors under different etching conditions are presented. The etching conditions are the combinations of chemical etching (CE) and electrochemical etching (ECE) at low and high frequency with different electric field strengths and etching times. The results show that under the conditions reported. The 2 step regime (CE + HF ECE) produces larger tracks (~2 to 31/2 times) than the 3 step (CE + LF ECE + HF ECE). While the track densities are almost the same. These etching conditions were applied to the CR-39 track detectors irradiated with the monoenergetic neutrons in the framework of the EURADOS-CENDOS joint neutron irradiation. The track densities and the size distributions for different neutron energies are reported. The results fit well with the previously evaluated response curve and are compared with similar measurements.

Track-size distribution of electrochemically etched CR-39

The track densities and track size distributions of polyallyl diglycol carbonate (PADC) track detector for various neutron energies under different etching conditions are presented. The etching regimes are the combination of chemical etching (CE) and electrochemical etching (ECE) at low and high frequencies (LF, HF) with different electric field strengths and etching times. The results show that the two-step regime (CE+HFECE) produces larger tracks (about 2 to 3 1 2 times, depending on neutron energy) than the three-step (CE+LFECE+HFECE), while the track densities are almost the same.