Total Track Density Research Articles

Rn progeny diffusion, deposition and track distribution in diffusion chamber with permeable membrane

Objective of this work is to define method by which sensitivities of CR-39 and LR-115 in diffusion chamber could be determined. Method is based on initial physical processes that occurs in diffusion chamber: diffusion, deposition and decay of radon (isotopes 222Rn and 220Rn) and their progeny. Cylindrical shape of chamber was considered due to availability of experimental data for validation of presented method. The shape was not limitation factor and can be extended to any geometry. Diffusion equations for radon in two mediums (membrane and chamber volume) and their progeny in volume were solved using Finite Difference Method – FEM, and solutions are their spatial distributions inside of diffusion chamber. Calculation of flux towards the chamber walls determine distribution pattern and deposited progeny fractions. It has been shown that volume and deposited distributions are not uniform. Visible tracks on CR-39 for defined etching conditions are determined by considering range of alpha particles in air and empirical critical angle function θC=θC(E). For LR-115 mean critical angle of 〈θc〉=500 and energy window from Emin=1.7MeV to Emax=4.2MeV was adopted from literature to determine number of visible tracks. The track density distributions on detector are found to be non-uniform and radially dependent.Thickness of permeable membrane has important influence on presence of thoron and its progeny tracks on detector. Sensitivities of CR-39 and LR-115 in diffusion chamber were determined using method presented in this work and compared with other theoretical models and experiment with good agreement. This shown applicability of the presented method.One of important conclusion is that detector sensitivity, given as one simple number, is not the best parameter for calibration due to the existence of radial variation of track density.For cylindrical chamber with 10cm length and 4cm radius, covered with membrane in form of one-layer filter paper 0.25mm thickness, and for equal concentrations of 222Rn and 220Rn in front of the chamber, contribution of 220Rn and its progeny to total track density is about 3%.

Dose Calibration and Track Diameter Distribution for 241Am-Be Neutron Source, Using CR-39 Nuclear Track Methodology

In neutron detection, the more common method is using electronic instrumentation associate with Bonner spheres, however, currently the Nuclear Tracks Methodology (NTM) is coming popular because of the simplicity, flexibility in size of the detector, no requirement for sophisticated instrumentation and installation, and low cost. In this work, a preliminary result of the dose calibration and track diameter distribution of Americium-Beryllium (241Am-Be) source using Nuclear Track Methodology is presented. As material detector, CR-39 polycarbonate, cut in 1.8 × 0.9 cm2 chips was chosen, and two step chemical etchings after neutron exposure was used to develop the tracks. The irradiations were made in environmental normal conditions, in the ORNL neutron calibration facilities. The CR-39 chips were placed in a phantom, with 3mm plastic (Lexan) sheet in between the source and detectorsto increase the proton generation. The total track density and track diameter distribution was performing in a Counting and Analysis Digital Image System (CADIS), developed at the Institute of Physics of the University of Mexico UNAM. The results are compared with a standard survey instrument and energy reference spectra of the International Atomic Energy Agency (IAEA).

Registration of proton induced spallation products of U, Pb and Au in mica track detectors

Detection of fission and spallation–evaporation residues resulting from interaction of relativistic protons with uranium, lead and gold targets in mica track detectors is investigated by the Monte Carlo method and using experimental data available in literature. It is shown that the contribution of spallation–evaporation residues to total track density is strongly dependent on target thickness and is the least for thick targets. This contribution in the case of thick target materials with Z≥79 is less than or is within the statistical uncertainty of a typical track density measurement. Although our results on registration and detection of the spallation residues in mica are based on the interactions of uranium and lead with protons at 1AGeV and gold with protons at 0.8AGeV, they are applicable to all targets with Z≥79 and for proton energies much higher than 1GeV.

Scenario changes in the climatology of winter midlatitude cyclone activity over eastern North America and the Northwest Atlantic

The present study explores how midlatitude winter cyclone activity can be modified under warming‐induced conditions due to enhanced greenhouse gas concentrations. We performed simulations with the Canadian Regional Climate Model (CRCM version 3.5) implemented on a domain that covers the Northwest Atlantic and eastern North America. These simulations are driven by control conditions (1975–1994) and high‐CO2 scenario conditions (2040–2059) suggested by the Canadian Climate Centre model, CGCM2 (Second Generation Coupled Global Climate Model), following the IPCC IS92a scenario. Comparisons between model simulations for the control period (1975–1994) and North America Regional analysis (NARR) suggest that both CGCM2 and CRCM reliably reproduce the overall NARR patterns of sea level pressure, tropospheric baroclinicity and Atlantic storm tracks. However, compared to CGCM2 results, CRCM offers an improvement in simulations of the most intense cyclones. Although both models underestimate the track density of intense cyclones, the CGCM2 underestimates are larger than those of CRCM. Under the high‐CO2 climate change scenario, the CRCM and CGCM2 model simulations show similar changes in sea level pressure, surface temperature, and total track density of midlatitude winter cyclones. Although we can see the northwest shift of the dominant Atlantic storm track, it is not statistically significant. Moreover, simulations from both models show a decrease in the total cyclone track density along the Canadian east coast; the decrease is more robust in CRCM simulations than in CGCM2 results. For intense cyclones, CRCM simulations show a slight decrease in the track density, while no such change is found in CGCM2 simulations.

Fission-track analysis of meteorites: Dating of the Marjalahti pallasite

The results of the Marjalahti pallasite fission-track age determination are presented. Thorough examination of fossil tracks in the phosphate (whitlockite) crystals coupled with U-content determination in whitlockites can make it possible to estimate the contributions of all possible track sources to the total track density and to calculate a model fission-track age. It is found that whitlockite crystals of the Marjalahti pallasite contain fossil tracks due to galactic cosmic rays (VH, VVH nuclei); fission of U and Th induced by cosmic rays; spontaneous fission of 238U; and spontaneous fission of extinct, short-lived 244Pu present in significant quantities in the early solar system. A great track density attributed to the extinct 244Pu testifies to the high fission-track age. The model fission-track ages of ( 4.31 ± 0.02 ) × 10 9 yr for the Marjalahti pallasite are calculated. Petrographic studies allow us to interpret the fission-track age as the time of the last shock/thermal event in the cosmic history of the pallasite.

Long-term measurements of radon progeny concentrations with solid-state nuclear track detectors

In this paper, we review existing methods for long-term measurements of radon decay products with solid-state nuclear track detectors. We then propose a method to determine the equilibrium factor using the bare LR 115 detector. The partial sensitivities p i of the LR 115 detector to Rn 222 and its α -emitting short-lived progeny, Po 218 and Po 214 , were investigated. We determined the distributions of lengths of major and minor axes of the perforated α -tracks in the LR 115 detector produced by Rn 222 , Po 218 and Po 214 through Monte Carlo simulations. The track parameters were first calculated using a track development model with a published V function, and by assuming a removed active layer of 6.54 μ m . The distributions determined for different α -emitters were found to be completely overlapping with one another. This implied equality of partial sensitivities for radon and its progeny. Equality of partial sensitivities makes convenient measurements of a proxy equilibrium factor F p possible which is defined in the present work as ( f 1 + f 3 ) and is equal to the ratio between the sum of concentrations of the two α -emitting radon progeny ( Po 218 + Po 214 ) to the concentration of radon gas ( Rn 222 ) . In particular, we have found F p = ( ρ / ρ i tC 0 ) - 1 , where ρ (track/m 2) is the total track density on the detector, ρ i = 0.288 × 10 - 2 m (for the V function mentioned above and for a removed active layer of 6.54 μ m ), t is the exposure time and C 0 (Bq/m 3) is the concentration of Rn 222 . If C 0 is known (e.g., from a separate measurement), we can obtain F p . The proxy equilibrium factor F p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor. Experimental irradiation of LR 115 detectors to known Rn 222 concentrations as well as known equilibrium factors were carried out to verify the present method. The relationship between ρ i and the removed layer was then derived for the V function specifically determined for the LR 115 detectors we were using for the experiments. The actual removed layers for individual detectors after etching were measured accurately using surface profilometry. A curve showing the relationship between the removed layer and the track diameter of normally incident 3 MeV α -particles is also provided for other researchers, who do not have access to surface profilometry, to use the present technique conveniently.

Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities ρ i of the LR 115 detector to 222Rn and its alpha-emitting short-lived progeny, 218Po and 214Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by 222Rn, 218Po and 214Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 μm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor F p , which is defined in the present work as ( F 1+ F 3) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny ( 218Po+ 214Po) to the concentration of radon gas ( 222Rn). In particular, we have found F p =( ρ/ ρ i tC 0)−1, where ρ (track/m 2) is the total track density on the detector, ρ i =0.288×10 −2 m, t is the exposure time and C 0 (Bq/m 3) is the concentration of 222Rn. If C 0 is known (e.g. from a separate measurement), we can obtain F p . The proxy equilibrium factor F p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.

Cosmic history of some pallasites based on fossil track studies

Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Examination of fossil charged-particle tracks in the phosphate and olivine crystals of 5 pallasites coupled with U content determination allowed the estimation of the contributions of all possible track sources to the total track density and calculation of a value of model fission-track age. Phosphate crystals from all studied pallasites were established to contain fossil tracks due to galactic cosmic rays (VH, VVH nuclei); induced fission of U and Th by cosmic rays; spontaneous fission of 238 U ; spontaneous fission of extinct short-lived 244 Pu nuclei presented in significant quantities in the early solar system. The discovery of a high track density attributed to the extinct 244 Pu pointed obviously to the high value of the fission-track age. Model fission-track ages of (4.37±0.02) Gyr for the Marjalahti pallasite; (4.37±0.01) Gyr for the Omolon pallasite; (4.19±0.02) Gyr for the Bragin pallasite; (4.18±0.03) Gyr for the Krasnoyarsk pallasite; (4.21±0.02) Gyr for the Brenham pallasite were calculated. The comparison of represented data with petrographic analyses allowed us to interpret a value of fission-track age as the time of the last intensive shock/thermal event in the cosmic history of a pallasite.

Let spectra measurements on LDEF: Variations with shielding and location

LET spectra measurements made with passive plastic nuclear track detectors (PNTDs) were found to depend on detector orientation, shielding and experiment location. LET spectra were measured at several locations on LDEF as part of the P0006 LETSME experiment (Benton and Parnell, 1984), the P0004 Seeds in Space experiment (Parks and Alston, 1984), the A0015 Free Flyer Biostacks and the M0004 Fiber Optics Data Link experiment (Taylor, 1984). Locations included the east, west and Earth sides of the LDEF satellite. The LET spectra measured with PNTDs deviated significantly from calculations, especially for high LET particles (LET ∞·H 2O ≥ 100 keV/ μm). At high LETs, short-range inelastic secondary particles produced by trapped proton interactions with the nuclei of the detector were found to be the principal contributor to LET spectra. At lower LETs, the spectra appeared to be due to short-range, inelastic and stopping primary protons, with primary GCR particles making a smaller contribution. The dependence of LET spectra on detector orientation and shielding was studied using the four orthogonal stacks in the P0006 experiment. Both measurements of total track density and LET spectra showed a greater number of particles arriving from the direction of space than from Earth. Measurements of LET spectra in CR-39 PNTD on the east (leading) and west (trailing) sides of LDEF showed a higher rate of production at the west side. This was caused by a larger flux of trapped protons on the west side as predicted by the east/west trapped proton anisotropy in the South Atlantic Anomaly (SAA). Track density measured in CR-39 PNTDs increased as a function of shielding depth in the detector stack. A similar measurement made in a thick stack of CR-39 interspersed with layers of Al and exposed to 154 MeV protons at a ground-based accelerator showed a similar result, indicating that a significant fraction of the particle events counted were from secondaries and that the total cross-section for production of proton-induced secondaries increased as the energy of primary protons attenuated. Little change was seen in either total differential or integral LET spectra as a function of shielding depth, indicating that the increase in cross section with decreasing proton energy affected mostly the shorter range secondary components. Similarity in the slopes of LET spectra from ground-based proton exposures and the A0015 LET spectra showed that modeling of a monoenergetic proton beam transported through a 1-D geometry was a useful first step in modeling the production of secondary particles by trapped protons in the SAA.

Improved Monte-Carlo calculation of the nucleon-meson cascade in shielding material

Abstract The nucleon-meson cascade in shielding material is calculated by a Monte-Carlo method. The principle of the method and the physical data used in the calculation are described. For primary proton beams in the GeV region we calculate the three dimensional densities of proton, neutron and pion stars inside the shielding materials as well as the total star density (sum of proton, pion and neutron star densities) and the total track density (sum of proton, pion and muon track densities). We calculate further the momentum spectra and the angular distributions of protons, pions and neutrons as function of the depth inside the shielding material. The results, which will be described in a second paper (p. 261 of this volume), are in good agreement with the available experimental data.