Characteristic response of plastic track detectors to 40-80 MeV neutrons

This paper investigates the characteristic response of plastic track detectors to high-energy neutrons. Three types of plastic nuclear track detector (PNTD), Baryotrak made of pure CR-39, TD-1 made of CR-39 containing an antioxidant and TNF-1 made of a copolymer of CR-39/N-isopropylacrylamide, were exposed in quasi-monoenergetic neutron fields generated by p-Li reactions. The total efficiencies for TD-1 and TNF-1 were more than double and triple that of Baryotrak respectively. In addition, the species of particles were classitied into three groups, i.e. proton relatives, alpha particles and heavy ions, by analysing the etch-pit growth curve obtained by step-by-step etching. In a 65 MeV neutron field about half of the tracks recorded in pure CR-39 were due to heavy ions, whereas the TNF-1 detector could effectively register the protons, accounting for 70% of the tracks. The results could be explained by the difference in the sensitivity to high-energy protons.     

Semi-automated,three-dimensional measurement of etched tracks in solid-state nuclear track detectors

We describe a new method for measuring the shapes and sizes of etched tracks in plastic or glass detectors, using a commercial digital image processing system. The method exploits the fact that in transmitted light any portion of the microscopic image of the track is in best focus when it is darkest. A minimization algorithm is used to produce a two-dimensional projected image of the three-dimensional etched track. The locus of points of maximum gradients in the image leads to a closed contour of the projected image. From this gradient image the profile, length and width of the conical etched track are automatically determined. The method is also applicable (a) to a track that penetrates a detector and has been etched until the cones from opposite surfaces are connected and (b) to a track with a curved profile due to a strongly slowing particle. The method is illustrated with measurements of tracks of 1 A GeV uranium ions in Tuffak polycarbonate and in CR-73 polycarbonate and of cosmic ray tracks in a CR-39 detector.     

Novel Al2O3:C,Mg fluorescent nuclear track detectors for passive neutron dosimetry

The latest advances in the development of a fluorescent nuclear track detector (FNTD) for neutron and heavy charged particle dosimetry are described and compared with CR-39 plastic nuclear etched track detectors (PNTDs). The technique combines a new luminescent aluminium oxide single crystal detector (Al(2)O(3):C,Mg) with an imaging technique based on laser scanning and confocal fluorescence detection. Detection efficiency was obtained after irradiations with monoenergetic neutron and proton beams. Dose dependences were measured for different configurations of the detectors exposed in fast- and thermal-neutron fields. A specially developed image processing technique allows for fast fluorescent track identification and counting. The readout method is non-destructive, and detectors can be reused after thermal annealing.     

Solid-state track detectors in laser plasma investigations

The possibility of application of the solid-state track detectors, developed earlier for experimental nuclear physics, in laser plasmas investigations is considered. A review of the main physical and metrological properties of the solid-state track detectors is given. Special attention to the detector on the basis of the CR- 39 polymer plastic is made. The experimental layouts of the CR-39 applications for investigation of both the properties of the fast heavy particles generated in the femtosecond laser plasma and the properties of the various materials by irradiation by the flows of the fast particles emitted by the laser plasmas are investigated.     

Novel shielding materials for space and air travel

The reduction of dose onboard spacecraft and aircraft by appropriate shielding measures plays an essential role in the future development of space exploration and air travel. The design of novel shielding strategies and materials may involve hydrogenous composites, as it is well known that liquid hydrogen is most effective in attenuating charged particle radiation. As precursor for a later flight experiment, the shielding properties of newly developed hydrogen-rich polymers and rare earth-doped high-density rubber were tested in various ground-based neutron and heavy ion fields and compared with aluminium and polyethylene as reference materials. Absorbed dose, average linear energy transfer and gamma-equivalent neutron absorbed dose were determined by means of LiF:Mg,Ti thermoluminescence dosemeters and CR-39 plastic nuclear track detectors. First results for samples of equal aerial density indicate that selected hydrogen-rich plastics and rare-earth-doped rubber may be more effective in attenuating cosmic rays by up to 10% compared with conventional aluminium shielding. The appropriate adaptation of shielding thicknesses may thus allow reducing the biologically relevant dose. Owing to the lower density of the plastic composites, mass savings shall result in a significant reduction of launch costs. The experiment was flown as part of the European Space Agency's Biopan-5 mission in May 2005.     

Gamma-ray response function of some polymeric nuclear track detectors

The effect of gamma dose on the bulk-etch rate measurements for some gamma-irradiated polymeric nuclear track detectors was extensively studied. Various plastic samples of CR-39 allyl diglycol carbonate, Makrofol-E and Lexan polycarbonates were used and exposed to gamma doses up to 30.0 Mrad. The bulk-etch rate ratioV _BD/V _BO, i.e. the bulk-etch rate of irradiated samples to the unirradiated ones, was measured at the most recommended optimum etching conditions. Fading behaviour of irradiated CR-39 samples was also studied at room temperature and for a duration of up to 8 days. It was found that the etch-rate ratio for the CR-39 specimens was dose-dependent. In contrast, the polycarbonate samples showed an extremely weak response to gamma irradiation. The results of the present work reflected great evidence of the gamma dosimetric potential of CR-39 plastic detectors, which can indeed be recommended as gamma-dosimeters within the studied dose range.     

A simple non-layered finite element for the elasto-plastic analysis of shear flexible plates

A simple and accurate non-layered plastic element which is capable of capturing the development of plastic curvatures across the thickness of the plates is presented in this paper. The influence of transverse shear forces on the plastic behaviour of plates is also investigated here. This non-layered plastic element is based on: (i) the four-node quadrilateral strain element for shear flexible elastic plates given by the authors; (ii) the plastic hinge formulation outlined by Shi and Atluri; and (iii) the modified Ilyushin's yield function which can account for both the development of plastic deformations across the thickness of plates and the effect of transverse shear forces. The numerical examples given here demonstrate that the present non-layered plastic element can achieve the results obtained by the layered element model and the transverse shear forces considerably affect the plastic behaviour of plates under certain load conditions.     

Investigations of doses on board commercial passenger aircraft using CR-39 and thermoluminescent detectors

Measurements of cosmic radiation dose rates (from the neutron and the non-neutron components) on board passenger aircraft were performed using environmental packages with thermoluminescent TL and CR-39 etched track detectors. The packages were calibrated at the CERN-EU high-energy Reference Field Facility and evaluated at the Institute of Nuclear Physics in Krakow (TL + CR-39) and at the German Aerospace Centre in Cologne (CR-39). Detector packages were exposed on board passenger aircraft operated by LOT Polish Airlines, flown between February and May 2001. The values of effective dose rate determined, averaged over the measuring period, ranged between 2.9 and 4.4 microSv h(-1). The results of environmental measurements agreed to within 10% with values calculated from the CARI-6 code.     

CR-39 acceptance test and optimisation for fast neutron dosimetry applications

The ENEA fast neutron dosemeter is based on a planar PADC (poly allyl diglycol carbonate) placed in a polyethylene holder. The CR-39 (registered trademark of PPG Industries Inc.) material, produced by Intercast Europe S.p.A., has been used in the routine of the Individual Monitoring Service (IMS) since 1998. Since then, acceptance tests on average sheet background track density and sheet neutron sensitivity have been made on new batches as a quality control within a quality assurance programme of the IMS of ENEA-Institute for Radiation Protection (IRP). Dosemeters were irradiated with a 241Am-Be source at ENEA-IRP and processed through a chemical etching procedure (pre-etching with 40% KOH water solution 6.25 N and 60% ethyl alcohol at 70 degrees C followed by 12 h of etching in 6.25 N KOH water solution). In this paper we present the analysis of acceptance testing data for more than 30 sheets of CR-39 plastic produced in 1998, 1999 and 2000. Moreover, we compare the performance of sheets of CR-39 of standard composition with that of sheets of CR-39 with the addition of DOP (dioctylphthalate), in different concentrations, on the hasis of average background density, neutron sensitivity and background fluctuation that limit the lower detectable dose. This study demonstrates the need for acceptance tests to assure the quality of the dosimetric performance of these dosemeters, which is considerably dependent on the quality of the CR-39 plastic.     

Radiation measured for ISS-Expedition 12 with different dosimeters

Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities.     

Identification of low energy ions (6 ≤ Z ≤ 10) in a plastic track detector CR-39

A method is developed for identifying low energy ions (6 ≤ Z ≤ 10) in a plastic track detector CR-39. After initial etching, rinsing in water and alcohol and final chemical etching of the detector, all in an ultrasound field, the etch rate ratio ($\text{V}{}_{\mathrm{<mtext>T</mtext>}}\text{V}{}_{\mathrm{<mtext>B</mtext>}}$) is directly measured at a defined distance from the end of the track. This method can be used to determine the etch rate ratio at several points along the track. The plastic track detector CR-39 is calibrated using ¹²C, ¹⁶O, ¹⁹F and ²²Ne ion energy in the interval from 2–7 MeV/amu.     

Contribution of cosmic ray heavy ions to the radiation hazard in manned space flights

Primary cosmic radiation arriving near the Earth may be classified into two general categories: the gamma component and the hadronic component. The hadronic component contains mainly protons, a small amount of alpha particles and a smaller amount of heavier charged nuclei (ions). Although the fluxes of these heavier ions are very small in comparison to those of protons, they are able to originate a huge linear energy transfer (LET). This work studies the contribution of heavy ions from cosmic rays to the radiation hazard to which the crew of a manned long duration space flight might be exposed. The geometry of the energy deposition by a heavy ion is studied, and it is found that energies of the order of up to 10(23) J kg-1 are deposited.     

金属裂纹板复合材料胶接修补强度的弹塑性有限元预测

金属裂纹板经复合材料补片胶接修补后,其结构强度明显提高,但裂纹板中的裂纹会导致严重的应力集中现象,并易产生塑性变形,呈现强烈的材料物理非线性特性,需要采用弹塑性力学原理,进行复合材料胶接修复结构的静强度预测。为此,考虑金属板材料的非线性特性,建立了金属裂纹板复合材料胶接修补结构的弹塑性有限元模型,并通过试验验证了模型的有效性。在此基础上,提出了基于裂纹尖端的张开位移(COD)判据的拉伸强度预测方法,分析了修复结构的塑性应变、COD以及静拉伸强度。结果表明:相对于应力强度因子K判据, COD判据能更有效地预测修复试件的静拉伸强度。      

Comparison of imaging plates with track detectors for fast-neutron dosimetry

Imaging plate (IP) radiation detectors are widely used in industrial radiography, medical imagery and autoradiography. When an IP is exposed to ionising radiation, some of the energy is absorbed to form a latent image. The energy stored, which is proportional to the dose received, can be liberated by a selective optical stimulation and collected to reconstitute the distribution of the ionising radiation on the IP. In this work, IPs for use in fast-neutron measurements are characterised. The response of our IP dosemeters in conjunction with their reading system was found to be linear in dose between 75 microSv and 10 mSv. This performance is compared with those of dosemeters based on the plastic track detectors PN3 and CR-39.     

Analysis of tracks in the stacked film track detector

A method to analyze the experimental data of a plastic track detector is presented. The charge distribution obtained for the cosmic ray heavy charged particles is shown, and it is used to criticize theories which have been proposed until now to explain the rate of chemical etching along ion tracks. The primary ionization J and the restricted energy loss REL are evaluated and compared at the same etching velocity for various charges.REL fits the etching rate well only for light elements Z < 15, and J is suitable either for Z < 15 or Z > 15, while overall fitting is not possible for either theory. The fine structures of the curves, REL, J, and $\text{(}\text{Z}{}^1\text{β}\text{)}{}^2$ vs Z, serve as a measure to estimate the real mean atomic mass of each element in cosmic rays.     

PAMELA sub-detectors capability in identifying nuclei: Status of art and perspectives

After almost three years in orbit, the statistic collected by PAMELA detector for what concern nuclei events from cosmic rays is sufficiently relevant to allow a systematic study of such a component. For this scope charge reconstruction from Time-of-Flight system, calorimeter and magnetic spectrometer is used, with different combinations, in order to cover the widest range of inspection in energy and atomic number permitted by the characteristics of the detector. Some results for performances, goals and limits from the different sub-detectors will be presented.     

Sizing alpha emitting particles of aged plutonium on personal air sampler filters using CR-39 autoradiography

Methods have been developed to assess the size distribution of alpha emitting particles of reactor fuel of known composition captured on air sampler filters. The sizes of uranium oxide and plutonium oxide particles were determined using a system based on CR-39 solid-state nuclear track detectors. The CR-39 plastic was exposed to the deposited particles across a 400 microm airgap. The exposed CR-39 was chemically etched to reveal clusters of tracks radially dispersed from central points. The number and location of the tracks were determined using an optical microscope with an XY motorised table and image analysis software. The sample mounting arrangement allowed individual particles to be simultaneously viewed with their respective track cluster. The predicted diameters correlated with the actual particle diameters, as measured using the optical microscope. The efficacy of the technique was demonstrated with particles of natural uranium oxide (natUO2) of known size, ranging from 4 to 150 microm in diameter. Two personal air sampler (PAS) filters contaminated with actinide particles were placed against CR-39 and estimated to have size distributions of 0.8 and 1.0 microm activity median aerodynamic diameter (AMAD).     

Dosimetric results from the Mir orbital station

The Mir Orbital Station provided a unique platform on which to carry out a variety of space radiation dosimetry measurements. A number of experiments were conducted using a combination of passive detectors on the interior of the Mir during 1996-97. Thermoluminescent detectors were used to measure absorbed dose. CR-39 plastic nuclear track detectors were used to measure the LET spectra > or =5 keV.microm(-1). Results from TLDs and CR-39 PNTDs were combined to determine total dose and dose equivalent. Mean dose rate was found to decrease while mean dose equivalent rate and average quality factor increased with increasing shielding. Secondary particles from proton-induced target fragmentation interactions, not primary HZE particles, were found to be the largest contributor to the LET spectrum above 100 keV.microm(-1). During the 1997 measurements, mean quality factor was found to vary from 1.7 to 2.1 as a function of location within the Mir.     

Radiation shielding of spacecraft in manned interplanetary flights.

During the interplanetary flights the crewmembers will be exposed to cosmic ray radiation with great risk for their health. The absorbed dose due to CR depends on the galactic (GCR) or solar (SCR) origin. GCRs are isotropic and relatively high in energy and deliver a dose nearly constant with time that can be reduced only by means of "heavy" passive protection. The outer walls of the spacecraft usually shield the SCRs up to a few tens of MeV, but during some exceptional solar bursts, a great number of particles, mainly protons, are ejected at higher energies. In this case the dose delivered in a few hours by a solar burst can easily exceed 1 year cumulated dose by GCRS. The high-energy component of SCRs is quasi-directional so that a shielding system based on a superconductive magnetic lens can reduce the daily dose of SCRs to the level delivered by GCRS.     

Three-dimensional static analysis of thick functionally graded plates by using meshless local Petrov–Galerkin (MLPG) method

In this paper, a version of meshless local Petrov–Galerkin (MLPG) method is developed to obtain three-dimensional (3D) static solutions for thick functionally graded (FG) plates. The Young's modulus is considered to be graded through the thickness of plates by an exponential function while the Poisson's ratio is assumed to be constant. The local symmetric weak formulation is derived using the 3D equilibrium equations of elasticity. Moreover, the field variables are approximated using the 3D moving least squares (MLS) approximation. Brick-shaped domains are considered as the local sub-domains and support domains. In this way, the integrations in the weak form and approximation of the solution variables are done more easily and accurately. The proposed approach to construct the shape and the test functions make it possible to introduce more nodes in the direction of material variation. Consequently, more precise solutions can be obtained easily and efficiently. Several numerical examples containing the stress and deformation analysis of thick FG plates with various boundary conditions under different loading conditions are presented. The obtained results have been compared with the available analytical and numerical solutions in the literature and an excellent consensus is seen.