Angular response characteristic of pyramid shape fast neutron dosimeter using CR-39 films

CR-39 is a highly sensitive etched track detector for neutron monitoring and dosimetry applications but its dose equivalent response is strongly direction dependent with respect to the incident neutrons. This is considered to be a major drawback for their use. In the present study, an attempt has been made to develop a pyramid shaped dosimeter, which consists of polyethylene material of thickness 1 mm with the provision to hold three CR-39 films at an angle of 35° to each other. The response of CR-39 in this configuration under optimum electrochemical etching at elevated temperature have been found nearly angular independent and therefore the dosimeter can be used for neutron monitoring, i.e. personnel as well as area monitoring.     

Computer simulation of the processes in a CR-39 neutron detector

The application of CR-39 as a fast neutron dosimeter, based on counting elastic recoil nuclei tracks of H, C and O nuclei in a geometrically matched pair of detectors, was studied. A computer simulation of the processes during the exposure of a detector pair to neutrons is presented. The energy and spatial distribution of the recoil nuclei was calculated with the MCNP 4B program package. On the basis of this distribution, a Monte-Carlo procedure for the generation of latent tracks in the CR-39 detectors was run. Additionally, a procedure for calculation of the chemical track etching for revealing the visible track parameters was performed to obtain the detector response.     

Range and energy-loss measurement of238U in Makrofol-N using CR-39 track detector

A simple experimental technique has been described for measuring range and energy-loss of any heavy ion in any complex medium with the help of a sensitive solid state nuclear track detectors (SSNTDs). In this paper we present the results obtained from our measurements of ranges and energy-loss of 16.34 MeV/u²³⁸U in Makrofol-N using CR-39 track detector. Experimental ranges are compared with the corresponding theoretical values. The significance and scope of the present work are discussed.     

Neutron,photon and proton energy spectra at high altitude measured using a phoswich-type neutron detector

Neutron energy spectrum from 7 to 180 MeV, photon energy spectrum from 4 to 50 MeV and proton energy spectrum from 94 to 145 MeV were measured simultaneously using a phoswich-type neutron detector with particle discrimination methods at atmospheric depth of 249 g/cm², a vertical cut-off rigidity of 10.2 GV and at a heliocentric potential of 312 MV. We compared our results with other measured and calculated particle energy spectra. Our measured results give a large, sharp neutron peak around 70 MeV, although Bonner balls show a broad peak around 100 MeV due to low energy resolution. The measured photon and proton spectra are between the calculated energy spectra. This onboard study provides the first experimental neutron energy spectrum over 10 MeV with a high-energy resolution.     

Development of a reader for the routine analysis of CR-39 fast neutron dosemeters: improvement of the dosimetric performance using automatic vision and motion tools

At the personal dosimetry service of the ENEA Radiation Protection Institute, a fast neutron dosemeter based on chemically etched CR-39 (Poly Allyl Diglycol Carbonate) is operating since more than 20 years. Since then the track counting has been performed with a system consisting of a microscope, a video camera and an image analyser. A new automatic analysis system has been developed, based on automatic motion and vision tools and the programming language Labview 6, from National Instruments. The system selects the correct number of reading fields on the basis of a preliminary scan of the dosemeter, therefore operating motion and vision procedures in order to perform the analysis. For each reading field the system collects the track area distribution to which a previously optimised algorithm is applied, in order to correct the energy dependence of the response. For each dosemeter, a record containing the barcode and all data necessary for assessing the personal dose equivalent is stored in a routine file. Taking advantage of automatic vision and motion, a CR-39 reader with innovative features in terms of reproducibility, velocity and accuracy is now available even for the routine purposes of dosimetric services.     

Theoretical and experimental study of the CR-39 behavior under electron beam

This work concerns the action of an electron beam on some physical properties of the poly(diethylene bis(allyl carbonate)) CR39 manufactured in Bristol and Limoges laboratories. The material undergoes structural, physical and chemical modifications induced by the incident electrons energy transfer in the substrate. This is similar to the processes generated by the secondary electrons created during ion beam-polymers interactions. An experimental study of the topographic modifications on the CR39 under electron beam is presented. In parallel, a theoretical study using Monte-Carlo simulations and concerning the 3D energy transfer for one diameter of the spot is developed in order to evaluate the radio induced process.     

Measurement of fast neutron induced fission cross section of thorium using Lexan plastic track detector

Fission-track registration characteristics of Lexan solid state nuclear track detectors have been used to measure the fast neutron induced fission cross section of²³²Th. The fast neutrons (?14.2MeV) were produced with the help of an AN-400 model Van-de-Graaff accelerator at Banaras Hindu University laboratory using³H(²H,n)⁴He reaction and were used to irradiate the fissile target deposited on the plastic detector. The track densityT, registered on the plastic detector is related to the fission cross sectionσ _f, through the relationT=knσ _føt wheren is the number of fissile atoms per cm² in the deposit, ø is the neutron flux,k is fission track registration efficiency andt is the time of irradiation. The fission cross sectionσ _f of²³²Th, relative to the well measured fission cross section of²³⁸U, was found to be 0.36±0.04 barn.     

Unfolding the fast neutron spectra of a BC501A liquid scintillation detector using GRAVEL method

Accurate knowledge of the neutron energy spectra is useful in basic research and applications. The overall procedure of measuring and unfolding the fast neutron energy spectra with BC501A liquid scintillation detector is described. The recoil proton spectrum of 241Am-Be neutrons was obtained experimentally. With the NRESP7 code, the response matrix of detector was simulated. Combining the recoil proton spectrum and response matrix, the unfolding of neutron spectra was performed by GRAVEL iterative algorithm. A MatLab program based on the GRAVEL method was developed. The continuous neutron spectrum of ²⁴¹Am-Be source and monoenergetic neutron spectrum of D-T source have been unfolded successfully and are in good agreement with their standard reference spectra. The unfolded ²⁴¹Am-Be spectrum are more accurate than the spectra unfolded by artificial neural networks in recent years.     

Indoor radon and radon daughters survey at Campinas-Brazil using CR-39: First results

The first results of a radon and radon daughters (RD) survey performed at Campinas-SP, Brazil, are presented. We employed a technique that, potentially, makes possible to measure the radon and RD activity in the air and to separate from this result the activity of radon, alone. In this preliminary paper only the former activity is studied.     

Direct determination of track etch rate and response of CR-39 to normal incidence high-energy heavy ions

Response of CR-39 to high-energy heavy ions was investigated by using optical microphotographs of track profiles for Ar (480 MeV/n) and Ni (300 MeV/n). The depth dependence of track etch rate (V_T) was determined experimentally by track length measurement. The results indicate that V_T for the low REL Ar tracks is depth independent but for the high REL Ni tracks V_T is gradually decreasing with depth. The region beyond 30 μm depth inside the detector shows a stable region regarding the detector response for both ions.     

CR-39 and Lexan calibrated as low-LET radiation dosimeter, for three Mexican irradiation facilities

An experimental calibration of two common nuclear track detectors, CR-39 and Lexan, for gamma and electrons radiation, was performed using various irradiation facilities. The dose response was obtained as a function of two parameters, the bulk etch rate and the UV absorbance for a wide dose range from 10 to 1000 kGy. The bulk etch rate sensitivity, for gamma and electrons, in CR-39 detector is higher than for Lexan detector. Lexan has a well-defined UV absorbance spectrum, but presents saturation for doses higher than 500 kGy, the same saturation characteristic is observed for the corresponding bulk etch rate response. For electron and gamma radiation, CR-39 shows a good response for doses from 10 kGy up to 1000 kGy, where data fit well an exponential curve for electrons and a lineal curve for gamma radiation.     

Comparison of responses of CR-39 and PM-355 track detectors to fast protons, deuterons and He ions within energy range 0.2–4.5 MeV

The paper presents new results of the calibration of the standard CR-39 and super-grade PM-355 plastic detectors, which are applicable for the registration of the protons, deuterons, and ⁴He-ions. The calibration diagram show track diameters vs particle energy for different etching times.     

The COMPLIS experiment on neutron deficient Au, Pt and Ir isotopes

The COMPLIS (COllaboration for spectroscopic Measurements using a Pulsed Laser Ion Source) experiment is carried out at the ISOLDE Booster facility at CERN. The aim is to measure the hyperfine structure and the isotope shift of a series of radioactive laser desorbed atoms by multiple step laser ionization. This technique is especially suitable for refractory elements not directly available as beams from the isotope separator. By collecting a primary radioactive beam, it is possible to delay the laser desorption as long as necessary to obtain the particular daughter of interest. Laser spectroscopy measurements have been carried out on very neutron deficient gold, platinum and iridium isotopes. Magnetic moments μ_I, spectroscopic quadrupole moments and changes of the nuclear mean square charge radius along each isotopes series have been extracted. From some results, a detailed comparison with the predictions of the models is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature and density measurements in a non-axisymmetric,continuously operating fusion experiment using a heavy ion beam probe

Two-dimensional electron temperature and density data have been obtained in the midplane of the non-axisymmetric magnetic confinement device ELMO Bumpy Torus (EBT) through the use of a heavy ion beam probe. This beam probe differs from others operated on toroidal or open magnetic geometries in its combination of complete computer control with the steady-state nature of EBT which allows, under normal operating conditions, for extensive calibration of the system in situ, minimizing both alignment and acquisition errors, along with the use of synchronous detection to dramatically improve the quality of the detected signal over what is typically possible in fast pulse devices. These techniques are important and applicable to long pulse devices where the beam probe may be an ideal diagnostic to measure, for example, parameters of the edge plasma. While the EBT beam probe was implemented to obtain profiles of plasma space potential, we have found that it can also be used effectively to measure the temperature and density profiles in the midplane between magnetic field coils. The data obtained support the contention that the formation of a hollow temperature profile in the T-Mode sufficiently inverts the plasma pressure such that stability of the core plasma would be expected even without diamagnetic effects from the hot electron rings which have previously been considered essential     

Influence of external and internal conditions of detector sample treatment on the particle registration sensitivity of Solid State Nuclear Track Detectors of type CR-39

The sensitivity of charged particle registration with SSNTD is the most important parameter to decide about the applicability of those detectors in research, technology and environmental dosimetry. The sensitivity is strongly influenced by the treatment of detector samples before, during and after the exposure and the final evaluation process by chemical etching. Whereas changes in detection properties by external environmental influences are generally considered, the dependences on the etching conditions are ignored. Commonly the sensitivity is assumed to compensate variations in the etching conditions for track revealing. In the present work the validity of this hypothesis will be checked. In the frame of the existing database the sensitivity is not really independent on variations in etching temperatures and should be corrected for differences in the activation energies for stimulation of the bulk and track etching process. Differences in the concentration dependence may be of minor importance. Furthermore, the registration sensitivity depends on environmental conditions before, during and after the irradiation with particles under investigation. Such external parameters are the air pressure, the sample temperature and modification of bulk material by out-gassing in vacuum and exposure to γ-rays. However, the available database is insufficient and inaccurate to draw final conclusions on the detection properties of SSNTD under various external and internal conditions.     

Neutron standing waves in layered systems: Formation,detection, and application in neutron physics and for investigation of nanostructures

Specific features of different regimes of the neutron’s wave field are theoretically considered. The results of experimental studies of the regime of a neutron’s standing waves both in the primary channel of neutron specular reflection and in different channels of registration of secondary emission are considered. Some studies of layered structures performed with the help of a neutron’s standing waves are considered. The prospects of application of a neutron’s standing waves in neutron physics and for investigation of layered nanostructures are considered.     

Neutron scattering from aerosols: intraparticle structure factor, guinier analysis of particle speed, and crossed beam kinematics

A theoretical formalism for neutron scattering from systems of particles is applied to liquid nanodroplet aerosols. A term arising from intraparticle, intermolecular correlations is identified. The kinematical theory of two body scattering is recast into a form convenient for interpreting the results of experiments with crossed beams of neutrons and aerosol particles. Based on a theoretical analysis of the scattered intensity in the Guinier region, a method for determining the particle velocity directly from the experimental data is outlined. The method is not restricted by assumptions about particle shape, composition, uniformity, or size distribution.     

Performance studies of compact GGAG:Ce,B thermal neutron detector coupled to Si-based photosensors

Pramana - This work concerns the modelling of the dynamics of polarisation of a centrosymmetric material subjected to an amplitude-modulated excitation (AME). The dynamic equation obtained for the...     

Comparison of responses of CR-39, PM-355, and CN track detectors to energetic hydrogen-, helium-, nitrogen-, and oxygen-ions

Samples made of the CR-39 and PM-355 plastic nuclear track detectors (NTDs) as well as of the CN films were irradiated with quasi-monoenergetic beams of protons, alphas, N⁺-, and O⁺-ions produced by various accelerators. For different samples an energy value of the particle beams was changed from several hundreds keV to 3 or 4.5 MeV. After irradiation the detector samples were etched chemically under controlled conditions during periods lasting from 2 hrs to 20 hrs. Every 2 hrs track diameters were measured by means of an optical microscope. Differences in the crater diameters in the detectors etched in steps, and those etched continously, have been found to be smaller than 10 percent. The paper results detailed calibration diagrams showing a dependence of track diameters on the ion energy value for different etching times.