PADC Detectors Research Articles

Computer program Neutron_CR-39 for simulation of neutrons from an Am–Be source and calculation of proton track profiles

A computer program called Neutron_CR-39.F90 for neutron simulation through a PADC detector and its detection was described and developed. In this work the neutron Am–Be source was considered for simulation. It was shown that the most intensive secondary particles, created in neutron interactions with the detector, are protons. The programming steps are outlined with detailed description of neutron simulation, determination of latent tracks of created protons, as well as, their development after detector etching in the same and opposite direction of particle motion. The outputs of the code are parameters of created protons (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron. Program summaryProgram title: Neutron_CR-39Catalogue identifier: AEIU_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIU_v1_0.htmlProgram obtainable from: CPC Program Library, Queenʼs University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 140 004No. of bytes in distributed program, including test data, etc.: 2 213 012Distribution format: tar.gzProgramming language: Fortran 90Computer: PCs and workstationsOperating system: Unix, Linux, Windows 95+RAM: 256 MBClassification: 17.5, 18External routines: For the Windows installation the entire code must be linked with the PORTLIB library.Nature of problem: The neutrons do not cause ionizations in the detector, and consequently no tracks are produced directly by them in the PADC. Due to the elastic and nonelastic interaction of neutrons with the atoms of PADC, recoil nuclei and secondary particles are created producing latent intrinsic tracks. After chemical etching in aqueous NaOH solution these tracks become visible under optical microscope and usually density of visible tracks is measured. Optical microscopes are often used for this purpose but the process is relatively tedious and time consuming. The present computer program has been written for neutron simulation through PADC detector; determination of parameters of secondary particles; calculation track profiles of secondary particles emitted in the same and opposite direction as etchant progression. The outputs of the code are parameters of secondary particles (coordinates of starting and stopping points, direction angles of particles, initial and deposited energies) and number of visible tracks per incident neutron.Solution method: A computer program is prepared to simulate neutronʼs interactions in a PADC by the Monte Carlo method using the Neutron data library ENDF/B-VII [B. Milenkovic, D. Nikezic, N. Stevanovic, Radiat. Meas. 45 (2010) 1338]. The parameters of the emitted secondary particles (emission angle, initial energy, deposited energy and starting and stopping coordinates) were stored in an enclosed file. The subroutine for calculation of track profiles by a finite difference method for particles emitted in the same direction was developed [D. Nikezic, N. Stevanovic, D. Kostic, S. Savovic, K.C.C. Tse, K.N. Yu, Radiat. Meas. 43 (2008) S76]. It was shown that there are many tracks formed in the opposite direction than the etchant progression. The method for calculation of track profiles for these particles is developed in [B. Milenkovic, N. Stevanovic, D. Krstic, D. Nikezic, Radiat. Meas. 44 (2009) 57]. It is very different than the method for track in the same direction. The separate subroutine for this purpose was developed here.Additional comments: The program distribution file contains an executable which enables the program to be run on a Windows machine. The source code is also provided, but in order to build an executable the PORTLIB must be available.Running time: Running time depends mainly on the neutron number for simulation, source and detector geometry and removed layer required by the user. Running time is several minutes.

An investigation on the response of PADC detectors to neutrons

The response of PADC was calculated by Monte Carlo simulation using MCNPX code. H, C and O recoils as well as nuclear reactions have been taken into account. The calculated results show important contribution to detection efficiency of PADC due to H, C and O recoils. The irradiated detectors with (241)Am-Be source and (241)Am-Be softened with a spherical polyethylene moderator were electrochemically etched. The paper presents the results of the experimental and Monte Carlo simulations, which are in a good agreement.

About ageing and fading of Cr-39 PADC track detectors used as air radon concentration measurement devices

Abstract PADC detectors are widely used as air radon concentration measurement devices and the typical procedure that a Radon Service Laboratory uses to manage the detectors provides a calibration phase followed by the field measurement. The calibration is performed in a reference radon concentration atmosphere, using high radon concentration values in order to achieve typical exposure values of few MBq h m −3 with an exposure time of few days. On the other hand the field measurement is characterized by long term exposures lasting up to six months and by radon concentrations that are quite lower than the ones used in the calibration. The aim of this study is to check whether the calibration procedure is actually representative of a field measurement, or, in other words, whether and how much ageing or fading can affect the calibration factor. We found that the ageing and fading effect can produce a decrease in the detector sensitivity leading to an underestimation of the radon concentration up to 40% for exposure lasting few months. An important issue is that both ageing and fading can be ascribed to a decrease in the track etching velocity V t . In the paper we also provide an algorithm to compensate for the sensitivity variation due to fading/ageing effect.

Performance of Convenient Film Scanner System for Automatic Counting of Track Etched Pits on PADC Detectors

Performance of Convenient Film Scanner System for Automatic Counting of Track Etched Pits on PADC Detectors

Sensitization of PADC track detector in carbon dioxide gas

The fading of carbon dioxide treatment on PADC detectors after alpha-particle irradiations has been confirmed to relate to the diffusion loss of carbon dioxide. Diffusion coefficient of carbon dioxide in the film is found to be D = 1.1 × 10 −9 cm 2/s at room temperature. The effect of the post-irradiation treatment has strong relation with the dissolving process of carbon dioxide into the etching solution through the renewing surface of the detector during etching. Absorbed carbon dioxide can modify the network structure of PADC with higher permeability for etching solution.

Design and test of an albedo personal neutron dosemeter based on PADC detectors

Albedo dosemeters, usually based on thermo-luminescence detectors, have been frequently employed in personal neutron dosimetry. Their main advantages are the high sensitivity and the reduced angular dependence, whilst the disadvantages are the sensitivity to photons and the significant energy dependence of the response, which drops dramatically above 0.1 MeV. The present paper proposes an albedo dosemeter based on a planar PADC coupled with a 10B converter. This dosemeter shows good potentials in terms of photon insensitivity, limited angular dependence and high neutron sensitivity. Its use coupled with a dosemeter sensitive in the MeV region, should result in promising dosimetric performances. The response of the PADC based albedo dosemeter was characterized through irradiations in reference neutron fields of 241Am-Be, 252Cf and 252Cf(D 2O) and Monte Carlo simulations with the code MCNP-4C. The paper presents the results of the experimental and computational studies and outlines the relevant dosimetric performance of the new albedo dosemeter.

Measurement and comparative evaluation of the sensitivity V for protons and hydrogen isotopes registration in PADC detectors of type CR-39

Detectors of the PADC type CR-39 are the only plastic material which can register protons up to an energy of about 13 MeV because their very high sensitivity V. This sensitivity is assumed to be independent of the real etching conditions and therefore convenient for generalising the complex track formation process. In the present paper the sensitivity for registration of protons and hydrogen isotopic ions deuterons and tritons are investigated and parameterised to find functions of V applicable in calculation of track geometry during the etching process. Experimental data of bulk and track etch rates v B and v T are checked with previous measurements. Finally, by fitting these experimental data, parameterised V functions are recommended for use in theoretical calculations in order to predict the response of CR-39 to proton, deuteron and triton radiation.

Monitoring the ambient neutron radiation around a high energy electron/positron collider using PADC dosemeters

At the INFN Frascati National Laboratories (INFN-LNF), the DA Φ NE accelerator complex for fundamental and applied physics is operating since 1997. The routine radiation protection monitoring of the ambient neutron radiation around the accelerator is performed by means of a homemade dosimetry service, based on chemically etched PADC detectors. The LNF dosemeter is based on a four-element configuration, in which the main characteristic is a new procedure to reduce the fraction of “false positives”, i.e. background dosemeters inferred as doses due to spurious high track densities. The calibration of the dosemeters has been performed with a standard 241Am-Be neutron field. In addition, field-specific calibration factors have been derived, relying on the measured neutron spectra in selected workplaces around the accelerator. This work shows the results of the first two months monitoring period and discusses the suitability of the PADC for the neutron dosimetry around particle accelerators. The implications in the accuracy of the measurement, due to the realistic calibration and the new four elements configuration, are also addressed.

Are ageing and fading really a problem for the quality of the passive radon measurements?

Since ageing and fading of alpha tracks in CR-39 are acknowledged to modify the sensitivity of radon measurement by an alpha track device (ATD), a Radon Service operating under quality assurance has to state how these effects affect the uncertainty of the measurements, especially when long term exposures are met. A test lasting one year has been carried out, by using a total of 624 PADC detectors, to analyse the effects of three different treatments (temperature, light and as used inside the ENEA holder) together with the factor of the duration of the treatment (1, 3, 4, 6, 9 and 12 months) on the detector response. The replications ( N = 6 ) and the target exposure ( 4000 kBq h m - 3 ) were so set to achieve a minimum of 2% as significant statistical difference between treatment and control exposures. The shift of the track effective minor axis distribution has been investigated and related to the reduction of the sensitivity, which resulted in correlation with the surface removed layer of the bulk material. The use of a sensitivity value dependent on how fading, ageing and other factors modify the track diameter distribution was able to reduce the bias of the measurement.

Performance review of a slide scanner based automated counting system for PADC radon detectors

The HPA operates a radon measuring service determining the radon concentration ( Bq m - 3 ) in enclosed areas using passive PADC (CR-39) detectors. Since 2003 over 116,000 radon detectors have been analysed in the laboratory using a Nikon LS2000 slide scanner. Digital images of the etched PADC are analysed by in-house etched-track and area counting software. The slide scanner method is briefly described along with its performance across the dynamic range of the detectors. Blind Tests, validation and other quality assurance performance results are reported and discussed.

Neutron-induced complex reaction analysis with 3D nuclear track simulation

Complex (multiple) etched tracks are analysed through digitised images and 3D simulation by a purpose-built algorithm. From a binary track image an unfolding procedure is followed to generate a 3D track model, from which several track parameters are estimated. The method presented here allows the deposited energy, that originated from particle fragmentation or carbon spallation by means of induced tracks in commercially available PADC detectors, to be estimated. Results of evaluated nuclear tracks related to 12C ( n , 3 α n ′ ) reaction are presented here. The detectors were exposed on the ISS in 2001.

Gamma effect on track properties of PADC detector

Effect of high gamma irradiation on track properties of PADC (Homalite) has been studied in the dose range of 10 1– 10 6 Gy . The properties like bulk-etch rates and track-etch rates of the detector are found to increase due to gamma exposure. Etching efficiency of the detector increases due to exposure and it is significant at the dose higher than 10 3 Gy . Another track property, the critical angle, is also influenced by gamma exposure and is found to decrease with increasing dose. In all cases it is observed that the post-gamma exposure has greater effect than the pre-gamma exposure. The experimental results are presented and discussed in details.

Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10 4 Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a 252Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C 60). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C 60 layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C 60 as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C 60 molecules by energetic protons.

Emission of relativistic heavy fragments at wide angles from the interaction of 58 GeV 16O ions with thick copper target

Relativistic projectile fragmentation has been studied with track detection methods. Heavy fragments produced in the interaction of 58 GeV 16O with thick copper target have been investigated using 10 cm thick stacks of PADC (sometimes called CR-39) nuclear track detectors placed at 25° with respect to the direction of the incoming beam. A computer-controlled automatic scanning system was employed to “trace” the etched damaged trails in respective detectors of the PADC stack. Heavy reaction products producing “through-tracks” in consecutive sheets of 0.82 mm of PADC detectors were observed. The spatial distribution of these tracks with end points at various depths have been recorded. After calibration it has been concluded that these “through-tracks” should be due to relativistic O, N and C. These fragments are emitted from the interaction of 58 GeV 16O ions with thick copper target, their actual number is very tiny. The differential angular cross-section for their formation was found to decrease with increasing angle with respect to the incident beam direction.

Use of a CSLM for the analysis of chemical etched tracks in PADC

The possibility of using a confocal scanning laser microscope (CSLM) for the analysis of different parameters of α tracks in PADC was investigated. For this, PADC detectors were irradiated with α particles from an americium source under different incidence angles. The detectors were chemically etched and the analysis of the etched tracks was done with a confocal scanning laser microscope under different conditions. These include reflective mode and fluorescent mode. The reflective mode showed a very low contrast. Better image quality was obtained by filling the tracks with a fluorescent solution. The CSLM is not limited to XY-scans. By changing the focal plane, Z-scans can be obtained. Depth-profiles of chemical etched tracks can be obtained with a resolution in the order of 0.5 μm.

Recent Developments on the CRS PADC Fast Neutron Personal Dosemeter

The Dosimetry Laboratory of the Radiation Protection and Safety Centre in Algiers has developed a fast neutron personal dosemeter using a PADC detector. This dosemeter has been type tested in terms of the ICRU calibration quantity, directional dose equivalent at 10 mm, H'(10). This paper gives the results of type test measurements. In addition, some properties of five different PADC materials were investigated in this study.

Recent Developments on the CRS PADC Fast Neutron Personal Dosemeter

The Dosimetry Laboratory of the Radiation Protection and Safety Centre in Algiers has developed a fast neutron personal dosemeter using a PADC detector. This dosemeter has been type tested in terms of the ICRU calibration quantity, directional dose equivalent at 10 mm, H'(10). This paper gives the results of type test measurements. In addition, some properties of five different PADC materials were investigated in this study.