CR-39 Sheets Research Articles

Applications of nuclear track detectors in space radiation dosimetry

Abstract Over the past twenty years, the radiation environment of manned spacecraft has been measured by a variety of detector types. The high-LET (linear energy transfer) spectrum produced by HZE particles has been measured by plastic nuclear track detectors which included different combinations of CR-39, polycarbonate and cellulose nitrate sheets. These detectors are light- weight, compact, and have provided an effective means of measuring the high LET on all the space shuttle flights to date, including Spacelab-1, as well as the past missions of Apollo and the Skylab series. For low LET, absorbed dose and dose rates as a function of such parameters as inclination, altitude, spacecraft type and shielding have been measured with thermoluminescent detectors (TLD's). For low Earth-orbit missions the dose encountered was found to be strongly altitude-dependent, with a smaller dependence on orbit inclination. This paper presents radiation data gathered on the last several space shuttle flights and discusses further experiments which are being planned.

Measurements of transversal etching rates of uranium tracks in CR-39

The transversal etch rate of tracks of 238 U-ions (410 MeV/nuc) has been measured by electrochemical etching. The irradiations of CR-39 sheets were carried out by the Bevelac Laboratory, Berkeley (USA). In a special two chamber etching equipment the sheets of CR-39 were etched from both sides using 6n-NaOH at a temperature of 50°C having electrodes in both chambers. During the etching process a current through a track is measured, from which the pore radius can be determined as a function of the etching time. Thus the transversal track development could be studied. This was done at different values of REL. The dimensions of the regions of preferred etching around the tracks were registered.

A new scanning system for large area track-etch detectors

A rapid automatic system based on a new method is developed to scan etch-holes on large area plastic track detectors. Deeply etched CR39 sheets are first black-dyed and then are exposed to an intense visible light. Optical filters make a sharp contrast between the light which passes through the etch-holes and the background infrared light through the plastic. The picture taken by a CCD camera is digitized and stored in a memory. After simple zero-suppression the data are read out by a personal computer, followed by an on-line analysis to determine the positions and brightness of the holes. With this system an etch-hole as small as 10 μm can be detected and a sheet of size 300×300 mm can be scanned within 10 s.

Studies on nitrogen mapping by various CR-39 track detectors

The possibility of using CR-39 track detectors for nitrogen distribution measurements via 14 N(n,p) 14 C reaction is studied. In this respect the proton detection properties of different CR-39 products have been analyzed. By PIXE and neutron activation methods the possible disturbing impurity content of the detector sheets is determined. It is found that the main contaminant is chlorine which remains in the CR-39 monomer during its manufacture. The variation of background track density induced in the bulk of detectors is examined under different conditions of neutron irradiation. The analysis of our experimental data has led to the conclusion that the sources of proton background tracks are the fast neutron component of neutron source, chlorine in detector and nitrogen diffused from air into the upper layer of detector. Efforts have been made to decrease the nitrogen content of diffusion origin by removing the upper detector layer and by outgassing the CR-39 sheet in vacuum before irradiation. Finally the “signal/noise” ratio for steel specimen and the sensitivity of nitrogen determination are given.

Calculation of thermal effects occuring during the manufacture of CR-39 sheets

To manufacture a good-quality, uniform CR-39 track detector, the polymerization rate should be chosen below a critical value to avoid the development of undesirable thermal gradients and internal temperature fluctuations in the sheet being cast. To improve curing cycles, especially for thick CR-39 sheets, a computer programme was developed by which we could study the trends of thermal effects under different casting conditions. Our calculations are based on the solution of the one dimensional heat transport equation, taking into account the relations proposed by Dial et al (1955) for describing the chemical kinetics of CR-39 polymerization. We have revised the empirical parameters available to such calculations. With new “Dial constant” we have calculated the critical initial bath temperature (which results in thermal runaway at the central plane of the sheet being cast) as a function of the CR-39 thickness and IPP initiator concentration. Results are also presented for the temperature profile developing in the depth of cast CR-39 sheets.

Cutting thin sheets of allyl diglycol carbonate (CR-39) with a CW CO 2 laser: Instrumentation and parametric investigation

Recent studies have shown that Allyl Diglycol Carbonate, commercially known as CR-39 (the most sensitive among etch track detectors) can detect relativistic oxygen and other heavier nuclei. We are using large sheets of special grade CR-39 (DOP) in our experiment in Space Shuttle Spacelab-3. As CR-39 is a highly brittle substance, special care is required to cut CR-39 sheets, especially in case of large sheets and circular cuts. A study of cutting of CR-39 sheets using laser light is described in this paper. It has been found that this method is sufficiently fast to handle large number of sheets and also equally safe for big sheets. A maximum speed up to 200 cm/min with a 5 × 10 4 W/cm 2 laser is obtained during the present study. This study also shows that laser cutting does not affect the track properties of CR-39.

ADC (CR-39) detector module for space shuttle spacelab-3 cosmic ray experiment

In recent years, some experimental studies have reported the presence of a new component in low energy heavy cosmic rays in near earth space. The Indian cosmic ray experiment aboard Space Shuttle Spacelab-3 is designed to study the ionization states of this new component in addition to its abundance and energy spectra. This experiment will be flown in space in Spacelab-3 in 1984. Our detector system consists mainly of CR-39 (DOP) sheets along with some Lexan Polycarbonate sheets. In this paper, we describe the detector module for this experiment along with its functioning.

Formation of ion-beam images in gelatine and various polymers

It has recently been reported by Najz̆er, Humar and Ilić (1982) that the pure gelatine can be used for producing relief images of high-fluence ion-beams after a treatment in water at room temperature for few minutes. The new method is proposed for high-resolution microradiography of boron in metals via 10B(n,α) 7Li reaction. In our present work studies are performed to understand the phenomenon observed. We have simulated the image formation by accelerated electron, proton and alpha-particle beams at different fluences. A narrow fluence region is found in which a highly enhanced dissolution rate of the irradiated gelatine is induced. We assume that when the fluence exceeds a critical value (tipically 10 12–10 13 ions·cm -2) the damage zones of individual tracks cover almost completely the irradiated area, transforming the irradiated layer into a huge damage zone. In this case the effective diameter of damage zone around a single track has to be d eff= =φ c -1 2 ≅(3–10) nm . We have found that the ion-induced image formation phenomenon observed in gelatine is a more general one and the method may be extended to almost all the etch-track and non-etch-track forming polymers and perhaps to insulating silicates. For example high-resolution α- microradiographs have been obtained with CR-39, CN-85, PC and PET sheets and even with hydrate-cellulose known as a non-track-forming material.

A new possibility for high-resolution spectroscopy of nuclear particles entering CR-39 at selected dip angles

In nuclear reaction studies a differentiation of the reaction products according to their type and energy is generally required. At right angle of incidence a particle identification method based on the relation netween the track diameter and particle energy can be well applied to plastic track detectors of low registration sensitivity. We have tried to extend this “track-diameter method” to the high-sensitivity CR-39 sheets by selecting special incident angles for particle detection. The utility of such a measuring procedure, called “track-size method”, is presented for alpha and proton spectroscopy. A theory is developed to calculate at arbitrary angles the main parameters affecting the energy resolving power of the “track-size method”, namely the critical layer thickness (which has to be removed from the detector surface for track-induction) and the depth and minor axis of etch-pits.

Mass resolution for iron isotopes in the plastic CR-39

In order to investigate its mass resolution, a stack of sheets of the plastic CR-39 was exposed to a beam of 600 MeV n 56Fe ions. From this exposure, a total of 74 iron events were analyzed. The mass resolution for 56Fe was obtained as 0.34 ± 0.14 amu.

An improved CR-39 track detector for cosmic ray applications

ABSTRACT Batches of CR-39 polymer have been produced using a temperature-time polymerisation cycle designed to minimise temperature gradients during curing. Track detector evaluation tests of these batches were carried out using Argon and Iron beams at the LBL Bevalac. The results indicate a significant improvement in the uniformity of track response compared with commercially available CR-39 sheet. This improvement is particularly relevant to the use of CR-39 for cosmic ray composition studies.

Improving the etching properties and tailoring the response of CR-39 plastic track detectors with dopants

ABSTRACT Following G. Tarie's discovery of the remarkable effect of a 1% addition of dioctyl phthalate to CR-39 monomer, we have cast sheets of CR-39 with no additive and with 1% of dioctyl phthalate, dioctyl teraphthalate, and diisodecyl phthalate. Sheets made from any of the additives are much more transparent after etching and the etched cones are more uniform than is the case with pure CR-39. In irradiations with Ar, Ne, C, and He, we find that the dependence of reduced etch rate, VT/VB-1, on Z/β is significantly different for the pure CR-39 and for each kind of additive. One can thus choose an additive that gives the optimal response for a particular application. All of our sheets with additives are more sensitive than those with dioctyl phthalate made for us by Pershore; our pure CR-39 is more sensitive than Pershore's pure CR-39.

Characteristics of CR-39 for detection of cosmic ray particles

ABSTRACT A stack of CR-39 sheets has been exposed to 96 MeV/n and 2.1 GeV/n Ar beams in order to study uniformity of response and the response curve. Variation in response of the area of about 50 cm × 50 cm for one sheet was within 1.5 %. Roughness of the surface after 27 hr etching and the charge resolution were improved by changing temperature-time curing cycles. Steeper response curve at high REL region was observed and it was confirmed that our CR-39 has higher sensitivity in the recording of nuclear tracks down to Z/β ≃ 6 for vertical incidence.

Track measurements on plastic sheets exposed to the CERN-SC carbon beam

ABSTRACT Track measurements on CR39 sheets exposed to the CERN-SC 86xA MeV Carbon beam are reported. The diameter of vertical tracks and the parameters of dipped tracks were measured. The p vs. REL trend is deduced. Charge discrimination for fully etched tracks is discussed.

Characteristics of neutron-irradiated CR-39 foils treated by sequential chemical and electrochemical etching

The density of background spots revealed by chemical (CE) and electrochemical (ECE) etching and by their sequential application (CE + ECE) has been measured in several sorts of CR-39 material. The trends in the variation of sensitivity to Am-Be neutrons have been determined in CR-39 sheets covered by thick proton-radiator, when changing the field strength (<35 kV/cm), frequency (< kHz), etchant concentration, pre-etch duration and the fluence of neutrons. The results are analyzed in order to find out an optimum set of experimental parameters which may be proposed to attain high registration sensitivity to neutrons.

Method for producing thin sheets of proton-sensitive CR-39 plastic track detectors

Uniform, high-quality sheets of CR-39 (allyl diglycol carbonate) from ∼25 to ∼500 μm thick can easily be made by curing the initiated monomer between thin glass plates within a suitable gasket in a hot water bath or in an air oven.

Variation Or Radon Activity Of Soil Samples With Colour Using Cr-39 Method

DOI: http://dx.doi.org/10.3329/diujst.v6i2.9348 DIUJST 2011; 6(2): 72-74