Polyallyldiglycol Carbonate Detectors Research Articles

Principal Component Analysis applied to neutron dosimetry based on PADC detectors and FNTDs

Solid State Nuclear Track Detectors (SSNTD) have been used as passive dosimeters for many decades. Fast neutron detection is performed by detecting recoil protons generated in a hydrogenous material (neutron converter). The dose is estimated by multiplying the recoil protons track-spots density present on the detector surface by a calibration coefficient obtained from reference irradiations. Therefore, one needs to automatically and reliably discriminate between the track-spots induced by recoil-protons and the spurious signal engendered either by material imperfections or by other ionising particles interactions. The objective of this work is to demonstrate and apply a method, based on the multivariate statistical tool named Principal Component Analysis (PCA), aiming at identifying and filtering out the spurious signal in track detectors. The advantage of this approach is that it can be applied to any type of SSNTD, provided apt definition of initial physical variables describing each track-spot. To show that, we applied the method to poly-allyl diglycol carbonate (PADC) detectors, to filter the signal generated by material imperfections, and to fluorescence nuclear track detectors (FNTDs), to remove the signal induced by other radiation field components. After filtering, dose assessments were compared with reference values of exposures, showing satisfactory agreement. In case of the FNTDs, the procedure proved to be effective regardless of the crystal colouration, which is known to affect signal-rejection techniques based on track-spots fluorescence intensity. The technique also offers the advantage of self-adjusting the filtering parameters based on the currently analysed detector set, as long as calibration and unirradiated detectors are included in the dataset.

Databank of proton tracks in polyallyldiglycol carbonate (PADC) solid-state nuclear track detector for neutron energy spectrometry

A computer program for studying etched proton tracks in the polyallyldiglycol carbonate (PADC) solid-state nuclear track detector was prepared. The program provided visualization of track appearance as seen under the optical microscope in the transmission mode. Measurable track parameters were also determined and displayed and written in a data file. Three-dimensional representation of tracks was also enabled. Application of this software in neutron dosimetry for energy up to 11MeV was demonstrated through the creation of a databank with a large number of tracks, which would be used to compare real-life tracks obtained in the PADC detector upon neutron irradiation. One problem was identified, viz., very similar tracks were obtained from protons with very different energies and incident angles, and strategies to solve this were proposed.

Determination of LET in PADC detectors through the measurement of track parameters

SSNTDs (solid-state nuclear track detectors), primarily made from PADC (poly(allyl diglycol carbonate)), are attractive detectors for dosimetric purposes. SSNTDs are more similar to human tissue than other passive detectors and the measurement of the track parameters provides information about the energy deposition of the incident particle. This paper describes a method for LET measurement based on the measurements of the major and minor axes of the track opening. The method was experimentally tested using alpha particles with energies ranging from 4.2MeV to 6MeV. The experimental results show that PADC can measure the total energy lost by a particle along a path of length Δx divided by the length itself, a quantity strictly related to the LET.

Gamma Irradiation Effects on Track Properties of PADC‐American Acrylics Track Detector

Gamma irradiation effects on track properties of Polyallyl Diglycol Carbonate (PADC) track detector (PADC‐American Acrylics) are studied in the dose range of 101‐106 Gy. It is observed that due to gamma exposure the bulk and track‐etch rates of the detector increases. This increase in both etch‐rates is more pronounced in post gamma exposed PADC detectors. The etch‐rate ratio (S) for both pre and post‐gamma exposed detectors decreases with increasing etching temperature at the dose of 106Gy. At a higher etching temperature of 70ºC, the etch rates ratio becomes almost equal for post gamma exposed detector. Etching efficiency of the detector is found to be much higher when exposed to gamma radiation. However it is observed that at the etching temperature of 70ºC, etching efficiency for both pre and post‐gamma exposed samples tends to become almost equal to the pristine one.

Influence of variation of etching conditions on the sensitivity of PADC detectors with a new evaluation method

At the Paul Scherrer Institut, a personal neutron dosimetry system based on chemically etched poly allyl diglycol carbonate (PADC) detectors and an automatic track counting (Autoscan 60) for neutron dose evaluations has been in routine use since 1998. Today, the hardware and the software of the Autoscan 60 are out of date, no spare components are available anymore and more sophisticated image-analysis systems are already developed. Therefore, a new evaluation system, the 'TASLIMAGE', was tested thoroughly in 2009 for linearity, reproducibility, influence of etching conditions and so forth, with the intention of replacing the Autoscan 60 in routine evaluations. The TASLIMAGE system is based on a microscope (high-quality Nikon optics) and an ultra-fast three-axis motorised control for scanning the detectors. In this paper, the TASLIMAGE system and its possibilities for neutron dose calculation are explained in more detail and the study of the influence of the variation of etching conditions on the sensitivity and background of the PADC detectors is described. The etching temperature and etching duration were varied, which showed that the etching conditions do not have a significant influence on the results of non-irradiated detectors. However, the sensitivity of irradiated detectors decreases by 5 % per 1°C when increasing the etching temperature. For the variation of the etching duration, the influence on the sensitivity of irradiated detectors is less pronounced.

Practical consequences for the use of a personal dosemeter for fast neutrons at high-energy accelerators based on PADC detectors exposed up to one year

Abstract Since 1998, Paul Scherrer Institut has employed the routine use of a personal neutron dosimetry system based on chemically etched PADC (poly allyl diglycol carbonate) detectors and automatic track counting. In 2004, a new concept for individual monitoring at high-energy accelerators was implemented. In this concept the photon dosemeter of a combined photon/neutron dosemeter is evaluated monthly. The neutron dosemeter is only evaluated if the personal photon dose exceeds 2 mSv, or if the exposition period of the neutron dosemeter exceeds one year. Significant consequences for the evaluation of the neutron dosemeter in the dosimetry service were evidenced in the new concept. The wearing period of the neutron dosemeter can range from 1 to 12 months, potentially longer. Therefore, the long-term behavior of background track density and variation of response to Am–Be within 17 months was studied. The effects of “fading” and “aging” that influence the response of PADC detectors are determined. The application of an algorithm for neutron dose calculation takes into account long-term behavior and is described. Furthermore, repeated field calibrations were performed at the CERN-EU high-energy reference field (CERF) facility.

A comparative study of gamma radiation effects on track properties of different PADC detectors

Track properties of gamma-irradiated polyallyldiglycol carbonate (PADC) detectors (Homalite, Pershore and Trastrack) are studied in the dose range of 101–106 Gy. Results show that the bulk and track etch rates of all three types of PADC detector increase at doses higher than 104 Gy. This increase is more pronounced in post-gamma exposed detectors. The change in etch rate ratio (S) for post-gamma exposed PADC–Homalite detectors is more significant when compared with the other detectors. The critical angle for etching shows that etching at a low temperature of 60 °C is more effective, and the critical angle value is decreased to a significant extent for all three types of PADC detectors. Etching efficiency of post-gamma exposed samples is found to be much higher than the pre-gamma exposed sample at the highest dose of 106 Gy. When compared, it was found that of the three PADC detectors, PADC–Homalite detectors seem to be more sensitive to gamma irradiation.

Characteristics of PADC detectors using new pre-soaking technique

PADC (Poly-allyl diglycol carbonate) has been widely used for personal neutron dosimeter. However, false pits are often observed on etched surfaces of non-irradiated PADC plastic, which are very similar to those induced by neutrons and difficult to distinguish under microscopic view. The purpose of this study is to investigate about an effective pre-soaking process for reducing the number of background pits with keeping the neutron sensitivity higher. The optimum pre-soaking condition was determined by a practical index of lower detectable dose (LDD). Under the condition, the response of the neutron dosimeter consisting of PADC plastic nuclear track detector and a polyethylene radiator was also investigated for several different neutron energies. An improvement in its energy dependence was experimentally confirmed.

Optical and electrical properties of gamma irradiated PADC detector

PADC (Polyallyldiglycol carbonate) detector subjected to gamma rays undergoes change in optical and electrical properties. The optical band-gap is determined using Tauc's plot. The band-gap is found to be unchanged up to the dose of 10 3 Gy , and then starts decreasing with increasing dose. The band-gap is lowered from 4.04 eV for the pristine material to 2.46 eV for the highest dose ( 10 6 Gy ). The dielectric constant of the detector is influenced due to the gamma exposure. At lower doses (up to 10 4 Gy ), the detector seems to be not polarised, so no change in dielectric constant is observed. But at the dose of 10 5 Gy , the value is increased slightly while at the highest dose ( 10 6 Gy ), the dielectric constant of the detector is found to be enhanced significantly. The results indicated a decrease in track registration sensitivity with increase in gamma dose.

Effect of high gamma doses on the etching behaviour of different types of PADC detectors

Polyallyldiglycol carbonate (PADC) detectors were exposed to different doses of gamma radiation ranging from 10 1 to 10 6 Gy from a 60Co source. The effect of gamma doses on etch-rates were studied. Etch-rate values were found to increase at the dose of 10 6 Gy for all types of PADC detectors. The influence of gamma exposure on sensitivity and etching efficiency of these detectors was also determined. The experimental results are presented and discussed.

Development of indigenous polyallyl diglycol carbonate (PADC) films for nuclear track detection

In an attempt to prepare PADC films for SSNTD applications, we have produced a home-made PADC detector called UC-95 by the benzoyl peroxide catalyzed bulk polymerization of allyl diglycol carbonate (ADC, PADC monomer) using an indigenously prepared mold. It was used for recording an autoradiograph of 239Pu alpha particle source and 252Cf fission fragment detection. The etching conditions of this detector were studied and some of the properties (background tracks, bulk etch rate and sensitivity) were compared with those of the commercially available PM PADC detector. UC-95 compared well with the commercial PM PADC with respect to bulk etch rate and track registration efficiency.

Development of a single element neutron personal dosemeter for thermal, epithermal and fast neutrons

A single element neutron personal dosemeter has been developed which has an approximately dose equivalent response to thermal, epithermal and fast neutrons. The detection element consists of 500 μm thick rectangle of poly allyl diglycol carbonate (PADC). The PADC used is that commercially available from Pershore Mouldings Limited. The rear surface of the PADC detector is in contact with a piece of polyamide plastic. The rear surface of the PADC detector is electrochemically etched. The fast neutron response results from development of the tracks of recoil protons produced mainly by interactions of neutrons in the PADC, with a contribution from interaction in the packaging and dosemeter holder for neutrons of energies greater than about 7 MeV. The thermal and epithermal neutron response is from protons (initial energy 600 keV) produced in capture reactions on nitrogen in the polyamide plastic.