Radiation Measurements 40 (2005) 396–400www.elsevier.com/locate/radmeas

Detection of fission tracks on resin plates formed from three kindsofDAPmonomers

T. Tsurutaa,b,∗, T.Yoshiokab,c,Y. Koguchib,d,Y. Koorib, K. HondaaaAtomic Energy Research Institute, Kinki University, Kowakae, Higashi-osaka, Osaka 577-8502, Japan

bInterdisciplinary Graduate School of Science and Engineering, Kinki University, Kowakae, Higashi-osaka, Osaka 577-8502, JapancKyoto Fission-Track Co. Ltd., 44-4 Minamitajiri-cho, Omiya, Kita-ku, Kyoto 603-8832, Japan

dOarai Research Center, Chiyoda Technol Co. Ltd., 3681 Narita-cho, Oarai-machi, Higashi-ibaraki, Ibaraki 311-1313, Japan

Received 27 August 2004; accepted 1 February 2005

Abstract

This work compares the response properties of ortho, meta and para diallyl phthalate (DAP) resin plates and their copolymerplates cast under the same curing conditions. The plates were irradiated with fission fragments and alpha-particles. Afterirradiation, the plates were etched with a potassium hydroxide, ethanol and water (PEW) solution or an aqueous solution ofpotassium hydroxide. Enlarged nuclear tracks were observed and counted using an optical microscope. All plates were foundto have a detection efficiency of almost 100% for fission fragments, and yet were found to be insensitive to alpha-particles.From the experimental results of finish in curing, ease in cutting, etching speed and heat resistance, the ortho-based plateshave been found to be superior to the meta- or para-based plates as a fission track detector.© 2005 Elsevier Ltd. All rights reserved.

Keywords:Ortho; Meta; Para; Diallyl phthalate; DAP resin; Copolymer; Fission track detector; PEW solution

1. Introduction

Diallyl phthalate (DAP) resins are known to have adetection efficiency of about 100% for fission fragments,and yet are known to be insensitive to alpha-particles.This property is suitable for selectively detecting fissionfragments, which sometimes coexist with alpha-particles(Tsuruta, 1999, 2000). In this study, 18 kinds of DAP plateshave been made from three kinds of DAP monomers andexamined to identify those with the best characteristics asfission track detectors.

∗ Corresponding author. Atomic Energy Research Institute, KinkiUniversity, Kowakae, Higashi-osaka, Osaka 577-8502, Japan. Fax:+81667213743.

E-mail address:tsuruta@msa.kindai.ac.jp(T. Tsuruta).

1350-4487/$ - see front matter © 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.radmeas.2005.02.015

A PEW solution containing KOH, ethanol and water wasused in an attempt to reduce the etching time of the DAPresin plate. This solution had been used for the etchingof polycarbonate (Somogyi et al., 1977) and CR-39 resin(Somogyi and Hunyadi, 1979). It has been reported thatPEW solution reduced the etching time for DAP resin plateto less than one-tenth the etching time of a conventionalaqueous solution (Tsuruta, 2001b). Three kinds of thermalhistories have been used in an attempt to cure the DAP resinplates. The under-cured plates have been found to be supe-rior to the full- or over-cured plates as a fission track detec-tor. (Koguchi and Tsuruta, 2002)

The above-mentioned DAP resin plates were made froma ortho-type DAP monomer. Meta- and para-type isomers ofthe ortho-type DAP monomer exist. When para-type DAPresin was irradiated with heavy ions, tree-like structureswere observed during the etching process (Schulz et al.,

T. Tsuruta et al. / Radiation Measurements 40 (2005) 396–400 397

1991). Except for this study, meta- or para-type DAP resinshave been hardly used as nuclear track detectors.

2. Materials and methods

2.1. Casting of the plates

The main constituents of the plates were ortho-, meta-and para-type DAP monomers. The constitutional formulaeof the monomers are shown inFig. 1. The compositionof the main constituents of the 18 kinds of investigatedDAP resin plates is shown inTable 1. Diisopropyl peroxydicarbonate (IPP) was added at a concentration of 3% asa polymerizing initiator. The solution of DAP monomersmixed with IPP was poured into sandwich moulds, whichcomprised two parallel flat glasses and an elastic gasket.The moulds containing the mixture were placed an electricoven and treated at under-curing conditions. The period ofcuring was about 27h. The plates formed were colorless andtransparent.

Fig. 1. Three kinds of DAP monomers used in curing DAP resinplates.

2.2. Irradiation with fission fragments and alpha-particles

The plates were arranged horizontally parallel to an elec-trodeposited plane standard source of252Cf. The distancebetween the source and the plates was set at 3 or 10mm.The fluence of incident particles was calculated from thedistance, the disintegration rate and radius of the source, andthe irradiation time. Fission fragments and alpha-particleswere slowed down by air, and hit the surface.

2.3. Etching and observation of etch-pits

After irradiation, one group of plates was etched in a PEWsolution, which consisted of 15% KOH, 65% ethanol and20% water, and was maintained at 60◦C. The etching timewas from 2 to 30min. Another group of plates was etchedin an aqueous solution of 30% KOH at 90◦C. The etchingtime varied from 15 to 240min.After etching, the plates were immediately rinsed in

flowing cold tap water and dried in clean air. The shape ofthe etch-pits was observed, and the number of etch-pits wascounted using an optical microscope with a magnificationof ×400.

3. Experimental results

The extraction of the plates from the mould was some-times problematic. Seven good (crackless) plates wereformed which were 550mm× 550mm and 1.0mm thick.However, eight plates were slightly cracked and three oth-ers broke in to pieces when they were removed from themoulds. Cracking and breaking seemed to be caused bythe shrinking of plates during curing. The behavior of eachplate is shown inTable 1(a). The plates which contained theortho-type DAP monomer as the main constituents (ortho-based plates) and the m100 plate had a smooth finish withno cracking or breaking.

Ease in cutting also depended on the composition of theplates. Seven plates could be cut easily with a plastic cutter.In the case of other plates, however, there was some difficultyin cutting caused by brittleness. The ease or difficulty ofeach plate is shown inTable 1(b). The ortho-based platesand the m100 plate have good cutting properties, too.

Fig. 2shows the shape variation of etch-pits at successivestages of etching on the three kinds of plates which wereetched using the PEW solution.Fig. 3 shows etch-pits onthe nine kinds of plates etched using the PEW solution.Fig. 4 shows etch-pits on the 12 kinds of plates etchedin the aqueous solution. In the photographs ofFigs. 2–4,the distance between the source and the plates was 3mm.Profiles of etch-pits on each plate at each etching stage aresummarized inTable 1(c).

The correlation between etching time and etch-pit diam-eter is shown inFig. 5, which shows the results of the o100,m100 and p100 plates using the PEW solution. The pit

398 T. Tsuruta et al. / Radiation Measurements 40 (2005) 396–400

Table 1Composition and characteristics of the 18 kinds of plates

Name of plate Composition (wt%) (a) (b) (c)

Ortho Meta Para PEW sol. Aqueous sol.

4 8 15 30 60 120

o100 100 � � � � � © � �o90/m10 90 10 � � � � � © � �o75/m25 75 25 � � � � � © � �o50/m50 50 50 � � © � � © � �o25/m75 25 75 © © © � � © � �o10/m90 10 90 © © © � � © � �

m100 100 � � © � � © � �m90/p10 90 10 � � © � � © � �m75/p25 75 25 © � © � � © � �m50/p50 50 50 © � © � � © � �m25/p75 25 75 © © � � � © � �m10/p90 10 90 © © � � � © � �

p100 100 � � � � � © � �p90/o10 10 90 � � � � � © � �p75/o25 25 75 © � � � � © � �p50/o50 50 50 © © � � � © � �p25/o75 75 25 � � � � � © � �p10/o90 90 10 � � � � � © � �

(a) Behavior of the plate on removal out from the mould�: crackless,©: slightly cracked,�: broken to pieces.(b) Difficulty in cutting caused by brittleness�: easy,©: slightly difficult, �: difficult.(c) Profile of etch-pits (unit of etching time is min.)©: immature,�: clear,�: over-etched.

Fig. 2. Growth of fission tracks on three kinds of DAP resin plates,etched with PEW solution at 60◦C.

diameter increases linearly with etching time. The slope in-dicates the etching speed. The etching speeds of the o100plate are higher than those of the p100 and m100 plates.

From a comparison between the density of the etch-pitsand the fluence of incident particles, we realized that the de-veloped etch-pits were caused by fission fragments. The de-

Fig. 3. Fission tracks on nine kinds of DAP resin plates, etchedwith PEW solution at 60◦C.

tection efficiency of the fission fragments was almost 100%for all plates. Etch-pits caused by alpha-particles could notbe found in any plates under the above-mentioned etchingconditions.After irradiation, part of the o100, m100 and p100 plates

were placed in an oven for 1 h at temperatures ranging from

T. Tsuruta et al. / Radiation Measurements 40 (2005) 396–400 399

Fig. 4. Fission tracks on 12 kinds of DAP resin plates, etched withaqueous solution of 30% KOH at 90◦C.

Fig. 5. Relationship between etching time and etch-pit diameter inthe case of etching with PEW solution at 60◦C.

Fig. 6. Relationship between temperature of heat-treatment andtrack detection efficiency. Etching conditions : aqueous solution of30% KOH at 90◦C for 30–120min.

100 to 260◦C.As shown inFig. 6, the detection efficiency offission tracks was unaffected at temperatures below 240, 200and 140◦C for the o100, m100 and p100 plates, respectively.

4. Discussion

Three kinds of DAP monomers were cast into plates.Different mixtures of DAP monomers were cast in arbitraryratios and they all formed copolymer plates.

It was found that all of the 18 kinds of plates had adetection efficiency of about 100% for fission fragments,and were insensitive to alpha-particles. Therefore, all theseplates can be used as fission track detectors. However, whenanalyzing finish in curing, ease in cutting, etching speed andheat-resistance, the ortho-based plates were superior to themeta- or para-based plates as fission track detectors.

Solid-state nuclear track detectors are generally insensi-tive to low-LET radiation such as�, � and X-rays. Analysing�-ray exposures from 1kGy to 5MGy of the under-curedortho DAP plates, it was found that the detection efficiencywas unaffected below 1MGy (Tsuruta, 2001a). The PEWsolution develops fission-tracks on a smooth surface withoutdeveloping recoil tracks caused by fast neutrons (Yoshiokaet al., 2003).

In conclusion, the under-cured ortho-based plates weresuperior for the detection of fission fragments in the environ-ment, with a background of alpha-particles, fast and thermalneutrons, and low LET radiations. These characteristics areadequate for use in the core of nuclear reactors. In order toprevent higher radioactivity in muscovite caused by thermalneutron exposure, the ortho-based DAP resin plates can alsobe adopted as external detectors in fission-track dating.

Acknowledgements

The authors wish to express their thanks to Mr. O. Murata,Mr. M. Okamoto and Mr. K. Kobayashi of the YamamotoKogaku Co. Ltd., for their assistance in the developing DAPresin plates.

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