Nucl. Tracks Radiat. Meas., Vol.20, No. 3, pp. 511-519, ht. J. Radiat. Appl. Instrum., Part D
1992 0
0735-245X/92 $5.00 + .OO 1992 Pergamon Press Ltd
Printed in Great Britain
SHORT
COMMUNICATION
PROPERTIES OF COMPANY CR-39
ON REGISTRATION
INTERCAST
A.N.GOLOVCHENKO Joint
Institute
for Nuclear
Research,
Dubna, Laboratory of Nuclear 101000 Moscow, Russia
Reactions,
P.O. Box 79,
(Received 18 December 1991) Abstract-The CR-39 response function, V(REL,), has been determined by using the accelerated particles of intermediate (*H, “He, ‘*C, 160, “Ne and 4oAr) and relativistic (‘sF) energies. The irradiated detectors were etched in 6 N NaOH kept at 70°C. It has been shown that the response curve can be expressed in the REL,, range under investigation (from ~0.03 MeV cm2 mg-’ to z 10.3 MeV cm* mg-‘) as follows: V(REL,,)
=
I + a,’ REL&, + a,.REL$,,
1. INTRODUCTION
THE SOLID STATE nuclear track detector, CR-39, made from the organic compound poly(allyldiglicol)carbonate (Cartwright et al., 1978) has been found to have a wide application in numerous fields because of its high sensitivity to charged particles. For the detection and identification of an unknown particle by a given detector one should know its response to particles of known charge and energy. Nowadays one of the track formation models, called the REL-model (REL-restricted energy loss) (Benton and Nix, 1969), more or less satisfies the experimental data. By following this model a simple relation between the etch rate ratio, I’( V = VT/ VB), where VT is the track etch rate, V, is the bulk etch rate, and REL has been found as follows: V = 1 + a .RELB (Somogyi et al., 1976). However, the function of the above form can be utilized in the limited REL range because the CR-39 response curve has two distinct regions, low and high ionization regions (e.g. Khan et al., 1983). The coefficients c(and B are different for each of them. This short paper presents results on the response of CR-39 which can be described by a function composed of two power terms.
2. EXPERIMENTAL
DETAILS
The CR-39 samples, with a thickness of about 1.4 mm, were cast by the Intercast Company of Parma (Italy). Table 1 gives the experimental conditions for the present investigation. The particle energies, with the exception of “F, were degraded by means of aluminium foils. The detectors were etched NT *o/s,
in 6 N NaOH at 70” f 1“C for sufficient time to allow measurement of the track parameters with suitable accuracy. A semiautomatic image analyser manufactured by MOP-Videoplan (Austria), combined with an optical microscope (Carl Zeiss, Jena, Germany), was used for track parameter measurements. The bulk etch rate, Ve, was determined by two independent methods: track diameter measurements of highly ionizing particles, and mass measurement before and after etching. It is worth noting that there is a good possibility for precise determination of V, by the above-mentioned methods (Henke et al., 1986). Firstly, taking into account the condition that VT % Ve, one can use the following relation (Somogyi and Szalay, 1973)
where D,, is the track diameter of normally incident 40Ar ions at the Bragg peak and t is the etching time. Secondly, the other method is based on the measurements of sample masses before and after etching. We have used a sample of 3 x 4cm* in size and the analytical balance accuracy was 0.05 mg. In order to remove the absorbed moisture a sample was kept in a desiccator for a few days before and after etching. The following results were obtained: Ve = 1.15 f 0.02 pm h-’ by using track diameter measurements and V, = 1.16 k 0.06 pm h-’ by using the weight method. It is clear that both values are in good agreement. The etch rate ratio, V, was determined by track diameter measurements of normally incident particles as well as track length measurements in oblique geometry of irradiation. One should note that the 517
A. N. GOLOVCHENKO
518
Table 1. Experimental conditions of the present investigation
Particle 2H “He r ‘2C I60 20Ne 40Ar ‘9F
Maximal energy of particle E (MeV nucl-‘)
Source of irradiation
Cyclotron y-200
9.1
Cyclotron y-400 Synchrophasotron
13.1 3200
Angle of incidence with respect to the detector surface 13(deg.) 90 90 90 and 45 45 45 90 and 30 90
All the irradiations were performed at JINR, Dubna, Russia.
method of diameter measurement is practical for use at V 5 3; for I’ 2 3 this method is unacceptable, so measurements of skew track lengths should be used (Somogyi et al., 1976).
INTERCAST
The etch rate ratio, P’, for *H, 4He, 12C and 19F was determined from the following relation (Fleischer et al., 1975) v=
1 +(D/2.V,.t)2
(2)
1 - (O/2. v,. ty
where D is the track diameter of a normally incident particle. For ion tracks 12C, I60 and 2oNe, incompletely etched to the end of the range, entering the detector at an angle of 45”, and totally etched ion tracks @Ar, with rounded tips, entering the detector at an angle of 30” relative to the detector surface,
V-values were determined from measurement of track lengths, according to Henke and Benton (1971). REL values were calculated by the method of Henke and Benton (1968) using w. = 200 eV (w. is the maximum energy of knock-on electrons). 3. RESULTS AND DISCUSSION In Table 2, examples of V value determination for carbon tracks entering the detector normally and at an angle, are presented. The etching was carried out for the same period-l0 h. V values obtained by length measurements are significantly higher than V values obtained by measurement of diameters. Thus, for plotting of the response curve starting from carbon, only the V values determined by track lengths were taken into account. In Fig. 1 the reduced etch rate ratio, V - 1, vs REL,, , is presented. The experimental results were
lo-‘-
“‘1”‘1 10 +
“““1 10 -’
“lWL 10
1
J
RELoo (MeV.cm?mg-‘) FIG. 1. The reduced etch rate ratio, V - 1, vs REL,: the points are the experimental values and the solid line is produced
by formula
(3).
q = 2.955, /I, = 1.068, x2 = 0.047 and where f12= 3.371. One should note that the etch rate ratio changes together with the decrease of ion velocity in plastic. That is why, in the case of track length measurements, the REL,, values were calculated to the point at a half track length relative to the unetched surface of the detector. One should also note that the CR-39 detector of the Intercast Company is more stable to vacuum conditions of irradiation in comparison with detectors of other producers (Golovchenko and Tretyakova, 1992). This important characteristic favours the given detector, as experiments with heavy ions are often carried out in vacuum.
best fitted by the following function V = 1 + CL,. REL&, + CL~. REL&,
(3)
Table 2. Examples of V-value determination for carbon tracks entering the detector normally and at an angle &eV nucl-‘) 9.1 7.0 9.1 6.9 *uy is a standard
Method of V determination
VfU”’ 2.42f0.11 3.06 k 0.19 4.44kO.13
e =45”
5.69+0.15 deviation
By track diameters 0=90” By track lengths
from
the mean value of V.
4. CONCLUSION In this paper the response function of the CR-39 detector of the Intercast Company is determined in a wide range of ionization conditions. The results obtained allow further particle identification to be carried out. Acknowledgements-The
author expresses appreciation Dr V. Bradnova for detector irradiation with F-ions Dr S. P. Tretyakova for her attention to the paper valuable remarks.
to and and
REGISTRATION
PROPERTIES
OF INTERCAST
REFERENCES Benton E. V. and Nix W. D. (1969) The restricted energy loss criterion for registration of charged particles in plastics. Nucl. Instrum. Meth. 67, 343-341. Cartwright B. G., Shirk E. K. and Price P. B. (1978) A nuclear-track-recording nolymer of unique sensitivity and resolution. Nucl. %&&. Meth. 153, 457-460. Fleischer R. L.. Price P. B. and Walker R. M. (1975) Nuclear Tracks in’&&& p. 50. University of California Press, Berkeley. Golovchenko A. N. and Tretyakova S. P. (1992) Registration properties of different types of CR-39 in vacuum conditions of irradiation. Nucl. Tracks Radial. Meas. 20, 521-523.
Henke R. P. and Benton E. V. (1968) Charged particle tracks in polymers: No. 5-A computer code for the computation of heavy ion range-energy relationships in any stopping material. U.S. Naval Radiological
COMPANY
CR-39
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Defense Laboratory, San Francisco, Report USNRDL-TR-67-122. Henke R. P. and Benton E. V. (1971) On geometry of tracks in dielectric nuclear track detectors. Nucl. Instrum. Meth. 97, 483-489.
Henke R., Ogura K. and Benton E. V. (1986) Standard method for measurement of bulk etch in CR-39. Nucl. Tracks Radial. Meas. 12, 307-310.
Khan H. A., Brandt R., Khan N. A. and Jamil K. (1983) Track-registration-and-development characteristics of CR-39 plastic track detector. Nucl. Tracks Radiat. Meas. 7, 129-139.
Somogyi G., Grabisch K., Schemer R. and Enge W. (1976) Revision of the concept of registration threshold in plastic track detectors. Nucl. Instrum. Meth. 134, 129-141.
Somogyi G. and Szalay S. A. (1973) Track-diameter kinetics in dielectric track detectors. Nucl. Instrum. Merh. 109, 21 l-232.