Channeling of 1.65 GeV 132Xe in mica

0191-278X/89 $3.00 + .o0 Pergamon Pressplc

Nucl. Tracks Radiat. Meas., Vol. 15, Nos. 1-4, pp. 349-352,1988 Int. J. Radiat. Appl. Instrum., part D

Printed in Great Britain

CHANNELING OF 1.65 GeV

132Xe IN MICA

SWARNAL1 GHOSH, ATUL SAXENA and K K DWIVEDI

Department of Chemistry) North-Eastern Hill University) Shillong 793 003) India

Abstract

- Crystalline track detectors such as muscovite mica has been

used to study channeling effects of 1.65 GeV 132Xe ions. Samples of mica were exposed to c o l l i m a t e d beam of

132Xe ions at different angles with

respect to the detector surface. Controlled chemical etching was performed in order to develop latent tracks in mica. Distributions of maximum etchable track lengths were obtained for

three incident angles and most probable

track lengths have been found in each case. It has been observed that the most probable track length of 132Xe ion in mica increases with the

incident

angle. This observation clearly indicates that Xenon ions undergo channeling in mica at higher angles whereas the effect of blocking seems to be operative at lower angles. The experimental results are discussed in terms of lattice structure of muscovite m i c a .

1. INTRODUCTION

Experimental evidence for the existence of channeling phenomenon has now become particularly widespread. Channeling effects for heavy ions such as Krypton and Iodine have been observed upto energy as high as 150 MeV. Most of the experimental work on channeling was confined to low mass particles in single crystals and amorphous solids involving ion implantation technique. But in the case of energetic heavy ions where the t o t a l penetration depth is of the order of hundreds of micrometers) the process of electrochemical stripping for range determination becomes tedious and time-consuming. Presumably due to this fact heavy ion channeling studies in Gev range bas not been carried out. Nuclear track technique is found particularly useful in studying channeling effects in inorganic crystals such as micas. In the present work we have studied channeling of 1.65 GeV 132Xe ions in muscovite mica in terms of maximum etchable track lengths .

2. E X P E R I M E N T A L

Background free samples of muscovite mica (thickness*~500 /Jm) were exposed to well collimated beam of 1.65 GeV 132Xe ions at UNILAC) GSl) Darmstadt. These irradiations were done cisely

at pre-

known angles of 30 ° ) 45 ° and 60 ° w i t h respect to the detector surface. An optimum ilux

of I04cm -2 was used to avoid overlapping of tracks. Mica detectors were then etched in 20%.HF at 50°C successively for periods of 30 minutes. A f t e r every etching the samples were thoroughly washed, dried and then examined under the microscope for tracks. The total etching time taken was 90 minutes after which rounded track-tips were observed. The projected track lengths of more than hundred tracks were then measured for each case with the help of an optical microscope and the true maximum etchable track lengths were obtained for three incident angles using equations given by Dwivedi and Mukherji I 15:1/4-x

349

350

S. G H O S H et al.

3. STRUCTURE OF MICA Muscovite mica - KAJ2(OH)2Si3AIOI0 (sp.gr. 2.68 g / m l ) is a silicate with layer or sheet type of structure. Fig. I (a) shows typical sheet-like silicon-oxygen networks and a cross-sectional view of the sheet is shown in Fig. l(b). Muscovite mica consists ol composite layers built ol two siliconoxygen layers (Fig. I(b)) combined w i t h two layers of hydroxyl groups bound to them by Al atoms. Fig. 2(a) shows such a complex layer in elevation and a simple two dimensional picture is given in Fig.2(b). The replacement ol one-quarter of the Si gives negatively charged layers which are then interleaved with K + ions. In muscovite mica~ the potassium ions occupy large holes between twelve oxygen atoms so that K-O bond strength remains only one-twelfth. These bonds are easily broken and the micas accordingly posess very perfect cleavage along the layers. It is clear from Figs. 1 and 2, that muscovite mica has more open structure perpendicular to the surface.

(o}

(b)

F i g . I . Typical sheet like silicon-oxygen networks in mica, (a) hexagonal arrangement of SiO~ tetrahedra and (b) a cross-sectional view of same sheet.

CHANNELING

O F 132Xe IN M I C A

351

0 S; )+ OH )~OH

Si 0

Fig. 2(b)

Fig.2 (a) Fig.2.

A composite layer of muscovite m i c a (O-Si-O(OH)-AI-O(OH)-Si-O)

shown (a) in elevation

and (b) in a sJmlde two dimensional network.

4. RESULTS AND DISCUSSION

Distribution of track lengths of 132Xe ions entering at three different angles in muscovite mica has been shown in Fig.3. The most probable track lengths are found to be 96. l) tJm, 103.5 IJm and 112.0 iJm for incident angles of 30% z)5° and 60 ° respectively. The theoretical track length of 1.65

I

'

I

I

132Xe in MICA

If)--

~=. 45"

~=30" (/)

'

K L>=103.5 urn

< L• = 9 6 . / , pm

{ E =1.65 GeV)

¢= 60" /.5>=112.0 pm

(3 o <~ no I--LL

0 EE iii o r n L~ :E Z

0

9O

J

I

100 TRACK

Fig.3.

110 LENGTH

120 (pro)

Distribution of t r a c k lengths of 132Xe ions incident at d i f l e r e n t angles in muscovite mica.

352

S. G H O S H et al.

GeV 132Xe in mica is 102.74 pm as calculated from computer code 'DEDXT '2 based on stopping= power equations of Mukherji and coworkers. 3-5. This theoretical value is quite comparable to measured value :[or 45% It is observed that the penetration depth of 132Xe in mica increases with the increase in incident angle. This finding indicates that xenon ions undergo channeling at higher angles which is evident from the open crystal structure of mica as shown in Figs I and 2. At lower angles, the passage of xenon appears to be comparatively blocked. 5. C O N C L U S I O N

The present work has shown that the nuclear track technique is quite suitable for studying heavy ion channeling in mica. This technique has certain advantages over other conventional methods as it is simple, fast and requires very low doses (104cm-2). Also, the channeling of very high energy ions can also be studied by track method. The only disadvantage of this technique is that it can not be used for metals and amorphous solids. More comprehensive experiments may be performed with different heavy ions in other crystalline solids before accepting nuclear track technique as a convenient tool for studying heavy ion channeling. ACKNOWLEDGEMENTS We wish to thank Dr. G. Fiedler for his cooperation. We appreciate the help from Dr. R. Spohr, Dr. 3. Vetter and UNILAC staff for sample irradiation at GSI, Darmstadt. Equipment grant from German Agency for Technical Cooperation (DGTZ) and DAAD, Bonn is gratefully acknowledged. REFERENCES

I.

K.K. Dwivedi and S. Mukherji, Nucl. Instrum. and Meth., 161, 317 (1979).

2. K.K. Dwivedi) 'A Program for Computation of Heavy Ion Ranges, Track Lengths and Energy-Loss Rate in Elemental and Complex Media', 14th Int. Conf. on SSNTD, Lahore (1988). 3. S. Mukherji and B.K. Srivastava) Phys. Rev., Bg) 3708 (1974). 4. B.K. Srivastava and S, Mukherji) Phys. Rev.) AI4) 718 (1976). 5. S. Mukherji and A.K. Nayak, Nucl. Instrum. and Meth., 159, t~21 (1979).