Nuclear track detector kit for use in teaching

0191-278X/86 $3.00+.00 Pergamon Journals Ltd.

Nuclear Tracks, Vol. 12, Nos I-6, pp. 299-302, 1986. Int. J. Radiat. Appl. Instrum., Part D Printed in Great Britain.

N U C L E A R T R A C K D E T E C T O R KIT F O R USE IN T E A C H I N G

L° M e d v e c z k y W M. N a g y ~

and G. Somogyi ~

I n s t i t u t e of N u c l e a r Research, ~Reformed

G r a m m a r School,

Debrecen,

Debrecen,

Hungar~4OOl

Hungary

ABSTRACT By the use of s o l i d state n u c l e a r track d e t e c t o r s (SSNTDs) one may carry out s e v e r a l u s e f u l and i m p r e s s i v e e d u c a t i o n a l e x p e r i m e n t s and d e m o n s t r a t i o n s to i l l u s t r a t e d i f f e r e n t p h e n o m e n a w h e n t e a c h i n g of n u c l e a r physics. R e a l i z i n g this s i t u a t i o n the a u t h o r s have p u b l i s h e d , since 1970, reports on several e x p e r i m e n t s for t e a c h i n g d e m o n s t r a t i o n s . B a s e d on the authors i n s t r u c t i o n s , a factory in H u n g a r y (TAN~RT, N a t i o n a l M a n u f a c t u r e r s and S u p p l i e r s of School Equipment, Budapest) c o n s t r u c t e d a kit for the use of n u c l e a r track d e t e c t o r s in teaching. The p o r t a b l e kit contains the f o l l o w i n g items: a l p h a - e m i t t i n g w e a k sources, s o l i d state n u c l e a r track d e t e c t o r s (unirradiated, irradiated, u n e t c h e d and etched sheets),simple tools for c a r r y i n g out e x p e r i m e n t s (facilities for irradiation and e t c h i n g , etc.), slides s h o w i n g p h o t o s of typical e t c h - t r a c k s of light and h e a v y nuclei, user manual. By the h e l p of the kit both pupils and t e a c h e r s can p e r f o r m v a r i o u s useful e x p e r i m e n t s andlor d e m o n s t r a t i o n s . KEYWORDS N u c l e a r tracks; school d e m o n s t r a t i o n s ; e d u c a t i o n a l e x p e r i m e n t s ics; fission; a l p h a - r a d i o a c t i v i t y ; n u c l e a r track detectors.

in n u c l e a r phys-

INTRODUCTION The t e c h n i q u e of solid state n u c l e a r track d e t e c t o r s (SSNTDs) p r o v i d e s a u s e f u l m e t h o d in v a r i o u s fields of science and technology. The a p p l i c a t i o n of SSNTDs is e s p e c i a l l y useful in s i t u a t i o n s w h e r e the s t r e n g t h of e - r a d i o a c t i v e sources is r e l a t i v e l y low. This is the s i t u t a t i o n in schools, w h e r e the use of i n t e n s i v e sources is not a l l o w e d . The authors r e a l i z e d [ M e d v e c z k y and co-workers, 1970] that the e x c e l l e n t p r o p e r t i e s , cheapness and s i m p l i c i t y of SSNTDs p r o v i d e an o p p o r t u n i t y to carry out a n u m b e r of useful and i m p r e s s i v e e d u c a t i o n a l exp e r i m e n t s and d e m o n s t r a t i o n s to i l l u s t r a t e d i f f e r e n t p h e n o m e n a w h e n t e a c h i n g n u c l e a r physics. We have p u b l i s h e d d e t a i l e d d e s c r i p t i o n of the method, the f a c i l i t i e s and several e x p e r i m e n t s [Somogyi and c o - w o r k e r s 1971; M e d v e c z k y and c o - w o r k e r s 1972, 1973; N a g y and c o - w o r k e r s 1972]. The a p p l i c a t i o n s of SSNTDs w e r e put into p r a c t i c e in t e a c h i n g in several schools, but in the w i d e - r a n g i n g use of SSNTDs in school the t e a c h e r s had to face several special d i f f i c u l t i e s . They h a d no o t h e r choice but to collect, personally, all the m a t e r i a l s , facilities, r a d i o a c t i v e sources r e q u i r e d to the experiments. Such an a c t i v i t y demands m u c h time and s p o n t a n e i t y from the teacher. It was also a d r a w b a c k that o n l y part of the process could be a c c o m p l i s h e d d u r i n g a lesson. By u s i n g CR-39 track d e t e c t o r s the t e a c h e r s are able to c o m p l e t e now the w h o l e p r o c e s s of several e x p e r i m e n t s even d u r i n g a lesson in g r a m m a r schools. It w o u l d be a m i g h t y aid for b u s y t e a c h e r s to make all the special m a t e r i a l s , facilities for d e m o n s t r a tion in school c o m m e r c i a l l y available. Based on the author's i n s t r u c t i o n s a H u n g a r i a n factory of school e q u i p m e n t (TAN~RT) has c o n s t r u c t e d a p o r t a b l e kit for the use of n u c l e a r track d e t e c t o r s in t e a c h i n g (Fig.l). The kit contains w e a k a l p h a - e m i t t i n g sources, d e t e c t o r s , s p e c i a l tools for c a r r y i n g out the e x p e r i m e n t s , but does not contain m a t e r i a l s and o t h e r simple f a c i l i t i e s (e. g. 299

300

L. MEDVECZKY et aZ.

chemicals, heater, m i c r o s c o p e ) since these can be found in the c o l l e c t i o n of p h y s i c a l a p p a r a t u s of any a v e r a g e school. By the h e l p of the kit both p u p i l s and t e a c h e r s can p e r f o r m a n u m b e r of u s e f u l e x p e r i m e n t s a n d / o r d e m o n s t r a t i o n s . In this r e p o r t a d e s c r i p t i o n of the c o m p o n e n t parts of the n u c l e a r t r a c k d e t e c t o r kit is g i v e n t o g e t h e r w i t h a list of school d e m o n s t r a t i o n s and e d u c a t i o n a l e x p e r i m e n t s that can be p e r f o r m e d w i t h it. COMPONENT

PARTS

OF THE KIT

R a d i o a c t i v e sources. The kit c o m p r i s e s t h r e e w e a k a l p h a - e m i t t i n g sources such as: - A m e r i c u m - 2 4 1 w i t h an a c t i v i t y of about 2.5-3 kBq d e p o s i t e d on a p r e c i o u s m e t a l disk . The disk is m o u n t e d on a m e t a l s e t t i n g and s t o r e d in a c l o s e d p l e x i g l a s s box. - T h o r i u m c o n t a i n i n g gas m a n t l e fixed on a m e t a l plate. 2 - A l p h a - e m i t t i n g rock sample on a m e t a l p l a t e w i t h an area of about 2-3 cm and 0.2 cm thickness. The s o u r c e s are safe to h a n d l e and r e q u i r e no licence.

Fig.l. N u c l e a r t r a c k d e t e c t o r and its c o m p o n e n t parts I

kit

Detectors. The kit c o n t a i n s u n i r r a d i a t e d , i r r a d i a t e d , u n e t c h e d and e t c h e d trac k d e t e c t o r s . The 14 u n i r r a d i a t e d sheets are M O M - A T O M K I n u c l e a r t r a c k detectors, type M A - N D / a (special sheet cast from CR-39 monomer) in two sizes (ix2 and 2x3 cm 2) c o a t e d w i t h a p r o t e c t i v e p l a s t i c sheet. The i r r a d i a t e d and e t c h e d d e t e c t o r s m o u n t e d on slides are ready for d e m o n stration. T h r e e of t h e m are a u t o r a d i o g r a m s of the t h r e e r a d i o a c t i v e sources c o n t a i n e d in the kit. T h r e e d e t e c t o r s are of type M A - N D / e , one is i r r a d i a t e d w i t h a l p h a p a r t i c l e s , a n o t h e r w i t h f i s s i o n f r a g m e n t s and the t h i r d w i t h fast neutrons. T h e r e are two m u s c o v i t e m i c a d e t e c t o r s i r r a d i a t e d w i t h a C f - 2 5 2 s o u r c e and e t c h e d for s i g n i f i c a n t l y d i f f e r i n g times. The n i n t h of the e t c h e d d e t e c t o r s is a g l a s s one i r r a d i a t e d w i t h a C f - 2 5 2 source. T w o sorts of i r r a d i a t e d but u n e t c h e d M A - N D / ~ type d e t e c t o r s are s u p p l i e d to the kit. Five s a m p l e s are i r r a d i a t e d w i t h f i s s i o n f r a g m e n t s and the o t h e r five w i t h fast neutrons.

I The nuclear track detector kit for use in teaching is produced by the Hungarian factory T k N ~ , National Manufacturers and Suppliers of School Equipment, Budapest (P.O.Box 2, H-1428) and orders should be adressed to KULTURA H ~ g a r i ~ Foreign Trading Company for Books and Newspapers, Budapest (P.O.Box 149, H-1389). The MOM-ATCMKI nuclear track detector, Type MA-ND/a (special sheet cast from CR-39 moncmer), as additional supply to the kit is also available frcm the manufacturer and/or KL~TURA Foreign Trading Ccrmpany.

NUCLEAR TRACK DETECTOR KIT

301

S p e c i a l tools for c a r r y i n g out e x p e r i m e n t s . F a c i l i t i e s for exposure. The kit c o n t a i n s s p e c i a l tools and f a c i l i t i e s for a l p h a - i r r a d i a t i o n and the e t c h i n g of the d e t e c t o r s . Two s i m p l e f a c i l i t i e s (Fig.2) p r o v i d e s e v e r a l opport u n i t i e s to e x p o s e the d e t e c t o r s to the A m - 2 4 1 source in air. For m a k i n g the i r r a d i a t e d area a s t e n c i l - p l a t e and a s c r a t c h - a w l are also s u p p l i e d to the kit.

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Fig.2. S c h e m a t i c side v i e w of the e x p o s u r e f a c i l i t i e s for ~ - p a r t i cles in air e n v i r o n m e n t .

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Fig.3. S e t - u p of the f a c i l i t y for radon level m e a s u r e m e n t .

For the d e m o n s t r a t i o n of a l p h a - r a d i o a c t i v i t y p r e s e n t in soil, w a t e r or air a m e t a l cup and o t h e r s m a l l e r n e c e s s a r i e s of the e x p e r i m e n t (e.g. h e a t - i n s u l a t i n g facing, b e a r i n g - c l i p s , tape etc.) are found in the kit (Fig. 3). F a c i l i t i e s for etchinq. The e t c h i n g of d e t e c t o r s is g e n e r a l l y p e r f o r m e d in a thermostat. In s c h o o l d e m o n s t r a t i o n s there is no n e e d to apply as a c c u r a t e e t c h i n g c o n d i t i o n s as in r e s e a r c h work, but it is e s s e n t i a l to p e r f o r m e t c h i n g d u r i n g a lesson. T h a t can be done by i n c r e a s i n g the t e m p e r a t u r e of the e t c h i n g solution. For M A - N D / e type d e t e c t o r s one can o v e r c o m e this d i f f i c u l t y if e t c h i n g is c a r r i e d out at the t e m p e r a t u r e of b o i l i n g water, b e c a u s e the bulk etch rate of this d e t e c t o r is about iO um/h at this t e m p e r a t u r e [Somogyi and Hunyadi, 1980 The kit also contains a glass b e a k e r w i t h a metal cover-disk. The cover serves as s u p p o r t for two test tubes for the e t c h a n t and a t h e r m o m e t e r . The r e q u i r e d stoppers, small boxes and wires for h a n g i n g the d e t e c t o r s in the e t c h i n g s o l u t i o n are e n c l o s e d w i t h the p o r t a b l e kit. A small r e c i p i e n t in the kit serves for e t c h i n g micas in HF solution. S I M P L E E X P E R I M E N T S W I T H THE KIT A m o n g the a c c e s s o r i e s of the kit there is a user m a n u a l too, c o n t a i n i n g the f o l l o w i n g items: list of the a c c e s s o r i e s and f a c i l i t i e s of the kit, safety r e g u l a t i o n s , i n t r o d u c t o r y i n f o r m a t i o n about SSNTDs, list of slides and e x p l a n a tory n o t e s of photos s h o w i n g typical e t c h - t r a c k s of light and heavy nuclei, i n s t r u c t i o n s to p e r f o r m d e m o n s t r a t i o n s and e x p e r i m e n t s using the kit. D e m o n s t r a t i o n @ using the a l p h a sources of the kit. A d e t e c t o r is p l a c e d in close contact w i t h A m - 2 4 1 s o u r c e of the kit for a m e a s u r e d time interval. The s t r e n g t h of the source is d e t e r m i n e d by c o u n t i n g tracks [Bull, 19801. On exp o s i n g the d e t e c t o r s to the Am source in 2~ g e o m e t r y only for a few m i n u t e s , the i r r a d i a t e d area b e c o m e s o p a q u e a f t e r etching, and the r a d i a t i o n d a m a g e p r o d u c e d by charged p a r t i c l e s is o b s e r v a b l e w i t h the naked eye. S i m i l a r autor a d i o g r a m s can be p r e p a r e d w i t h the o t h e r two sources too, but with e x p o s u r e times of a few days or weeks. The a u t o r a d i o g r a m s , at the same time, show the l o c a l i z a t i o n of s - r a d i o a c t i v e nuclei. There are m a n y p o s s i b i l i t i e s of e x p e r i m e n t s u s i n g the e x p o s u r e facilities and the Am source. The i r r a d i a t i o n of an M A - N D / e type d e t e c t o r in a p o s i t i o n as shown in Fig. 2a, gives q u a l i t a t i v e i n f o r m a t i o n about the range of alpha p a r t i c l e s in air. We can get i n f o r m a t i o n on the range of alphas in air if a n u m b e r of d e t e c t o r s are i r r a d i a t e d to the same m e a s u r e with the Am source in the slits of the d i s t a n c e a d a p t e r (Fig. 2b) and the track d e n s i t i e s are counted.

302

L. MEDVECZKY et al.

In this w a y we can also get i n f o r m a t i o n on the a b s o r p t i o n of c h a r g e d particles. At longer i r r a d i a t i o n d i s t a n c e s the t r a c k d e n s i t i e s are s m a l l e r but the t r a c k d i a m e t e r s are l a r g e r w i t h the d e c r e a s e of e n e r g y if the e t c h i n g c o n d i t i o n s are the same. For the study of alpha a b s o r p t i o n a l u m i n i u m and p l a s t i c foils are also s u p p l i e d to the kit. It is a very i n s t r u c t i v e e x p e r i m e n t w h e n an a l u m i n i u m foil (6 mg cm -2) w i t h a t y p e w r i t t e n text on it is used as absorbent. The alpha particles r e a c h the detector, p e n e t r a t i n g t h r o u g h the a l u m i n i u m foil, but the t h i c k n e s s of the a b s o r b e r is not u n i f o r m due to the d e f o r m a t i o n s made by the t y p e w r i t e r , so the text can be read after etching. E x p e r i m e n t s using the i r r a d i a t e d detectors. The i r r a d i a t e d d e t e c t o r s of the kit p r o v i d e p o s s i b i l i t i e s of e x p e r i m e n t s w i t h tracks of p a r t i c l e s not a v a i l a b l e for schools. W h e n o b s e r v i n g w i t h m i c r o s c o p e an e t c h e d M A - N D / a d e t e c t o r i r r a d i a t e d w i t h a Cf-252 source, the tracks of f i s s i o n p r o d u c t s and alpha p a r t i c l e s can be seen s i m u l t a n e o u s l y . By c o u n t i n g both types of tracks and k n o w i n g the h a l f - l i f e of alpha decay, the h a l f - l i f e of the s p o n t a n e o u s f i s s i o n of C f - 2 5 2 can be estimated. In order to have a good s t a t i s t i c the tracks must be c o u n t e d in a large n u m b e r of fields of view. The i r r a d i a t e d but u n e t c h e d d e t e c t o r s of the kit serve for that purpose. S i n c e two f i s s i o n f r a g m e n t s are e m i t t e d in each fission d e c a y event, the m e a s u r e d ratio of alnha tracks to f i s s i o n tracks w i l l be r o u g h l y half of the real value of a - d e c a y to f i s s i o n events. B e s i d e s t r a c k s of r e c o i l n u c l e i one can o b s e r v e t h r e e - p r o n g e d e v e n t s in the d e t e c t o r s i r r a d i a t e d by fast neutrons. T h e s e are the results of 1 2 C ( n , n , ) 3 a n u c l e a r r e a c t i o n s and the d e m o n s t r a t i o n of this type of a n u c l e o n i n t e r a c t i o n is a u n i q u e p o s s i b i l i t y in the school. O b s e r v a t i o n of environmental a l p h a - r a d i o a c t i v i t y . The p u p i l s of a d v a n c e d and s p e c i a l classes can p e r f o r m m e a s u r e m e n t s on a - e m i t t i n g r a d i o n u c l i d e s p r e s e n t in the e n v i r o n m e n t . The f a c i l i t i e s n e e d e d for the e x p e r i m e n t s are found in the kit and the m a n u a l gives all the n e c e s s a r y information. The m e a s u r e m e n t of a l p h a - r a d i o a c t i v i t y in the o u t d o o r and i n d o o r air of dwellings, caves, in different soils and in the d i f f e r e n t s e a s o n s of the y e a r may be very i n s t r u c t i v e for the pupils. The e x p e r i m e n t s listed above are only e x a m p l e s from the n u m e r o u s p o s s i b i l i t i e s p r o v i d e d by the kit in its p r e s e n t c o m p o s i t i o n since the u t i l i z a t i o n of the f a c i l i t i e s d e p e n d s on the local r e q u i r e m e n t s and, above all, on the i n g e n u i t y and a m b i t i o n of the users. REFERENCES Bull, R.K. (1980). The use of s o l i d state track d e t e c t o r s in teaching-I. Nucl. T r a c k s 4, 59-66. M e d v e c z k y , L . , G. S o m o g y i and M. N a g y (1970). D e m o n s t r a t i o n s using solid state track detectors. Proc. XIII N a t i o n a l C o n f e r e n c e of H u n g a r i a n School T e a c h e r s of P h y s i c s , D e b r e c e n 9-11 April. pp. i-iO (in Hungarian) M e d v e c z k y , L . , G. S o m o g y i and M. N a g y (1972). A p p l i c a t i o n of solid state t r a c k d e t e c t o r s in t e a c h i n g of r a d i o a c t i v i t y . A F i z i k a T a n i t ~ s a ii, 48-51 (in Hungarian). M e d v e c z k y , L . , M. Nagy, and G. S o m o g y i (1973). Some e d u c a t i o n a l e x p e r i m e n t s w i t h d i e l e c t r i c t r a c k detectors. I s o t o p e n p r a x i s 9, 224-227. Nagy,M., L. M e d v e c z k y and G. S o m o g y i (1972). D e m o n s t r a t i o n of n u c l e a r fission in s c h o o l education. A F i z i k a T a n i t ~ s a ii, 173-179 (in H u n g a r i a n ) . S o m o g y i , G . , L. M e d v e c z k y and M. N a g y (1971). Solid state n u c l e a r track d e t e c t o r s in s c h o o l education. F i z i k a i Szemle, 21, 344-354 (in Hungarian). Somogyi, G. and I. H u n y a d i (1980). E t c h i n g p r o p e r t i e s of the CR-39 p o l y m e r i c n u c l e a r t r a c k detector. S o l i d State N u c l e a r T r a c k D e t e c t o r s , Proc. iOth Int. Conf., Lyon, P e r g a m o n Press, pp. 443-452.