Indian J. Fhys. MA (5), 381-386 (1990)
Characterization of X-ray film base and overhead projector transparency as nuclear track detector
Swarnali Ghosh, AtuI Saxena*^ and K K Dwivedi
Departm ent of C h e m istry , N orth-Eastern H ill U n iversity, S h illo n g -7 9 3 0 0 3 , India
A b s t r a c t : In th e search for newer detector m aterials at low cost and easy p ro cu rab ility attem pts have been made to characterize X -ray film base and overhead p ro jecto r transparency. “* ’ C f so urce w a s used to irradiate the m aterials and the optim um etch in g co n d itio n s for both the detectors w ere determ ined.
T h e detecto rs w e re ch aracterised in term s of the different param eters of etched track s of ^“ '^Pb io n s and fis s io n fragm ents. T h e e f f e c t o f U V -ra d ia tio n prior to track registration in X -ray film b ase w a s also stu d ied .
K e y w o r d s ; “ ' C f so u rce . X -ray film b a se , overhead projector transparency, true track length, n uclear track d etectors.
P A C S N o s : 2 9 .4 0 .- n, 2 9 .7 0 . e
I . In tro d u c tio n
Low cost, uniformity, high sensitivity and easy availability of a dielectric material are some of the important factors which decide its ultimate utility as a nuclear track detector. Two types of plastics, viz. X-ray film base and overhead projector transparency, can be easily procured and employed as particle track detectors.
In the present work we have assessed the applicability of these two plastics as track detectors for ^'’ “Cf fission fragments and 17.1 MeV/u *°®Pb ions. The optimum conditions for track development have been determined in these detectors and the influence of UV-radiation on the X-ray film base have been studied.
These new detectors are also characterized in terms of maximum etchable track lengths of *** Cf fission fragments and *«*Pb ions. The experimental track lenghts are compared with theoretical values and the results are discussed.
1. Experimental
2.1.
P reparation o f detector foilsX-ray film base was prepared for use by first dipping ordinary X-ray films in hot concentrated NaOH solution. The gelatine layer was removed and a pale blue
^Present address : Department of Physics, Pachhunga University College, NEHU, Aizawl (Mizoram). India.
381
382
Swornali Ghosh AtuI Saxena and K K DwivediX-ray film base w as obtained. This w as then washed, dried and observed under the microscope for surface uniformity. Elemental analysis of X-ray film base was done. It w as characterized as cellulose acetate with the chemical composition C
10
H14
O , and density 1.30 g/ml. Small pieces (1 c m x1
cm) of X-ray film base (thickness 190 pm) were used for the present experiment.Transparent plastic sheets of overhead projector (PHOTOPHONE) have also been used for track registration and development. Small pieces
(1
cm x 1 cm) were cut from the triacetate roll of overhead projector transparency and examined under the microscope for surface texture. The surface w as found to be fairly smooth with no interfering background. This plastic has been characterized as cellulose triacetate (CgH^Oa) having density 1.08 g/ml. The averge thickness of the transparency foil w as ~
100
j«m.2.2. Irradiation
A 20 ng ®®®Cf source having an activity of ~
6
x 10® fission fragments w as used for irradiation of these detectors. The foils were mounted on a holder in such a w ay that the collimated ions were allowed to enter at an angle of 3 0 ’C with respect to the surface. An aluminium collimator (length » 9 mm) w as used for Irradiation w ith several holes of diameter1
mm each. The irradiation w as carried out in a vacuum desiccator for 15 mins. Several pieces of X-ray film base as well as the overhead projector transparency were irradiated in this manner. The X-ray film base w as also irradiated at 45'’ with 17.1 MeV/u Pb ions at U N ILA C, G S I Darmstadt. One sample w as pre-exposed to UV radiation for1
hr prior to irradiation by ®°»Pb beam,2.3. Etching conditions
The m ost suitable etching condition for X-ray film base w as found to be 2N NaOH at 5 5'C . For the overhead projector transparency (OPT) the best etching of fission fragment tracks w as found to occur in
6
N NaOH at 55 C . On etching for 9 0 minutes, fully etched tracks were obtained in overhead projector transparency irradiated by ®“®Cf source, w hile in 75 minutes fully etched tracks were obtained In X-ray film base. For X-ray film base irradiated wifh Pb beam at an energy of 17.1 MeV/u tracks were fully etched in 225 minutes. After etching the samples were washed, dried and the track lengths and diameters were measured w ith a Leitz 'Laborlux D' optical microscope at a magnification of 625X .2.4. Measurement a f track parameters
The etched tracks were found to be conical in shape and parallel to each other.
Projected track lengths were measured from end to end. The track diameters were also measured as the minor axes of the elliptical track face. About 200 tracks were
Characterization of X -ra y film base
etc 383
measured in each foil. The bulk-etch rate (Vg) w as determined by the track diameter method. It w as found to be 0 .0 1 1 7 /i^m/min for X-ray film base and 0.0146 /im/min for overhead projector transparency. The true track length was calculated from the projected track length (I) taking into account the surface etching corrections (A s). The true track length (L) w as calculated from the following equation (Dwivedi and Mukherji 1979).
L 1 + M
(1)cos <l> sin <f>
where tf> is the incident angle.
2.5. Computation
of track lengthA computer code 'RF' (Dwivedi 1988) w as used to calculate the track lengths of median light and median heavy fission fragments. The track lengths are first calculated in individual elemental constituents of complex material and then by Bragg's additivity rule the track length in complex media are computed. The values of mass, charge and kinetic energies of median light and median heavy fragments are taken from Schmitt et ol (1966) and are given in Table 1. Using these data
Table I. V a lu e s of th e m a s s , c h a rg e and e n erg y of th e m e d ia n lig h t and m e d ia n h e a v y fis s io n frag m en t p a rtic le s fro m ^ 'C f s o u r c e .
T y p e of p a rtic le M e d ia n lig ht M e d ia n h eavy
the most probable track lengths of fission fragments in X-ray film base and OPT were calculated from the followiug equation.
M a ss C h a rg e E n e rg y
1 0 8 .5 5 4 2 .5 5
IOe.2
M eV1 4 3 .4 5 5 5 .4 5 8 0 .3 M eV
< L > i-«f r +
(2
)where and L,f„ are the track lengths of median light and median heavy fragments respectively. The theoretical track langth for ’“""Pb ions w as calculated from the computer code 'RAN GE' (Dwivedi 1988) based on stopping power equations of Mukherji and coworkers (Mukherji and Srivastava 1974, Srivastava and Mukherji 1976, Mukherji and Nayak 1979).
3. Results and discussion
The X-ray film base detector w hich w as pre-irradiated with UV-radiation w as found to bend during the etching process. Therefore tracks due to 17.1 MeV/u ®°"Pb ions could not be measured. On the other hand, the UV-unexposed detector foil 7
384
SwarnallGhosh AtuI Soxena and K K
Dwlvedlrevealed narrow and well developed tracks on etching for 225 mins in 2N NaOH at 55°C. Figure
1
shows the track length distribution curve of ®®®Pb in X-ray film base. The maximum etchable track length w as found to be 213 ± 3.0 ^m for 17.1 MeV/u ®°«Pb ions. The corresponding theoretically calculated value fromT a b le 2 . Exp erim en tal and th e o re tica l v a lu e s o f th e m axi*
mum etch a b le tra ck len g th s o f ’ ' * C f f is s io n fra g m en ts in X -ray film b a se and o verhead p ro je c to r tra n sp a re n c y .
Nam e of th e m aterial
X -ra y film b a se O verh ead p ro ie cto r tra n sp are n cy
M axim u m e tch a b le tra c k length in ^m
E x p e rim e n ta l T h e o r e t i c * 1 9 .8 ± 2 . 1
2 3 .3 ± 1 . 9
2 0 .3 2 4 .7
* C a lc u la te d from co m p u ter co d e R F (D w iv e d i 1 9 8 8 ) .
the computer code RANGE (Dwivedi 1988) w as found to be 225 /im which is nearly 6% higher than the experimental value.
Projected lengths of fission fragment tracks were measured in X-ray film base detector. The maximum'etchable true track lengths were then obtained from eq (1).
2 0 8 p ^ in X ray-film base E = 1 7 1 M eV/u 4 0 | - < L> «2 13 0t3yjm
30
*20i Wh
HO 200 220
Track ie n g fh (/m l
240
F ig u r e I . T r a c k length d is trib u tio n c u rv e fo r 17,1 M e V / u i n X -ra y film b a s e d e te cto r. T h e m o st p ro b a b le tra ck length w a s fo u n d to be 2 1 3 ± 3 .0 y/m.
A track length distribution curve w as plotted and Is shown in Figure
2
. The most probable track length of fission fragments in X-ray film base w as found to be 1 9.8± 2.1 #rm. The theoretically calculated value from the computer code RF (Dwivedi 1988) w as found to be 20.3 pm. In the case of overhead projector transparency, the track length distribution is shown in Figure3
. The maximumCharacterization
of X-roy film
base etc385
etchable track length w as found to be 2 3 .3 ±
1.9
/xm. The theoretically calculated value Was found to be equal to 24.7 Aim.80
70
60 h
252 cf* fission frogm ints in X -r a y film base
< L> = 1 9 8 ^ m
50 -
J2
40 -
"o
» 30
I
2010 •
10 15 20 25 30
Track Length (>im)
F ig u r e 2 . H isto g ra m s h o w in g tra c k length d istrib u tio n of fis s io n fra g m e n ts in X - r a y film b a s e d e te cto r.
It has been observed that in these tw o track detectors the theoretical ranges of fission fragments are in fairly good agreement with the experimental values of maximum etchable track lengths.
2 S 2 ,
T
i t
I ,
4020 -
Cf fission fragments
m
Overhead Projector Transparency
<L>>23 3>jin
' 5 10 15 20 25 30
Track Length (>im)
Figure 3. Histogram showing track length distribution o f ’*'*Xf fission frag
ments In overhead projector transparency.
Earlier reported work (Dwivedi and Mukherji 1979) on ®*®Cf fission fragment tracks in mica, Lexan and cellulose acetate showed a good agreement of
386 Swarnoll Ghosh AtuI Soxeno
a n d K K D w lv e d lexperimental values with the theoretically calculated values from the stopping power equations of Mukherji and co-workers (Mukherji and Srivastava 1974, Srivastava and Mukherji 1976 and Mukherji and Nayak 1979). This indicates that the computer code RF (Dwivedi 1988) gives fairly reliable range and track length values of fission fragments in complex materials.
Acknowledgments
W e thank the staff of U N IL A C , G S I Darmstadt for irradiation of X-ray film base detector with ^°^Pb ions. W e are also grateful to the German Agency for technical cooperation (DGTZ), FRG for an equipment grant.
