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Study on the effect of NaOH concentration and etchingduration on some properties of g-irradiated PADC

T.M. Hegazy a, M.Y. Shoeib b,*, G.M. Hassan b

aDepartment of Physics, Women’s College, Ain Shams University, Cairo, EgyptbBasic Science Department, Modern Academy for Engineering & Technology in Maadi, Cairo, Egypt

a r t i c l e i n f o

Article history:

Received 30 July 2012

Accepted 5 December 2012

Available online 13 September 2013

Keywords:

CR-39

g-Dose

Etchant concentration

Bulk etch rate

Track density

Surface damage

* Corresponding author.E-mail address: drmarwashoeib@hotmail

Peer review under the responsibility of Ben

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a b s t r a c t

In the present study the dependence of both the bulk etch rate for Solid state nuclear track

detectors (SSNTD) on etching time and the removal thickness percentage on etchant

concentration of the NaOH solution and etching time have been studied for CR-39 detector

irradiated with 0, 10, 50 and 100 (kGy) g-ray. The dependence of track density on the

etchant concentration of NaOH solution for CR-39 samples irradiated with doses of 0, 10, 50

and 100 (kGy) g-ray at constant etching time has also been studied. The damage on the

samples surface due to irradiation with different g-dose was determined and noticed with

electronic microscope.

Copyright 2013, Beni-Suef University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction and diethylene glycol groups into a dense 3D network with an

Solid state nuclear track detectors (SSNTD) are used widely in

several technical applications for the detection of charged

particles from protons to heavy ions, as well as the simple

registration of the particle flux density or the fluencies in the

environmental dosimetry (Hermsdorf et al., 2007). The CR-39

detector is a commonly used solid-state nuclear track detec-

tor (SSNTD). In the present study, CR-39 plastic (Allyl diglycol

carbonate) has been chosen as detector which consists of

short polyallyl chains joined with links containing carbonates

.com (M.Y. Shoeib).

i-Suef University

sevier

13, Beni-Suef University.

initiating monomer unit as given below:

(CH2-CH-CH2-OCOO-CH2-CH2-O-CH2-CH2-OCOO-CH2-CH-

CH2) (Cartwright et al., 1978; Ambika et al., 2011).

Light and penetrating radiations represent important

physical action on polymers which is capable of including

chemical reactions in them. This causes deep changes in the

chemical structure of polymers, and consequently in their

physical and mechanical properties. A series of chemical

transformations develops causing the degradation, cross

linking, detachment of side groups, and other chemical

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b e n i - s u e f u n i v e r s i t y j o u r n a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 3 6e4 0 37

changes in the polymer macromolecules. Deep chemical

changes occur in polymers under the action of ionizing radi-

ations, regardless of their kind. Such radiations can, therefore,

break bonds in a chain, but this does not always occur because

of the redistribution and dissipation of energy (Kuleznev and

Shershnev, 1990). These radiations do not themselves make

tracks but can have significant and sometimes profound effect

on the properties of track recorders (Durrani and Bull, 1987).

In recent years, the modification of polymers using radia-

tion has been largely used to modify the chemical and phys-

ical properties of polymers. These modifications are called

radiation processing. The effect of radiation on polymers de-

pends not only on the polymer structure but also upon the

characteristics of the radiation source, namely type and en-

ergy of radiation species. Then careful selection of radiation

processing conditions can result in significant improvements

of material properties, including mechanical, thermal and

many others (Cleland et al., 2003).

When ionizing particle passes through a plate of plastic, it

produces a latent track as a result of damage caused by the

energy deposition of the particle. This track can be made

optically visible by means of chemical etching. Two simulta-

neous etch rates control the development of conical etch pits:

the general etch rate (Vb), which removes the bulk of material

isotropically, and the track etch rate (Vt), which etches along

the particle path (Fleischer et al., 1975). Chemical etching is

the most widely used technique for revealing the latent

damage trails of ionizing particles in solid. The response of a

SSNTD depends strongly on the etching conditions and the

etchant characteristics. The concentration of the etchant in-

creases by using the same etchant for a longer duration due to

water evaporation (Khan et al., 2002). The chemical etching of

CR-39 produced from diethylene-glycol bis (allyl carbonate)

has been studied by Gruhn et al. (1980).

The following formula shows the attack by thehydroxide ion

results in the hydrolysis of the carbonate ester bonds and the

release of polyallylalcohol from the polymer network (Brydson,

1975). In addition to the polymeric etch product polyallylalcohol

(PAA), 2,2-Oxydiethanol is also formed in the above reaction.

For polymeric detectors, the most frequently used etchant

is the aqueous solution of NaOH with concentrations typi-

cally within the range of 1 to 12 N and temperature ranges

from 40 to 70 �C (Amin and Henshow, 1981). When CR-39

etched in NaOH, such polymers give rise to sodium carbon-

ate (Na2CO3), which forms different crystalline structures

depending upon its concentration in water, and are

commonly known as sodium bicarbonate, thermonatrite,

natrite, nahcolite, trona, etc. Other reaction products

including poly-allyl alcohol, 2-2-oxy di- ethanol, allyl-alcohol

and isopropyl alcohol are produced in abundance particularly

during the prolonged etching of polymer detectors in NaOH

solutions (Husaini et al., 2002).

2. Materials and methods

The samples of CR-39 polymer of average thickness of 1 mm

obtained from TASTRAK (manufactured and provided by

Track Analysis Systems Ltd. (TASL), Bristol, UK) were cut into

small pieces of 1 � 1 cm2. The samples were irradiated with

different doses of gamma rays from Gamma Irradiation Unit,

at Nuclear Research Center at the Atomic Energy Authority of

Egypt (EAEA), using 60Co as a gamma-ray sourcewith 3.09 kGy/

h dose rate. The irradiated samples were exposed to radon in

air to collect a-tracks. These samples were etched in NaOH

solution at different concentrations at temperature 70 � 1 �Cfor different time intervals. A group of samples were etched

with 6.25 N NaOH for different etching times ranging from 1 to

25 h to determine the relation between the bulk etch rate and

the etching time. After etching process, the removal thickness

and bulk etch rate were measured using digital micrometer

with 1 mmaccuracy and the removal thickness percentage dL%

calculated from the relation:

dL% ¼ DLL2

� 100

Where, DL ¼ L1�L2

DL: is the removal thickness,

L1: is the initial thickness,

L2: is the final thickness after etching (Malik et al., 2002).

The bulk etch rate (Vb) was determined using thickness

measurement technique from the equation:

Vb ¼ DL2Dt

Where Dt: is the etching time (Malik et al., 2002).

The number of tracks was determined using optical micro-

scope, and the track density was calculatedwhere the samples

were etched with 2, 4, 6, 8 and 10 N NaOH for 4 h as etching

duration. The damage of sample surface due to irradiation, and

the etching process were noticed by Analytical Scanning Elec-

tron Microscope [JEOL, JSM-6510LA] at the Egyptian Nuclear of

Radiological Regulatory Authority (ENRRA).

3. Results

To study the effect of gamma dose and the etchant concen-

tration of the removal thickness percentage, the samples for

gamma irradiated detectors and the un-irradiated one were

etched with 2, 4, 6, 8 and 10 N NaOH for 4 h. Fig. 1 shows the

increasing relation between the etchant concentration and

the removal thickness percentage for different gamma doses.

The effect of etching time for 6.25 N NaOH solution on the

bulk etch rate is shown in Fig. 2, the blank un-irradiated sam-

ples and the samples irradiated with low dose 10 kGy show

approximately stability in the behavior of bulk etching rate

0 5 10 15 20 250

2

4

6

8

10

12

14

Bulk

etc

h ra

te(V

b)

Etching Time (hr)

Irradiated dose 0 KGy 10 KGy 50 KGy 100 KGy

Fig. 2 e The relation between the etching time and bulk etch rate at 6.25 N NaOH solution.

2 4 6 8 100

1

2

3

4

5

6

7

8

9

10

11

Rem

ovel

thic

knes

s %

concentration(Normal)

Irradiated dose 0 KGy 10 KGy 50 KGy 100 KGy

Fig. 1 e The relation between the etchant concentration and the removal thickness percentage.

0 5 10 15 20 25

0

10

20

30

40

50

60

70

Rem

ovel

Thi

ckne

ss%

Etching Time (hr)

Irradiated dose 0 KGy 10 KGy 50 KGy 100 KGy

Fig. 3 e The relation between the etching time and the removal thickness percentage at 6.25 N NaOH solution.

b e n i - s u e f un i v e r s i t y j o u rn a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 3 6e4 038

2 4 6 8 1020

40

60

80

100

120

Trac

k de

nsity

(Tra

ck/

m2 )

Concentration(Normal)

Irradiated dose 0 KGy 10 KGy 50 KGy

µ

Fig. 4 e The relation between the etchant concentration and the track density at etching time 4 h.

b e n i - s u e f u n i v e r s i t y j o u r n a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 3 6e4 0 39

with the etching time. The samples irradiated with 50 kGy

showslight increase in bulk etching ratewith the etching time,

where the irradiated samples with 100 kGy show real increase

in bulk etch rate with increasing the etching time specially for

long etching times. Fig. 3 shows the increasing relation be-

tween the removal thickness percentage and etching time.

Fig. 4 illustrates the increase of track density against the

etchant concentration of NaOH solution for un-irradiated

samples and irradiated one with 10 and 50 kGy of gamma

ray. Irradiated samples with 50 kGy g-dose show increase in

track density with etchant concentration up to 6 N samples.

For concentrations more than 6 N, the sample surface gets

damaged and the tracks could not be detected. The surface

Fig. 5 e Photomicrographs of CR-39 detector un- etched and irrad

samples irradiated with 100 kGy g-doses have been damaged

so that tracks could be detected. To illustrate this damage in

un-etched and etched samples surface, the samples scanned

under electronic microscope as shown in Figs. 5 and 6.

4. Discussion

The present findings clearly indicate the increasing relation

between the bulk etching rate and gamma dose agree with

that previously reported by Abu-Jarad et al., 1997. The

behavior of the removal thickness percentage with etching

time is in agreement with that previously reported by Malik

iated with (a) unirradiated (b) 10 kGy (c) 50 kGy (d) 100 kGy.

Fig. 6 e Photomicrographs of CR-39 detector irradiated with (a) 50 kGy and etched at 8 N for 4 h (b) 50 kGy and etched at 8 N

for 6 h and (c) 100 kGy and etched at 2 N for 4 h.

b e n i - s u e f un i v e r s i t y j o u rn a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 3 6e4 040

et al., 2002. The increasing relation between the removal

thickness percentage and etchant concentration may be

related to the attack by hydroxide ion results in the hydrolysis

of the carbonate ester bonds and the release of polyallyalcohol

from the polymer network (Brydson, 1975).

The damage that appears in Figs. 5 and 6 may be according

to the thermal degradation caused by the gamma ray inter-

action with the samples in addition to the etchant solution

attack with the polymeric material of samples (Kuleznev and

Shershnev, 1990).

5. Conclusion

From the experimental work calculated in this study, it could

be concluded that:

1. The dependence of the removal thickness percentage on

both of etchant concentration and etching time.

2. The bulk etching rate shows weak dependence on the

etching time.

3. The track density behavior and the damage in samples

surface show the thermal degradation and the hydrolysis in

polymeric material especially for high irradiation doses.

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