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Laser Effect on the Activation Energies, Bulk Etch Rate and Track Etch Rate of CR-39 Polymeric Detector

Ahmed A. Ibrahim*, Sozan Bhaa-al-deen

Department Physics, College of Science, Kirkuk University, Kirkuk, Iraq

Abstract: The aim of this paper is to find the effect of Nd: YAG laser of wavelength (532 nm), laser power 150 MW on the CR-39 polymer. Twenty three detectors were divided in to three sets. The first set (ten detectors) (post-exposed) was first exposed to alpha radiation from ²⁴¹Am source at 3MeV and then treated in air with laser at different exposure time started from 10 minutes to 100 minutes with ten minutes differ between them (alpha + laser). For the second set (ten detectors) (pre-exposed), the process was reversed (laser +alpha) under the same conditions, for the last set (three detectors) (un-exposed to laser), used as a control set, was irradiated with an alpha source (241Am). Alpha track diameters, bulk etching velocity (VB), track etching velocity (VT), etching efficiency (η), etching ratio (V) were determined. The activation energies of bulk etch (EB) and track etch (ET) for unexposed, post- exposed and pre-exposed are found to be equal to 1.10, 0.92, 0.82 eV and 1.07, 0.86, 0.79 eV respectively.

Keywords: nuclear track detectors, CR-39, activation energy of bulk etch (EB) and track etch (ET), etching conditions

Citation: Ahmed A. Ibrahim, Sozan Bhaa-al-deen, Laser Effect on the Activation Energies, Bulk Etch Rate and Track Etch Rate of CR-39 Polymeric Detector. International Journal of Physics, 4 (1). 1-4. January 2016. doi:10.12691/ijp-4-1-1

1. Introduction

Nuclear track techniques are very important in many fields of science and technology. A solid state nuclear track detector namely CR-39 [poly-allyl-diglycol carbonate (C12H18O7)] is widely used for the detection of low Z and high Z particles. [1]. The interaction of electromagnetic radiation with the detector material results in structural changes. These changes depend on several factors such as detector structure, exposure condition, radiation type and energy, irradiation condition, etching process etc. Two competing processes, bond secession and crosslink, occur as a result of irradiation with (LLET) radiation. Bond secession lead to the degradation of the surface and as a result increases the bulk and track etch rates while crosslink results in hardening of the

Surface and subsequently decreases the bulk and track etch rates.[2]. The laser effect on the (SSNTDs) depends on laser properties (laser wavelength, laser repetition rate and energy density) and on the detector properties (density, thickness, etc). In general, infrared (IR) laser interaction with SSNTDs can induce thermal effects [3], while ultraviolet (UV) laser will give rise to photoablation or photodecomposition [4]. Many authors reported the effects of incoherent UV radiation on the etching properties of SSNTDs. These effects depend on several factors: radiation parameters, detector property and irradiation condition [5]. Activation energy of CR-39 polymer detector (bulk or track) is deﬁned as the energy required to activate the reaction between the detector material and the etchant solution. Many works studied the activation energy of the CR-39 polymer detector [6,7]. The effect of gamma irradiation on the activation energy of CR-39 polymer detector was reported by [8].

2. Materials and Method

2.1. To find Laser effect on CR-39

CR-39 detector (1cm2) of thickness (0.5 mm). Twenty three detectors were divided into three sets, The third set( three detectors) served as a control set and its samples were exposed only to alpha radiation with close contact to 241 Am, The first set (ten detectors) (post-exposed) was first exposed to alpha radiation from 241Am source and then treated in air with laser at different exposure time started from 10 minutes to 100 minutes with ten minutes differ between them (alpha + laser). For the second set (ten detectors) (pre-exposed), the process was reversed (laser +alpha) under the same conditions. All the samples were etched in 6.25 M NaOH solution at 343 oK.

2.1.1. To Find the Activation Energy:

Fifteen detectors were divided into three sets, The first set (five detectors) (post-exposed) was first exposed to alpha radiation from 241Am source and then treated in air with laser at 60 minutes (alpha + laser), the second set (Five detectors) (pre-exposed), the process was reversed (laser +alpha) under the same conditions and the the third set served as a control set and its samples were exposed only to alpha radiation with close contact to 241 Am,. All the samples were etched in 6.25 M NaOH solution at ﬁve different temperatures, ranging from 338 K to 358 K, for 3 h. An equal temperature increment of 5 K was used. After etching, CR-39 detectors were thoroughly washed with distilled water and dried in open air. The thickness of the removed layer as a result of etching was found using a sensitive micrometer with digital camera. The bulk etch rate, VB, is calculated by

[picture] | (1)

Where d1 and d2 are the detector thickness (in mm) before and after etching;

t: is the etching time (in h).

The track etching rate VT for a given alpha particle was determined by measuring the etch –cone length Le after an etching time t, such that

[picture] | (2)

with VB and t known [9], the measured value of Le immediately yields the value VT.

The etch rate (sensitivity) V for circular tracks is given by

[picture] | (3)

The dependence of VB, VT on temperature follows the Arrhenius

Type of law and is given by

[picture] | (4)

Where EB is the activation energy for bulk etch rate and A is a constant.

K is the Boltzmann constant, A similar equation applies for track etch rate, VT, by replacing EB by ET by taking a natural log of above equation and plotting the graph between ln VB (VT) and 10³/Tk⁻¹, the slope gives the value of EB (ET).

3. Result and Discussion

Figure 1. laser effect on CR-39

Figure 1 shows the effect laser radiation on CR-39 at different exposure time, The results showed that we have obtained an increase in the response of the detector irradiated with alpha particles and exposure to lasers, the increasing the size and speed of growth diameters effects formed a gradual increase with increasing to laser exposure time that value reached the highest value at exposure time is equal to 30min This indicates an increase in ductility Detector and get the decomposition in molecular chains and resulted in the acceleration of the process of the emergence of impact, and increase the time of exposure to a laser beam at 60min began diameters decreasing gradually until it reached a minimum value close to the diameters Detector record, which is due to increase in the complexity of chains of polymeric (Cross Linking) and hardening Detector this results agree with results in [10] references.

Table 1 and Table 2 shows the VB and VT value under at 60 minutes exposure time for laser radiation at different solution temperatures of three cases (laser+ alpha), (alpha +laser) and alpha only

Table 1. The value of VB under laser radiation at different temperatures

Table 2. The value of VT under laser radiation at different temperatures

Figure 2. The activation energies for bulk (EB) etch rate for alpha

The linear dependence of ln VB and ln VT versus reciprocal temperature, for reference, post-exposed and pre-exposed samples are depicted in Figs. Figure 2 and Figure 3 shows the variation of ln (vb) versus 1/T for alpha + laser, laser +alpha and alpha only of tracks to find the activation energies bulk in CR-39 by using the Arrhenius equation, the results of alpha only case is equal to 0.82 eV was less than from the another two cases alpha+ laser and laser + alpha there were 0.92 eV and 1.01eV respectively. The differences in value because the laser effects on the CR-39 polymer detector such as the (Cross Linking) and hardening Detector these effects lead to increase in activation energies of bulk etching. Again we can shows in Figure 5, Figure 6 and Figure 7 the variation of ln (VT) versus 1/T for alpha + laser, laser +alpha and alpha only of tracks to find the activation energies track etching in CR-39 by using the Arrhenius equation, the results of alpha only case is equal to 0.79 eV was less than from the another two cases alpha+ laser and laser + alpha there were 1.07 eV and 0.86eV respectively. The activation energies for bulk (EB) and track (ET) etch rates, for each set, were calculated from the slopes of these linear plots. These values are listed in Table 3.

Figure 3. The activation energies for bulk (EB) etch rate for laser+alpha

Figure 4 The activation energies for bulk (EB) etch rate for alpha + laser

Figure 5. The activation energies for bulk (ET) etch rate for alpha

Figure 6. The activation energies for bulk ET etch rate for laser+ alpha

Table 3. The values of The activation energies for bulk (EB) and track (ET) etch rates, for each set

Figure 7. The activation energies for bulk (ET) etch rate for alpha +laser

The measured values shows change in the activation energy of bulk etch rate for the irradiated samples as compared to the reference un-exposed sample. The activation energy of track etch rate for pre-exposed sample show an appreciable increases compared to that corresponding to the unexposed sample. This observed increase is indicative of the increase in hardening of CR-39 polymer detector resulting from the increase in cross-linking in the polymer. Also, the obtained values of ET, in each set, are found to be less than those of EB. This implies that the downward etch rate along the track is larger than that of bulk etch rate.

4. Conclutions

1: The activation energy of bulk etch rate, EB, of CR-39 polymer detector is slightly affected by the laser treatment, This supports the proposal that EB is a characteristic of the bulk material of the detector.

2: The signiﬁcant increase in ET for pre-exposed samples, compared to un-exposed and post-exposed samples, Track activation energy, ET, has found to be lower than the bulk activation energy, EB, for CR-39 detector in all different cases.

References

[1]   | Fleischer R.L, Price R.B and Walker R.M, Nuclear Tracks in Solids: Principles and Applications, University of California Press, Berkeley, USA, 1975.
[2]   | Saffarini G., NidalD waikat, Mousa El-Hasan, Fuminobu Sato, Yushi Kato and Toshiyu kiIida “The effect of infrared laser on the activation energy of CR-39 polymeric detector” Nuclear Instruments and Methods in Physics Research” (A 680), 82-85, 2012.
[3]   | Durrani S.M.A and. Abu-Jarad F., “The heat effect on CR-39 nuclear track detectors irradiated by a pulsed IR laser” Nuclear Instruments and Methods 100 (1), 97-102, 1995.
[4]   | Babak Jaleh, Parviz Parvin, Kavoos Mirabaszadeh, and Mehran Katouz, KrF laser irradiation effects on nuclear track recording properties of polycarbonate,” Radiation Measurements, 38,(2), 137-254, April, 2004.
[5]   | Benton E.V, and HenkeR.P, Charged particle tracks in polymers no. 7: sensitivity enhancement of lexan. Naval Radiological Defense Lab.(NRDL), San Francisco, CA, Report Number(s):AD-682922; USNRDL-TR(1968) 68-136.
[6]   | Awad E.M and EL-Samman H.M, Activation energy of etching for CR-39 as a function of linear energy transfer of the incident ions. ”Radiation Measurements” 31, 109-114, 1999.
[7]   | Virk H.K, Modgil S.K and Bhatia R.K, Activa -tion energy for the annealing of radiation damage in CR-39: An intrinsic property of the detector,” Nuclear Tracks and Radiation Measurements”, 11(6) 323 -325, 1986.
[8]   | Surinder S. and Neerja. The effect of gamma-irradiation on the activation energy of bulk and track etching in CR-39 plastic track detector “Radiation Measurements “, 42, 1507-1507, 2007.
[9]   | Khayrat A. H.and ; Durrani, S.A., variation of alpha-particle track diameter in CR-39 as a function of residual energy and etching “Radiation measurements”, 30, 15-18, 2012.
[10]   | G.Saffarini, D. Nidal, M.El-Hassan. Kato and T.Lida, Discovery new solution etchant, “Nucl.Instr.and math in phy. Research'“, A. 680., 82-85, 2012.