Scholarly article on topic 'Alpha particle energy response of CR-39 detectors by 50Hz–HV electrochemical etching method'

Alpha particle energy response of CR-39 detectors by 50Hz–HV electrochemical etching method Academic research paper on "Physical sciences"

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Abstract of research paper on Physical sciences, author of scientific article — M. Sohrabi, Z. Soltani

Abstract High inherent sensitivity of CR-39 to detect relatively lower-LET particles, proved efficacy of 50Hz–HV electrochemical etching method and need to efficient alpha detection methods prompted this study. Alpha detection energy dependence (∼0.3 to ∼4.5MeV) of 500μm CR-39 detectors was studied. Detection efficiency increases to ∼90% flat over ∼0.8.0 to ∼4.5MeV alpha energy for 10N and 15N KOH solutions for 8h at 26°C. Efficiency versus stopping power responses follow the efficiency-energy responses while mean track diameters are linear functions of stopping power of a helium ion. The method provides some advantages over 2kHz–HV method.

Academic research paper on topic "Alpha particle energy response of CR-39 detectors by 50Hz–HV electrochemical etching method"

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Results in Physics

journal homepage: www.journals.elsevier.com/results-in-physics

Alpha particle energy responses of CR-39 detectors by 50 Hz-HV electrochemical etching method

M. Sohrabi *, Z. Soltani

Health Physics and Dosimetry Research Laboratory, Department of Energy Engineering and Physics, Amirkabir University of Technology, Tehran, Iran

ARTICLE INFO

ABSTRACT

Article history:

Received 23 September 2016

Received in revised form 27 November 2016

Accepted 27 November 2016

Available online xxxx

Keywords: Alpha particle CR-39

50 Hz-HV ECE Efficiency

Energy response, KOH normality

High inherent sensitivity of CR-39 to detect relatively lower-LET particles, proved efficacy of 50 Hz-HV electrochemical etching method and need to efficient detection methods prompted this study. Alpha detection energy dependence (~0.3 to ~4.5 MeV) of 500 im CR-39 detectors was studied. Detection efficiency increases to ~90% flat over ~0.8.0 to ~4.5 MeV alpha energy for 10 N and 15 N KOH solutions for 8 h at 26 °C. Efficiency versus stopping power responses follow the efficiency-energy responses while mean track diameters are linear functions of stopping power of a helium ion. The method provides some advantages over 2 kHz-HV method.

© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND

license (http://creativecommons.org/licenses/by-nc-nd/4XI/).

Introduction

Registration of charged particle tracks in CR-39 has been advanced either by chemical etching (CE) [1,2], or by high frequency-high voltage (HF-HV) electrochemical etching (ECE) [3-16]. The HF-HV ECE process of CR-39 is usually carried out in 6 N NaOH or 6 N KOH solutions at temperatures up to 70 °C either by a 2-step pre-etching/ECE process [5-7,10] or by 2-step ECE process [11-14], or 2-step ECE/post-etching process [15], or by a single-step ECE at 26 ± 1 °C [16].

The 50 Hz-HV ECE method of either 250 im thick [17] or 1 mm thick polycarbonate track detectors (PCTD) [18,19] detects alpha particles with an efficiency much higher and detection energy range much broader than those of 2 kHz-HV ECE method [20]. Recently alpha particles of 0.8 MeV energy were detected efficiently for the first time in 500 im thick CR-39 detectors by a single-step 50 Hz-2 kV ECE method at 26 ± 1 °C [16]. Using the 50 Hz-2 kV method, the effects of ECE duration, KOH normality (6, 10 and 15 N) and fluence on the detection efficiency and track diameter of ~0.8 MeV alpha particles as well as background track (BGT) density and minimum detection limit (MDL) were studied leading to ~90% efficiency by 8 h ECE at 26 ± 1 °C [16]. The 50 Hz-HV ECE CR-39 detectors provide small tracks, linearity flu-ence responses for 3 KOH normalities up to near 106 alpha tracks.cm~2 and simplicity in equipment. Therefore, it seemed rea-

* Corresponding author. E-mail addresses: dr_msohrabi@yahoo.com, m.Sohrabi@aut.ac.ir (M. Sohrabi).

sonable and highly necessary to also study detection characteristics (efficiency and diameter) of 500 im CR-39 detectors over a broad alpha energy range and stopping powers for 6 N, 10 N and 15 N KOH solutions in order to promote applications of such detectors in radiation protection and other fields. The results obtained in this study are also compared to those of alpha particle detection in CR-39 detectors by HF-HV ECE method.

Material and methods

The material and methods applied in this study are the same as previously reported on detection characteristics of ~0.8 MeV alpha particles in 500 im CR-39 by studying the responses of different fluences, ECE durations and KOH normalities [16]. In this present study, CR-39 detectors 2 cm x 2 cm in size cut by a laser gun from a 500 im thick A-4 size sheet masked on both sides were exposed to a fixed alpha fluence of 1.0 x 104 alphas.cm2 but for different alpha energies from ~0.3 to ~4.5 MeV. The alpha exposures were made by an 241Am alpha source fixed at the end of a cylindrical col-limated calibrator with an 8 mm diameter aperture designed to provide various calibrated fluences at fixed alpha energies.

The CR-39 detectors were processed at optimized ECE conditions obtained in a previous study by 50 Hz-2 kV ECE process in 6 N, 10 N and 15 N KOH solutions at 26 ± 1 °C for 8 h by applying no pre-etching. The track density, registration efficiency and mean track diameters were determined. The alpha tracks at different energies were photographed under a light microscope.

http://dx.doi.org/10.1016/j.rinp.2016.11.061 2211-3797/® 2016 The Authors. Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativec0mm0ns.0rg/licenses/by-nc-nd/4.0/).

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The ECE chamber used is a triplet ECE (TECE) chamber with two semi-chambers each with a row of single semi-chambers, as described before [21]. A simple home-made 50 Hz-HV generator was used for which a 50 Hz-220 V electricity main upgraded by an autotransformer and a step-up transformer to provide high voltages up to 50 kV with any desired field strength on any relatively thick polymer track detector [19,22].

The mean track diameter versus energy responses for the 3 KOH normalities studied were compared with the stopping power (dE/dX) versus a helium ion energy obtained by using SRIM-2013 software [23]. Also the mean alpha track diameters as functions of the stopping power were obtained for the three normality responses as discussed in the results section.

Results and discussion

In a previous study, CR-39 detectors responded efficiently to detection of ~0.8 MeV alpha particles by 50 Hz-HV ECE method as studied for different alpha fluences and ECE durations for 6 N, 10 N and 15 N KOH solutions even at 26 ± 1 °C (room temperature) [16]. In this present study, the effects of alpha energy on alpha particle detection characteristics of CR-39 in terms of efficiency and mean track diameter were studied for different KOH normalities applying a single-step 50 Hz-HV ECE method with no pre- or post-ECE processing. Fig. 1 shows alpha detection efficiency as functions of alpha energy in 500 im thick CR-39 by applying 50 Hz-2 kV field conditions for 6 N, 10 N and 15 N KOH solutions at 26 ± 1 °C. As it can be seen in Fig. 1, the detection efficiency for the three KOH solutions increases as the alpha energy increases reaching plateaus after 6-8 h of ECE. The efficiency in particular increases from ~20% at ~0.3 MeV to ~90% at ~0.8 MeV at 26 ± 1 °C for 6 N, 10 N and 15 N KOH solutions. As the alpha energy increases further, efficiency responses are on almost flat plateaus up to ~4.5 MeV energy studied with almost equal efficiencies of ~90% for 10 N and 15 N KOH solutions but with a slow reduction in efficiency with increase in energy for 6 N KOH solution. Having such a flat energy response from ~0.8 to ~4.5 MeV energy or even possibly broader for different application is ideal for alpha particle detection.

The effectiveness of the ECE process is highly dependent on many parameters including electric field conditions in particular the frequency. Fig. 2 compares alpha particle detection efficiency versus alpha energy in 500 im thick CR-39 by two ECE methods

Fig. 1. Alpha particle detection efficiency as functions of alpha energy in 500 im thick CR-39 by 50 Hz-2 kV ECE method in 6 N, 10 N and 15 N KOH solutions at 26 ± 1 °C for 8 h.

Fig. 2. Comparison of alpha particle track registration efficiency versus alpha energy for a fluence of 1.0 x 104 alphas.cm-2 in 500 im thick CR-39 processed by 50 Hz-40 kV.cm-1 (this study) and 2kHz-1.2kV [9] methods, at the stated ECE conditions.

at applying two different frequencies; the 50 Hz-2 kV method as obtained in this study and by 2 kHz-1.2 kV method for 6 N, 10 N and 15 N KOH solutions at the stated ECE conditions [9]. Although the two responses seem to have the same trend in terms of having the same efficiency over a long flat plateau from ~0.8 to ~4.5 MeV, the lower and upper energy thresholds seem to be quite different. For example, while the efficiency for 50 Hz-2 kV method seems to stay on plateau with further extension to higher alpha energies, the response of the 2 kHz-1.2 kV ECE method seems starting to drop at ~4.0 MeV down to an upper energy threshold of ~5.5 MeV. The same trend of differences in the lower and upper energy thresholds was noted in the thresholds of alpha particle energy responses of PCTDs processed by the two ECE methods applying 50 Hz and 2 kHz [17]. While the efficiency of the two ECE methods for 500 im thick CR-39, as shown in Fig. 2, have the same percentage from ~0.8 to ~4.5 MeV alpha energy under the ECE conditions applied, the efficiency of PCTDs processed by 50 Hz-HV ECE method is much higher and the alpha detection energy range is much broader than those of 2 kHz-800 V ECE method [17]. The efficiency of PCTDs processed by the 50 Hz-HV ECE method is in general higher within a broader energy range of ~0.3 to ~ 4.5 MeV compared to that of 2 kHz-800 V ECE methods which is ~0.3 to ~ 2.5 MeV obtained in our recent studies [17]. Also the registration energy range of the 50 Hz-HV ECE CR-39 detectors is broader to some extent as it can be seen in Fig. 2.

Another characteristic parameter of concern in 50 Hz-2 kV ECE of 500 im thick CR-39 is the mean alpha track diameter versus alpha energy which was performed for 6 N, 10 N and 15 N KOH solutions at 26 ± 1 °C for 8 h, as shown in Fig. 3. All the 3 different KOH normality responses more or less follow an alpha Bragg-type response peaking at around ~0.8 MeV alpha energy which can be considered for alpha spectrometry purposes. However, the Bragg-type response is more pronounced for 6 N and 10 N KOH solutions and less pronounced for 15 N KOH solution the response of which is flattened after ~0.8 MeV. This flattening of the response seems to be due to domination of bulk chemical etch rate of 15 N KOH solution in the ECE process applied, which make this normality not suitable for alpha spectrometry purposes [24,25]. The mean alpha track diameters at the Bragg peaks have maximum values of ~52, ~26 and ~18 im for the 6 N, 10 N and 15 N KOH solutions respectively.

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Fig. 3. Mean alpha particle track diameter (im) as functions of alpha energy for a fluence of 1.0 x 104 alphas.cm"2 in 500 im thick CR-39 by 50 Hz-2 kV ECE method in 6,10 and 15 N KOH solution at 26 ± 1 "C for 8 h.

In Fig. 3, also the stopping power of a helium ion as a function of its energy when passing through CR-39 target is shown as obtained by using the SRIM-2013 software. It is interesting to note that the SRIM-2013 response match well with the mean alpha track diameter versus energy obtained by the 10 N KOH solution response.

Due to strong relation of stopping power (dE/dX) with alpha particle energy, the efficiency and mean track diameter are also strongly dependent on the stopping power. Fig. 4 shows the alpha particle detection efficiency (%) as functions of a helium ion stopping power in 500 im thick CR-39 by 50 Hz-2 kV method in 6 N, 10 N and 15 N KOH solutions at 26 ± 1 °C for 8 h. As it can be seen in Fig. 4, the general trend of the responses is the same as those of the detection efficiency versus alpha energy of 10 N and 15 N KOH solutions with a flat response from ~0.8 to ~4.5 MeV except at stopping power points such as 171.6 keV/im (0.3 MeV) and 201.0 keV/im (0.5 MeV) where the detection efficiencies have dropped. In fact, these stopping powers are almost respectively equal to the stopping powers of 1.5 MeV (172.3 keV/im) and 1.0 MeV(202.2 keV/im)alpha particles. Similar points between ~ 0.3 to ~ 0.8 MeV in the back of the Bragg peak and

100 90 - I 1 i 0.8 MeV UMeV t ^ t I -\ 4 ii) ' 10 MèV ' 3.0 MeV 4.0 MeV 4.5 MeV t Î * Î S '

80 - y ■ m ■

70 - 1.0 MeV 1.5 MeV

60 - V

50 - y 0.5 MeV

40 - A

30 - Detector: CR-39, 500 fun thick

20 - V ECE Conditions: 50 Hz-2 kV, 26 *C, 8 h -•- 6 N KOH

10 0.3 MeV -m- 10N KOH

-A- 15 N KOH

0 I . I . ........

240 220 200 180 160 140 120 100 80 Helium Ion Stopping Power (dE/dX) (keV/pm)

Fig. 4. Alpha track detection efficiency (%) as functions of a helium ion stopping power for a fluence of 1.0 x 104 alphas.cm-2 in CR-39 developed by 50 Hz-2 kV method in 6,10 and 15 N KOH solution at 26 ± 1 "C for 8 h.

Fig. 5. Mean alpha particle track diameter (im) as functions of a helium ion stopping power for a fluence of 1.0 x 104 alphas.cm-2 in CR-39 developed by 50 Hz-2 kV ECE method in 6,10 and 15 N KOH solution at 26 ± 1 "C for 8 h.

Table 1

Coefficients of the 3 linear stopping power response versus mean alpha track diameter for 6 N, 10 N and 15 N KOH solutions for alphas (with energies ~0.3MeV<Ea < ~4.5 MeV and stopping powers ~88 keV/im < dE/dX < ~212 keV/im.

KOH Normality (nN) Coefficients

a b R-squared value

Ï 6 N 10 N 15 N 7.80 4.16 0.84 84 -9.6 142 0.93 0.99 0.01

Fig. 6. Comparison of mean alpha particle track diameter versus alpha energy in 500 im thick CR-39 by 50 Hz-40 kV.cm^1 (this study) and 2 kHz-24 kV.cm^1 [9], at the stated optimized conditions.

between ~0.8 and ~1.5 MeV on the front of the Bragg peak have similar situations with equal stopping powers at relevant points on the response. Therefore, the data points on Fig. 4 for 0.3 and 0.5 MeV may be not considered as part of the flat response after the Bragg peak.

Fig. 5 shows the mean alpha particle track diameter (im) as functions of a helium ion stopping power in CR-39 developed by 50 Hz-2 kV method in 6 N, 10 N and 15 N KOH solution at 26 ± 1 "C for 8 h. As it can be seen, the mean alpha track diameters

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0.3 MeV 0.5 MeV 0.8 MeV

(g l , . " * * * 1 * • * » * • • • • • • • \ * * \ ' \ • ' ' '. \ ■ • *. ; .•• « •• • « • • • i • / » •

1.0 MeV 2.0 MeV 3.0 MeV

4.0 MeV Background

Fig. 7. Microphotographs of alpha particle tracks (100x) of different energies in 500 im thick CR-39 exposed to 1.0 x 104 alphas.cm 2 processed by 50 Hz-2 kV ECE method in 6 N KOH solution at 26 ± 1 "C for 8 h.

195 (D) for the 6 N KOH (6ND), 10 N KOH (10ND) and 15 N KOH (15ND)

196 solutions are linear functions of the stopping power (keV/im)

197 studied except the discontinuity points as observed above. The

198 observation of these linearity of responses may be somehow corre-

199 lated to the linearity of the effective track core radius for the loss of

200 ether and carbonate ester bonds in PADC films exposed to protons

201 and heavy ion beams against the stopping power [26]. No matter

202 what the cause of this linearity is, the linear responses can assist

203 in determination of unknown alpha energies just by determining

204 the mean track diameter of the unknown alpha particle energy

205 (provided that the alpha fluence is the same), and use the graphs

206 to obtain the relevant stopping power and accordingly the alpha

207 energy. For this purpose, the linearity of responses can be very

instrumental for alpha spectrometry purposes or possibly other 208

applications. The stopping power versus mean track diameter 209

responses for 6 N, 10 N and 15 N KOH solutions for alphas with 210

energies ~0.3 MeV< Ea < ~4.5 MeV and relevant stopping power 211

~88 keV/im < dE/dX < ~212keV/^m are formulated as Eq. (1) 212

with coefficients for the three linear responses as given in Table 1. 213

nNS = nN(dE/dX)=a x nND + b (1) 216

One of the specific characteristics of the 50 Hz-HV ECE process- 217

ing either in CR-39 or in PCTDs is that the mean track diameter is 218

highly dependent on the applied field conditions in particular the 219

frequency [16]. Fig. 4 compares mean alpha particle track diameter 220

versus alpha energy in 500 im thick CR-39 as processed by 50 Hz- 221

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0.3 MeV 0.5 MeV 0.8 MeV

ft •• ' A • • • • • •• • J* •• ft • m ft • f II •• • • y • ft* • • v.« % .V t.\ » • s • \ V I'/

1.0 MeV 2.0 MeV 3.0 MeV

Fig. 8. Microphotographs of tracks (100x) of alpha particles of different energies in 500 im thick CR-39 exposed to 1.0 x 104 alphas.cm 2 by 50 Hz-2 kV ECE method in 10 N KOH solution at 26 ± 1 "C for 8 h.

222 40 kV.cm-1 (this study) and under 2 kHz-24 kV.cm-1 field strength

223 [9], at the stated optimized conditions. It can be seen that although

224 the field strength of 24 kV.cm-1 for 2 kHz ECE is much lower than

225 40 kV.cm-1 applied in this study, the track sizes are still near three

226 times smaller. This is due to the fact that as frequency increases,

227 the dielectric heating and thus local track heating which highly

228 depends on the frequency of the applied field increase leading to

229 larger tracks [16,27]. Therefore, 50 Hz ECE method is much more

230 advantageous from this point of view leading to much smaller

231 tracks. Having smaller track sizes extends the linearity of a

232 response to higher track density which is of importance for detect-

233 ing high alpha particle fluences Fig. 6.

Figs. 7-9 show microphotographs of tracks of alpha particles at 234

energies 0.3, 0.5, 0.8, 1.0, 2.0, 3.0 and 4.0 MeV and BGT density 235

respectively in 500 im thick CR-39 detectors exposed to 104 236

alphas.cm 2 processed by 50 Hz-2 kV for 6 N, 10 N and 15 N 237

KOH solutions at 26 ± 1 "C for 8 h. These microphotographs show 238

the appearance of alpha tracks and their dependence on the alpha 239

energy and also on the KOH normality. 240

For 6 N KOH solutions, the alpha tracks as shown in Fig. 7 are 241

relatively small for the alpha energy range of ~0.3 to ~4.5 MeV 242

studied. Also the track diameter, as it can be seen, is very much 243

energy dependent and are the largest in size at the Bragg-peak, 244

as also shown in Fig. 3. 245

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0.3 MeV 0.5 MeV 0.8 MeV

1.0 MeV

2.0 MeV

3.0 MeV

4.0 MeV

Background Tracks

Fig. 9. Microphotographs of tracks (100x) of alpha particles of different energies in 500 im thick CR-39 exposed to 1.0 x 104 alphas.cm 2 by 50 Hz-2 kV method in 15 N KOH solution at 26 ± 1 "C for 8 h.

246 For 10 N KOH solutions, alpha track diameters, as shown in

247 Fig. 8, are the larger than those of the two other solutions. The

248 tracks are more distinct against the detector surface in particular

249 at the Bragg peak at ~0.8 MeV. Such larger tracks while are of high

250 benefit for low-fluence alpha or in general charged particle detec-

251 tion applications, it can be problematic in applications for example

252 in ion detection in plasma focus devices where the ion fluence is

253 relatively high per pinch shot [22,28,29]. However, as it can be

254 seen in Fig. 3, the mean track diameter fits well the SRIM dE/dX

255 response of a helium ion making the detector more suitable for

256 alpha spectrometry applications.

For 15 N KOH solutions, as shown in Fig. 9, alpha particle tracks 257 are still larger than those of 6 N KOH solution but smaller than 258

those of 10 N KOH solution. However, the alpha track diameter is 259

not distinctly energy dependent as the other two solutions. As it 260

can be seen from Figs. 3 and 8, the alpha tracks are more or less 261

the same size within a small margin. This is due to the fact that 262

at higher KOH concentrations, such as 15 N KOH solution, ion accu- 263 mulation in the vicinity of a damaged track region is too high with 264 reduced ion mobility under the field conditions applied [30]. Under 265

such conditions, chemical etching rate of tracks is dominant and 266

consequently the track diameters become less energy dependent. 267

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At this stage of development, 15 N KOH solution at the ECE conditions applied, cannot be applied for alpha spectrometry purposes. However, since the efficiency of the alpha detection is rather constant over an alpha energy range of ~0.8 to ~4.5 MeV, CR-39 applications at this concentration is also efficient to be used depending on the application.

Having said the above, alpha particle detection by CR-39 under a single ECE method with no pre-or-post etching either at 50 Hz-2 kV or 2 kHz-HV ECE conditions has rather unique characteristics in particular having flat efficiency response of ~0.8 to ~4.5 MeV energy studied. However, it should be brought to the attention that CR-39 provides specific behavior when appropriate pre-etching is applied [6]. It has been well demonstrated for fast-neutron-induced recoil particle tracks that the sensitivity and mean track diameter of CR-39 versus KOH normality responses for a number of pre-etching durations applied up to 5 h in 6 N KOH solution at 60 "C show two peaks with near 3 times higher sensitivity than the rest of the responses at 6 N and 15 N KOH solutions. However, from practical point of view, the 50 Hz-2 kV ECE method applied in this study provides high flat efficiency response over relatively broad energy range for different applications.

Regarding BGT density and MDL of CR-39 detectors under optimized 50 Hz-2 kV conditions, they have been well reported in a recent article [16]. In summary, the BGT increases linearly versus ECE duration for the 6 N, 10 N and 15 N KOH solutions; 6 N KOH solutions produce the lowest and 15 N KOH solutions produce the highest BGT densities. The CR-39 detectors processed by 50 Hz-2 kV method in 6 N KOH solution can be considered from any practical and efficiency points of view such as relatively low normality, high efficiency, small track diameter, extended fluence range and the lowest BGT density and thus MDL with no need to pre-or-post ECE etching even at room temperature, a preferred method. As stated above, depending on the type of application of concern, other conditions with or without pre-etching can be applied.

As experienced in our laboratory and by others, in general CR-39 detectors vary in terms of BGT density from producer to producer, batch to batch, foil to foil in the same batch, and one side to another side of the same detector as well as very much depending on the processing type and conditions such as chemical and/or ECE. For example, the BGT density of 500 im thick CR-39 detectors under a two-step high-frequency ECE process is 34.4 ± 13.8 tracks.cm~2 [13], 70 tracks.cm~2 [14] and 43 ±17 tracks.cm~2 [31]. The BGT density of chemically processed CR-39 in 6.5 N NaOH solution at 60 "C is 157 tracks.cm"2 [32] and 38.86 ±4.3 tracks. cm~2 [33]. As regards to BGT density of CR-39 under 50 Hz-HV ECE method, it is 59 ± 6, 76 ± 7 and 94 ± 7 tracks.cm"2 for 6 N, 10 N and 15 N KOH solutions respectively [16].

Conclusion

Alpha particles of ~0.3 to ~4.5 MeV energy were efficiently detected in 500 im thick CR-39 detectors by applying a simple, single and low-cost 50 Hz-2 kV ECE method as studied for 6 N, 10 N, and 15 N KOH solutions at 26 ± 1 "C for 8 h. The efficiency increases from ~20% at ~0.3 MeV to ~90% at ~0.8 MeV beyond which flat plateaus up to ~4.5 MeV was for 10 N and 15 N KOH solutions with a slow decrease in efficiency for the 6 N solution down to 77 ± 7% at 4.5 MeV. The mean alpha track diameter versus alpha energy responses for the 3 KOH solutions follow a Bragg-curve trend but 10 N KOH solution response fits well with the Bragg curve of a helium ion obtained by SRIM-2013 software. Having such a flat energy response is ideal for alpha particle detection from ~0.8 to ~4.5 MeV energy or even possibly to detect broader energy ranges for different applications. The mean alpha track diameters versus dE/dX of a helium ion for the 3 KOH solutions studied follow linear responses from ~0.3 to ~4.5 MeV proposing

a method for identifying unknown alpha energies. From practical points of view, 6 N KOH solution provides high efficiency over a broad energy range, small track diameters, highly extended fluence range and in particular being a lower normal KOH solution at room temperature for 8 h with no pre-or-post etching. However, depending on the type of application of concern, other KOH solutions and ECE conditions with or without pre-or-post etching can be applied. The 50 Hz-HV method provides a number of advantages as discussed in particular due to simply in having higher power and stability compared to HF-HV generators. Therefore, it can be easily applied to thick polymeric detectors as experienced by us in a number of reported or on-going studies to be yet reported.

Acknowledgments

Research was conducted under the current budget of the Department of Energy Engineering and Physics, Amirkabir University of Technology and there is no conflict of interest.

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