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Nuclear Instruments and Methods in Physics Research B 248 (2006) 117–120

NIMBBeam Interactions

with Materials & Atoms

Range behaviour of swift heavy ions in muscovite mica

Lakhwant Singh *, Mohan Singh, Kawaljeet Singh Samra, Ravinder Singh

Department of Physics, Guru Nanak Dev University, Amritsar 143 005, India

Received 9 November 2005; received in revised form 17 January 2006Available online 24 May 2006

Abstract

The range behaviour of swift heavy ions in layered crystal has been investigated by bombarding the basal surface of natural muscovitemica with 93Nb (18.00 MeV/n) and 238U (10.00 MeV/n) ions at four different angles of incidence (viz: 30�, 45�, 60� and 75�). The rangeprofiles and track etch rates of these ions were measured experimentally using simple and straightforward track etch technique. Theexperimental data reveals that with the increase of incident angle there is a systematic increase in range and optimum etching time, whiletrack etch velocity decreases. The ranges of number of ions [viz: 197Au (15.69,13.42,11.40 MeV/n); 58Ni (11.56 MeV/n); 238U(15.36,5.90 MeV/n) and 208Pb (13.80 MeV/n)] incident at 45� were also measured in the laboratory to test the reliability of SRIM codes.It is found that the prediction of range deficit is better for ions having high specific energy (18.00 MeV/n).� 2006 Elsevier B.V. All rights reserved.

Keywords: Muscovite mica; Swift heavy ions; Range; Track etch rate; SRIM codes

1. Introduction

The evaluation of range and energy loss of swift heavyions in solids continues to evoke considerable researchinterests because of their vital importance in many scientificdisciplines [1–5]. The calibration of most charged parti-cle detectors, including solid state nuclear track detectorsdepends on the reliability of theoretical formulations[6–10]. Muscovite mica provides a unique opportunity tomeasure the range of heavy ions because the completetrajectory of the ion track from its entrance nearly to itsend point can be viewed under optical microscope afteretching [11–14].

A number of studies in muscovite mica and phlogopite[15–17] have been carried out to understand the trackmorphology and to relate the shape and geometry of theetch pits with crystalline structure of the material. Further,these studies reveal the dependence of etch pit geometry onrate of energy loss in layered crystal. The XRD measure-ments [18] indicate that the perturbed area along the heavy

0168-583X/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.nimb.2006.03.197

* Corresponding author. Tel.: +91 183 2450926; fax: +91 183 2258820.E-mail address: lakhwant@yahoo.com (L. Singh).

ion trajectory in muscovite mica is composed of an amor-phous region. However, these experiments do not provideinformation regarding the range profiles of heavy ions inthe layered crystal.

In the present investigations, a simple and straightfor-ward track etch technique [2] was employed to measurethe range of different heavy ions in natural muscovite mica(collected from Nilore Mica belt, India) irradiated at GSIDarmstadt, Germany. The maximum etched track length[19,20] of swift heavy ions bombarded along four differ-ent directions has been measured to observe the anisotropiceffect of layered crystalline structure on range variation. Tostudy the effect of anisotropic structure on etching kinetics,the track etch rates have also been measured for 235U(10.00 MeV/n) and 93Nb (18.00 MeV/n) ions in the layeredcrystal.

2. Muscovite mica

The muscovite mica [K2Al4(Si6Al2O20)(OH,F)4; q =2.8 g/cm3] has layered structure consisting of series ofsheets stacked parallel to each other [21]. Each sheet consistof edge sharing AlO6 octahedral layer sandwiched between

Fig. 1. Schematic diagram of muscovite mica [K2Al4(Si6Al2O20)(OH,F)4]showing the octahedral layer (AlO6) sandwiched between two layers ofSiO4 tetrahedra [21].

Table 1Experimental values of projected track length and range of 93Nb(18.0 MeV/n) and 238U (10.0 MeV/n) ions incident at four different angles

Ion (energy) Angle ofincidence (�)

Projected tracklength (lm)

Range (lm)

93Nb (18.0 MeV/n) 30 117.2 ± 2.0a 135.4 ± 2.3a

45 100.0 ± 1.8 141.5 ± 2.560 73.0 ± 1.3 146.0 ± 2.675 38.7 ± 0.7 149.6 ± 2.7

238U (10.0 MeV/n) 30 54.0 ± 1.5 62.6 ± 1.745 49.0 ± 1.2 69.4 ± 1.360 37.0 ± 0.5 74.5 ± 0.875 20.0 ± 0.5 78.0 ± 1.3

a Standard deviation.

118 L. Singh et al. / Nucl. Instr. and Meth. in Phys. Res. B 248 (2006) 117–120

two tetrahedral layers made up of corner sharing (Al/SiO4)tetrahedral (Fig. 1). The distribution of Al and Si in tetra-hedral site in muscovite shows no long range ordering [15].The most stable surface [001] was produced for heavy ionirradiation after cleaving the muscovite crystal above andbelow the loosely bond interlayers.

3. Experimental details

A freshly cleaved thin sheet (�250 lm) of natural musco-vite mica was cut into a number of disks of 3 cm diametereach. The basal plane [001] of these samples was irradiatedwith 93Nb (18.0 MeV/n) and 238U (10.0 MeV/n) ions inci-dent at four different angles (30�, 45�, 60� and 75�) to observeanisotropic effect on maximum etchable track length.

In order to observe the reliability of SRIM codes [6,7],the samples were exposed to more ions [197Au (15.69,13.42, 11.40 MeV/n); 58Ni (11.56 MeV/n); 238U (15.36,5.90 MeV/n) and 208Pb (13.80 MeV/n)] incident at 45� ofangle from UNILAC heavy ion accelerator at GSI Darms-tadt, Germany. The ion fluence in each exposure was keptat 104 ions per cm2 to avoid the overlapping of etchedtracks. For range comparison purposes, we have consid-ered 45� angle of incidence for evaluation of range in thepresent investigations [19]. The standard deviation in therange measurements is within 2.5%.

The samples were then etched in 40% HF at constanttemperature of 27 �C to reveal the maximum etchable tracklength. All measurements have been made at a total magni-fication of 900· with an accuracy of 0.2 lm. Measuring theetched cone length and applying the corrections due to thebulk etching, the total etchable range for these ions in thesedetectors have been measured [20]. In order to observe theanisotropic effect on etching kinetics, the track etch rates,

VT [11] were also measured along four different orienta-tions of heavy ion tracks in muscovite mica. The meanvalue of track etch rates, V T were determined after dividingthe mean experimental range to the optimum etching time.

4. Results and discussion

The results for the projected and maximum etchabletrack length (range) as a function of incident angle of93Nb (18.00 MeV/n) and 238U (10.00 MeV/n) ions bom-barded on the basal plane of natural layered crystal(muscovite mica) are given in Table 1. It is found that thereis a systematic increase in range with the increase in angleof incidence. It has to be noted here that the theoreticalcodes [6,7] do not take into account the angle of incidencewhile calculating the average energy loss and range ofheavy ions in the crystalline target materials. The increasein range with the increase in angle of incidence from 30�to 75� (Table 1), corresponding to a gradual increase inthe number of layers crossed by ions shows clearly theeffect of anisotropy of crystal structure on the range ofheavy ions. This experimental observation may be due tothe reason that transition time of the ion from layer tolayer in muscovite mica decreases as it penetrates fromgrazing angle to normal direction of the basal plane.

To test the reliability of the SRIM codes [6,7] for rangevalues in muscovite mica, we have experimentally measuredthe maximum etchable track length (range) of a variety ofions [197Au (15.69, 13.42, 11.40 MeV/n); 58Ni (11.56 MeV/n); 238U (15.36, 5.90 MeV/n) and 208Pb (13.80 MeV/n)] inci-dent at 45� with basal [001] plane. The results for the exper-imental and computed values of range from SRIM codes[6,7] are given in Table 2. It is found that all the measuredvalues of ranges are lower than the ones computed from the-oretical codes. This may be attributed to the fact that theformation of etchable latent tracks follows a certain crite-rion of critical energy loss; below to critical value the etchingprocess does not reveal the track near the end portion of thetrajectory. The percentage of range deficit in each value isalso shown in the parentheses against the theoretically cal-culated values (Table 2). It is observed that the range deficitfor very high energy ions [93Nb (18.00 MeV/n)] is low (�7%)

Table 2Experimentally measured and theoretically computed values of range and energy loss of different heavy ions incident at 45� dip angle with basal plane ofmuscovite mica

Ion (energy) (MeV/n) Mean range (lm) Corrected mean range (lm) SRIM-98 SRIM-03

Range (lm)(deficit) (%)

Energy loss

(eV/A)

Range (lm)(deficit) (%)

Correcteddeficit (%)

Energyloss (eV/A)

197Au (15.69) 108.9 111.6 127.8 (14.8) 2323 129.7 (16.0) 14 2303197Au (13.42) 90.0 92.7 104.7 (14.0) 2446 108.5 (17.0) 14.6 2427197Au (11.40) 79.2 81.9 94.7 (16.4) 2516 92.5 (14.4) 11.5 253058Ni (11.56) 80.5 84.9 92.3 (12.7) 566.5 92.9 (13.3) 8.6 571.8238U (15.36) 107.8 108.9 124.7 (13.6) 2871 119.0 (9.4) 8.5 3049238U (10.00) 69.4 70.5 84.5 (17.9) 3087 79.6 (12.8) 11.4 3415238U (5.90) 41.7 42.8 52.8 (21) 3240 51.8 (19.4) 17.4 3582208Pb (13.80) 95.6 96.8 112.3 (14.9) 2536 112.3 (14.9) 13.8 250593Nb (18.00) 141.5 144.7 152.0 (6.9) 818.1 152.5 (7.2) 5.1 852

0

5

10

15

20

5 10 15 20Specific energy [MeV/n]

Cor

rect

ed r

ange

def

icit

[%

]

Fig. 2. The corrected range deficit (%) as a function of specific energy(MeV/n) in muscovite mica.

L. Singh et al. / Nucl. Instr. and Meth. in Phys. Res. B 248 (2006) 117–120 119

as compared to (�20%) of low energy ions [238U (5.90 MeV/n)]. However, the experimental range values were correctedfor the etch threshold of 3.4 keV/nm [22] using the SRIMcode [7]. Nevertheless, the corrected values show a misfitbetween the experimental and theoretical values (Table 2).The corresponding corrected range deficit for very highenergy ions [93Nb (18.00 MeV/n)] is now reduced to �5%,while for very low energy ions [238U (5.90 MeV/n)], itreduces to �17% (Table 2). This shows that range deficit

Table 3Track etch rate and optimum etching time of heavy ion tracks etched with 40%muscovite mica

Ion (energy) Dip angle (�) Track etch rates,VT (lm/min)

MV

93Nb (18.00 MeV/n) 30 1.65 1.45 1.51 1.60 1.32 1.75 1.20 1.

238U (10.0 MeV/n) 30 1.04 0.45 0.89 0.60 0.71 0.75 0.59 0.

is a function of ion energy and is better for ions having highspecific energy. The range deficit for specific energy of stud-ied ions is represented in the graph (Fig. 2).

Table 3 shows the variation of track etch rate with thedirection of ion trajectory in the muscovite mica underthe same etching conditions of concentration and tem-perature of etchant. It is found that track etch velocitydecreases as the direction of incident ion changes fromgrazing angle toward normal to the surface [001] of musco-vite mica. Possibly the anisotropic structure affects theetching process and it takes much more time (126 min) toetch the latent track along 75� as compared to the time(84 min) to etch the track along 30� to the surface in caseof 93Nb (18.00 MeV/n) ion tracks.

The results for the optimum etching time of 93Nb(18.00 MeV/n) and 238U (10.00 MeV/n) ion tracks bom-barded along different direction in basal plane of muscovitemica are given in Table 3. It is found that there is also a sys-tematic increase in the optimum etching time with theincrease in angle of incidence. However, it is interestingto note that anisotropic structure of layered crystal showsthe reverse trends in track etch rate and range of heavy ionsin muscovite mica.

5. Conclusion

The experimental observations lead to the conclusionthat SRIM codes [6,7] do not account for the anisotropic

of HF at constant temperature (27 �C) along four different dip angles in

ean track etch rate,

T (lm/min)Mean observedrange (lm)

Optimum etchingtime (min)

61 135.4 8449 141.5 9530 146.0 11219 149.6 126

99 62.6 6387 69.4 8070 74.5 10757 78.0 136

120 L. Singh et al. / Nucl. Instr. and Meth. in Phys. Res. B 248 (2006) 117–120

effect while computing the range and energy loss of heavyions in layered crystal. Therefore, it is strongly recom-mended that one should be aware of the significant effectof anisotropic structure while computing the range in crys-talline solids using SRIM codes. However, the predictionof range deficit is better in case of very high specific energyions as compared to low specific energy ions. It is also con-cluded that with the increase of incident angle there is a sys-tematic increase in the range and optimum etching time,while track etch velocity decreases. This clearly indicatesthe anisotropic effect on the etching kinetics of heavy iontracks in the layered crystal of muscovite mica.

Acknowledgements

Authors are thankful to Department of Science andTechnology (DST), New Delhi for providing financialsupport under the project no. SP/S2/M-24/99. We wishto thank Dr. J. Vetter and Dr. R. Spohr at GSI, Germanyfor providing irradiation facilities. We are also thankful tothe referee for his useful comments and suggestions.

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