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L subshell ionisation cross section of gold by 8–15 MeV Si ions
Nuclear Instruments and Methods in Physics Research B 152 (1999) 207±211
L subshell ionisation cross section of gold by 8±15 MeV Si ions D. Mitra a, M. Sarkar a, D. Bhattacharya a b
a,*
, P. Sen a, G. Lapicki
b
Saha Institute of Nuclear Physics, 1/AF, Bidhan nagar, Calcutta 700064, India Department of Physics, East Carolina University, Greenville, NC 27858, USA Received 23 June 1998; received in revised form 29 December 1998
Abstract L subshell ionisation cross section of Au induced by 8±15 MeV Si2;3;4 ions have been measured. The data are compared with the theoretical predictions of the ECPSSR, and ecacy of incorporating the intra shell (IS) coupling into ECPSSR is examined. The eect of simultaneous multiple ionisation on the data is discussed qualitatively. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 34.50.Fa
1. Introduction The present work is a continuation of our earlier investigations [1±3] on the L shell ionisation induced by low velocity heavy ions. Discrepancies between the predictions of the ECPSSR theory and L subshell [L1 (2s1=2 ), L2 (2p1=2 ) and L3 (2p3=2 )] ionisation data have been reported earlier in the literature. Quite often, there exist order of magnitude dierences, especially for low projectile velocities. We are mainly interested to ®nd out the extent to which the introduction of the intra shell (IS) coupling bridges the gap between the measured values and the theoretical predictions of ECPSSR. Using data for Z1 6, 7 and 8 we had observed [2] that the IS coupling is, indeed, im-
* Corresponding author. Tel.: +91 337 5345 49; fax: +91 033 3374 637.
portant, especially for the L2 subshell. It is expected that the IS factor would be more pronounced as the nuclear charge of the projectile increases. In the present work we have investigated the L subshell ionisation of Au induced by 8±15 MeV Si ions. 2. Experiment Details of the experimental arrangement are described in our earlier papers [1,3] and only a short description is given here. The experiment was performed with the 3 MV 9SDH-2 Tandem Pelletron at the Institute of Physics, Bhubaneswar, India. Ions of Si2 (8.09 MeV), Si3 (10.82 MeV) and Si4 (13.43, 14.90 MeV) were used for this measurement. The beam passed through two graphite collimators of diameter 3 mm located at a distance of 75 mm from each other so that the
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 0 1 6 - 6
208
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
rx
rR h dX Yx F; e Yp
1
where rx is the X-ray production cross section, rR h is the Rutherford scattering cross section at an angle h, dX is the solid angle subtended by the particle detector at the target, e is the eective ef®ciency of the Si(Li) detector including solid angle, Yx is the X-ray yield, Yp is the back scattered particle yield and F is the correction factor due to slowing down of the projectile and self absorption of the X-rays inside the target. Writing a similar expression for silicon ions and taking the ratio one gets rx silicon
Fig. 1. Lc spectrum of gold bombarded by 10.82 MeV silicon ions.
beam spot on the target is approximately 3 mm. The target was placed at 45° with respect to the beam. A Si(Li) detector having a resolution of 160 eV at 5.9 keV was placed at 90° to the beam. Simultaneous measurements of the back scattered particles were done with a Si surface barrier detector kept at an angle of 135°. The ionisation cross section measurement was normalized to that for the protons of 2 MeV. The Au target was 70 lg/cm2 thick on a 20 lg/cm2 carbon backing. To suppress the high count rate due to M X-rays, a thin foil of Al (5 mg/cm2 ) was placed in front of the Si(Li) detector. A typical X-ray spectrum is shown in Fig. 1. The total count rate was always less than 1000 cps. The average current was 10 nA and the time taken for one run was 1 h. 3. Data analysis and results The X-ray production cross section for a particular X-ray line induced by protons can be written as
rR h Yx =Yp F silicon rx proton : rR h Yx =Yp F proton
2
The areas under the required peaks e.g. La , Lc1 and Lc2;3;6;8 were obtained using the program ACTIV [4], with a linear background. The correction factor (F) ± which accounts for the slowing down of the projectile and also the self absorption of the X-rays inside the target was calculated using Eq. (2) of Braziewicz et al. [5]. Its magnitude increased from 1.12 to 1.20 with decreasing velocity of the incident silicon ions in the present investigation, while the calculated F factor for 2 MeV protons is '1.01. One should also consider a possible eect of anisotropy of X-rays emitted from subshells having j > 1=2. In our experiment only La had to be corrected for this eect while Lc1 and Lc2;3 are isotropic as they originate from the j 1/2 states. From the anisotropy measurements of Jitschin et al. [6,28] on Au L X-rays induced by Si, it follows that in our energy range and the X-rays being measured at 90° the increase in the intensity of La line due to anisotropy would be 0.2% and for 2.1 MeV protons this increase would be 0.3%. Hence the anisotropy correction in the present experiment is negligible. Using the recommended proton cross sections of Reis and Jesus [7] in our Eq. (2), the silicon induced X-ray production cross sections of gold for the lines La , Lc1 and Lc2;3 were obtained following the method of analysis prescribed by Semaniak et al. [8]. These are given in Table 1. From these production cross sections ± with the ¯uorescence
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211 Table 1 Measured L X-ray production cross sections of gold bombarded by silicon ions Energy (MeV)
La (mb)
Lc1 (mb)
Lc2;3 (mb)
8.09 10.82 13.43 14.90
952 105 4266 469 12278 1351 18250 2008
72 9 391 51 980 127 1640 213
31 4 112 16 222 31 360 50
yields and Coster±Kronig transition rates from set 1 of Ref. [9] and the radiative widths from [10], the subshell ionisation cross sections were derived using the standard prescription given by Datz et al. [11]. All the three L subshell ionisation cross sections so obtained are shown in Fig. 2 as solid circles.
Fig. 2. L subshell ionisation cross sections of gold bombarded by silicon ions. . . . . . . First Born Approximation, ÐÐ ECPSSR, --- ECPSSR + IS, This work, M Malhi and Gray [12] and Dhal et al. [13]. The size of the data points re¯ects the statistical errors in the measurements.
209
The main sources of error in the present measurement arise from: (1) a 10% error in the proton cross sections from [7], (2) a 5% error in the correction factor F for silicon from [5] and (3) a statistical error arising from X-ray and back scattered yields for the Si and proton bombardment. 4. Discussion Our data are shown in Fig. 2 along with the measurements of Malhi and Gray [12], and those of Dhal et al. [13]. Malhi and Gray had published the production cross sections of La , Lc1 , Lc2;3;6 from which the L subshell ionisation cross sections have been calculated using the atomic parameters used in the present work. These are shown in Fig. 2. L subshell ionisation cross sections as predicted by the First Born Approximation [14], ECPSSR theory [15] and ECPSSR including IS eect [16±20] are also displayed in Fig. 2. As seen in Fig. 2, our data are generally an order of magnitude lower than those of Malhi and Gray [12] and a factor of 5 above those of Dhal et al. [13]. These discrepancies, especially an enormous gap between Refs. [12,13], raise serious concerns. While we cannot pinpoint with full knowledge as to why the work of others exhibits such disparities, a few comments are appropriate here. Malhi and Gray's analysis requires a signi®cant correction for projectile energy loss in the target which was a thick gold foil. We cannot estimate this correction because the authors did not report the thickness of their Au foils. Furthermore, with the clarity of their proton-induced spectrum being comparable to our Si-induced spectrum, one may seriously question the reliability of the data extracted from their much more obscure silicongenerated spectrum. Malhi and Gray state that the data are normalised to La X-ray production cross section in Au by 3 MeV protons of Ref. [11]; however, Datz et al. have not given a value for such a cross section in their Ref. [11]. For a consistent comparison of these data with our measurement and ionisation theories, we have converted them to ionisation cross sections using
210
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
the same atomic parameters. A choice of a dierent set of atomic parameters practically does not aect the gap between our data and those of Ref. [12]. To trace reasons for the discrepancies with the data of Dhal et al. [13], we went to Dhal's thesis [21] which describes the methods of measurements and analysis in details that are not present in Ref. [13]. As mentioned in the pioneering work of Datz et al. [11], a standard practice of extraction of the L-subshell ionisation cross sections is based on a careful separation of the Lc2;3;6 line into its components e.g., Lc2;3 and Lc6 Dhal et al. have not followed this standard practice; instead they took recourse to an iterative method [22]. This procedure may have resulted in a systematic underestimate of the extracted subshell ionisation cross sections. Moreover, we were unable to determine what reference cross section was used in the normalisation of the data of Dhal et al. who also have not reported their measured values of X-ray production cross sections. It should be noted that a contemporaneous publication of the same group [23] was sharply criticized by Sarkadi et al. [24]. For all the subshells, the predictions of First Born Approximation exceeded both our and Dhal et al. measurements by an order of magnitude, while yielding a surprisingly good agreement with the data of Malhi and Gray. The predictions of ECPSSR ®t our L1 subshell data well but they underestimate the data for L2 and L3 subshells by factors of 10 and 5 respectively. In contrast, the data of Dhal et al. are lower by a factor of 3 for L1 , and higher by a factor of 3 and 1.5 for the L2 and L3 subshell respectively. Incorporation of the IS eect [25] into ECPSSR spoils the agreement with our data by a factor of 5 for L1 , diminishes the gap between our data and theory for L2 subshell while for the L3 it makes virtually no dierence. When compared with Dhal et al., the ECPSSR+IS gives nearly perfect ®ts both for L1 and L2 subshell but no change for the L3 subshell. We had shown in our earlier analysis [2], that within the range of nR /f 0.20±0.45, the ECPSSR + IS substantially improved the agreement with the L2 subshell data although still predicting a lower value than the measurement. For the L1 subshell, ECPSSR without inclusion of IS eect
appeared to be quite good, but inclusion of IS lowered the theoretical values by a factor of 2±3. For the L3 subshell, there was practically no change after the inclusion of the IS eect and the predictions of both theories were always lower than measurements by a factor of 2. In the present collision system, the ranges of nR /f 0.20±0.28 overlaps with the low velocity part of our earlier analysis [2]. The conclusions of [2] are consistent with our present ®ndings. It is a well established fact that heavy ions cause more simultaneous multiple ionisation (MI) than protons or helium ions. The energy shift of different L lines induced by heavy ions relative to the lines induced by protons is a measure of MI occuring in ion±atom collisions. In the present case, the energy shift of the Au La line was found to be 40 eV. According to Uchai et al. [26], such an energy shift would correspond to 1±2 spectator vacancies in the M5 (3d5=2 ) subshell. Jitschin et al. [27] noted that the presence of a single vacancy in the M shell may increase the ¯uorescence yield of the L1 subshell by a factor of 2, while the increase in the ¯uorescence yields for L2 and L3 subshells would be of lesser signi®cance. With these enhanced values of the ¯uorescence yields, our ionisation cross section for the L1 subshell would have been reduced by at least a factor of two and thus would agree well with the ECPSSR + IS predictions while the data of Dhal et al. would fall below by the same factor. For the L2 and L3 subshells, as the increase in eective ¯uorescence yield is less than that of x1 , the downward shifts of the data points would be less dramatic. It is dicult to arrive at a de®nitive conclusion from a few data sets for L subshell ionisation of gold by silicon ions. Not only is there paucity of experimental information, but these few data sets show unacceptable dierences between themselves. Margins of error claimed in these works are dwarfed by the size of the very large dierences between the reported measurements. Certainly, more data taken with low velocity heavy ions are needed to sort out the present disagreement between the data taken by various groups. Ultimately, the data that are proven to be reliable and accurate will help to quantify the ecacy of incorporation of the IS eect into the ECPSSR theory.
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
Acknowledgements The authors thank the crew of the pelletron machine for supply of the various ion beams and Prof. Laszl o Sarkadi for his ECPSSR+IS calculations. The authors are also grateful to T. Czyzewski for the kind donation of the ACTIV program. References [1] D. Bhattacharya, M. Sarkar, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Phys. Rev. A 49 (1994) 4616. [2] M. Sarkar, D. Bhattacharya, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Nucl. Instr. and Meth. B 103 (1995) 23. [3] D. Mitra, M. Sarkar, D. Bhattacharya, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Phys. Rev. A 53 (1996) 2309. [4] V.B. Zlokazov, Comp. Phys. Commun. 28 (1982) 27. [5] J. Braziewicz, M. Pajek, E. Braziewicz, J. Ploskonka, G.M. Osetynski, J. Phys. B 17 (1984) 1589. [6] W. Jitschin, R. Hippler, R. Shanker, H. Kleinpoppen, R. Schuch, H.O. Lutz, J. Phys. B 16 (1983) 1417. [7] M.A. Reis, A.P. Jesus, At. Data and Nucl. Data Tables 63 (1996) 1. [8] J. Semaniak, J. Braziewicz, M. Pajek, T. Czyzewski, L. Glowacka, M. Jaskola, M. Haller, R. Karschnick, W. Kretschmer, Z. Halabuka, D. Trautmann, Phys. Rev. A 52 (1995) 1125. [9] L. Sarkadi, T. Mukoyama, J. Phys. B 13 (1980) 2255. [10] J.L. Campbell, J.-X. Wang, At. Data and Nucl. Data Tables 43 (1989) 281. [11] S. Datz, J.L. Duggan, L.C. Feldman, E. Laegsgaard, J.U. Andersen, Phys. Rev. A 9 (1974) 192.
211
[12] N.B. Malhi, T.J. Gray, Phys. Rev. A 44 (1991) 7199. [13] B.B. Dhal, H.C. Padhi, D. Trautmann, Nucl. Instr. and Meth. B 117 (1996) 218. [14] E. Merzbacher and L.W. Lewis, in X-ray Production by Heavy Charged Partcles ± edited by S. Fl ugge, Encyclopedia of Physics Vol. 34, Springer, Berlin 1958; B. -H. Choi, E. Merzbacher and G. S. Khandelwal, At. Data 5 (1973) 291, for direct ionisation in the Plane Wave Born Approximation (PWBA) and the V. S. Nikolaev, Zh. Eksp. Teor. Fiz. 51 (1966) 1263 [ Sov. Phys. ± JETP 24 (1967) 847] formula in the OBK approximation for electron capture, with the projectile charge state taken as the charge state of the incident ion. [15] W. Brandt and G. Lapicki, Phys. Rev. A 23 (1981) 1717, for direct ionisation and G. Lapicki and F. D. McDaniel, Phys. Rev. A22 (1980) 1896; A23 (1981) 975(E) for electron capture, with the projectile charge state taken as the charge state of the incident ion. [16] L. Sarkadi, T. Mukoyama, J. Phys B 14 (1981) L255. [17] L. Sarkadi, T. Mukoyama, Nucl. Instr. and Meth. B 4 (1984) 296. [18] L. Sarkadi, T. Mukoyama, Phys. Rev. A 37 (1988) 4540. [19] L. Sarkadi, T. Mukoyama, J. Phys, B 23 (1990) 3849. [20] L. Sarkadi, T. Mukoyama, Nucl. Instr. and Meth. B 61 (1991) 167. [21] B.B. Dhal, Ph. D. Thesis (1996) Utkal University, India. [22] C.N. Chang, J.F. Morgan, S.L. Blatt, Phys. Rev. A 11 (1975) 607. [23] H.C. Padhi, B.B. Dhal, T. Nandi, D. Trautmann, J. Phys. B 28 (1995) L59. Smit, [24] L. Sarkadi, T. Mukoyama, Z J. Phys. B 29 (1996) 2253. [25] L. Sarkadi (Private Communication). [26] W. Uchai, C.W. Nestor, S. Raman Jr, C.R. Vane, At. Data and Nucl. Data Tables 34 (1986) 201. [27] W. Jitschin, R. Hippler, K. Finck, R. Schuch, H.O. Lutz, J. Phys. B 16 (1983) 4405. [28] W. Jitschin, H. Kleinpoppen, R. Hippler, H.O. Lutz, J. Phys. B 12 (1979) 4077.
L subshell ionisation cross section of gold by 8±15 MeV Si ions D. Mitra a, M. Sarkar a, D. Bhattacharya a b
a,*
, P. Sen a, G. Lapicki
b
Saha Institute of Nuclear Physics, 1/AF, Bidhan nagar, Calcutta 700064, India Department of Physics, East Carolina University, Greenville, NC 27858, USA Received 23 June 1998; received in revised form 29 December 1998
Abstract L subshell ionisation cross section of Au induced by 8±15 MeV Si2;3;4 ions have been measured. The data are compared with the theoretical predictions of the ECPSSR, and ecacy of incorporating the intra shell (IS) coupling into ECPSSR is examined. The eect of simultaneous multiple ionisation on the data is discussed qualitatively. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 34.50.Fa
1. Introduction The present work is a continuation of our earlier investigations [1±3] on the L shell ionisation induced by low velocity heavy ions. Discrepancies between the predictions of the ECPSSR theory and L subshell [L1 (2s1=2 ), L2 (2p1=2 ) and L3 (2p3=2 )] ionisation data have been reported earlier in the literature. Quite often, there exist order of magnitude dierences, especially for low projectile velocities. We are mainly interested to ®nd out the extent to which the introduction of the intra shell (IS) coupling bridges the gap between the measured values and the theoretical predictions of ECPSSR. Using data for Z1 6, 7 and 8 we had observed [2] that the IS coupling is, indeed, im-
* Corresponding author. Tel.: +91 337 5345 49; fax: +91 033 3374 637.
portant, especially for the L2 subshell. It is expected that the IS factor would be more pronounced as the nuclear charge of the projectile increases. In the present work we have investigated the L subshell ionisation of Au induced by 8±15 MeV Si ions. 2. Experiment Details of the experimental arrangement are described in our earlier papers [1,3] and only a short description is given here. The experiment was performed with the 3 MV 9SDH-2 Tandem Pelletron at the Institute of Physics, Bhubaneswar, India. Ions of Si2 (8.09 MeV), Si3 (10.82 MeV) and Si4 (13.43, 14.90 MeV) were used for this measurement. The beam passed through two graphite collimators of diameter 3 mm located at a distance of 75 mm from each other so that the
0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 0 1 6 - 6
208
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
rx
rR h dX Yx F; e Yp
1
where rx is the X-ray production cross section, rR h is the Rutherford scattering cross section at an angle h, dX is the solid angle subtended by the particle detector at the target, e is the eective ef®ciency of the Si(Li) detector including solid angle, Yx is the X-ray yield, Yp is the back scattered particle yield and F is the correction factor due to slowing down of the projectile and self absorption of the X-rays inside the target. Writing a similar expression for silicon ions and taking the ratio one gets rx silicon
Fig. 1. Lc spectrum of gold bombarded by 10.82 MeV silicon ions.
beam spot on the target is approximately 3 mm. The target was placed at 45° with respect to the beam. A Si(Li) detector having a resolution of 160 eV at 5.9 keV was placed at 90° to the beam. Simultaneous measurements of the back scattered particles were done with a Si surface barrier detector kept at an angle of 135°. The ionisation cross section measurement was normalized to that for the protons of 2 MeV. The Au target was 70 lg/cm2 thick on a 20 lg/cm2 carbon backing. To suppress the high count rate due to M X-rays, a thin foil of Al (5 mg/cm2 ) was placed in front of the Si(Li) detector. A typical X-ray spectrum is shown in Fig. 1. The total count rate was always less than 1000 cps. The average current was 10 nA and the time taken for one run was 1 h. 3. Data analysis and results The X-ray production cross section for a particular X-ray line induced by protons can be written as
rR h Yx =Yp F silicon rx proton : rR h Yx =Yp F proton
2
The areas under the required peaks e.g. La , Lc1 and Lc2;3;6;8 were obtained using the program ACTIV [4], with a linear background. The correction factor (F) ± which accounts for the slowing down of the projectile and also the self absorption of the X-rays inside the target was calculated using Eq. (2) of Braziewicz et al. [5]. Its magnitude increased from 1.12 to 1.20 with decreasing velocity of the incident silicon ions in the present investigation, while the calculated F factor for 2 MeV protons is '1.01. One should also consider a possible eect of anisotropy of X-rays emitted from subshells having j > 1=2. In our experiment only La had to be corrected for this eect while Lc1 and Lc2;3 are isotropic as they originate from the j 1/2 states. From the anisotropy measurements of Jitschin et al. [6,28] on Au L X-rays induced by Si, it follows that in our energy range and the X-rays being measured at 90° the increase in the intensity of La line due to anisotropy would be 0.2% and for 2.1 MeV protons this increase would be 0.3%. Hence the anisotropy correction in the present experiment is negligible. Using the recommended proton cross sections of Reis and Jesus [7] in our Eq. (2), the silicon induced X-ray production cross sections of gold for the lines La , Lc1 and Lc2;3 were obtained following the method of analysis prescribed by Semaniak et al. [8]. These are given in Table 1. From these production cross sections ± with the ¯uorescence
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211 Table 1 Measured L X-ray production cross sections of gold bombarded by silicon ions Energy (MeV)
La (mb)
Lc1 (mb)
Lc2;3 (mb)
8.09 10.82 13.43 14.90
952 105 4266 469 12278 1351 18250 2008
72 9 391 51 980 127 1640 213
31 4 112 16 222 31 360 50
yields and Coster±Kronig transition rates from set 1 of Ref. [9] and the radiative widths from [10], the subshell ionisation cross sections were derived using the standard prescription given by Datz et al. [11]. All the three L subshell ionisation cross sections so obtained are shown in Fig. 2 as solid circles.
Fig. 2. L subshell ionisation cross sections of gold bombarded by silicon ions. . . . . . . First Born Approximation, ÐÐ ECPSSR, --- ECPSSR + IS, This work, M Malhi and Gray [12] and Dhal et al. [13]. The size of the data points re¯ects the statistical errors in the measurements.
209
The main sources of error in the present measurement arise from: (1) a 10% error in the proton cross sections from [7], (2) a 5% error in the correction factor F for silicon from [5] and (3) a statistical error arising from X-ray and back scattered yields for the Si and proton bombardment. 4. Discussion Our data are shown in Fig. 2 along with the measurements of Malhi and Gray [12], and those of Dhal et al. [13]. Malhi and Gray had published the production cross sections of La , Lc1 , Lc2;3;6 from which the L subshell ionisation cross sections have been calculated using the atomic parameters used in the present work. These are shown in Fig. 2. L subshell ionisation cross sections as predicted by the First Born Approximation [14], ECPSSR theory [15] and ECPSSR including IS eect [16±20] are also displayed in Fig. 2. As seen in Fig. 2, our data are generally an order of magnitude lower than those of Malhi and Gray [12] and a factor of 5 above those of Dhal et al. [13]. These discrepancies, especially an enormous gap between Refs. [12,13], raise serious concerns. While we cannot pinpoint with full knowledge as to why the work of others exhibits such disparities, a few comments are appropriate here. Malhi and Gray's analysis requires a signi®cant correction for projectile energy loss in the target which was a thick gold foil. We cannot estimate this correction because the authors did not report the thickness of their Au foils. Furthermore, with the clarity of their proton-induced spectrum being comparable to our Si-induced spectrum, one may seriously question the reliability of the data extracted from their much more obscure silicongenerated spectrum. Malhi and Gray state that the data are normalised to La X-ray production cross section in Au by 3 MeV protons of Ref. [11]; however, Datz et al. have not given a value for such a cross section in their Ref. [11]. For a consistent comparison of these data with our measurement and ionisation theories, we have converted them to ionisation cross sections using
210
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
the same atomic parameters. A choice of a dierent set of atomic parameters practically does not aect the gap between our data and those of Ref. [12]. To trace reasons for the discrepancies with the data of Dhal et al. [13], we went to Dhal's thesis [21] which describes the methods of measurements and analysis in details that are not present in Ref. [13]. As mentioned in the pioneering work of Datz et al. [11], a standard practice of extraction of the L-subshell ionisation cross sections is based on a careful separation of the Lc2;3;6 line into its components e.g., Lc2;3 and Lc6 Dhal et al. have not followed this standard practice; instead they took recourse to an iterative method [22]. This procedure may have resulted in a systematic underestimate of the extracted subshell ionisation cross sections. Moreover, we were unable to determine what reference cross section was used in the normalisation of the data of Dhal et al. who also have not reported their measured values of X-ray production cross sections. It should be noted that a contemporaneous publication of the same group [23] was sharply criticized by Sarkadi et al. [24]. For all the subshells, the predictions of First Born Approximation exceeded both our and Dhal et al. measurements by an order of magnitude, while yielding a surprisingly good agreement with the data of Malhi and Gray. The predictions of ECPSSR ®t our L1 subshell data well but they underestimate the data for L2 and L3 subshells by factors of 10 and 5 respectively. In contrast, the data of Dhal et al. are lower by a factor of 3 for L1 , and higher by a factor of 3 and 1.5 for the L2 and L3 subshell respectively. Incorporation of the IS eect [25] into ECPSSR spoils the agreement with our data by a factor of 5 for L1 , diminishes the gap between our data and theory for L2 subshell while for the L3 it makes virtually no dierence. When compared with Dhal et al., the ECPSSR+IS gives nearly perfect ®ts both for L1 and L2 subshell but no change for the L3 subshell. We had shown in our earlier analysis [2], that within the range of nR /f 0.20±0.45, the ECPSSR + IS substantially improved the agreement with the L2 subshell data although still predicting a lower value than the measurement. For the L1 subshell, ECPSSR without inclusion of IS eect
appeared to be quite good, but inclusion of IS lowered the theoretical values by a factor of 2±3. For the L3 subshell, there was practically no change after the inclusion of the IS eect and the predictions of both theories were always lower than measurements by a factor of 2. In the present collision system, the ranges of nR /f 0.20±0.28 overlaps with the low velocity part of our earlier analysis [2]. The conclusions of [2] are consistent with our present ®ndings. It is a well established fact that heavy ions cause more simultaneous multiple ionisation (MI) than protons or helium ions. The energy shift of different L lines induced by heavy ions relative to the lines induced by protons is a measure of MI occuring in ion±atom collisions. In the present case, the energy shift of the Au La line was found to be 40 eV. According to Uchai et al. [26], such an energy shift would correspond to 1±2 spectator vacancies in the M5 (3d5=2 ) subshell. Jitschin et al. [27] noted that the presence of a single vacancy in the M shell may increase the ¯uorescence yield of the L1 subshell by a factor of 2, while the increase in the ¯uorescence yields for L2 and L3 subshells would be of lesser signi®cance. With these enhanced values of the ¯uorescence yields, our ionisation cross section for the L1 subshell would have been reduced by at least a factor of two and thus would agree well with the ECPSSR + IS predictions while the data of Dhal et al. would fall below by the same factor. For the L2 and L3 subshells, as the increase in eective ¯uorescence yield is less than that of x1 , the downward shifts of the data points would be less dramatic. It is dicult to arrive at a de®nitive conclusion from a few data sets for L subshell ionisation of gold by silicon ions. Not only is there paucity of experimental information, but these few data sets show unacceptable dierences between themselves. Margins of error claimed in these works are dwarfed by the size of the very large dierences between the reported measurements. Certainly, more data taken with low velocity heavy ions are needed to sort out the present disagreement between the data taken by various groups. Ultimately, the data that are proven to be reliable and accurate will help to quantify the ecacy of incorporation of the IS eect into the ECPSSR theory.
D. Mitra et al. / Nucl. Instr. and Meth. in Phys. Res. B 152 (1999) 207±211
Acknowledgements The authors thank the crew of the pelletron machine for supply of the various ion beams and Prof. Laszl o Sarkadi for his ECPSSR+IS calculations. The authors are also grateful to T. Czyzewski for the kind donation of the ACTIV program. References [1] D. Bhattacharya, M. Sarkar, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Phys. Rev. A 49 (1994) 4616. [2] M. Sarkar, D. Bhattacharya, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Nucl. Instr. and Meth. B 103 (1995) 23. [3] D. Mitra, M. Sarkar, D. Bhattacharya, M.B. Chatterjee, P. Sen, G. Kuri, D.P. Mahapatra, G. Lapicki, Phys. Rev. A 53 (1996) 2309. [4] V.B. Zlokazov, Comp. Phys. Commun. 28 (1982) 27. [5] J. Braziewicz, M. Pajek, E. Braziewicz, J. Ploskonka, G.M. Osetynski, J. Phys. B 17 (1984) 1589. [6] W. Jitschin, R. Hippler, R. Shanker, H. Kleinpoppen, R. Schuch, H.O. Lutz, J. Phys. B 16 (1983) 1417. [7] M.A. Reis, A.P. Jesus, At. Data and Nucl. Data Tables 63 (1996) 1. [8] J. Semaniak, J. Braziewicz, M. Pajek, T. Czyzewski, L. Glowacka, M. Jaskola, M. Haller, R. Karschnick, W. Kretschmer, Z. Halabuka, D. Trautmann, Phys. Rev. A 52 (1995) 1125. [9] L. Sarkadi, T. Mukoyama, J. Phys. B 13 (1980) 2255. [10] J.L. Campbell, J.-X. Wang, At. Data and Nucl. Data Tables 43 (1989) 281. [11] S. Datz, J.L. Duggan, L.C. Feldman, E. Laegsgaard, J.U. Andersen, Phys. Rev. A 9 (1974) 192.
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[12] N.B. Malhi, T.J. Gray, Phys. Rev. A 44 (1991) 7199. [13] B.B. Dhal, H.C. Padhi, D. Trautmann, Nucl. Instr. and Meth. B 117 (1996) 218. [14] E. Merzbacher and L.W. Lewis, in X-ray Production by Heavy Charged Partcles ± edited by S. Fl ugge, Encyclopedia of Physics Vol. 34, Springer, Berlin 1958; B. -H. Choi, E. Merzbacher and G. S. Khandelwal, At. Data 5 (1973) 291, for direct ionisation in the Plane Wave Born Approximation (PWBA) and the V. S. Nikolaev, Zh. Eksp. Teor. Fiz. 51 (1966) 1263 [ Sov. Phys. ± JETP 24 (1967) 847] formula in the OBK approximation for electron capture, with the projectile charge state taken as the charge state of the incident ion. [15] W. Brandt and G. Lapicki, Phys. Rev. A 23 (1981) 1717, for direct ionisation and G. Lapicki and F. D. McDaniel, Phys. Rev. A22 (1980) 1896; A23 (1981) 975(E) for electron capture, with the projectile charge state taken as the charge state of the incident ion. [16] L. Sarkadi, T. Mukoyama, J. Phys B 14 (1981) L255. [17] L. Sarkadi, T. Mukoyama, Nucl. Instr. and Meth. B 4 (1984) 296. [18] L. Sarkadi, T. Mukoyama, Phys. Rev. A 37 (1988) 4540. [19] L. Sarkadi, T. Mukoyama, J. Phys, B 23 (1990) 3849. [20] L. Sarkadi, T. Mukoyama, Nucl. Instr. and Meth. B 61 (1991) 167. [21] B.B. Dhal, Ph. D. Thesis (1996) Utkal University, India. [22] C.N. Chang, J.F. Morgan, S.L. Blatt, Phys. Rev. A 11 (1975) 607. [23] H.C. Padhi, B.B. Dhal, T. Nandi, D. Trautmann, J. Phys. B 28 (1995) L59. Smit, [24] L. Sarkadi, T. Mukoyama, Z J. Phys. B 29 (1996) 2253. [25] L. Sarkadi (Private Communication). [26] W. Uchai, C.W. Nestor, S. Raman Jr, C.R. Vane, At. Data and Nucl. Data Tables 34 (1986) 201. [27] W. Jitschin, R. Hippler, K. Finck, R. Schuch, H.O. Lutz, J. Phys. B 16 (1983) 4405. [28] W. Jitschin, H. Kleinpoppen, R. Hippler, H.O. Lutz, J. Phys. B 12 (1979) 4077.