- Email: [email protected]
Erratum to “On the gas-solid difference in stopping power for low energy ions” [Nucl. Instr. and Meth. B 262 (2007) 13]
Available online at www.sciencedirect.com
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 857–858 www.elsevier.com/locate/nimb
Erratum
Erratum to ‘‘On the gas-solid difference in stopping power for low energy ions” [Nucl. Instr. and Meth. B 262 (2007) 13] Helmut Paul * Institut fu¨r Experimentalphysik, Atom- und Oberfla¨chenphysik, Johannes-Kepler-Universita¨t, Altenbergerstrasse 69, A 4040 Linz, Austria Received 30 November 2007 Available online 30 January 2008
Abstract Recently, we claimed that the gas–solid difference in stopping powers persists from high down to low ion energies. This claim was based on a comparison between experimental data and the table of ICRU Report 73. We reconsider this claim in view of a recent article by Sigmund and Schinner where the claim was rejected. We find that the apparent gas–solid difference shown in our calculations is an artifact: it really points to an inadequacy of the table of ICRU 73 for low energy ions. Ó 2008 Elsevier B.V. All rights reserved. PACS: 34.50.Bw Keywords: Energy loss; Stopping power; Ions; Gases; Solids; ICRU Report 73
In [1] we have claimed that the gas–solid difference in mass stopping powers for positive ions persists from high energies – where it is well known [2] – down to low energies. This claim was originally [3] based on a consideration of stopping data for nitrogen ions at the Bohr velocity, v0; it was substantiated more recently [1] by a statistical comparison of experimental stopping power data with the recent stopping power table in ICRU Report 73 [4] which is based on the PASS code by Sigmund and Schinner [5]. In a more recent paper [6], however, Sigmund and Schinner have plausibly demonstrated that the stopping power differences discussed by us are mainly not due to differences in state of aggregation, but rather due to the Z2-structure, i.e., to the periodicity of target properties as a function of the target atomic number Z2. In light of this serious objection it appears therefore that – although all the calculations and the figures presented in our recent paper [1] are correct – our conclusion has to be reconsidered. If the difference found is not due to the differ-
*
DOI of original article: 10.1016/j.nimb.2007.04.283. Tel.: +43 732 2468 8514; fax: +43 732 2468 8509. E-mail address: [email protected]
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.068
ence in state of aggregation, then where does it come from? Fig. 1 shows, graphically, the result of statistical analyses obtained by means of program ‘‘Judge” [7]. It shows the average, D, of the normalized differences (Sexp Stable)/ Sexp, and its standard deviation r, for ions from 3Li to 18Ar, in 17 elemental solids, and in 8 elemental gases (which have been augmented by air, CO2 and CH4 in order to improve the statistical accuracy). Experimental data Sexp have been taken from our collection [8], and the values Stable from ICRU Report 73 which uses a mean ionic charge independent of the state of aggregation, so that an unbiased comparison between solids and gases was to be expected. As Fig. 1 shows, there is perfect agreement between experiment and theory at high energy; but with decreasing energy, the PASS theory becomes too large, much more so for gases than for solids. Therefore, if one assumes the table values to be correct (and, in particular, to be independent of the target state of aggregation) one seemingly gets stopping powers for gases much lower than for solids. We must therefore change the interpretation of the results presented in [1]: the differences found are not due to stopping power differences, but due to inaccuracies of the table in ICRU Report 73 at low energy. P. Sigmund
858
Erratum / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 857–858
is well aware of this problem (see Sec. 6 of [6]), but the problem remains to be solved. Acknowledgement Helpful discussions with Dr. Pedro Grande are gratefully acknowledged. References
Fig. 1. Mean normalized difference D ± r (in %) between experimental stopping data and the table in ICRU Report 73 [4], for substances covered by ICRU Report 73, and for ions from 3Li to 18Ar, in five different ranges of specific energy. According to our sign definition, a negative difference means that the theory is high with respect to experiment. Evidently, the table is too high compared to the data at low energy, much more so for gases than for solids.
[1] H. Paul, Nucl. Instr. and Meth. B 262 (2007) 13. [2] H. Geissel, Y. Laichter, W.F.W. Schneider, P. Armbruster, Nucl. Instr. and Meth. B 194 (1982) 21. [3] H. Paul, Nucl. Instr. and Meth. B 217 (2004) 7. [4] ICRU Report 73, International Commission on Radiation Units and Measurements, J. ICRU 5 (1) (2005). [5] P. Sigmund, A. Schinner, Nucl. Instr. and Meth. B 195 (2002) 64. [6] P. Sigmund, A. Schinner, Nucl. Instr. and Meth. B 263 (2007) 349. [7] H. Paul, A. Schinner, Nucl. Instr. and Meth. B 179 (2001) 299. [8] H. Paul, Stopping Power for Light Ions.
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 857–858 www.elsevier.com/locate/nimb
Erratum
Erratum to ‘‘On the gas-solid difference in stopping power for low energy ions” [Nucl. Instr. and Meth. B 262 (2007) 13] Helmut Paul * Institut fu¨r Experimentalphysik, Atom- und Oberfla¨chenphysik, Johannes-Kepler-Universita¨t, Altenbergerstrasse 69, A 4040 Linz, Austria Received 30 November 2007 Available online 30 January 2008
Abstract Recently, we claimed that the gas–solid difference in stopping powers persists from high down to low ion energies. This claim was based on a comparison between experimental data and the table of ICRU Report 73. We reconsider this claim in view of a recent article by Sigmund and Schinner where the claim was rejected. We find that the apparent gas–solid difference shown in our calculations is an artifact: it really points to an inadequacy of the table of ICRU 73 for low energy ions. Ó 2008 Elsevier B.V. All rights reserved. PACS: 34.50.Bw Keywords: Energy loss; Stopping power; Ions; Gases; Solids; ICRU Report 73
In [1] we have claimed that the gas–solid difference in mass stopping powers for positive ions persists from high energies – where it is well known [2] – down to low energies. This claim was originally [3] based on a consideration of stopping data for nitrogen ions at the Bohr velocity, v0; it was substantiated more recently [1] by a statistical comparison of experimental stopping power data with the recent stopping power table in ICRU Report 73 [4] which is based on the PASS code by Sigmund and Schinner [5]. In a more recent paper [6], however, Sigmund and Schinner have plausibly demonstrated that the stopping power differences discussed by us are mainly not due to differences in state of aggregation, but rather due to the Z2-structure, i.e., to the periodicity of target properties as a function of the target atomic number Z2. In light of this serious objection it appears therefore that – although all the calculations and the figures presented in our recent paper [1] are correct – our conclusion has to be reconsidered. If the difference found is not due to the differ-
*
DOI of original article: 10.1016/j.nimb.2007.04.283. Tel.: +43 732 2468 8514; fax: +43 732 2468 8509. E-mail address: [email protected]
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.068
ence in state of aggregation, then where does it come from? Fig. 1 shows, graphically, the result of statistical analyses obtained by means of program ‘‘Judge” [7]. It shows the average, D, of the normalized differences (Sexp Stable)/ Sexp, and its standard deviation r, for ions from 3Li to 18Ar, in 17 elemental solids, and in 8 elemental gases (which have been augmented by air, CO2 and CH4 in order to improve the statistical accuracy). Experimental data Sexp have been taken from our collection [8], and the values Stable from ICRU Report 73 which uses a mean ionic charge independent of the state of aggregation, so that an unbiased comparison between solids and gases was to be expected. As Fig. 1 shows, there is perfect agreement between experiment and theory at high energy; but with decreasing energy, the PASS theory becomes too large, much more so for gases than for solids. Therefore, if one assumes the table values to be correct (and, in particular, to be independent of the target state of aggregation) one seemingly gets stopping powers for gases much lower than for solids. We must therefore change the interpretation of the results presented in [1]: the differences found are not due to stopping power differences, but due to inaccuracies of the table in ICRU Report 73 at low energy. P. Sigmund
858
Erratum / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 857–858
is well aware of this problem (see Sec. 6 of [6]), but the problem remains to be solved. Acknowledgement Helpful discussions with Dr. Pedro Grande are gratefully acknowledged. References
Fig. 1. Mean normalized difference D ± r (in %) between experimental stopping data and the table in ICRU Report 73 [4], for substances covered by ICRU Report 73, and for ions from 3Li to 18Ar, in five different ranges of specific energy. According to our sign definition, a negative difference means that the theory is high with respect to experiment. Evidently, the table is too high compared to the data at low energy, much more so for gases than for solids.
[1] H. Paul, Nucl. Instr. and Meth. B 262 (2007) 13. [2] H. Geissel, Y. Laichter, W.F.W. Schneider, P. Armbruster, Nucl. Instr. and Meth. B 194 (1982) 21. [3] H. Paul, Nucl. Instr. and Meth. B 217 (2004) 7. [4] ICRU Report 73, International Commission on Radiation Units and Measurements, J. ICRU 5 (1) (2005). [5] P. Sigmund, A. Schinner, Nucl. Instr. and Meth. B 195 (2002) 64. [6] P. Sigmund, A. Schinner, Nucl. Instr. and Meth. B 263 (2007) 349. [7] H. Paul, A. Schinner, Nucl. Instr. and Meth. B 179 (2001) 299. [8] H. Paul, Stopping Power for Light Ions.