This is an authorised electronic reprint of the paper published as Journal of Synchrotron Radiation, 2003, 10 (2), p. 197. This paper is available from http://scripts.iucr.org/cgi-bin/paper?S0909049503002656. Doi: 10.1107/S0909049503002656Two typographical errors have been observed in the paper by Roy et al. [J. Synchrotron Rad. (2001), 8, 1103-1108]
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