Effect of electron correlation on positronium formation in positron-helium scattering P. Chaudhuri, S. K. Adhikari, B. Talukdar and S. Bhattacharyya Eur. Phys. J. D, 5 2 (1999) 217-220 Published online: 15 February 1999 DOI: 10.1007/s100530050247