Techniques for Studying Systems Containing Many Positrons, Mills AP, Edited by Humbertson JW and McDowell MRC, Plenum Publishing Corporation, pp. 121-138, 1984
Measurement of the Positronium 13S1-23S1 Interval by Doppler-Free Two-Photon Spectroscopy, Chu S, Mills AP, Hall JL, Physical Review Letters, Volume 52, Number 19, pp. 1689-1692, 5/7/1984