The spectra in total neutral energy, ETOT0, have been measured in pp, dd and αα collisions at centre-of-mass energy per nucleon pair, sNN, of 31 GeV. The range in ETOT0 covered was 1 to 19 GeV in pp, 18 to 24 GeV in dd and 1 to 34 GeV in αα interactions. The ratio of the αα to the pp spectra rises monotonically from 7 at ETOT0 = 1.5 GeV to 105 at ETOT 0 = 19 GeV. Since ETOT0 is the sum over many particles in the detector, it is directly sensitive to multiple nucleon-nucleon collisions in the interacting α particles. The αα spectrum in the range 8 < ETOT0 < 17 GeV is consistent with being described by a simple model of 4 simultaneous nucleon-nucleon collisions with a cross section about equal to 10% of the observed αα interaction cross section. The spectrum of ETOT0 above 17 GeV is even flatter than this extreme case where four nucleon pairs are interacting.
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We wish to thank the ISR division for the superb performance of the ISR, Robert Gros for his excellent technical help and Marie-Ann Huber for her painstaking secretarial and data reduction duties. The assistance of Keith Potter and Alasdair M. Smith of the ES group is gratefully acknowledged. Ernst Appel and Bernard Pirollet were invaluable at keeping the cryogenics of the solenoid operative. This research has been supported in part by the U.S. Department of Energy under Contract DE-AC02-76CH00016.