Observation of a triple correlation in ternary fission: is time reversal invariance violated?

In ternary fission, besides the two main fission fragments, a third (usuall y light) charged particle is emitted. A triple correlation has been studied involving the momenta for a specific fission fragment (p) over cap(f), the momenta of the ternary particle (P) over cap(t) and the spin of the polari zed cold neutron inducing fission <(sigma)over cap>. The correlation observ able B = <(sigma)over cap> . [(P) over cap(f) x (P) over cap(t)] reverses s ign upon time reversal and thus a non-vanishing value for the expectation v alue [B] could possibly be due to TRI being violated. However, final-state interactions or specific properties of the emission mechanism for ternary p articles could equally well lead to a non-zero [B] with TRI being perfectly conserved. The reaction chosen was U-233(n,f). An unexpectedly large corre lation was observed. From the raw data the value for [B] is [B] = - (0.78 /- 0.02) x 10(-3) with the sign corresponding to light fragments. Correctio ns for neutron polarization, geometric efficiency, resolution of detectors and background increase this figure by a factor of (1.5 +/- 0.3). (C) 2000 Elsevier Science B.V. All rights reserved.