Nuclear Physics B75 (1974) 77-92. North-Holland Publishing Company AN EXPERIMENTAL INVESTIGATION OF ~r PHOTOPRODUCTION PROCESSES ON 3 He G. GOGGI, G.C. MANTOVANI, A. PIAZZOLI and D. SCANNICCHIO lstituto di bTsica dell'Universita di Pavia, lstituto Nazionale di Fisica Nucleare - Sezione di Pavia Received 21 May 1973 (Revised 28 January 1974) Abstract: Experimental results are reported on single and double n photoproduction on 311e up to E7 = 800 MeV. The cross sections per equivalent quantum, total cross sections as a function of the photon energy and angular distributions are given, In the double charged photoproduction channel the Prt + and Pn- invariant mass distribu- tions are presented and compared with the predictions of an isobaric model assuming the im- pulse approximation. There is also evidence for n+n + photoproduction in analogy with n+n + and rr n produc- tion on 4 He seen in a previous experiment. The data seem generally consistent with the available theoretical predictions based on the impulse approximation. 1. Introduction We report the results of an analysis of single and double pion photoproduction on 3He carried out with a diffusion cloud chamber exposed to the 1 GeV brems- strahlung beam of the Frascati electrosynchrotron. The 3He nucleus still presents some well known and unsolved problems, such as the anomaly of the magnetic moment and the possible relevant presence of a three- body interaction [ 1-8]. The lack of experimental data, mainly above the pionic threshold [9-16, 33], justified the interest for an overall investigation of the photo- reactions on 3 He as a general approach to the study of its dynamical properties and in order to detect possible effects related to these problems. Recently elastic and inelastic n ÷ photoproduction processes were investigated theoretically; total cross sections and angular distributions were calculated under various assumptions, mainly in the usual frame of the impulse approximation (I.A.) [17-19,34]. The available experimental data concern mainly elastic rr÷ photoproduction [9], for which the differential cross section at various energies was determined. We mea- sured cross sections of different photoproduction processes; for some reactions