Two-neutron emission induced by stoppedπ−onBe9,B10, andC12

The (${\pi }^{-},2n$) process has been studied in a kinematically complete experiment on three neighboring $1p$-shell nuclei. Distributions of excitation energy of the residual nuclei, of recoil momentum, of the angle between the emitted neutrons, and the angle between the sum and the difference of the neutron momenta have been measured. From the excitation spectra a striking analogy with ($p,2\mathrm{}p$) data has been found in the region of $p$-shell nucleon removal. The possibility of $s$-shell nucleon removal has been investigated. The data are compared with theoretical predictions.