Correlations between pairs of particles and fragments from 40Ar reactions of 7–34 A MeV

Abstract For the reactions 7–34 A MeV 40 Ar + nat Ag, careful measurements have been made of the average transverse momenta for α-particle pairs at a laboratory angle of 67°. They exhibit small but distinct shifts for different relative azimuthal angles Δϕ. Detection on the same side of the beam (Δϕ ≈ 24°) yields a smaller average transverse momentum or energy than on the opposite side (Δϕ ≈ 168°). These small shifts are analyzed with a recoil model to extract the average mass of the first α-particle emitter, i.e. A = 130 ± 10 to 115 ± 10 for reactions of 107,9 Ag with 40 Ar for 7 and 34 A MeV respectively. The overall pattern suggests incomplete fusion with formation of a hot thermalized composite nucleus and its evaporationlike decay.