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

For the reactions 7-34 A MeV ⁴⁰Ar + ^natAg, 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{symbol}. Detection on the same side of the beam (Δφ{symbol} ≈ 24°) yields a smaller average transverse momentum or energy than on the opposite side (Δφ{symbol} ≈ 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 ^107,9Ag with ⁴⁰Ar 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.