Small-angle proton elastic scattering from the neutron-rich isotopes 6He and 8He, and from 4He, at 0.7 GeV in inverse kinematics

Absolute differential cross sections for elastic p4He, p6He and p8He small-angle scattering were measured in inverse kinematics with secondary 4,6,8He-beams at an energy near 0.7 GeV/u. The experiment was performed using beams from the heavy-ion synchrotron SIS and the fragment separator FRS of GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. Projectile scattering angles were measured with multi-wire tracking detectors. For proton scattering from the neutron-rich isotopes 6He and 8He, differential elastic-scattering cross sections dσ/dt were deduced in the range 0.002⩽|t|⩽0.05 (GeV/c)2 of the four-momentum transfer squared t. For elastic p4He scattering, the data obtained in the t-range 0.002⩽|t|⩽0.02 (GeV/c)2 supplement the results from an earlier work performed in direct kinematics. From the differential cross sections the integral elastic-scattering cross sections σel, the total cross sections σtot, and the total reaction cross sections σr for the proton–nucleus strong interaction were evaluated. The data obtained on dσ/dt allow the radial matter distributions in the 6He and 8He nuclei to be determined and the corresponding root-mean-square matter radii to be deduced.