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

Abstract Absolute differential cross sections for elastic p 4 He, p 6 He and p 8 He small-angle scattering were measured in inverse kinematics with secondary 4,6,8 He-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 6 He and 8 He, differential elastic-scattering cross sections d σ/ d t were deduced in the range 0.002⩽|t|⩽0.05  (GeV /c ) 2 of the four-momentum transfer squared t . For elastic p 4 He 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 σ el , the total cross sections σ tot , and the total reaction cross sections σ r for the proton–nucleus strong interaction were evaluated. The data obtained on d σ/ d t allow the radial matter distributions in the 6 He and 8 He nuclei to be determined and the corresponding root-mean-square matter radii to be deduced.