Projectile fragmentation reactions and production of nuclei near the neutron drip line

Abstract

The reaction mechanism of projectile fragmentation at intermediate energies has been investigated observing the target dependence of the production cross sections of very neutron-rich nuclei. Measurement of longitudinal momentum distributions of projectile-like fragments within a wide range of fragment mass and its charge was performed using a hundred-MeV/n 40 Ar beam incident on Be and Ta targets. By measurement of fragment momentum distribution, a parabolic mass dependence of momentum peak shift was observed in the results of both targets, and a phenomenon of light-fragment acceleration was found only in the Be-target data. The analysis of production cross sections revealed an obvious enhancement of the target dependence except target size effect when the neutron excess is increased. This result implies the breakdown of factorization (BOF) of production cross sections for very neutron-rich nuclei near the drip line.

Projectile fragmentation reactions of40Ar at 57 MeV/nucleon

“…Similar results have been found in experiments of 86 Kr at 64 MeV/nucleon and 40 Ar at 90-94 MeV/nucleon on 9 Be and 181 Ta targets [19,20]. In addition, experiments have also shown that the production cross sections of the isotopes far from the stability valley are enhanced in the reactions on 181 Ta target, which implies that the factorization hypothesis is invalid for * sunzhy@impcas.ac.cn very neutron-rich and very proton-rich isotopes, maybe due to the transfer reaction involved [20,21].…”

“…But at intermediate energies, different results have already been observed by many groups [19][20][21]42].…”

Modified EPAX2 parameterization for estimating the fragment cross sections at intermediate energies

“…In Fig. 9(a), (b), (c), (d), (e) and (f), we plot the cross section ratios σ exp /σ EPAX2 for many reaction systems [10][11][12]. The ratios calculated by EPAX2 are shown as dashed lines, and the ones calculated by modified EPAX2 are shown as solid lines.…”

“…The experimental results show that at intermediate energies the fragmentation cross sections for fragments far from the stability line are over-estimated in EPAX2 calculations [10][11][12][13]. Especially for proton-rich fragments, the EPAX2 calculations over-estimated some cross sections by nearly a factor of 100 [13].…”

“…Especially for proton-rich fragments, the EPAX2 calculations over-estimated some cross sections by nearly a factor of 100 [13]. In addition, the phenomenon that the cross sections for the fragments far from the stability line are enhanced for a given isobar with 181 Ta target has been observed [11,12], and this enhancement decreases rapidly with increasing projectile energy and finally becomes negligible at relativistic energies [13]. This invalidity of limiting factorization for fragments far from the stability line at intermediate energies makes the accuracy of the EPAX2 calculations worse.…”