Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes

Abstract

Background: Models describing nuclear fragmentation and fragmentation-fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool to reach the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes.Method: We have measured projectile fragments from 10,12-18 C and 10-15 B isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent dataset. We compare our data to model calculations.Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic 10,12-18 C and 10-15 B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that EPAX is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well.Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data have allowed for a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

Quasifree ( p , 2p ) Reactions on Oxygen Isotopes: Observation of Isospin Independence of the Reduced Single-Particle Strength

“…A detailed description of the setup can be found in Refs. [25,[29][30][31][32]. The experiment was performed with CH 2 (458 and 922 mg=cm 2 ) and C (558 and 935 mg=cm 2 ) targets as well as with an empty target frame.…”

Energy dependence of the reduced single-particle strength for strongly-bound proton removal on 16C

“…For the 12 C( 16 C, 15 B) reaction at 400 MeV/nucleon, the cross section was measured to be 20.5(4) mb [23], resulting a R s of 0.40 (1). As shown in figure 1, this value is larger than that extracted at 75 MeV/nucleon, but is within the shaded area of figure 1.…”

“…It is suggested that, for strongly-bound nucleon knockout, the beam energies below 100 MeV/nucleon are not sufficiently high for the approximations to be valid and relatively high incident energies are needed [12]. Recently, Thies et al [23] have measured the cross section for one-proton removal from 16 C at a much higher energy of around 400 MeV/nucleon. The 16 C nucleus has a large difference in individual nucleon separation energies of ΔS=18.35 MeV (S p =22.6 MeV and S n = 4.25 MeV).…”

Fragmentation of stable and neutron-rich 12-16C into boron fragments at approximately 240 MeV/nucleon *

“…The NUCFRG2 model [17] is developed upon the abrasion-ablation model [43]. It is based on the fragmentation data of the proton beam and assumes that the nuclei are solid spheres with uniform nuclear matter distributions.…”

“…When designing experiments, reliable fragmentation reaction models are required to accurately predict the yield of fragments produced from stable or unstable beams. The statistical abrasion-ablation model [13], intranuclear-cascade approach [14], and empirical models, such as EPAX [15], FRACS [16], and NUCFRG [17] are widely used to predict fragmentation cross sections. However, most of the existing experimental data are obtained from the fragmentation of stable nuclei, and the empirical models are developed by mainly relying on stable nuclear fragmentation data.…”