Measurement of cross sections for charge pickup by 12C on elemental targets at 400 MeV/n
Introduction
The physics of nuclear charge pickup cross sections in heavy ions induced interactions at relativistic and intermediate high energies was interesting in many basic researches and applications such as astrophysics, cosmic radiation and space flight, as well as the production of radioactive beams [1], [2]. Theoretically, it was clear that the nuclear charge pickup reactions were conjecturally very peripheral and surface collisions. As a peripheral collision the cross sections may be expected to depend on the impact parameter , and as a surface collision the cross sections may also be expected to depend on the cross sectional or surface area, proportional to . Combining these two processes, the cross sections may be expected to depend on linearly. Experimentally, the nuclear charge pickup cross sections were investigated at the Lawrence Berkeley Laboratory Bevalac (LBL) energy [3], [4], [5], [6], [7], [8], [9], [10], [11], at the Brookhaven Alternating Gradient Synchrotron (AGS) energy [12], [13], [14], [15], [16], [17], [18], at the CERN Superproton Synchrotron (SPS) energy [19], [20], [21], [22], [23], and GSI Synchrotron (SIS) energy [24], [25], [26], [27], [28], [29], [30], [31]. G.X. Ren et al. [9] studied the charge pickup cross sections for 1.7 GeV/n 56Fe, 1.46 GeV/n 84Kr, 1.28 GeV/n 139La, and 0.8 GeV/n 197Au on a CR-39 target, combined their results with data on charge pickup cross section by 12C, 18O, and 20Ne ions [3], [4], [5], [6], [7], they found that the cross section for charge pickup by ∼ GeV/n heavy ions was generally followed the expression of (in mb), where implied peripheral interactions. This stronger dependence of the cross section for charge pickup on the projectile mass was hardly understood physically for a nuclear process. For the dependence of nuclear charge pickup cross section on target mass at LBL energy, a power law relation of (in mb) was found, with an exponent range from 0.2 to 0.45 which depended on the type of projectile. Nilsen et al. [12] studied nuclear charge pickup reactions by relativistic heavy ions (LBL and BNL energies), for the target mass dependence, were fitted to data, the fitted exponent range from -0.04 to 0.36 depended on projectile mass and energy; for the projectile mass dependence, were fitted to C-target data, a very strong dependence, of the form , was found, for other target data the same dependence were found.
Based on the experimental results of the nuclear charge pickup cross sections, a very strong projectile mass dependence, with fitting parameter , was obtained [9], [12]. For the target mass dependence, a form of with the fitted parameter , which depended on projectile mass and energy, was obtained. These results were not consistent with the theoretical prediction based on the nuclear charge pickup reactions as a very peripheral and surface collisions.
Due to the sparse and sporadic data of the nuclear charge pickup reaction cross sections, the nuclear charge pickup process was not well understood. It was clear that the nuclear cross sections for charge pickup was a function of the masses of target and projectile, as well as of the energy per nucleon of the projectile. It was also probable that there was a correlation with the masses of the produced nuclei. Generally, it was believed that the nuclear charge pickup cross section decreases with the increase of beam energy, and increases with projectile and target size.
At energies below the Fermi energy, the mechanism of nuclear charge pickup processes was transfer reaction where the final states were populated by sequential proton-pickup neutron-stripping processes (or vice versa). The velocity of beam ion was smaller than the Fermi velocity of nucleons inside the nucleus, the Fermi spheres of projectile and target overlapped each other at the moment of collision, the proton can jump from target Fermi sphere into projectile Fermi sphere. At high energies, however, the Fermi spheres of projectile and target were totally non-overlapping each other, preventing a transfer of a target proton to the projectile. Instead, we can assume Δ-resonance formation and decay in nucleon-nucleon interactions to be the most likely elementary processes in which a projectile neutron can be converted into a projectile proton. At intermediate and high energies, two mechanisms, e.g., proton transfer through the nuclear overlap zone and Δ-resonance formation and decay in nucleon-nucleon interactions, may make a contribution simultaneously.
The nuclear charge pickup reactions of 500 MeV/n 56Fe and 400 MeV/n 84Kr on Al, C and CH2 targets were studied in our recent publications [32], [33]. The target mass dependence, , were fitted to data, with the fitted exponent for 56Fe and for 84Kr.
For the study of nuclear charge pickup reaction of 12C on elemental targets, Olson et al. [3] reported very small cross sections (less than 0.1 mb) at LBL energy (1.05 and 2.10 GeV/n). Results from the Saturne charge-exchange program [5], [6], [7] confirmed Δ-resonance formation for the nuclear charge pickup reaction of 12C on elemental targets at 1100 MeV/n, but Δ excitation was almost absent for 900 MeV/n. Yamaguchi et al. [34] reported the nuclear charge pickup cross sections of 18,19,20C on a liquid hydrogen target at 40 MeV/n, very larger cross sections were found ( mb for 18C, mb for 19C, and mb for 20C).
In this paper, the nuclear charge pickup cross sections of 12C on Pb, Cu, Al, C and CH2 targets at the highest energy of 398 MeV/n were investigated using CR-39 nuclear track detector.
Section snippets
Experimental details
Five stacks of the sandwiched targets, composed of different targets (T) interleaved with polymeric plastic CR-39 detectors (D) in the sequence DDTDDTDDTDDTDD as shown in Fig. 1, were normally exposed to 400 MeV/n 12C beam at the HIMAC (the Heavy Ion Medical Accelerator in Chiba, Japan) facility in the Japanese National Institute of Radiological Sciences (NIRS). For the stack of Cu-target, only three targets were used. The beam fluence was about 3000 ions/cm2. The detector was CR-39 nuclear
Results and discussion
To study the charge-pickup cross sections the main experimental requirement was to achieve a charge resolution sufficient to distinguish the relatively rare fragments emerging from the projectile with an increased charge from the much more abundant survived beam ions. To do this, the reconstructed events matching the possibilities of 12C ions passing through the target without changing charge and 12C ions passing through the target forming projectile fragment with an increased charge were
Conclusions
The nuclear charge pickup cross sections of 12C on Pb, Cu, Al, C, and CH2 targets at the highest energy of 398 MeV/n were investigated using CR-39 nuclear track detector. The cross sections for H were calculated from those measured on C and CH2 targets. The correlation of charge pickup cross section and target mass was investigated. The charge pickup cross section of 12C at our studied beam energies seems linearly depend on the target mass, which can be well explained by the peripheral and the
CRediT authorship contribution statement
First author: data measurement; Corresponding author: manuscript writing, data analyses, and plot all of figures; Other authors: data measurement; Satoshi Kodaira: Help to expose the stack.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work has been supported by the National Natural Science Foundation of China under Grant Nos: 11075100 and 11565001, the Natural Foundation of Shanxi Province under Grant 2011011001-2, the Shanxi Provincial Foundation for Returned Overseas Chinese Scholars, China (Grant No. 2011-058). We are grateful to staff of the HIMIC for helping to expose the stacks.
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