Evaluation Activities at JCPRG

SINGH Jagjit and DAGVADORJ Ichinkhorloo
Faculty of Science, Hokkaido UniversityAbstract
In this report, we briefly summarize the evaluation activities in Japan ChargedParticle Nuclear Reaction Data Group (JCPRG) in 2018. Along with nuclear datacompilation, the evaluation is also one of the important activities that are carriedout at JCPRG. The evaluation at JCPRG covers the theoretical investigation on awide range of nuclear systems close to the stability line, at and beyond the driplines.

1Introduction

Evaluation of nuclear reaction data requires a vigilant process of correlation, selective collection,renormalization and averaging of the available experimental data, supported by theoretical calculations. The extensive challenge that theoretical approaches bump into is the expensive computational cost. Thanks to the major advancements in the nowadays technology, which have somewhat eased the situation over this challenge by providing accesses to the super computers at various computing facilities. We at JCPRG [1] deal with various theoretical approaches and evaluate
nuclear data used for various applications like positron emission therapy (PET) and to improve theEXFOR database, such as missing data, wrong order of data etc.
This report presents the activities on the evaluation of the nuclear data at JCPRG in 2018.
The report is organized as follows: section 2 describes the analysis of 16 O + p reaction using thecontinuum discretized coupled channel (CDCC) method [2]. Section 3 presents the two-neutron
correlations in the ground state of the weakly-bound two-neutron (2n) halo nucleus 22 C sitting at
the edge of the neutron dripline and also in the 2n-unbound nucleus 26 O sitting beyond the neutron
dripline [3, 4]. Finally, section 4 presents our conclusions.

2Analysis of 16 O + p reaction using CDCC method

In this fiscal year, we applied the CDCC analysis to the proton induced reaction on a 16 O target with
the incident proton energy up to 70 MeV. The 16 O(p, pn)15 O reaction is studied within the threebody (15 O + n + p) framework of the CDCC approach. We calculate the 16 O + p elastic angular
distribution and breakup cross sections of the 16 O(p, pn)15 O reaction. The breakup cross sections
as a function of the incident energy are shown in Fig. 1. The obtained results are in good agreementwith the experimental data [5–9].

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Figure 1: The integrated breakup cross sections of the p+ 16 O reaction.

3Two-neutron correlations in the ground state of neutron-richnuclei

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θ12 (deg)θ12 (deg)

In recent years, there has been rapidly increasing interest in the study of the Borromean nuclei
sitting right on the top of neutron dripline and two-neutron (2n) decays of unbound systems beyond
the neutron dripline. These systems demand a three-body (3b) description with a proper treatmentof continuum, the conventional shell-model assumptions being insufficient. Very recently a highprecision measurement of interaction cross-sections for 22 C was made on a carbon target at 235
MeV/nucleon [11] and also the unbound nucleus 26 O has been investigated, using invariant-mass
spectroscopy [12] at RIKEN Radioactive Isotope Beam Factory. These high precision measurements
give us the motivation for selecting these systems for the present study. We have studied the pairingcollectivity in the ground state of the Borromean nucleus 22 C and in the 2n-unbound system 26 O.

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810Figure 2: Two-particle density for the ground state of 22 C (left-panel) and 26 O (right-panel) as afunction r1 = r2 = r and the opening angle between the valence neutrons θ12 .

-18-For this study we have used our recently implemented 3b-structure model (core+n + n) for groundand continuum states of the Borromean nuclei [13, 14].
The neutron single-particle unbound spdf -continuum states of the 21 C and 25 O system arecalculated in a simple shell model picture for different continuum energy cut-off’s of 5, 10 and
15 MeV by using a Dirac delta normalization and are checked with a more refined phase-shift
analysis. The sensitivity of the (core+n) potential has been explored for the emergence of different
dominant configurations in the ground states of 22 C and 26 O. After fixing convergence with thecontinuum energy cuts and bin size, a reasonable energy cut of 5 MeV and bin size of 0.1 MeV
is used for the present study. These (core+n) continuum wavefunctions are used to construct thetwo-particle 22 C and 26 O states by proper angular momentum couplings and taking contribution
from different configurations. Our results show that, the ground state displays a collective nature,taking contribution from many different oscillating continuum states that coherently sum up to givean exponentially decaying bound wavefunction in 22 C and an oscillating unbound wavefunction incase of 26 O.
The two particle density of 22 C and 26 O as a function of two radial coordinates, r1 and r2 ,for valence neutrons, and the angle between them, θ12 in the LS-coupling scheme is calculated byfollowing Refs. [14, 15]. The distribution at smaller and larger θ12 are referred to as “di-neutron”and“cigar-like”configurations, respectively. One can see in Fig. 2 that the two-particle density is wellconcentrated around θ12 ≤ 90◦ , which is the clear indication of the di-neutron correlation andthe di-neutron component has a relatively higher density in comparison to the small cigar-likecomponent for both 22 C and 26 O. The reflection of dominance of s-component in the ground stateof 22 C can be seen in the left panel of Fig. 2 showing extended di-neutron component in comparison
to 26 O (in the right panel of Fig. 2), which has sharper dineutron component due to the mixing ofl > 0 components in its ground-state [3, 4].

4Summary

For the study of the 16 O + p reaction, the calculated breakup cross sections give a satisfactorily
good agreement with the available experimental data. For the two-neutron correlations study,
our results show the emergence of the bound 2n-halo ground state of 22 C from the coupling ofseven unbound spdf -waves in the continuum of 21 C and 2n-unbound ground state of 26 O from thecoupling of three unbound pdf -waves in the continuum of 25 O due to presence of pairing interaction.
Also two-neutron correlation for these systems showing dominance of the di-neutron component isdiscussed. More investigations are needed to study the 2n-decay properties.

Acknowledgment
We gratefully acknowledge the financial support from Nuclear Reaction Data Centre (JCPRG),
Hokkaido University, Sapporo for attending NN2018-13th International Conference on NucleusNucleus Collisions, Saitama, Japan. to present our work.

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