States of the 12N Nucleus with Increased Radii

Abstract

The differential cross sections of the 12 C( 3 He,t) 12 N reaction leading to formation of the 1 + (ground state), 2 + (0.96 MeV), 2 − (1.19 MeV), and 1 − (1.80 MeV) states of 12 N are measured at E( 3 He)=40 MeV. The analysis of the data is carried out within the modified diffraction model (MDM) and distorted wave Born approximation (DWBA). Enhanced rms radii were obtained for the ground, 2 − (1.19 MeV), and 1 − (1.80 MeV) states. We revealed that 12 B, 12 N, and 12 C in the IAS with T=1, and spin-parities 2 − and 1 − have increased radii and exhibit properties of neutron and proton halo states.

Possible neutron and proton halo structure in the isobaric analog states of A=12 nuclei

“…The detected tendency can be traced in the corresponding IAS of the 12 N nucleus, where a very enlarged rms radius (3.3 ± 0.2 fm) was found by the MDM in Ref. [23]. Thus, we can propose that the excited 1 − states at 17.23 MeV in 12 C and 1.80 MeV in 12 N possess the proton halo structure.…”

“…Table III shows the summary of the rms radii, R rms , of the 12 B, 12 C, and 12 N nuclei in the IASs with T = 1 calculated in this work and obtained by other different methods in Refs. [22,23,[54][55][56]. The rms radii of 12 C and 12 B are calculated accordingly to Eq.…”

“…[43][44][45], but we believe that the differential cross sections of the 11 B( 3 He, d ) 12 C reaction to the high-lying states of 12 C with excitation energies of 16.57 and 17. 23 MeV are reported for the first time.…”

“…Also, these reactions are widely used to search for the states with increased radii [6,7,9,11,16,22]. Charge-exchange reactions, in particular the ( 3 He, t ) reaction, are also useful for obtaining this information and have the advantage for studying unbound states in the continuum spectrum [21,23]. Note that the interpretation of a nucleon halo in the excited states located above the particle emission threshold remains an open question.…”

“…Hence, one can expect the existence of excited states with enlarged radii and a possible proton halo in 12 N. The proton-emission threshold in 12 N is located only 0.60 MeV above the ground state, thus the IASs in 12 N with spin-parities 1 − and 2 − belong to the continuum spectrum. Recently, the 12 C( 3 He, t ) 12 N reaction at E ( 3 He) = 40 MeV, in which the 1 + (g.s), 2 + (0.96 MeV), 2 − (1.19 MeV), and 1 − (1.80 MeV) states of 12 N were populated, has been studied [23]. The distorted wave Born approximation (DWBA) calculations and the modified diffraction model (MDM) [21,[35][36][37] were applied to analyze the data.…”