Measurement of the spin and magnetic moment ofAl23

Abstract

For the first time, we obtained the g factor for the ground state of 23 Al by use of a β-NMR measurement. 23 Al has a small proton separation energy and is a potential proton-halo candidate. The obtained g factor, |g| = 1.557 ± 0.088, clearly shows the spin and parity, J π = 5/2 + , for 23 Al, which is the same as that of its mirror partner, 23 Ne. The possible nuclear structure of 23 Al is also discussed. Studies of exotic nuclei far from the stability line have attracted much interest during the past two decades since the first observation of the neutron halo in 11 Li [1]. Further experiments have confirmed the neutron halo in 11 Li, and have also shown the existence of a neutron halo in other neutron-rich nuclei [2]. However, the number of experiments on the proton halo are relatively few compared with those on the neutron halo. Recently, experimental evidence for the proton halo in very proton-rich nuclei has become available: 8 B [3][4][5], 17 Ne [6,7], and 26,27,28 P [8]. 23 Al is one of the potential candidates for a proton-halo nucleus, because its proton separation energy is quite small (125 keV). Recently, a large reaction cross section of 23 Al was measured at the intermediate energy (∼36A MeV), although the error was still large [9,10]. The authors of Ref. [9,10] analyzed the data by a Glauber model with simply a core nucleus ( 22 Mg) plus a valence proton (p) configuration. According to their analysis, the density distribution of 23 Al should have a halolike long tail. Because the density of a loosely bound s-wave proton can be extended, it is suggested that the spin and parity (J π ) of 23 Al might be 1/2 + . However, the J π of its mirror partner, 23 Ne, is 5/2 + . Thus, if the ground-state J π of 23 Al is 1/2 + , the proton halo structure can be anticipated, but the mirror symmetry will be broken between the bound ground states of mirror pairs, which has not been observed for known nuclei so far. Because the magnetic moment of its mirror partner, 23 Ne, is known to be −1.077±0. 004 [11], the magnetic moment of 23 Al allows one to discuss the spin expectation value [12] of the A = 23 mirror pair with T = 3/2, where T is the isobaric spin. In p-shell nuclei, the 9 C-9 Li mirror moments (T = 3/2) yield an anomalous large spin expectation value, which suggests an exotic structure of proton-rich 9 C [13]. A similar anomaly may be found in the sd-shell region.Determining

Precise nuclear moments of extremely proton-rich nuclus 23 Al

“…The obtained μ( 23 Al) is consistent with the previous value of 3.89(22)μ N[2], however, the precision is remarkably improved to discuss details of the nuclear structure. From (2) and the eqQ of 27 Al in Al 2 O 3[6] and Q( 27 Al)[7], e.g.…”

“…The polarized 23 Al nuclei were produced through the pick-up and fragmentation process of the intermediate-energy nuclear collisions of 100-AMeV 24 Mg 12+ ions and 9 Be atoms in a 2.5-mm-thick production target [3,4]. The production cross section of the pick-up fragmentation is about ten times larger than that of the pure fragmentation process, 28 Si + 9 Be, which was utilized in the previous work [2]. Furthermore, due to the one-proton pickup, the momentum of 23 Al shifted to low-momentum side, and therefore the analyzing power based on beam-rigidity difference was gained especially for separation of the proton-rich nuclei.…”

“…The mirror symmetry of nuclear structure can be tested through comparison of the nuclear moments of the mirror pair 23 Al and 23 Ne. In previous work, the spin-parity of 23 Al was determined as I π = 5/2 + by means of the β-ray detecting nuclear magnetic resonance (β-NMR), and was consistent with that of the ground state of 23 Ne [2]. However, the statistics was insufficient to discuss further details of the nuclear structure because of very small production rate of 23 Al nuclei.…”

Proton-proton correlations in distinguishing the two-proton emission mechanism of Al23 and Mg22

“…The proton-rich nuclei 23 Al and 22 Mg are very important in determining some astrophysical reaction rates and have attracted a lot of attention in both astrophysics and nuclear structure studies [22][23][24][25][26][27][28][29]. Recently, we have reported the experimental results for kinematically complete measurements of two-proton emissions from two excited proton-rich nuclei, namely, 23 Al → p + p + 21 Na and 22 Mg → p + p + 20 Ne [30].…”

Magnetic moments ofT=3/2mirror pairs

“…Values of γ p and γ n from theory (USDB) and from data on magnetic dipole moments[2,[10][11][12]. The contributions γ p and γ n have been estimated from 0hω shell-model calculations using Eqs.…”