Core excitations and narrow states beyond the proton dripline: The exotic nucleus21Al

Abstract

We present the first predictions for the widths of resonance states in a so-far unobserved exotic isotope beyond the proton dripline, 21 Al. For this purpose we employ mirror symmetry between the widths of low-lying resonance states and the asymptotic normalization coefficients (ANC) of their mirror analogs. The latter are extracted from a recently measured peripheral reaction 20 O(d,p) 21 O while the positions of resonances are estimated within a microscopic cluster model and a two-body potential model. We have found that 21 Al should have two low-lying states decaying into the 20 Mg + p channel and three states at higher energy, built on the 2 + core excited state and decaying into the 20 Mg(2 + ) + p channel. The widths of all these states are much smaller than their energies, which makes experimental spectroscopic studies of this isotope beyond the proton dripline possible.

Mass-15 nuclei and predicting narrow states beyond the proton drip line

“…Narrow states have now been observed in other proton rich nuclei, e.g. 19 Na [15], 16 Ne [13], 15 Ne [16], and 23 Al [17], with narrow resonances of the latter found with an MCAS study [18]. They have been predicted for 21 Al [19] and 25 P [20].…”

ANC From Experimental Perspective

“…This method was applied e.g., for 7 Be(p, γ) 8 B (Trache et al, 2003), deduced from 8 Li → 7 Li + n using 13 C( 7 Li, 8 Li) 12 C reaction. Other cases in which the mirror nuclei procedure have been used are 20 Mg(p, γ) 21 Al (Timofeyuk et al, 2012) from 20 O(n, γ) 21 O using reaction 20O(d,p) 21O, 22 Mg(n, γ) 23 Mg (Al-Abdullah et al, 2010) capture from 22 Ne(p, γ) 23 Na using 13 C( 22 Ne, 23 Ne) 12 C.…”

Spectroscopic study of the exotic nucleusP25

“…Examples of experimental evidence of such states can be found in 19 Na [1], 16 Ne [2], 15 F [2], 15 Ne [3], and 23 Al [4]. Theory also predicts excited-core-based narrow states in 17 Na [5][6][7] and 21 Al [8].…”

“…Here we present the first predictions for the 25 P low-lying energy spectrum. Earlier, we made the first predictions of the widths of a lighter T = 5/2 nucleus beyond the proton drip line, 21 Al [8], showing that several narrow states should be expected there. It was shown later in ab initio calculations [16] that the positions of the 21 Al levels can place important constraints on two-and three-nucleon (NN + NNN) chiral forces in nuclei.…”

“…[8] have been made by taking the theoretical positions of the proton resonances in 21 Al and exploiting the link between the widths of proton resonances and the asymptotic normalization coefficients (ANCs) of their mirror analogs, proposed in Ref. [17].…”