Matter radii of32−35Mg

Abstract

The interaction cross sections of [32][33][34][35] Mg at 900A MeV have been measurmed using the fragment separator at GSI. The deviation from the r 0 A 1/3 trend is slightly larger for 35 Mg, signaling the possible formation of a longer tail in the neutron distribution for 35 Mg. The radii extracted from a Glauber model analysis with Fermi densities are consistent with models predicting the development of neutron skins. The shell structure of nuclei has formed a fundamental basis for understanding their properties. As nuclei accumulate a large excess of neutrons, the conventional shell structure starts to show signs of mutation. Investigations of ground-state properties of neutron-rich nuclei are a key toward the search for the effects leading to the breakdown of the conventional shell structure. The matter radii of neutron-rich nuclei are one of the fundamental properties that constrain nuclear wave functions and carry crucial information on deformation, shell effects, and formation of neutron skins and halos [1].In this Rapid Communication we report on the first determination of the matter radii of [33][34][35] Mg in the N = 20 island of inversion from a measurement of the interaction cross section. The results are consistent with development of neutron skins with 35 Mg showing the possibility of a longer density tail.The breakdown of the N = 20 shell gap was observed through the low excitation energy of the 2 + state in 32 Mg [2]. Much effort has been devoted since then to the study of level schemes in attempting to understand this. The large B(E2) values deduced from the Coulomb excitation * ritu@triumf.ca measurements [3,4] were suggestive of 32 Mg being a deformed nucleus. It should be noted here that the extraction of the deformation value (β) in [3] is obtained under the assumption of a collective model. For a proper understanding of deformation in these nuclei, measured radii are important.The level scheme of 32 Mg from β delayed γ spectroscopy of 32 Na [5] suggests that 32 Mg is not an axially symmetric rotor. It is not a vibrational nucleus either. It was in fact discussed [6], based on a Skyrme-Hartree-Fock description, that this nucleus probably exhibits γ unstable deformation. A relativistic mean-field (RMF) calculation with three-dimensional angular momentum projection involving triaxial degrees of freedom [7] gives a ground state having β = 0.6 and γ = 10 • . Density and radii from such models would be useful for comparison with the present data. Recently, a shape coexistent 0 + state has been found in 32 Mg [8].The Monte Carlo shell model (MCSM) [9] has been considered to be fairly well suited to describe the levels in nuclei around the island of inversion. The predicted level scheme of 32 Mg also does not show features of an axially symmetric rotor.Mean-field models based on the Hartree-Fock (HF) or Hartree-Fock-Bogoliubov (HFB) approximations have been developed by several groups [10][11][12] for the neutron-rich 021302-1 0556-2813/2011/83(2)/021302(4)

Examination of the C22 radius determination with interaction cross sections

“…The NTG approximation has been applied to a number of examples in the nucleus-nucleus total reaction cross-section calculations including stable and neutron-rich isotopes [2,18,23,[27][28][29]41,[59][60][61][62][63]. Here we quantify the extent to which the higher-order terms are included in the NTG approximation in comparison with the complete Glauber calculation and the standard OLA.…”

Two-neutron sequential decay ofO24

“…So far, there has been no correlation measurement of a state decaying by sequential emission of two neutrons, although evidence for sequential decay has been reported for the high-energy continuum of 14 Be [12]. The structure of 24 O, the heaviest bound isotope for which the neutron drip-line is established [17], has been well studied and there is substantial evidence for the appearance of a new magic number N = 16 [18][19][20][21][22]. Two unbound resonances have been observed in 24 O above the one-neutron separation energy [19,23,24], and there is also evidence for resonances above the two-neutron separation energy [19,23] around 7.5 MeV.…”

Extracting nuclear sizes of medium to heavy nuclei from total reaction cross sections

“…The cross section is accurately measured with recent intense beam facilities and the measurement now reaches beyond the sd-shell nuclei [9][10][11]. Compared to other methods, e.g., proton-nucleus scattering [12][13][14] and isotope shift measurements [15][16][17], the method has the great * whoriuchi@nucl.sci.hokudai.ac.jp advantage that it can be applied to almost all nuclei as long as they are produced in sufficient number.…”