Neutron skin thickness ofZr90determined by charge exchange reactions

Abstract

Charge exchange spin-dipole (SD) excitations of 90 Zr are studied by the 90 Zr(p, n) and 90 Zr(n, p) reactions at 300 MeV. A multipole decomposition technique is employed to obtain the SD strength distributions in the cross section spectra. For the first time, a model-independent SD sum rule value is obtained: 148 ± 12 fm 2 . The neutron skin thickness of 90 Zr is determined to be 0.07 ± 0.04 fm from the SD sum rule value.PACS numbers: 21.10. Gv, 24.30.Cz, 25.40.Kv, 27.60.+j Proton and neutron distributions are among the most fundamental properties of nuclei. Proton distributions are precisely known from the charge distributions determined by electron scattering [1]. On the other hand, our knowledge of neutron distributions, which have been studied mainly by hadron-nucleus scattering, is limited because descriptions of strong interactions in nuclei are highly model-dependent [2]. Reliable neutron distributions will improve the understanding of the nucleus and nuclear matter [3,4,5,6,7]. Recent theoretical studies using the Skyrme Hartree-Fock (HF) and relativistic mean-field models [3,4,8] have shown that the neutron skin thickness, defined as the difference between the root mean square (rms) radii of the proton and neutron distributions, imposes a strict constraint on the neutron matter equation of state, which is an important ingredient in studies of neutron stars [5,6]. It is also known that the neutron skin thickness is strongly correlated with the nuclear symmetry energy [7,9]. Reliable neutron distributions are also needed for analyses of atomic parity violation experiments [10,11] and of pionic states in nuclei [12].Several attempts have been made to determine neutron distributions [2,13,14,15,16]. Ray et al. analyzed proton elastic scattering on several nuclei at 800 MeV using impulse approximation and obtained a neutron thickness of 0.09 ± 0.07 fm for An alternative method for determining the neutron rms radius is provided by the model-independent sum rule strength of charge exchange spin-dipole (SD) excitations [19]. The operators for SD transitions are definedwith the isospin operators t 3 = t z , t ± = t x ± it y . The model-independent sum rule is derived aswhere S ± are the total SD strengths. The mean square radii of the neutron and proton distributions are denoted as r 2 n and r 2 p , respectively. Thus, the rms radius of the neutron distribution r 2 n or the neutron skin thickness δ np = r 2 n − r 2 p can be derived from Eq. (2) by using the rms radius of the proton distribution r 2 p obtained from the charge radius if the sum rule value (S − − S + ) is obtained experimentally.To obtain the SD sum rule value, Krasznahorkay et al. measured the ( 3 He, t) reaction on tin isotopes at 450 MeV [20]. The cross section spectra at θ = 1• were analyzed by a peak fitting technique assuming the Lorentzian shape, and the S − value was obtained. Since there was no (n, p)-type measurement, they determined the S + value by assuming the energy-weighted sum rule in a simple model where the unperturbed particl...

Global description ofβ−decay in even-even nuclei with the axially-deformed Skyrme finite-amplitude method

“…[28][29][30][31][32], the spin-dipole resonance energies from Refs. [33,34], and the half-lifes from Ref. [35].…”

Neutrino beams as a probe of the nuclear isospin and spin–isospin excitations

“…On the other hand, experiments with (p,n) and ( 3 He,t) have been realized [23]. Calculations based on RPA overestimate the experimental results in the Gamow-Teller region, while they underestimate them in the 30-60 MeV energy range [21]. Therefore if quenching of the forbidden states is necessary is an open issue.…”

“…Using sumrules, one can relate the spin-dipole strength distribution to the neutron skin thickness defined as the difference between the root mean square radii of the proton and neutron distributions. This is an useful information to establish the nuclear matter equation of state of neutron stars [21]. Some information on these states has been extracted thanks to various weak and hadronic probes.…”

Symmetry energy from the nuclear collective motion: constraints from dipole, quadrupole, monopole and spin-dipole resonances

“…Recently, SD excitations were studied in 90 Zr by the charge-exchange reactions 90 Zr(p,n) 90 Nb [54] and 90 Zr(n,p) 90 Y [55], and the model-independent sum rule for the SD excitations were extracted in Ref. [56] by using multipole decomposition analysis (MDA) [57]. The charge exchange reactions ( 3 He,t) on Sn isotopes were also studied to extract the neutron skin thickness [58].…”