High spin study of 104Ag nucleus

Abstract

Dynamical symmetries like wobbling, chirality, magnetic and anti-magnetic rotation in nuclei with mass number ‘A’ ~ 100 have attracted a lot of attention in recent times [1-4]. In these nuclei the proton orbitals πg_9/2 and neutron orbitals ν(d_5/2, g_7/2, h_11/2) are available near Fermi surface and play a significant role in the above mentioned phenomena.

The odd-odd Ag isotopes, has three proton-holes below the Z=50 shell closure and few neutron-particles above N=50 shell closure, exhibit small quadrupole deformation. The partial level scheme for ¹⁰⁴Ag shown in Fig. 1 below. The electric-quadrupole rotational bands B and C based on πg⁻¹_9/2 ⊗νd_5/2 and πg⁻¹_9/2⊗νg_7/2 configurations have been reported by Z. G. Wang et al., in reference [1]. Spin and parity of many states of these bands were only tentatively assigned. As part of the present study, we have confirmed the spin of many states of these bands by the directional correlation (DCO) ratio methodology [5]. The high spin states of ¹⁰⁴Ag were populated using ⁷⁶Ge (³²S, p3nγ) fusion evaporation reaction at a beam energy of 110 MeV by the TIFR-BARC Pelletron facility, Mumbai. The de-exciting γ-rays were detected by the Indian National Gamma Array (INGA) at TIFR [6], with 18 clover detectors. The detectors were mounted at six different angles viz., 40^o, 65^o, 90^o, 115^o, 140^o, and 157^o, to the beam direction.

The data reduction involved building γ-γ asymmetric matrices and was further, analyzed with RADWARE program "SLICE" [7]. The asymmetric matrices were used to obtain directional correlation ratio of oriented states.

In the asymmetric matrices, the γ-transition recorded by detectors placed at θ₁=±40° correspond to the x-axis and the γ-transition recorded by detectors placed at θ₂=90^o correspond to the y-axis. In order to obtain the gamma intensities, the gate was set on the x-axis and projected on the y-axis. In the same way, the same gate was set on the y-axis and projected on the x-axis. If the γ-gate was applied on a stretched dipole transition, then the DCO ratio for a stretched dipole (quadrupole) transition was found to be ≈ 1(≈ 2). On the other hand, if the gate was on a stretched quadrupole transition, then the DCO ratio for a stretched quadrupole (dipole) transition was found to be ≈ 1 (≈ 0.5).

The present study contributes to confirming the spin assignments based on DCO measurements. The values of DCO ratios determined from this study are tabulated in Table 1.

Table 1. γ-ray’s energies, level energy, initial and final state spins, DCO ratios in ¹⁰⁴Ag in the present experiment.

E_γ

E_Level

J_i ^π→J_f ^π

R_DCO

368

480

7⁽⁺⁾ →6⁺

0.96(0.05) ^a

317

797

8⁽⁺⁾ →7⁽⁺⁾

1.03(0.06) ^a

631

1750

10⁽⁺⁾ →9⁺

0.58(0.11) ^b

640

2820

12⁽⁺⁾ →11⁺

0.53(0.10) ^c

876

3056

13⁽⁺⁾ →11⁺

0.84(0.18) ^c

^aDCO ratio obtained from gate on stretched dipole (M1) 346 keV transition

^bDCO ratio obtained from gate on stretched quadrupole (E2) 907 keV transition

^cDCO ratio obtained from gate on stretched quadrupole (E2) 1061 keV transition