Magnetic And Chiral Rotation In ～(106)Ag

Many properties of nuclear rotation can be easily understood as consequenceof certain symmetries. Among them magnetic rotation in weakly deformed nucleiand chiral rotation of triaxial nuclei are two noval phenomena which have attractedsignificant interest during the recent years. Magnetic rotations and chiral rotationsare well interpreted by S. Frauendorf using the planer and aplaner TAC, and werepredicted in A≈100 mass region. The chiral doublet bands were firstly found in¹⁰⁴Rh of this mass region. Now, ¹⁰⁶Ag as the isotone of ¹⁰⁴Rh is selected as theobject to investigate magnetic and chiral rotation bands.The high-spin states of ¹⁰⁶Ag were populated via the fusion-evaporationreaction ¹⁰⁰Mo(¹¹B,5n)¹⁰⁶Ag at a beam energy of 60 MeV. The ¹¹B beam wasdelivered by the HI-13 tandem accelerator of China Institute of Atomic Energy(CIAE). The target consisted of a 2.5mg/cm² layer of ¹⁰⁰Mo enriched to 97.4% andevaporated on an 11mg/cm² lead backing.γ-γcoincidence events were collectedusing a multidetedtor array consisting of 15 HPGe detectors, each of which wasequipped with a BGO Anti-Compton Shield.. A total of 130×10⁶γ-γcoincidenceevents were collected in the experiment in event-by-event mode. After carefulenergy calibration and gain matching of each detector, theγ-γcoincidence datawere sorted offline into conventional E_γ-E_γ, matrices and asymmetry DCO matrices.These matrices were analyzed by using the RADWARE package based on aLinux-PC system. By analyzing theγ-γ, coincidence and their DCO ratios, the levelscheme of ¹⁰⁶Ag has been expanded, in which twenty-six newγtransitions and tennew levels were added. Additional, a new band and linking transitions betweenpositive and negative parity bands were firstly found in the present experiment. Inall, 6 bands were built up in the new level scheme.Configuration assignments were made for each of the rotational bands basedon the single particle Nilsson diagram, aligned angular momentum of quasi-particles, systematics comparison, and electromagnetic properties analysis.Band 1 was assigned as the configuration ofÏ€g_9/2(?)v)[h_11/2² (g_7/2/d_5/2)], and it iscrossed by a 6qp-band with the configuration ofÏ€g_9/2(?)v[h_11/2²(g_7/2/d_5/2³] athω=0.6MeV. The main characters of band 1 are the follows: 1) It is aâ–³l=1 band, 2)The ratios of B(M1)/B(E2) are much larger than the ratios of E2 band, 3) There isno signature splitting or the signature splitting is nearly zero, 4) The angularmomentum is dominated by aligned quasi-particles. The above characters accountfor the magnetic rotation property of band1. Theoretical calculation of the effectiveinteraction with TAC mode is well fitted with the experimental value. This alsoaccounts for the shears coupling mode of band 1.The configuration ofÏ€g_9/2(?)vh_11/2 is assigned to both band 3 and band 4. Thechiral symmetry character of them is discussed: A) they are near degenerate twinâ–³l=1 bands (i.e. have the same spins and parities) at about 14 h, B) the vaule ofS(I)=[E(I)-E(I-1)]/2 for these bands varies smoothly as a function of spin, C) thephase of staggering in the in-band B(M1)/B(E2) ratios as a function of spin isrestricted by the chiral symmetry, the values for odd spin are lower than the valuesfor even spin. These three characters are similar with the chiral bands in ^104,106Rh,¹⁰⁰Tc. So band 3 and band 4 in ¹⁰⁸Ag are probably chiral doublet bands. In addition,several new questions about chiral bands were briefly discussed.The negative yrast rotational structure with configurationÏ€g_9/2(?)vh_11/2 has beencompared with its neighboring odd-odd isotopes. The level energy with same spinis getting lower and lower with neutron number increasing. This probably due to thestronger nuclear collectivity. The systematic feature of the signature inversion of thebands with configuration ofÏ€g_9/2(?)vh_11/2 in A=100 mass region has also beeninvestigated. It is shown that the signature inversion of the bands with configurationofÏ€g_9/2(?)vh_11/2 in A=100 mass region is most probably caused by the p-n interactionof g_9/2 quasi-proton and h_11/2 quasi-neutron.