Coulomb Excitation ofSn104and the Strength of theSn100Shell Closure

Abstract

A measurement of the reduced transition probability for the excitation of the ground state to the first 2 þ state in 104 Sn has been performed using relativistic Coulomb excitation at GSI. 104 Sn is the lightest isotope in the Sn chain for which this quantity has been measured. The result is a key point in the discussion of the evolution of nuclear structure in the proximity of the doubly magic nucleus 100 Sn. The properties of many composite quantum objects that represent building blocks of matter, such as hadrons, atomic nuclei, atoms, and molecules are governed by energy gaps between quantum states which originate in the forces between their fermionic constituents. In the case of atomic nuclei, the energy gaps manifest themselves by the existence of specific stable isotopes. These include, e.g., the double shell-closure nuclei 4 He, 16 O,40;48 Ca, and 208 Pb, which are particularly robust against particle separation and intrinsic excitation. The -unstable isotopes 56 Ni, 78 Ni, and 100;132 Sn are also expected to correspond to double shell closures. However, data for 78 Ni and 100 Sn are scarce due to their exotic neutron-to-proton ratios. Therefore, there is considerable interest in finding more proof for the magicity of these isotopes. In addition, the single particle energies relative to 100 Sn are largely unknown experimentally. Data are limited to the energy splitting between the two lowest-energy orbitals [1,2] while extrapolations from nearby nuclei are available with a typical uncertainty of a few hundred keV for the orbitals of higher energy [3]. Since 100 Sn is predicted to be a doubly magic nucleus, it would provide an approximately inert core on top of which simple excitations can be formed by adding few particles or holes. For this reason, it presents an ideal testing ground for fundamental nuclear models. Another cause for increased interest in nuclear structure in this region comes from the rp process of nuclear synthesis [4]. It has been concluded recently that this reaction sequence comes to an end near 100 Sn [4]. In addition, 100 Sn itself is expected to be the heaviest self-conjugate PRL 110,

Intermediate-energy Coulomb excitation ofSn104: ModerateE2strength decrease approachingDoornenbal1, Takeuchi2, Aoi3 et al. 2014Phys. Rev. CSelf Cite562280View full textAdd to dashboardCite

“…[18] with largely overlapping error bars, but deviates significantly from the value of 0.10(4) e 2 b 2 obtained in Ref. [17]. It corresponds to only about 30% excitation strength decrease compared to the even-A 106−114 Sn isotopes and confirms that the reduction is much more shallow than first suggested.…”

“…While the B(E2)↑ value of 102 Sn remains missing for a complete pattern of the tin isotopes within the major shell, a first attempt for 104 Sn with limited statistics has recently been made [17]. The result of 0.10(4) e 2 b 2 indicates a steep decrease of excitation strength in agreement with LSSM calculations.…”

“…Here, we report on the first B(E2)↑ extraction in the unstable, proton-rich tin nuclei from absolute Coulomb excitation cross sections. Previously deduced values relied on target excitation at "safe" [10,11] and intermediate [12] energies or used an isotope with known excitation strength as normalization [9,17,18]. In fact, all reported values from intermediate-energy Coulomb excitation measurements above 100 MeV/nucleon rely on the latter method [9,19,20] and so far no attempt has been made to determine absolute cross sections at these high energies.…”

Nuclear-structure studies of exotic nuclei with MINIBALL

“…Transfer reactions gave access to the direct neighbors of 68 Ni at N=40 and 79 Zn at N=50 providing an excellent tool to probe the size of the shell gaps and test the singleparticle character of unknown neutron orbitals. One of the first g-factor measurements with a radioactive ion beam was successfully performed in 72 Zn using the low-velocity transientfield technique [24].…”

“…In contrast, the contaminant In is released within seconds. Yield measurements show that ca 85% of the In isotopes with half lifes above [29,30] are indicated with blue crosses and the results from high-energy CE from GSI [76,79], NSCL [80] and RIKEN [81] are given by green stars, and pink and brown triangles, respectively. The results from a typical LSSM calculation [76] and an RQRPA calculation [82] Sn.…”