Berlin 2005 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 38: Kernphysik/Spektroskopie

HK 38.1: Gruppenbericht

Mittwoch, 9. März 2005, 14:00–14:30, TU MA004

Structure studies of the neutron-rich isotopes ¹⁷C, ¹⁶C and ¹⁵C — •H. G. Bohlen¹, W. von Oertzen^1,2, R. Kalpakchieva³, T. N. Massey⁴, A. A. Ogloblin⁵, G. de Angelis⁶, M. Milin⁷, Ch. Schulz¹, Tz. Kokalova¹, and C. Wheldon¹ — ¹Hahn-Meitner-Institut, Berlin — ²Freie Universität, Berlin — ³FLNR, JINR, Dubna — ⁴Dept. Phys. Astr, Ohio University — ⁵Kurchatov Institute, Moscow — ⁶INFN, LNL, Legnaro — ⁷RBI, Zagreb

Nothing was known about excited states of ¹⁷C above the neutron threshold (S_n= 0.729 MeV). We observed thirteen new states up to 16.3 MeV excitation energy with a resolution of 0.25 MeV using the three-neutron transfer reaction ¹⁴C(¹²C,⁹C)¹⁷C at 231 MeV incident energy (the reaction Q-value is Q₀= -46.930 MeV). The (¹²C,⁹C) reaction has also been used on ¹²C and ¹³C targets, and excited states of ¹⁵C and ¹⁶C have been populated up to 19 MeV and 17.4 MeV, respectively. In the comparison of excitation energies, widths and cross sections of states, a striking correspondence of states in the three isotopes is revealed for ten groups of states, when the spectra of ¹⁶C and ¹⁵C are shifted in excitation energy by a constant value. This behavior could be understood in the weak-coupling model, assuming an almost complete decoupling between cores and (sd)³ neutron configurations populated in the three-neutron transfer. The structure of ¹⁷C states is further investigated in shell-model calculations and by comparison to ¹⁹O levels. The neutron decay of the observed resonances in the three carbon isotopes could be understood using the parentage between the structure of mother and daughter states as derived in the weak-coupling model.