Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (J^{π}=1^{+}, T=1) state→ground state (J^{π}=0^{+}, T=0) and the isoscalar magnetic dipole 18.15 MeV (J^{π}=1^{+}, T=0) state→ground state transitions in ^{8}Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of >5σ. This observation could possibly be due to nuclear reaction interference effects or might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70±0.35(stat)±0.5(syst)  MeV/c^{2} and J^{π}=1^{+} was created.

Three sets of chiral doublet band structures have been identified in the 103 Rh nucleus. The properties of the observed chiral doublet bands are in good agreement with theoretical results obtained using constrained covariant density functional theory and particle rotor model calculations. Two of them belong to an identical configuration, and provide the first experimental evidence for a novel type of multiple chiral doublets, where an "excited" chiral doublet of a configuration is seen together with the "yrast" one. This observation shows that the chiral geometry in nuclei can be robust against the increase of the intrinsic excitation energy.PACS numbers: 21.10. Hw,21.10.Re,23.20.Lv A novel form of spontaneous symmetry breaking, the chiral rotation of triaxial nuclei, was suggested in 1997 [1]. It was shown that in special circumstances, referred to as chiral geometry, in the intrinsic frame of the rotating triaxial nucleus the total angular momentum vector lies outside the three principal planes. Thus, its components along the principal axes can be oriented in leftand right-handed ways. In the laboratory frame the chiral symmetry is restored, which manifests itself as a pair of ∆I = 1 nearly degenerate bands with the same parity. Such chiral doublet bands were first identified in four N = 75 isotones in 2001 [2]. So far, many chiral candidate nuclei have been reported experimentally in the A ∼ 80, 100, 130, and 190 mass regions [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Besides the simplest chiral configurations composed of one unpaired proton and neutron, composite chiral configurations, containing more than one unpaired protons and/or neutrons, have also been observed in the odd-mass or even-even neighbors of the odd-odd chiral nuclei [10,18]. These observations show that chirality is not restricted to a certain configuration in a mass region, i.e. the chiral geometry can be robust against the change of configuration. It was even demonstrated recently by Meng et al. [22][23][24][25], based on adiabatic and configuration-fixed constrained triaxial covariant density functional theory (CDFT) calculations, that it is possible to have multiple pairs of chiral doublet bands in a single nucleus, and the acronym MχD was introduced for this phenomenon. The first experimental evidence for the predicted MχD has been reported in 133 Ce [26], and also possibly in 107 Ag [27].It is also interesting to study the robustness of chiral geometry against the increase of the intrinsic excitation energy, i.e. if the chiral geometry is sustained in the higher-lying bands of a certain chiral configuration. In all the known cases the chiral doublet corresponds to the two lowest-lying bands of a configuration. Even for MχD in133 Ce [26] and 107 Ag [27], each chiral doublet structure corresponds to two lowest-lying bands with a distinct configuration. Therefore, study of the third and forth bands of the same chiral configuration is needed to answer the question of the investigated robustness. Very recent ...

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