Manipulation of Giant Multipole Resonances via Vortex γ Photons.

Traditional photonuclear reactions primarily excite giant dipole resonances, making the measurement of isovector giant resonances with higher multipolarities a great challenge. In this Letter, the manipulation of collective excitations of different multipole transitions in even-even nuclei via vortex γ photons is investigated. We develop the calculation method for photonuclear cross sections induced by the vortex γ photon beam using the fully self-consistent random-phase approximation plus particle-vibration coupling (RPA+PVC) model based on Skyrme density functional. We find that the electromagnetic transitions with multipolarity J<|m_{γ}| are forbidden for vortex γ photons due to the angular momentum conservation, with m_{γ} being the projection of total angular momentum of γ photon on its propagation direction. For instance, this allows for probing the isovector giant quadrupole resonance without interference from dipole transitions using vortex γ photons with m_{γ}=2. Furthermore, the electromagnetic transition with J=|m_{γ}|+1 vanishes at a specific polar angle. Therefore, the giant resonances with specific multipolarity can be extracted via vortex γ photons. Moreover, the vortex properties of γ photons can be meticulously diagnosed by measuring the nuclear photon-absorption cross section. Our method opens new avenues for photonuclear excitations, generation of coherent γ photon laser and precise detection of vortex particles, and consequently, has significant impact on nuclear physics, nuclear astrophysics and strong laser physics.

ΔI=2 Bifurcation as a Characteristic Feature of Scissors Rotational Bands.

We report microscopic many-body calculations indicating that rotational bands based on nuclear scissors vibrations exhibit systematic splitting between neighboring spin states (ΔI=2 bifurcation) in which the magnitude of the moment of inertia oscillates between states having even and odd spins. We show that this unexpected result is caused by self-organization of the deformed proton and neutron bodies in the scissors motion, which is further amplified by the K^{π}=1^{+} two-quasiparticle configurations near the scissors states. We propose that the puzzling excited state found above the 1^{+} scissors state in ^{156}Gd [Phys. Rev. Lett. 118, 212502 (2017)PRLTAO0031-900710.1103/PhysRevLett.118.212502] is the first evidence of this effect, and predict that bifurcation may generally appear in all other scissors rotational bands of deformed nuclei, and possibly in other systems exhibiting collective scissors vibrations.