Polariton Induced Conical Intersection and Berry Phase

We investigate the Polariton induced conical intersection (PICI) created from coupling a diatomicmolecule with the quantized photon mode inside an optical cavity, and the corresponding BerryPhase effects. We use the rigorous Pauli-Fierz Hamiltonian to describe the quantum light-matterinteractions between a LiF molecule and the cavity, and exact quantum propagation to investigatethe polariton quantum dynamics. The molecular rotations relative to the cavity polarization directionplay a role as the tuning mode of the PICI, resulting in an effective CI even within a diatomic molecule.To clearly demonstrate the dynamical effects of the Berry phase, we construct two additional modelsthat have the same Born-Oppenheimer surface, but the effects of the geometric phase are removed.We find that when the initial wavefunction is placed in the lower polaritonic surface, the Berryphase causes aπphase-shift in the wavefunction after the encirclement around the CI, indicatedfrom the nuclear probability distribution. On the other hand, when the initial wavefunction is placedin the upper polaritonic surface, the geometric phase significantly influences the couplings betweenpolaritonic states and therefore, the population dynamics between them. These BP effects are furtherdemonstrated through the photo-fragment angular distribution. PICI created from the quantizedradiation field has the promise to open up new possibilities to modulate photochemical reactivities.

Polariton Induced Conical Intersection and Berry Phase

We investigate the Polariton induced conical intersection (PICI) created from coupling a diatomicmolecule with the quantized photon mode inside an optical cavity, and the corresponding BerryPhase effects. We use the rigorous Pauli-Fierz Hamiltonian to describe the quantum light-matterinteractions between a LiF molecule and the cavity, and exact quantum propagation to investigatethe polariton quantum dynamics. The molecular rotations relative to the cavity polarization directionplay a role as the tuning mode of the PICI, resulting in an effective CI even within a diatomic molecule.To clearly demonstrate the dynamical effects of the Berry phase, we construct two additional modelsthat have the same Born-Oppenheimer surface, but the effects of the geometric phase are removed.We find that when the initial wavefunction is placed in the lower polaritonic surface, the Berryphase causes aπphase-shift in the wavefunction after the encirclement around the CI, indicatedfrom the nuclear probability distribution. On the other hand, when the initial wavefunction is placedin the upper polaritonic surface, the geometric phase significantly influences the couplings betweenpolaritonic states and therefore, the population dynamics between them. These BP effects are furtherdemonstrated through the photo-fragment angular distribution. PICI created from the quantizedradiation field has the promise to open up new possibilities to modulate photochemical reactivities.

Angular distribution of fragments in neutron-induced nuclear fission at energies 1−200 MeV: Data, theoretical models and relevant problems

In recent years, investigations of angular distributions of fragments in neutron-induced nuclear fission have been extended to intermediate energies, up to 200 MeV, as well as to a wide range of target isotopes. Using as an example the latest data obtained by our group for the reaction 237Np(n; f), we discuss the specific features of fission fragment angular distribution and present a method for their simulation based on the code TALYS. It is shown that a simplified model reasonably describes energy dependence of the angular distribution in the whole range 1–200 MeV. The ways to improve the model are discussed along with the possibilities to use it for obtaining new information on fission and pre-equilibrium processes in neutron-nucleus interaction. We consider also the relevant problems of describing fission fragment angular distributions.

Investigation on Neutron-Induced Fission Fragment Angular Distribution of 232Th and 238U

Fission fragment angular distribution (FFAD) data would help obtain new insights into both the fission process and the mechanism of the projectile’s interaction with the nucleus. Recently, a structure has been reported in neutron-induced FFAD of even-even actinide nuclei near threshold. Statistical modelling is used in this article to analyse FFAD from neutron-induced fission of 238U and 232Th. The statistical variance K02 is obtained by fitting the measured fragment anisotropies with a theoretical model. Accurate analysis is performed to deduce the variance K02 of the K-distribution of the levels in the transition nucleus at neutron energies from threshold to 50 MeV. We show the method by which quantitative values of K02 can be obtained. The results not only present high-resolution data in these even-even nuclei but also show that for the 238U(n,f) reaction, the strength for the K-transition states comes mainly from the higher angular momenta, in agreement with the Nilsson model orbitals. We also study the periodic structure of anisotropy related to the set of (n,f) reactions in comparison with the related cross section performed with the TALYS code. The comparison of the variance with the cross section clearly illustrates the strong correlation between the value of the variance and the opening of a fission chance. We show that whenever the probability of reaction in a new channel and cross section increases, K02 decreases versus the incident neutron energy, so the minimum of K02 can show the maximum probability of the (n,f)xn reaction.

MEASUREMENT OF PHOTOFISSION CROSS-SECTION OF 238U USING MICROTRON FACILITY

Photofission cross-section of 238U was measured using bremsstrahlung radiation energy 7.4–9.0 MeV with energy step of 0.4 MeV by employing Lexan polycarbonate film as solid state nuclear track detector (SSNTD). The photon intensity from the Microtron accelerator at a distance of 15 cm from the bremsstrahlung converter (tantalum target) facility was estimated to be 1010 photons/sec using the code EGS-4. In this paper, details of the fission fragment angular distribution measurements of 238U target using Lexan polycarbonate have been discussed. The photofission cross-section was calculated using the angular distribution of fission fragments and the results were compared with those obtained using the code EMPIRE-II and various barrier parameters of the RIPL-1, RIPL-2 libraries and with the new analytical fission barrier formula based on the Hugenholtz–Van Hove theorem. The present experimental measurements were in good agreement with the results obtained from the Empire-II code predictions for potential parameter taken from RIPL-1 and a newly developed analytical fission barrier formula.