4,268 research outputs found
New parameter-free polarization potentials in low-energy positron collisions
The polarization potential plays a decisive role in shaping up the cross sections in low energy positron collisions with atoms and molecules. However, its inclusion without involving any adjustable parameter, is still a challenge. Various other techniques employed so far for positron collisions are summarized, and a new, nonadjustable and very simple form of the polarization potential for positron-atom (molecule) collisions below the threshold of positronium formation is discussed. This new recently proposed potential is based on the correlation energy of a single positron in a homogeneous electron gas. The correlation energy was calculated by solving the Schrodinger equation of the positron-electron system and fitted to an analytical form in various ranges of the density parameter. In the outside region, the correlation energy is joined smoothly with the correct asymptotic form. This new positron correlation polarization (PCOP) potential was tested on several atomic and molecular targets such as the Ar, CO, and CH4. The results on the total and differential cross sections on these targets are shown along with the experimental data where available
Odd tensor electric transitions in high-spin Sn-isomers and generalized seniority
The similar behavior of the B(E1) values of the recently observed 13- odd
tensor E1 isomers and the B(E2) values of the 10+ and 15- even tensor E2
isomers in the Sn-isotopes has been understood in terms of the generalized
seniority for multi-j orbits by using the quasi-spin scheme. This simple
approach proves to be quite successful in explaining the measured transition
probabilities and the corresponding half-lives in the high-spin isomers of the
semi-magic Sn-isotopes. Hence, we show for the first time the occurrence of
seniority isomers in the 13- Sn-isomers, which decay by odd-tensor E1
transitions to the same seniority states.Comment: 4 pages, 3 figure
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