Speaker
Description
To experimentally quantify isoscalar proton–neutron pairing correlations in atomic nuclei, we plan systematic measurements of nucleon-pair transfer reactions. In order to separate the isoscalar (T = 0) and isovector (T = 1) pair-transfer strengths, it is effective to combine the (α,⁶Li) reaction, in which both components can be excited, with the (d,α) reaction, in which preferentially selects the isoscalar component. A new physics quantity called pair polarizability has been suggested, which can be determined by measuring the pair-removal and pair-addition strengths up to the high-excitation-energy region. Theoretically, an enhancement of the proton-neutron pair polarizability around $^{116}$Sn along the tin isotope chain is predicted.
For this purpose, we are upgrading an experimental system based on the Large Acceptance Spectrometer (LAS). The typical energy of the reaction products, $^6\rm{Li}$ and $^4\rm{He}$, is 10 - 15 MeV/u and the typical total rate at the focal plane is expected to be 6 Mcps with a signal-to-noise ratio of 0.1% due to inelastic scattering. In such a high-rate environment, pile-up becomes a primary limiting factor, and detector compactness, which helps suppress event overlap, is therefore an important design guideline. In addition, from the viewpoint of long-term and sustainable operation, the replacement of cathode foils with cathode-wire configurations, which offer better material availability, as well as the reduction of readout channels to suppress overall costs, are important issues. Furthermore, comprehensive optimization is required, taking into account practical aspects such as fabrication, installation, operation, and maintenance.
The design of a low-pressure vertical drift chamber (LP-VDC) for the LAS upgrade is ongoing .Assuming an operation with 10-kPa iso-butane gas, for the various geometrical configurations, including the wire arrangement, plane spacing, and cathode structure (foil or wire), the detection efficiency and the position resolution are estimated by using a simulation toolkit Garfield++.
In this presentation, the procedure of the simulation and the results for the several configurations will be discussed.