Selective Field-Ionization Electron Detector at Low Temperature of 10 mK Range (NUCLEAR SCIENCE RESEARCH FACILITY?Particle and Photon Beams)

Combined with a dilution refrigerator, selective field-ionization detection system with a channel electron multiplier optimized at 10 mK-range temperature was developed. The detection efficiency of the ionized electrons from the n~110 Rydberg states of Rb is 98% at the lowest achieved temperature of 12 mK

Different mechanism of two-proton emission from proton-rich nuclei 23^{23}Al and 22^{22}Mg

Two-proton relative momentum ($q_{pp}$) and opening angle ($\theta_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim20$ MeV/c as well as a peak in $\theta_{pp}$ around 30$^\circ$ are seen in the two-proton break-up channel from a highly-excited $^{22}$Mg. In contrast, such peaks are absent for the $^{23}$Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$Mg is quite different from the $^{23}$Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process

Coherent Time Evolution of Highly Excited Rydberg States in Pulsed Electric Field: Opening a New Scheme for Stringently Selective Field Ionization (NUCLEAR SCIENCE RESEARCH FACILITY-Beams and Fundamental Reaction)

Coherent time evolution of highly excited Rydberg states in Rb (98 n 150) under pulsed electric field in high slew rate regime was investigated with the field ionization detection. We observed for the first time a discrete transition of the threshold ionization field with slew rate, the behavior of which depends also on the position of the low l states relative to the adjacent manifold. The experimental results strongly suggest that the coherent interference effect plays decisive role for such transitional behavior, and bring us a new, quite effective scheme for the stringently selective field ionization