A system to measure isomeric state half-lives in the 10 ns to 10 μs range

Abstract

The Isomeric State Measurement System (SISMEI) was developed to search for isomeric nuclear states produced by fusion-evaporation reactions. The SISMEI consists of 10 plastic phoswich telescopes, two lead shields, one NaI(Tl) scintillation detector, two Compton suppressed HPGe γ-ray detectors, and a cone with a recoil product catcher. The new system was tested at the 8 UD Pelletron tandem accelerator of the University of São Paulo with the measurement of two known isomeric states: (54)Fe, 10(+) state (E = 6527.1 (11) keV, T(1/2) = 364(7) ns) and the 5/2(+) state of (19)F (E = 197.143 (4) keV, T(1/2) = 89.3 (10) ns). The results indicate that the system is capable of identifying delayed transitions, of measuring isomeric state lifetimes, and of identifying the feeding transitions of the isomeric state through the delayed γ-γ coincidence method. The measured half-life for the 10(+) state was T(1/2) = 365(14) ns and for the 5/2(+) state, 100(36) ns.

Isomeric state in the odd-odd 68Ga nucleus

“…Such a technique measures the time interval between the detection of the particles, evaporated in the reaction, and the delayed gamma-ray, emitted by the isomeric state, making it possible to identify the gamma rays coming from the nucleus of interest and analyze the time evolution of the γ-ray events. A system called SISMEI (Isomeric State Measurement System) that implements this technique has been used [11]. The SISMEI is composed of 10 phoswich-type particle detectors arranged around a dodecahedron-shaped chamber, called SACI (Ancillary Scintillator System) [12], and two gamma-ray detectors (one HPGe, and one NaI(Tl)), facing a lead stopper placed 20.9(1) cm away from the target.…”