Speaker
Description
Charge-changing cross section ($\sigma_{\mathrm{CC}}$) measurements play an essential role in advancing our understanding of nuclear structure. In heavy-ion beam experiments, atomic number ($Z$) identification is performed by combining the measurement of energy loss ($\Delta E$) with that of the particle velocity ($\beta$). Under typical conditions, the flight path is long enough to determine $\beta$ with high precision, and therefore the achievable $Z$ resolution is mainly limited by the $\Delta E$ resolution. However, in the $\sigma_{\mathrm{CC}}$ measurements, where $Z$-identification is required for all particles downstream of the reaction target, the flight path between the target and the downstream magnetic analyzer is too short to measure time-of-flight (TOF). To address this problem, we attempted $Z$-identification downstream of the target by using the combination of $\Delta E$ from an ionization chamber and $\beta$ measured precisely under a short flight path of approximately 2 m using fast plastic scintillators.
The experiment was carried out at RIKEN RIBF. Secondary beams, such as Sn isotopes, were produced from a primary beam of $^{238}$U and irradiated onto a reaction target placed at the F8 focal plane. The $Z$-identification of the reaction products downstream of the target was performed using the ionization chamber in combination with a newly developed short flight-path TOF measurement system. This system employs fast plastic scintillators together with a processing circuit configured for high-precision time measurement.
In this study, we investigated the timing resolution and its position dependence of the developed plastic detectors, as well as the achieved $Z$-identification capability when combined with the ionization chamber. The result will be discussed in detail.
