Abstract:
HFRS (High energy FRagment Separator), an advanced in-flight radioactive separator at HIAF (High Intensity heavy ion Accelerator Facility), which is a new accelerator facility under construction in China, will provide promising opportunities for the high-energy radioactive beam physics research. The beam intensity of HFRS is extremely high (1\times 10^11 ppp for the primary beam), so that the energy loss measurement detectors used for particles identification should be able to operate at very high counting rate. However, the conventional energy loss detectors suffer from slow electronics response, severe pulse pile-up, and it is difficult to operate at high counting rate. In this paper, we propose a method to measure the energy loss at higher counting rate. We use a radiation-resistant multiple sampling ionization chamber as the energy loss measurement detector, and optimize the detector structure and readout methods to enhance detector response speed, then employ fast charge-sensitive preamplifiers for preliminary signal amplification, directly sample the pulse waveforms with a waveform digitizer. Finally, better performance can be obtained with subsequent digital algorithms. The method was validated and tested using both radioactive sources and beams. During the test with a compound components α source, a good energy resolution (FWHM) of 1.31% was achieved. During the test with a ^56\rmFe beam (300 MeV/u) provided by RIBLL2 (the second Radioactive Ion Beam Line in Lanzhou), no significant pulse pile-up was found at high counting rate even close to 1MHz, when a suitable time constant (\tau _\rmf=2 \; \mu \rms) of the preamplifier was set.
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