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Register a new userThe construction of the Fiber-SiPM beam monitor system of the R484 and R582 experiments at the RIKEN-RAL muon facility
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Added by
Maurizio Bonesini M.
Publication date
2017
fields
Physics
and research's language is
English
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The scintillating fiber-SiPM beam monitor detectors, designed to deliver beam informations for the R484 and R582 experiments at the high intensity, low energy pulsed muon beam at the RIKEN-RAL facility, have been successfully constructed and operated. Details on their construction and first performances in beam are reported
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The goal of the FAMU experiment at RIKEN RAL is the measure of the hyperfine splitting of the ground state of the muonic hydrogen, to allow a determination of the proton Zemach radius with a precision better than $5 times 10^{-3}$ . The comparison of this measurement with the ones done with ordinary hydrogen may help to solve the so-called proton radius puzzle, triggered by the $6 sigma$ discrepancy in the proton charge radius value as extracted from muonic Lamb shift and the value based on e-p scattering and ordinary hydrogen spectroscopy.
Muon beam monitoring is indispensable for indirectly monitoring accelerator-produced neutrino beams in real time. Though Si photodiodes and ionization chambers have been successfully used as muon monitors at the T2K experiment, sensors that are more radiation tolerant are desired for future operation. We have investigated the electron-multiplier tube (EMT) as a new sensor for muon monitoring. Secondary electrons produced by the passage of muons at dynodes are multiplied in the tube and produce signal. Two prototype detectors were installed at the T2K muon monitor location, and various EMT properties were studied based on in situ data taken with the T2K muon beam. The signal size is as expected based on calculation, and the EMTs show a sufficiently fast time response for bunch-by-bunch beam monitoring. The spill-by-spill intensity resolution is 0.4%, better than the required value (1%). Signal linearity within $pm$1% is achieved at proton beam powers up to 460 kW (with +250 kA focusing horn operation). A gradual signal decrease was observed during the initial exposure, due to the stabilization of dynode materials, before the response became stable within $pm$1%. This work demonstrates that EMTs are a good candidate for future muon monitoring at T2K, and may also have other more general applications.
BRIKEN is a complex detection system to be installed at the RIB-facility of the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants, $beta$-particles, $gamma$-rays and $beta$-delayed neutrons. The whole detection setup involves the Advanced Implantation Detection Array (AIDA), two HPGe Clover detectors and a large set of 166 counters of 3He embedded in a high-density polyethylene matrix. This article reports on a novel methodology developed for the conceptual design and optimisation of the 3He-tubes array, aiming at the best possible performance in terms of neutron detection. The algorithm is based on a geometric representation of two selected parameters of merit, namely, average neutron detection efficiency and efficiency flatness, as a function of a reduced number of geometric variables. The response of the detection system itself, for each configuration, is obtained from a systematic MC-simulation implemented realistically in Geant4. This approach has been found to be particularly useful. On the one hand, due to the different types and large number of 3He-tubes involved and, on the other hand, due to the additional constraints introduced by the ancillary detectors for charged particles and gamma-rays. Empowered by the robustness of the algorithm, we have been able to design a versatile detection system, which can be easily re-arranged into a compact mode in order to maximize the neutron detection performance, at the cost of the gamma-ray sensitivity. In summary, we have designed a system which shows, for neutron energies up to 1(5) MeV, a rather flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid and compact modes, respectively. The performance of the BRIKEN system has been also quantified realistically by means of MC-simulations made with different neutron energy distributions.
We have developed a method for achieving excellent resolving power in in-flight particle identification of radioactive isotope (RI) beams at the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory (RIBF). In the BigRIPS separator, RI beams are identified by their atomic number Z and mass-to-charge ratio A/Q which are deduced from the measurements of time of flight (TOF), magnetic rigidity (Brho) and energy loss (delta-E), and delivered as tagged RI beams to a variety of experiments including secondary reaction measurements. High A/Q resolution is an essential requirement for this scheme, because the charge state Q of RI beams has to be identified at RIBF energies such as 200-300 MeV/nucleon. By precisely determining the Brho and TOF values, we have achieved relative A/Q resolution as good as 0.034% (root-mean-square value). The achieved A/Q resolution is high enough to clearly identify the charge state Q in the Z versus A/Q particle identification plot, where fully-stripped and hydrogen-like peaks are very closely located. The precise Brho determination is achieved by refined particle trajectory reconstruction, while a slew correction is performed to precisely determine the TOF value. Furthermore background events are thoroughly removed to improve reliability of the particle identification. In the present paper we present the details of the particle identification scheme in the BigRIPS separator. The isotope separation in the BigRIPS separator is also briefly introduced.
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