Toward new frontiers : Encounter and synergy of state-of-the-art astronomical detectors and exotic quantum beams

Program D01-7	New development of pulsed beam experiments by real-time image correlation analysis
Principal Investigator	KADONO, Ryosuke (High Energy Accelerator Research Organization (KEK))

[Research Goals]  In order to overcome the most serious limitation of pulsed muon experiments, which is the difficulty in identifying the correspondence between the incident muon and the subsequent measurement events such as electrons, positrons, and negative muon capture X-rays, the time and position of each muon in the beam pulse are detected with a two-dimensional detector (hodoscope) that transmits muons. In addition, the time and two-dimensional positional information of subsequent events from muons stopped in the sample is measured with a pixel detector, and a one-to-one correspondence between events is identified by correlating these two two-dimensional images. We apply this method to muon spin rotation (μSR) measurements, where the subsequent event is a decaying positron, to realize μSR measurements with high temporal resolution that is not limited by pulse width. Furthermore, we will verify the possibility of spatially resolved nondestructive elemental analysis by combining this method with a slow negative muon whose trailing event is a characteristic X-ray. Through these experiments, we will demonstrate the principle of high temporal and positional resolution measurement using pulsed muon beams while taking advantage of the high intensity beam.


Fig. 1. Principle of the Real-time Image Correlation Analysis (RICA) method.

[Research Plan]  Using the μSR experiment as the main model case, we are planning the following experiments in cooperation with C01 group. A flat specimen with a thickness of about 1 mm, which is typical for surface (slow) muon beam irradiation experiments, is prepared and sandwiched closely between two two-dimensional detectors. The two-dimensional detector at the front of the sample is a hodoscope (a detector that can transmit a surface muon beam and measure the position and time of its passage), which records the transmission time and position information for every muon in the pulse during beam irradiation (real-time muon image). A two-dimensional detector placed on the back of the sample records the time and position information of decay electrons/positrons, and the position and energy information of X-rays (real time subsequent event image). Finally, the positional correlation between the muon image and the subsequent event image is analyzed, and the time difference between the muon and the subsequent event is histogrammed or the information corresponding to the energy is recorded for the pairs that are judged to correspond to the muon and the subsequent event. In this study, this is called the Real-time Image Correlation Analysis (RICA) method. By adapting the RICA method, μSR involves the detection of muon decay at each event by a small pair of muon and positron counters. Therefore, the μSR measurement which is essentially equivalent to that of a DC muon beam can be realized for a pulsed beam. For the two-dimensional hodoscope through which the muon penetrates, we used a plastic fiber (0.1 mm^φ cross section), an avalanche photodiode for readout (128×128 pixels equivalent), and a silicon pixel detector for positron imaging (ToA mode operated TimePix3 implemented in the readout integrated circuit, 55 μm pitch, 256×256 pixels equivalent) is applied for positron imaging. Since both the hodoscope and the silicon pixel detector are expected to have a time resolution of about 1.5 ns, the observation of rotation signals of up to 300 MHz can be realized. In the first year of the project, we will conduct a proof-of-principle study of the RICA method for the μSR experiment using pure iron (48.7 MHz rotation signal at zero field at room temperature) and quartz (144 MHz rotation signal at 10 mT at room temperature), assuming the muon beam intensity at J-PARC. In the second year of the project, we will optimize the method for practical use by addressing the problems identified in the previous RICA-μSR study. In addition, we will change the operation mode of TimePix3 so that it can read signals proportional to the energy imparted to silicon. By combining this with a slow negative muon beam, we will measure the energy of characteristic X-rays corresponding to negative muon injection events, and verify the possibility of nondestructive analysis of light elements with spatial resolution by the RICA method.

Members

Reference Materials

• R. Kadono, I. Watanabe, K. Ishida, T. Matsuzaki, and K. Nagamine, “Development of a new μSR spectrometer ARGUS,” RIKEN Accel. Prog. Rep. 29, 196 (1995).
• K. M. Kojima, T. Murakami, Y. Takahashi, H. Lee, S. Y. Suzuki, A. Koda, I. Yamauchi, M. Miyazaki, M. Hiraishi, H. Okabe, S. Takeshita, R. Kadono, T. U. Ito, W. Higemoto, S. Kanda, Y. Fukao, N. Saito, M. Saito, M. Ikeno, T. Uchida, and M. M. Tanaka, “New μSR spectrometer at J-PARC MUSE based on Kalliope detectors,” J. Phys. Conf. Ser. 551, 012063 (2014).
• R. Kadono, K. H. Satoh, A. Koda, K. Nishiyama, and M. Mihara, “High transverse field μSR with π/2-RF pulse spin control technique,” Physica B 404, 996–998 (2009).