Particle Physics Group,Department of Physics, Graduate School of Science, Kobe University
The Micro Pixel Chamber (μ-PIC) is a real-timeimaging detector that offers high spatial resolution (approximately 100 μm), high time resolution (less than 100 nanoseconds), and a high particle flux tolerance (> 10⁷ particles/mm²/s).
This detector is expected to be applied not only in the field of high-energy physics, but also in various areas such as
material structure analysis, medical diagnostics, astrophysics, and non-destructive testing.
Our research group is conducting studies with a focus on ensuring stable operation and reducing radioactivity of the μ-PIC.
Underground environments are ideal for experiments in cosmic and particle physics that require extremely low background noise, such as observations of solar and supernova neutrinos and direct searches for dark matter, because they significantly reduce the influence of cosmic rays. One of the major common background sources in underground experiments is the radioactive noble gas radon-222 (hereafter referred to as radon).
For example, in order to achieve high-precision solar neutrino observations, the radon concentration inside the Super-Kamiokande detector must be kept below approximately 1 mBq/m³. However, commercially available devices are not capable of measuring such trace levels of radon.
We are developing radon detectors with the sensitivity required for underground experiments, as well as technologies for radon removal.
We are developing a gaseous Time Projection Chamber (TPC) detector for dark matter searches. In order to detect the direction of nuclear recoil scattered by a dark matter, we are working on a low-pressure, low-diffusion gaseous TPC capable of pricise track reconstruction. It is important for track reconstruction not only to develop multi readout gaseous detector such as MPGD (Micro-Pattern Gas Detectors), but also to obtain higyly integrated readout electronics technology. At Kobe University, we are developing a gaseous TPC filled with Negative-ion gas (SF₆), aiming to improve track reconstruction accuracy and reduce background events. Dedicated electronics for the negative-ion gaseous TPC are also under development. Furthermore, we are working on the development of a fine-pitc pixelized detector (with a pitch of 250 μm) using high-density dedicated ICs and SoCs for data acquisition technology, for next-generation detectors.
We are developing a surface alpha radiation imaging detector (AICHAM), based on the operating principle of a Time Projection Chamber (TPC) using μ-PIC technology. This detector enables high-sensitivity sample analysis, and has been used not only within the underground experiment group but also for material analysis in neutrino experiments, dark matter searches, and neutrinoless double beta decay (0νββ) experiments.
Since the detector can reconstruct alpha particle tracks in three dimensions, it allows precise identification of the emission points on the sample surface. This unique analytical method enables highly sensitive measurements with extremely low radioactive background noise.
Currently, we have achieved an analysis sensitivity of approximately 10⁻⁴ alpha/cm²/hr (90% confidence level), and continue to perform measurements. In parallel, we are also conducting research and development to further improve the detection sensitivity.
We are developing
a low-material detector capable of measuring high-rate charged particles,
specifically a resistive plate gas amplification detector (RPC) using diamond-like carbon (DLC)
.
An RPC consists of high-resistance plates or thin films arranged in parallel with a gap of about 1 mm, across which a high voltage is applied. When a charged particle passes through, it triggers an electron avalanche with a high amplification factor, allowing detection. As the charge is collected through the high-resistance plates, the local voltage drops, preventing continuous electron avalanches.
Traditionally, oil was used to maintain the smoothness of the surface of the high-resistance plates, but stability remained a challenge. In this study, we successfully developed a radiation-resistant detector capable of measuring particles at higher rates than before by using mechanically smooth and strong DLC as the resistive material. Furthermore, by forming this thin film on a thin organic substrate, we succeeded in significantly reducing the thickness of the resistive plates.
This detector has been developed with the intention of being installed on the muon beamline of the MEG II experiment. However, development continues with a view toward applications in other environments where low material budget is required, and where high-rate and high time-resolution detection is needed.
