Fumihiko Takasaki

Performance and radiation damage of a BaF2 calorimeter

The performance of a barium fluoride (BaF2) scintillator as an electromagnetic shower calorimeter is investigated for electrons in the energy range 0.25–5 GeV. The energy resolution (fwhm) is expressed by 0.098E14 [GeV] and compared with a Monte Carlo simulation. For radiation damage a dose of 1 × 105 Gy (1 Gy (1 Gy = 100 rad) shortens the optical attenuation length to 14%. The deterioration is compared with that of BGO.

Performance of a photomultiplier tube with transmissive dynodes in a high magnetic field

Abstract The performance of a photomultiplier tube with transmissive dynodes was examined. We found that the amplification gain was higher than 104 even in a magnetic field of 7.8 kG. The energy resolution for 662 keV gamma rays from 137Cs was 12% fwhm measured using a NaI crystal at 7.8 kG. The time resolution was as good as about 200 ps at 7.8 kG for the light generated by 2 GeV pions when they passed through a 1 cm thick scintillator mounted on the tube.

Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons

The Great Pyramid, or Khufu’s Pyramid, was built on the Giza plateau in Egypt during the fourth dynasty by the pharaoh Khufu (Cheops), who reigned from 2509 bc to 2483 bc. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built. To understand its internal structure better, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone. The resulting cosmic-ray muon radiography allows us to visualize the known and any unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross-section similar to that of the Grand Gallery and a minimum length of 30u2009metres) situated above the Grand Gallery. This constitutes the first major inner structure found in the Great Pyramid since the nineteenth century. The void, named ScanPyramids’ Big Void, was first observed with nuclear emulsion films installed in the Queen’s chamber, then confirmed with scintillator hodoscopes set up in the same chamber and finally re-confirmed with gas detectors outside the pyramid. This large void has therefore been detected with high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of the internal structure of Khufu’s Pyramid. Although there is currently no information about the intended purpose of this void, these findings show how modern particle physics can shed new light on the world’s archaeological heritage.

Development of a multi-pixel photon sensor with single photon sensitivity

Abstract A multi-pixel photon sensor with single-photon sensitivity has been developed. Based on a hybrid photo-detector (HPD) technology, it consists of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity-focused structure, where the photocathode and MP-AD face each other with a small gap of 2.5xa0mm. The MP-AD, which has an effective area of 16xa0mm×16xa0mm, is composed of 8×8 pixel and has been specially designed for the HPD. The maximum gain of the HPD is 5×10 4 , sufficiently high to detect single photons with a timing resolution better than 100xa0ps. Up to four photoelectrons can be clearly identified as distinct peaks in a pulse-height spectrum, thanks to the low-noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5xa0T.

Performance of a remotely located muon radiography system to identify the inner structure of a nuclear plant

The performance of a muon radiography system designed to image the inner structure of a nuclear plant located at a distance of 64 m was evaluated. We concluded absence of the fuel in the pressure vessel during the measurement period and succeeded in profiling the fuel material placed in the storage pool. The obtained data also demonstrated the sensitivity of the system to water level changes in the reactor well and the dryer-separator pool. It is expected that the system could reconstruct a 2 m cubic fuel object easily. By operating multiple systems, typically four identical systems, viewing the reactor from different directions simultaneously, detection of a 1 m cubic object should also be achievable within a few month period.

Development of a multi-pixel hybrid photodetector with high quantum efficiency and gain

A hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD) has been developed for these years. One of the features of the HPD is a good energy resolution, and it was shown in our previous study that the further improvement would be possible by reducing the fluctuation of charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the result of the improvement with the newly developed HPD whose MP-AD encapsulated has a thinner dead layer than before. It is demonstrated that the new HPD has a much better energy resolution which enables the clear counting up to nine photoelectrons. Other features like a uniformity among the pixels or a photocathode sensitivity of the HPD are also presented.A hybrid photodetector (HPD) consisting of a photocathode and a multipixel avalanche diode (MP-AD) was developed a few years ago. Our previous studies showed that its inherent potential for high resolution photon counting could be further enhanced by reducing fluctuations in charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the improvement with the newly developed HPD whose encapsulated MP-AD has a thinner dead layer than before. It is demonstrated that the new HPD has much better energy resolution, which enables clearer counting up to nine photoelectrons. Further enhancement of the photocathode sensitivity of the HPD is also discussed.

Monolithic shaper amplifier for multianode PMT readout

Abstract A monolithic dual-channel shaper amplifier chip was designed and fabricated with a semicustom bipolar IC technology to be used for a readout system of a scintillation-fiber calorimeter with a multianode PMT.

Phase shift analysis of the reaction K+N → KN below 1.6 GeV/c

Abstract An energy-dependent partial wave analysis was made for the K + nucleon scattering in the energy range between 0.2 and 1.6 GeV/ c using the data including our new polarization data of K + n elastic and charge-exchange scattering. Counterclockwise Argand plots were found for the partial waves P 13 , P 01 and D 03 .

Magnetic field mapping of the Belle solenoid

The mapping of the magnetic field of the Belle detectors large superconducting solenoid is described. The mapping was done with the accelerator magnets located inside the Belle solenoid excited to their nominal field values. To cope with geometrical constraints, we developed a novel moving mechanism for the field probes that uses an ultrasonic motor located in the strong magnetic field.

Experimental results from Tristan

SHIP; A magnetic spectrometer with large angular coverage and with good momentum and energy resolution, approved in March 1983, rolled in in September 1986, A compact magnetic spectrometer with strong magnetic field (3 T), and with good position resolution of calorimeter, approved in December 1983, rolled in in November 1986, A magnetic spectrometer with large angular coverage and with good particle identification capability with TPC, approved in March 1983, rolled in in March 1987, A heavily ionizing particle detector with plastic sheet, CR-39, approved in October 1984, installed in September 1986.