Milestones:20-inch Diameter Photomultiplier Tubes, 1979 - 1987

Date Dedicated
Dedication #
Iwata City, Japan
IEEE Regions
IEEE sections
Achievement date range


20-inch Diameter Photomultiplier Tubes, 1979 - 1987


Hamamatsu Photonics K.K. began developing 20-inch diameter photomultiplier tubes at Toyooka Factory in 1979 for a 3000-ton water-filled Cherenkov particle detector, Kamiokande-II, in response to a request by Professor Masatoshi Koshiba. 1071 PMTs on it collected photons induced in the water by the particles falling on it. Kamiokande-II detected a neutrino burst in the Supernova SN1987A in 1987, earning Professor Koshiba a Nobel Prize in 2002.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

The address of the milestone plaque site is: HAMAMATSU PHOTONICS K.K. Electron Tube Division, Toyooka Factory 314-5, Shimokanzo, Iwata City, Shizuoka Prefecture, Japan GPS coordinates: 34 48” 47. 1” N, 137 50” 10. 0” E Milestone Plaque-Replica 1: Kamiokande II Kamioka Observatory, Institute for Cosmic Ray Research Mozumi Mine of the Kamioka Mining and Smelting Co. Hida City, Gufu Prefecture, Japan

Details of the physical location of the plaque

The plaque is on a plinth of the grounds near the front entrance gate of the Toyooka Factory.

How the intended plaque site is protected/secured

The factory is surrounded by a fence, but the front gate is kept open during the daytime. Visitors can go to the plaque site without going through the security during the daytime.

Historical significance of the work

Technological significance: (1) Successful production of 20 inch diameter photomultiplier tubes, the world largest. [1, 4, 5, 6] (2) High gain, 10⁷, to be able to detect a single-photon event. [4, 5, 6, 7, 8] Scientific significance: Detection of the neutrino burst in the supernova SN1987A, which brought the Nobel Prize in Physics in 2002 to Professor Masatoshi Koshiba. [7, 8, 9]

Features that set this work apart from similar achievements

The following technological features do it: 1. Large diameter Diameter of 20 inch (508 mm) makes it possible to achieve a photosensitive coverage of 20 % of the surface of a cylindrical Cherenkov detector with 15.6 m diameter and 16.1 m height filled with the purified water. [1, 5, 7, 8, 9] 2. Direct immersion of the PMTs in the Water A total of 1071 PMTs are placed around the water tank (15.6 m diameter x 16.1 m height) filled with 3000 metric tons of purified water. The PMTs are immersed directly in the water. The PMTs must withstand the water pressure, must prevent the water from leaking into the tubes, and must maintain the electric insulation to be able to maintain the device voltage across the PMT above 2000 V, for over a period of about 10 years. [1, 6, 8, 9] 3. High gain The gain of the PMT defined by the ratio of the anode output current to the emitted photo current is 10⁷ at 2000 V between the anode and the cathode. The gain of 10⁷ makes it possible to detect single-photon event taking place in the Cherenkov radiation detector. Electron trajectory simulation in a water tank was used, at the early phase of the development in 1979-1980, to find the optimum electrode configuration of the photocathode, focusing electrode, and the first dynode. [4, 10] 4. Quantum efficiency A quantum efficiency of 22 % at the wavelength of 400 nm is obtained with using the photocathode formed by depositing a thin layer of antimony on the inner surface of the tube by vacuum evaporation. The antimony layer is then activated by evaporating the alkali metal in vacuum on to the layer. [4, 5, 6] 5. Uniformity The anode uniformity depends mainly on two factors, i.e., the uniformity of the photocathode quantum efficiency and that of the collection efficiency between the photocathode and the first dynode. The change of anode uniformity over the large view angles is within ±40 %. [4, 5, 6] 6. Mean transit time The mean transit time is found to be 90 ns. [4] 7. Transit time spread The transit time spread (TTS), which is a distribution of transit time for a single PMT, is an important parameter when timing information is required. TTS is found 7 ns at FWHM. [4] 8. Number of the PMTs in a Cherenkov radiation detector A total of 1071 units of the PMTs are employed to construct the Kamiokande II, cylinder-shape Cherenkov radiation detector with a height of 16.1 m filled with the purified water, as mentioned earlier in 9.1. Of the 1071 PMTs, 948 units are viewing the space inside the cylinder with a diameter of 15.6 m (fiducial volume of 2040 tons of the water), while 123 units viewing a thin tubular space just outside the cylinder filled with the purifier water. The outside tubular space gives rise to signals responding to radiations from the rocks in earth surrounding the detector and radiations of stray particles from the space. After appropriate signal processing, the signal-to-noise ratio of the signal from the 948 PMTs for detection of neutrinos hitting the fiducial volume was improved considerably. Tightly controlled TTS (7 ns) permits the use of a large number (1071) of PMTs in a Cherenkov detector. Because the TTS of all the units of PMTs is well controlled, it is possible to calculate the direction of cone axis of Cherenkov radiation from the output signals of 948 PMTs with a high degree of precision. [1, 8, 9, 10]

Significant references

[1] Development of 20-inch PMT. [2] T. Hayashi, “RECENT DEVELOPMENTS IN PHOTOMULTIPLIERS FOR NUCLEAR RADIATION DETECTORS,” Nuclear Instruments and Methods 196 (1982), pp.181-186.Media:RECENT DEVELOPMENTS IN PHOTOMULTIPLIERS FOR NUCLEAR RADIATION DATECTORS.pdf [3] “Photon is our business,” HAMAMATSU, Corporate Outline.Media:Photon is our business.pdf [4] H. Kume, S. Sawaki and M. Ito, K. Arisaka, Hamamatsu TV Co., Ltd., K. Arisaka and T. Kajita, Dept. of Physics, University of Tokyo, A. Nishimura and A. Suzuki, KEK National Laboratory of High Energy Physics, “20 INCH DIAMETER PHTOMULTIPLIER,” Nuclear Instruments and Methods 205 (1983), pp.443-449.Media:20 INCH DIAMETER PHOTOMULTIPLIER.pdf [5] Kenji Suzuki, “Developing the 20-inch semispherical photomultiplier tubes,” - The Nobel Prize winning achievement seen from a company R&D perspective”, Spectroscopy Research, Vol.52, No.5, 2003.Media:Developing the 20-inch semispherical photomultiplier tubes.pdf [6] HAMAMATSU TECHNICAL DATA SHEET, R1449, PHOTOMULTIPLIER TUBE, 20 INCH HEMISPHERICAL.Media:HAMAMATSU TECHNICAL DATA SHEET on R1449.pdf [7] K. Hirata, T. Kajita, M. Koshiba, et al, “Observation of a Neutrino Burst from the Supernova SN1987A,” Physical Review Letters, Vol. 58, No. 14, 6 April 1987, pp.149-1493.Media:Observation of a Neutrino Burst from the Supernova SN1987A.pdf [8] Masatoshi Koshiba, “BIRTH OF NEUTRINO ASTROPHYSICS,” Nobel Lecture, December 8, 2002.Media:BIRTH OF NEUTRINO ASTROPHYSICS.pdf [9] T. Kajita, M. Koshiba, and A. Suzuki, “On the origin of the Kamiokande experiment and neutrino astrophysics,” The European Physical Journal H, Volume H 37, pp.33-73 (2012).Media:On the origin of the Kamiokande experiment and neutrino astrophsics.pdf [10] A. Suzuki and M. Mori, National Lab. High Energy, K. Kaneyuki and T. Tanimori, Dept. of Physics, Tokyo Institute of Technology, J. Takeuchi, H. Kyushima and Y. Ohashi, Hamamatsu Photonics KK., “Improvement of 20 in. diameter photomultiplier tubes,” Nuclea Instruments and Methods in Physics Research A329 (1993), pp.299-313.Media:Improvement of 20 in. diameter photomultiplier tubes.pdf

Supporting materials

Please refer to the above.


Loading map...