Milestone-Proposal:The 20 inch Diameter Photomultiplier Tubes

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Docket #:2013-10

This Proposal has been approved, and is now a Milestone

To the proposer’s knowledge, is this achievement subject to litigation?

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:

1979 - 1987

Title of the proposed milestone:

20-inch Diameter Photomultiplier Tubes, 1979 - 1987

Plaque citation summarizing the achievement and its significance:

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.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?

IEEE Nagoya Section

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Nagoya Section
Senior Officer Name: Yukio Mizuno

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Nagoya Section
Senior Officer Name: Yukio Mizuno

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Nagoya Section
IEEE Section Chair name: Kenji Mase

Milestone proposer(s):

Proposer name: Atsushi Tsujimura
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

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

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The photomultiplier tubes were developed and manufactured at the Toyooka Factory, Hamamatsu Photonics, 314-5, Shimokanzo, Iwata City, Shizuoka Prefecture, Japan. Iwata City is in the area covered by the IEEE Nagoya Section. (Iwata City is located next to Hamamatsu City.)

Are the original buildings extant?


Details of the plaque mounting:

The plaque will be placed on a plinth of the grounds near the front entrance gate of the Toyooka Factory.

How is the site protected/secured, and in what ways is it accessible to the public?

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.

Who is the present owner of the site(s)?


What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

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]

What obstacles (technical, political, geographic) needed to be overcome?

Technical obstacle needed to be overcome:

(1) Forming the large area uniform-sensitivity photocathode on the inner surface of the view window of the tube. [1, 5]

(2) Direct immersion of the large photomultiplier tubes in the water of Cherenkov detector. [1, 5, 9]

(3) Glass blowing of the 20 inch diameter tube. [1, 4, 5]

What features 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]

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

[1] Development of 20-inch PMT.


[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


[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 (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to Please see the Milestone Program Guidelines for more information.

Please refer to the above.

Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).

Please recommend reviewers by emailing their names and email addresses to Please include the docket number and brief title of your proposal in the subject line of all emails.