Milestone-Proposal:The 20 inch Diameter Photomultiplier Tubes
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Is the achievement you are proposing more than 25 years old? Yes
Is the achievement you are proposing within IEEE’s fields of interest? (e.g. “the theory and practice of electrical, electronics, communications and computer engineering, as well as computer science, the allied branches of engineering and the related arts and sciences” – from the IEEE Constitution) 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 Electrical Engineering Milestone? Yes
Year or range of years in which the achievement occurred:
1979 - 1987
Title of the proposed milestone:
The 20 inch Diameter Photomultiplier Tubes, 1987
Plaque citation summarizing the achievement and its significance:
The 20 inch Diameter Photomultiplier Tubes, 1979 – 1987
In 1979, Hamamatsu Photonics K.K. started developing 20 inch diameter photomultiplier tubes at the Toyooka Factory for the Cherenkov radiation detector Kamiokande II which was equipped with 948 tubes with gain of 107. It detected the neutrino burst in the Supernova SN1987A in 1987, and brought the Nobel Prize to Professor Masatoshi Koshiba in 2002 opening a new window of the Astrophysics.
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):
IEEE Organizational Unit(s) arranging the dedication ceremony:
IEEE section(s) monitoring the plaque(s):
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 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 (Iwata City is located next to Hamamatsu City.) 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)?
HAMAMATSU PHOTONICS K.K.
A letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property:
A letter or email from the appropriate Section Chair supporting the Milestone application:
What is the historical significance of the work (its technological, scientific, or social importance)?
(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]
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:
9.1. 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]
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]
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]
9.4. 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]
9.5. 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]
9.6. Mean transit time The mean transit time is found to be 90 ns. 
9.7. 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. 
9.8. 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]
References 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 citations to pages in scholarly books. At least one of the references must be from a scholarly book or journal article.
 Development of 20-inch PMT. http://www.hamamatsu.com/jp/en/technology/projects/20inch_pmt/index.html
 T. Hayashi, “RECENT DEVELOPMENTS IN PHOTOMULTIPLIERS FOR NUCLEAR RADIATION DETECTORS,” Nuclear Instruments and Methods 196 (1982), pp.181-186.
 “Photon is our business,” HAMAMATSU, Corporate Outline.
 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.
 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.
 HAMAMATSU TECHNICAL DATA SHEET, R1449, PHOTOMULTIPLIER TUBE, 20 INCH HEMISPHERICAL.
 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.
 Masatoshi Koshiba, “BIRTH OF NEUTRINO ASTROPHYSICS,” Nobel Lecture, December 8, 2002.
 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).
 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.
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