The Princess Sirindhorn Neutron Monitor on Doi Inthanon, Thailand

The Princess Sirindhorn neutron monitor at Doi Inthanon is a multinational project organized by Mahidol University (Thailand), Chulalongkorn University (Thailand), Shinshu University (Japan), and University of Delaware (United States of America). The detector tubes and enclosing polyethylene and lead were donated by Iwate University (Japan) using materials from the retired Morioka neutron monitor. The official dedication of the monitor occurred on Doi Inthanon on January 2008, with Princess Sirindhorn in attendance.

Features of the Princess Sirindhorn neutron monitor:

  • highest geomagnetic cutoff in the world (about 17 GV)
  • second most sensitive detector of relativistic solar neutrons
  • in the "top 5" worldwide in terms of total cosmic ray count rate

Here is a map of Thailand showing the location of Doi Inthanon.

Detector Type: 20-tube NM64
Latitude: 18 35 11 North
Longitude: 98 29 17 East
Altitude: 2565 m
Official Dedication: January 2008

Moving Day. (Photo courtesy of K Munakata)

Some Cosmic Ray History: Morioka Neutron Monitor. Long-term cosmic ray observations at Morioka started in 1970 with IGY-type detectors. These were replaced with more sensitive NM64 detector tubes in 1977, which gradually increased in number until 1984 when 18 detector tubes began operation in the modern style1,2. Principal contributors to the Morioka neutron monitor project are Professors Toshimi Chiba, Hachirou Takahashi, and Naohiro Yahagi of Iwate University.

Upon his retirement Prof Chiba kindly arranged to transfer ownership of the Morioka equipment to Shinshu University. In September 2001 the monitor was disassembled and prepared for shipping by Prof Kazuoki Munakata of Shinshu University with assistance from Dr Hiromasa Miyasaka of the Institute of Physical and Chemical Research in Japan (RIKEN).

(1) T. Chiba, and H. Takahashi, "A search for the directional distribution of the cosmic ray intensity by means of super neutron monitors," Proceedings 18th International Cosmic Ray Conference, (Bangalore), Volume 10, pages 205-208, 1983.
(2) T. Chiba, H. Takahashi, and K. Nagashima, "Directional observation of the cosmic ray diurnal variation by neutron monitor," Proceedings International Symposium on Cosmic Ray Modulation in the Heliosphere (Morioka), pages 303-307, 1984.


Arrival at Chula. (Photo courtesy of D Ruffolo)
The Travels of a Neutron Monitor. The Morioka equipment shipped from Sendai port on 2001 October 22 and arrived in Bangkok November 10. After a sojourn with Thai customs, the equipment was moved to a temporary storage site at Chulalongkorn University on December 17.

Current Status: The former Morioka monitor currently resides at a Thai air force base atop Doi Inthanon, Thailand's highest mountain. It is fully operational.


Acknowledgments. K. Munakata supported in part by the joint research program of Solar-Terrestrial Environment Laboratory, Nagoya University. University of Delaware participation funded by the U.S. National Science Foundation.