Cosmic-ray Research Division
Institute for Space–Earth Environmental Research, Nagoya University

Solar-Neutron Observations

Involving Research Members

Professor Yoshitaka ITOW
Associate Prof. Yutaka MATSUBARA
Designated Assoc. Prof. Kazutaka YAMAOKA
  1. Observation of Solar neutrons
  2. The purpose of the experiment
  3. A new project in progress-Observation of solar neutrons by using the very sensitive cosmic ray detector-

Observation of Solar neutrons

The group in which the Solar-Terrestrial Environment Laboratory plays the main role studys the acceleration mechanism of high energy particles by observing solar neutrons using seven solar neutron telescopes at various longitudes in the world. We are the only group in the world who observe solar neutrons by using specialized detectors.

Solar Neutron Experiment official web site

The purpose of the experiment

We study the acclereration mechanism of high energy particles associated with solar flares by detecting solar neutrons. These neutrons are produced at the solar surface by the interation between accelerated ions and the solar atmosphere. To study the particle acceleration mechanisms associated with solar flares, neutron measurements are preferable to charged particle (e.g., proton), as the neutron is not deflected by the interplanetary magnetic field (IMF). The precise moment a neutron is emitted is determined from the neutron energy. We developed seven solar neutron telescopes that measure the energy and direction of neutrons on mountains at various longitudes to detect solar neutrons over an entire day. The number of solar neutrons detected so far is about 10, and we need to accumulate more events in order to understand the acceleration mechanism of high energy particles. The Sun entered solar cycle 24 in 2008, and its activity is predicted to be maximum in 2013. We have observed the Sun continuously to detect more solar neutron events.

A new project in progress-Observation of solar neutrons by using the very sensitive cosmic ray detector-

Adding to the world-wide network of solar neutron telescopes promoted by STEL, we plan to install scintillator Bar (SciBar), which was used for the accelerator experiment at Fermi National Accelerator Laboratory (FNAL) in USA, on Sierra Negra, Mexico (97°W, 4600 m), as the new solar neutron telescope with the support of Kyoto University and KEK group, and the Universidad Nacional Autonoma de Mexico. The new detector uses 15,000 scintillator bars to measure the particle tracks. The new design will provide much higher energy resolution and better particle discrimination than the current solar neutron telescopes. This experiment is called as SciCRT (SciBar for the Cosmic Ray Telescope). In 2010, we installed a detector prototype on Sierra Negra and started to measure cosmic rays to obtain preliminary data necessary for the real experiment. We also shipped SciBar from FNAL to the Instituto Nacional de Astrofisica, Optica, y Electronica (INAOE) in Mexico, and it arrived in INAOE in April 2011. All the data taking electronics and computers were prepared in Nagoya, and sent to INAOE in March 2012. We start observing cosmic rays in INAOE and test the whole system. We hopefully start the observation of solar neutrons before the maximum of the activity of solar cycle 24 in 2013.