Neutron Monitor

The neutron monitor detects the hadronic component of cosmic particles. A world-wide network of almost 50 neutron monitors takes continuously data to register cosmic weather events like sun eruptions which are able to disturb or to destroy electronics system in satellites and even on Earth.

The North-West University of Potchefstroom in South Africa has built mini neutron monitors which are compared to the standard neutron monitors light and transportable. One of them was installed at the “Polarstern” research vessel, a second at the Neumayer III station in Antarctica (see photo).

The shell structure of the detector is shown in the schematic illustration. The outer shell (1) is a polyethylene moderator to reduce the energy of high energy neutrons and to absorb low energy neutrons of the background radiation. In shell (2) neutrons interact with the 5 cm lead layer and produce in average 8 new neutrons which hit with an energy of few MeV the following moderator shell (3). Most of the protons will be absorbed by the lead. The moderator (3) reduces the energy of neutrons which will be detected in the proportional counting tube (4) filled with gas ¹⁰BF₃. In the reaction:

n + ¹⁰BF₃ → α + ⁷Li        

The alpha-particles generate an electrical pulse in the tube which will be registered by the electronics box (5) and stored in a computer together with time, air pressure and temperature.
Since other particles than neutrons do not create a signal in the detector only nuclons will be detected.