Large Chalk River BF3 Proportional Counter (ca. 1960)



This rather substantial  neutron detector came from the Deep River Neutron Monitoring Station where it was used in cosmic ray investigations. It is 183 cm long, 14.5 cm in diameter, copper walled and filled with BF3. The construction of the tube is described in the Chalk River publications  1961 Solar Geophysical Data, Part B, CRPL-F-204 and 205 by Steljes, J.F. and Carmichael, H.  In use, it would have been encased in paraffin to moderate the fast neutron component of the cosmic rays.

This is the predecessor to what became known as the NM-64 (or IQSY) detector. NM-64 refers to "neutron monitor 1964."  The year 1964 was designated by cosmic ray investigators as the international quiet year of the sun, hence IQSY. The NM-64 detector was designed by Hugh Carmichael at Chalk River Laboratories and they became the worldwide standard neutron detector  for cosmic ray studies. 

The modifications were as follows.

1. The NM-64 counter was surrounded with polyethylene instead of paraffin wax.

2. The heavy copper tubing that served as the cathode in this older design was replaced by thin stainless steel in the NM-64.

3 The NM-64 was 10% longer.




Donated by Chalk River Laboratories

The specifications for the NM-64 are as follows:

      Counter material: Stainless Steel

      Active length: 191 cm

      Internal diameter: 14.5 cm

      Gas: BF3, 96% 10B

      Pressure: (0 degrees C) 18.5 mm

      Active Volume: liters 33

      Volume BF3: liters 8.04

Thanks go to George Ewan and Cliff Hargrove for their assistance in identifying this detector. 

Proportional Counters                   Museum Directory

Last updated: 05/10/11
Copyright 1999, Oak Ridge Associated Universities