An approximate simple formula for the shielding effect of the cadmium jacket designed for the use of fast neutrons among reactor neutrons

If a pneumatic tube in an experimental hole of a reactor is covered with a cadmium jacket, a sample inserted in the pneumatic tube will be exposed to not only fast and epithermal neutrons but also the few thermal neutrons that will not have been obstructed by the jacket. To obtain a simple method of estimation for the flux of these thermal neutrons, a formula has been made. The ratio of change in thermal-neutron flux due to the setting of the jacket has been expressed as a function of 5 dimensionless numbers. The formula enables one to design a wellproportioned jacket. (author)