In the mid-20ᵗʰ century, two units used in radiobiology to express quantities of fast neutrons. They were based on a particular device, the Victoreen R meter.
The n-unit was the quantity of fast neutrons that produced the same reading in a Victoreen R meter equipped with a 100-r chamber as 1 roentgen of x-rays would.
The N-unit was the quantity of fast neutrons that produced the same reading in a Victoreen R meter equipped with a 25-r chamber as 1 roentgen of x-rays would.
“Note: These are not actually proposed units, but have been employed as convenient interim methods of specifying neutron doses until satisfactory units and methods of measurement can be devised.”¹
1. National Research Council.
A Glossary of Terms in Nuclear Science and Technology.
New York: American Society of Mechanical Engineers, 1955.
For a picture and description of an R meter:
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Last revised: 2 August 2008.