BRL Radiac Slide Rule

The Radiac Slide Rule below was designed  by B. W. Soole at the Admiralty Research Laboratory in  England in the early 1950s.  Its purpose is to allow a user to calculate radiation exposure levels at selected times after a nuclear explosion.Radiation decays according to the 7/10 rule.  Seven hours after an explosion, the radiation is 1/10 the original level. After seven times seven hours (49 hours, or two days) it is 1/10 of that, or 1/100 the original. After seven times two days it is 1/1000 the original intensity.

The source data for the rule appears to have been taken from the the Radiation Dosage Calculator  developed  in 1950/51 by  Orr  for the Connecticut State Office of Civil Defense. The data in Orr’s calculator was used by several radiac calculator designers.

The rule is heavy duty plastic and 12 inch long by 2.5 inch wide. It was made by Blundell Rules Limited (BRL) of Luton and Weymouth, England. BRL later produced two circular radiac calculators; Radiac Calculators 1 & 2. These will be the subject of a later post. Check this site for information on BRL and their slide rules.

The two slides are reversible. Scales A and C should be used for contamination produced by explosions over land. Scales E and F should be used for contamination produced by radioactive sea water.

Set to compute contamination produced by radioactive sea water

Set to compute radioactive contamination produced by an explosion over land

A note on the radiac slide rule.

For more posts about Cold War calculators click on the Cold War Calculators category on the right.

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