A scintillation counter for gamma rays is to be used with a stated check source
PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Uncertainty in measurement · Designing and running experiments
Measurement and Method, Ch Running it: troubleshooting, the systematics hunt, safety and the record
Problem
A scintillation counter for gamma rays is to be used with a stated check source. The manufacturer's specification gives the background (no source present) counting rate as 0.15±0.05s−1. The calibration certificate for the check source states that, in the standard geometry used with this counter, it should give a rate of 45±2s−1.
((a)) Name the two entry tests this counter should be given before it is trusted with an unknown sample, and state what a reading would have to be, in each case, for the counter to pass.
((b)) The counter is then tested, counting for 100s each time: with the source in place it records 3100 counts, 31s−1; with the source removed it records 18 counts, 0.18s−1. Using the combined standard uncertainty of each observed rate and its expected value, state which test passes and which fails, and what the failing result suggests about where to begin troubleshooting.