to measure the activity of a rock thought to be radioactive, a physicist puts th

Question

to measure the activity of a rock thought to be radioactive, a physicist puts the rock beside a detector and counts 225 particles in 10minutes. To chck for background, she removes the rock and hen records 90 particles in 6 minutes. She converts both answers into rates, in particle per hour, and takes their differences to give the activity of the rock alone.
What is he final answer, in particles per hour, and what uncertainty?
Does she have significant evidence that the rock is radioactive?

( do we need to use subtracting a backdground equation?)

Explanation / Answer

A physics put a rock beide the detector

                The detector counts 225 particles in 10 minutes

                    per 1 minute   the detector count 22.5 counts

                  per 1 hour the detector coounts   1350 couts

she removes the rock

                 The detector count   90 particles in 6 minutes

                  per 1 hour   the detector couns 900 counts

           The activity of the roc k

                      = 1350 - 900   = 450 particles/ per hour

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