3. [1pt] A student (Lisa) measures the background radiation due to energetic par

Question

3. [1pt]
A student (Lisa) measures the background radiation due to energetic particles in
the Dunn laboratory with a Geiger counter. She samples the radiation rate by
recording the number of events in twelve, consecutive, one-minute intervals. Her
count record is as follows:

19, 17, 13, 19, 14, 14, 8, 15, 17, 19, 15, 17

What is the average background count rate (in cpm)?

Correct, computer gets: 15.6

4. [1pt]
What is the standard deviation of this count rate?

Correct, computer gets: 3.2

5. [1pt]
If the radiation events obey Poisson statistics, what should Lisa expect for the standard deviation if she counted for 1900 intervals?

Correct, computer gets: 3.9

6. [1pt]
If a source of gamma radiation is at hand that is known to have an average
activity of 64 cpm, alone, what should Lisa expect to measure
for the average count rate when measuring this source's activity in the
laboratory?

I just need help with question 6. Thank you!

Explanation / Answer

6. Average activity or count per minute Ns= 64 cpm,

If a geiger counter counts for some period T,

Total count NT= Ns+NB

Ns is the count due to source

NB is the background count

i.e. NT= 64 cpm+ 15.6 cpm = 79.6 cpm

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