Please show all work and reasoning 1) Suppose you measure the background radiati

Question

Please show all work and reasoning

1) Suppose you measure the background radiation and obtain 100 counts in a time of 10 minutes. You then put a source under your detector and obtain 100 counts in a time of 1 minute. The corrected counts for your one-minute source measurement is

a) 90 counts

b) 0 (the source is dead)

c) 99 counts

2) Which of the following statements best describes the time dependence of the activity of a source?

a) The activity decreases exponentially with time. That is, the activity decreases by the same factor in equal time intervals

b) The activity is constant, independent of time

c) The activity decreases linearly with time

3) The background radiation in a lab is measured using a G-M counter and found to be 20 Bq. A small sample of a short-lived radioactive isotope is prepared in the lab, and the same G-M counter is used to measure the activity when the source is placed under the G-M counter. The raw activity versus elapsed time data obtained from the G-M counter is:

80 Bq at t = 0
62 Bq at t = 1 minute
50 Bq at t = 2 minutes
41 Bq at t = 3 minutes
35 Bq at t = 4 minutes
31 Bq at t = 5 minutes

What is the half-life of the radioactive isotope?

a) 2 minutus

b) 4 minutes

c) 3 minutes

Explanation / Answer

1 a) is correct. (100-100/10=90)

2)a) The activity decreases exponentially with time. That is, the activity decreases by the same factor in equal time intervals. Radioactivity is a first order reaction.

3) We get 60 Bq to 30 Bq in 2 min. (subtract 20 Bq of background radiation from all readings)

2 min is the half life, then.

a) is correct.

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