FOLLOW US ON TWITTER
SHARE THIS PAGE ON FACEBOOK, TWITTER, WHATSAPP ... USING THE BUTTONS ON THE LEFT


YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Tuesday, May 5, 2020

A counter recording radioactive decays from a radioactive source gives the following counts in equal intervals of time.


Question 20
A counter recording radioactive decays from a radioactive source gives the following counts in equal intervals of time.

time / min        counts
0–10                424
10–20              395
20–30              413
30–40              363
40–50              366
50–60              294
60–70              301
70–80              253
80–90              212

What can be deduced from these readings?
A that radioactivity is random and that the half-life is 90 minutes
B that radioactivity is random and that the half-life is uncertain
C that radioactivity is spontaneous and that the half-life is 90 minutes
D that radioactivity is spontaneous and that the half-life is uncertain





Reference: Past Exam Paper – November 2010 Paper 12 Q40





Solution:
Answer: B.


The half-life is uncertain because of the randomness of the decay – random counts are obtained in equal intervals of time.

Half-life is the time for the count to be halved.


Consider the values 424 (at time 0-10 min) and 212 (at time 80-90 min). If we are considering the lower limit for the count of 424 (that is, we are considering the 0 min instead of the 10 min), the same should be done for the count of 212.

Thus, half-life = 80 – 0 = 80 min.


Similarly, if we consider the upper limit.
Half-life = 90 – 10 = 80 min

So, the tine interval between the 424 and 212 readings is 80 min, not 90 min.

No comments:

Post a Comment

If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation

Currently Viewing: Physics Reference | A counter recording radioactive decays from a radioactive source gives the following counts in equal intervals of time.