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###### Nuclear physics half-life MCQ

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1 year ago

Hi Can anyone help with this question?

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

Reply 1

1 year ago

Original post by Terry Li

Hi Can anyone help with this question?

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

How many half-lives have each isotope undergone after 18 minutes?

Because you know how many nuclei of y there were at the start, you should be able to work out how many nuclei there are of y after 18 minutes.

Reply 2

1 year ago

Original post by Terry Li

Hi Can anyone help with this question?

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

X and Y are two radioactive nuclides. X has a half-life of 3.0 minutes and Y has a half-life of 9.0 minutes.

Two freshly prepared samples of X and Y start decaying at the same time. After 18 minutes the number of radioactive nuclei in both samples is the same. The sample of Y initially contained N radioactive nuclei.

What was the initial number of radioactive nuclei in the sample of X?

A 4N

B 16N

C 32N

D 64N

Another way of solving the question is as follows.

Do you know the exponential decay equation?

(number of remaining nuclei) N = N

where N

You can write the decay equations for X and Y respectively and then equate them to solve for the initial number of radioactive nuclei in the sample of X.

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