Radioactivity

A freshly prepared sample contains 4.0 μg of iodine-131. After 24 days, 0.5 μg of iodine-131 remain. The best estimate of the half-life of iodine-131 is

• 8 days.

• 12 days.

• 24 days.

• 72 days.

The half-life of a radioactive isotope is 10 days. What is the percentage of the sample remaining after 25 days?

• 0 %

• 18 %

• 25 %

• 40 %

Two samples of radioactive substances X and Y have the same initial activity. The half-life of X is T and the half-life of Y is 3T. After a time of 3T the ratio

• 8

• 4

• 1/4

• 1/8

A radioactive substance S has a decay constant λS, substance T has a decay constant λT. Initially, a sample of S contains NS nuclei and a sample of T contains NT nuclei. The initial activity of both samples is the same. The ratio Ns/NT is

• A

• B

• C

• D

Which of the following correctly identifies the three particles emitted in the decay of the nucleus 4520Ca into a nucleus of 4521Sc?

• A

• B

• C

• D

A nucleus of the isotope potassium-40 decays to a nucleus of the isotope argon-40. The reaction equation for this decay may be written as

4019K---->40ZAr + X + v

Which of the following correctly identifies the proton number of argon-40 and the particle X?

• A

• B

• C

• D

The graph below shows the number of nuclei N of a radioactive isotope as a function of time t.

The slope of the curve at any given time is

• independent of the decay constant.

• proportional to the half-life of the isotope.

• proportional to the number of radioactive nuclei remaining at that time.

• proportional to the number of radioactive nuclei decayed.

A radioactive isotope has a half-life of two minutes. A sample contains sixteen grams of the isotope. How much time elapses until one gram of the isotope remains?

• 6 minutes

• 8 minutes

• 10 minutes

• 12 minutes

A sample contains an amount of radioactive material with a half-life of 3.5 days. After 2 weeks the fraction of the radioactive material remaining is

• 94 %.

• 25 %.

• 6 %.

• 0 %.

A radio-isotope has an activity of 400 Bq and a half-life of 8 days. After 32 days the activity of the sample is

• 200 Bq.

• 100 Bq.

• 50 Bq.

• 25 Bq.