Suppose that you start with 3.65 g of a pure radioactive substance and determine 19.6 h later that only 0.228125 g of the substance is left undecayed. What is the half-life of this substance? Answer in units of h.

Determine the half-life (in s) of a radioactive sample that has a decay rate of 3.30 ✕ 1011 Bq when it contains 1.70 ✕ 1015 nuclei.  s

The two samples A and B consist of an equal number of radioactive nuclei to begin with. 5 days later there are 5 times as many A as there are B nuclei. The half-life of B is 2 days. Find the half-life of A nuclei.

A radioactive sample is prepared; 10.78 hours later, only 1/16th of the original sample remains. What is the half-life of this radioactive sample in hours? Round to one decimal place.

A radioactive isotope has a half-life of 72.0 min. A sample is prepared that has an initial activity of 1.60×1011 Bq A) How many radioactive nuclei are initially present in the sample? B) How many are present after 72.0 min? C) What is the activity after 72.0 min? Express your answer in becquerel. D) How many are present after 144 min? E) What is the activity after 144 min? Express your answer in becquerel.

A radioactive sample has a decay constant of 0.219 3/minute. (a) What is its half-life? (b) If at the start of an experiment ,there are 3.2×10¹⁵ nuclei present ,how much Will remain after 1 he?

A radioactive sample studied in a lab is found to have a half-life of 25 hours. If the initial sample contained 7.5x10¹⁰ radioactive nuclides estimate the number of radioactive nuclides present in the sample after 10 hours.

2. Given the vectors à = i - j+ k and b = 2i - j- 2k, determine the following: a. the scalar projection and vector projection of å on b b. the angle that b makes with each of the coordinate axes c. the area of the parallelogram formed by the vectors a and b

The half-life for the a decay of uranium 2U is 4.47 x 10° yr. Determine the age (in years) of a rock specimen that contains 48.6% of its original number of U atoms. t-Number i Units

After 1.86 days, the activity of a sample of an unknown type of radioactive material has decreased to 88.2% of the initial activity. What is the half-life of this material?