Chem 2/5 Laboratory 468 Radioactivity
FS97
Post Lab. Questions

1.(2pts) A radioactivity counter gives a reading of 350 cts per min for a 12.5 mg sample of Cobalt (II) Chloride partially enriched with Cobalt-60 (t1/2 = 5.26 yr.). What percentage of Cobalt atoms are Cobalt-60?

2.(2pts) A radioactive nuclide of mass number 94 has been prepared by neutron bombardment. If 4.71g of this nuclide register 20 counts per minute on a radioactivity counter, what is the half life of the nuclide?

3.(1pt) Given:

N = No(exp)-kt where N is the number of counts and t is time.

Find a simple expression for the half life.

4.(1pt) Write the appropriate nuclear equation for each of the following descriptions.

(1) K-40, a beta particle emitter, is a naturally occurring potassium isotope found in some foods.

(2) In Earth's upper atmosphere, energetic cosmic rays cause atmospheric gas atoms to emit neutrons. When one of these neutrons collides with a nitrogen - 14, a carbon - 14 atom and a proton, 1H result.

5.(1pt) What is the charge number, mass number and symbol for each of the following:

(a) an alpha particle

(b) a beta particle