3. 22. 19. 40 K decays by positron emission to give 40 Ar
K decays by positron emission to give 40 Ar. If yellow spheres represent 40 K atoms and blue spheres represent 40 Ar atoms, how many half-lives have passed in the following sample? 19 18 19 18

4. 22.20 Write the symbol of the isotope represented by the following drawing. Blue spheres represent neutrons, and red spheres represent protons. Do you expect this nuclide to decay by positron emission or emission? Explain.

5. 22.21 Identify the isotopes involved, and tell the type of decay process occurring in the following nuclear reaction:

6. 22.22 Isotope A decays to isotope E through the series of steps shown in the graph. The series has two kinds of processes: one represented by the shorter arrows pointing right and the other represented by the longer arrows pointing left.
(a)
What kind of nuclear decay process does each kind of arrow correspond to?
Identify and write the symbol for each isotope in the decay series:
(b)

7. 22.23 What is the half-life of the radionuclide that shows the following decay curve?