Cs -137 has a half life of about 30 years. If 60 years pass, there is two half lives passed so 1/2 * 1/2= 1/4. Take 1/4 and multiply it with the mass given:
(1/4)*20mg=5mg left
Answer:
yes they are same thing by E=MC^2 EINSTEIN'S EQUATION
Psychical(you see the changes visible) and Chemical properties(they react and combine, you may see fizzing or bubbles).
