Ch24_2
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1) You start out with radioactive nuclei. After minute are left over. What is the average activity (
sheet 22
) ?
2) A sample of radioactive nuclei with a decay constant of
hour
-1
has an activity of decays per
second
. How many radioactive nuclei does the sample contain (
sheet 22
) ? Indicate with a positive (negative) sign whether the number of radioactive nuclei increases (decreases) with time.
3) The decay constant of radioactive C
14
nuclei is 3.83x10
-12
s
-1
. After how many
years
has their number decreased by (is their number divided by) a factor of (
sheet 23
) ?
4) The half life of radioactive C
14
nuclei is 5730
years
. If the activity of a sample today is decays per
day
, what was its activity thousand
years
ago (in decays per
day
) (
sheet 23,23'
) ? Indicate with a negative (positive) sign whether the number of radioactive nuclei as a function of time obeys the same (a different) exponential decay law as the activity as a function of time.
5) A proton is at a distance of x10
-14
m
from the center of a nucleus which contains protons. What is the electrical potential energy of the proton (
sheet 31
) ? Indicate with a positive (negative) sign whether the potential energy increases (decreases) with decreasing distance.
6) An alpha particle (a He
++
ion) is launched toward a gold nucleus (79 protons) and comes to rest at a distance of x10
-14
m
from the center of the nucleus. What is its kinetic energy in
MeV
(
sheet 31,32
)? Indicate with a negative (positive) sign whether the result would be the same (different) for an incoming particle with the same charge but twice the mass of the alpha particle.
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