PHYS 252 TEST #5 DR. HOLMES 4/18/08 NAME
Do all nine problems. The worth of each problem is circled by the space for the answer. Show your work for partial credit.
Mass of Hydrogen atom (proton + electron) = 1.00782 amu;
mass of neutron = 1.008665 amu; mass of electron = .00055 amu;
rest mass energy of an amu = 931.5 MeV.
If you do not know the symbol of an element but only know its atomic number and mass number, then use X as the symbol of the element.
1) a) What is the total nuclear binding energy for Uranium-235 (92U235) which has an atomic mass of 235.0439 amu)?
1,783.5 MeV
b) What is the binding energy per nucleon?
7.589 Mev/amu
c) Is this binding energy per nucleon greater, the same, or less than that for lead-206 (82Pb206 has an atomic mass of 205.9745 amu)?
Less.
2) a) What is the activity of a sample of 1 gram of 53I131 given that its half life is 8.05 days?
in Bq: 4.58 x 1015 Bq. in Curies: 123,777 Ci
b) What will be the activity of the 1 gram sample of I131 (in Bq) after 1 year?
103 Bq.
3) Fill in the missing particle(s), given that there are no stable isotopes of Radon (Rn); there is 1 stable isotope of Cobalt (Co): 59; there are two stable isotopes of Carbon: (C): 12 and 13.
94Pu239 goes to + 92X235 + alpha + energy
53I131 goes
to 54X131
+ -1b +
anti- 0n 0
53I122 goes
to 52X131
+ +1b +
0n 0
6C14 goes to 7X14 + -1b + anti- 0n 0
4) C14 has a half life of 5730 years, and the ratio of C14 to C12 is 1.3 x 10-12.
a) What is the present activity of 2 grams of carbon taken from a modern "bone" ? Express your answer in two forms:
in dis/minute: 29.9 dis/min
and in Curies: 13.5 pCi
b) Assuming the ratio of C14 to C12 in the atmosphere has remained the same, what should the age of a bone be if 2 grams of carbon taken from the bone have an activity of 0.5 dis/minute ?
33,.819 years.
5) a) What are the three main mechanisms for x-ray absorption?
Photoelectric effect; Compton Scattering; Pair Production.
b) Which mechanism dominates at extremely high x-ray energies?
Pair Production.
which at very low x-ray energies?
Photoelectric Effect.
c) Can exposure to b -rays make atoms radioactive?
No.
d) Can exposure to g -rays make atoms radioactive?
No.
e) Can exposure to neutrons make atoms radioactive?
Yes.
f) If the answers to d, e, and f are ALL NO, THEN explain what can make atoms radioactive: (If any or all of the answers to d, e, and f are YES, then simply write N/A as the answer).
N/A.
6) a) Thorium decays until it reaches lead or bismuth. If you start with 90Th232, which of the following stable isotopes will you end up with: 82Pb206, 82Pb207, 82Pb208 or 83Bi209 ? (answer by specifying 206, 207, 208 or 209):
208.
b) How many alphas and how many betas will be emitted in the process of going from the 90Th232 down to the 82Pb20? or 83Bi209 ?
# of alphas: 6
# of betas: 4 .
7) a) Define the four measures of radioactivity and tell what each measures (absorbed dose, exposure dose, activity).
1) Roentgen:
2) Curie:
3) Rad:
4) Rem:
b) What is the average background radiation (in millirems/year) ?
200 mrem/year.
c) What acute dose of radiation will begin to cause some people to die of radiation sickness (in millirems) ?
200,000 mrem.
d) What is the linear hypothesis as applied to long-term dangers from radiation?
e) What is the idea of hormesis as applied to long-term dangers from radiation?
f) Which of the two (linear or hormesis) has been proven to be correct?0
g) Justify your answer to part f.
8) a) What is a moderator and why is it used in a fission reactor?
b) What are three characteristics of a good moderator?
(1)
(2)
(3)
c) Name two materials commonly used as moderators?
(1)
(2)
d) Can a nuclear reactor explode as a nuclear bomb?
No.
e) Explain your answer to part d above:
9. a) Given that the activity of air is 1 picoCurie per liter due to Radon gas, and given that the Radon (86Rn222 ) has a half life of 3.8 days, how much Radon is in the one liter of air:
in grams: 5.82 x 10-18 grams
in numbers of atoms: 15,800 .
b) Given that one mole of air occupies 24.5 liters, what is the fraction of air molecules that are Radon?
6.4 x 10-19 .
c) Is this fraction more than 1 part per billion, between 1 part per billion and 1 part per trillion, or less than 1 part per trillion?
Much less than 1 part in a trillion - about 1 part in a million trillion!