PHYS 202 TEST #5 DR. HOLMES 5/02/11 NAME
Do all the problems. The worth of each problem is marked beside the problem. Show your work for partial credit. If you do not know the name of an element but only know its atomic number and mass number, then use X as the name of the element.
1) a) Is there a minimum or a maximum photon wavelength from an x-ray machine?
Minimum
b) Is there a minimum or maximum x-ray photon energy from an x-ray machine?
Maximum
c) What is this (minimum or maximum) photon wavelength of the x-rays from an x-ray machine using 8,200 volts?
1.52 x 10-10 = .152 nm.
d) What is this (minimum or maximum) photon energy of the x-rays from an x-ray machine using 8,200 volts?
8,200 eV = 1.31 x 10-15 Joules
c) Is this wavelength much smaller than, about the same size as (within a factor of 100), or much larger than the size of an atom?
About the same.
d) If 24Cr is the target material and the above voltage is used, will characteristic radiation occur?
Yes.
g) If 30Zn is the target material and the above voltage is used, will characteristic radiation occur?
No.
2 a) Explain what happens in alpha decay:
b) Explain what happens in b - decay:
c) Explain what happens in b + decay:
d) Can a, b, and/or g radiations make atoms radioactive?
No.
e) If yes, which of these can; if no, what can?
Neutrons.
3) Fill in the missing particle(s):
92U233 goes to 90Th229 + alpha + energy
73Ta182 goes to 74W182
+ -1b
0 + anti-0n 0.
73Ta178 goes to 72Hf178 +
+1b 0 + 0n 0
53I131 goes to 54Xe131 + -1b 0 +anti-on o
(the one stable isotopes of Ta are 180 and 181; the one stable isotope of 53I is 127)
4) a) Given that the half life of 53I131 is 8 days, what is the decay constant for this isotope?
0.087/day = 1.0 x 10-6 /sec.
b) How many atoms of I131 are there in 1 gram?
4.58 x 1021 .
c) What is the activity of 1 gram of I131 ?
in dis/sec? 4.58 x 1015 Bq. In Curies ? 124,000 Ci.
d) What will be the activity of this one gram after 1 year (in dis/sec) ?
84.4 Bq.
5) 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 decay constant for C14 ?
1.21 x 10-4/year = 3.84 x 10-12 /sec.
b) How many atoms of C14 are there in 2 grams of carbon, assuming the ratio given above?
1.3 x 1011 .
c) What is the present activity of 2 grams of carbon taken from a modern "bone" (this assumes the present ratio of C14 to C12 ) ? Express your answer in two forms:
in dis/sec: 0.50 and in Curies: 13.5 pCi. = 1.35 x 10-11
Ci.
d) 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 0.22 counts/sec ?
6,787 years.
6) The half life of 53I131 is 8 days and the half life of 73Ta182 is 115 days.
a) If there is one gram of each, which (I131 or Ta182) will have the higher activity initially?
I131 .
b) Which will have the higher activity after 1 year?
Ta182 .
7) The radioactive isotope 92U235 is found in the ground.
a) Which stable isotope will it eventually decay into?
82Pb207 .
b) How many alphas will be emitted as it does decay to this stable isotope?
7.
c) How many betas will be emitted in this decay process?
4.
8) a) Define the four measures of radioactivity and tell what each measures (absorbed dose, exposure dose, activity).
1) Curie:
2) Roentgen:
3) Rad:
4) Rem:
b) What is the average background radiation (in millirems/year) ?
about 200 mrems/year.
c) What acute dose of radiation will begin to cause some people to die of radiation sickness (in millirems) ?
about 200,000 mrems.
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?
9) a) What is a chain reaction with respect to nuclear energy?
b) What is a moderator and why is it used in a nuclear reactor?
c) Name two materials that can be effectively used as a moderator in a nuclear reactor:
1.
2.
d) Can a nuclear reactor explode as a nuclear bomb?
NO
e) Explain your answer to part d above: