Nuclear Review
1.
The half-life of plutonium-239 is 24 000 years.  What fraction of a sample will remain after 1 000 years?

2.
The isotope 23190Th has a half-life of 25 hours.  If you begin with a sample of 1.0 kilograms, how much  of the original sample matieral is left after 100 hours?

3.
An element has a half-life of 20 minutes.  How much of an original substance of 500 grams would be left after 1.0 hour?

4.
An isotope of 20781Tl, has a half-life of 4.8 minutes.  Calculate the amount of original material that would be left after the following times if we begin with 4000 grams.

5.
Calculate the mass in kilograms of a 1.00 kg object when its velocity, relative to us is
a)  3.00 X 107 m/s
b)  2.90 X 108 m/s
c)  2.99 X 108 m/s

6.
Calculate the quantity of mass in nanograms that is charged into energy when one mole of liquid water forms by the combustion of hydrogen, all measurements being made at 1 atm and 25oC.

7.
Americium-243 (t1/2 = 7.37 X 103 years) is one radionuclide in radioactive waste.  If such wate is to be kept out of reach of people and their food and water for a period of 20.0 half-lives, how many years of safekeeping are involved for this isotope?  What will be the activity (in Bq/g) of this isotope after this period if the initial acticity is 120 Bq/g?

8.
Potassium-40, which has a half-life of 1.3 X 109 years, decays by electron capture to argon-40, a stable isotope.  If this decay occurs in dense rocks, the argon cannot escape.  A 500 mg sample of such rock was analysed and found to have 2.45 X 10-6 mole of argon-40 and 2.45 X 10-6 mol of potassium-40.  How old is the rock and what assumptions must be made for this to be true?

9.
Crate Lake in southern Oregon formed after the volcanic cone of ancient Mount Mazama collapsed.  During long periods of volcanic activity, pumice blown out during one eruption covered thousans of square miles, burying extensive forests.  A sample of buried wood with a mass of 152 mg was found to have an activity of 61.2 Bq.  Calculate the age of this specimen. (The activity for current C-14 is 918 Bq/g)  (T1/2 for C-14 is 5730 y)
 
10.
At 1.5 m from a small radioactive source the radiation intensity was 40 units.  If the operator moves to a distance 4.5 m from the source, what will be the radiation intensity?

11.
In the late 1940's,  a number of manuscripts were found in caves near the northwestern corner of the Dead Sea region of the Middle East.  They became known as the Dead Sea scrolls.  When one parchment scroll was analzyed by the carbon-14 dating method, its specific activity was found to be 708 Bq/g.  Calculate the age of this scroll.  The activity of C-14 normally is 918 Bq/g and the C-14 half-life is 5730 y.

12.
One mole of a radioactive isotope of Rn emits all its particles into a catcher "foil."  If the particles are charged, in effect a battery will be formed with a voltage between the catcher adn the remaining residual nuclei. (Such batteries, atomic batteries, are used in space applications.)  What will be the sign of the charge on the "catcher" if the particles are:
a) alpha
b) beta
c) gamma

13.
Articles found in the Lascaux Caves in France have a C-14 disintegration rate of 0.04 Bq/g of C.  How old are these articles?   The normal activity of C-14 is 918 Bq/g and the half-life of C-14 is 5730 y.

14.
When an electron and positron encounter each other, they are annihilated and two photons of equal energy are formed.  Calculate the wavelength of these photons.  This would be an matter-antimatter reaction.

15.
Calculate the binding energy in joules per nucleon of Uranium-235.  The observed mass of one atom is 235.0439 u.

16.
What is the alpha activity in distintegrations per min for a 0.001 g sample of Ra-226?  (t1/2 = 1620 years)

17.
Cesium-137, is one of the radioactive wastes from a nuclear power plant or an atomic bomb explosion.  It emits beta and gamma radiation.  Write the nuclear eqaution for the decay of Cs-137.

18.
Marie Curie (1867-1934) earned one of her Nobel prizes for isolating the element radium, which soon became widely used to treat cancer.  Radium-226, is an alpha and gamma emitter.  Write a balanced nuclear equation for the decay of Ra-226.

19.
Strontium-90 is one of the many radionuclides present in the radioactive wastes of an operating  nuclear power plant.  Strontium-90 is a beta emitter.  Write the balanced nuclear equation for its decay.

20.
The hlaf-life of Th-234 is about 24.5 days.  Consequently whatever quantities of this isotope that were originally present on the Earth have long since decayed into other elements. Yet several metric tons of Th-234 exist in the Earth's crust today.  How can this be so?

21.
Persons who have been exposed toa  heavy dose of radiation often develop lesions and other disorders of the body that are particularly unpleasant in appearance.  If you were near such a person, could you "catch" the radiation poisoning disease from them and get their symptons.  Why or why not?

22.
Predict the kinds of decay you might expect for the following radioactive nuclides
a)  Co-60  (no/p+ ratio is too high)
b)  Na-11  (no/p+ ratio is too low)
c)  Ra-224
d)  U-238
e)  C-11  (no/p+ ratio is too low)

23.
Lanthanum-139 is a stable nuclide but Lanthanum-140 is unstable (t1/2 = 40 hr).  What  "rule of thumb" concerning nuclear stability is involved?

24.
As the atomic number increases, the ratio of neutrons to protons increases.  What does this fact suggest is a factor in nuclear stabiliy?

25.
Although lead-164 has two magic numberts, 82 protons and 82 neutrons, it is unknown, whereas lead-208 is known and stable.  What accounts for the fact that lead-164 cannot exist?

26.
The ratio of neutrons to protons in atomic nuclei grows larger with increasing atomic number.  What is the explanation for this?