||The half-life of
plutonium-239 is 24 000 years. What fraction of a sample will remain
after 1 000 years?
||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?
||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?
||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.
||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
||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.
= 7.37 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?
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?
||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)
||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
||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.
||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:
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.
||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.
||Calculate the binding
energy in joules per nucleon of Uranium-235. The observed mass of one
atom is 235.0439 u.
||What is the alpha
activity in distintegrations per min for a 0.001 g sample of Ra-226?
(t1/2 = 1620 years)
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.
||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.
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.
||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?
||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?
||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)
e) C-11 (no/p+ ratio is too low)
a stable nuclide but Lanthanum-140 is unstable (t1/2 = 40 hr).
What "rule of thumb" concerning nuclear stability is involved?
||As the atomic number
increases, the ratio of neutrons to protons increases. What does this
fact suggest is a factor in nuclear stabiliy?
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
||The ratio of neutrons
to protons in atomic nuclei grows larger with increasing atomic number.
What is the explanation for this?