4. “I can’t be hurt by something I can’t see or feel.”
Too much radiation can indeed be harmful. Just because
it isn’t visible doesn’t mean it isn’t real.
5. “All uranium can be used as nuclear fuel.”
Only the 235U isotope of uranium is fissionable; most uranium
ore (>90%) is 238U, which is not fissionable.
6. “The number of counts from a Geiger counter is equal to the number
of nuclei that decay.”
The Geiger counter detects and records only a small fraction of particles
emitted from decaying nuclei. Some reasons for this inability to count
all
disintegrations are:
a. Window thickness of the Geiger tube. Not all particles will
penetrate the
tube.
b. Geiger tube dead time. While the tube is busy reacting to
a particle, other
particles go undetected.
c. Counter geometry. Radioisotopes emit radiation in all directions
(4-p
geometry). A typical Geiger tube can only monitor a small fraction or
small angle of all the radiation direction angles.
A typical counter only counts the relative number of disintegrations.
Pattern Recognition/Problem Solving
1. To balance nuclear equations, conservation of both mass number
and
charge on the nucleus must be achieved. Mass number (A) is the sum
of the
numbers of protons and neutrons in the nucleus. It is also the approximate
mass of a particle or isotope to the nearest whole atomic mass unit, u.
Charge is the positive or negative whole units of electrical charge.
One unit
equals 1.60 x 10 –19 C (coulombs).
2. Nuclear Symbols. — AZ X
A = mass number, and Z = positive charge on nucleus or
A = sum of the protons and neutrons, and Z = number of protons
e.g., for 23892U 238 = mass number, and
92 = charge on nucleus or
238 = protons + neutrons, and 92 = protons
other:
proton: 11H
electron: 0–1e
neutron: 10n
alpha (a) particle: 42He beta (b or b – ) particle: 0–1e positron (b + ): 0+1e
3. Balancing Nuclear Equations. — In a nuclear equation charge and
mass
must be conserved.
Examples:
a. Alpha radiation ( 42He emitted from nucleus)
23892U => 42He + AZX
238= (4 + A)
A must be 234 (conservation of mass number)
92 = (2 + Z)
Z must be 90 (conservation of charge)
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