Introduction to SAT II Physics - FreeExamPapers

number of the carbon is equal to the sum of the atomic number of the nitrogen and the
electron: 6 = 7 – 1. Because the neutrino has no charge and negligible mass, its presence
has no effect on any aspect of beta decay that we will study. Still, it’s important that you
know the neutrino’s there.
Gamma Decay
Gamma decay is the most straightforward kind of decay. An element in a high-energy
state can return to a lower energy state by emitting a gamma ray, , which is an
electromagnetic photon of very high frequency. No other particles are ejected and the
nucleus doesn’t transform from one element to another. All we get is an ejected gamma
ray, as in this example with technetium:
EXAMPLE
The reaction schematized above is an example of what form of radioactive decay? What are
the values for A, Z, and X?
WHAT FORM OF RADIOACTIVE DECAY?
In the above reaction, a sodium nucleus transforms into some other element and gives off
an electron. Electrons are only released in beta decay. A neutrino is also released but,
because its effects are negligible, it is often left out of the equation.
WHAT ARE THE VALUES FOR A, Z, AND X?
We can calculate A and Z because the sum of the atomic numbers and the mass numbers
on the right must add up to the atomic number and the mass number on the left. We can
solve for A and Z with the following equations:
So A = 24 and Z = 12. The resulting element is determined by the atomic number, Z.
Consult a periodic table, and you will find that the element with an atomic number of 12
is magnesium, so X stands in for the chemical symbol for magnesium, Mg.
Binding Energy
Atomic nuclei undergo radioactive decay so as to go from a state of high energy to a state
of low energy. Imagine standing on your hands while balancing a box on your feet. It
takes a lot of energy, not to mention balance, to hold yourself in this position. Just as you
may spontaneously decide to let the box drop to the floor and come out of your
handstand, atomic nuclei in high-energy states may spontaneously rearrange themselves
to arrive at more stable low-energy states.
Nuclear Forces
So far, all the physical interactions we have looked at in this book result from either the
gravitational force or the electromagnetic force. Even the collisions we studied in the
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