Vocabulary Notes
Radioactive:
Occurs when an atom's nucleus becomes unstable and the
atom spontaneously releases a particle and/or energy in order
to become more stable.
Radiation:
When a radioactive substance emits particles (aplha or beta)
and/or energy (Gamma).
Nuclear strong force:
The force that keeps the nucleons together in the nucleus BUT
it will weaken as the distance between the nucleons gets
bigger. Once the distance is too great the electrical repulsion
between the protons is the greater force into nucleus and the
nucleus becomes unstable (a.k.a. radioactive). Neutrons help
to counteract this instability by binding the nucleons together.
Hence the more protons are in a nucleus (electrical repulsion)
the more neutrons there needs to be to counteracts this
(strong force)
Transmutations
Transmutation:
Vocabulary Notes
When an element's atoms have a change in the # of pt in the
nucleus, and the element becomes a different element. Occurs
because of either alpha or beta decay.
Natural Transmutations:
Alpha Decay:
When the alpha particle (42He) is release from the nucleus, because two
protons are released, this will change or transmutate the element itself into
a completely different element. Fro example, Uranium-238 was
transmutated into Thorium-234. Notice the mass number has changed
also by four because two protons and two neutrons were released.
Beta Decay:
0
When the beta particle (-1e) is release from the nucleus, because a neutron
was broken down and a proton and an electron were created, the proton
will stay in the nucleus, but the electron is released from the nucleus. This
will increase the atomic number by one, but there is no overall change to
the mass number because overall one nucleon was replaced another
nucleon. For example, when Thorium-234 releases a beta particle it
transmutates into Protactinium-234. Notice the mass numbers are the
same but the element is different.
Artificial Transmutations:
Artificially, or in a lab setting, transmutations can be forced to occur. By
using a radioactive source, an alpha or beta particle can be force to interact
with a non-radioactive element and force the element to be changed. For
example, when the alpha particle collides with the nucleus of the nitrogen
atom, two neutrons and one of the protons that make up the alpha particle
stay in the nucleus, while one proton is released. Thus, leaving in an
oxygen and a hydrogen behind, instead of nitrogen.
Ernest Rutherford was the first to succeed in artificially transmutating an
element. Many other elements have been artificially transmutated. In
fact, all the elements beyond Uranium were produced by this process, so
we call them transuranic elements.
Radioactive Particles
Radioactive
Particle/Ray
Symbol
Alpha Particle
4
2
Beta Particle
0
-1
Gamma Ray
0
0
Charge
Is stopped Affects on nucleus when
by
released
He
+
Thick Paper
Atomic # ↓ 2
Atomic mass ↓ 4
e
-
Aluminum
Atomic # ↑ 1
Atomic mass = no change
0
Lead
No change
Radioactive Half-life
The amount of time it takes for half of a
radioactive substance to decay. For
example, it takes 1620 years for a 1 kg
sample of radium to decay to half that or
1/2 kg.
Amount remaining = (initial amount)(1/2)n,
where n = number of half-lives
Radioactive Uses
Carbon Dating:
When cosmic rays from the universe collide
with the Earth's uper atomosphere many
elements in the atmosphere are
transmutated, in particular the nitrogen gas
in the atmosphere. The nitrogen gas
changes to an isotope of carbon (carbon-14
or C-14). Plants take in the carbon-14, then
the plants are consumed by animals so they,
too, have C-14 into their bodies. Once the
plant or animal dies it no longer takes in
addition C-14, so scientist can compared the
ratio of C-14 to C-12, to see how long that
plant or animal died because C-14 decays at
a constant and specific rate (half-life).
Uranium Dating:
When dating very old objects or materials that did not come from
a living/organic source, scientist often use uranium dating to
determine their age. Uranium-235 and uranium-238 decay slowly
into lead-207 and lead-206, respectively. The higher the
percentage of lead in the material means it has had a longer
amount of time for the uranium to decay into lead.
Radioactive Tracer:
A radioactive isotope that we use to follow the
path of a substance and can be measured with
radiation detectors called Geiger counters.