Download Alpha, Beta, and Gamma Radioactive Decay Given the nature of the

Alpha, Beta, and Gamma Radioactive Decay
Given the nature of the decay, these six forms of radioactive
decay can be grouped in three main categories:
 Decay that decreases the atomic number of the
radionuclide (a form of transmutation)
 Decay that increases the atomic number of the
radionuclide (a form of transmutation)
 Decay that does not affect the atomic number of the
radionuclide
Transmutation – radioactive decay that results in a change of
the radionuclide into an atom of another element. Any change
to the atomic number (the number of protons) is the evidence
that transmutation has occurred.
Decay that decreases the atomic number of the
radionuclide:
Alpha Decay
 A positively charged particle emitted from certain
radioactive nuclei that consists of two protons and two
neutrons (α)
 Is identical to a helium atom except that it has no
electrons.
 Most common in atoms possessing heavier nuclei.
 Alpha particles have low penetrating ability and cannot
damage or penetrate skin protected by clothing. They
are safe enough to be used in smoke detectors.
Pu →
240
236
U +
4
He2+
Positron Emission
 Only a few nuclei are susceptible to positron emission.
 If sufficient energy is present in the nucleus, a proton is
converted into a neutron and a positively charged
particle with the same mass of an electron and the same
magnitude of charge, the positron, is released from the
nucleus.
 The neutron remains in the nucleus and the positron
leaves the atom. Therefore, the product nuclei have the
same mass number, but a lower atomic number.
22
Na →
22
Ne + e+
Electron Capture
 Some nuclei can spontaneously capture one of
the elements electrons. These nuclei are the
same as those that undergo positron emission,
but without the energy to cause that form of
decay. When this occurs, the electron fuses with
a proton in the nucleus.
 The products of this reaction are an element with
a lower atomic number with the same mass
number and the emission of an extremely small,
electrically neutral particle called a neutrino that
travels very close to the speed of light.
Be + e- →
7
7
Li + neutrino
Decay that increases the atomic number of
the radionuclide:
Beta Decay
 A fast-moving electron that is formed when a neutron
breaks down into a proton and an electron (the beta
particle – β-)
 The proton remains in the nucleus and the electron (the
beta particle) leaves the atom Since the proton remains
in the nucleus, the number of protons has changed –
therefore the original element is no longer present and
a new element has been formed
 Mass number of the nucleus is unchanged
 Happens in nuclei of almost any size where the
instability is related to the number of neutrons
 Beta particles are much more penetrating than Alpha
particles; they can be stopped by a 2.2 mm aluminum
plate. They can burn skin severely but can cause only
minimal damage to internal organs.
228
Ra →
228
Ac + e-
Decay that produces no change in the atomic
number of the radionuclide:
Gamma emission (γ)
 Some unstable nuclei become more stable through the
release of energy in the form of electromagnetic (EM)
radiation (visible light is also part of the EM spectrum, but
at a much higher frequency and cannot be seen)
 Electromagnetic radiation released as gamma radiation has
such a high frequency that it can’t be stopped. It can only
slowed with lead walls
 The mass and composition of the nucleus are unchanged
 The element remains unchanged
 Usually accompanies other types of decay.
Neutron emission
 Some very large, very unstable radionuclides (and only a
few smaller ones) become more stable by a neutron leaving
the nucleus spontaneously.
 This only occurs when the energy inside the nucleus is such
that the release of this energy is so high that a neutron is
released instead of only gamma radiation.
 By emitting a neutron, the mass changes but the identity of
the element is unchanged.
Penetrating Power of and Cellular Damage from
Radiation
All radiation can produce cellular damage. The type of damage
and the amount of damage is dependent on the type of
radiation, the amount of radiation, and the type and amount of
shielding that is provided. The most dangerous form of
radiation is gamma radiation. The least dangerous is alpha
radiation.
 Gamma radiation cannot be stopped by shielding, but its
danger can be reduced by reducing the amount of energy as
it passes through a very dense material such as lead.
 Alpha radiation, if not shielded, can cause considerable
damage to skin as a direct result of its very large mass. But
alpha radiation is easily stopped by a sheet of paper
because of its large size.
 Beta radiation falls in between the other two. It has
considerably less mass but also has considerably more
energy. Tissue can be protected from beta radiation by tin
foil or plastic sheeting.
Medical Uses of Radiation
The most common form of using radiation for medical purposes
is the X-ray. In small enough dosage, this form of radiation can
be used to produce a kind of photo negative on film specifically
produced for this purpose. The X-rays penetrate the soft body
tissues and pass through unimpeded, but the X-rays cannot pass
through the much more dense bone tissue. This allows doctors
to diagnose and treat broken bones.
Certain forms of radiation can be targeted to kill cancerous
tissues and thereby allow cancer patients to live much longer
lives than would be otherwise possible. Other forms of
radiation can be used as tracers to ensure the proper functioning
of organs. Since the radiation can be detected outside of the
body the concentration of tracer radionuclides can be monitored
to diagnose gastro-intestinal problems, cancer, heart disease and
other abnormalities.