Download Ch. 21.1 Nuclear Radiation

Changes in Matter
• Matter can undergo three types of changes.
– Physical Change – change in appearance but not
identity.
– Chemical Change – production of new substances
with different properties – same elements just
rearranged – usually involves valence electrons.
– Nuclear Change – form different element from what
you started.
• Nuclear changes involve changes in
the nucleus of an atom.
Radioactivity
• Radioactivity – spontaneous emission of rays or
particles from certain elements. (like uranium)
– also known as radioactive decay
– rays and particles emitted from a radioactive source are
called nuclear radiation
• Radioactivity is an example of a nuclear reaction.
– Purpose of radioactive decay is for an unstable nucleus to
become stable.
– Nuclear reactions begin with unstable isotopes
known as radioisotopes.
– Atoms become stable when changes occur
in the nuclei.
– These changes are always accompanied by the
emission of large amounts of energy.
– Unlike chemical reactions, nuclear reactions are
not affected by changes in temperature, pressure,
or the presence of catalysts.
– Nuclear reactions of given radioisotope cannot be
slowed down, speeded up, or stopped.
– Radioactive decay is a spontaneous process.
– If the product of a nuclear reaction is unstable, it
will decay again.
– The process continues until unstable isotopes of one
element are changed, or transformed, into stable
isotopes of a different element.
– These stable isotopes are not radioactive.
– Nuclear radiation is emitted during radioactive decay.
– There are three main types of nuclear radiation:
alpha radiation, beta radiation, and gamma radiation.
Types of Radiation
Alpha Radiation
– An alpha particle (α) is two protons and two
neutrons bound together and is emitted from the
nucleus during some kinds of radioactive decay.
(also referred to a as a helium nucleus)
– Alpha particles have a positive charge
– In nuclear equations, an alpha particle is written as
– Example:
• When an atom loses an alpha particle, the atomic
number of the product is lowered by two and the mass
number decreases by four.
• In balanced nuclear equations, the sum of the mass
numbers on the right must equal the sum on the left.
• This is also true for the atomic numbers.
• Alpha particles are the least penetrating type of
radiation .
– Sheet of paper or the surface of your skin can stop them.
Beta Radiation
– A beta particle (β) is an electron emitted from the
nucleus during some kinds of radioactive decay.
– A beta particle is formed when a neutron breaks
apart into a proton and an electron.
– The proton remains in the nucleus while the electron
is ejected.
– The -1 refers to the charge of the electron and the 0
refers to the mass. (essentially zero)
– Example:
• When an atom loses a beta particle, the atomic
number of the product is increased by one; however,
the mass number remains the same.
• Since a beta particle has less charge and much less
mass than an alpha particle, beta particles are more
penetrating than alpha particles.
– Beta particles can pass through paper but are
stopped by aluminum foil or thin pieces of wood.
Gamma Radiation
– Gamma rays () are high-energy waves emitted
from a nucleus as it decays.
– Gamma rays have no mass and no electrical
charge. Therefore, gamma radiation does not
alter the atomic number or mass number of an
atom.
– Nuclei often emit gamma rays along with alpha or
beta particles.
• Gamma rays are the most penetrating type of
nuclear radiation.
• Easily pass through paper, wood, and human body
(extremely dangerous).
• They can be stopped, although not completely, by
several meters of concrete or several centimeters of
lead.
Nuclear Equations and Radioactive Decay
• Radium-226 is a radioactive isotope that decays by
releasing an alpha particle. Write a nuclear equation
for the radioactive decay of radium-226.
• Potassium-40 decays by releasing a beta particle.
Write a nuclear equation that represents the
radioactive decay of potassium-40.
Balancing Nuclear Equations
Nuclear Equations Sample Problems
1. Identify the product that balances the following
nuclear reaction:
2. Radium-226 is a radioactive isotope that decays by
releasing an alpha particle. Write a nuclear
equation for the radioactive decay of radium-226.
3. Potassium-40 decays by releasing a beta particle.
Write a nuclear equation that represents
the radioactive decay of potassium-40.
Reflection
• Fill in the following table on your page.