Transcript Nuclear Decay

Nuclear Decay
Radioactivity
• The emission of high-energy radiation or
particles from the nucleus of a radioactive
atom.
3 Types of Radiation
• Alpha Radiation
• Beta Radiation
• Gamma Radiation
Alpha Radiation
• Radiation in the form of alpha particles
• What are alpha particles?
– Particles that consist of 2 protons and 2
neutrons with an atomic mass of 4
• Alpha particles have an atomic mass of 4
and an atomic number of 2
– Why an atomic number of 2?
Problems with Alpha Particles
• Alpha particles can burn your skin
however they can also be stopped by a
piece of paper
Beta Radiation
• Radiation given off as beta particles
– What are beta particles?
• Particles consisting of:
– An electron emitted from a decaying neutron in
the nucleus
– Does not have an atomic mass
– Atomic number of -1
Problems with Beta Particles
• 100 time greater penetrating ability than
alpha particles
– Can penetrate through 3 mm of aluminum
Gamma Rays
• Electromagnetic wave (study this more
when we cover physics)
• Carry a lot of energy
• Atomic Mass of 0
• No atomic number
Problems With Gamma Rays
• Carry a lot of energy
• Most penetrating of the three types of
radiation
– Pass through several cm of lead
Radioactive Decay
• Are radioactive elements stable?
No
• Radioactive Decay is the process by which
atomic nuclei emit particles or rays to
become lighter and more stable
– 3 types of decay
• Alpha Decay
• Beta Decay
• Gamma Decay
Alpha Decay
• Step 1. A nucleus releases an alpha
particle (2 neutrons and 2 protons)
decreasing the mass number of the
nucleus
• What does that mean?
– The original atom is no longer the same
– The atomic number is decreased by 2
• Why?
– Because the atomic number is based on the #
of protons, and now the # of protons is
different by 2
Alpha Decay
Beta Decay
• A neutron inside a nucleus spontaneously
decays producing a proton and electron
• A beta particle in the form of an electron is
released from the nucleus
• Because a proton is produced, so is a new
atom. The atomic number of the original
atom is increased by one
• However the mass number does not change
– Carbon 14 (6 protons and 8 neutrons)
– Nitrogen 14 (7 protons and 7 neutrons)
Beta Decay
Gamma Decay
• When gamma rays are emitted by a
nucleus the nucleus does not change into
a different nucleus
• However, since the gamma ray is an
extremely high-energy wave the nucleus
makes a transition to a lower energy state
Gamma Decay
Half-Life
• What is a half-life?
– The fixed rate of decay of a radioactive
element in which the element will decay into
another element.
– The half life of carbon 14 is 5730 years
• In 5730 years the isotope has decayed by 50%
– Left with 50% C-14 and 50% N-14
• In another 5730 years the isotope has decayed
by another 50%
– From 50% to 25%
» Left with 25% C-14 and 75% N-14