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RadioactivityNuclear Chemistry
RadiationRadiation: The process of emitting energy in the form of waves or particles.
Where does radiation come from?Radiation is generally produced when particles interact or decay.
A large contribution of the radiationon earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial).
Radiation is going through you atthis very moment!
• Nucleons – particles found in the nucleus of an atom ex. Neutrons and Protons
• Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus
• Isotopes – atoms with identical atomic numbers but different mass numbers
Review Atomic Terms
XA
Z
Mass number
Atomic number
Element symbol
= number of protons + number of neutrons
= number of protons
Number of neutrons = Mass Number – Atomic Number
Writing Isotopes
Writing IsotopesAn isotope is an atom with a different number of neutrons:
Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.
Notice that the mass number is different. How many neutrons does each isotope have?
• Most of the isotopes which occur naturally are stable.
• A few naturally occurring isotopes and all of the man-made isotopes are unstable.
• Radioactive Decay– the spontaneous decomposition of a nucleus – Unstable isotopes can become stable by releasing
different types of particles.
• Radioactive - a substance that is capable of ALWAYS emitting radiation under any conditions
• Radioisotope - simply an isotope that is radioactive or that undergoes radioactive decay.
RadioactivityThree types of radiation (or radioactivity):•Alpha particles ()•Beta particles ()•Gamma-rays ()
Three types of radiation (or radioactivity):•Alpha particles ()•Beta particles ()•Gamma-rays ()
Alpha Decay ()
Radium
226Ra
88 protons138 neutrons
Radon
Rn222
Mass #
86 protons136 neutrons
+ nnp
p
He)
2 protons2 neutrons
The alpha-particle is a Helium nucleus.
It’s the same as the element Helium, with the electrons stripped off !
Unstable nucleus
New nucleus Alpha particle
2
• These are examples of Radioactive Equations
• Result: 2 less protons and 2 less neutrons– loss of 4 in mass number and loss of 2 in atomic number.
Alpha Decay
Example 1
Example 2
Beta Decay ()
CarbonC14
6 protons8 neutrons
NitrogenN14
7 protons7 neutrons
+ e-
electron(beta-particle)
Unstable nucleus
New nucleus
Beta particle
Beta DecayA beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta decay occurs when a neutron changes into a proton and an electron.
Result: the nucleus has one less neutron, but one extra proton.
Gamma particles ()
In much the same way that electrons in atoms can be in an excited state, so can a nucleus.
NeonNe20
10 protons10 neutrons
(in excited state)
10 protons10 neutrons
(lowest energy state)
+gamma
NeonNe20
A gamma is a high energy light particle.
A gamma is a high energy light particle.
Unstable nucleus
New nucleus
Gamma radiation
After or decay, surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed.
Gamma Decay• Gamma rays are not charged particles like and
particles.• Gamma rays are electromagnetic radiation with high
frequency.• When atoms decay by emitting or particles to
form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
• This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10-12 J).