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Radioactivity
Radioactivity
Atomic Physics – the
study of the clouds of
electrons that make up the
atom.
But now we need to delve
deeper…
… into the atomic nucleus.
Radioactivity
Wilhelm Roentgen
1895
Radioactivity
Radioactivity
Antoine Henri Becquerel
1896
Radioactivity
Antoine Henri Becquerel
Radioactivity
◼ Radioactivity is the process of the atomic
nucleus emitting energetic subatomic
particles.
◼ This process is nothing new – it has been
around far longer than the human race!
Radioactivity
Three Distinct Types of Radiation
◼ Alpha - α
◼ Beta - β
◼ Gamma - Ɣ
Radioactivity
Radioactivity
Radioactivity
Radioactivity
Radioactivity
Environmental Radiation
Units of Radiation
◼ Radiation dosage is commonly measured
in rads.
◼ 1 rad = 0.01 joule of radiant energy absorbed
per kg of tissue.
◼ The measure for radiation dosage based
on potential damage is the rem (roentgen
equivalent man)
Units of Radiation
◼ A lethal dose of radiation for a human is
about 500 rems. You have about a 50%
chance of surviving a dose of this
magnitude delivered over a short time.
◼ Average person in U.S. is exposed to 360
millirem each year (a millirem is 1/1000th
of a rem)
The Strong Force
The Strong Force
The nucleus is made up of nucleons, the
collective name for protons and neutrons.
Quarks
Each nucleon is made up of three fundamental
particles called, quarks.
The Strong Force
Just like there are energy levels for the orbital
electrons, there are energy levels within the
nucleus. Changes of energy states in radioactive
nuclei result in the emission of gamma-ray photons.
Question: If like charges
repel, what holds all those
positively charged protons
close together in the
nucleus?!
The Strong Force
Comparison of the strengths of the
STRONG force and the ELECTRIC force
over distance.
The Strong Force
Since the strong force is only “strong” over extremely short
distances, a large nucleus is not as stable as a small one.
The Strong Force
In the Helium-4 nucleus, all four nucleons attract by the
strong force. Only two (the protons) feel the repulsive
electric force.
The Strong Force
Neutrons act as
“Nuclear cement”,
adding to the attractive
force ONLY.
Elements toward the
end of the periodic
table have many more
neutrons per proton
than the lighter ones!
The Strong Force
Lithium-6
Uranium-238
U-238 has about 1.5 times as many neutrons per proton
as Li-6. Neutrons add to nucleus stability!
The Strong Force
A neutron all by itself, however, is radioactive! It
spontaneously transforms to a proton and an electron!
The Strong Force
Summing Up So Far
1.Which two fundamental forces have visible
effects within the nucleus of an atom?
2.Which one acts over greater distance?
3.Which force acts on ALL nucleons?
4.Which force acts only on protons?
Summing Up So Far
1. In the nucleus of ordinary hydrogen,
does the strong force play a role?
2. How about the electric force?
Radioactive Half-Life
◼ The radioactive decay rate of an element
is measured in terms of a characteristic
time called the half-life.
Radioactive Half-Life
◼ The radioactive decay rate of an element
is measured in terms of a characteristic
time called the half-life.
◼ This is the time it takes for half of an original
quantity of a radioactive isotope to decay.
Radioactive Half-Life
◼ The radioactive decay rate of an element
is measured in terms of a characteristic
time called the half-life.
◼ This is the time it takes for half of an original
quantity of a radioactive isotope to decay.
The half-life of Uranium-238 is 4.5 billion years!
Radioactive Half-Life
Radioactive Half-Life
Radioactive Half-Life
Radium-226 has a half-life of 1620 years.
Radioactive Half-Life
Check Question:
If a sample of a radioactive isotope has a half-
life of 1 day, how much of the original sample
will be left at the end of the second day?
Radiation Detectors
A Geiger counter detects
incoming radiation by a
short pulse of current
triggered when radiation
ionizes a gas in the tube.
A scintillation counter
detects incoming radiation
by flashes of light
produced by particles or
gamma rays passing
through the counter.
Review of Elements
Review of Elements
Transmutation
Transmutation
The changing of one chemical element into another is
called atomic transmutation.
Alpha Decay
Beta Decay
Gamma Decay
Electron Capture (EC)
Positron Emission
Five types of Decay
◼ Alpha Decay
◼ Beta Decay
◼ Gamma Decay
◼ Electron Capture
◼ Positron Emission
Transmutation
Radioactive elements can decay backward or
forward in the periodic table.
Transmutation
Transmutation
Transmutation
What nucleus results when Krypton-81
undergoes electron capture?
What nucleus results when Silicon-27
undergoes positron emission?
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating
Carbon Dating