Nuclear Physics
and
Radioactivity
Lectures 21
Ch 30
Mural painted on the birthplace of Marie Curie in
Warsaw, in 2011. To mark the 100th anniversary
of her second Nobel prize, which she shared
with her daughter Irene.
Units of Chapter 30-31
•  Radioactivity
•  Alpha Decay
•  Beta Decay
•  Gamma Decay
•  Structure and Properties of the Nucleus
•  Binding Energy and Nuclear Forces
•  Conservation of Nucleon Number and Other Conservation Laws
•  Half-Life and Rate of Decay
•  Radioactive Dating
•  Detection of Radiation
•  Nuclear Reactions and the Transmutation of Elements
•  Nuclear Fission; Nuclear Reactors
•  Nuclear Fusion
30.3 Radioactivity - and Ionizing Radiation
•  Towards the end of the 19th century,
minerals were found that would darken a
photographic plate even in the absence of
light.
• This phenomenon was named radioactivity
by Marie Curie.
• Marie and Pierre Curie isolated two new
elements from a uranium-bearing ore called
Pitchblende: Radium and Polonium
• Most of the effects associated with
“radiation” are due to ionization by high
energy particles and photons.
•  Find the Curie’s full story, with photos,
original notes, etc… at the American Institute
of Physics website:
http://www.aip.org/history/curie/
Types of High energy Radiation
30.3 Radioactivity
Radioactive rays were observed to be of three
types:
1.  Alpha rays, which could barely penetrate a piece
of paper
2.  Beta rays, which could penetrate 3 mm of
aluminum
3.  Gamma rays, which could penetrate several
centimeters of lead
We now know that alpha rays are helium nuclei,
beta rays are electrons, and gamma rays are
electromagnetic radiation.
30.13 Detection of Ionizing Radiation
• 
The Geiger counter is a
gas-filled tube with a wire in
the center.
• 
The wire is at high voltage;
the case is grounded.
• 
When a charged particle
passes through, it ionizes
the gas.
• 
The ions cascade onto the
wire, producing a current
pulse.
Using our Geiger counter to investigate
samples of radioactive elements…..
What type of ionizing radiation
is emitted by Polonium ?
A. 
B. 
C. 
D. 
Alpha
Beta
Gamma
Radio
Polonium is a chemical element with the
symbol Po and atomic number 84, discovered
in 1898 by Marie and Pierre Curie.
A rare and highly radioactive element with no
stable isotopes, polonium is chemically
similar to bismuth and tellurium, and it occurs
in uranium ores.
Applications of polonium include heaters in
space probes, and antistatic devices.
Infamous for its use in the 2006 radioactive
poisoning case of Russian dissident
Alexander Litvinenko in London.
Using our Geiger counter to investigate
samples of radioactive elements…..
What type of ionizing
radiation is emitted by
Caesium?
A. 
B. 
C. 
D. 
Alpha
Beta
Gamma
Radio
A radioactive isotope of caesium is formed as
one of the more common fission products by
the nuclear fission of uranium-235 in nuclear
reactors and nuclear weapons.
Caesium-137 is among the most problematic of
the short-to-medium-lifetime fission products
because it easily moves and spreads in nature
due to the high water solubility of caesium's
most common chemical compounds, which
are salts.
Using our Geiger counter to investigate
samples of radioactive elements…..
What type of ionizing
radiation is emitted by
Strontium?
A. 
B. 
C. 
D. 
Alpha
Beta
Gamma
Radio
Radioactive strontium is
used in bone cancer therapy,
as it mimics calcium, and is
preferentially incorporated
by regions of increased bone
growth
Unstable isotopes Strontium
are present in nuclear
weapon fallout, and are a
component of nuclear waste.
30.13 Detection of Radiation
A scintillation counter uses a
scintillator – a material that emits
light when a charged particle
goes through it. The scintillator
is made light-tight, and the light
flashes are viewed with a
photomultiplier tube, which has a
photocathode that emits an
electron when struck by a
photon and then a series of
amplifiers.
Cloud Chamber
photographs
Above: Ionization tracks made
by high energy particles.
Right: The addition of a
magnetic field causes the
particles to form curved,
circular, or even spiral tracks.
30.3 Radioactivity
Alpha and beta rays are bent in opposite directions in a
magnetic field, while gamma rays are not bent at all.
Remember the Right Hand Rule
ConcepTest 30.4b Particle Emission II
A radioactive substance decays
and the emitted particle passes
through a uniform magnetic field
pointing into the page as shown.
In which direction are gamma rays
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
deflected?
source
×
×
×
×
B field
ConcepTest 30.4b Particle Emission II
A radioactive substance decays
and the emitted particle passes
through a uniform magnetic field
pointing into the page as shown.
In which direction are gamma rays
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
deflected?
source
Gamma rays are uncharged,
so they will not be deflected
by a magnetic field.
Follow-up: What particles are bent to the right?
×
×
×
×
B field
Most Nuclear Radiation is Natural
Fun facts:
•  The most radioactive thing most of us encounter in a year is a banana.
•  Your radiation dose from flying in a plane is greater than your dose
from the security X-ray scanner at check-in.
Lise Meitner
Discoverer of Nuclear Fission
Discovered the reason that no stable elements beyond uranium
(in atomic number) existed naturally; the electrical repulsion of
so many protons overcame the strong nuclear force.
Her theoretical work correctly predicted the elements created by the
splitting (fission) of Uranium
Meitner was the first to realize that Einstein’s famous equation: E=mc2
explained the source of the tremendous releases of energy in nuclear
fission, by the conversion of rest mass into kinetic energy, popularly
described as the conversion of mass into energy.
Meitnerium: element 109
30.1 Structure and Properties of the
Nucleus
Nucleus is made of protons and neutrons
Proton has positive charge:
Neutron is electrically neutral:
Neutrons and protons are collectively called nucleons.
The different nuclei are referred to as nuclides.
Number of protons: atomic number, Z
Number of nucleons: atomic mass number, A
Neutron number: N = A - Z
30.1 Structure and Properties of the
Nucleus
A and Z are sufficient to specify a nuclide.
Nuclides are symbolized as follows:
• Where X is the chemical symbol for the element.
•  Nuclei with the same Z – so they are the same element – but
different N are called isotopes.
•  For many elements, several different isotopes exist in nature.
•  Natural abundance is the percentage of a particular element
that consists of a particular isotope in nature.
30.1 Size of the Nucleus
Because of wave-particle duality, the size of the nucleus is somewhat
fuzzy. Measurements of high-energy electron scattering yield:
(30-1)
Masses of atoms are measured with reference to the
carbon-12 atom, which is assigned a mass of exactly
12u. “u” is the unified atomic mass unit.
ConcepTest 30.1 The Nucleus
There are 82 protons
in a lead nucleus.
Why doesn’t the
lead nucleus burst
apart?
1) Coulomb repulsive force doesn’t act
inside the nucleus
2) gravity overpowers the Coulomb
repulsive force inside the nucleus
3) the negatively charged neutrons balance
the positively charged protons
4) protons lose their positive charge inside
the nucleus
5) none of the above
ConcepTest 30.1 The Nucleus
There are 82 protons
in a lead nucleus.
Why doesn’t the
lead nucleus burst
apart?
1) Coulomb repulsive force doesn’t act
inside the nucleus
2) gravity overpowers the Coulomb
repulsive force inside the nucleus
3) the negatively charged neutrons balance
the positively charged protons
4) protons lose their positive charge inside
the nucleus
5) none of the above
The Coulomb repulsive force is
overcome by the even stronger
Strong nuclear force
Isotopes of the same element differ
by the number of _______ ?
A.  Neutrons
B.  Protons
C.  Electrons
D.  Protons and Electrons
E.  Neutrons and Electrons
30.1 Structure and Properties of the
Nucleus
Note the difference in Mass of Proton, Neutron, Hydrogen atom
The total mass of a stable nucleus is always
less than the sum of the masses of its
separate protons and neutrons.
Where has the missing mass gone?
A.  Particles with a small mass, such as electrons are
emitted when the nucleus forms
B.  The lost mass was converted into energy according
to E=mc2
30.2 Binding Energy and Nuclear Forces
•  The “missing mass” is also called the mass
deficit or mass defect.
•  It has become energy, such as radiation
(usually gamma rays) or kinetic energy,
released during the formation of the nucleus.
•  Energy released is related to the lost mass
by E=mc2
•  This difference between the total mass of the
constituents and the mass of the nucleus is
called the total binding energy of the nucleus.
Nuclear Binding Energy
Comparing the mass of Helium to its
constituents: (Example 30.3 in Giancoli)
Review this type of calculation as a possible exam question!
There are a couple of these in the HW.
Open the book on Document camera…….