Nuclear Science
What is in a nucleus? Why do
nuclei decay? Where does
radiation come from?
Inside Atoms
An atom is ~10 nm in
diameter (1x10-10 m)
The electrons are the
particles in the atom
that “fill” most of this
space
At the center of the atom
is a nucleus, which is
typically about 5
femtometers across
(5x10-15 m)
Inside Nuclei


Neutrons and
protons form the
nucleus of the atom
Neutrons and
protons have masses
that are 5000 times
that of the electron,
so their mass makes
up most of the mass
of an atom
More about nuclei



Neutrons and
protons are called
nucleons
Protons have a
positive charge
(same size, but
opposite sign as
electron)
Neutrons are have
no net charge
More about atoms
Chemical properties of
atoms are determined by
the number of electrons
and protons in a neutral
atom, so the number of
protons in the nucleus
determines chemical
properties of an
element.
The number of neutrons
does not affect most of
the chemical properties
of an element.
Example: The element
Carbon has 6 electrons
and 6 protons
Elements and isotopes
Different nuclei (isotopes) of the same element
can have different numbers of neutrons.
11
6
C
12
6
Carbon-11
Z=6 (protons)
N=5 (neutrons)
C
Carbon-12
Z=6 (protons)
N=6 (neutrons)
13
6
C
Carbon-13
Z=6 (protons)
N=7 (neutrons)
14
6
C
Carbon-14
Z=6 (protons)
N=8 (neutrons)
Chart of Elements OR
Chart of Nuclides
Element - Carbon
Carbon isotopes
Z
N
What does the chart tell us?
Z
N




There are LOTS of nuclides
There are many isotopes
of most elements
Blue nuclides are “stable”
Nuclides with N≥Z are
more stable than nuclides
Z
N
What happens to “unstable” nuclei
Is that all?


Nuclei can also emit nucleons
(neutrons and protons)
Nuclei can break into chunks (fission)