Nuclear ScienceNuclear ScienceWhat is in a nucleus? Why do What is in a nucleus? Why do

nuclei decay? Where does nuclei decay? Where does radiation come from?radiation come from?

Inside AtomsInside Atoms

An atom is ~10 nm in An atom is ~10 nm in diameter (1x10diameter (1x10-10-10 m) m)

The The electronselectrons are the are the particles in the atom that particles in the atom that “fill” most of this space“fill” most of this space

At the center of the atom is At the center of the atom is a nucleus, which is a nucleus, which is typically about 5 typically about 5 femtometers across femtometers across (5x10(5x10-15-15 m) m)

Inside NucleiInside Nuclei

NeutronsNeutrons and and protonsprotons form the form the nucleus of the atomnucleus of the atom

NeutronsNeutrons and and protonsprotons have masses have masses that are 5000 times that are 5000 times that of the electron, that of the electron, so their mass makes so their mass makes up most of the mass up most of the mass of an atomof an atom

More about nucleiMore about nuclei

NeutronsNeutrons and and protonsprotons are called are called nucleonsnucleons

ProtonsProtons have a have a positive charge positive charge (same size, but (same size, but opposite sign as opposite sign as electron)electron)

NeutronsNeutrons are have are have no net chargeno net charge

More about atomsMore about atoms

Chemical properties of Chemical properties of atoms are determined by atoms are determined by the number of the number of electronselectrons and and protons protons in a neutral in a neutral atom, so the number of atom, so the number of protons in the nucleus protons in the nucleus determines chemical determines chemical properties of an element.properties of an element.

The number of The number of neutronsneutrons does not affect most of does not affect most of the chemical properties the chemical properties of an element.of an element.

Example: The element Example: The element Carbon has 6 electrons Carbon has 6 electrons and 6 protonsand 6 protons

Elements and isotopesElements and isotopes

Different nuclei (isotopes) of the same element Different nuclei (isotopes) of the same element can have different numbers of neutrons. can have different numbers of neutrons.

C126 C136 C146C116Carbon-11Z=6 (protons)N=5 (neutrons)

Carbon-12Z=6 (protons)N=6 (neutrons)

Carbon-13Z=6 (protons)N=7 (neutrons)

Carbon-14Z=6 (protons)N=8 (neutrons)

Chart of Elements OR Chart of Elements OR Chart of NuclidesChart of Nuclides

Element - Carbon

Carbon isotopes

Z

N

Z

N

What does the chart tell us?What does the chart tell us?

Z

N

There are LOTS of nuclidesThere are LOTS of nuclides There are many isotopes of There are many isotopes of

most elementsmost elements Blue nuclides are “stable”Blue nuclides are “stable” Nuclides with N≥Z are Nuclides with N≥Z are

more stable than nuclidesmore stable than nuclides

What happens to “unstable” nucleiWhat happens to “unstable” nuclei

Is that all?Is that all?

Nuclei can also emit nucleons Nuclei can also emit nucleons (neutrons and protons)(neutrons and protons)

Nuclei can break into chunks (fission)Nuclei can break into chunks (fission)