Nuclear Physics

Nuclear Structure Nucleus – consists of nucleons (neutrons and protons) Nucleus – consists of nucleons (neutrons and protons) Atomic Number Z  number of protons Atomic Number Z  number of protons Atomic Mass Number A  nucleon number Atomic Mass Number A  nucleon number  total number of neutrons and protons

Atomic Radius r = (1.2 x m) A 1/3 r = (1.2 x m) A 1/3 r  radius A  atomic mass number

Strong Nuclear Force One of three fundamental forces that have been discovered (others  gravitational force, electroweak force) One of three fundamental forces that have been discovered (others  gravitational force, electroweak force) Almost independent of electric charge Almost independent of electric charge Nearly the same nuclear force of attraction exists between 2 protons, 2 neutrons, or between a proton and a neutron. Nearly the same nuclear force of attraction exists between 2 protons, 2 neutrons, or between a proton and a neutron.

Strong Nuclear Force Range  short; very strong when nucleons are as close as m Range  short; very strong when nucleons are as close as m  zero at larger distances This limited range prevents extra neutrons from balancing longer range electric repulsions of extra protons and atoms become unstable This limited range prevents extra neutrons from balancing longer range electric repulsions of extra protons and atoms become unstable Bismuth  largest stable nucleus Bismuth  largest stable nucleus

Radioactivity All nuclei above bismuth, Z > 83, will have unstable nuclei and spontaneously break apart or rearrange structure of internal structure All nuclei above bismuth, Z > 83, will have unstable nuclei and spontaneously break apart or rearrange structure of internal structure This spontaneous disintegration or rearrangement is radioactivity This spontaneous disintegration or rearrangement is radioactivity

Nuclear Binding Energy The required energy to break a nucleus apart The required energy to break a nucleus apart  E = (  m)c 2  E = (  m)c 2  E  binding energy  m  mass defect of the nucleus (the difference in mass of the nucleus and the individual masses of the separated protons and neutrons) c  speed of light

Radioactive Decay When unstable or radioactive nuclei disintegrate spontaneously particles or high-energy photons are released When unstable or radioactive nuclei disintegrate spontaneously particles or high-energy photons are released These particles and photons are called rays These particles and photons are called rays There are three kinds of rays produced by naturally occurring radioactivity There are three kinds of rays produced by naturally occurring radioactivity  ,  & 

 Decay When a nucleus decays and emits  rays When a nucleus decays and emits  rays  rays  ray of positively charged particles; He +2 nuclei  4 2 He  rays  ray of positively charged particles; He +2 nuclei  4 2 He A Z P  A-4 Z-2 D He A Z P  A-4 Z-2 D He P  Parent D  Daughter

 Decay Energy released = difference in beginning and ending total atomic mass units Energy released = difference in beginning and ending total atomic mass units 1 amu or u = MeV 1 amu or u = MeV Since the parent and daughter nuclei are different this is a process called transmutation Since the parent and daughter nuclei are different this is a process called transmutation

 Decay  rays consist of negatively charged particles  rays consist of negatively charged particles  – particles  electrons 0 -1 e  – particles  electrons 0 -1 e  - decay  A Z P  A Z+1 D e  - decay  A Z P  A Z+1 D e  + decay  A Z P  A Z-1 D e (positron)  + decay  A Z P  A Z-1 D e (positron) Use masses from Periodic Table to determine energy release Use masses from Periodic Table to determine energy release

 Decay The emission of high energy photons when a nucleus changes from an exited energy state(*) to a lower energy state The emission of high energy photons when a nucleus changes from an exited energy state(*) to a lower energy state Does not cause a transmutation Does not cause a transmutation A Z P*  A Z P +  A Z P*  A Z P + 

The Neutrino Another particle emitted during b decay Another particle emitted during b decay Accounts for the energy missing from the KE  after emission Accounts for the energy missing from the KE  after emission Verified experimentally in 1956 Verified experimentally in 1956 Has zero electric charge Has zero electric charge Interacts weakly with matter Interacts weakly with matter Has mass, a fraction of an electron’s, and travel at less than the speed of light Has mass, a fraction of an electron’s, and travel at less than the speed of light