Nuclear PhysicsNuclear Physics

Nuclear StructureNuclear StructureNucleus – consists of Nucleus – consists of nucleonsnucleons

(neutrons and protons) (neutrons and protons)Atomic Number Z Atomic Number Z number of protons number of protonsAtomic Mass Number A Atomic Mass Number A nucleon nucleon

numbernumber total number of neutrons and protonstotal number of neutrons and protons

Atomic RadiusAtomic Radius

r = (1.2 x 10 r = (1.2 x 10 -15-15 m) A m) A 1/31/3

r r radius radiusA A atomic mass number atomic mass number

Strong Nuclear ForceStrong Nuclear ForceOne of three fundamental forces that have One of three fundamental forces that have

been discovered (others been discovered (others gravitational gravitational force, electroweak force)force, electroweak force)

Almost independent of electric chargeAlmost independent of electric chargeNearly the same nuclear force of attraction Nearly the same nuclear force of attraction

exists between 2 protons, 2 neutrons, or exists between 2 protons, 2 neutrons, or between a proton and a neutron.between a proton and a neutron.

Strong Nuclear ForceStrong Nuclear ForceRange Range short; very strong when short; very strong when

nucleons are as close as 10nucleons are as close as 10-15-15 m m zero at larger distanceszero at larger distances

This limited range prevents extra neutrons This limited range prevents extra neutrons from balancing longer range electric from balancing longer range electric repulsions of extra protons and atoms repulsions of extra protons and atoms become become unstableunstable

Bismuth Bismuth largest stable nucleus largest stable nucleus

RadioactivityRadioactivityAll nuclei above bismuth , Z > 83, will have All nuclei above bismuth , Z > 83, will have

unstable nuclei and spontaneously break unstable nuclei and spontaneously break apart or rearrange structure of internal apart or rearrange structure of internal structurestructure

This spontaneous disintegration or This spontaneous disintegration or rearrangement is rearrangement is radioactivityradioactivity

Nuclear Binding EnergyNuclear Binding EnergyThe required energy to break a nucleus The required energy to break a nucleus

apartapartE = (E = (m)cm)c22

E E binding energy binding energym m mass defect of the nucleus mass defect of the nucleus(the difference in mass of the nucleus and the individual (the difference in mass of the nucleus and the individual

masses of the separated protons and neutrons)masses of the separated protons and neutrons)

c c speed of light speed of light

Radioactive DecayRadioactive DecayWhen unstable or radioactive nuclei When unstable or radioactive nuclei

disintegrate spontaneously particles or disintegrate spontaneously particles or high-energy photons are releasedhigh-energy photons are released

These particles and photons are called These particles and photons are called raysrays

There are three kinds of rays produced by There are three kinds of rays produced by naturally occurring radioactivitynaturally occurring radioactivity

, , & &

DecayDecay When a nucleus decays and emits When a nucleus decays and emits rays rays

rays rays ray of positively charged ray of positively charged particles; Heparticles; He+2+2 nuclei nuclei 44

22HeHe

AAZZP P A-4A-4

Z-2Z-2D + D + 4422HeHe

P P Parent ParentD D Daughter Daughter

DecayDecayEnergy released = difference in beginning Energy released = difference in beginning

and ending total atomic mass unitsand ending total atomic mass units1 amu or u = 931.5 MeV1 amu or u = 931.5 MeVSince the parent and daughter nuclei are Since the parent and daughter nuclei are

different this is a process different this is a process called called transmutationtransmutation

DecayDecay rays consist of negatively charged rays consist of negatively charged

particlesparticles –– particles particles electrons electrons 00

-1-1ee

- - decaydecay A AZZP P AA

Z+1Z+1D + D + 00-1-1ee

++ decay decay AAZZP P AA

Z-1Z-1D + D + 0011ee (positron)(positron)

Use masses from Periodic Table to determine Use masses from Periodic Table to determine energy releaseenergy release

DecayDecayThe emission of high energy photons The emission of high energy photons

when a nucleus changes from an exited when a nucleus changes from an exited energy state(*) to a lower energy stateenergy state(*) to a lower energy state

Does Does notnot cause a transmutation cause a transmutation

AAZZP* P* AA

ZZP + P +

The NeutrinoThe Neutrino Another particle emitted during b decayAnother particle emitted during b decay Accounts for the energy missing from the Accounts for the energy missing from the

KEKEafter emissionafter emission Verified experimentally in 1956Verified experimentally in 1956 Has zero electric chargeHas zero electric charge Interacts weakly with matterInteracts weakly with matter Has mass, a fraction of an electron’s, and Has mass, a fraction of an electron’s, and

travel at less than the speed of lighttravel at less than the speed of light