Nuclear Reaction: involves a change in the atom’s nucleus.

Image of Becquerel's photographic plate which was exposed to radiation from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium salt is clearly visible.

Radioactive Decay: an unstable nucleus spontaneously breaks apart and emits radiation.

Types of Radiation:  alpha radiation (α)  beta decay (β)  gamma rays (γ)

Alpha Radiation, α : 4 He 2+ 2  low penetrating ability. Thickness of a sheet of paper can stop it.

Beta Decay, β : 0 e − −1  turns a neutron into a proton and emits an electron.  shielded by metal foil since it’s lighter than α.

Gamma Rays, γ:  no mass and no charge  dangerous radiation: emitted when nucleus undergoes alpha decay.  stopped by heavy lead or concrete shielding.

2+

+

 Ra → α Rn

 U → α Th

 C → β − N

U+ n→ Ba + Kr + ? n

Problem:  Write the equation for I undergoing beta decay

Problems:  α + N → ?+ H  Rb → ? + ?

Problems:  H + ? → He  C → ? + β

Write a balanced nuclear equation for the alpha decay of the following radioisotope U

U → Th + α

Write the symbols for the following: neutronalpha protonbeta (electron)gamma positron

neutron proton electron positron alpha beta gamma n p e β α β γ

The difference between the mass of an atom’s nucleus and the sum of the masses of its protons and neutrons. Mass Defect Cu-63: 29 protons( amu/p + ) + 34 neutrons( amu/n) = amu Mass defect = amu amu = amu

The energy released when a nucleus is formed from nucleons (protons & neutrons) Einstein’s equation E = mc 2 shows mass can be converted to energy, and energy to mass. Nuclear Binding Energy

Example: The atomic mass of S-32 is amu. 1)What is the mass defect? 2)What is the binding energy? 3)What is the binding energy per nucleon? 1.Determine total mass of proton, neutrons & electrons 16 p x amu = amu 16 n x amu = amu 16 e ‒ x amu = amu Total = amu 2.Find the mass defect: amu ‒ amu = amu x 10 ‒ 27 kg/amu = x 10 ‒ 28 kg

Example: The atomic mass of S-32 is amu. 2) What is the binding energy? 3) What is the binding energy per nucleon? E=mc 2 E = ( x 10 ‒ 28 kg)(3.00 × 10 8 m/s) 2 = 4.36 × 10 −11 kgm 2 /s 2 = 4.36 × 10 −11 J Per nucleon: 4.36 × 10 −11 J / 32 nucleons = 1.36 × 10 −12 J/nucleon

Half-Life (t 1/2 ):  time required for half of the atoms in a sample to decay.

Radioactive Decay Rates

Determining Decay:  fraction of a radioisotope remaining after n half- lives is (½) n  m final = m initial (½) n

Half-Life calculations Variables: Equations:  m final  m initial  n  t 1/2  t total t total = n t ½ m final = m initial (½) n Final mass initial mass # of half lives Time length of a half life Total length of time

Problem:  N-13 has a half-life of 10 minutes. How much of 2.00 g. N-13 will exist after 3 half-lives?  How long is 3 half- lives?

Nuclear fission

Nuclear fusion