Nuclear Reactions

BalancingBalancing Nuclear Nuclear EquationsEquations

Conservation of:Conservation of:

Atomic NumberAtomic Number (subscript) (subscript)

Atomic MassAtomic Mass (superscript) (superscript)

Balancing Nuclear EquationsBalancing Nuclear Equations

1616N N 00e + e + 1616OO7 -1 8

Conservation of mass number: 16 = 0 + 16

Conservation of atomic number: 7 = -1 + 8

Natural TransmutationNatural Transmutation

1 term on reactant side1 term on reactant side Original isotopeOriginal isotope

2 terms on product side2 terms on product side Emitted Particle Emitted Particle New IsotopeNew Isotope

Happens all by itselfHappens all by itself -- Not affected Not affected by by anythinganything in environment in environment

Natural TransmutationNatural Transmutation

1616N N 00e + e + 1616OO7 -1 8

1 term reactant side

2 terms product side

Artificial TransmutationArtificial Transmutation Man: Man: causes it to happencauses it to happen by by

smashing particles into one smashing particles into one anotheranother

2 terms on reactant side2 terms on reactant side Original IsotopeOriginal Isotope Particle that hit it: neutron, Particle that hit it: neutron, proton, or proton, or -particle-particle

Product side usually 2 termsProduct side usually 2 terms

Artificial TransmutationArtificial Transmutation

2727Al + Al + 44He He 3030P + P + 11nn1

3

2 15 0

Original isotope (target nucleus)

“Bullet”

Bombarding with Protons, Bombarding with Protons, protons and protons and -particles -particles - do damage - do damage

when hit target nucleuswhen hit target nucleus

(+) charge & large mass: must be (+) charge & large mass: must be accelerated to high speeds to accelerated to high speeds to overcome repulsive forcesovercome repulsive forces•magnetic and electric fields used to magnetic and electric fields used to

accelerate accelerate

What is an accelerator?What is an accelerator?

accelerator is vacuum chamber (long accelerator is vacuum chamber (long pipe) surrounded by vacuum pumps, pipe) surrounded by vacuum pumps, magnets, high voltage instruments & magnets, high voltage instruments & electronic circuitselectronic circuits

inside pipe, particles are accelerated inside pipe, particles are accelerated to very high speeds & smashed into to very high speeds & smashed into each othereach other

FermiLab

ring circumference = 4mi !(≈ 21km)

Neutron CaptureNeutron Capture

Neutrons:Neutrons:•neutral - aren't repelled by (+) neutral - aren't repelled by (+)

nucleusnucleus•no need to be accelerated no need to be accelerated

good thing since can’t accelerate good thing since can’t accelerate them!them!

Artificial TransmutationArtificial Transmutation

2727Al + Al + 44He He 3030P + P + 11nn1313 22 1515 00

1414N + N + 44He He 1717O + O + 11HH77 22 88 11

7575As + As + 44He He 7878Br + Br + 11nn3333 22 3535

00

3737Cl + Cl + 11n n 3838ClCl1717 00 17

All have 2 reactants!

FissionFission ReactionReaction

InvolvesInvolves splitting heavy splitting heavy nucleus into 2 lighter nucleinucleus into 2 lighter nuclei

FissionFission FFiissssiion = Don = Diivviissiionon

heavy nucleus: FM heavy nucleus: FM > > 100 amu100 amu

reactant side 2 terms:reactant side 2 terms: 1 heavy isotope (U-235, Pu-239)1 heavy isotope (U-235, Pu-239) Bombarding particle – usually neutronBombarding particle – usually neutron

product side at least 2 terms:product side at least 2 terms: 2 medium-weight isotopes2 medium-weight isotopes 11++ neutrons neutrons Huge amount energy releasedHuge amount energy released

FissionFission235235U + U + 11n n 9191Kr + Kr + 142142Ba + 3Ba + 311n + energyn + energy

9292 00 3636 5656 00

235235U + U + 11n n 7272Zn + Zn + 160160Sm + 4 Sm + 4 11n + energyn + energy9292 00 3030 006262

>>200 different product isotopes have 200 different product isotopes have been identifiedbeen identified

small amount mass is converted to small amount mass is converted to energy by E = mcenergy by E = mc22

Fission Chain ReactionFission Chain Reaction

Fission Chain ReactionFission Chain Reaction

Controlled – nuclear reactorControlled – nuclear reactor

Uncontrolled – bombUncontrolled – bomb

FFuusionsion nnuuclei clei uunitenite

reactant side 2 small nucleireactant side 2 small nuclei • H + H; H + He; He + He … (no larger than Li)H + H; H + He; He + He … (no larger than Li)

Product side: Product side: • 1 nucleus (still pretty small) &1 nucleus (still pretty small) &• maybe a particlemaybe a particle

Source of sSource of suun’s energyn’s energy

22H + H + 33H H 44He + He + 11n + energyn + energy11 11 22 00

CERN particles travel just below speed of light;

particles make 400 million revs of ring in 10 hrs

27 km ring

SLAC LBL