Nuclear ReactionsNuclear Reactions

Natural Transmutation

1 term on reactant sideOriginal isotope

2 terms on product sideEmitted Particle New Isotope

Happens all by itself (spontaneous)Happens all by itself (spontaneous)Not affected by Not affected by anythinganything in environment in environment

Natural Transmutation

16N 0e + 16O7 -1 8

1 term on reactant side

2 terms on product side

Artificial Transmutation• Cause it to happen by smashing

particles into one another

• 2 terms on reactant side• Original Isotope• Particle that hits it

–neutron, proton, or -particle

• Product side: usually 2 terms

Artificial Transmutation

27Al + 4He 30P + 1n13 2 15 0

Original isotope or target nucleus

“Bullet”-what hits isotope

Artificial Transmutation

27Al + 4He 30P + 1n1313 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 of these equations have 2 reactants!

Bombarding with Protons or

Protons and -particles have positive charge and mass • do some damage when hit target nucleus• must be accelerated to high speeds to overcome

repulsive forces between nucleus & particle (both are +)

What is an accelerator?

• vacuum chamber (usually a long pipe)– surrounded by vacuum pumps, magnets,

radio-frequency cavities, high voltage instruments and electronic circuits

• inside the pipe particles are accelerated to very high speeds then smashed into each other

Fission ReactionFission Reaction SSplitting heavy nucleus into 2 lighter plitting heavy nucleus into 2 lighter nucleinuclei

Requires a critical mass of fissionable isotopeRequires a critical mass of fissionable isotopeControlled – nuclear reactorControlled – nuclear reactorUncontrolled – bombUncontrolled – bomb

FissionReactant side: 2 terms

• 1 heavy isotope (examples: U-235 or Pu-239)• Bombarding particle – usually a neutron

• Product side: at least 2 terms• 2 medium-weight isotopes• 1 or more neutrons• Huge amount of energy is released

• Fission = Division

Fission235U + 1n 91Kr + 142Ba + 31n + energy

9292 00 3636 5656 00

235235U + U + 11n n 7272Zn + Zn + 160160Sm + 4Sm + 411n + energyn + energy9292 00 3030 006262

More than 200 different product More than 200 different product isotopes identified from fission of U-235 isotopes identified from fission of U-235

A small amount of mass is converted to A small amount of mass is converted to energy according to E = mcenergy according to E = mc22

Fission Chain ReactionFission Chain Reaction

Fusion• Reactant side has 2 small nuclei:

– H + H; H + He; He + He

• Product side: – 1 nucleus (still small) and maybe a particle

• Source of sun’s energy• 2 nuclei unite

2H + 3H 4He + 1n + energy

11 11 22 00

CERN

•Particles travel just below speed of light

•In 10 hrs: particles make 400 million revolutions of the ring

27 kilometer ring

FermiLab

4 miles in circumference!

Balancing Nuclear Equations

Nuclear Equations - tasks

• Identify type (4 types)

• Balance to find 1 unknown term

Natural Transmutation – ID

• 1 term on reactant side – starting isotope

• 2 terms on product side – ending isotope and emitted particle

• Type of particle emitted characteristic of isotope – Table N

Nuclear Equations

• To balance: use conservation of both atomic number & mass number

• Mass number = left superscript

• Atomic Number = left subscript

Balancing Nuclear Equations

16N 0e + 16O7 -1 8

Conservation of mass number: 16 = 0 + 16

Conservation of atomic number: 7 = -1 + 8

Writing Equations

• Write the equation for the decay of Thorium-232

• Use Table N to find the decay mode: α

• Write the initial equation: 232Th 4He + X

figure out figure out what element what element it turned intoit turned into

9090 2

Write an equation for the α decay of Am-241

241 Am 4He + YX What’s X?

95 2 Z

232Th 4He + X9090 22

Conservation of Mass Number:Conservation of Mass Number:

sum of mass numbers on left side must = sum of mass numbers on left side must = sum of mass numbers on right sidesum of mass numbers on right side

YY

Z

232 = 4 + Y so Y = 228

232Th 4He + 228X9090 22

Conservation of Atomic Number:Conservation of Atomic Number:

sum of atomic numbers on left side must = sum of atomic numbers on left side must = sum of atomic numbers on right sidesum of atomic numbers on right side

ZZ

90 = 2 + Z so Z = 88

232Th 4He + 228X90 2 88

Use the PT to find X: X = Ra

232232Th Th 44He + He + 228228RaRa90 2 88

Alpha (α) decay:233U 229Th + 4He 92 90 2

232Th 228Ra + 4He 90 88 2

175Pt 171Os + 4He 78 76 2

How does the mass number or atomic number change in α,β or γ

decay?• go to Table N:

– find isotope that decays by alpha or β decay– write the equation– see how the mass number (or atomic number)

changes

• 22688Ra 4

2 + X so X has to be 22286X

• X is Rn-222 – mass number decreases by 4; atomic number

decreases by 2

Write an equation for the decay of Am-241

241 Am 4He + YX95 2 Z

241 = 4 + Y

95 = 2 + Z

so Y = 237

so Z = 93

What’s X? X = Np

Radioactive Decay Series

• Sometimes 1 transmutation isn’t enough to achieve stability

• Some radioisotopes go through several changes before they achieve stability (and are no longer radioactive)

β- 14C 14N + 0e

ββ++ 1818F F 1818O + O + 00ee

6 7 -1

8 +1

9

How does the mass number or atomic number change in or decay?

• Go to Table N; find an isotope that decays by α, or , write the equation; see how the mass number (or atomic number) changes

• 226Ra 4 + X so X has to be 222X

• X is Ra-222 – mass number decreases by 4– atomic number decreases by 2

8888 22 8686