Nuclear ReactionsNuclear Reactions

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 (spontaneous)(spontaneous)Not affected by Not affected by anythinganything in environment in environment

Natural TransmutationNatural Transmutation

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

1 term on reactant side

2 terms on product side

Artificial TransmutationArtificial Transmutation cause to happen:cause to happen: smash particles smash particles into one anotherinto one another

2 terms on reactant side2 terms on reactant side Original IsotopeOriginal Isotope Particle that hits it Particle that hits it

•neutron, proton, or neutron, proton, or -particle-particle

Product side: usually 2 termsProduct side: usually 2 terms

Artificial TransmutationArtificial Transmutation

2727Al + Al + 44He He 3030P + P + 11nn13 2 15 0

original isotope or target nucleus

“bullet”-what hits isotope

ArtificialArtificial Transmutation 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 these equations have 2 reactants!

Bombarding with protons or Bombarding with protons or

protons & protons & -particles have positive -particles have positive charge and mass charge and mass

• do some damage when hit target nucleusdo some damage when hit target nucleus

• must be accelerated to high speeds to must be accelerated to high speeds to overcome repulsive forces between overcome repulsive forces between nucleus & particle (both are +) nucleus & particle (both are +)

What is an accelerator?What is an accelerator?

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

radio-frequency cavities, high voltage radio-frequency cavities, high voltage instruments & electronic circuitsinstruments & electronic circuits

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

FissionFission ReactionReaction ssplitting heavy nucleus into 2 lighter plitting heavy nucleus into 2 lighter nucleinuclei

requires critical mass of fissionable isotoperequires critical mass of fissionable isotope• controlled: nuclear reactorcontrolled: nuclear reactor• uncontrolled: bombuncontrolled: bomb

FissionFission reactant side: 2 termsreactant side: 2 terms

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

product side: at least 2 termsproduct side: at least 2 terms 2 medium-weight isotopes2 medium-weight isotopes 1 or more neutrons1 or more neutrons huge amount energy releasedhuge amount energy released

FFiissssiion = on = DDiivviissiionon

Fission Chain ReactionFission Chain Reaction

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

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

FFuusionsion reactant side has 2 small nuclei:reactant side has 2 small nuclei:

• H + H; H + He; He + HeH + H; H + He; He + He

product side: product side: • 1 nucleus (slightly larger; still small) and maybe 1 nucleus (slightly larger; still small) and maybe

a particlea particle

source of ssource of suunn ’’s energys energy

2 n2 nuuclei clei uunitenite 22H + H + 33H H 44He + He + 11n + energyn + energy

11 11 22 00

CERN

•particles travel just below speed

of light

•10 hrs: particles make 400 million revolutions of ring

27 kilometer ring

FermiLab

4 miles in circumference!

Balancing Nuclear Equations

Nuclear Equations - tasksNuclear Equations - tasks

identify type (4 types)identify type (4 types)

balance to find unknown termbalance to find unknown term

Natural Transmutation – IDNatural Transmutation – ID

1 term on reactant side1 term on reactant side • starting isotope starting isotope

2 terms on product side2 terms on product side • ending isotope & emitted particleending isotope & emitted particle

type of particle emitted characteristic type of particle emitted characteristic of isotope – Table Nof isotope – Table N

Nuclear EquationsNuclear Equations

to balance: use conservation of to balance: use conservation of both atomic number & mass both atomic number & mass number number

• mass number = left mass number = left supersuperscriptscript

• atomic number = left atomic number = left subsubscriptscript

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

Writing EquationsWriting Equations write equation for decay of Thorium-232write equation for decay of Thorium-232 use Table N to find decay mode: use Table N to find decay mode: αα write initial equation:write initial equation:

232232Th Th 44He +He + XX

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

9090 2

What’s under the hat?

Little cats X, Y, & Z!

Write an equation for the Write an equation for the αα decay of Th-232 decay of Th-232

232 Th 4He + YX what’s X?

95 2 Z

232232Th Th 44He + XHe + X9090 22

conservation of mass number:conservation of mass number:

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

YY

Z

232 = 4 + Y so Y = 228

232232Th Th 44He + He + 228228XX9090 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

232232Th Th 44He + He + 228228XX90 2 88

use PT to find X: X = Ra

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

Alpha (α) decay:Alpha (α) decay:

233233U U 229Th + 4He 92 90 2

232232Th Th 228Ra + 4He 90 88 290 88 2

175175Pt Pt 171Os + 4He 78 76 2

How does the mass number or How does the mass number or atomic number change in atomic number change in αα,,ββ or or

γγ decay? decay? go to Table N: go to Table N:

• find isotope that decays by find isotope that decays by αα or or ββ decaydecay• write equationwrite equation• see how mass number (or atomic number) see how mass number (or atomic number)

changeschanges 226226

8888Ra Ra 4422 + X so X has to be + X so X has to be 222222

8686XX

αα decay of decay of Ra-226: Ra-226: • mass number decreases by 4mass number decreases by 4• atomic number decreases by 2atomic number decreases by 2

Radioactive Decay SeriesRadioactive Decay Series

sometimes 1 transmutation isnsometimes 1 transmutation isn’’t t enough to achieve stabilityenough to achieve stability

some radioisotopes go through some radioisotopes go through several changes before achieve several changes before achieve stability (no longer radioactive)stability (no longer radioactive)

ββ-- 1414C C 1414N + N + 00ee

ββ++ 1818F F 1818O + O + 00ee

6 7 -1

8 +1

9

beta

positron

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

decay?decay?

go to Table N; find isotope that decays by go to Table N; find isotope that decays by αα, , or or ; write equation; see how mass number ; write equation; see how mass number (or atomic number) changes(or atomic number) changes

226226Ra Ra 44 + X so X has to be + X so X has to be 222222XX

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

8888 22 8686

  Element (atom)

UNSTABLE STABLE

n/p ratio >1.5:1 1:1 up to 1.5:1

atomic number

83 and above ≤ 82

radioactive Yes Not

So how do you know if an element is radioactive or not?

the key is the proton to neutron ratio