Nuclear Reactions Nuclear Reactions
Jan 03, 2016
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