Nuclear Reactions

Natural Transmutation 1 term on reactant side original isotope (naturally radioactive) 2 terms on product side emitted particle new Isotope Happens all by itself (spontaneous) Not affected by anything in environment

Natural Transmutation 16N  0e + 16O 7 -1 8 2 terms on product side 1 term on reactant side

Artificial Transmutation cause to happen: smash particles into one another 2 terms on reactant side original Isotope (non-radioactive) particle that hits it neutron, proton, or -particle product side: usually 2 terms

Artificial Transmutation 27Al + 4He  30P + 1n 15 13 2 original isotope or target nucleus “bullet” - thing hits isotope

Artificial Transmutation 27Al + 4He  30P + 1n all these equations have 2 reactants! 13 2 15 14N + 4He  17O + 1H 1 2 8 7 75As + 4He  78Br + 1n 2 35 33 37Cl + 1n  38Cl 17 17

Bombarding with protons or  protons & -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 long pipe) surrounded by vacuum pumps, magnets, radio- frequency cavities, high voltage instruments & electronic circuits inside pipe particles are accelerated to very high speeds then smashed into each other

splitting heavy nucleus into 2 lighter nuclei Fission Reaction splitting heavy nucleus into 2 lighter nuclei requires critical mass of fissionable isotope controlled: nuclear reactor uncontrolled: bomb

Fission Fission = Division reactant 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 energy released Fission = Division

Fission 235U + 1n  91Kr + 142Ba + 31n + energy 56 92 36 92 36 235U + 1n  72Zn + 160Sm + 41n + energy 62 92 30 more than 200 different product isotopes identified from fission of U-235 small amount of mass is converted to energy according to E = mc2

Fusion 2H + 3H  4He + 1n + energy reactant side has 2 small nuclei: H + H; H + He; He + He product side: 1 nucleus (slightly larger; still small) and maybe a particle source of sun’s energy 2 nuclei unite 2H + 3H  4He + 1n + energy 2 1 1

CERN 27 kilometer ring particles travel just below speed of light 10 hrs: particles make 400 million revolutions of ring

FermiLab 4 miles in circumference!

Balancing Nuclear Equations

Nuclear Equations - tasks identify type (4 types): natural transmutation artificial transmutation fission fusion balance to find unknown term

Natural Transmutation – ID 1 term on reactant side starting isotope 2 terms on product side ending isotope & 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 + 16O -1 7 8 conservation of mass number: 16 = 0 + 16 conservation of atomic number: 7 = -1 + 8

Writing Equations write equation for decay of Thorium-232 use Table N to find decay mode: α write initial equation: 232Th  4He + X 90 2 figure out what element it turned into

What’s under the hat? Little cats X, Y, & Z!

Write an equation for the α decay of Th-232 232 Th  4He + YX what’s X? 95 2 Z

so Y = 228 232 = 4 + Y conservation of mass number: 232Th  4He + X Y Z 90 2 conservation of mass number: sum mass numbers on left side must = sum mass numbers on right side

so Z = 88 90 = 2 + Z conservation of atomic number: 232Th  4He + 228X 2 90 Z 90 = 2 + Z so Z = 88 conservation of atomic number: sum of atomic numbers on left side must = sum of atomic numbers on right side

232Th  4He + 228X 90 2 88 use PT to find X: X = Ra 232Th  4He + 228Ra 90 2 88

Radioactive Decay Series sometimes 1 transmutation isn’t enough to achieve stability some radioisotopes go through several changes before achieve stability (no longer radioactive)

radioactive decay series: Th-232 transmuting to Pb-208

β- 14C  14N + 0e 6 7 -1 beta β+ 18F  18O + 0e positron 9 8 +1

How does the mass number or atomic number change in α,β or γ decay? go to Table N: find isotope that decays by α or β decay write equation see how mass number (or atomic number) changes 22688Ra  42 + X so X has to be 22286X α decay of Ra-226: mass number decreases by 4 atomic number decreases by 2

So how do you know if an element is radioactive or not?   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 the key is the proton to neutron ratio