Chapter 24, 25, 26 - Particle, Nuclear, Radioactivity Flashcards
JJ Thompson’s Atomic Model
The Plum Pudding Model
Atoms were uniform spheres of positive charge with tiny electrons embedded within.
Rutherford’s Gold Foil Experiment
Alpha Particles were fired at a thin gold foil sheet in a vacuum.
· Most ⍺ particles passed through the foil undeflected, so most of the atom was empty space.
· Some ⍺ particles were partially deflected by the foil, there is a positively charged nucleus.
· Occasionally ⍺ particles were fully deflected, only possible if the alpha particle interacted with another positive charge.
Rutherford deduced that the atom was mainly empty space with a dense nucleus were the majority of the mass was concentrated, but there was also a cloud of negative charge around the nucleus. Creating the Planetary Model.
Isotope
An atom of the same element and number of protons but a different number of neutrons. Undergo the same chemical reactions but different nuclear reactions due to their stability.
Nucleon
A subatomic particle that resides in the nucleus of an atom, protons and neutrons.
Atomic Number
Total number of protons in an atom.
Mass Number / Nucleon Number
The Sum of the Number of Proton and Neutrons in the Nucleus.
What is Unified Atomic Mass
1u = 1.661x10⁻²⁷ kg
This is a twelfth of the mass of carbon 12.
Rough Estimates for the Radius of an Atom and Nucleus
Nucleus - x10⁻¹⁵
Atom - x10⁻¹⁰
Radius of a Nucleus
R = rₒA^⅓
rₒ is 1.2x10⁻¹⁵ m
A is the relative atomic mass
What are the Four Fundamental Forces?
· Gravitational Force - acts on all particles with mass, infinite range but weak.
· Electromagnetic Force - Infinite range and acts on charged particles.
· Weak Nuclear Force - Responsible for Beta decay, changes quark types over very small distances.
· Strong Nuclear Force - acts between all nucleons and quarks. Attractive force when between 0.5fm and 3fm but a repulsive force at any other distance.
Einstein’s Mass Energy Equation
ΔE = Δmc²
Binding Energy
Binding energy is the minimum energy required to break a nucleus into its constituent components.
Mass Defect
The difference between the mass of the constituent nucleons against the mass of the nucleus.
What is the Significance of Iron-56?
Iron-56 is the most stable isotope of an atom because it has the highest binding energy per nucleon.
Antimatter
· Every particle has a corresponding antiparticle, with equal mass and opposite charge.
· When these particles collide they annihilate each other.
Pair Production
A high energy photon spontaneously creates a matter-antimatter pair.
The photon must have an energy greater than the combined rest masses of the two particles.
Hadrons
Hadrons are made up of quarks.
Mesons are quark-antiquark pairs.
Baryons are groups of three quarks.
Types of Quarks
Up - u - +⅔
Down - d - -⅓
Strange - s - -⅓
And there corresponding anti quarks
Leptons
Fundamental Particle
Electrons, Positron
Neutrinos, Antineutrinos
Muons, Anti-muons
Radioactive Decay
Radioactive decay is the spontaneous breakdown of an atomic nucleus resulting in the release of energy and matter from the nucleus.
Half Life
This is the average time it takes for half the active isotopes in a radioactive sample to decay.
Types of Radiation
Alpha - Helium nuclei so mass of 4u and charge of 2+. Highest Ionising ability but the lowest penetrating power.
Beta - Electron or Positron. Medium ionising ability and penetrating power.
Gamma - EM radiation so no mass or charge. No ionising ability but high penetrating power.
Beta minus Decay
Weak nuclear force causes the transformation of quarks via beta emission. Neutron to a proton.
ⁿₖX → ₖ₊₁ⁿY + ⁰₋₁β + ṽ
Produces an electron and an antineutrino, to conserve lepton number.
Beta plus Decay
Weak nuclear force causes the transformation of quarks via beta emission. Neutron to a proton.
ⁿₖX → ₖ₋₁ⁿY + ⁰₁β + v
Produces a positron and a neutrino, to conserve lepton number.
Alpha Decay
Occurs in very unstable nuclei, the strong nuclear force isn’t great enough to overcome the electrostatic repulsion between protons in the nucleus.
ⁿₖX → ₖ₋₂ⁿ⁻⁴Y + ⁴₂⍺
Usually with nuclei with more than 82 protons.
Gamma Decay
A nucleus has surplus energy following alpha or beta emission, this energy is released in the form of a gamma photon.
Activity
Activity of a source is the rate at which nuclei decay measured in Becquerels (Bq).
A = λN
λ is the decay constant
N is the number of active nucleons
Decay Constant
The decay constant is the probability that an individual nucleus will decay per second.
λ = ln(2) / t
For very small time periods -Nλ = ΔN/Δt
Exponential Decay
N = N₀e^(-λt)
A = A₀e^(-λt)
Carbon dating
The ratio of C14 to C12 in an organism will match the atmospheric ratio, and will become unchanged when the organism dies. C-14 has a half life of 5700 so comparing the ratio of C12 to C14 of the dead tissue and then comparing this is atmospheric composition over time an estimation of the organisms death can be calculated.
Nuclear Fusion
Small nuclei are fused together to produce a larger nuclei and energy. For two nuclei to form the particles must overcome the electrostatic repulsion between them.
Nuclear Fission
Fission is the breaking apart of large nuclei into small nuclei and causing a reduction in the total binding energy, a mass defect, and energy to be released.
A thermal neutron (a neutron with a similar kinetic energy to the thermal energy of the reactor) is fired at a unstable U256 atom, causing it to split into two daughter atoms.
Nuclear Fission Reactor
Reaction takes place in a reaction core, which is insulated by a thermal coolant.
Fuel rods contain the fuel.
Control rods absorb excess thermal neutron preventing the reaction from increasing at an exponential rate.
Fuel rods and control have to be soaked in water to cool them and to absorb the radiation they produce. They are then buried deep in lead lined bunkers.
