G485 - Nuclear Physics Flashcards
Describe Rutherford’s alpha particle scattering experiment
A beam of alpha particles (helium nuclei) was directed at a thin sheet of gold leaf
The leaf was surrounded by a ring of detectors to pick up where the alpha particles went after passing through the gold leaf
What were the observations from Rutherford’s alpha particle scattering experiment?
Most alpha particles passed straight through the gold leaf with little or no deflection
A few alpha particles were deflected through large angles
What conclusions can be drawn from Rutherford’s alpha particle scattering experiment?
Atoms are mostly empty space
Mass is concentrated at a single point, the nucleus
The nucleus is positively charged as it repelled the positively charged alpha particles
Nucleus Diameter
10^-15
Atom Diameter
10^-10
Relative mass of a neutron
1
Relative mass of a proton
1
Relative mass of an electron
1/1840
Nucleon / Mass Number Definition
The number of nucleons in the nucleus
Proton / Atomic Number Definition
The number of protons in the nucleus
Isotope Definition
Different form of the same element containing the same number of protons in the nucleus but a different number of neutrons
What quantities are conserved in nuclear decay?
charge momentum lepton number baryon number mass / energy spin
List the four forces in the universe from strongest to weakest
Strong Nuclear Force
Electromagnetic Force
Weak Nuclear Force
Gravitational Force
Properties of the Strong Nuclear Force
Short ranging
Attractive at longer distances
Repulsive at very short distances
Acts on quarks
Properties of the Electromagnetic Force
Only acts between objects with charge Attractive between opposite charges Repulsive between like charges Long ranging Obeys the inverse square law
Properties of the Weak Nuclear Force
Can effect any particle
Governs nuclear decay
Properties of the Gravitational Force
Acts between objects with mass
Always attractive
Long ranging
Obeys the inverse square law
Fundamental Particle Definition
A particle which cannot be broken down any further
What is the exchange particle for the Strong Nuclear Force?
gluon
What is the exchange particle for the Electromagnetic Force?
photon
What is the exchange particle for the Weak Nuclear Force?
W and Z bosons
What is the exchange particle for the Gravitational Force?
graviton
Hadron Definition
a particle which is made up of quarks
Baryon Definition
a hadron which is made up of three quarks
Meson Definition
a hadron which is made up of a quark and an anitquark
Lepton Definition
fundamental particles which are not effected by the strong nuclear force
Examples of Mesons
pion
kaon
Examples of Baryons
proton neutron lambda sigma omega
Examples of Leptons
electron
muon
tau
neutrino
Antimatter Defintion
the opposite of matter in every way
What happens when a particle collides with its antiparticle?
They annihilate
The equivalent of their mass is released as two photons in opposite directions
What is a β- particle?
electron
What is a β+ particle?
positron
Beta Minus Decay
neutron -> proton + electron + antielectronneutrino
ExchangeParticle = W- Boson
Beta Plus Decay
proton -> neutron + positron + electronneutrino
ExchangeParticle = W+ Boson
Alpha Decay
(X,Y)^A -> (X-4,Y-2)B + (4,2)He
Gamma Decay
(X,Y)A -> (X,Y)A + gammaphoton
What is the quark composition of a proton?
uud
What is the quark composition of a neutron?
udd
What are the 6 types of quark?
up down strange top bottom charm
Binding Energy Definition
minimum energy required to separate all of the nucleons in a nucleus
Binding Energy per Nucleon Definition
energy required to remove a nucleon from the nucleus of an atom
Mass Defect Definition
during nuclear decay the mass of particles before the decay is always greater than the total mass after the decay, the difference in mass is the mass defect and is equivalent to the energy released in the decay, E=mc²
What is the most stable nucleus?
Iron, has the greatest binding energy per nucleon
Nuclei smaller than iron fuse to make iron which releases energy
Elements larger than iron fission to release energy
Describe Nuclear Fission
U-235 nucleus absorbs a slow moving neutron
The new nucleus is very unstable, it decays to form two daughter nuclei which are roughly equal in size
Three neutrons are also released as well as energy
Describe how a chain reaction can start
When an unstable nucleus decays it releases three neutrons which can go on to cause a further three nuclei to decay and release another three neutrons each
Reaction rate will increase exponentially if uncontrolled
Describe the role of fuel rods in a nuclear reactor
Contain unstable nuclei which will decay when bombarded with slow moving neutrons
Spontaneous Fission
some radioactive isotopes contain nuclei that are highly unstable
at some point they will naturally decay
Induced Fission
fisson can be induced by bombarding atoms with neutroms
Describe the role of control rods in a nuclear reactor
Control rods can be lowered to absorb neutrons and slow down the rate of the chain reaction
Control rods can be raised so that more neutrons can collide with nuclei and cause decay to increase the reaction rate
Describe the role of the moderator in a nuclear reactor
the moderator (made of graphite) slows down neutrons so the they can be absorbed by the uranium nuclei
this process generates heat
coolant absorbs heat
Advantages of Nuclear Fission to Produce Energy
high energy yield
efficient
doesn’t produce greenhouse gases
Disadvantages of Nuclear Fission to Produce Energy
radioactive waste
nuclear meltdown
radiation
initially very expensive and expensive to decommission
Why is nuclear fusion possible inside stars?
Extremely high pressure and temperature
Radioactive Decay
spontaneous and random
it is impossible to predict when an individual nucleus will decay
Alpha Radiation
Nature
helium nucleus (2 protons, 2 neutrons)
Beta Radiation
Nature
electron
Gamma Radiation
Nature
electromagnetic radiation
Alpha Radiation
Range
short
Beta Radiation
Range
medium
Gamma Radiation
Range
long
Alpha Radiation
Penetration
absorbed by thin paper
Beta Radiation
Penetration
absorbed by a few mm of aluminium
Gamma Radiation
Penetration
absorbed by a few cm of lead
Activity Definition
A, the number of radioactive decays per unit time (Bq)
Decay Constant Definition
λ, the probability that an individual nucleus will decay n a unit time (s^-1)
Half Life Definition
the time taken for the number of radioactive nuclei to decrease by half
Radiocarbon Dating
Living things take in carbon, after death this stops, carbon-14 in the organism decays to carbon-12
The ratio of carbon-14 to carbon-12 in the sample can be determined
Compared with the ratio of carbon-14 to carbon-12 in a loving organism
Age of sample found using X = X0e^(-λt)
