Nuclear Physics Flashcards
Describe the relative charges and masses of the 3 particles in an atom.
Proton - relative charge of +1 - mass of 1 u
Neutron - relative charge of 0 - mass of 1 u
Electron - relative charge of -1 - mass of 1/1840 u
(u = 1.66x10 -27 kg)
Define atom.
Smallest part of matter that can take part in a chemical reaction.
Estimate diameter of an atom: 0.1 to 0.5 nm.
Charge of a proton: +1.6x10 -19 C or +1e where e is the elementary charge.
«Rest» mass of a proton = 1.67x10 -27 kg
What is u in nuclear physics?
u is the unified atomic mass.
u = 1.66x10 -27 kg
Define isotope.
Atoms of the same element(i.e. have the same proton number) but different numbers of neutrons.
Describe radioactive decay.
Any unstable isotope decays to give out radiation until a stable nuclide (daughter nuclide) is formed.
This radiation can be alpha, beta plus, beta minus or gamma-rays.
Describe gamma rays.
Electromagnetic wave
Photon of radiation -> packet of energy able to interact with matter.
Describe nuclear fission.
Large nucleus is broken into smaller nuclei, releasing energy
Eg. (235)(92) U + (1)(0) n -> (141)(56) Ba + (92)(36) Kr + 3(1)(0) n
Why are neutrons used in nuclear fission?
Protons would get repelled, however neutrons would not get repelled, thus being able to start the nuclear fission process.
Describe nuclear fusion.
Two smaller nuclei are joined to form one larger nucleus.
Eg. (2)(1) H + (3)(1) H -> (4)(2) He + (1)(0) n
What do nuclear reactions demonstrate?
Conservation of mass and energy
Mass and energy are interchangeable and we can use the equation: deltaE = deltamc2 where deltam is change in mass and deltaE is change in energy.
Describe ionisation.
Occurs when alpha and beta particles move through air.
It is the process of making things charged (ions), therefore the air is ionised as they move past.
Describe the penetration of alpha, beta and gamma rays.
Alpha is stopped by paper, beta passes through paper but is stopped by 10mm aluminium, gamma passes through both paper and 10mm aluminium and is only stopped by 10cm of lead.
Describe the Alpha Scattering Experiment.
Alpha particles are fired from a source onto a piece of thin gold foil.
A ZnS screen is placed around the gold foil.
Results:
The majority of the alpha particles passed straight through the foil with virtually no deflection.
A few, about 1 in 10000 alpha particles were deflected through angles greater than 90 degrees.
The alpha particles were deflected.
Conclusions:
Nucleus is positive, since alpha particles are deflected
Atom is made up of mostly empty space since most alpha particles passed with little to no deflection
Nucleus is very small compared with the size of the whole atom since the majority of the alpha particles pass undeflected.
Describe Alpha Decay.
(A)(Z) X -> (A-4)(Z-2) Y + (4)(2) He
X - unstable nuclide
Y - more stable nuclide
He - alpha particle
Examples:
(226)(88) Ra -> (222)(86) Rn + (4)(2) He
(222)(86) Rn -> (218)(84) Po + (4)(2) He
Describe Beta Minus Decay.
(1)(0) n -> (1)(+1) p + (0)(-1) B + (0)(0) VN
n - neutron
p - proton
B - Beta
VN - Antineutrino
(A)(Z) X -> (A)(Z+1) Y + (0)(-1) B
Example:
(218)(84) Po -> (218)(85) At + (0)(-1) B
Describe Beta Plus Decay.
(1)(1) p -> (1)(0) n + (0)(+1) B + (0)(0) V
p - proton
n - neutron
B - Beta
V - Neutrino
(A)(Z) X -> (A)(Z-1) Y + (0)(+1) B
Example:
(218)(84) Po -> (218)(83) Bi + (0)(+1) B
(234)(90) Th -> (234)(89) Ac + (0)(+1) B
Describe Gamma Decay.
Gamma rays are not charged particles like alpha and beta particles.
Gamma rays are electromagnetic radiation with high frequency.
When atoms decay by emitting alpha and beta particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
This excess energy is emitted as gamma rays (gamma ray photons have energy of ~1x10 -12 J)
Define fundamental particle.
Cannot be split into anything smaller.
Describe leptons.
Eg. Beta plus, beta minus, antineutrino, neutrino
Have little to no mass
Fundamental particles
Describe hadrons.
Eg. p, n
Not fundamental as they are made up of three quarks
Define quark.
Small indivisible particle that can only exist in pairs or in groups of three, held by a force called the strong nuclear force (the strong force)
