Particles and Radiation Flashcards
What is a nucleon?
A particle in the nucleus (protons and neutrons)
What is the relative mass of an electron?
1/1840
What is the proton number?
Number of protons in the nucleus
What defines what an element is?
The number of protons
What do an element’s reactions and chemical behaviour depend on?
Number and arrangement of electrons
What is the mass number?
Number of protons and neutrons in the nucleus
In physics, what does ‘specific’ mean?
Per unit mass
What is the specific charge of a particle?
The ratio of its charge to its mass
What is the SI units of specific charge?
C kg^-1
What is the equation for specific charge?
Specific charge = Charge / Mass
What is a fundamental particle?
A particle that cannot be split up into anything smaller, such an electron
What is an isotope?
An atom of an element with the same number of protons, but a different number of neutrons
What does changing the number of neutrons of an atom affect?
The stability of the nucleus
In general, the greater the number of neutrons compared with the number of protons…?
The more unstable the nucleus is
What do unstable nuclei do?
Decay to make themselves more stable
What isotopic data?
The relative amounts of isotopes in a substance
What is the electromagnetic force?
A fundamental force that causes interactions between charged particles
What does the electromagnetic force cause in the nucleus?
The positively charged protons to repel each other
What does the gravitational force in the nucleus cause?
All the nucleons in the nucleus to attract each other due to their mass
Which is a bigger force in the nucleus, the repulsion from the electromagnetic force or attraction from the gravitational force?
The repulsion from the electromagnetic force
What is the strong nuclear force?
A fundamental force with a short range which is attractive at short separations, but repulsive at very small separations
What is the strong nuclear force responsible for?
The stability of the atom
What are interactions that use the strong nuclear force called?
Strong interactions
What separation of nucleons is the strong nuclear force repulsive for?
Less than 0.5 fm (5x10^-16 m)
Describe the strong nuclear force once the nucleon separation has increased past 0.5 fm?
The strong nuclear force becomes attractive, reaching a maximum attractive value, the falling rapidly to zero after about 3 fm (3x10^-15)
What is nuclear decay?
When unstable nuclei will emit particles to become more stable
What is an alpha particle?
The nucleus of a helium atom
Alpha decay can only happen in…?
Very large atoms with more than 82 protons
Why are very large atoms, such as uranium, very unstable?
Because they’re so big that the strong nuclear charge can’t keep them stable
How do very large atoms become more stable?
They release an alpha particle from their nucleus
What happens to the proton number when an alpha particle is released from the nucleus?
The proton number decreases by 2
What happens to the mass number when an alpha particle is released from the nucleus?
The mass number decreases by 4
Describe the range of an alpha particle in air
Only a few cm
What does a Geiger Counter do?
Measure the amount of ionising radiation
How does a Geiger counter work?
The counter consists of a tube filled with an inert gas that becomes conductive of electricity when it is impacted by a high-energy particle. When a Geiger counter is exposed to ionizing radiation, the particles penetrate the tube and collide with the gas, releasing more electrons
What is beta-minus decay?
The emission of an electron from the nucleus along with an antineutrino particle
What does beta decay normally occur with?
Isotopes that are ‘neutron rich’ (have to many neutrons compared to protons)
What happens when the nucleus ejects a beta particle?
One of the neutrons in the nucleus turns into a proton
Which has a greater range, alpha or beta particles?
Beta particles can travel a few metres in air
What is the evidence that the electron wasn’t the only particle to be emitted in beta-minus decay?
The energy of the particles before the beta decay was less than the energy before, which goes against the principle of the conservation of energy
What did Wolfgang Pauli suggest about beta decay in 1930?
That another particle was being emitted that carried away the missing energy
What would have to be 2 characteristics of the other particle that Pauli suggested was emitted in beta decay?
Neutral (or charge won’t be conserved)
Almost zero mass (as it had never been detected)
What is the other particle that is emitted in beta decay called?
Electron Antineutrino ( ̅νe)
What is the electromagnetic (EM) spectrum?
A continuous spectrum of all the possible frequencies of EM radiation
What are the 7 different types of EM radiation (in order of increasing wavelength)
Gamma X-Ray UV Visible Light Infrared Microwave Radio
Which has a bigger wavelength, gamma rays or radio waves?
Radio waves
Which has a bigger frequency, UV or visible light?
UV
Which has a bigger frequency, gamma rays or radio waves?
Gamma rays
The higher the frequency of the EM radiation, the…?
Greater its energy
What are photons?
Packets of EM radiation
How suggested that EM waves only existed in discrete packets called photons?
Einstein
What is the equation for the energy of a photon (in J)?
E = hf
In the equation for the energy of a photo, what does the h mean?
Planck’s constant (6.63x10^-34 Js)
In the equation for the energy of a photo, what does the f mean?
Frequency of light, Hz
What equation links the energy of a photon, Planck’s constant, wavelength and speed of light in a vacuum?
E = (hc) / λ
What is an antiparticle?
A particle with the same rest mass and energy as its corresponding particle, but an equal and opposite charge
What is an antiproton?
A negatively charged particle with the same mass as a proton
What is matter?
Name given to all particles
What is antimatter?
Name given to all antiparticles
What is pair production?
A process of converting energy to mass in which a gamma ray photon has enough energy to produce a particle-antiparticle pair
What do you get when energy is converted into mass?
Equal amounts of matter and antimatter
Pair production can only happen if there is enough of what?
If there is enough energy to produce the masses of the particles
Why do you need a large amount of energy to fire 2 protons at each other to make them collide?
Because they’re both positively charged, so they repel each other
If a photon has enough energy, what can be produced from 2 photons being fired into each other?
An electron-positron pair
When does an electron-positron pair most commonly get produced?
When a photon passes near a nucleus
What is the minimum amount of energy needed for pair production?
The total of the rest energy of the particles that are produced
What is rest energy?
The amount of energy that would be produced if all the particle’s mass was converted to energy
What is the minimum amount of energy need for pair production equal to?
2 x rest energy of particle (Emin = 2Eo)
How do you convert MeV to J?
Multiply by 1.60 x10^-13
Why do you normally get electron-positron pairs produced, rather than any other pair?
Because they have a relatively low mass, so less energy is need for pair production to happen
What is it called when a particle meets its antiparticle?
Annihilation
What is annihilation?
The process when a particle and antiparticle meet and their mass gets converted to energy in the form of a pair of gamma ray photons