Nuclear physics Flashcards
(46 cards)
Nuclear decay is said to be random and spontaneous. What is meant by random?
Random: you cannot identify which nucleus will decay next/ when an individual nucleus will decay
Nuclear decay is said to be random and spontaneous. What is meant by spontaneous?
Spontaneous: decay cannot be influenced by any external factors
What is meant by ionising radiation?
Ionising radiation removes electrons from atoms/ molecules
What is an alpha particle, its mass and its charge?
Helium nucleus
Mass 4u
Charge +2
What is the ionising ability, speed and penetration power of alpha particles?
Strong ionising ability
Slow
Not very penetrating- absorbed/ stopped by paper or a few cms of air
When a nucleus is unstable, it will break down to become more stable. Explain why an alpha particle is emitted and what happens to the proton number and nucleon number?
Too many nucleons in total / nucleus too heavy
The proton number decreases by 2 and the nucleon number decreases by 4
Why aren’t alpha particles very penetrating?
Alpha particles are strongly positive so can easily pull electrons off atoms/ are strongly ionising
When an alpha particle ionises an atom it transfers some of its energy to the atom
Alpha particles quickly ionise lots of atoms and lose all their energy quickly so can’t travel very far/ have a low penetrating power
What is a beta-minus particle, its mass and its charge?
Electron, negligible mass, -1
What is a beta-plus particle, its mass and its charge?
Positron, negligible mass, +1
State ionising ability, speed and penetration power of beta-minus particles.
Weak/ moderate ionising ability
Fast
Moderately penetrating- absorbed/ stopped a few mm of aluminium
When a nucleus is unstable, it will break down to become more stable. Explain why a beta- minus particles is emitted, what happens when it is emitted and what happens to the proton number and nucleon number.
Emitted due to nucleus being neutron-rich/ has too many neutrons
One of the neutrons in the nucleus decays into a proton and ejects a beta-minus particle/ electron and an electron antineutrino
Proton number increases by one and nucleon number stays the same
Explain why a beta-plus particle is emitted, what happens when it is emitted and what happens to the proton number and the nucleon number.
Emitted due to the nucleus having two few neutrons
One of the protons in the nucleus changes into a neutron and releases a beta-plus particle/ positron and an electron neutrino
Proton number decreases by one and nucleon number stays the same
Explain why beta-minus particles are more penetrating than alpha particles.
Beta-minus particles are moderately ionising because they travel at high speed
They are less ionising than alpha particles because they have a lower mass
This means they lose less energy so can travel further and are more penetrating
State why beta-plus particles have virtually zero range.
After being produced they are almost immediately annihilated by an electron
State what gamma radiation is, its mass and its charge.
Short-wavelength, high frequency electromagnetic wave/ photon.
0
0
State ionising ability, speed and penetration power of gamma radiation.
Very weak ionising ability
Speed of light
Very penetrating- absorbed/ stopped by many cm of lead/ several m of concrete
When a nucleus is unstable, it will break down to become more stable. Explain why a gamma ray is emitted and how gamma emission affects the nuclear equation.
Nucleus is excited/ has excess energy
This energy is lost by emitting a gamma ray
Nuclear equation is unchanged because there is no change to the nuclear constituents- the nucleus just loses excess energy
Explain why gamma radiation is very penetrating.
Gamma radiation isn’t/ is very weakly ionising
Because it has no charge or mass/ it is photons of light
This means it loses barely any energy when travelling so can travel very far and is very penetrating
State why and how readings from a Geiger counter must be corrected when you take readings from a radioactive source.
Because you have to subtract the background count rate from each reading to get the actual radiation count for the source.
Measure the background radiation in absence of the source
State the 3 things conserved in nuclear equations and the 2 things conserved in nuclear reactions.
Nuclear equations: charge, nucleon number and electron lepton number
Nuclear reactions: energy and momentum
State the other type of radiation and why it would not be detected by a film badge that relies on ionisation.
Neutron emission
Uncharged particles are not ionising so would not be detected
State what is meant by the activity of a radioactive source.
Rate of decay of unstable nuclei/ the number of nuclei that decay per second/ per unit of time
Explain why it is necessary to repeat the radioactive count when taking readings.
So you can take an average as nuclear decay is random so fixed count for a period will vary
State why external exposure to gamma radiation is dangerous.
Gamma rays will pass through skin because they are very penetrating
Gamma rays can damage healthy cells/ DNA