Particles and radiation Flashcards
Explain why an atom has no overall charge
An atom has an equal number of protons and electrons which have equal and opposite charges that cancel out, so since neutrons have no charge anyway the overall charge must be zero
What is meant by the term isotope?
A different form of the same element that has the same number of protons but a different number of neutrons so the same atomic number but different mass number
What is isotopic data?
The relative amounts of different isotopes present in a substance
Give a use of isotopic data
Carbon dating (this is done by calculating the percentage of radioactive C-14 left in an object to calculate its approximate age)
Explain why the nucleon numbers on the periodic table are not whole numbers
Because it represents the average nucleon number of all of the isotopes of that element
Describe how a positive ion is formed
When an atom looses one or more electrons
Describe how a negative ion is formed
When an atom gains one or more electrons
What is meant by specific charge?
The ratio of a particles electric charge to its mass
What is a nucleon?
A particle found in the nucleus (protons and neutrons are nucleons)
Describe the range of the strong nuclear force
It is repulsive at very short ranges between 0 fm and 0.5 fm to prevent the nucleus from collapsing in on itself and then it becomes attractive between 0.5 fm and 3 fm and within this range it reaches a maximum value of attraction and then at around 3 fm the size of attraction rapidly falls to zero and the force no longer has an effect
What is the range of the electromagnetic force?
Infinite
What is the importance of the strong nuclear force?
The electromagnetic force causes the positively charged protons to repel eachother in the nucleus and the gravitational force causes all of the nucleons to attract eachother due to their masses, however, the electromagnetic force of repulsion is much stronger than the gravitational attraction so there must be the strong nuclear force of attraction (that is stronger than the electromagnetic repulsion) to prevent the nucleus flying apart
Why does the graph of neutrons against protons curve upwards as the nucleus gets larger?
As the number of protons in a nucleus increases the electromagnetic force of repulsion gets stronger and so more neutrons are needed to maintain stability because adding more neutrons helps to increase the strong nuclear force without contributing to the electromagnetic repulsion
What is an alpha particle?
A Helium nucleus (He2+) meaning it has 2 protons and 2 neutrons
What happens during alpha decay?
A nucleus emits 2 protons and 2 neutrons (an alpha particle) in order to become more stable, this causes the nucleon number to fall by 4 and the proton number to fall by 2
What is a beta-minus particle?
A high speed, high energy electron
What happens during beta-minus decay?
A neutron in the nucleus turns into a proton and in the process a beta-minus particle and an anti-electron neutrino are emitted
What is a beta-plus particle?
A high speed, high energy positron
What happens during beta-plus decay?
A proton in the nucleus turns into a neutron and in the process a beta-plus particle and an electron neutrino are emitted
What was the problem that arose when observing beta decays and how was this solved?
The energy before the decay was not the same as the energy after the decay which violates the law of energy conservation this meant that another particle must be being emitted during the decay but it just hadn’t been detected yet, until Pauli observed the neutrino being emitted
What can you deduce about the neutrino based on its emission in beta-decay?
It has a very tiny mass as it was difficult to detect and also it must have a neutral charge to ensure charge is conserved
What is a gamma ray?
An electromagnetic wave with a high frequency
What happens during gamma emission?
Excess energy is released from the nucleus as it de-excites
Compare a particle with its corresponding antiparticle
They have the same mass and rest energy but they have an equal but opposite charge to each other
How do you convert from Joules to electron volts?
Divide by the charge of the electron, e
What happens during annihilation?
A particle collides with its its corresponding antiparticle which causes both of their masses to get converted back into energy which is emitted in the form of two gamma ray photons
Why do the two gamma rays produced in annihilation move in opposite directions?
To conserve momentum
What happens during pair production?
A high energy photon can convert its energy into masses to produce a particle and its corresponding antiparticle (but only if it has enough energy to produce both masses)
Why must a photon have atleast a certain frequency for pair production to occur?
A certain amount of energy is required to produce the masses of both particles and so because the energy of a photon depends on its frequency (E=hf) it means a certain frequency is required
Why does pair production happen close to a nucleus?
To conserve momentum as the nucleus recoils with the same momentum as the momentum of the new particle and its antiparticle
What would happen if a photon has more energy than the minimum energy required to produce a particle and its antiparticle via pair production?
Any excess energy will be converted into kinetic energy so they will be able to move about a bit after they’re produced
Describe how a PET scanner works
A patient is injected with a radioactive tracer that undergoes beta-plus decay, this tracer travels to the tumour and when it decays it emits positrons. These positrons are annihilated when they meet with an electrons which causes gamma ray photons to be emitted, travelling in opposite directions making them easy to detect by a PET scanner which then rotates around the patient allowing an image of the inside of a patient to be formed
What does it mean for a particle to be fundamental?
It is not composed of any other smalller particles, they appear to have no inner structure and cannot be broken down into smaller pieces (they are the building blocks of matter)
What are leptons?
Fundamental particles that do not feel the strong nuclear force and mainly interact via the weak interaction
Give 4 examples of leptons
electrons, electron neutrinos, muons and muon neutrinos
What is the difference between an electron and a muon?
An electron is a stable lepton whereas a muon is like an electron but heavier and unstable (they eventually decay into electrons)
What is a hadron?
A class of particles that are made up of quarks and so experience the strong nuclear force
What is a baryon?
A type of hadron that contains 3 quarks (for example protons and neutrons)
What are the most stable baryons?
Protons (meaning all other baryons eventually decay into protons)
What is a mesons?
A type of hadron that contains 2 quarks, a quark and an antiquark pair (for example pions and kaons)
What is a pion?
The lightest type of meson and it is the exchange particle for the strong nuclear force
What is a kaon?
Heavier and more unstable mesons that pions, they have strangeness and a short lifetime (they eventually decay into pions)
How are strange particles produced?
Via the strong interaction
How do strange particle decay?
Via the weak interaction
When is strangeness conserved and when is it not conserved?
It is conserved in the strong interaction and not conserved in the weak interaction (strangeness can change by -1, 0 or +1 in the weak interaction)
Why are strange particles created in pairs?
Because they are created in the strong interaction meaning strangeness must be conserved, so a when they are created a strange and an anti-strange particle are produced together (so strangeness = 0)
What properties must be conserved in particle interactions?
Energy, momentum, charge, Baryon number, Lepton number (both electron lepton and muon lepton numbers) and strangness (in the strong interaction)
Why is it not possible to get a quark by itself?
Due to quark confinement, the idea that the energy needed to separate a quark from its particle is enough energy to produce an antiquark to go with the quark
Why does the progression particle physics rely on the collaborative efforts of scientist and engineers?
As validating new ideas requires large teams to peer review and verify research, experiments and observations and because particle accelerators are expensive to build and run so it requires funding from lots of skilled scientists and engineers across the world
Name the four fundamental forces and put them in order from weakest to strongest
Gravity, the weak nuclear force , electromagnetic force and the strong nuclear force
What are bosons?
They are a general term for exchange particles and they are fundamental particles
Describe how exchange particle transfer forces between other particles
The exchange particle carries the mometum from one particle to the other, so the particle that emits the exchange particle looses some of its momentum (causing it to recoil in the opposite direction) and the recieving particle gains momentum transferred by the exchange particle (causing them to move in the direction of the transferred momentum) This causes a change in momentum for both partices, leading to a force between them
Describe the link between the mass of an exchange particle and the range of the interaction
The greater the mass of the exchange particle the greater the range of the interaction
What are the exchange particles of the electromagnetic interaction?
Virtual photons
What are the exchange particles of the strong interaction?
Pions
What are the exchange particles of the weak interaction?
W+ and W- bosons
What happens during electron capture?
A proton-rich nucleus captures and electron from inside the atom so that it can react with the electron to form a neutron and a neutrino
What happens during an electron-proton collision?
An electron collides at high speed with a proton and they react to form a neutron and an electron neutrino
Draw Feynman diagrams for the following interactions:
1) The strong nuclear interaction
2) The electromagnetic interaction
3) Beta-minus decay
4) Beta-plus decay
5) Electron capture
6) Electron-proton collision
Look in booklet for answers
Describe in terms of quarks what happens during beta-minus decay
A down quark changes into an up quark
Describe in terms of quarks what happens during beta-plus decay
An up quark changes into a down quark
