NUCLEAR AND PARTICLE PHYSICS Flashcards
Nucleon number (Mass number)
Total number or protons and neutrons in an atom or nucleus.
Thermionic emission
When a metal is heated, electrons can gain enough energy to be released from the surface of a metal.
Rest mass energy
E= mc2 is the energy associated with an object’s mass. ‘Rest mass’ means the mass of the object when it is not travelling at relativistic speeds. At relativistic speeds, the mass of the particle increases, as does its particle lifetime.
Geiger Marsden experiment:
- Most of the alpha particles were undeflected–> the atom is mostly empty space – most alpha particles did not get near enough to matter to be deflected.
- A few alpha particles were deflected by small angles –> the charge is concentrated in the centre of the atom – most alpha particles did not get near enough to a sufficiently large charge to be affected.
- A very small proportion of alpha particles were deflected through more than 90 degrees –> The nucleus must contain a high mass in order to cause this deflection because the mass of the atom is concentrated in a very small space relative to the size of the atom.
Standard model
- All matter is made of two types of fundamental particles – quarks and leptons.
- Hadrons are particles made from quarks. These consist of baryons (3 quarks – eg. protons and neutrons ) and mesons (quark and antiquark – eg pions).
- Leptons are electrons, muons, taons and neutrinos. There are six quarks. Every particle has a corresponding antiparticle that has opposite charge, baryon number, lepton number and the same mass.
- The symmetry of the model predicted the top quark.
What happens to momentum in particle interactions?
In particle interactions, baryon number, lepton number, charge, mass-energy and momentum are all conserved.
Compare the properties of antiparticles to particles
- Same mass as the original particle.
- Opposite charge to the original particle.
- Opposite value of the baryon/lepton number and strangeness.
Name the antiparticle to the electron and write its symbol
The positron can be written as e^+ or e line on top or a beta plus particle.
Name the antiparticles to the proton and electron neutrino.
The antiparticle to the proton is the anti-proton. The antiparticle to the electron neutrino is the antielectron neutrino.
Describe what is meant by annihilation and explain why photons are produced when particle annihilate
Annihilation is when a particle meets an antiparticle and produces two photons. Two photons are formed as energy and momentum have to be conserved.
Define ‘rest mass’
The mass of a subatomic particle when it is stationary ‘at rest’.
Define ‘rest energy’
E=mc^2 where:
E= is the energy
m= the rest mass
c^2= speed of light squared
List all six examples of leptons and what is special about antiparticles, stating the charge.
- Electron (-1)
- Muon (-1)
- Tau (-1)
- Tau neutrino (0)
- Muon neutrino (0)
- Electron neutrino (0)
They all have their own antiparticles
State the lepton number of all leptons
1
State the lepton number of all anti-leptons
-1
Name the two types of hadrons
Baryons and mesons
Explain why baryons are not classed as fundamental particles
Fundamental particles are not composed of other particles baryons however are.
Name the only stable baryon
Proton
Explain what happens to the neutron when it is outside the nucleus and write an equation for this process, naming each symbol you write
Outside of the nucleus, a neutron has a half-life af about 13 minutes and decays to produce a proton, an electron and an electron neutrino.
Name five mesons and write their charge and their antiparticles
- pion + = +1
- pion 0 = 0
- kaon + = +1
- kaon 0 = 0
- eta = 0
For antiparticles see sheet
State what all hadrons are made from
All hadrons are made from quarks
State the number of quarks that baryons are made from
3 quarks
Describe what mesons are made from
A quark and anti-quark
What does it mean to say ‘quarks have not been observed in isolation’?
They have always been found within hadrons.
State the baryon number of a quark and antiquark
- quark: 1/3
2. anti-quark: -1/3
State the lepton number of a quark
zero
Explain why the baryon number of a baryon is 1
There is one baryon in a baryon so the number is 1.
Explain why the baryon number of a meson is 0
Baryons don’t consist of mesons so the baryon number is zero.
Explain the lepton number of a baryon. List the names of all 6 quarks
- up
- down
- strange
- charm
- top
- bottom
The lepton number of a baryon is zero as no lepton consists of baryons
Draw the summary of particle classification on paper
See particle physics notes
Draw the symbols for quarks and their antiquarks
See particle physics notes
Draw the symbols for mesons and their antiparticles
See particle physics notes
Draw the symbols for leptons and their antiparticles
See particle physics notes
Define binding energy
- The energy released when a nucleus is formed from its constituent nucleons.
- The energy required to split a nucleus into its constituent nucleons.
Explain why energy is required to split a nucleus up into its separate protons and neutrons
The protons and neutrons are held together by the strong nuclear force so it would require energy to split them.
Define binding energy per nucleon
The total binding energy/total number of nucleons
Explain why a high binding energy per nucleon would indicate a high degree of stability
A high binding energy means a lot of energy is required to break the nuclei apart.
Explain why energy is always given out in radioactive decay
The nucleus decays to form a more stable nucleus so energy is always given out.
Define mass defect
The mass defect of a nucleus is the difference between the mass of the nucleus and the mass of its nucleons.
State the equation for mass defect
Mass of nucleus- Mass of particles
Explain what is meant by a ‘chain reaction’
The neutrons produced from nuclear fission collide with other atoms causing them to also undergo fission hence the chain.
List the environmental hazards of nuclear reactors
- Radiocatve dust or gases can escape and be absorbed by humans/ animals via food, air, water.
- If the chain reaction is not controlled the reactor may act as a bomb.
List the environmental benefits of nuclear fission
- No gaseous products produced.
Describe the process of nuclear fusion
Two light nuclei combine to form one heavy nucleus and energy and neutrons are also produced.
List the potential benefits of nuclear fusion
- The raw materials can be obtained from seawater.
- Waste products are not radioactive.
- Uncontrolled chain reaction cannot develop.
What is radioactivity?
The spontaneous mission of an alpha or beta particle from the nucleus of an atom.
List the constituents, range and ionising properties of beta radiation
Constituents: Fast electrons
Range: up to a few meters in air ( can be stopped by a few mm of aluminum)
Ionising properties: less than alpha
List the constituents, range and ionising properties of alpha radiation
Constituents: helium nuclei ( 2 protons and 2 neutrons)
Range: 5cm in air ( cane be stopped by a thick sheet of paper)
Ionising properties: highly ionising
List the constituents, range and ionising properties of gamma radiation
Constituents: very high frequency/energy electromagnetic waves
Range: significantly reduced by several cm of lead or meters of concrete.
Ionising properties: very weak - much less than beta
Define the term nucleon
proton or neutron
Which part of the nucleus is involved in radioactivity?
unknown
Define the term isotope
Isotopes of an element have the same proton number but different nucleon numbers.
State what is meant by the nucleon number
The mass number ( number of protons and neutrons)
State what is meant by the atomic number
The proton number - it tells you the number of protons.
List four sources of background radiation
- rocks (e.g granite)
- radon gas ( formed from the ground)
- cosmic rays which come from space
- artificially produced radioisotopes
Describe the effect of alpha decay on the nucleus.
- Alpha decay removes 2 protons and 2 neutrons from the nucleus.
- So Z, the proton number, decreases by 2, 3. A the nucleon number decreases by 4.
Describe the effect of beta decay on the nucleus
- In beta decay, a neutron in the nucleus emits an electron and changes to a proton.
- So Z increases by 1 and A stays the same
Describe the rules for the A and Z values.
A – the nucleon number (or mass number)
Z – the proton number (or atomic number)
Describe what is meant by a ‘radioactive decay series
in some cases, the atom produced is also radioactive so that will decay too until an atom that is not radioactive and doesn’t decay is produced.
Describe what is meant by the phrase ‘radioactive decay is a random process
You cannot predict whether an atom will decay or not
Define activity and state its unit
The number of decays per second of a sample is called its activity, and is measured in bequerels
Describe the effect of gamma radiation on the A and Z number
Gamma radiation only involves the emission of energy, and so does not change either A or Z.
Explain what is meant by the equation ‘A = lambda N’
The number of atoms decaying over a given period is proportional to the number remaining.
Where:
- A = activity,
- lambda = decay constant ( the probability of any given atom of that element decaying in one second)
- N = no. of undecayed atoms
State the key features of the exponential decay curve for activity
- Activity never decreases to zero
- There is a constant half life – for a given radioactive element, the time taken for the activity to halve will always be the same.
- The half-life in seconds is given by T½ = 0.69/lambda Where: lambda is the decay constant.
List the safety precautions when handling radioactive sources
- Always lift with forceps
- Hold so that the open end is directed away from the body
- Never bring close to the eyes
Define ‘corrected count rate’ and describe how it should be determined
- The corrected count rate is the count rate due to the source alone.
- It is determined by measuring and taking an average of the background radiation and subtracting it from all the readings to get the count rate from the source alone.
Describe the relationship between the intensity of gamma radiation and the distance from the source
Their intensity is inversely proportional to the square of the distance from the source .
I = K/d^2 where k is a constant.
Explain how radioactivity can be used to determine the age of wooden objects from antiquity. Describe an assumption made in the method.
By measuring the residual activity, it is possible
to estimate how many half-lives there have been since the plant died,
and how long ago it lived.
The assumption is that the proportion of carbon-14 in the atmosphere has stayed the same.
Describe what is meant by a radioactive tracer and why a gamma source would not be a suitable choice as a tracer.
Radioactive tracers are used to follow the path of a compound in a system e.g ( human body or pipelines).
For example, a radioactive tracer can
be used to detect a leak in a pipe, since the count-rate will increase
where the leak occurs as the pipe will block alpha and beta emissions.
A gamma emitter would not be suitable, since the pipe would not block this.
Explain how radioactive sources can be used in cancer treatment
Radiotherapy uses gamma sources to attack cancer cells as cancer cells are more affected by radiation than normal ones. Normal cells however are affected too.
