Matter and radiation (topic 1) Flashcards
What two things does every atom contain?
- A positively charged nucleus made up of protons and neutrons
- Electrons surrounding the nucleus
Nucleon (definition)
Particles within the nucleus of an atom (protons and neutrons)
How are electrons held int he atom?
Electrostatic force between the negatively charged electrons and the positively charged nucleus
Relative mass of an electron
0.0005
In coulombs, how much charge is 1 relative charge?
1.6 x 10^-19
In kg, how much mass is 1 relative mass
1.67 x 10^-27
In kg, how much mass is 0.0005 relative mass?
9.11 x 10^-31
What is the proton number also called? (2)
The atomic number
Z
Isotope (definition)
Atoms of the same element with different numbers of neutrons
What is the total number of nucleons in a nucleus called? (3)
nucleon number
mass number
A
Where do the labels for atomic and mass number go when symbolising an isotope?
Z - bottom left
A - top left
Nuclide (definition)
Each type of nucleus for an element (i.e. each type of isotope’s nucleus)
Specific charge (definition)
Charge per unit mass of a charged particle (charge/mass)
Which particle has the largest specific charge?
Electron
What does the strong nuclear force do?
The force that overcomes the electrostatic repulsion between protons, holding them together with neutrons in the nucleus
How large is the range of the strong nuclear force?
3-4 fentometres, or around the same as the diameter of a small nucleus
What is the range of the electrostatic force between two particles
Infinite, though it decreases in magnitude as distance increases
How does the effect of the strong nuclear force differ between proton/proton, neutron/neutron, and proton/neutron interactions?
It doesn’t. It has the same effect on all of those interactions.
What happens when the strong nuclear force has a very small range? From what range does this happen?
For ranges smaller than 0.5fm, it becomes repulsive, preventing neutrons and protons from colliding
What effect does the strong nuclear force have for distances between 0.5-4fm?
It is an attractive force, pulling protons and neutrons together.
What is an alpha particle?
Two protons and two neutrons
How is a beta (-) particle created?
A neutron changes into a proton in the nucleus
What is the symbol for a new element due to radiation?
Y
What is a beta particle?
A fast moving electron
What, apart from an electron, is released during beta (-) decay?
An anti-neutrino
What is gamma radiation?
Electromagnetic radiation with no mass and no charge
What special property makes gamma radiation useful?
It can pass through thick metal plates and metres of concrete
When is gamma radiation released?
When a nucleus has too much energy due to alpha or beta emission
What is the speed of electromagnetic waves (in a vacuum)? What is the symbol for it?
c = 3.00 x 10^8
What is an electromagnetic wave?
An electric wave and a magnetic wave, travelling together
What are the three fundamental qualities of an electromagnetic wave?
The electric and magnetic wave are travelling at right angles to each other AND in phase with each other
the wave is transverse
When are electromagnetic waves emitted by a charged particle? (2)
- when a fast-moving electron is stopped/slows down/changes direction
- when an electron in a shell moves to a different shell of lower energy
What is a photon?
A “packet” (short burst) of electromagnetic waves which are emitted from the source in a random direction.
How was photon theory established?
Einstein used the theory to explain the photoelectric effect
What is the photoelectric effect?
emission of electrons from a metal surface when light is directed at the surface
How is the energy of a photon related to it’s frequency?
Directly proportional: E = hf
(h is Planck’s constant)
What is the Planck constant?
6.63 x 10^-34 Js
What should always be checked if you’re stuck on a calculation with wavespeed needed?
The wave may be electromagnetic - c = 3 x 10^8
What is a laser beam?
Photons of the same frequency moving in the same direction
What is the power of a laser beam?
energy transferred per second by photons
In the equation power = nhf, what is n?
Number of photons passing a fixed point per second
What happens when antimatter and matter particles meet?
Annihilation - their mass is converted into radiation energy and released as two photons travelling in different directions
How does a PET scanner work? (4)
- A positron-emitting isotope is administered to the patient.
- Some reaches the brain and annihilates with the electrons within them, releasing two gamma photons which are sensed by detectors.
- The calculation to find where the annihilation was by using the time difference between where gamma photons were detected.
- Using these positions, an image of where matter is in the brain can be built up
What does PET stand for?
positron emission tomography
How does positron emission happen? What is this called?
Beta(+) decay - a proton turns into a neutron, releasing a positron and a neutrino
How are positron-emitting isotopes created? Where does this happen?
A stable isotope is placed in the a path of a beam of protons. Some of the nuclei in the substance absorb extra protons and become unstable positron-emitters. This does not happen naturally, only in manmade conditions.
How was antimatter predicted by Dirac?
Einstein showed that a particle’s rest mass (mass when stationary) was the rest energy that it had locked up as mass. Dirac then predicted “antiparticles” that could unlock rest energy through annihilation.
What is Dirac’s theory of antiparticles? (3)
Prediction that for every type of particle there is a corresponding anti-particle that:
- annihilates the particle and itself if they meet, converting total mass into photons
- has exactly the same rest mass as the particle, but opposite charge
What is an electron volt?
energy transferred when an electron is moved through a potential difference of 1 volt
What is the value of 1 MeV?
1.60 x 10^-13 J
Why are there always two photons produced in annihilation?
They conserve momentum by travelling in different directions
How do you find the (minimum) energy of a photon created in annihilation?
hf (min) = E(0)
(minimum energy of photon) = (rest energy of particle)
What is pair production?
A photon creates a particle and corresponding antiparticle
What are the requirements for pair production?
The photon must be travelling at enough speed (i.e. have enough energy) and will be passing near a nucleus or electron
How do you find the minimum energy (and frequency) needed for a photon to undergo pair production?
hf(min) = 2 E(0)
What does a force do?
Changes the momentum of the object it acts upon
How is momentum calculated?
mass x velocity
What happens when two objects interact?
They exert equal and opposite forces on each other and transfer momentum between each other.
How do protons interact with each other as they approach?
There is an electromagnetic force between them due to the exchange of virtual photons, which causes them to repel each other
Why are the photons exchanged in electromagnetic interactions called “virtual photons”?
They cannot be detected directly. If we intercept them, we stop the force acting.
How does transferring a virtual photon lead to repulsion between two charged objects?
The particle releasing the virtual photon experiences a force in the opposite direction to photon travel, as momentum is conserved. The particle receiving the photon receives the transferred momentum going in the same direction as its travel.
How does transferring a virtual photon lead to attraction between two charged particles?
The particle releasing the virtual photon throws it “away”, creating momentum towards the other particle. The particle that receives the virtual photon from the other side (imagine the virtual photon moving like a boomerang) then gains momentum in the same direction, towards the first particle.
How do we know that beta- and beta+ decay are NOT due to electromagnetic interaction OR strong nuclear reaction? (2)
- It can’t be strong nuclear as the force only affects the position of nucleons, not their charge
- It can’t be electromagnetic as neutrons are uncharged and would not be affected
Why is the weak nuclear force “weak”?
We know it must be weaker than the strong nuclear force because it does not affect stable nuclei
How can neutrinos/antineutrinos interact? (2)
- neutrinos make neutrons change into protons
- antineutrinos make protons change into neutrons
Both of these happen via the weak nuclear force (W boson transfer)
What particle is responsible for interaction via the weak nuclear force?
W bosons
What are the characteristics of W bosons (3)
- have a non-zero rest mass
- very short range
- positive or negative charge
What is the range of a W boson?
0.001fm
What happens in a neutron-neutrino interaction?
A W- boson is transferred neutron > neutrino, transferring -1 charge. The neutron becomes a proton (has +1 charge), and the neutrino becomes a beta- particle/electron (-1 charge).
How is an antineutrino-antineutron interaction different to a neutron-neutrino interaction?
Complete opposite charges e.g. a W+ boson is used instead of a W-
What happens when a W- boson (released from neutron/proton) does NOT meet a neutrino/antineutrino?
The W- boson decays into a beta(-) particle and an antineutrino
(opposite is true for W+)
What is electron capture?
A proton in a proton-rich nucleus turns into a neutron (+ neutrino created from electron) through weak nuclear interaction with an inner-shell electron
What happens when a proton and an electron collide at high speeds? (2)
Electron capture
If the electron is moving fast enough, a W- interaction from electron > proton could also cause change
What are the force-carriers of the four fundamental forces?
Strong nuclear - pion
Weak nuclear - W boson
Electromagnetic - photon
Gravity - graviton (theoretical)
