Particles and Radiation (1): Matter and Radiation Flashcards
What does the term nucleon refer to?
A proton or neutron in the nucleus
What is the charge of an electron?
- 1.6 x 10^-19
What is the charge of a proton?
+ 1.6 x 10^-19
What is the mass of a free proton?
1.673 x 10^-27
What is the mass of a free neutron?
1.675 x 10^-27
What is the mass of an electron?
9.11 x 10^-31
What is the mass of a nucleon bound in a nucleus?
1.661 x 10^-27
An uncharged atom contains equal numbers of…
protons and electrons
What is the definition of an isotope?
An atom of an element with the same number of protons but a different number of neutrons
What is the proton number also known as?
atomic number (bottom number on the periodic table)
What letter is used to represent the proton number?
Z
What is the term nucleon number/ mass number referring to?
The total number of neutrons and protons in an atom/ mass of the atom in relative units (the top number on the periodic table)
What does the term nuclide mean?
The type of nucleus that you are referring to
What letter is used to represent the nucleon/mass number?
A
How are nuclides labelled?
Using isotope notation e.g 12/6 C for carbon - 12
What is the definition of the specific charge of a charged particle?
Its charge divided by its mass
What are the units of specific charge?
Ckg^-1
Which particle has the highest specific charge?
the electron
What is the definition of a stable isotope?
One that will not undergo radioactive decay
What are the two types of force that act between nucleons in the nucleus?
- The strong nuclear force
- Electrostatic forces of repulsion
Which subatomic particles does the strong nuclear force act between?
neutrons and protons
Which subatomic particles does the electrostatic forces of repulsion act between? Why?
protons - as they are positively charged
What is the range of the strong nuclear force?
3-4 fm (femtometres, 10^-15)
What is the range of the electrostatic force of repulsion?
Infinite
How does the intensity of the electrostatic forces of repulsion fall off with distance?
The intensity falls off following the inverse square law, 1/d^2
At what value does the strong nuclear force become repulsive?
Values < 0.5 fm
Why does a -ve force mean attraction?
This is because 0 potential energy is at the infinity point, therefore, attraction means the objects are pulled together so their potential is more negative.
Why does a positive force mean repulsion?
This is because 0 potential energy is at the infinity point, therefore, the objects are moving closer to that infinity point so their potential is getting more positive.
What is an alpha particle?
A helium nucleus
When is an alpha particle emitted?
When the nucleus has too many protons, but it chucks out neutrons at the same time
What is a beta particle?
A high speed electron/positron
When is a beta(-) particle emitted?
When the nucleus has too many neutrons - a neutron is turned into a proton and electron (+ antineutrino)
When is a beta(+) particle emitted?
When the nucleus has too many protons - a proton is turned into a neutron and positron (+ neutrino)
What is gamma radiation?
EM radiation
When is gamma radiation emitted?
By an unstable nucleus with too much energy that has already emitted an alpha or beta particle
In a vacuum what is the speed of an EM wave?
3.00 x 10^8 ms^-1
What is the equation for the wavelength of EM waves?
(lambda) = c/f
What are the 7 types of EM waves in order and their wavelength ranges?
RADIO WAVES
>0.1m
MICROWAVE
0.1m -> 1mm
INFRARED RADIATION
1mm -> 700nm
VISIBLE LIGHT
700nm -> 400nm
UV RADIATION
400nm -> 1nm
X-RAYS
10nm -> 0.001nm
GAMMA RAYS
<1nm
What are EM waves emitted by?
Charged particles when they lose energy
When are EM waves emitted?
- When a fast moving electron is stopped, slowed down or had its direction changed
- When an electron in a shell of an atom moves to a different shell of a lower energy
What is the definition of a photon?
A photon is a quantised/discrete packet of EM waves
What is the definition of the Photoelectric Effect?
The emission of photoelectrons from the surface of a metal when light is shone on it
What is the equation for the energy of a photon?
E = hf
What is the value of Planks Constant?
6.63 x 10^-23 Js
What is the equation for the power of a laser beam?
Power/energy per second of the beam = nhf
n - the number of photons in the beam passing a fixed point each second
What happens when matter and antimatter meet?
EM radiation is released
What are three characteristics of antiparticles?
- They annihilate the particle and itself if they meet, converting their total mass into photons
- has exactly the same rest mass as the particle
- has exactly opposite charge to the particle if it has charge
What did Einstein prove with his equation E = mc^2
That when a particle is stationary, its rest mass, m0, corresponds to its rest energy m0c^2 locked up as mass.
What did Dirac predict?
The existence of antiparticles which would unlock their rest energies
What is annihilation?
When a particle and antiparticle pair annihilate to produce two photons that are expelled outwards with equal energy and on opposite directions to conserve momentum.
What is pair production?
When 1 photon interacts with a large mass/ catalyst particle e.g an atomic nucleus a particle-antiparticle pair will be produced. The nucleus absorbs the kickback that the photon experiences so that momentum is conserved.
What is the definition of 1 eV?
The energy transferred when an electron is accelerated across a potential difference of 1 V
How do you convert from eV to J?
E = QV
V - eV
Q - charge on the electron
What is the equation that links the energy of the photons with the energies of the particle-antiparticle pair in annihilation?
2hf = 2mc^2
What is the equation that links the minimum energy of the photons with the rest energies of the particle-antiparticle pair in annihilation?
2hf (min) = 2E0
E0 - Rest energy of the particle/antiparticle
What is the equation that links the minimum energy of the photon with the rest energies of the particle-antiparticle pair in pair production?
hf (min) = 2E0
E0 - Rest energy of the particle/antiparticle
What is the definition of a Boson/exchange particle?
The undetected particles that carry momentum and energy between the particles experiencing the force
NB: each fundamental force has its own exchange particle
What is the boson that mediates the strong nuclear force interactions?
Gluon
What is the boson that mediates the weak nuclear force interactions?
W+/- or Z+
What is the boson that mediates the electromagnetic force between two charged particles ?
virtual photon
Where does the weak nuclear force interact? Between what?
Acts in the nucleus between all particles, specifically leptons e.g electrons, neutrinos etc. and uncharged particles
NB: the force can attract or repel
Which force is responsible for radioactive decay?
Weak nuclear force
When does electron capture occur?
When a nucleus is proton rich
Describe the process of electron capture?
There is a small, but still possible, probability that an electron in the lowest energy level can be found inside the nucleus. If this happens a proton turns into a neutron as a result of a weak interaction with this electron. The W+ boson mediates this interaction and a neutron an electron neutrino is produced.
What are the rules when drawing Feynman diagrams?
- Straight line - represents a particle
- Squiggly line - represents bosons
- The charge, and all other quantum numbers, must be conserved at each junction
- Attraction and repulsion is visually the same on a Feynman diagram it is only the particles that are different
- Time progresses upwards
- The direction of lines does not show the direction of the particles
What is a life application of annihilation? Explain?
PET scanners - A positron emitting isotope is injected into the blood stream and some of it reaches the brain. The positrons travel a few mm at most before they are annihilated by an electron producing two gamma photons as a result. The detectors connected to computers outside the body sense the photons emitted and are, therefore, able to build up an image from the signals of the brain.
Write the decay equation for electron capture
p + e- (W+) -> n + electron neutrino
Describe the Feynman diagram for an electron-proton interaction?
Same as for electron capture except a W- boson mediates the interaction which goes from the electron to the proton
Write the equation for an electron-proton interaction
p + e- (W-) -> n + electron neutrino
