1.1 Flashcards
What is a nucleon
The number of protons + neutrons in the nucleus
Proton Number
The number of protons in the nucleus
Isotope
Isotopes are atoms with the same number of protons and different numbers of neutrons
How to display an element
A
X
Z
What does A stand for
Nucleon number (number of protons + neutrons)
What does Z stand for
Number of protons
What does X mean
Chemical symbol for element
Formula to calculate specific charge
Charge
________
Mass
Units for specific charge
CKg-1
How to calculate specific charge of a nucleus
Number of protons x charge of 1 proton
_________________________________________
Number of nucleons x mass
How to calculate specific charge of an ION
Net charge of ion
_________________________________
Number of nucleons x the mass
What is the strong nuclear force
The force that holds nucleons together
It overcomes the electrostatic force of repulsion between the protons
Points about the strong nuclear force
- max range = 3-4fm
- same effect between protons as it does between two neutrons/proton and a neutron
- attractive force from 3-4 to 0.5fm.
Why are some nuclei unstable
When the atoms of an element have extra neutrons or protons it creates extra energy in the nucleus and causes the atom to become unbalanced or unstable
Beta radiation equation
Make sure to note about the anti neutrino: __
V
Gamma radiation
Electromagnetic radiation emitted by an unstable nucleus
Electromagnetic waves consist of an electric wave and a magnetic wave which travel together and vibrate:
- at right angles to each other in the direction that they were travelling in
- in phase with each other (reach peaks and troughs at the same time)
When are electromagnetic waves emitted?
When a charged particle loses energy
What is a photon?
A particle representing a quantum (smallest divisible unit) of light or other electromagnetic radiation
When is electromagnetic waves emitted
- a fast moving electron is stopped or slows down or changes direction
- an electron in a shell of an atom moves to a different shell of lower energy
How to calculate photon energy
Photon energy E = hf
H = Planck’s constant
F = frequency
How to calculate wavelength
Wavelength = velocity/frequency
What is the value of Planck’s constant?
6.63 x 10^-34
How to calculate the power of a source of light? (Written)
The power is the energy per second transferred by the photons
Formula to calculate the power of a beam of light consisting of photons of frequency f
Power of the beam = nhf
N = number of photon passing a point per second
H = Planck’s constant
f = frequency
What is antimatter?
Particles that have the same rest mass, but equal and opposite charge to their corresponding particle
Positron
Particle of antimatter that is the antiparticle of the electron
Symbol for positron
0
B
+1
Thing to remember for positron equation
A neutrino is added
How to positron emitting isotopes occur?
Placing a stable isotope (liquid or solid) in the path of a beam of protons.
Some of the nuclei in the substance absorb extra protons and therefore emit them as positrons because they have now become unstable.
What did Dirac predict?
For every particle there is a corresponding antiparticle that:
- annihilates 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 the particle has a charge
What is pair production
When a photon with sufficient energy passing near a nucleus/electron can suddenly change into a particle-antiparticle pair which would then separate from each other
One electron volt definition
The energy transferred when an electron is moved through a potential difference of 1 volt
How to calculate rest energy of a particle
E=mc2
When does annihilation occur?
When a particle and its corresponding antiparticle meet and their mass is converted into radiation energy
2 photons are produced in this process
Why are 2 photons emitted?
To ensure a momentum of 0 after the collision
How to calculate the minimum energy of each photon produced
hf min = E0
E0 is the rest energy of the particle
What happens in pair production
A photon creates a particle and a corresponding antiparticle and vanishes in the process
How to calculate the minimum energy of the photon needed for pair production
hf min = 2E0
Eg the electron has a rest energy of 0.511MeV. Therefore for park production of an electron and a positron from a photon:
- X 0.511 MeV = 1.022 MeV = 1.64 x10-13J
A photon with less energy could not therefore create a positron and an electron.
Positron emission equation
A A 0
X —-> Y + B + V
Z Z-1 +1
What happens to the electron/positron after pair production
They collide with another electron/positron and annihilate
Beta decay equation
A A 0 __
X —-> Y + B + V
Z Z+1 -1
Explain the process of pair production
When a photon interacts with an orbital electron or a nucleon within the nucleus, the energy of the photon is used to create a particle-antiparticle pair. In order to conserve momentum, the photon needs to interact with interacting particle
Explain why pair production cannot take place if the frequency of the photon is below a certain value
E = hf so the energy of photon is proprtional to its frequency. When pair production occurs the energy is converted to mass according to the equation E = mc2. If the energy/frequency is below the conversion to the mass/rest energy of the particle and antiparticle pair the event will not occur.
Gravitational fields
Acts on, range, exchange particle
Due to mass
- All masses
- Infinite
- Bosons, gravitons
Electromagnetic
- Acts on
- Range
- Exchange particle
Due to charges
- Stuff that has charge
- Infinite
- Photons
Weak nuclear force
- Acts on
- Range
- Exchange particle
Controls radioactive decay
- All particles
- 1x10-18 fm
- W+, W-, 20Boson
Strong nuclear force
- Acts on
- Range
- Exchange particle
Holds the nucleus together
- Acts on nucleons only
- 3x10-15 fm
- Pions between nucleons,has mass + Charge
What does an exchange particle do?
Transfers: energy, momentum, force and charge
Feynman diagram for 2 protons
2 proton in, 2 photons out with a virtual photon
Feynman diagram for neutron and neutrino
Neutron + neutrino ——> (W- boson) proton + electron
Feynman diagram for proton and antineutrino
Proton + antineutrino —-> (W+ boson) neutron + positron
Feynman diagram for beta minus decay:
Neutron —-> (W- boson) proton + electron + antineutrino
Feynman diagram for beta plus decay
Proton —-> (W+ boson) neutron + positron + neutrino
Feynman diagram for electron capture
Proton + electron —-> (W+ boson) neutron + neutrino
Difference between W bosons and photons
- W bosons have a non-zero rest mass
- W bosons have a very short range of no more than ≈ 0.001fm
- Are positively charged (eg W+ or W- )
Why are photons and W boson known as force carriers?
Because they are exchanged when the electromagnetic force and the weak nuclear force act
