Chapter 1 - Matter and radiation Flashcards
Describe model of an atom
Positively charged nucleus (composed of protons and neutrons) surrounded by orbiting electrons
What is the charge of a proton?
1.6x10^-19C
What is the charge of an electron?
-1.6x10^-19C
equal and opposite to charge of proton
What is the charge of a neutron?
0
What is the mass of a nucleon (proton and neutron)?
1.67x10^-27Kg
What is the mass of an electron?
9.11x10^-31Kg
What is the atomic number of an element?
Number of protons
What is the mass number?
Number of protons and neutrons
Write the isotopic notation
a - number of protons/neutrons
X
z - number of protons
What are isotopes?
Atoms of an element with the same number of protons but different number of neutrons
What is specific charge?
Charge divided by mass of particle
‘specific means ‘per unit mass’
What is the specific charge of a proton?
Charge/mass = 1.6x10^-19C/1.67x10^-27Kg = 9.58x10^7CKg^-1
Which subatomic particle has the largest specific charge?
Electron
Calculate the specific charge of a 2+ magnesium ion?
Charge/mass = 3.2x10^-19/3.98x10^-26 = 8.04 x 10^6 CKg^-1
ignore mass of electrons when calculating specific charge of ion
What stops a stable nuclei from disintergrating?
Strong nuclear force
What does the strong nuclear force act between?
Nucleons (protons and neutrons)
Is the strong force attractive or repulsive?
Both
Why is the strong nuclear force attractive and repulsive?
Attractive to keep nucleons together but also repulsive to prevent nucleus collapsing
When is the strong nuclear force attractive?
From 3-4 fm to 0.5fm
What are the particles emitted by a unstable nucleus called?
Nuclear decay
Name the types of radiation emitted by an unstable nucleus
- Alpha radiation
- Beta radiation
- Gamma radiation
Which type of atoms feature alpha decay?
Very big atoms
Uranium and radium
What is the composition of an alpha particle?
2 Protons and 2 neutrons
same as a helium atom
Write the equation for alpha decay of uranium
238 234 4
U -> Th + a
92 90 2
What kind of atoms does beta minus decay occur in?
Neutron rich isotopes
What happens in beta minus decay?
Neutron changes into a proton, a beta particle is ejected and an antineutrino is released
Give the equation for the beta minus decay of Rhenium
186 187 0
Re -> Os + B + V^ e
75 76 -1
Who discovered the neutrinos and how were they discovered?
Wolfgang Pauli in 1930
Energy of particles after beta decay was not the same as it was before, so neutrinos must be released to conserve energy
What are the properties of a a neutrino?
- Neutral (charge was already conserved in beta decay)
- Zero or almost zero mass (never detected before)
What is the equation linking wavelength, speed of light and frequency?
speed of light = frequency x wavelength
What is a photon?
packet/ burst of electromagnetic waves
When are electromagnetic waves/photons released from a charge particle?
When it loses energy
- When a fast moving electron is stopped
- An electron in a shell of an atom moves to a lower energy shell
What is the equation for photon energy?
E = hf or E = hc/wavelength
energy (J) = planck’s constant (6.63x10^-34) x frequency (Hz)
What is the equation for the power of a beam?
Power of a beam = nhf
n = number of photons in beam passing a fixed point each second
What properties do antiparticles have compared to their corresponding particles?
Same mass and rest energy but with opposite charge
What are the antiparticles of the electron, proton, neutron and neutrino?
electron - Positron
proton - antiproton
neutron - antineutron
neutrino - antineutrino
What occurs in annihilation?
When a particle and a corresponding antiparticle meet and their mass is converted into radiation energy (photons)
Two photons produced (to conserve momentum)
What is the equation for minimum energy of each photon produced?
hf(min) = Eo (rest energy of particle)
What is pair production?
Photon creates a particle and corresponding antiparticle, and vanishes in the process.
How do you calculate minimum energy of photon needed for pair production?
hf(min) = 2Eo
What does PET scan stand for?
Positron emitting tomography
What happens in a PET scan?
positron emitting isotope is administrated to the to the patient and some of it reaches the brain via the blood system. Each positron emitted travels no more than a few millimetres before it meets an electron and annihilate each other. Two gamma photons produced are detected an an image is built up from where the positron emitting nuclei are inside the brain.
What are virtual photons?
- Causes electromagnetic force between two charged objects
- Virtual as we can’t detect them directly
- Infinite range
Draw the feynman diagram for electromagnetic force between 2 photons
Look at paper flashcards
What is the weak nuclear force responsible for?
B- and B+ decay
What happens when a neutrino interacts with a neutron?
Makes it change into a proton. A B- particle (electron) created and emitted
What happens when an antineutrino interacts with a proton?
Makes proton change into neutron. B+ particle (positron) created and emitted as well
What are the exchange particles of these interactions? What are their properties?
W bosons
- Have non-zero rest mass (unlike photon)
- Very short range - no more than 0.001fm
- Positively charged (W+ boson) and negatively charged (W- boson)
Write feynman diagrams for neutron-neutrino and proton-antineutrino interactions
What is the role of W boson in beta decay?
- W- boson decays into B- particle and antineutrino
- W + boson decays into a B+particle and a neutrino
Draw feynman diagrams for beta decay
What is electron capture?
Proton in proton rich nucleus turns into neutron as a result of interacting through weak interaction with an inner shell electron. Also forms electron neutrino
Draw feynman diagram for electron capture
What is an electron volt? What’s its value?
- Very small measurement of energy. It is the energy transferred to an electron when passing through a potential difference of 1 volt.
- 1.6x10^-19 J
What roles do exchange particle play in an interaction?
Transfers:
- energy
- momentum
- force
- charge (sometimes)
What are antiparticles?
Particles that have opposite properties/quantum numbers (e.g. charge and strangeness) to a particle but has the same mass
