Unit 1 Flashcards
What is an isotope
An atom with a different neutron number but equal proton number
What is a nuclide
A species of nucleus with unique set of protons and neutrons
What is meant by the specific charge of a particle?
What determines the ratio between the electrical and gravitational forces on the particle.
Specific charge equation with units
Specific charge(Ckg^-1) = q(C) / m(Kg)
What is the contents of an atom
A positively charged nucleus containing protons and neutrons which is orbited by electrons
Wha does the electrostatic attraction do?
Hold the electrons in the atom
What keeps protons and neutrons together and how does it work
The strong nuclear force overcomes the electrostatic force of repulsion between the protons in the nucleus and keeps the protons and neutrons together
2 Strong nuclear force facts
Has a range of 3-4fm (3x10^-15m)
Has the same effect between two protons, neutrons, or one of each.
Fact about the electrostatic attraction between two charged particles
Infinite range
When do unstable nuclei occur, give a general point and the 3 requirements for instability and 1 for stability
Too many protons as too high repulsion force causing the forces to be unbalanced
P>n - unstable
P>83 - unstable
P
Structure of an alpha particle
Two protons
Two neutrons
Helium nucleus
Alpha decay of:
X
A
Y
X X-4 4
A —> B + a
Y Y-2 2
Beta radiation consists of ____ and where what happens?
Electrons
A neutron changes into a proton
Beta decay of
X
A
Y
X X 0
A —> B + β
Y Y+1 -1
+ antineutrino (emitted by the sun too)
What is gamma radiation (4)
Em radiation emitted by unstable nucleus
Pass through thick metal plates
No mass/charge
Emitted by nucleus with too much energy following alpha/beta emission
How to calculate wavelength
λ = c/f
c=speed of light=?
3x10^8m/s
The _______ doesn’t affect a _____
The electrostatic force doesn’t affect a neutron
Em waves travel at ____ in a vacuum
3x10^8m/s
1nm=?m
10^-9m
Em waves are ______ waves
Transverse
Em waves consist of electric and magnet waves which….(2)
Oscillate in field strength perpendicular to the direction of wave propagation
And in phase with eachother
Em waves are emitted by _____ when…
A charged particle when it loses energy
When does a charged particle lose energy (2)
When an electron is stopped, slows down, or changes direction
When an electron moves down a shell
What is a photon
A packet of em waves
What does a laser beam consist of
Photons of equal frequency
What is meant by the power of the laser and how is it calculated
Energy per second transferred by the photons
Power of laser = nhf where n is the number of photons passing a fixed point each second
Em waves in descending order of wavelength (state wavelength) and increasing frequency and radiation
Radio= >0.1m Microwave = 0.1-1mm Infrared = 1mm-700nm Visible = 700nm-400nm Ultraviolet = 400nm-10nm X-rays = 1-10nm Gamma rays = <1nm
MeV to J conversion
1.6x10^-13
Why doesnt the strong nucleur force affect anything outside the nucleus
Because it only has a range of 3-4fm which is only roughly the diameter of a nucleus so cannot affect anything beyond it as it is out of reach
What are the four fundamental forces?
Gravity
Electromagnetic
Weak nuclear
Strong nuclear
Describe how the strong nuclear force between two nucleons varies with the separation of the nucleons quoting suitable values for separation.
The strong nuclear force has a short range of 3-4fm and is an attractive force with separations from 3-0.5fm however at less than 0.5fm it becomes a repulsion force that acts to prevent protons and neutrons from pushing into each other
Describe and name the process of PET (5)
Positron Emission tomography – positron rich isotope is used as a tracer through the blood
because it emits positrons into the brain which comes up against an electron
and they annihilate and emit two photons
which are picked up by detectors that trace the location
so they can see if blood is flowing in order to locate cancers etc…
Where to positron rich isotopes come from
Do not occur naturally, manufactured by placing stable isotope in the path of a beam of protons, some of the nuclei absorb extra protons and become unstable positron emitters
When does positron emission occur and what is emitted
Positron emission occurs when a proton changes into a neutron in an unstable nucleus with too many protons. A neutrino is also emitted
Positron decay
X X 0
A —> B + β
Y Y-1 +1
+ neutrino
What type of energy are photons
radiation energy
What happens when a antiparticle and its corresponding particle meet
They annihilate, converting their total mass into two photons
Why are there two photons produced during annihilation
two photons because momentum must be conserved not taken away
Compare antiparticle to a particle
All quantum numbers/properties are opposite for example opposite charges, if charged, however equal rest masses
What is meant by 1 electron Volt
energy transferred when an electron is moved through a PD of 1 volt (1JC-1)
Pair production is where
A photon is converted into a particle and its antiparticle if it has enough energy
Minimum energy of photon needed =
hfmin = 2E0
Momentum =
mass*velocity
If the force between two particles takes time to act the effect is carried by…
an exchange particle moving at finite speed
What is the feynman diagram for the electromagnetic force between two protons
p–>p
p–>p
y (virtual photon)
What is the virtual photon
the boson carrying the electrostatic repulsion between two positively charged protons
Why it the photon virtual
Because it cannot be picked up by a detector without preventing interaction to occur
What does the strong nuclear force do
Holds the neutrons and protons in the nucleus together
What is the Feynman diagram for a neutrino-neutron interaction
Neutron—>Proton
Electron Neutrino—>Electron
W- boson
(Neutrino absorbs W- boson –> electron)
What is the Feynman diagram for an antineutrino + proton interaction
Electron Antineutrino –> Positron
Proton –> Neutron
W+ boson
(Antineutrino absorbs W+ boson –> positron)
Three facts about the W bosons
have a non-zero mass, very short range of 0.001fm, positively or negatively charged
In Feynman diagrams, total charge is ____
always conserved
What force do electrons and positrons use
Weak nuclear force
What force do protons and neutrons use
Strong nuclear force
When a W boson meets a (i) neutrino (ii) antineutrino, they change into…
(1) an electron
(2) a positron
What is the Feynman diagram for beta decay
Neutron —> Proton
Electron antineutrino —> electron
W- boson
W- boson decays into an electron and an antineutrino
What is the Feynman diagram for positron decay
Proton –> Neutron
Electron antineutrino –> Electron
W+ boson
W+ boson decays into a positron and neutrino
What is K-capture?
In large atoms, the inner-most shell of electrons is the K-shell. Sometimes an electron in this K-shell is captured by the nucleus causing the emission of a neutrino and a decrease in atomic number
What is electron capture?
Sometimes a proton in a proton-rich nucleus turns into a neutron as a result of interacting through the weak interaction with an inner-shell electron from outside the nucleus
(If arrow reversed then sign reversed)
What is the decay equation for K-capture
E- + 1A1 —> 1B0 + v
e + p –> n + v
What is the Feynman diagram for electron capture
Proton –> Neutron
Electron –> Neutrino
W+ boson
What is electron-proton collision
At very high speeds, an electron can turn into a Proton via the exchange particle of the W- boson
What is the Feynman diagram for Electron capture
Proton –> Neutron
Electron –> Neutrino
W- boson
Compare the W boson to the virtual photon (3)
W boson has mass, charge, very short range, weak interaction
Virtual photon, no mass, charge, infinite range, electromagnetic interaction
Where do cosmic rays come from
supernova
Describe the changes that take place in a proton-rich nucleus when it emits a positron
a proton in the nucleus changes into a neutron and a positron and neutrino are created and emitted from the nucleus
State two ways in which pair production of a positron and an electron differs from positron emission
positron emission uses isotopes not photons, pair production doesn’t emit a neutrino.
How does the alpha particle energy spectrum show there are two particles present
the unstable isotope has split into two parts, the daughter nucleus and an alpha particle. The daughter nucleus causes a spike in the alpha particle energy spectrum which must be conserved as energy can only be distributed one way.
Antiparticle Vs particle
Deflection by electric field
Opposite
Antiparticle Vs particle
Deflection by magnetic field
Opposite
Antiparticle Vs particle
Deflection by gravitational field
Same
Antiparticle Vs particle
Mean lifetime
Same
Why does a photon need a minimum energy and what happens if there is more than this minimum energy
To form rest masses of both particles
Particles have more kinetic energy
Where were neutrinos discovered
In a nuclear reaction
69nm to m
69x10^-9m
How are particles places into hadrons or leptons (6)
Hadron: proton/kaon
Lepton: muon
hadrons affected by strong nuclear reaction and are made of quarks
Leptons are fundamental and do not experience the strong nuclear reaction.
Hadrons are divided into baryons and mesons.
Baryons three quarks, mesons quark anti-quark pair.
Similarities between groups all experience weak interaction and if charged the electromagnetic interaction. All have rest mass.
Repulsion between electrons
4 electrons and a photon
A proton (p) and an electron (e–) combine to form a
neutron and neutrino and W+ boson
If arrow reversed in feynman diagram then
Change charge of boson
