Particles and Radiation Flashcards
Isotopes
? Same number of protons but different number of neutrons. Same atomic number but different atomic mass.
Specific Charge
? Charge / Mass
Z
? Atomic number of elements
A
? Nucleon number/atomic mass
Describe strong nuclear force
Acts between nucleon at a very short range to overcome electrostatic force by holding the nucleus together. Attractive between 3fm -0.5fm and repulsive below 0.5fm.
Carbon dating
? A process that uses the decay of radioactive carbon-14 atoms that are present in all living organisms in order to determine the age of organic material.
What are the types of decay ?
Beta minus, beta plus, alpha decay,
Describe a beta minus decay
When a neutron turns into a proton. Emitting an electron and an antielectron neutrino.
n –> p + e- + _Ve
Describe a beta plus decay.
When a proton turns into a neutron. Emitting a positron and an electron neutrino.
p –> n + e+ + Ve
Describe alpha decay
When a helium nucleus is emitted
X –> Y + He
What is the equation to calculate photon energy?
E=hf = hc/λ
When is E=hf used?
As photons have wave-like properties.
We know that electromagnetic waves (and therefore photons) travel at the speed of light.
Define antiparticles
Particle that have the same mass but the opposite charge.
Law of conservation of energy
Mass and energy is always conserved
define Electron volt (eV)
? One electron volt is the amount of energy transferred when an electron is moved through a potential difference of 1 volt.
Convert eV –> J
1eV = 1.6*10^-19J
Describe annihilation
When a particle and its corresponding antiparticle collide releasing two photons. The photons must go in different directions to conserve momentum.
hf = E(rest) + E(k)
Describe pair production
Opposite of annihilation.
A photon interacts with a nucleus and its energy is converted into the mass of a particle and its corresponding antiparticle.
hf = 2E(rest) + E(k)
Define electromagnetic interactions
? An exchange of a virtual photon causing a change in momentum.
- Massless
- Undetectable
What are the 4 fundamental forces?
Gravitational - Between masses
Electromagnetic - Between charges (virtual photon)
Weak - Decay of nuclei (Boson W&Z)
Strong - Holds protons and neutrons together (Gluon)
What are the roles of exchange particles?
? they are force carriers for the fundamental forces
transfer
- energy
- momentum
- charge
The size of the exchange particles determines the range of the force; the bigger the particles the shorter the range
How is particle interactions shown?
Feynman diagrams
Electron capture
? Occurs within a proton heavy nucleus, if the electrons stray close to the nucleus then it can interact via the weak interactions to form an electron neutron and a neutrino.
p + e- –>(W+) n + Ve
Electron-proton Collision
Same equation as electron capture but different exchange particle. (W-) and Different direction (left)
What are the symbols of these quarks. Up, down, strange
u,d,s
Equation to calculate power of each photon
p=nhf
Why is a neutrino produced in beta and alpha decays?
To conserve the total electron family number
Quark combination of proton
uud
Quark combination of a neutron
udd
What does the existence of a neutrino suggest?
to account for the conservation of energy in beta decay
Why do every particle have its own antiparticle
To converse charge during collisions
What are the two big classes when classifying particles
Hadrons and Leptons
Describe the properties of leptons
? fundamental particles that do not interact by strong interactions only weak interactions. Lepton no is always conserved
Eg: electrons (stable), muons (decay into electrons), neutrino (No mass, no charge)
Describe the properties of hadrons
? non-fundamental, interact via strong nuclear force and are made up of quarks.
What are the two classes of hadrons
Mesons and Baryons
Describe the properties of baryons
Made of 3 quarks, all decay into a proton (only stable baryon).
Eg; Proton, Neutron
Describe the properties of mesons
made of a quark and an antiquark.
Includes pions (exchange particles for strong nuclear force) and heavier kaons decay into pions.
What are the factors that are always conserved in interactions
Charge, Baryon number, Lepton number, strangeness (strong interactions)
Describe the properties of strange quarks
Strangeness number (-1). Created through strong interaction in pairs and decay through weak interactions.
What the PET Scanners
Positron Emission Tomography Scanners.
Take advantage of the process of annihilation to create images that can be used in medicine. Positron is used as tracers, the scanner tracks the tracers.
Using tracers and tracking them (PET)
- Inject the right level of radioactivity
- Brain absorbs the tracer, the radioactive atom loss its radioactivity (giving of positrons+)
- Positron hits an electron at the right speed combine and destroy each other.
- Energy is released, (2 gamma rays) which travel at straight lines out of the body in 2 opposite directions.
- PET Scanner (big ring of Geiger counters) detects the rays and calculates the location of the tracer.
Many of these events happen at the same time, revealing brain activity in 3 dimensions.
define quantum numbers
? describe the values of conserved quantities in the dynamics of a quantum system.
Describe the change in quark character in beta decays
beta (+) - udd –> uud
Beta (-) - uud –> udd
Define photoelectric effect
? process by which the a metal with photons incident on it emits electrons.
? An electron can leave the metal surface if the energy gained from a single photon exceeds the work function.
Shows the particle behaviour of light.
Define threshold frequency (f0)
? the minimum frequency of the light required for an electron to be emitted
Equation to calculate hf
hf = φ + Ekmax
f0 = φ/h
the number of photoelectrons emitted per second increases as intensity increases. One electron absorbs one photon
Define stopping potential
? The potential that would provide enough energy to ensure that the emitted electrons had zero kinetic energy.
Energy provided from the battery = Kinetic energy of emitted electrons.
Work done/ionisation energy = charge(e)×potential (V)
Define ionisation
? Process by which an atom acquires a positive or negative charge by gaining or losing electrons.
Define work function
? the minimum amount of energy needed for an electron to be emitted.
What is gas discharge tube used for
? a practical example of excitation by collision
define excitation by collision
? the movement of electrons up to a higher energy level; an electron collides with an orbital electron
Explain how a gas discharge tube(fluorescent tube) work
? Tubes that are filled with gas that emit light in a specific region of the EM spectrum when an electric current is passed through them.
As electrons flow from the cathode to the anode, they collide with Mercury atoms, transferring K.E.
This results in excitation of electrons from the ground state to a higher energy level.
As these electrons relax back to the ground state. They emit UV & visible photons.
These photons collide with the phosphor coating, causing excitation.
As the electrons in the phosphor coating relaxes they emit visible photons.
Define energy levels
? Energy of an emitted photon can be measured by calculating the difference between two energy levels it falls.
You are EXPECTED to realise that this radiation would fall within the visible part of the spectrum.
what is used to represent energy levels
Line spectra; represents discrete energy levels.
hf = E1-E2
What are the practical examples of wave nature of matter
Diffraction ( De Broglie’s experiment)
λ=h/mv
Quark structure of K+
u s
Quarks structure of K0
d s
Quark Structure of K-
s u
Quark structure of π + :
u d
Quark structure of π 0 :
u u or d d
Quark structure of π − :
d u
