What is an Isotope?
Different forms of the same element.
Same number of protons and electrons.
Different number of neutrons.
What are three forms of Hydrogen isotope?
1/1 Hydrogen (1 proton, no neutron)
2/1 Deuterium (1 proton, 1 neutron)
3/1 Tritium (1 proton, 2 neutron)
What are unstable nuclei?
Stability dependent on relative number proton/neutron
Unstable nucleus decay in several steps (decay chain) creating daughter nucleus.
Can take microseconds -> millions of years!
What are unstable isotopes?
They are radioactive radioistopes:
- > Alpha (helium nucleus)
- > Beta minus (high speed electron)
- > Beta plus (high speed positron (positively charged anti-electron)
- > Gamma (electromagnetic wavelength 10X10-14m)
NB. Nucleus excited when particles emitted / decay, releasing gamma (excess energy).
What is an N-Z curve?
- Determines how likely decay is
- Stability line: not radioactive / no decay.
- Above: + neutrons, beta minus, neutron ->proton, moves closer to stability.
- Below: + protons ->neutron, emitting positron.
- +82 protons = heavy elements; alpha decay (particle emitted), reduce 2 protons & 2 neutrons.
What is alpha decay?
- Usually occurs with +82 protons (heavy elements)
- Unstable nuclide emits alpha particle (He 2p2n)
- Energy (Q) also released, KE of released particle.
What is typical alpha decay?
Th 228/90 -> Ra 224/88 + He 4/2 + Q
What is the top and bottom number before abbreviation?
Top: Mass. Bottom: Proton.
What is beta minus decay?
- neutron-rich nuclei decay by beta minus emission
- high-seed electron ejected from nucleus (not cloud)
- formed by decay of neutrons.
- Proton number +1, new element formed.
- Neutron decays-> proton, emitting W- boson (exchange particle) from the nucleus which decays into ~electron & anti-electron neutrino~
- electron emitted from nucleus, thus is beta particle (b-) distinguishing from orbiting electrons
What is a typical beta decay particle?
Al 29/13 -> Si 29/14 + e 0/1 + /ve 0/0 + Q
What are neutrinos?
- Conform to conservation of energy principle
- Ghost like particle, difficult to detect.
- electron neutrino & anti-electron neutrino
What are the four properties of neutrinos?
- Interact weakly with other matter (pass through it)
- No charge
- Very very small mass
- Interact via the weak nuclear force (and gravity)
What is a Gamma Ray?
Alpha and beta particle emitted, nucleus is excited state, releasing excess energy in the form of a gamma ray.
What do exchange particles do?
- transfer force
- transfer charge
- transfer momentum
- transfer energy
How do electrons interact?
- Send out virtual photons, hit and exert force on electrons, then return.
- Other forces (gravity, strong/weak nuclear) behave similarly by transmitting via emitting virtual exchange particles.
What is electron interaction called?
Electron-magnetic force
What does a Feynman Diagram look like?
- Vertical direction represents time.
- Horizontal is space.
- Particles solid line in direction of travel
- Virtual particles, wavy and no direction
- Beta -decay emits W-, anti-electron neutrino & electron
- Beta +decay emits W+ (conservation of charge: proton -> neutron).
- W+ change in quark, from proton to neutron (up to down)
- W- change in quark, from neutron to proton (down to up)
- W+/W- are exchange particles, bosons.
