PARTICLES AND NUCLIDES Flashcards
Define an Ion.
An atom that has gained or lost electrons and so is charged.
Define a Isotope.
Atoms with the same number of protons but a different number of neutrons.
State equation for specific charge.
Specific charge = charge/mass
Describe the Strong Nuclear Force.
The force that holds the nucleoside together in the nucleus (holds protons against electrodtatic repulsion.)
Define the ranges of The Strong Nuclear Force.
VERY SHORT range acting within the nucleus. Nucleons are held at a fixed separation of 0.5fm.
Describe Alpha Emission.
An alpha particle is composed of 2 protons and 2 neutrons. Alpha radiation occurs when Alpha particle emitted from nucleus.
Describe Beta Minus Emission.
B‐ is a fast moving electron.
B‐ radiation emitted from the nucleus when a neutron decays into a proton.
Describe Beta Plus Emission.
B+ is a positron.
Emitted from the nucleus when a proton decays into a neutron.
Describe Electron Capture.
Occurs when proton in the nucleus captures an electron from the inner shell. Proton decays into a neutron.
Xray photon emitted following electron capture as an electron from a higher energy level falls to fill the vacancy.
Describe Gamma Emission.
Gamma particle is a high energy photon. Occurs when excited nucleus de-excites.
Describe Antimatter.
Predicted by Dirac and discovered using cloud Chambers.
Every particle has a corresponding antiparticle:
Same mass.
Opposite Lepton or Baryon Number.
Opposite Charge.
Opposite Spin.
Define Pair Production.
Where a high energy photon decays into a particle and corresponding antiparticle.
Can occur when photon passes too close to a nucleus.
Creating a pair of particles conserves properties such as charge.
E =mc² more mass must have a photon of greater energy.
Define Annihilation.
When a particle and corresponding antiparticle meet, they annihilate eachother.
Mass of the particles converted into energy in the form of pair of photons travelling in opposite directions (to conserve momentum).
Describe Cloud Chambers.
One of earliest ways of detecting ionising nuclear radiation.
Invented by Charles Wilson in 1911.
Created clouds artificially by rapidly expanding air saturated with water vapour in sealed chamber.
Passed xrays through chamber.
Discovered xrays left wide cloudy tracks.
Highly ionising alpha left broad,straight, define length tracks.
Ionising B left thin, straight or curved tracks.
Weakly ionising gamma rays left no tracks at all.
Describe The Spark Counter.
Only detects highly ionising alpha particles.
B + gamma not ionise enough of the air between metal gauze and thin wire underneath.
Air particles ionised by alpha particle causes spark to be produced.
Spark jumps 5000 V gap between gauze and the wire.
Can be observed and counted.
Shows alpha has very short range in air.
