2. Particles and Radiation Flashcards
What are the main constituents of an atom?
● Proton
● Neutron
● Electron
What is meant by specific charge?
The charge to mass ratio:
Specific charge = charge / mass
Units C/kg.
What is the specific charge of a proton?
Protons have charge +1.6 x10^-19 and mass 1.67 x 10^-27 kg
Specific charge = 1.6 x 10^-19/1.67 x 10^-27
= 9.58 x 10^7 C/kg
What is the letter associated with a proton number?
Z
What is a nucleon?
A constituent of the nucleus: a proton or a neutron.
What letter represents nucleon number?
A
Which is the correct notation?
A
Z X
or
Z
A X
A
Z X
What is an isotope?
A version of an element with the same number of protons but a different number of neutrons.
State a use of radioactive isotopes
Carbon dating - the proportion of carbon-14 in a material can be used to estimate its age
What is the strong nuclear force?
The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons.
Describe the range of the strong force?
● Repulsive up to 0.5fm
● Attractive from 0.5-3fm
● Negligible past 3fm
What makes a nucleus unstable?
Nuclei which have too many of either protons or neutrons or both.
How do nuclei with too many nucleons decay?
Alpha decay (emission of a helium nucleus formed of 2 protons and 2 neutrons)
How do nuclei with too many neutrons decay?
Beta minus decay in which a neutron decays to a proton by the weak interaction (quark character has changed from udd to uud).
How was the existence of the neutrino hypothesised?
The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.
What is meant by beta minus decay?
When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino.
What is an alpha particle?
A particle contains two protons and two neutrons, the same as a helium nucleus.
What is an antiparticle?
For each particle there is an antiparticle with the same rest energy and mass but all other properties are the opposite of its respective particle.
True or false:
‘Every particle has a antiparticle’
True
What is the name of the antiparticle of an electron?
Positron
What is the antiparticle of π0 (pion with 0 charge) ?
π0, its antiparticle is itself
What occurs when a particle and antiparticle meet?
Annihilation:
The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum.
What is pair production?
A gamma ray photon is converted into a particle-antiparticle pair.