Deck 'B' Flashcards
What forces are in the nucleus?
- Electromagnetic forces - unstable; protons repel
* Short range, strong nuclear forces - hold the nucleus together
Describe electron orbitals.
- Circle in discrete orbits/shells
- Shells K, L, M, N, O
- Fixed, specific distances
- Electrical equilibrium
How do electrons remain in their orbits?
- Electrostatic attraction (binding force) pulls electrons IN
- Centrifugal force pulls electrons AWAY
How much energy is required to release a tungsten K-shell from orbit?
Tungsten (Z=74) = 69.5 keV
What does the symbol Z represent?
The atomic number; the number of protons in the nucleus.
What does the symbol A represent?
The atomic mass number; the total number of nucleons in the nucleus.
What is a nuclide?
Any particular nucleus with a specific Z and A.
What is an isotope?
A nucleus with the same Z as a given nucleus but a different A due to a different neutron number.
Define radioactive.
A nucleus is unstable and will decay until it reaches a more stable form.
What is radioactive decay?
When radionuclides undergo transformation from one nuclear configuration to another.
What is the law of radioactive decay?
The rate of decay of a particular nuclide is proportional to the number of nuclei left in the sample.
Define activity.
Number of nuclear transformations which occur in that quantity per unit time.
Define half-life.
Time taken for activity of a sample to decrease by one half.
What is the decay constant?
A measure of the rate at which a nuclide releases radioactive emissions.
What is gamma decay?
Often occurs when the nucleus is excited after beta emission; same A and Z, nucleus reaches ‘ground state’
What is a metastable state?
When nuclei are excited long enough to have their duration measured.
Isomer —(isomeric transition)—> stable and gamma emission
What is internal conversion?
When an excited nucleus transfers energy to an inner electron and ejects it. The inner electron is replaced by a more outer electron and the transition produces and X-ray photon –> characteristic radiation.
What is beta decay?
Beta(+) decay
- positron
- p^+ –> n^0 + Beta^+ + n
- Z - I
- A = A
- New element
Beta(-) decay
- negatron (electron)
- n^0 –> p^+ + Beta^- + antineutrino
- Z + I
- A = A
- New element
What is a ‘potential well’?
The strong nuclear force which keeps high kinetic energy alpha trapped in a nucleus. Less influential with increasing atomic number.
How are gamma, beta and alpha used?
- Gamma - nuclear medicine (technetium-99m)
- Beta - image and treat thyroid gland (iodine-131)
- Alpha - not used clinically due to being too damaging and short-range
What are conduction, convection and radiation?
- Conduction - heat transfer through solids
- Convection - heat transfer through fluids
- Radiation - heat transfer via infrared (so can occur in a vacuum)
How does heat spread through an X-ray tube?
- Tungsten target –> oil and glass envelope (radiation through vacuum)
- Tungsten target –> copper anode block and anode stem (conduction)
- Anode stem –> oil, which expands (convection)
- Oil –> metal casing (conduction)
- Metal casing –> air in room (convection and radiation)
Copper has a LARGE thermal capacity
Tungsten has a REASONABLE thermal capacity
