Physics Week 2 Flashcards
(32 cards)
What is radioactive decay?
A process where an unstable nucleus spontaneously emits ionising particles, transforming into a different atom (daughter).
What are the three main ionising particles emitted during decay?
Alpha (α), beta (β), and gamma (γ) radiation.
What is a decay constant (λ)?
A value related to the half-life that indicates how quickly a radionuclide decays.
What is the equation for radioactive decay over time?
N(t)=N(0) e^−λt
What is the equation for activity over time?
A(t)=A(0)e^−λt
How is decay constant (λ) related to half-life?
λ= ln2/ t 1/2
What is alpha decay?
Emission of a helium nucleus (2 protons, 2 neutrons), occurs in heavy atoms (A > 200, Z > 83). Unstable nuclei below the line of stability with 82 or greater number of protons.
What is beta minus (β⁻) decay?
A neutron turns into a proton, emitting an electron and antineutrino. Occurs above the line of stability.
What is beta plus (β⁺) decay?
A proton converts to a neutron, emitting a positron and a neutrino. Occurs below the line of stability.
What is electron capture decay?
- The strong nuclear force within the nucleus is disrupted due to excess number of protons. Electrons in the closest orbital shells will collapse into teh nucleus, forming bonds with a posutuvely charged proton and therefore neutralising it into a neutron.
Equation:
Basically, with the adition of an electron, atomic number stays the same, one proton is lost, and a neutrino is emitted.
parent isotope + electron –> daughter isotope + neutrino.
What is gamma decay?
An excited nucleus releases energy via a photon (γ-ray) without changing its identity.
This can occur after alpha or beta decay or electron capture. Particulalry after electron capture, to replenish the lost electron and return the nucleus into ground state.
What happens during positron annihilation?
A positron combines with an electron, producing two gamma rays (0.511 MeV each).
Which decay has the highest ionisation power but lowest penetration?
Alpha particles.
What are the ranges of α, β, and γ particles in tissue?
α: 0.1 mm, β: few mm, γ: up to 30 cm.
What is the relationship between energy, frequency, and wavelength?
E=hf=hc/λ
Which radiation type has the highest energy on the EM spectrum?
Gamma radiation.
What defines ionising radiation?
Radiation in the form of photons with energy (hf) equal to or greater than the binding energy of the electron in the orbital will come and eject electrons from the atom.
During this process the electron is emitted, and a photon with energy hf-E(b) is also released.
What defines non-ionising radiation?
A photon which does not have enough energy to release an electron from an atom. It has enough energy to excite an atom by causing the electrons to jump from a lower orbital shell to a higher one. Since atoms prefer to have lower orbitals full, the electron will drop back down and emit a photon as a result. This photon has energy equal to the energy difference btween its initial and final orbits.
What is the ALARA principle?
Keep radiation exposure As Low As Reasonably Achievable, balancing benefit and risk.
What is the “sensitive volume” of a detector?
The part of the detector that responds to ionising radiation.
What is “dead time” in radiation detectors?
The period after detection during which a detector cannot record another event.
What are the three main types of detectors?
Gas-filled, scintillation, and solid-state (semiconductor).
How do ionisation chambers work?
They collect ion pairs created by radiation; current produced is proportional to ionisation.
What’s a key advantage of Geiger-Müller counters?
High sensitivity to low radiation levels.
