{Year 2} Chapter 11 - Radioactive Decay [Complete] Flashcards
What is a metastable state?
When an atom or nucleus is left for an extended period of time in a state that is not the one of least energy for it - e.g. when the electrons are not in the ground state, or when protons or neutrons are sometimes left on a higher energy level due to emitting a radioactive particle
When does gamma emission take place?
After the processes of either beta or alpha emission, or K-capture
What is the notation used to tell when an atom/element is in a metastable state?
An m next to its mass number, e.g. Silver-107m
What is K-capture, and why is it called as such?
The lowest electron energy level in the atom is called the K shell. These electrons are often very close to, or even pass through, the nucleus. Sometimes, they can become captured and turn a proton into a neutron, resulting in the emission of a neutrino
In beta+ emission what particles are emitted?
A neutrino, as well as the beta+ particle itself - a fast moving positron
In beta- emission what particles are emitted?
An antineutrino, as well as a the electron
What nucleus is emitted during alpha decay?
A helium one
In what type of element is alpha emission most commonly found?
Ones which are rich in protons - having atomic numbers most commonly exceeding 82
How can alpha particles be used as a source of energy?
They are placed within a solid, but since they cannot get through it, their energy dissipates within it before they can exit, resulting in the energy being transferred to the solid and heating it up
What are two ways that radiation can be used to treat cancer?
From the outside of the body inwards, by sending gamma rays from a source into the tumour and rotating the source around it // From the inside out, by putting a piece of the radioactive (beta) source within the tumour and letting it kill the tumour
What are Carbon-14 and Argon-40 used for?
To date archaeological remains and rocks respectively
What is the main activity equation?
Activity = decay constant (lambda) x number of nuclei (N) = 0.693N/half life
What is the equation linking half life and ln2?
Half life (T1/2) = ln2 / decay constant (lambda)
What is a half-life?
The time it takes for half of the nuclei in one radioactive sample to decay
What is the decay equation?
N = Number of nuclei at the beginning x e^(-lambda x time)
What is the equation for rate of decay?
Difference in nuclei number / Difference in time = - lambda x number of nuclei
What is the mass of one mole of an element with an atomic mass of 30?
30 grams exactly
What is the decay constant of a radioactive source?
The probability of a nucleus decaying per unit time
What is the activity of a radioactive source?
The amount of disintegrations per second => A = decay constant x number of nuclei
What are the two buzzwords when it comes to describing radioactive decay?
It is both random and spontaneous
What is a good comparison to show the random nature of probability?
To throw 600 die - would think that 100 of them would face upwards on 6, and the rest on other numbers, but in reality it would vary from this and would not turn out perfectly with the 100 on 6 and rest evenly distrubuted
On the plot of N against Z, where is which decay?
Alpha, Beta+ and K-capture happen below the line, and just Beta- happens above it (it is recommended you draw a graph to help here)
What is technetium-99m used for and why is it so good?
Technetium-99m is used as a gamma-emitting diagnostic tracer in patients. It has an ideal half-life of 6 hours - making it a high emitter but for a conveniently short time, but the element it is derived from, molybedenum-99, has a long enough half- life to get to the hospital easily where it can be separated. The technetium is in a metastable state - which is why the m is next to its 99.
