Radiochemistry Flashcards
What is radiochemistry?
Also known as nuclear pharmacy which is a specialty in pharmacy practice dedicated to the compounding and dispensing of radioactive materials for nuclear medicine procedures.
What are radiopharmaceuticals?
Radiopharmaceuticals are a chemical substance containing radioactive atoms within its structure.
They must be suitable for administration to humans for diagnosis or treatment of disease.
What is the medical use of radionuclides?
Radionuclides such as 32P emits only beta radiation whilst 131I emits both beta and gamma radiation and hence can be utilised for both therapeutic and diagnostic purposes.
What do imaging procedures do?
Imaging procedures provide diagnostic information based on the distribution of radioactivity in the body.
Dynamic studies measure rate of accumulation and removal of isotopes from an organ, providing functional information.
Static studies enable morphological information to be obtained on the presence of lesions, their shape, size and position.
Measurement is via an electronic device such as a gamma camera facilitating detection of organ radioactivity. Old tech gave rise to expression “scans”.
What is SPECT/PET?
Single photon emission computer tomography or positron emission tomography cameras are able to construct computerized image slices through an organ in three planes: transverse, sagittal and coronal planes.
These organ slices enable a 3D model to be constructed.
Tomographic imaging provides a greater depth of
resolution and delineation of the structural and functional information present.
What are the 2 types of isotopes?
Unstable - Isotopes that continuously and spontaneously break down/decay in an attempt to gain a stable configuration.
Stable - isotopes that do not naturally decay but can exist in natural materials in differing proportions.
What are radioisotopes?
Unstable isotopes are known as Radioisotopes.
Radionuclides and the spontaneous transformation process is radioactive decay.
They behave chemically the same as stable isotopes.
Radioactivity is unchanged by physical conditions; state, temperature, pressure.
Radioisotopes are detectable at very low levels.
What is radioactivity?
The process in which an unstable isotope undergoes changes until a stable state is reached and in the transformation emits energy in the form of radiation (alpha particles, beta particles and gamma rays).
Radioactivity is a nuclear reaction in which an unstable nucleus decomposes spontaneously.
Artificial radioactive decay occur when stable isotopes are bombarded with particles such as neutrons.
How do you work out rate of decay?
Rate of decay = - No of nuclei decaying / Time taken for decay = Decay constant characteristics of radionuclide x No of nuclei decaying
What are the kinetics of radioactive decay?
Nuclear decay is a first order reaction.
Rate of decay is directly proportional with the amount of radioactive isotope present.
Rate of decay is exponential.
Rate of decay is independent of physical (temp, pressure etc.) or chemical state (e.g. 14C- diamond, graphite, ethane).
For a radioactive nuclides, the rate of decay
A is the rate of disintegration of nuclei. Initially (at t = 0), we have No nuclei, and at time t, we have N nuclei. This rate is proportional to N, and the proportional constant is called the decay constant.
What factors influence nuclear stability?
The stability of a nucleus depends mainly on A- the mass number, and Z- the atomic number.
The ratio of neutrons to protons (N/Z) is key to stability.
Z > 20 (heavier atoms), the number of neutrons must increase to stabilise the nuclides (N/Z= 1.15 - 1.5).
All nuclides with Z > 83 are unstable.
Nuclides with an even number of protons tend to be more stable.
An unpaired nucleon like an unpaired electron is less stable.
There is a strong selection for even numbers of both N and Z.
Very heavy nuclides decay by alpha emissions to reduce both N and Z.
An unstable nuclide tends to decay such that there is a shift in the N/Z ratio towards the band of stability (if the N/Z ratio is too high or too low the nuclide is unstable and decays).
What is radioactive decay?
Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation (a change takes place within the nucleons in the nucleus of the radioisotope and this is accompanied by one or more emissions).
Results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter nuclide.
Explain the chart of the nuclides:
As the No of protons increases, the neutron to proton ratio required for nuclear stability also increases.
Neutron to proton ratio gives an indication of the type of decay.
Nuclides with Z > 83 (Bismuth) are unstable.
Neutron rich areas undergo -1 Beta decay (converts a neutron into a proton).
Proton rich areas undergo +1 Beta decay or electron capture (converts a proton to neutron).
What happens during alpha decay?
During alpha decay, a nucleus is able to reach a more stable state by allowing 2 protons and 2 neutrons to escape the nucleus.
This results in a smaller nucleus with a more stable arrangement.
The particle emitted is helium-4 containing 2 protons and 2 neutrons.
This helium is unlike the natural helium atom but rather generated from nuclear decay it is called an alpha particle.
Alpha particles leave the nucleus as nucleons without electrons and so alpha particles have a charge of +2e.
What happens during beta decay?
Beta particles have a charge of -1. This means that beta particles are the same as an electron.
Beta decay occurs in nuclei with a high neutron: proton ratio.
A neutron is converted to a proton inducing a shift down and to the right on the stability plot.
When beta decays occurs the atomic mass is unchanged but the atomic number increases by 1.
