Radiopharmacy Flashcards
(51 cards)
What is radiopharmacy?
- Use of radioactivity in clinical diagnosis and treatment
Preparation and use of appropriate radiopharmaceuticals
A radiopharmaceutical is…
“A radiopharmaceutical is a radioactive diagnositc or therapeutic pharmaceutical that targets a specific organ or system by virtue of its molecular design, and that is used for imaging, in vitro testing or treatment”
Basic physics of atomic structure and radioactivity
- Some isotopes are more stable than others
- As an unstable isotope breaks down, it emits radioactivity
- Isotope stability is really the stability of the nucleus
What governs the stability of the nucleus?
○ Relative amount of neutrons and protons
○ Nucleonic binding energy
○ Mass defect
Magic numbers
2, 8 20, 28, 50, 82, 126
Full shells are more stable than non full shells
Isotopes with magics numbers of either protons or neutrons have a higher nuclear binding energy and are therefore more stable than other, non-magic isotopes
Examples of doubly magic nuclides
○ 4He is one of the most stable and abundant nuclei in the universe
208Pb is the heaviest stable nuclide
For non magic isotopes
○ Even numbers of nucleons promotes stability
High neutron: proton ratio promotes instability
The mass defect can be used to
Assess the stability of an isotope
How can the mass defect be used?
○ The actual total mass of a nucleus is always less than the theoretical total mass of a nucleus
○ By Einstein’s equation, mass and energy are interconvertible
This calculated energy is the nuclear binding energy
How to separate nucleons completely
need to input energy equivalent to the nuclear binding energy
○ Higher binding energies = greater isotope stability
○ Approc 6-9 Me V per single nucleon
* Over 3000 isotopes have been discovered or man-made - most are unstable
Unstable isotopes will revert to more stable isotopes by emitting radioactivity
Gamma
Form - photon
Range - Air: 1km Water: 1m
External exposure
Moderate contamination
Diagnostic use
Beta
Form - Charged particle
Range - Air: 5m Water: 5mm
No external exposure
High contamination
Therapeutic use
Alpha
Form - Charged particle
Range - Air: 1mm Water: <1mm
No external exposure
High contamination
Therapeutic use
What is an alpha particle
Helium nucleus
No electrons so a 2+ charge
Occurs if the nucleus is very heavy
Daughter nuclide has - atomic number 2 less than the parent, and mass number 4 less than the parent
Beta minus particle
Electron so a 1- charge
What is beta minus radioactivity
Occurs if the nucleus is “neutron rich”
Neutron breaks down to a proton, an electron and an anti-neutrino (without mass or charge, to conserve energy)
Daughter nuclide has atomic number 1 more than the parent and mass number the same as the parent
Beta plus particle
Anti-electron = positron = 1+ charge
What is beta plus radioactivity
Occurs if the nucleus is relatively “neutron poor”
but need an energy diff of >1.02MeV to happen
Proton -> Neutron, positron and neutrino
Daughter nuclide has atomic number 1 less than the parent and mass number the same as the parent
A positron will
collide with an electron (anti particles)
Mutual annihilation
Two 511 keV photons moving in opposite directions
Gamma rays and X rays
Electro-magnetic radiation
No mass
No charge
Photons of high energy
Some overlap in electro-magnetic character, therefore distinguished by source:
gamma rays from the nucleus
X rays from electrons outside the nucleus
Gamma rays generally have
Gamma rays generally have frequences >10^18 Hx, wavelengths <10^-11 m and energies >100keV
X rays generally have
Frequences 10&15 to 10^8
Wavelengths 10^-8 to 10^-11m
and energies >120eV to 120keV
Gamma rays are generated from
Generated from isomeric transition
Occurs if the nucleus is metastable (m)
* in an excited state above its ground state =isomeric state
* release of gamma energy allows nuclide to transform to its ground state
* no particle release
Daughter nuclide has atomic and mass number the same as parent
Two ways X ray ionisation occurs
Generation from electron capture and Bemsstrahlung
