301 Radiopharmaceuticals Flashcards
What is an atomic number?
Number of protons
What is a mass number?
Number of protons (Z) + number of neutrons (N)
What is isotope stability dependent on?
Nucleus stability
What is nucleus stability dependent on?
No. of protons and neutrons
Nuclear binding energy and mass defect
What is the “shell model” of nucleus stability?
If arranged shells are full then they are stable
What are magic numbers?
Shell is full = 2, 8, 20, 28, 50, 82, 126 - so not likely radioactive
Magic numbers can refer to either protons or neutrons or both
Isotopes with magic numbers
Either protons or neutrons have higher nuclear binding energy and therefore more stable than other, non-magic isotopes
What are doubly magic nuclei?
Both proton and neutron shells are full, making binding even stronger
Examples of doubly magic nuclides
4He (2+2) is one of most stable and abundant nuclei in universe
208Pb (82+126) is heaviest stable nuclide
What are no-magic isotopes?
Even numbers of nucleons promotes stability (even-even nuclei) (6P and Ns)
High (neutron : proton) (N/Z) ratio promotes instability - 238 92 U (92P and 146N) (highest N/Z ratio and so most unstable and radioactive)
1.5 ratio is border between stable and unstable (neutron : proton)
What is nuclear binding energy?
Keep protons and neutrons (nucleons) together (protons have repulsive nature)
To separate a nucleon completely, input energy equivalent to nuclear binding energy is needed
The energy required to split a nucleus of an atom into component parts: protons and neutrons
What do higher binding energies do?
Greater isotope stability, approx. 6-9 MeV per single nucleon
What is the difference between a nucleon and a separated nuclei?
Energy has a mass
The actual total mass of nucleus is always less than theoretical total mass of nucleus
What is mass defect?
Difference in mass of atom and sum of masses protons and neutrons
Assess stability of isotope
Difference in mass defect = nuclear binding energy
What will unstable isotopes do?
Unstable isotopes will revert to more stable isotopes by emitting radioactivity
What does a high mass defect value indicate?
More stable nucleons (high nuclear binding energy) means nucleus has high binding energy and so it is more stable
What are particulate and non-particulate (waves) radioactivity?
- Alpha and beta (+ and -) radiation
- Gamma and X rays
Alpha particle radioactivity
Occurs in heavy nuclei
Daughter nuclide has atomic number 2 less than parent (lose 2P) & mass number 4 less than parent (loses 2P and 2N)
Slow, weak penetration (paper) and high ionisation due to +2 charge (wants to attract)
Beta (-) particle radioactivity
Occurs in “neutron rich” nuclei (high P)
Neutron breaks down into proton, electron & anti-neutrino
Daughter nuclide atomic number 1 more than parent (create P), mass number same as parent (rid of N and form P)
Faster, better penetration (small particle) (stopped by 0.5cm aluminium sheet), ionisation not as strong as -1 over +2
Properties of anti-neutrino
No mass and no charge
Why is beta (-) lighter than alpha?
Has 1 electron over 2P and 2N
Beta (+) particle [Positron emission] radioactivity
Occur in relatively “neutron poor) (higher P)
Converts P breaks down to N, positive charge released (+1) as positron with a neutrino
Daughter nuclide has atomic number 1 less than parent (P to N change), mass number same as parent (conversion)
Beta (+) has same properties as (-)
What is a positron?
Positively charged electron
Do gamma and X rays have charge or mass?
No, not particles
Properties of electromagnetic radiation
No mass
No charge
Photons of high energy (speed of light)
Short wavelength (means radiation has high energy being short)
Gamma radioactivity
Occurs in excited metastable (m) state (higher energy) above ground isomeric state (normal)
Daughter nuclide has same atomic and mass number (no particles)
Speed of light so fast, high penetration (lead), ionisation less due to no particles
When do metastable nuclei revert to isomeric state?
Always, by releasing gamma energy/radiation to relax to isomeric with no particle release
X ray radioactivity
Occurs in relatively “neutron poor” (high P) nuclei
Electron capture when K1 shell is captured by nucleus
Daughter nuclide has atomic number 1 less parent (P reacts w/ E to make N) & mass number stays same, (P to N)
Bremsstrahlung (production of X rays - braking radiation)
Electron attracted by nucleus, pulling closer & loses speed, deflecting electron, losing energy & released as X ray
Produced as 2ndary radiation when electron is deflected by mass & charge of nucleus
Electrons lose speed (braking) [Bremsen] & their excess energy is released as X ray radiation (Strahlung)
2 cases of X ray production (Bremsstrahlung)
- Close proximity so released X ray has high energy
- Passes further away so less attraction and so less energy released
Alpha particles
Short range (heavy)
0.03mm in body tissues
Stopped by few sheets of paper
Beta particles
Short range but further than alpha
1mm in tissue
Stopped by 0.5cm aluminium
Gamma rays and X rays
Long range
70cm in water
Penetrates lead - need thick shielding (around ovaries)
Why does lead stop gamma rays?
Dense nuclei
What happens with ionising radiation on the body?
Loses energy through collision as it goes through body tissues cause localised heating
Creates ion pairs when going through tissue, will cause damage of DNA and cell deaths
Tissue damage from within or outside
W: problem with alpha & beta
Less an issue with gamma & X rays
O: less an issue with alpha & beta
Problem with gamma & X rays
What radiations are used for diagnosis and which to treat?
Gamma & X rays for diagnosis
Alpha & beta to treat
How do we use beta radiation in cancer treatment?
Injection or ingestion destroy cancer cells due to penetration range
What order is radioactive decay?
1st (exponential decay)
rate of decay (proportionate to) no. of radioactive atoms
High nuclei means higher rate of radioactive decay
Rate law
R (proportionate to) N
So, R = kN
k being constant
R = rate of decay
N = no. of radioactive nuclei
Integrated rate law
lnN(t) = ln N(0) - k x t
N0 = no. radioactive nuclei at t = 0
Nt = no. of radioactive nuclei at time = t
Half life
t1/2 = 0.693/k
(k= 0.693/t1/2)
t1/2 = time for half radioactive nuclei present to decay
Works out nuclei after half-life or figure out half-life
Examples of gamma and beta decay mode
Iodine-131
Used for treatment of thyroid conditions
Examples of gamma decay mode
Technetium-99m
Indium-111
Used for diagnostic imaging
What is nuclear medicine?
Medical modality that utilises radioactivity (radiopharmaceuticals) to diagnose and treat disease
What is radiopharmaceuticals?
Preparations of constant composition, radiochemical, radionuclidic purity & uniformity of physiological action for nuclear medicine use as diagnostic or therapeutic agents
Radiography vs Nuclear medicine
R: radiation outside of body to diagnose to see organ function with X rays
NM: radiation within body, inject or ingest to treat (beta emitter) or diagnose (gamma emitter) - use gamma rays
What is the optimum dose of a radiopharmaceutical?
Which treat/diagnose with least amount of radiation dose or exposure to patient
What is a radionuclide in radiopharmaceuticals?
Tagged onto chosen pharmaceutical so after admin. of radiopharmaceutical, radiations emitted from it are detected by radiation detector so organ is assessed
Radiopharmaceuticals applications: diagnostic images
Radionuclide short half-life and emits only gamma radiation
Tc-99m: example
Half life is 6 hours and gamma emission 140KeV ideal for diagnostic imaging
Radiopharmaceuticals applications: therapeutic use
Radionuclides should emit particulate radiation (beta particles) which deposits radiation within target organ
Iodine-131 used for hyperthyroidism & metastatic disease of thyroid eradication
Emits both beta and gamma radiation to diagnose and therapeutic
What is theranostics?
Form of precision medicine that combines radioactive materials (radioisotopes) with molecules designed to target cancer cells
Becquerel (Bq)
1Bq = 1 radioactive decay per second
Curie (Ci)
1 Curie = 37 GBq
Radiopharmaceutical doses are dispensed to patients in units of activity so mCi or µCi
Gray (Gy) = 1J/kg
Measure of how much energy from radiation has been deposited in body (absorbed dose)
1 Gy = 1J absorbed by 1kg of tissue
Sievert (Sv) = 1J/kg
Same as Gy but different interpretation
Equivalent dose (Sv) = absorbed dose (Gy) x radiation weighting factor (Q)
What does radiation weighting factor depend on?
Radiation type and tissue type & distance
Production of radionuclides: cyclotron
Daughter nuclide is relatively neutron-poor, decays beta + emission or X rays
Production of radionuclides: nuclear reactor
Daughter nuclides usually neutron-rich, decay by beta emission (iodine-131 produced by nuclear fission of uranium-235 in nuclear reactors
Production of radionuclides: generator
Used in hospital for Tc-99m production, emits gamma radiation
