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