Lecture 3 Flashcards
How is an isotope written?
N = chemical symbol
A = number of nucleons (protons and neutrons)
Z = atomic number
What is the equation for the total weight of the constituent parts of an atom?
W = total weight
Z = atomic number
A = number of nucleons (protons + neutrons)
mₑ = electron mass
mₚ = proton mass
mₙ = neutron mass
Define mass deficit
The difference between the sum of the parts of an atom (W) and the actual mass (M). This can be given by the equation W - M.
Define binding energy
The energy ascribed to the missing mass (mass deficit) in amu.
What is the equation for binding energy?
BE = binding energy
W = total weight
M = actual mass
Define binding energy per nucleon
The binding energy divided by the number of nucleons.
What is the equation for binding energy per nucleon?
E = binding energy per nucleon
W = total weight
M = actual mass
A = number of nucleons
Describe the shape of a plot of binding energy per nucleon against the number of nucleons
What is a Segre chart?
A diagram in which the number of protons in a nucleus is plotted against the number of neutrons.
The general trend of the Segre chart shows that _______ elements are alpha emitters.
Heavier
Where are beta emitters found on the Segre chart?
Above and below the band of stability (before the heavy alpha emitters). Beta+ is found above the band and beta- is found below the band.
Define alpha radiation
Ionising radiation that consists of alpha particles, emitted by some substances undergoing radioactive decay.
What is emitted in alpha decay?
A helium nucleus
What energy does an alpha particle have?
Energy in the order of 5 MeV
What are alpha particles stopped by?
Skin
What elements usually undergo alpha decay?
Heavier elements with an atomic number, Z, greater than 82.
How often is alpha radiation used for therapy?
Rarely (except for some radio-pharmaceuticals)
What happens to an element when it undergoes alpha decay?
2 protons (and 2 electrons) are lost from the atom so the element is transmuted and changes into a different one.
Define beta radiation
Beta radiation is a high-energy, high-speed electron or positron emitted by the radioactive decay of an unstable nucleus during the process of beta decay.
What is emitted in beta decay?
An electron (or positron) and an antineutrino (or neutrino)
What energy does a beta particle have?
0.6 - 2 MeV
What are beta particles stopped by?
Foil
Give an example of when beta decay is used for therapy
Iodine-131 is used to treat thyroid cancer. It has a half-life of 8 days and an energy of 610 keV.
What happens to an element when it undergoes beta decay?
The atomic number increases but the mass number decreases.
Define gamma radiation
A penetrating form of electromagnetic radiation in the form of a gamma ray.
What is emitted in gamma decay?
A photon
When does gamma decay occur?
It is usually a by-product of beta decay from meta-stable states.
What energy does a gamma ray have?
0.1 - 1.5 MeV
What are gamma rays stopped by?
They aren’t easily stopped so travel in straight lines.
What is gamma radiation used for in therapy?
- Tracer detection
- Radio-label for pharmaceuticals
- SPECT
- gamma cameras
How is 99-Tc made?
99-Mo (molybdenum) undergoes beta decay in a process known as elution, becoming a metastable state of technetium (99m-Tc). 99m-Tc then undergoes gamma decay to become 99-Tc.
What is the energy of 99-Tc?
140 keV
