Physics Flashcards
What is the atomic number (Z)
Number of protons
What is the Pauli exclusion principle?
Maximum number of electrons per shell
X=2n^2
What is binding energy?
How does atomic number affect it? How does the shell distance affect it?
Energy required to remove an electron from an atom
The electric force is inversely proportional to the shell distance, so farther shell electrons have a lower binding energy
A higher atomic number has a higher net positive charge, and thus a higher net energy to overcome
What is “ground state”
An atom with no vacancies in its inner shell
What are the 2 processes that occur when energy is applied to an atom?
Ionization and excitation
What is the difference between ionization and excitation?
Ionization results in an energized electron going free (net charge +1)
Excitation results in an energized electron jumping a level (net charge 0)
What is a “characteristic x ray”
When an inner shell electron leaves, an outer shell electron will jump to fill its place, releasing energy equal to the difference in binding energies of the two shells - known as the characteristic X-ray
What is the auger electron
The energy released from the expulsion of an inner shell electron can transfer to an outer shell electron, which is expelled without production of the characteristic X-ray - termed to auger electron
Which elements (heavy/light) are more likely to produce characteristic X-rays?
Heavier, as they have more electrons and thus a higher TOTAL number of reactions
What is the atomic mass (A)
Protons + neutrons
What is an isotope
Example?
Same atomic number (z), different atomic mass (n)
Hydrogen -> tritium
I123 vs I131
What is an isobar?
Example?
Same atomic mass (a), different elements
I131 vs Xe131
What are isotones?
Example?
Same neutrons, different atomic number (z)
O18, F19, N20
isotoNe = same N
What is an isomer?
Example?
Same N and Z, different energy state
99tc vs 99mTc
Why do heavier elements (A>40) have a ground state where N>Z?
Because the amount of repulsive forces between the higher amount of protons means more attractive forces between N-P and N-N are needed, which requires more N
Eg Pb has Z=82 and N=125
What are two factors that may cause nuclear instability?
Nonstable N:Z
Excessive energy carried by nucleus
What is gamma decay?
What are the end products?
A nucleus in its excited state transforms to a more stable lower energy state by emitting a gamma photon to carry away the excess energy
No compositional changes occur, only a loss of energy in the form of a gamma photon
Eg 99mTc -> 99Tc + gamma where gamma = 140.5 kev
What is B-decay?
What are the end products?
A nuclear neutron changes to a proton plus an electron and an antineutrino
n -> p + e + uu
a. a
X -> Y
z z+1
What happens to the mass in B-decay?
The atomic mass stays the same,that is, A is constant because we’re are exchanging a Z for an N
The actual mass will be slightly lower because of the mass carried away by the electron and kinetic energies of e and uu
What are the 2 main differences between internal conversion and beta-decay?
1) in Beta-decay, the electron comes from the nucleus. In IC, the electron comes from orbit
2) beta-decay electrons are on a continuous spectrum of energy, whereas IC electrons are discrete in energy
Give a clinical example of beta-decay
99Mo -> 99mTc + e-
In vivo,
99mTc -> 99Tc + gamma (and conversion electrons)
What causes harm during use of 99mTc
Isomeric transmission of 99mTc to 99Tc releases gamma and conversion electrons. The conversion electrons damage the tissue
What is electron capture?
What are the end products?
An orbital electron in an inner shell is captured by the nucleus
The captured electron then combines with a proton to form a neutron
p + e -> n + neutrino
a. a
X. Y
z. z-1
What is internal conversion?
The nucleus releases excess energy by imparting it onto an orbital electron, which can be ejected if the energy supplies is higher than the binding energy
Excess energy becomes kinetic energy for the lost electron
