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Flashcards in Physics Deck (36):

What is the atomic number (Z)

Number of protons


What is the Pauli exclusion principle?

Maximum number of electrons per shell



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


Same atomic number (z), different atomic mass (n)

Hydrogen -> tritium

I123 vs I131


What is an isobar?


Same atomic mass (a), different elements

I131 vs Xe131


What are isotones?


Same neutrons, different atomic number (z)

O18, F19, N20

isotoNe = same N


What is an isomer?


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


WHat two processes release excess energy

Gamma decay and internal conversion


What is beta+decay and annihilation?

What are the end products?

The release of a positron from the nucleus with a neutrino

P -> n + e + neutrino

a. a
X. Y + e
z. z-1


What is annihilation?

Two particles of opposite charge combine to make photons

The loss of a positron in beta+decay loses kinetic energy in collisions after a few mm. The positron will then combine with an electron and create two be photons

e+ + e- -> 2p


In beta+ vs electron capture, which is more likely to occur in heavier elements? Lighter?

Lighter = beta+

Heavier = electron capture, electrons tend to be closer to the nucleus


What is alpha decay?

What are the end product?

Nucleus releases an alpha particle containing 2p and 2n

a. a-2
X. Y + alpha
z. z-2


What is nuclear fission

A heavy nucleus spontaneously bursts into two lighter nuclei


What is the activity equation?


A(t) = - deltaN(t) / delta t

SI: Becquerel (Bq), one decay per second

Traditional: Curie (Ci), 1 Ci = 3.7 x 10^10 dps

Thus, 1Ci = 37 MBq


What is the decay equation

N(t) = N(0) x e^-(lambda x t)


What is the relationship between radioactive decay and half life

Lambda (decay constant) = ln2/t(1/2)


What is the average life? Effective half life?

The average half life is the expected lifetime of an individual radioactive nucleus in sample

It's longer than half life because some individual nuclei are longer lived and skew distribution

T(avg) = 1.44 t(1/2)

Effective half life takes into account the physical decay (Tp) as well as biological excretion (Tb)

Te = (TpTb)/(Tb+Tp)


What is secular equilibrium? Transient equilibrium?

Secular: quantity of an isotope remains stable because its production rate is equal to its decay rate

Occurs when half life of child is much less than parent

Transient: occurs when child half life is slightly less than parent


What is the Bohr model?

Central nucleus surrounded by rotating electrons