01- Atoms, Radiation And Radioactivity

Front 1

What determines the chemical properties of Atoms?

Back 1

The number of electrons; in electrically neutral atoms, #of electrons =Z

Front 2

What is Z?

Back 2

Z=Number of protons

Front 3

What is the Pauli exclusion principle?

Back 3

The maximum number of electrons allowed for an inner shell = 2n^2

K=1; 2 electrons
L=2; 8 electrons
M=3; 18 electrons

Front 4

What is the binding energy of an electron?

Back 4

Energy required to remove an electron from an atom

Front 5

Is electrical force directly or indirectly proportional to distance

Back 5

Electrical force is inversely proportional to the square of the distance between two charged particles; 1/d^2

K shells are the most 'tightly bound.'

Binding energy increases with larger Z values (larger nuclear charge)

Front 6

What are the 2 possible outcomes when energy is imparted on an atom's electron?

Back 6

1) energy is stong enough to overcome binding energy of inner shell electron which creates a vacancy (ionization)

2) energy is not strong enough, electrons may jump to an outer shell electron and holds the energy (excitation)

Front 7

What are the 2 possible outcomes of an excited electron?

Back 7

1) Release of "characteristic x-ray"
2) Release of "Auger Electron"

Front 8

What is a 'characteristic x-ray'?

Back 8

Xray photon released released when an excited outer shell electron fills the vacancy of an inner shell electron.

Energy is equal to difference in binding energy between the 2 shells.

Front 9

What is an 'Auger Electron'?

Back 9

Outer shell electron released when excited inner shell electron falls to its ground state. No x-rays are released in this process.

Front 10

Are heavy elements more likely to generate characteristic xrays or Auger electrons?

Back 10

Heavy elements: Characteristic xrays
Light elements: Auger electrons

Front 11

What is a A?

Back 11

A = mass number= number of protons + neutrons
(aka: number of 'nucleons')

Protons carry a +charge
Neutrons are neutral

Front 12

Atomic Nomenclature: Define Variables

Back 12

X= Element symbol; defined by Z:

A= Mass number
Z= Atomic number
N= Number of Neutrons = A-Z

Front 13

What are the opposing forces in a nucleus

Back 13

Repulsive forces between protons
Attractive forces between nucleons (protons and neutrons)

Front 14

What is the half life of Tc99m
When it decays, how is the energy released?
What is the energy released?

Back 14

6hrs
gamma radiation
140.5 keV

Front 15

What are isotopes

Back 15

isotoPe= same number of Protons = same Z

Front 16

What are isobars

Back 16

isobAr= same atomic mass number = same A

Front 17

What are isotones

Back 17

isotoNe= same number of Neutrons = same N

Front 18

What are isomers

Back 18

isomer= same composition but different energy= same N and Z.

Front 19

What is line of stability

Back 19

The N/Z ratio needed to maintain nuclear stability.
For low Z elements N/Z=1
For high Z elements N/Z approaches 1.5
Rationale: Attractive forces occur between protons:neutrons and neutrons:neutrons. As repulsive forces increase (Z), more neutrons are necessary to maintain attraction.

Front 20

What is gamma decay?

Back 20

An excited nucleus transforms to a more stable lower energy state by emitting the extra energy as a gamma photon. No change in composition of nucleus (therefore called ISOMERIC transition)

Front 21

What is B- decay?
Does this occur in a neutron-rich or neutron-poor nucleus

Back 21

Occurs in neutron-rich nucleus
N-> P + e- + V(antineutrino)
Net conversion is neutron to proton.

Front 22

What is V(antineutrino)?

Back 22

antiparticle that carries energy but neither mass nor charge.

Front 23

How does the mass number change after B- decay

Back 23

It doesn't. The total number of nucleons are unchanged.

Front 24

How does the atomic number change after B- decay

Back 24

Z+1

Front 25

What's the difference between the free electron emitted in B- decay and the electron released from internal conversion?

Back 25

B- decay electron is released from the nucleus (and have a continuous energy spectrum)
internal conversion electron is an orbital electron (and caries a discrete series of energies)

Front 26

What form of radioactive decay is used to PRODUCE
Tc99m

What is the formula?

Back 26

B-decay

99Mo-> 99mTc +e- + V(antinutrino)

Front 27

How does 99mTc decay?

What are the 2 possible release products?

Back 27

gamma decay

99mTc->99Tc + gamma photon (or conversion electron)

The gamma photon contributes to image formation
The conversion electron will be completely absorbed by the patient.

Front 28

What is electron capture?
What is the net effect?
This results in a similar effect on the nucleus to what other form of decay?

Back 28

An orbital electron is "captured" by the nucleus, combines with a proton to form a neutron.

Z-1

Same net result as B+ decay

Front 29

With respect to B+ decay and Electron capture, which occurs among heavier elements and lighter elements

Back 29

Heavy elements= electron capture
light elements= B+ decay

rationale: electrons are closer to nucleus in heavy elements, increasing likelihood of "capture"

Front 30

What happens to the vacancy in the electron shell after electron capture?

Back 30

Vacancy is filled by an outer shell electron and produces either a characteristic xray or Auger electron.

Front 31

What is internal conversion?
What happens to the electron if the energy released can overcome the binding energy.

Back 31

Alternative to gamma decay where energy is transferred to orbital electron.

It it released from the atom and is termed a conversion electron.

Front 32

Which orbital electrons are most likely to participate in electron capture, or internal conversion?

Back 32

Inner shell, K and L

Front 33

What is B+ decay
What is the formula
What is the net effect on the nucleus

Back 33

P->N + e+ +V(neutreno)
Z-1

Front 34

Does beta decay occur in proton-rich or proton-poor excited nuclei

Back 34

Proton-rich

Front 35

What happens to the positron released during B+ decay?

Back 35

combines with an electron in the environment to undergo annihilation.

Front 36

What are the products of annihilation

Back 36

Two 511keV gamma rays which travel in opposite directions

Front 37

What is the prototypic imaging modality based on B+ decay?
What is the nuclide?
What is the formula?

Back 37

PET imaging
F18
18F ->18O +e+ + Neutreno
e+ + e- -> 2 gamma photons

Front 38

What is alpha decay/ alpha particle

Back 38

Nucleus ejects alpha particle (2 protons and 2 neutrons)

same as 4He nucleus

Front 39

What is the only form of radioactive decay that alters the atomic mass?

Back 39

alpha decay

Front 40

What is nuclear fission?
What are the products?

Back 40

Heavy nucleus spontaneously breaks into 2 lighter nuclei

Front 41

What is the formula to measure radioactivity (A)?
What is the SI unit of decay?
What is the Traditional unit of decay?
How are they related?

Back 41

A(t)=-dN/dt
SI unit= bacquerel (Bq) = 1decay/sec
Traditional unit= Curie (Ci)= 3.7X10^10 decay/sec
1mCi=37 MBq

Front 42

Radioactivity Example:
N(0)=1000
decay constant 0.1/sec= 10%/sec
how many radioactive nuclei remain after 3 sec?

Back 42

729

Front 43

What is physical half life?
What is the equation?

Back 43

Time it takes to decrease the number of radioactive nuclei by 1/2
0.693/(lambda) decay constant

Front 44

What is average life?
What is the formula

Back 44

The average life of a large quantity of nuclei
1.44 x T1/2

Front 45

What is effective half life (Te)?
What is the formula?

Back 45

Life of a radionuclide in a patient that factors physical half-life (Tp) and biologic half-life (Tb)

Te=TpTb/(Tp+Tb)

The product divided by the sum

Front 46

What is parent-child-grandchild decay?

Back 46

An unstable parent nuclide decays to a child nuclide which may not be stable. This will undergo another decay to produce a grandchild nuclide.

example 99mTc
1. 99Mo->99mTc +e- + V(antinutrino)
2. 99mTc->99Tc +2 gamma photons (or conversion electrons)

The decay of the child is dependent on the both the half lives of the parent (Tp) and child (Tc)

Front 47

What pattern of equilibrium occurs when the half life of the parent is long (approaches infinity)

Tp>>>Tc

Back 47

Secular equilibrium
Ac will increase and by 5 child half live (Tc) will =Ap

Example (226Ra)

Front 48

What pattern of equilibrium occurs when the half life of the parent is longer than the child but not that long?

Tp>Tc

Back 48

Transient equilibrium
Ac will peak and then decline at the same rate of Ap

Ex: 99mTc: Peaks by 24hrs then degrades
Why we whould extract from generator once/day for maximal activity

Front 49

What pattern of equilibriium occurs when half life of the child is longer than the parent?
Tc>Tp

Back 49

No equilibrium,
Ac will peak and decline at a rate with no relationship to the parent activotu

Front 50

T1/2 example:
If a radionuclide decays at 1%= lambda=0.01/day), how long will it take to decay to half of its original activity

Back 50

70 days

T1/2= 0.693/lambda

Front 51

Effective halflife example:
If the biological and physical half lives of a radionuclide are both 3hrs, the effective half life is how long?

Back 51

1.5 hrs

Te=TpTb/(Tp+Tb)

Front 52

The binding energy of an electron depends one what?

Back 52

distance from nucleus.
Inner shell electrons have higher binding energies than outer shell electrons

Front 53

B+ decay example:
In B+ decay of potassium to 40Ar18, A, N and Z of potassium are:

Back 53

A=40
Z=19

Front 54

How may half lives must pass for the radioactivity to decay to 10%

Back 54

3-4 half lives

Front 55

What is the half life of 99mTc?

Back 55

6 hours