Radiation and Radionuclides Flashcards
Typical distance traveled by an alpha particle (4-8 MeV) in tissue
.03 mm
Amount the mass number (A) decreases in alpha decay
4
Designated by “A”, refers to the number of protons plus neutrons
Mass Number
Designated by “Z”, refers to the number of protons
Atomic Number
The atomic number above which K shell electrons have an energy > 25 KeV (useful for imaging)
50
Electron capture is sometimes called the inverse of
β- decay
The force keeps the nucleus bound
Strong Nuclear Force
Transition energy required for β+ decay
1.022 MeV
True or False, transitions from any electron orbital shell to any other orbital shell are allowed
False, some transitions are not allowed due to selection rules of quantum mechanics
The average β- energy is
1/3 E Beta Max
c = ?
c = λν
(wavelenth × frequency)
Name two isotopes that decay solely by β- decay
3H
14C
32P
Internal conversion
Energy is transferred directly to an inner shell electron, which is ejected from the atom.
In this decay chart, the atomic number does what?
Atomic number is increasing, going to 14N
This chart illustrates what type of decay?
Isomeric Transition
An alternative to γ emission
Internal conversion
True or False
There can be subtle differences in chemical behavior based on varying isotope mass, e.g., 3H
True
Internal conversion and electron capture can be very slightly altered by the chemical environment
True
β- decay produces this massless particle
Anti neutrino
β+ decay produces this massless particle
Neutrino
ν
Two medically relevant isotopes that undergo β- decay are
131I
137Cs
133Xe
A medically relevant isotope that undergoes isomeric transition
99mTc
This graph illustrates what type of decay
Internal conversion
2 forms of radiation following internal conversion
characteristic x-rays
auger electrons
True or False
As compared to β- decay, electrons from internal conversion have a discrete series of energies.
True
The most popular radionuclide for nuclear imaging studies.
99mTc
Medically important radionuclides that decay via (EC,γ)
57Co
67Ga
111In
123I
125I
201Tl
In electron capture, Z
decreases
True or False
The K-xrays of lighter elements and all L-xrays are of lower energy and not suitable for external measurments.
True
Sometimes called inverse beta decay
Electron Capture
Average β+ energy
1/3 E β+, Max
In β+ decay, Z ___________
decreases
Medically important β+ radionuclides include
18F
15O
13N
11C
EC tends to occur in _________elements while β+ occurs more frequently in __________elements
heavier
lighter
Fraction of 18F decaying by β+
97%
True or False
Odd-odd nuclei tend to be more stable than even-even nuclei
False
Even-even nuclei are relatively stable because of pairing of alike particles within the nucleus.
For a giving decay mode, the branching ratio (B.R.) for the ith decay mode is given by
B.R. = λi / λ
For a nuclei with multiple decay paths, the decay constant =
λ = λ1 + λ2 + λ3 + …
Given the half-life of an isotope, the decay constant can be calculated as
λ = ln(2) / t½
or
.693 / t½
1 Ci = ____________dps (Bq)
3.7 E10
1 mCi = _______________MBq
37
The average half-life of a radionuclide =
τ = 1 / λ
or
1.44 t½
Image frame decay corrections may be needed when the imaging time is ____________ relative to the half-life of the isotope.
long
e.g., F-18
The effective decay factor for image count correction can be calculated as
DFeff (t, Δt) ≈DF[t + Δt/2]
accurate to within 1% for
x<0.5 where x = ln(2) × Δt/T½
The specific activity (Bq/g) of an isotope can be calculated as
Bq/g = λ × 6.023E23 / GAW
GAW ≈ gram atomic weight [g/mol]
The highest specific activity of a radionuclide is its ___________
CFSA
carrier-free specific activity
For a mixture of radioisotopes, the total activity =
A = A1 + A2 + A3 + …
The Bateman equation describes _________________ relationships.
parent-daughter
The Bateman equation is given by
_________________________
and describes the activity of the ________________ as a function of time
daughter
In secular equilibrium, the relationship of the parent daughter half-lives is
λd>>λp
or
Td << Tp
In secular equilibrium the Bateman equation simplifies to
This graph illustrates
Secular equilibrium
An example of medically relevant transient equilibrium is
99Mo (T½ = 66 hr) ⇒ 99mTc (T½ = 6 hr)
This figure represents
Transient equilibrium
For a radionuclide approaching secular equilibrium with a branching ratio of 1, the daughter activity at 1 and 2 daughter half-lives can be estimated as _____________, _______________. The activity of the daughter will effectively equal the activity of the parent after about ___________ .
Ad = (1/2) Ap
Ad = (3/4) Ap
5 Td
In transient equilibrium, the ratio of daughter to parent is
Ad / Ap = [Tp/ (Tp - Td)] × B.R.
Remember in transient equilibrium Tp > Td so to keep things positive the equation must be Tp - Td
In transient equilibrium, the maximum daughter activity is at
tmax = [1.44 TpTd / (Tp - Td)] ln(Tp/Td)
ln() must be positive so (Tp/Td)
No equilibrium occurs in what circumstance?
td>tp
The parent isotope of 99mTc is mainly 99Mo, extraced from __________ ___________
fission products
An alternative approach to the production of 99mTc is through an accelerator, based on the reaction __________________
100Mo(p,2n)99mTc
Most I-131 production is via
neutron activation
irradiation of a tellurium (Te-130) target which becomes Te-131 and decays with a half-life of 25 min to I-131
Neutron activated radionuclides of medical importance include
14C
32P
125I
131I
Radionuclides produced via neutron activation tend to decay via _______
β-
Two nuclear reactions commonly used to produce radionuclides using an accelerator are
(p,n)
(d,n)
Cyclotron radionuclides of medical importance include
11C
13N
15O
18F
67Ga
111In
123I
201Tl
The branching ratio of Mo-99 to Tc-99m is
.876
Reaction cross sections are measured in units of
barns
(1b = 10-24 cm2)
Flux density (ɸ) is measured in terms of
particles / unit area · sec
Activation rate (R) per unit mass of target material is
R≈Δɸ/m
R≈(6.023× 1023)σ ɸ/A {activations / g sec}
A = gram atomic weight
Anion
negatively charged ion
Effective half-life equation
1/te = 1/tp + 1/tb
Roentgen
It is the amount of gamma or x-rays required to produce ions resulting in a charge of 0.000258 coulombs/kilogram of air under standard conditions. Named after Wilhelm Roentgen, the German scientist who discovered x-rays in 1895.
2.58E-4 C/kg
Nuclie
A general term referring to all known isotopes both stable (279) and unstable (about 2700) of the chemical elements.
Measurement errors at the bottom of the dose calibrator can be between
3-6 %
Dose calibrator response can be up to ________ off for sources placed laterally from the central axis.
10%
For the geometry test - when pulling saline into the syringe (diluting the source volume), use a bent needle to
break the vacuum and prevent backflow into the dilution vial
In geometry test for dose calibrator, one approach is to use multiple syringe, reading at 20% intervals. Syring sizes could be
1cc
3cc
5cc
10cc
Geometry testing fails if the error exceeds
5%
Dose calibrators are very long-lived systems, often used for well over
a decade or more
Survey meter (Geiger-Mueller Detector) checks should be performed
daily with use
Three different quality control measures for survey meters are
battery check
sealed source check
calibration
The selection, use, calibration and quality assurance of dose calibrators is described in AAPM TG Report
181 (June 2012)
The PET technologist should ensure the clock in the hotlab matches the clock in the console room this frequently
daily
Clock accuracy should be within
1 minute , synchronized to a standard time (e.g., values transmitted to a cellular telephone or those maintained by NIST
Physical inspection of a radionuclide calibrator should include
visual check for damaged source holders, keypads, buttons, switches
visual check for any small items in the well
visual check of the display screen
System electronics associated with a radionuclide calibrator are gennerally done
using a manufacturer-provided diagnostic test
Ba-133 half-life, decay mechanism and primary radiation
10.74 yr
e- capture
356 keV (62%)
Energies of photons MeV (intensity %/d):
.031 (.969), .035 (22.6%), .053 (2%), .0796 (3%), .081 (34%), .276 (7%), .303 (18%), .356 (62%), .383 (9%)
Iodine escape peaks are more prominent with
lower energy x-rays due to the probability of photoelectric absorption interactions
Secular equilibrium will occur when the half-life of the parent is roughly ________ x that of the daughter
100
