Radioactivity

Question 1

What are the units of activity? SI? Common units?

Answer 1

SI: Bq
Common: Ci

1 Ci = 3.7 x 10^10 dps or Bq
1 Bq = 2.7 x 10-11 Ci

Question 2

What is specific activity?

Answer 2

activity/MASS of the radionuclide
*carrier free

Question 3

What does carrier free mean?

Answer 3

samples that only contain the radionuclide in question

Question 4

What does carrier mean?

Answer 4

samples that contain the radionuclide PLUS a stable or longer lived isotope of radionuclide in question

Question 5

Why is knowing a specific activity important?

Answer 5

• Toxicity of a chemical or drug is always dependent on the amount of the chemical or drug administered to the patient.
• distribution of a radiochemical in a biological system may depend on the amount of carrier present in the sample
• labeling efficiency of a radionuclide to a chemical is also sometimes dependent on the specific activity of the radionuclide

Question 6

What is the formula for the exponential decay law?

Answer 6

Nt = N0e^-λt

Nt = remaining number of atoms after time (t)
N0 = initial number of atoms
λ = decay constant
e = base of natural log (2.71828)

Question 7

When can the exponential decay law be used?

Answer 7

when the number of atoms is large enough for statistical averaging.

Question 8

How is the decay constant calculated?

Answer 8

λ = 0.693/T1/2

Question 9

What is specific weight?

Answer 9

• it is used to determine the actual mass of a radionuclide
• need to be calculated to determine the standpoint of toxicity

Question 10

What is the formula for specific weight?

Answer 10

Specific weight = (atomic weight (g/mole) x # of atoms)/avogadroes # (atoms/mole)

1 mole = 6.02 x 10^23 atoms
# of atoms = activity (Bq)/λ (/sec) –> Nt = At/λ

Question 11

What is the formula to calculate # of moles?

Answer 11

Nt = At/λ

Question 12

Physical half-life of Cesium-137 (Cs-137).

Answer 12

30 years

Question 13

Physical half-life of Cobalt-57 (Co-57).

Answer 13

272 days

Question 14

Physical half-life of Fluorine-18 (F-18).

Answer 14

110 minutes

Question 15

Physical half-life of Gallium-67 (Ga-67).

Answer 15

78 hours

Question 16

Physical half-life of Indium-111 (In-111).

Answer 16

2.8 days

Question 17

Physical half-life of Iodine-123 (I-123).

Answer 17

13.2 hours

Question 18

Physical half-life of Iodine-131 (I-131).

Answer 18

8.05 days

Question 19

Physical half-life of Molybdenum-99 (Mo-99).

Answer 19

66.7 hours

Question 20

Physical half-life of Phosphorus-32 (P-32).

Answer 20

14.3 days

Question 21

Physical half-life of Technetium-99m (Tc-99m).

Answer 21

6.0 hours

Question 22

Physical half-life of Thallium-201 (Tl-201).

Answer 22

74.0 hours

Question 23

Physical half-life of Xenon-133 (Xe-133).

Answer 23

5.29 days

Question 24

How do you calculate the average mean life?

Answer 24

T = 1.443 * T1/2

Question 25

What is biological half-life?

Answer 25

time required for the body to eliminate one half of a radiopharmaceutical dose by regular elimination processes

Question 26

What is effective half-life?

Answer 26

the time required for a given dose of a radiopharmaceutical in the body to be reduced to one half of its original value due to its decay process AND biological elimination

Question 27

Physical half-life of Iodine-125 (I-125).

Answer 27

60 days