Radioactive Decay and Half-Life

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What is the physical half-life of a radionuclide?

The time taken for its activity to decay to one-quarter of its original value

The time taken for its activity to decay to three-quarters of its original value

The time taken for its activity to decay to zero

The time taken for its activity to decay to half of its original value (correct)

What happens to the number of radioactive nuclei over time?

It decreases exponentially (correct)

It remains constant

It fluctuates randomly

It increases exponentially

How many half-lives does it take to reduce the activity of a radionuclide by a factor of 1000?

5

20

10 (correct)

15

What is the effect of heat, pressure, electricity, or chemical reactions on the physical half-life?

It has no effect on the physical half-life Signup and view all the answers

What happens to the number of radioactive nuclei in two successive half-lives?

It decreases to one-quarter of its original value Signup and view all the answers

What is the shape of the graph of the number of nuclei present as a function of time?

Exponential Signup and view all the answers

What is a characteristic of the physical half-life?

It is a fixed characteristic of the radionuclide Signup and view all the answers

What is the range of physical half-life of radionuclides?

From fractions of a second to millennia Signup and view all the answers

Which radionuclide has a physical half-life of 67 hours?

Molybdenum-99 Signup and view all the answers

What is the term for the pharmaceutical that has been labelled with a radionuclide?

Radiopharmaceutical Signup and view all the answers

What is the biological half-life of a pharmaceutical referring to?

The rate of elimination from the body Signup and view all the answers

Why do radionuclides form part of a salt or organic compound in medical imaging?

To ensure they concentrate in the tissues or organ of interest Signup and view all the answers

What is the term for the time it takes for the concentration of a radionuclide to decrease by half in the body?

Effective half-life Signup and view all the answers

What happens to a radiopharmaceutical when it is administered alone?

It is gradually eliminated from the body by metabolic processes Signup and view all the answers

What determines the decay of radioactivity in a specific tissue or organ when a radiopharmaceutical is administered to a patient?

Both the physical half-life and the metabolic turnover and excretion of the radiopharmaceutical Signup and view all the answers

What is the relationship between the effective half-life and the physical and biological half-lives?

teff < tbiol, tphys Signup and view all the answers

What is a desirable property of a radionuclide for imaging?

A physical half-life of a few hours Signup and view all the answers

What is the significance of the daughter nuclide in a radiopharmaceutical?

It should have a very long half-life Signup and view all the answers

Why is it important to consider the disease state of the patient when using radiopharmaceuticals?

It affects the effective half-life of the radiopharmaceutical Signup and view all the answers

What happens if the physical half-life of a radionuclide is too short?

Too much activity is prepared Signup and view all the answers

What is the relationship between the effective half-life and the physical and biological half-lives in terms of their reciprocals?

1/teff = 1/tbiol + 1/tphys Signup and view all the answers

What type of radiation is desirable for imaging due to its ability to exit the patient?

Gamma rays Signup and view all the answers

What is the ideal energy range of gamma rays for imaging?

50-300 keV Signup and view all the answers

What property of gamma rays is useful for eliminating scattered radiation?

Monoenergetic Signup and view all the answers

Why is it important for a radionuclide to be easily attached to a pharmaceutical at room temperature?

To prevent its metabolism Signup and view all the answers

What is a desirable property of a radionuclide for imaging in terms of availability?

Readily available at the hospital site Signup and view all the answers

What is the significance of high specific activity in a radionuclide?

It reduces the dose to the patient Signup and view all the answers

What is a desirable property of a radiopharmaceutical in terms of localization?

It localizes largely and quickly in the target tissue Signup and view all the answers

Why is it important for a radiopharmaceutical to have a low toxicity?

To minimize its side effects Signup and view all the answers

What is a desirable property of a radiopharmaceutical in terms of elimination?

It is eliminated quickly from the body Signup and view all the answers

What is a desirable property of a radiopharmaceutical in terms of stability?

It forms a stable product both in vitro and in vivo Signup and view all the answers