NM Radiation Safety

The inverse square law in words, says:

• If you double the distance from the source of activity, you reduce exposure to 25% of the original activity.

• If you halve the distance from the source of activity, you decrease exposure to 25% of the original activity.

• If you halve the distance from the source of activity, you increase exposure to 25% of the original activity.

• If you double the distance from the source of activity, you reduce exposure to 50% of the original activity.

Answer explanation

By doubling the distance, the intensity is reduced to one quarter of the original activity, as shown in the formula below, where I₁ is the original intensity, I₂ is the new intensity, d₁ is the original distance from the source , and d₂ is the new distance from the source.

I₁ = (d₂)²/I₂ = (d₁)2

rearranged as

(I₁)(D₁)² = (I₂)(D₂)² for easy solving

Which of the following should be used when administering an intravenous pharmaceutical to a patient?

• Lead syringe shield

• Leaded eyeglasses

• Gloves

• (a) and (b) only

Answer explanation

Pharmaceutical not radiopharmaceutical

What is the dose rate limit at the package surface for a Yellow III radioactive package?

Gaseous radiopharmaceuticals may only be used in rooms that:

• Have heating/cooling capibilities

• Contain wall oxygen

• Are at positive pressure compared to surrounding rooms

• Are at negative pressure compared to surrounding rooms

Answer explanation

Airborne radiation such as aerosols or gasses should be administered in rooms that are at negative pressure to surrounding areas

A type A package bears a DOT Class II Yellow radioactive label, has a transport index of 0.8 and contains 10mCi of In111 oxine. What is the exposure rate at 3 ft from the package?

• 0.4 mR/h

• 0.8 mR/h

• 10 mR/h

• Cannot be determined from the given information

What is the transport index maximum of a White I radioactive package?

• Background

• 0.5 mR/hr

• Less than or equal to 0.5 mR/hr

• 1 mR/hr

What is the annual dose limit allowed to the lens of the eye?

• 1.5 mrem

• 15 rem

• 50 rem

• 5 mrem

What’s is the annual dose limit to the skin of extremities?

• 5 rem

• 50 rem

• 5 mrem

• 50 mrem

Is the dose rate at 3 m from a radioactive source is 100 mrem/hr what will the dose rate be at 6 m?

• 25 mR/hr

• 50 mR/hr

• 75 mR/hr

• 12.5 mR/hr

Answer explanation

Using the inverse squared law, one can recognize that the distance has been doubled so the intensity is reduced to 1/4 of the orignal.

If the exposure rate at 4 m from a radioactive source is 5 mR/hr, what will the exposure rate be at 3 m?

• 2.8 mR/hr

• 6.5 mR/hr

• 7.4 mR/hr

• 8.9 mR/hr

Answer explanation

I₁ = (d₂)²/I₂ = (d₁)2

rearranged as

(I₁)(D₁)² = (I₂)(D₂)² for easy solving