Radiation: equivalent dose: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Radiation: equivalent dose

Sample item

A worker's lungs receive an absorbed dose of 5 mGy from alpha particles emitted by inhaled radon progeny. The radiation weighting factor for alpha particles is 20. What is the equivalent dose?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. 100 mSv

The equivalent dose in sievert equals the absorbed dose in gray multiplied by the radiation weighting factor, which is 20 for alpha particles and 1 for gamma and X-rays. Here 5 mGy x 20 = 100 mSv. The weighting reflects the greater biological damage per unit energy of densely ionising alpha particles.

Option by option

  • A. 0.25 mSv

    This divides by 20 instead of multiplying.

  • B. 25 mSv

    This applies a weighting factor of 5, which does not correspond to alpha particles.

  • C. 5 mSv

    This would apply with a weighting factor of 1, as for gamma rays.

  • D. 100 mSv (correct)

    Correct. 5 x 20 = 100 mSv.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, 100 mSv. The equivalent dose in sievert equals the absorbed dose in gray multiplied by the radiation weighting factor, which is 20 for alpha particles and 1 for gamma and X-rays.

Why is "0.25 mSv" not the answer?

This divides by 20 instead of multiplying.

Why is "25 mSv" not the answer?

This applies a weighting factor of 5, which does not correspond to alpha particles.

Why is "5 mSv" not the answer?

This would apply with a weighting factor of 1, as for gamma rays.

What concept does this question test?

It tests Radiation: equivalent dose in PSM. Here 5 mGy x 20 = 100 mSv. The weighting reflects the greater biological damage per unit energy of densely ionising alpha particles.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Radiation: equivalent dose?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.