Ionising Radiation

    Ionising Radiation
    Which of the following is NOT a principle used to set radiation safety standards?
    This is often not achievable.
    Author: rikazzz Comment
    Ionising Radiation
    What may the term “radioactive” be correctly used to describe?
    A patient who has been prepared for a NM scan has had a radioisotope incorporated into their body, so are themselves (temporarily) radioactive.
    Author: rikazzz Comment
    Ionising Radiation
    A particular radionuclide has a half-life of 6 h. When first measured, its activity is 10,000 Bq. Twelve hours later, what will its activity be?
    After one half-life, the starting activity of 10,00 Bq will be halved to 5000 Bq. After another half-life, the activity will be halved again from 5000 to 2500 Bq.
    Author: rikazzz Comment
    Ionising Radiation
    The lead aprons that are used for protection of staff in diagnostic radiography procedures do not provide protection against the ionising radiation used in nuclear medicine or radiotherapy. Why is this? Because:
    Diagnostic radiography uses x-rays with an average energy of 70 keV or less, which can be stopped by relatively thin amounts of lead (or lead-like) material. In order to stop the gamma rays used in nuclear medicine imaging, the thickness of the “aprons” would make them prohibitively heavy to wear.
    Author: rikazzz Comment
    Ionising Radiation
    Which statement about the atom and its nucleus is correct?
    The nucleus is tiny compared to the atomic diameter. Choice A is wrong as protons have the positive charge, and neutrons have no charge.
    Author: rikazzz Comment
    Ionising Radiation
    Why do some x-ray photons will pass through the human body without deflection? Because:
    Apart from the positions where electrons and the nuclei are located, the rest of the body is empty space through which photons can travel unimpeded. They will interact only if they “hit” these subatomic particles. The other answers contain errors.
    Author: rikazzz Comment
    Ionising Radiation
    A caesium 137 source produces an absorbed radiation dose of 400 mg/h at a distance of 1 m. What would be the dose received at a distance of 5 m in 2.5 hours? (Consider the effect of distance first)
    At a distance of 5 m, the dose would be (1/5)2 = 1/25 of that at a distance of 1 m. Hence dose would be 400/25 = 16 mGy/h. If exposed for 2½ h, dose would be 2½ × 16 = 40 mGy.
    Author: rikazzz Comment
    Ionising Radiation
    Which of the following does NOT contribute to the background radiation?
    Fluorescent lights contain mercury vapour at low pressure which emits ultraviolet light when excited by the passage of electrons through the tube. The UV photons are absorbed by the phosphor that coats the inside of the tube which re-emits the energy as visible light. No ionising radiation is emitted.
    Author: rikazzz Comment
    Ionising Radiation
    Given that a radiopharmaceutical containing the radionuclide technetium 99 m ( 9943Tc ) has an activity of 4 MBq immediately prior to injection into a patient, about 12 h later the patient is measured to have an activity of about 1 MBq. How long is the half-life of technetium 99 m?
    After one half-life, half of the radioactive atoms have decayed, so only half remain. One MBq which is one quarter of 4 MBq (= ½ × ½) remains after 12 h, so two half-lives have elapsed in the 12 h period. 12/2 = 6 h.
    Author: rikazzz Comment
    Ionising Radiation
    Which of the following statements about radioactivity is correct?
    Radioactivity involves the nucleus of an atom. Microwaves are not produced by radioactivity. While radiation from a nucleus could remove an inner shell electron from another atom, and when this electron is replaced by another “falling” into its place while emitting an x-ray photon, this is not classed as radioactivity.
    Author: rikazzz Comment