Ionising Radiation

800 keV gamma photons are more penetrating than 150 keV photons, so fewer of them will be detected by the “camera”. Hence longer exposure or a greater dose of radiopharmaceutical would be required to produce an image.

The electron volt, keV or MeV, is preferred than the joule as the energy of a photon is a tiny fraction of 1 J.

X-rays are produced in an x-ray tube with a range of energies. Filtration will absorb the lowest-energy photons more than the higher energy ones. This will result in the average energy of the remaining spectrum increasing.

The blackest part on an x-ray image is air, while the whitest is the bone.

Mass number must be conserved; hence, 99 = s + 99; this means s = 0. Atomic number must be conserved; hence, 42 = a + 43; this means a = −1. The particle X with zero mass and charge of negative one is an electron (a beta negative particle).

After every 6 h, the amount of technetium 99 m that remains is one half of the amount that was present 6 h ago. 36/6 = 6, so six half-lives will elapse over 36 h, thus the amount remaining is: ½ × ½ × ½ × ½ × ½ × ½ = (½)⁶ = 1/64

Having a short half-life means that a lot of radiation is emitted in a short time period. If the radiation was emitted over a long time, the patient would be required to lie motionless for that long time while the image (the scintigram) was produced.

There is a trade-off where the photons should be penetrating enough so that they are not stopped within the body, but not so penetrating that too few are stopped by the detector placed next to the body. This energy range satisfies both needs.

“Inverse square” means at double distance, the flux will be one half squared of the original flux (½)² = ¼. At 4x the distance, the flux will be (¼)² = 1/16.

CT machines generate x-rays. The others are all nuclear medicine procedures.