Electric charge is the property that determines how a particle responds to electric and magnetic fields. The neutron has no net electric charge, so it doesn’t experience electric forces like charged particles do. Its quark composition is two down quarks and one up quark (udd), whose charges add to zero (-1/3 -1/3 + 2/3 = 0). In contrast, a proton is positively charged (uud sums to +1), an electron is negatively charged (-1), and a positron is the positively charged antiparticle of the electron (+1). So the particle with no electric charge is the neutron.

Anode heel effect describes a gradient of x-ray intensity across the field caused by the angled target in the anode. Because the anode is tilted, photons emitted toward the anode side have to pass through more tungsten and are partly absorbed within the target, so fewer exit toward that side. In contrast, the cathode side has higher intensity because fewer photons are absorbed in the anode. This creates a brighter area on the image receptor toward the cathode side and a darker area toward the anode side. The effect is more noticeable with larger field sizes and steeper anode angles (and is less pronounced with small fields or longer distances). In practice you can use this to your advantage by placing the thicker part of the anatomy toward the cathode side so the higher exposure helps compensate for greater attenuation there, or by adjusting technique to achieve more uniform density if positioning cannot optimize the heel effect.

Effective dose is a single value that estimates overall stochastic risk by combining how much radiation different tissues receive with how sensitive each tissue is to radiation-induced effects. For X-ray imaging, each tissue’s dose is weighted by a tissue weighting factor that reflects its contribution to cancer and hereditary risk, and then those weighted doses are summed across all tissues. This is why the statement describing summing tissue-weighted doses across the whole body to estimate stochastic risk is the correct one. It’s not the absorbed dose in the most irradiated tissue, nor just the dose to the skin, and the effective dose is expressed in sieverts (not grays), reflecting its basis in risk rather than a single tissue’s energy deposition.

After a Compton interaction, the atom is ionized and a vacancy is created in one of its electron shells. When an electron from a higher shell drops to fill that vacancy, the energy difference is released as a photon with a discrete energy specific to the element—that discrete emission is known as characteristic radiation. This is a hallmark of atomic structure: the emitted photon energies are fixed by the binding energies of the shells involved, giving a line-spectrum-like X-ray unique to the element. This isn’t the same as the primary photon (the original beam) or the remnant transmitted photon, and it’s not primarily bremsstrahlung, which comes from the recoil electron decelerating in the nuclear field and yields a continuous spectrum.