Yes, nosebleeds do tend to occur more often during pregnancy. Pregnancy can cause the blood vessels in your nose to expand, and your increased blood supply puts more pressure on those delicate vessels, causing them to rupture more easily. Although it's unpleasant and inconvenient, an occasional minor nosebleed is generally harmless.
The higher the energy of the gamma rays, the thicker the shielding made from the same shielding material is required. Materials for shielding gamma rays are typically measured by the thickness required to reduce the intensity of the gamma rays by one half (the half value layer or HVL).
A gamma ray is electromagnetic radiation (similar to visible light, but at a much higher energy in the electromagnetic spectrum) given off by the nucleus of an atom as a means of releasing excess energy, and is oftentimes released when an atom undergoes decay by emitting an alpha or a beta particle.