Any rock can be radioactive, but igneous rocks tend to have radioactive properties because they may have radon gas trapped in their crystals. When under pressure radon gas is released from the rock. Radon gas is a radioactive gas, when it is inside the crystals of an igneous rock it will make the rock itself radioactive. It changes over time as the unstable isotopes decay, thus the amount of radioactive element goes down, but the amount of the new element goes up.
An attachÃ© is a thin briefcase used for carrying papers. It is sometimes called an attachÃ© case. You may notice that in spy movies, an attachÃ© is often swapped out by the bad guy, and then the good guy spends the rest of the movie trying to get it back. AttachÃ© comes from the French attacher, which literally means attached, and it was first applied to someone working for a diplomat, such as a junior officer. Now an attachÃ© is a technical expert assigned to the staff of a diplomatic mission.
impinge. 1  to make an impression; have an effect or impact (usually followed by on or upon): to impinge upon the imagination; social pressures that impinge upon one's daily life. 2  to encroach; infringe (usually followed by on or upon): to impinge on another's rights.