Detection of heavy ions for cancer therapy using amorphous carbon nitride a-CN_x films prepared by a nitrogen radical sputter method

摘要

Secondary-electron (SE) yields from amorphous carbon nitride (a-CN_(CHI)) films on Al foil were measured by using fully-stripped and fixed-velocity (6 MeV) heavy ion beams, C~(6+). The purpose of our research is to study the characteristics of a-CN_(CHI) films for the application to heavy particle detectors. a-CN_(CHI) films were prepared by a nitrogen radical sputter method, and were deposited on one side of an Al foil. SE yields from both surfaces of forward and backward (Q_F, Q_B) by the impact of 6 MeV C~(6+) ions were independently measured. When a-CN_(CHI) film was on the backside of the Al foil in the beam direction, the SE yield (Q_B) from a-CN_(CHI) was significantly larger than Q_F from the Al surface side. This was an unexpected result from the well-known knowledge. Comparing the SE yields between the Al surface side with the backward of a-CN_(CHI) and the pure Al foil (without a-CN_(CHI)), Q_B from a-CN_(CHI) was significantly large than Al, suggesting a promising possibility of a-CN_(CHI) for the application of a new detector; meanwhile Q_F from Al (with a-CN_(CHI)) was smaller than that from the pure Al by a factor of 3.4. We found the latter phenomenon can be explained by a decrease in a vacuum level of a-CN_(CHI) film side.