Positron beams in SuperKEKB will be produced from electromagnetic showers originating from the interaction between primary electron beams and a tungsten target. Since the emittance of primary beams is very small, the target is easy to be destroyed if focused beams are irradiated. In the SuperKEKB LINAC, a plate called spoiler is placed in the upstream of the target to enlarge the beam spot size. If the beam control is in a correct way, radioactive rays will be observed near both the spoiler and the target. However, if the beam control is not successful and primary beams are irradiated directly on the target, significant radiations are observed only near the target. If such a behavior is observed, primary beams must be stopped to protect the target. Since the number of electrons in a bunch is quite large(~10nC), the radiation dose is expected to be very high. Therefore, the radiation detector is required to have a high radiation-tolerance over a long period of time. Diamond has a high radiation tolerance due to its strong covalent bond, and we are now developing radiation detectors using diamond crystals. In this talk, current status including beam test measurements will be shown.