[en] The energy of the linear accelerator in Japan Atomic Energy Research Institute was increased from 20 MeV to 100 MeV, and the normal operation was started in August, 1972. In this report, the measured and evaluated results on the intensity of induced activity of targets and radioactive gas concentration produced in the target room and at the exhaust outlet are summarized. The target room and the accelerating tube room are shielded with heavy and ordinary concrete of 2 to 3 m thick. The radioactive gases and ozone produced by activation in the target room are sucked from the exhaust grille and released from the stack of 5.5 m high. Since the intensity of residual activity of a target and the adjacent materials attenuates significantly during an hour after stopping operation, personnel can enter into the target room after then, taking the content of works into account. Since platinum and tantalum are used as the targets in addition to the adjacent structural materials, the nuclides to contribute to radiation dose were ¹⁸⁰Ta, ¹⁹⁷Pt, ⁵⁴Mn, ⁵⁶Mn, ⁶²Cu, ⁶⁰Co and ²⁴Na. Due to the activation of oxygen and nitrogen in the air near the target, radioactive gases of ¹³N and ¹⁵O are produced. In the target room, also the nuclides ³⁸Cl and ³⁹Cl were found. The measured results show that the concentrations of both ¹⁵O and ¹³N in the target room decrease to below 10^-6 μCi/cm³ or exposure dose (submersion) to below 1 mrem/h, after 3 minutes from stopping the operation. (Wakatsuki, Y.)