Most of the ionizing radiation from an H bomb is produced by nuclear fusion or from fission from the trigger and decay products. An asteroid impact wouldn't pr

Most of the ionizing radiation from an H bomb is produced by nuclear fusion or from fission from the trigger and decay products. An asteroid impact wouldn't produce any of that. The only ionizing radiation it might produce are some x-rays from the fireball plasma (but I'm not sure the plasma would even be hot enough for that). The blast and thermal effects would presumably be comparable, however, so at 16 km you'd definitely notice (and might be in a very uncomfortable situation).