The atmosphere was indeed virtually free of all but natural ambient radiation.

When you include other sources of natural radiation, the geographic variations are quite large.

You see, it's short on mutations; it does not enjoy Earth's high level of natural radiation.

In reality, our amendments on natural radiation have nothing to do with the ridiculous stories fed to the media.

Where the employer finds a risk associated with natural radiation, information will be provided to workers.

For workers, cancer is no less real whether caused by natural or artificial radiation.

People must continue to take responsibility for whether or not they expose themselves to natural radiation.

Dramatic changes in climate make it necessary that more attention be given even to natural radiation.

The phenomenon I am talking about is, of course, natural radiation.

It was the first time she had felt natural solar radiation in more than fifty years.