As taught by Yogi Bhajan on May 17, 1978.  Even in 1978 Yogi Bhajan said that radiation was affecting people.

“If your inside is in turmoil, this meditation will prevent you from dying. It can be done anytime, and its effect will be to calm you, to energize you, and to relax you.” – Yogi Bhajan

Meditation Instructions

Posture
Sit with a straight spine. Let your upper arms hug your sides.  Hold your lower arms up so the hands are as high as your neck, palms facing away from your body. Hands are in Gyan Mudra (tip of thumb and index fingers touching).

Mantra
Chant the following mantra three times on one deep breath:  Praanaa, Apanaa, Shushmanaa, Haree; Haree Har, Haree Har, Haree Har, Haree

Time

Continue for as long as you want, singly or in a group.

This is a very powerful meditation. Prana is life force corresponding to the electron; Apana is eliminating force corresponding to the proton; and Shushmana is the central force corresponding to the neutron. The beauty of this mantra is in the touch of palate and tongue.
Yogi Bhajan said that in the event of an atomic war, radiation will not kill you if your ‘gene aura’ is one inch thick.

Here’s a PDF of the meditation for atomic radiation 

Here’s an audio of this lecture.  He starts teaching the kriya at about 1:06:30 hours.