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altitudes the ionization is mainly due to x rays rather thanX-rays. )
It is slightly sensitive to yield.
3. Radar Blackout by Fission Product Cloud. The fission product
cloud, through its y-rays, will cause much stronger radar blackout
than the direct X-rays and *-rays from the bomb, but onlyin the
direction in which the cloud travels. Blackout of radar reflection up
to several hundred megacycles for some minutes is predicted, and for
1-10 megacycles the blackout will last for many hours or even days if
the radar beam intercepts the cloud. The rate of spread of the cloud
_at thevery high altitudes involved cannot be predicted at present. -cena’
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The Y-ray activity of the cloud is proportional to the fission
yield so that this blackout effect is strongly dependent on yield. It will
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certainly be strong for altitudes between 100,000 and 300,000 feet.
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At still higher test altitudes, the effects may either be greater (Argus
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4. Acoustic Signal. This signal will be of long period (over 100
seconds), and of similar strength as the long-period signalfrom a
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effect} or smaller. Between 50,000 and 100,000 feet the blackout
effect will still exist but will extend over a smaller area at any time.
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observed. for ground shots will be very weak.
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5. Seismic Signal.
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There may be a long-period, seismic signal
which might be observable.
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6. Light.
At 500 miles distance, the light from a one-megaton
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bombin the first millisecond will be about 20 times stronger than
direct sunlight in one millisecond. This is so provided the bomb is
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at smaller distance.
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It can be used to determinethe yield.
7. Argus Effects may be observable, especially for explosions
above 400, 000 feet.
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Within the horizon, the light can be observed even
if there is cloud cover.
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in the direct line of sight. At 500 miles, this implies a test height of
at least 200,000 feet, for smaller height the light is observable only
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