short half-life; within 1/2 hour after burst almost all the radioactive aluminum has decayed. Most soils
also contain significant quantities of manganese which decay with a half-life of about 2.6 hours. From
1/2 hour after burst until 10 to 20 hours after burst, both manganese and sodium are the principal
contributors to the radiation. After 10 to 20 hours, sodium, which decays with a half-life of about 15
hours, is the principal source of radiation.
A commander will desire to expose personnel to as little radiation as is compatible with the military
situation. The commander knows the approximate ground zero of recent or planned detonations and will
select a course of action that will avoid the expected areas of induced radiation, or unexpected
advantage may cause a commander to move a unit through an area of induced radiation.
The boundary of the significant area of induced radioactivity is considered to be the distance to which a
2 cGyph dose rate 1 hour after burst will extend. The maximum horizontal radius of this dose rate
contour for yields of 1 MT or less at times later than 1 hour after burst is about 1,400 meters; it is
usually substantially less, depending on the yield and height of burst of the weapon.
Any route, whether a straight line or a peripheral course, that avoids the area in the vicinity of ground
zero will reduce doses below those from a route which passes through or near ground zero. However,
this option as to route selection may be influenced by the terrain. Obstacles formed by tree blowdown,
fires, and buildings collapsing may limit not only the number of routes available but also movement on
foot or in vehicles. If there is an option as to the method of transportation to be used in crossing an area
of induced activity, it should be selected in the following priority:
Armored vehicles and personnel carriers.
Wheeled vehicles, preferably with sandbagged floors and sides.
When crossing an area of induced radiation, the commander should note the point of maximum dose
rate. At this point the unit is closest to ground zero, and as a rough estimate, it can be assumed that the
total crossing dose will equal two times the current dosimeter reading at the point of maximum dose
rate; that is, assuming the dosimeter reading was zero before entering the area. Beyond this maximum
dose rate point, it will usually be just as safe to continue to advance or to move laterally away from
ground zero rather than to withdraw. If the dose rate is