..::Phenomenology::..

The phenomenology of a nuclear explosion is well known.
Generally, more than fifty percent of the energy of
an explosion is delivered in the form of soft x-rays.
Smaller amounts are delivered in the form of other radiations;
usually about one percent in the form of neutrons,
and about point-three percent in the form of gamma rays.
Most of the rest of the energy is carried
away by the kinetic energy of the bomb debris.
When a nuclear event occurs near the Earth's atmosphere,
almost all the energies of the x-rays, gamma rays,
and neutrons is absorbed by the atmosphere and
reemitted as light, heat, and the kinetic energy of a shockwave.
There is no atmosphere associated with a detonation in space,
however; the x-rays, gamma rays,
and neutrons radiate in a four-PI-inverse-square geometry.
Scientists from the Los Alamos Scientific Laboratory estimate that
the x-rays from a ten-kiloton explosion can be
detected from as far away as 200 million miles.
This distance is equal to the
diameter of the Earth's orbit around the Sun.
Gamma and neutron detectors can be used to
provide additional information at lesser distances.
If space were clean--that is,
a true void--the detection capability for a nuclear
event by a series of detectors would be predictable.

However, space is not clean.
There are solar x-rays,
and solar winds consisting of protons and
electrons; there are cosmic particles, and gamma rays.
The Van Allen belt could be another
possible source of background radiation.
There may be even other radiations
that we do not know anything about today.
To evaluate the effects of these backgrounds,
it was decided to build a system of x-ray, gamma ray,
and neutron detectors,
and their associated logical decision
circuitry, which could be used to measure a nuclear event.
The signal is known, and the purpose of the present Vela Program is t-