Geoscience Reference
In-Depth Information
If the explosion gives rise to the spherically symmetrical system of currents
and electric charges like the spherical condenser, then the electromagnetic field is
strongly equal to zero outside this system. Actually always there are some causes for
the non-symmetrical gamma-quantum spatial distribution. The irregularities of the
gamma-quantum flux can be due to the construction features of the nuclear device
or they could be excited by nonuniformity and anisotropy of the medium in which
the gamma-quantums move. The asymmetry of gamma-quantum fluxes results in
the asymmetrical distribution of the currents caused by Compton's electrons which
in turn give rise to the generation of the dipole moment of the current system. The
evolution of the dipole moment defines the temporal dependence of the EMP at far
distance from the explosion site. However Latter et al. (
1961
) have noted that at the
distances about several thousands kilometers from the detonation point the spectrum
of the signals radiated by the atmospheric nuclear detonation is practically the same
as that of typical atmospherics.
Leypunskiy (
1960
) has assumed that the EMP of the atmospheric nuclear
detonation could be radiated because of the GMP caused by the fast extension of
strongly heated plasma generated by the detonation. Since the plasma conductivity
is so high as 10
3
S/m, the plasma motion in the geomagnetic field gives rise to the
generation of electric currents, which screen the geomagnetic field. This results
in the displacement of the geomagnetic field lines by the expanding plasma from
the ionized area into the surrounding space. Such an effect which is often referred
to as the “magnetic bubble effect,” is followed by a subsequent current relaxation
after the arrest and cooling of the plasma. These processes are accompanied by the
radio-emission of the magneto-dipole type (Karzas and Latter
1962a
; Kompaneets
1977
). Additional effects can be due to the secondary gamma-quantums resulted
from inelastic scattering and capture of the thermal neutrons by nuclei of atoms in
the molecules of air and explosion products. A lot of aspects of the excitation of
electromagnetic fields due to gamma and neutron radiation have been studied (e.g.,
see Sandmeier et al.
1972
; Medvedev and Fedorovich
1975
). The EMP of nuclear
explosions in the outer space is different from that in the atmosphere in respect
to the great value of mean free path of gamma-quantums and electrons. Johnson
and Lippman (
1960
) and Karzas and Latter (
1962b
,
1965
) have pointed out that
the electrons in a so high-rarefied medium can produce cyclotron radiation in the
Earth's magnetic field.
11.1.3
GMP Due to a Strongly Heated Plasma Ball Produced
by Underground Explosions
The gamma radiation of the underground nuclear explosion is resulted from the
fission of atomic nuclei, directly, as well as from the inelastic scattering of neutrons
in the material of nuclear device and in the rock surrounding the underground
chamber. Considering the Compton electrons mechanism of the EMP, we note
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