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DEY (201.10)
Project 18.4 - Chord Experiment and Time~Interval = H, Hoerlin
Westervelt, Bennet, Day, Hoerlin
CHORD EXPERIMENT
Objectives:
All optical observations of an expanding fireball at early times
are affected by the characteristics of the strongly disturbed air ahead
of the radiating front.
The brightness temperatures observed during this
phase of expansion are in the range of 2000° to 10000° K which is
sever~
al hundred times lower than the true temperatures of the expanding rade
dation or shockfronts,
This obscuration is partially due to effects of
the gamma-rays and neutrons on a large volume of the surrounding air and
more locally due to the disturbance of the air immediately ahead of the
radiating surface by soft x-rays and ultraviolet radiation.
Past studies, mainly conducted by the Optics Division of the NRL
(Stewart) under LASL sponsorship, have resulted in qualitative identification and semi~quantitative time histories of the absorbing reaction
products of the disturbed air,
More specifically the presence of these
main specimens has been established in spectroscopic work:
035 absorb=
ing in the ultraviolet; excited OH and 02, also in the ultraviolet; HNO,
and NOs, in the ultraviolet and blue; NS
in the blue.
Whereas these
molecules have well known absorption structures the analysis of past
data indicates that their presence alone does not fully account for the
strength of the observed fireball obscuration.
It is reasonable to as-
sune that additional strong absorption must be caused by transitions fran
bound into therhingesptates and that negative ions like 035 and O” contrib-
LANL Re
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