Note: Descriptions are shown in the official language in which they were submitted.
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PHOTODECONTAMINATION
BACRGROUND OF THE 1 N V ~:N '1' ION
The present invention relates to a method of
decontamination and more particularl~, to the
photoremoval of chemical warfare ~C.W.) agents and other
contaminants.
One method of decontaminating a surface of a
chemical deposit is to expose the surface to
high-intensity radiation until the energy absorbed
decomposes or evaporates the chemical.
"Decontamination", as used herein, refers to
detoxification, cleaning, and other processes by which a
chemical is removed or its noxious gualities are
neutrali2ed. Vig, et al., U.SO Patent No. 4,208,135
disclose~ a method of removing contaminants from
surfaces by precleaning the surface and air, and then
irradiating the surface with shortwave ultraviolet
radiation in the presence of oxygen. Shortwave
ultraviolet is generally defined by the wavelength range
of 1700 angstroms to 3000 angstroms. Di Vita, et al.,
U.S. Patent No. 4,028,080, discloses a similar method
used to clean optical fibers.
A problem arises with respect to some C.W.
agentsO as well as other chemicals, in that they
~5 strongly absorb radiation only in the deep vacuum
ultraviolet region, below 2000 angstroms. Vacuum
ultraviolet radiation is strongly absorbed by air, and
hence, irradiation of surfaces requires an evacuated
; chamber. Howevèr, it is not usually practical to place
a surface in need of decontamination in an evacuated
chamber. Furthermore, the deep vacuum ultraviolet
region is generally devoid of economical high-intensity
radiation sources. Hence, large scale decontamination
of surfaces exposed to such C.W. agents is not feasible
using known methods.
It is an object of the present invention to
provide an improved method for decontamination that is
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applicable to contaminants which do not absorb strongly
optical frequencies generated by readily available
radiation sources.
SUMMARY OF THE PRESENT INVENTION
In accordance with the present invention, an
improved method of decontamination employs a chemical
additive capable of absorbing radiation of wavelengths
greater than that of vacuum ultraviolet The additive
may be mixed with the contaminant, or alternatively,
disposed upon and in contact with the contaminant. The
combined chemical system is then exposed to
high-intensity radiation of a frequency range strong:Ly
absorbed by the additive until a contaminant is
destroyed, altered, or removed by evaporation,
decomposition or alternative process. A laser or flash
lamp may be used to supply the high-intensity radiation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In instances where a contaminant cannot be
destroyed, altered or removed removed readily by
irradiation because the contaminant does not strongly
absorb radiation from readily available sources, a
chemical additive which is strongly absorbed by
radiation from a readily available source may be added
to the contaminant~ The resulting contaminant/additive
chemical system can be irradiated with radiation which
is absorhed by the additive until decontamination is
complete. The contaminant may be a chemical deposit or
film upon a surface, or may be in another form.
The contaminant may be a C.W. agent or any
other substance the removal, alteration, or destruction
of which is re~uired. The additive strongly absorbs
radiation characteristic of a predetermined radiation
source. The radiation source may have narrow frequency
spectrum, such as a laser, or a broad frequency range,
such as a flash lamp.
The additive may be mixed with the contaminant,
layered over the contaminant, or otherwise situated so
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that an energy transfer may take place between the
additive and the contaminant. The transfer may be
thermal. More specifically, the radiation absorbed by
the additive may be converted to therma:L agitation of
S the additive. Molecular collisions between the additive
and the contaminant then lead to the thermal agitation
of the additive.
Other energy transfer mechanisms are
appropriate for speciic contaminant systems. For
example, radiation may induce vibrational or electronic
excitation in the additive. The energy stored may be
transferred by re-radiation or by collisions to excite
molecules of the contaminant.
Depending upon the contaminant, the energy
transfer may effect decontamination in a variety of
ways. Thermal energy may result in the evaporation of
the contaminant. Alternatively, the heat may lead to
the decomposition of the contaminant. Heat or electron
- excitation may lead to the ioniza~ion of the
contaminant. The ionized contaminant molecules may
combine with other chemicals so that the noxious
qualities of the contaminant are neutralized. The
neutralizing chemicals may be provided with the
additive.
-- In a preferred embodiment of the present
invention, a solution of para-aminobenzoic acid (PABA)
is added to a contaminant such as a COW. agent. PABA
solutions strongly absorb radiation in the near
ultraviolet region and thus is amenable to many
high-intensity radia~ion sources. The C.W. agent/PABA
system may be irradiated by means of a high-intensity
radiation source. The radiation source may be a laser
such as an excimer, dye or N2 laser. Alternative~y, a
high-intensity pulsed xenon flash lamp, or other
incoherent flash lamp, may be used to irradiate the
chemical system. Once the radiation is absorbed, some
manner of energy transfer occurs to the C.W. agent,
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leading to its photoremoval.
The PABA is particularly well suited for
decontamination by means of a 1ash }amp, such as a
xenon flash lamp. PABA which is widely used to pro~ect
human skin ~rom ultraviolet rays from the sun, is widely
available in large quantities and is nontoxic. PABA
absorbs ultraviolet radiation over a broad section of
the near ultraviolet region. Hence, it is a safe and
available chemical which is an efficient absorber of
radiation over the frequency range of a flash lamp.
PABA is also well suited for absorbing the
radiation of lasers. However, specific additives may be
- more efficient energy absorbers in a narrow spectrum of
a particular laser. For example, ferrocine might be
used as an additive in conjunction with an
argon-fluoride laser.
r
Tests have been performed to evaluate the
efficacy of the present method. PABA solution and
malathion were mixed in a test tube and then layered on
2C a glass slide. Malathion is a C.W. agent analog, which
means that it behaves physically and chemically like
many of the chemicals developed for chemical warfare.
After evaporation of the solvents, a residue remained on
the slide. Slides of this type were irradiated with KrF
laser pulses (248 nm). The residue was completely
removed from the irradiated area. Removal was also
' complete when similar slides were irradiated with a
Flashblaster. ~Flashblaster is a high-intensity pulsed
xenon ~lash lamp developed by Maxwell Laboratories).
~ 30 In one set of control tests, pure PABA solution
; was deposited on a slide. The PABA was completely
removed from the irradiated areas o~ the slides when
exposed to either the KrF laser or the Flashblaster. In
a second set of control tests, pure malathion was
deposited on glass slides. The malathion residue was
not removed when irradiated by either radiation source.
These ~ests support the proposition that the method of
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the present invention permits the photoremoval of
contaminants not always readily removable by economical
radiation sources.
In accordance with the above disclosure, a
method of decontamination is presented which allows the
photoremoval of contaminants from surfaces. It is
apparent that alternative chemicals may be applied.
These chemicals may absorb in the near ultraviolet or
other portion of the spectrum in which high-intensity
radiation sources are economic~1 and practical. Other
embodiments are within the spirit and scope of the
present invention.
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