Compositions – X-ray or neutron shield
Reexamination Certificate
1999-09-22
2003-04-08
Medley, Margaret (Department: 1714)
Compositions
X-ray or neutron shield
C252S301170, C252S301180, C252S301350, C252S646000, C252S625000, C250S518100
Reexamination Certificate
active
06544442
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates generally to a composition of matter comprising a tributylphosphate (TBP) complex of a salt of an element selected from the group consisting of group 3, lanthanide, actinide and group 13 elements, and an organic carrier. These materials may be used as scintillators, radiation absorption standards, and x-ray resonance fluorescence standards.
Determining the elemental composition of a sample material is an important objective in a variety of disciplines. Various approaches involving radiation may be used to determine the elemental composition of a material. In one method, a sample of unknown composition may be exposed to an x-ray beam, which causes it to fluoresce with the x-rays characteristic of its constituent elements. The abundances of the constituent elements may be determined by performing ab initio calculations of the response of the system as a function of the composition and physical characteristics of the sample. However, this approach is fairly complicated. A simpler, easier to use method of identifying and quantifying elemental constituents in an unknown sample involves comparing the measurement of x-rays emitted from the sample with measurements obtained from a series of standards of known composition and with physical characteristics similar to those of the sample. Although the latter method is easier to use than the former, it depends on the availabilty of accurate standards. Manufacture of such standards is often difficult.
The radiation absorption properties of materials are important in the fields of industrial and medical radiography, and dosimetry. Standards that mimic the absorption properties of the human body or manufactured articles are used to set exposure parameters of radiation generating equipment so that optimal images may be obtained.
Organic scintillators have been used to detect radiation for many years. Because they are formulated as solids or liquids, these scintillators are effective in detecting particulate radiation. However, these materials are made up largely of hydrocarbons (98%), which are relatively poor at detecting electromagnetic radiation; therefore, they are efficient detectors of only low energy (a few tens of keV) electromagnetic radiation. Although organic scintillators effective at detecting electromagnetic radiation of up to about 100 keV have been produced commercially using alkyl lead and tin additives, light output from the scintillator is greatly decreased by the presence of lead and tin.
What is needed in the art is a composition of matter that permits the easy, accurate, and rapid fabrication of radiation absorption standards to specified properties, and organic scintillators with enhanced sensitivity to electromagnetic radiation.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Not applicable.
BRIEF SUMMARY OF THE INVENTION
The present invention includes a composition of matter comprising a tributyl phosphate complex of a salt of an element selected from the group consisting of group 3, lanthanide, actinide, and group 13 elements and an organic solvent.
Another aspect of the present invention provides a method for making a composition of matter comprising a tributyl phosphate complex of a salt of an element selected from the group consisting of group 3, lanthanide, and actinide, and group 13 elements, and an organic solvent, the method comprising the steps of: combining the tributyl phosphate complex of a salt of an element, the element selected from the group consisting of group 3, lanthanide, actinide and group 13 elements, and a suitable carrier selected from the group consisting of an organic liquid carrier and an organic solid carrier precursor, under conditions that allow uniform dispersion of the complex in the carrier.
It is an object of the present invention to provide a composition of matter that may be useful as radiation absorption standards, as x-ray resonance fluorescence standards, or as organic scintillators with enhanced sensitivity to electromagnetic radiation.
It is a further object of the present invention to provide a material with specified radiation absorption characteristics that can conveniently be formulated in solid or liquid form.
It is an advantage of the present invention that tributylphosphate complexes of group 3, lanthanide, actinide, and group 13 salts can be incorporated in an organic solvent to form a clear liquid or solid material.
Another advantage of the present invention is that tributyl phosphate complexes of group 3, lanthanide, actinide and group 13 salts have a high solubility in organic solvents and in silicones, which allows loading of group 3, lanthanide, actinide or group 13 salts at relatively high concentrations.
Other objects, features, and advantages of the present invention will be apparent on review of the specification and claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes composition of matter comprising a tributyl phosphate (TBP) complex of a salt of an element selected from the group consisting of group 3, lanthanide, actinide and group 13 elements incorporated into an organic solvent or silicone liquid or in silicone rubber or a solid polymeric hydrocarbon matrix.
It is envisioned that the composition of the present invention may be modified or adapted for the fabrication of radiation absorption standards, fluorescence standards, or for purposes for which materials with specific radiation absorption characteristics are needed.
The present invention capitalizes on the discovery tributylphosphate complexes of nitrate salts of Group 3, lanthanide, actinide and group 13 elements are clear liquids that are miscible with phosphors in vinyltoluene and silicones. The resulting solutions can be polymerized to hard plastics or rubbers that retain the mechanical properties of the unadulterated material. Group 3, lanthanide, actinide and group 13 metals span the range of atomic numbers from 21 through 103 and offer the possibility of tailoring the x ray absorption properties of the loaded material.
The TBP complexes of group 3, lanthanide, actinide and group 13 metals, when added to organic scintillators, will enhance their efficiency in detecting gamma and x-rays. The usual formulation of organic scintillators includes only hydrocarbon carrier (plastic or liquid) and a small amount (<2%) of organic (primarily hydrocarbon) phosphors. These materials have very small photoelectric cross sections, which limits the range of incident energies for which spectral information can be obtained. The presence of even a small amount of an element with a relatively high atomic number, such as an actinide or a lanthanide, increases the probability of absorption of electromagnetic radiation via the photoelectric effect, thereby extending the range of incident incident energies for which an organic scintillator can provide spectral information. For example, the addition of 1% (w/w) Gd to an organic scintillator increases the photoelectric cross section by a factor of 22 at 60 keV and increases the ratio of photoelectric to Compton absorption by a factor of 14. This ratio and the photoelectric cross section determine what fraction of interactions in the scintillator contribute to peaks in the pulse height spectrum. TBP complexes of group 3, lanthanide, actinide, and group 13 metals can be used to load organic carriers with at least 1% (w/w) metal.
The TBP complexes have been demonstrated to have a high solubility in aromatic hydrocarbons and phenyl-substituted silicones, including, but not limited to, benzene, vinyl toluene, and similar liquids. Some of these organic liquids can be polymerized to form a solid. In most cases, the resulting liquid or solid takes on the color and optical clarity of the TBP complex. Materials made in this manner can form the basis or organic scintillators with enhanced gamma ray and/or neutron detection properties. In at least one case (Eu(NO
3
)
3
TBP
3
), the complex itself is phosphorescent and emits light in re
Bell Zane W.
Brown Gilbert M.
Huei-Ho Chuen
Hurlbut Charles
Akerman & Senterfitt
Medley Margaret
UT-Battelle LLC
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