Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1998-11-12
2001-10-16
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
Reexamination Certificate
active
06303936
ABSTRACT:
TECHNICAL FIELD
This invention pertains to a dual-purpose extraction-scintillation medium. More particularly, this invention pertains to a substantially free-flowing particulate extraction-scintillation medium and use of the particulate medium in a radiochemical sensor.
BACKGROUND OF THE INVENTION
Facilities, such as, hospitals, universities, research laboratories and nuclear power reactors, that use radioactive material, can have planned or unplanned, continuous or batch discharges of radioactive material to the environment. Much of this material is in the form of a liquid. These releases can result in surface water, ground water and drinking water contamination.
Radiochemical analysis methods are known and used to quantify the level of contamination. Using these methods, the contaminant is either co-precipitated with a carrier or concentrated on an ion-exchange or extraction chromatographic material. In the ion-exchange/extraction chromatography method, the contaminant is eluted from the material and concentrated into a small volume. This concentrated volume of solution is processed for quantification using a radiation sensor.
Advances have been made using extraction chromatography that lowered the sample analysis cost and time necessary for the analysis. However, the extraction chromatography augmented traditional methods are still time consuming and expensive, and do not facilitate real-time on-line analysis.
One alternative to traditional radiochemical methods, is on-line real-time flow monitoring. In one example of such an on-line arrangement, a flow cell sensor for real-time quantification is preceded by the elemental separation of a contaminant through high-performance liquid chromatography. The radioactive effluent is then separately characterized by a flow cell sensor. In this application, the counting time, that is the length of time that the sensor is permitted to count radioactive disintegrations from the material, is quite short, on the order of 20 to 25 seconds. When high-performance liquid chromatography is used to concentrate the contaminant, the resulting detection limit for a 10 milliliter sample of 500 bequerels/liter (Bq/L) for alpha-emitting nuclides, Reboul, et al.,
J. Health Physics
, 68:585-89 (1995), and 350 Bq/L for high-energy beta-emitting nuclides was achieved, Reboul, et al.,
Radioactivity and Radiochemistry
, 5:42-49 (1994). However, the above technique requires substantial concentration of the contaminant before it can be used for near real-time monitoring, and the separation and detection systems can be quite costly.
Continuous water monitors for effluent monitoring have been developed that quantify the gamma ray-emitting isotopes with a detection limit of about 0.2 Bq/L for a 60 minute counting time, Bronson, et al., 27
th
Midyear Topical Meeting of the Health Physics Society
, Feb. 13-17, 1994. Two tritium (low-energy beta-emitter) flow cell sensors are known that monitor effluent at the Department of Energy Savanna River Site. The sensors have achievable detection limits, for a 60 minute counting time, of about 750 Bq/L for the heterogeneous flow cell sensor, Hofstetter, et al., Westinghouse Savannah River Co. WSRC-MS-92-163, and about 7 Bq/L for the homogeneous flow cell sensor, Sigg et al.,
Nucl. Instr. And Meth. In Phys. Res
., A353:494-98 (1994).
These effluent monitoring sensors have reasonably low detection limits because a long counting time is used, which is achieved through a physical hold-up system. Although this hold-up system functions well for providing accurate radiation detection, it requires large physical samples to achieve low detection limits. Moreover, requiring long physical or chemical hold-up times prior to quantification is completely counter to the desire to provide on-line, real-time or near real-time detection of effluent stream contamination.
Concentration and quantification of contaminants in an aqueous stream using ion-exchange material has been achieved. Europium-doped calcium fluoride has also been investigated as a dual-purpose sensor material. DeVol, et al.,
IEEE Trans. Nucl. Sci., Vol
. 43, No. 3:1310-15 (1996); Branton, Clemson University, Private Communication (1996). However, high selectivity has not been achieved using this material.
Attempts have also been made to provide an organic extractant on nonporous scintillator supports, such as cerium-doped lithium silicate glass beads, scintillating polyvinyltoluene beads, and the aforementioned europium-doped calcium fluoride crystals. The physical properties of these nonporous media were quite undesirable in that the resulting medium was not in a free-flowing or substantially free-flowing physical form. Rather, these non-porous media were a “sticky” glue-like suspension of the nonporous media in a viscous liquid carrier, which was difficult to handle and created problems in properly packing columns for use.
Accordingly, there exists a need for a dual-purpose extraction-scintillation medium that is highly chemically selective in extraction of the analyte of interest, is in a free-flowing or substantially free-flowing physical form, and is used in a radio-chemical sensor to provide on-line, real-time or near real-time detection of the sorbed analyte. Desirably, such an extraction-scintillation medium further includes the light output characteristics necessary for a successful scintillation medium.
SUMMARY OF THE INVENTION
An extraction-scintillation medium comprises substantially free-flowing, porous, solid particulate matter having one or more fluors retained within the particulate matter and an extraction agent adsorbed on or chemically bound to the surface of the particulate matter.
The medium is capable of extracting one or more selected radionuclides, such as americium, uranium, thorium, plutonium, strontium, technetium, iodine, neptunium or curium from an aqueous stream, and permits transmission of light through the medium, which light is emitted from the scintillator in response to radiation absorbed thereby from the selected radionuclide.
In an extraction-scintillation medium in which the extraction agent is adsorbed on the surface of the particulate matter, the extraction agent can be ionically charged, and preferably has a neutral charge. In an extraction-scintillation medium in which the extraction agent is chemically bound to the particulate matter, the extraction agent can have an ionically negative charge, and preferably has a neutral charge at a pH value of use.
Preferably, the particulate matter is an inert bead resin, and most preferably, the bead resin is cross-linked polystyrene. The inert resin does not react or degrade during assay.
In a contemplated extraction-scintillation medium the scintillator is a mixture of 2,5-diphenyloxazole (PPO) and 1,4-bis(4-methyl-5-phenyloxazol-2-yl)benzene (DM-POPOP) and can include naphthalene. Preferably, the PPO is present in a concentration of about 2 percent to about 20 percent and preferably about 2 percent to about 5 percent by weight of the solid particulate matter and the DM-POPOP is present in a concentration of about 0.3 percent to about 2.6 percent and preferably about 0.3 percent to about 1.0 percent by weight of the solid particulate matter. Naphthalene, if used, is present in a concentration of about 0.5 percent to about 12 percent, and preferably about 0.5 percent by weight of the solid particulate matter.
The extraction agent can be adsorbed on or chemically bound to the surface of the bead resin. In one contemplated extraction-scintillation medium, the extraction agent is alkyl(phenyl)-N-N-dialkylcarbamoylmethylphosphine oxides (CMPO) with a phase modifier such as tri-n-butyl phosphate (TBP) that is adsorbed on the surface of the bead resin. In another contemplated extraction-scintillation medium, the extraction agent is a crown ether, and preferably, bis-4,4′(5′)[(t-butyl)cyclohexano]-18-crown-6 (DtBuCH18-C-6) that is adsorbed on the surface of the bead resin.
In yet another contemplated extraction-scintillation medium, the extraction agent is a cross-linked p
Brown David D.
DeVol Timothy A.
Duffey Jonathan M.
Harvey James T.
Roane James E.
Clemson University
Hannaher Constantine
Welsh & Katz Ltd.
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