Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/204—Measuring radiation intensity with scintillation detectors the detector being a liquid
  • G01T1/2042—Composition for liquid scintillation systems
  • G01T1/2047—Sample preparation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/204—Measuring radiation intensity with scintillation detectors the detector being a liquid

Definitions

• This invention relates to measurement of a radioactively labeled sample material by an automated scientific instrument for radioisotope detection and measurement, such as for example a liquid scintillation counter, which detects light emissions generated from a scintillator material responsive to the radioactive substance labeling the sample.
• an automated scientific instrument for radioisotope detection and measurement such as for example a liquid scintillation counter, which detects light emissions generated from a scintillator material responsive to the radioactive substance labeling the sample.
• Liquid scintillation counting and automated instruments known as liquid scintillation counters are widely utilized to analyze samples having radioactively labeled substances.
• a sample in solution is mixed with a liquid scintillator, commonly referred to as a cocktail, and light events produced from the sample and cocktail mixture are detected according to their energy and frequency.
• the light events are caused when particles, emitted from the radioactive isotope labeling a select substance of the sample in solution, are received by a molecule of liquid scintillator in solution. This produces a light emission having an energy characteristic of the radioactive particle received.
• Detecting the energy of the light events and number of light events in a particular energy range provides an assemblage of information known as a spectrum from which the select substance of the sample, that material which is radioactively labeled, can be quantitatively analyzed.
• Liquid scintillation counting and automated instruments to perform liquid scintillation counting have been widely discussed in a multitude of publications and patents. Scintillation counting of liquid samples possesses some characteristic disadvantages due to the nature of the liquid solution which is being utilized; One is a phenomenon known as quench. Quench commonly refers to an effect in the scintillation process of a chemical or optical nature which results in loss of light events or reduction in light emission energy.
• a method of scintillation counting a radioactively labeled sample is presented which utilizes a solid scintillator and requires no liquid solution to mix a sample material and scintillator to perform scintillation counting.
• the solid scintillator is dispersed on a support material referred to herein as a counting support.
• the material of which the counting support is made may be a number of substances including glass, metal, plastics and fibrous materials such as those used in common filters including glass fibers compatible with the scintillation material and its process of deposition.
• the solid scintillator material is either adhered to, bonded to or embedded on or in the counting support so that it is uniformly dispersed across its surface area and securely held.
• a volume of sample material is deposited on the counting support over the solid scintillator and dried if in liquid form.
• the counting support containing the scintillator and sample material is then placed in a common scintillation counter to detect light events produced by interaction of the radioactive isotope labeling the sample with the scintillator.
• the information obtained is used to analyze the sample.
• the counting support is transparent so that light events can be detected by both of two photodetectors commonly used in a liquid scintillation counter, when counting support is interposed between them.
• the counting support may be opaque if it is positioned in a manner to permit light emission from the scintillator to be received by the photodetectors.
• Fig. 1 illustrates a counting chamber including two photodetectors found in a liquid scintillation counter in which a transparent counting support is interposed between the photo detectors.
• Fig. 2 illustrates a counting chamber including two photo detectors found in a liquid scintillation counter in which a typical vial for containing a liquid scintillation solution which has a solid scintillator bound to its interior surface is positioned within the chamber.
• a typical liquid scintillation counter generally has a counting chamber in which a sample vial is placed for detecting light events emitted by the liquid scintillator/sample solution.
• At least two photodetectors are positioned to receive light emissions from the sample vial when it is placed in the counting chamber. This is generally shown in Figs. 1 and 2 by the photodetectors 10 and 12 directed to the interior of a counting chamber 14 which is sealed from ambient light.
• a liquid scintillation counter is used to analyze a sample interacting with a solid scintillator which is supported on a sample counting support such as transparent support 16 shown in Fig. 1.
• a typical liquid scintillation counter having an ability to analyze a sample placed on a counting support with a solid scintillator as described herein, such as support 16, may be any one of a number of modern liquid scintillation counters manufactured by various companies such as Beckman Instruments, Inc., Packard Instruments, Inc., and others.
• a Model 3801 or 5801 Liquid Scintillation Counter presently manufactured by Beckman Instruments, Inc. of Fullerton, California is capable of performing scintillation counting according to the invention described herein.
• the scintillation counting method set forth herein comprises counting a radioactively labeled sample material by placing the sample material on a counting support which has a dry solid scintillator dispersed about its surface.
• the sample may be in a liquid, semi- liquid or dried form, however, it generally will be in solution with a volatile liquid and dried to leave only the solid elements of the sample remaining in intimate contact with the solid scintillator. This is important to obtain an efficient interaction between the particles of the radioactive isotopes labeling select sample material and the scintillator to produce light emission.
• the counting support containing the solid scintillator and sample is placed in the counting chamber of a typical liquid scintillation counting instrument and detected in a manner in which common liquid scintillation analysis is performed, as exemplified by the above referenced liquid scintillation instruments. It is found that positioning of the counting support within the counting chamber of the liquid scintillation instrument is not a critical characteristic to obtain accurate analysis of the sample material. However, advantages may be obtained by placing the counting support within the chamber in a manner in which light emissions are directed toward the photodetectors comprising the liquid scintillation instrument, and in particular where the counting support is made of a transparent material advantages are obtained by interposing the counting support between the photo detectors.
• the counting support may be comprised of any material which is inert and nonreactive to the solid scintillator, to the materials utilized in the deposition of scintillator onto the support, and to the sample and sample carrier materials. Glass and fibrous materials commonly including glass utilized in laboratory filters are preferable. Plastics, metals and others are clearly adequate.
• the counting support illustrated in Fig. 1 is flat, such as a flat glass slide commonly used in laboratories. The shape of the counting support, however, is not a limitation in the scintillation counting method presented herein, and many differing shapes may be utilized for the counting support to provide various advantages in containing sample material or scintillator, or permitting easy placement within the liquid scintillation instrument counting chamber.
• the solid scintillator material dispersed on the sample counting support is generally deposited on the surface of the counting support by bonding or other methods of attraction which are appropriate for the selected solid scintillator and the material from which the sample counting support is made.
• the solid scintillator may, however, be embedded into the material from which the counting support is made if it is porous or it may be physically embedded onto the surface of the material from which the counting support is made, e.g., embedded in a filter material.
• Counting supports which may be utilized with the method of scintillation counting presented are described in a copending patent application filed concurrently herewith for SAMPLE COUNTING SUPPORT WITH SOLID SCINTILLATOR FOR USE IN SCINTILLATION COUNTING in the names of Stephen W.
• Typical solid scintillators which are deposited on ' a counting support are any one or combination of the following: calcium fluoride doped with europium, CaF2(Eu), zinc sulfide doped with silver ZnS(Ag), yttrium silicate doped with cerium Y2Si ⁇ g (Ce), lithium glass doped with cerium, anthracene,. PPO, . (2,5-diphenyloxazole) polystyrene or poly(vinylaryl) functions doped with common liquid scintillation fluors.
• Other solid scintillation materials may be utilized and the method described herein is not limited to any select solid scintillation compound. Use of the smallest size particles of solid scintillator, preferably in a range of 2-10 microns, obtains the best counting efficiency.
• a solid scintillator may be deposited on the sample counting support by preparing a slurry of a solid scintillator and a binding agent in water. For example, 20 milligrams of solid scintillator may be mixed with 5 milligrams of binder in 10 milliliters of water.
• the binder may be any number of substances such as, for example, a binder used to bind silica gel to hard surface backings.
• the slurry of solid scintillator and binder may be coated on the surface of the counting support to obtain a proper thickness of scintillator when dried.
• a thickness such as the final weight of solid scintillator and binder is 70 milligrams, plus or minus 50 milligrams over a 25 millimeter diameter area is adequate.
• Deposition of the solid scintillator on the support should be as uniform as possible and the particle size of the solid scintillator should be as fine as possible.
• Fig. 2 shows the use of a typical sample vial used in liquid scintillation counting, which has had the interior surface, either the floor , walls or both, coated with a solid scintillator into which a sample may be placed to obtain light events for detection.
• Sample material is generally mixed in a solution with volatile material which readily evaporates or vaporizes so that the sample material, which must be nonvolatile, comes into intimate contact with the dry solid scintillator when it is dried. This provides highly efficient interaction between the radioactive isotope labeling the sample material and the solid scintillator.
• Sample material may be deposited directly onto the surface of the sample counting support having the solid scintillator deposited thereon. Sample deposition can be accomplished either by spotting, dabbing, blotting or absorbing the sample material directly on one or both sides of the counting support. A simple pipetting technique would be used.
• the counting support then is placed into the counting chamber of a typical liquid scintillation counter.
• a scintillation counting process is performed on the counting support under normal conditions and as the liquid scintillation counter would normally operate, with the exclusion of any quench measurement or compensation operations.
• the liquid scintillation counter should have its coincidence gate circuitry modified to vary the coincidence time period or. window to match the larger decay times generally exhibited by solid scintillators as compared to liquid scintillators. This circuitry permits light events to be measured only when more than one photodetector in a multiple photodetector system receives a light emission within the time period a coincidence window specified.
• E B is a measure of the effectiveness of a scintillation counting instrument to measure disintegrations of the radioactive isotope labelling the sample material.
• the coincidence gate period may be 50-100 nanoseconds, preferably 100 nanoseconds. If PPO were utilized as a solid scintillator the coincidence gate period may be 5 nanoseconds.

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• 1988
  • 1988-05-16 JP JP1989600024U patent/JPH02500026U/ja active Pending
  • 1988-05-16 EP EP19880905489 patent/EP0329720A1/de not_active Withdrawn
  • 1988-05-16 WO PCT/US1988/001656 patent/WO1989002089A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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