Scintillation counting apparatus

• US 3,898,463 A
• Filed: 08/13/1973
• Issued: 08/05/1975
• Est. Priority Date: 08/13/1973
• Status: Expired due to Term

• Current Assignee: John E. Noakes
• Original Assignee: John E. Noakes
• Inventors: Noakes, John E.
• Primary Examiner(s): Borchelt, Archie R.
• Assistant Examiner(s): Willis, Davis L.
• Application Number:
  US05/387,764
• Time in Patent Office: 722 Days
• Field of Search: 250/328,361,362,363,366,367,369
• US Class Current: 250/367
• CPC Class Codes: G01T 1/202 the detector being a crystal
• CPC Class Codes: G01T 1/204 the detector being a liquid

Abstract

In the measurement of radiation by means of scintillation counters one drawback has been the scarcity of radiation counters which efficiently measure both gamma and beta radiation. There has also been the problem of scintillation counting in the face of external or background radiation. A scintillation counting apparatus is provided herein which measures scintillations arising from both beta and gamma radiation. The apparatus also effects a better separation of sample radiation from background radiation. The apparatus can also be used solely as a gamma detecting instrument. In such apparatus a radioactive sample, is placed in a housing coupled to a photomultiplier. In this apparatus the housing itself is an inorganic phosphor.

Claims

1. In liquid scintillation counting apparatus for measuring the energy of beta particle decay events, the apparatus including a light-tight housing impermeable to beta radiation, a photomultiplier tube encased in said housing by means such that outside light does not enter the housing, a well-type sample chamber, a transparent sample vessel therefor, an optical coupling medium interposed between the sample vessel chamber and photomultiplier tube so that substantially all of the photons generated by a scintillator in the sample vessel are transmitted through the optical coupling into the photomultiplier tube, and means such as shielding and independent deTection for excluding background radiation, the improvement wherein background radiation is simultaneously counted and sorted from true beta events, including (a) as the optical coupling medium, an inorganic phosphor, (b) an optical sample well liner to protect the inorganic phosphor from atmospheric attack, the optical liner having a photon absorbency of less than 20 per cent as wavelengths in the range of 3500 to 4200 Angstroms, and (c) discriminator means for differentiating low amplitude, fast rise time, liquid scintillator-generated pulses from large amplitude, slow rise time, inorganic phosphor-generated pulses.

2. The apparatus of claim 1 wherein the optical coupling medium is a large single crystal of thallium activated sodium iodide.

3. The apparatus of claim 1 wherein the optical coupling medium is a large single crystal of thallium activated cesium iodide.

4. The apparatus of claim 1 wherein the optical coupling medium is two or more crystals of thallium activated sodium iodide bonded together to form the coupling medium.

5. The apparatus of claim 2 wherein the well liner is a quartz sleeve optically coupled to the NaI(T1) crystal chamber walls with silicone grease.

6. The apparatus of claim 2 wherein the discriminator means is a bialkali cathode, gallium phosphide dynode, end-on, photomultiplier tube optically coupled to the NaI(T1) crystal with epoxy glue.

7. The apparatus of claim 2 wherein a quartz sample chamber liner and the photomultiplier tube are optically coupled to the NaI(T1) crystal with epoxy glue, wherein a photon reflecting coating, an oxide of a metal having a molecular weight of 40 to 150, covers all of the surfaces of the NaI(T1) crystal except those containing the epoxy glue, and wherein the housing is of low atomic number metal selected from the group consisting of aluminum, magnesium, and beryllium.

8. The apparatus of claim 2 wherein the sample chamber is formed in one end of the housing, a single photomultiplier tube is optically coupled to the opposite end, and the discriminator means is an electronic circuit means including a pulse amplification means, pulse height discriminator, and anti-coincidence gates for pulse height analysis.

9. The apparatus of claim 2 wherein the sample chamber is formed in one end of the housing, a single photomultiplier tube is optically coupled to the opposite end, and the discriminator means is an electronic circuit means which includes rise time sensitive circuitry and anti-coincidence gates for pulse shape analysis.

10. The apparatus of claim 2 wherein the sample chamber is formed in the center of the light-tight housing between two photomultiplier tubes optically coupled to each end of the optical coupling medium, and wherein the discriminator means is an electronic circuit means which includes pulse amplification means, a coincidence gate, pulse summing means, pulse height discriminator means and anti-coincidence gates for pulse height analysis.

11. The apparatus of claim 2 wherein the sample chamber is formed in the center of the light-tight housing between two photomultiplier tubes optically coupled to each end of the optical coupling medium, and wherein the discriminator means includes rise time sensitive circuitry, a coincidence gate and an anti-coincidence gate for pulse shape analysis.