Method and apparatus for measuring uranium isotope enrichment

• US 4,629,600 A
• Filed: 03/15/1984
• Issued: 12/16/1986
• Est. Priority Date: 04/13/1983
• Status: Expired due to Term

• Current Assignee: Japan Nuclear Cycle Development Institute
• Original Assignee: Doryokuro Kakunenryo Kaihatsu Jigyodan
• Inventors: Kurosawa, Akira, Ishiguro, Nobuharu
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US06/590,915
• Time in Patent Office: 1,006 Days
• Field of Search: 376/157, 376/153, 376/257
• US Class Current: 376/257
• CPC Class Codes: G01N 23/02 by transmitting the radiation through the material
• CPC Class Codes: G01N 23/221 by activation analysis
• CPC Class Codes: G01T 1/167 Measuring radioactive content of objects, e.g. contamination whole body counters G01T1/163

Abstract

A method and apparatus for measuring uranium isotope enrichment in a sample uranium solution. In the invention, the concentration of uranium in the uranium solution is determined by K-edge densitometry. The quantity of uranium-235 in the uranium solution is then measured by detecting the gamma rays emitted from the uranium-235 by using a high-purity germanium detector. A value of the uranium isotope enrichment is obtained from the ratio of the quantity of uranium-235 in the uranium solution to the uranium concentration. The invention is designed to provide the improved construction of a radiation source suitable for the K-edge densitometry and to provide the accurate measurements by correcting any error in the measured quantity of uranium-235 in the uranium solution due to the self-absorption of the gamma rays emitted from the uranium-235.

Claims

1. A method for measuring uranium isotope enrichment including the steps of irradiating photons of an energy lower than the uranium K-edge energy and other photons of an energy higher than that energy onto a sample containing uranium to determine the concentration of uranium in the sample from the respective intensities of the photons which penetrate the sample, measuring an intensity of gamma rays emitted from the sample due to the alpha decay of uranium-235 in the sample, and obtaining a value of uranium isotope enrichment from the measured intensity of gamma rays emitted from the uranium-235 in the sample and the concentration of uranium in the sample, characterized in that the photons irradiated onto the sample are produced by an interaction of a sealed radiation source of cobalt-57 with an uranium foil, and that a piece of highly-enriched uranium metal is disposed in the vicinity of the sample so as to separately measure intensities of gamma rays emitted from the highly-enriched uranium metal at the time of no sample present and at the time of the sample being present, and a self-absorption correction factor of gamma rays in the sample is obtained from the function of the intensity of gamma rays at the time of no sample present and of the intensity of gamma rays at the time of the sample being present, thereby correcting the measured intensity of gamma rays emitted from the uranium-235 in the sample.

2. An apparatus for measuring uranium isotope enrichment including a radiation source emitting photons of an energy lower than the uranium K-edge energy and other photons of an energy higher than that energy, a collimator system arranged along an optical path through which the photons emitted from the radiation source pass, a movable shutter mechanism provided across the optical path and capable of selectively shutting off the photons from the radiation source, a sample containing uranium disposed in the optical path and onto which the photons are irradiated through the shutter mechanism and the collimator system, a photon detector for detecting the intensity of the photons which penetrate the sample and the intensity of gamma rays emitted from the sample due to the alpha decay of uranium-235 in the sample, and a measuring electronic system including a pulse height analyzer for processing outputs of the photon detector, characterized in that said radiation source comprises a sealed radiation source of cobalt-57 and a uranium foil disposed adjacent to the sealed radiation source, and that said shutter mechanism has a piece of highly-enriched uranium metal such that gamma rays emitted from the highly-enriched uranium metal are irradiated towards the sample when the shutter mechanism is driven to shut off the photons from said radiation source.

3. The apparatus according to claim 2, wherein the photon detector comprises a high-purity germanium detector.

4. The apparatus according to claim 2, wherein said shutter mechanism has a through-hole at a first portion thereof, and said highly-enriched uranium metal is embedded in a second portion of the shutter mechanism with its one surface exposed in the direction of said sample, said first and second portions being selectively positioned in said optical path in accordance with the movement of said shutter mechanism.

5. The apparatus according to claim 2, wherein said uranium foil in said radiation source is a foil of uranium-235 or natural uranium.

6. The apparatus according to claim 2, wherein said collimator system has a first collimator disposed between said radiation source and said shutter mechanism, a second collimator disposed between said shutter mechanism and said sample, and a third collimator disposed between said sample and said photon detector.

7. The apparatus according to claim 2, wherein said sample is contained in a removable sample cell.

8. The apparatus according to claim 2, wherein said optical path is provided in a shield block, and said radiation source, said collimator system, said shutter mechanism, said sample and said photon detector are disposed within said shield block along said optical path.