Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Patent
1996-12-02
1998-07-21
Glick, Edward J.
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
250361R, 250362, G01T 1205
Patent
active
057838283
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an apparatus and a method for measuring tritium specific activity in gaseous form when it is mixed in carrier streams of certain gases which serve as scintillation detection media.
Photons emitted in the interaction of tritium beta particles with the scintillating gas are detected by photomultiplier tubes or photodiodes and are converted to charge pulses.
Tritium is found in various chemical and physical forms in tritium extraction plants, experimental fusion centers and other nuclear facilities. An important aspect in fusion technology development is the assessment of new real time detection and accountancy methodology of tritium in gaseous forms.
Liquid and solid phase scintillation detectors are widely used as tritium detectors. Experience has been gained for the scintillation properties of some noble gases such as xenon, argon, and helium. Gas scintillator detectors have been used in the past for alfa particles, fission fragments and heavy ions spectroscopy. Another application of this technique is thermalized and fast neutrons detection by means of (n,.alpha.) e (n,p) nuclear reactions. At the present, proportional scintillation counters are used to measure low energy cosmic X rays, as well as .gamma. and beta radiations.
The mechanism giving rise to the scintillation photons is as follows: the incident radiation or charged particle produces a population of excited gas molecules as it passes through the scintillator. As these excited molecules return to their ground state, through a variety of different mechanisms, photons are emitted during the transition from the two lowest molecular excited states to the ground state and much of the emission lies in the ultraviolet and a part in the visible region of the spectrum. Scintillations can be detected directly by means of photomultiplier tubes or photodiodes that are sensitive in the near ultraviolet region.
The overall scintillation efficiency of gases is characteristically quite low, due to a number of parallel modes of de-excitation, such as intermolecular collisions or internal interference processes normally referred to as a quenching effect. The major disadvantage of gas scintillators is their low light yield, which is at best an order of magnitude below that of Nal(Tl) for equivalent particle energy loss. On the other hand gas scintillators have some advantages compared with other detectors as they have a fast response time and high flexibility, variable shape and sensitive volume. A considerable amount of experimental data is available in the spectrometry of alfa radiations introduced inside the detector as solid sources or to detect external sources of low energy X and .gamma. rays.
According to the invention, the gas scintillation detection method is applied to the measurement of tritium in carrier gases. The measurement of tritium specific activity in inert carrier gases, under either static or dynamic conditions, is suitable for several subsystem configurations of tritium fuel cycle facilities, such as storage of tritium to be purified, tritium distribution system and gaseous detritiation system.
An example of application of this detection method is the on-line real time tritium measurement in the inert atmosphere purification system of a glove box for argon environments. Glove boxes atmospheres, for tritium handling purposes, are normally dry argon, nitrogen or helium as inert gases.
According to the invention, there is provided a method for measuring the specific activity of a tritiated gaseous stream using the scintillation property of some carrier gases which carry tritium in the gas phase. some advantages in comparison with other well established flow-through tritium process monitors, in particular applications, as follows:
no active part of the instrument is present in the sensitive volume of the detector, and in particular in the tritiated carrier flow, and no feed throughs are necessary so that tritium compatible materials, as reflective as possible for UV photons, can be used as internal detector walls to min
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patent: 4092539 (1978-05-01), Pao et al.
patent: 4975575 (1990-12-01), Perlman
Chiles, "Evaluation of a Thin CaF.sub.2 (Eu) Scintillator for Detecting Tritium" IEEE Trans. on Nuclear Science, vol. ns-34, No. 1, Feb. 1987, ISA, pp. 386-388.
Baron, et al., "A Gas Scintillation Detector for Soft X Radiation", Instruments and Experimental Techniques, vol. 17, No. 3i, May 1994, New York, USA, pp. 693-695.
Campi Fabrizio
Mascherpa Cristina
Pacenti Paolo
Sterlini Claudia
European Atomic Energy Community (EURATOM)
Glick Edward J.
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