JPH0915147A - Method for analyzing helium isotope - Google Patents

Abstract

PURPOSE: To analyze the He isotope with a semiconductor laser of relatively low cost by irradiating a discharge tube filled with a gas containing He-3 of unknown concentration and He-4 of known concentration with near-infrared laser light, and detecting the small change in the current flowing in the discharge tube. CONSTITUTION: A sample gas containing He-3 of unknown concentration and He-4 of known concentration is introduced in a discharge tube 1, near-infrared laser lights are cast alternately from semiconductor lasers 2 and 3 adjusted to emit at wavelengths exactly coinciding with the atomic spectra of He-3 and He-4, minute changes in current flowing in the tube 1 from a power source 6 (opto galvanic effect) are detected with a lock-in amplifier 7, and the unknown concentration of He-3 is obtained from the ratio of the detected values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing helium isotopes used for He-3 analysis in a nuclear reactor plant, especially in a fusion facility.

[0002]

2. Description of the Related Art In a fusion facility, in addition to He-3, there are compounds having a mass number of 3 such as hydrogen isotopes such as T and HD. Therefore, in order to selectively identify these compounds, Since an inexpensive mass spectrometer cannot be used, an expensive and complicated mass spectrometer is needed. Therefore, if He-3 is to be analyzed at a plurality of places in the plant, the analysis cost will be enormous.

[0003]

Therefore, the present invention solves the drawbacks of the prior art and enables the use of a relatively inexpensive near-infrared semiconductor laser to analyze and quantify He-3 isotopes of helium. It is intended to provide a method.

[0004]

SUMMARY OF THE INVENTION The present invention is based on H of unknown concentration.
A gas containing e-3 and a known concentration of He-4 was introduced into the discharge tube, and the near-infrared laser light of the wavelength exactly matched to the atomic beams of He-3 and He-4 was alternately irradiated to discharge. It is a method of analyzing a helium isotope characterized by detecting a minute change in a current flowing through a tube and obtaining an unknown He-3 concentration from a ratio of the detected values. As the near-infrared laser light in the present invention, a normal near-infrared semiconductor laser for spectroscopy having a resolution of about several tens MHz can be used.

[0005]

[Function] When the present inventors analyze helium isotopes,
While paying attention to the characteristics of the compound other than the mass, the inventors have made an intensive study on a method for selectively identifying the compound, and succeeded in the identification by focusing on the spectroscopic characteristics. That is, since He-3 and T, HD have different absorption wavelengths in the electronic spectrum, they can be identified,
Further, in He-4 and He-3, there is an isotope shift of the spectrum, and it is possible to distinguish them. It is known that the helium isotope shift in the near infrared region is several hundred to several thousand MHz, so that a gas containing helium is guided to the discharge tube,
By using the optical galvanic effect, helium can be detected by light in the near infrared region. And in the near infrared region,
A semiconductor laser that is easy to maintain can be used,
The entire apparatus can be made inexpensive, and He-3 can be distinguished from T and HD without using an expensive mass spectrometer.

[0006]

FIG. 1 shows an embodiment of the present invention. A sample gas is introduced into the discharge tube 1 to cause discharge. On the other hand, the semiconductor laser 2 and the semiconductor laser 3 are He-3 and He, respectively.
It is adjusted to oscillate a wavelength corresponding to the atomic beam of −4. If He-3 or He-4 is present in the discharge tube, the current flowing from the power source 6 changes slightly. This change is called the optical galvano effect, which is detected by the lock-in amplifier 7. Here, the chopper 4 and the chopper 5 modulate to obtain a trigger signal.

Here, by setting the modulation speeds of the choppers to different frequencies in the chopper 4 and the chopper 5, if only the signal of that frequency is amplified, an optical transition that occurs only when the laser light is irradiated, It is possible to separate the noise component generated even when the laser light is not irradiated. If the two semiconductor lasers oscillate at different wavelengths and are modulated to different frequencies, it is possible to observe only the transition occurring in one of the semiconductor lasers, and the same lock-in amplifier The optical transitions produced by the two semiconductor lasers can be observed independently.

In this system, since the reproducibility of discharge closely affects the reproducibility of signal strength, it is difficult to find the absolute value of helium. However, the isotope ratio can be accurately determined. If the sample gas is He-4
If it is known that no H
The absolute concentration of He-3 can be determined by mixing e-4 with the sample gas. Further, even when He-4 is already mixed, it is possible to calculate the absolute concentration of He-3 by mixing several kinds of known concentrations of He-4 stepwise and calculating the isotope ratio. .

[0009]

The present invention can provide a method for analyzing a helium isotope, which employs the above-mentioned structure and makes it possible to use a relatively inexpensive semiconductor laser.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an apparatus for carrying out the helium isotope analysis method of the present invention.

Claims (1)

[Claims] 1. An unknown concentration of He-3 and a known concentration of He.
A gas containing −4 is introduced into the discharge tube, and He-3 and He−
Alternately irradiate the near-infrared laser light with a wavelength that exactly matches the atomic beam of 4, detect minute changes in the current flowing in the discharge tube, and obtain the unknown He-3 concentration from the ratio of the detected values. A method for analyzing helium isotopes characterized by.