Using an Omegatron for the Analysis of Solid Compounds
Abstract Generated abstract
The paper addresses the difficulty of identifying very small quantities of gaseous products formed during radiolysis of solid inorganic salts, most of which remain trapped in the crystal matrix and are poorly suited to conventional mass spectrometric inlet methods. It describes a simple apparatus using an RMO-4S omegatron mass spectrometer connected to a thermostated irradiation cell, with preliminary background recording and controlled admission of gases evolved during irradiation. In an example study of ammonium perchlorate irradiated by X-rays at room temperature, the observed mass spectrum indicates the formation of nitrous oxide, oxygen, nitric oxide, and water, while some carbon oxide signals are attributed to secondary cathode combustion effects. The experiment suggests that this arrangement can detect partial gas pressures down to about 10^-10 mm Hg, although identification becomes difficult for species with molecular weights above 44.
Full Text
Using an Omegatron for the Analysis of Gaseous Products of Radiolysis of Solid Compounds
V. A. Nevostruev, Yu. A. Zakharov
(Presented by the scientific seminar of the Department of Radiation Chemistry)
In numerous works (reviews [1, 2]) it has been shown that, during the radiolysis of solid inorganic salts under the action of penetrating radiation, only an insignificant portion of the gaseous radiolysis products leaves the crystal and enters the space surrounding it. The main portion of them (up to 90–95%) is retained in the crystal matrix. This circumstance, as well as the comparatively small values of the radiation yields of the products, makes it difficult to use mass spectrometers with ordinary inlet systems for the purpose of analyzing the composition of the gaseous radiolysis products.
Apparently, in connection with the above, work on the mass-spectrometric study of products released directly during the radiolysis of inorganic salts is practically nonexistent.
In the investigations that have been carried out, the products are analyzed either after heating the irradiated salts (in order to remove the retained gases) to the melting temperatures or to the temperature of a polymorphic transition, or after dissolving them in water. Naturally, after such treatment the composition of the complex gas mixture may differ substantially from the original one.
The analysis of small amounts (less than \(10^{-6}\) mole) of gases on mass spectrometers with ion separation in constant electrostatic and magnetic fields (of the MX type) requires either their evacuation to ultrahigh vacuum or the construction of more complicated inlet systems.
We have established that, for the purposes of analyzing complex gas mixtures that are direct products of the radiolysis of salts, an omegatron mass spectrometer can be used successfully and in a simple version.
A diagram of the setup for analyzing radiolysis products is shown in Fig. 1. The thermostated irradiation cell (1), made of glass, has a thin end wall, which makes it possible to study radiolysis in the field of soft X-radiation. With the needle inlet valve (2) closed, the cell is evacuated to a pressure of about \(10^{-4}\) mm Hg, after which the gallium seal (3) is closed. Gas evolution during irradiation of the sample in the cell is monitored by an LT-2 thermocouple gauge; during radiolysis the pressure must increase by no less than 2 orders of magnitude. The RMO-4S omegatron tube (4) is preliminarily evacuated by a combination of mechanical, mercury-vapor, and
Fig. 1. Diagram of the apparatus. Explanation in the text.
... of the titanium sorption pumps to a pressure of about \(10^{-7}\) mm Hg, and under these conditions the mass spectrum of the residual gases is recorded. In Fig. 2 the spectrum of the residual gases (background) at a total pressure of \(2.6 \cdot 10^{-6}\) mm Hg is shown by the dashed line. With the aid of the inlet valve, the gas under investigation is admitted into the system of the RMO-4S omegatron tube to a pressure not exceeding \(10^{-5}\) mm Hg, and the spectrum is recorded.
We investigated the spectrum of the gaseous products of radiolysis of ammonium perchlorate in an x-ray radiation field (absorbed dose rate \(1.2 \cdot 10^{16}\) eV/g sec) at a temperature of \(20^\circ\)C—Fig. 2, solid line.
Fig. 2. Mass spectrum of gaseous products of radiolysis of ammonium perchlorate (solid line) at a total pressure of \(6.2 \times 10^{-6}\) mm Hg. The background mass spectrum is shown by the dashed line.
From this spectrum it is seen that the increase in the total pressure upon admission of the radiolysis products of ammonium perchlorate by \(3.6 \cdot 10^{-6}\) mm Hg is due to an increase in the partial pressures chiefly of \(\mathrm{N_2O + CO_2}\), \(\mathrm{O_2}\), \(\mathrm{NO}\), \(\mathrm{N_2 + CO}\), and \(\mathrm{H_2O}\). The contribution of carbon oxides to the ion current with mass numbers 44 and 28 is due to an increase in the oxygen concentration and to combustion of the cathode in this atmosphere, as evidenced by the appearance of an ion current of \(\mathrm{C^+}\).
Thus, \(\mathrm{N_2O}\), \(\mathrm{O_2}\), \(\mathrm{NO}\), and \(\mathrm{H_2O}\) may be named as the gaseous products of radiolysis.
The experiment performed showed that the apparatus makes it possible to record small partial pressures of gases (down to \(10^{-10}\) mm...
mm Hg). However, identifying gases with molecular weight greater than 44 becomes difficult.
References
- V. V. Sviridov. Photochemistry and Radiation Chemistry of Solid Inorganic Substances, Higher School, Minsk, 1964.
- Yu. A. Zakharov, V. A. Nevostruev. Russian Chemical Reviews, 37, 143 (1968).
Observed Misprints
| Page | Line | Printed | Should read |
|---|---|---|---|
| 4 | Table 4 | Splitting | Splitting, gauss |
| 8 | Fig. 2 | \(1000\ \mathrm{A}^{\circ}\) | \(10000\ \mathrm{A}^{\circ}\) |
| 19 | 1st from bottom | V. M. Likhin USSR Academy of Sciences |
V. M. Lykhin USSR Academy of Sciences |
| 22 | 24 from top | \(O^{-}=\square+2e+1/2O_{2}\) | \(O^{-}=\square^{-}+e+1/2O_{2}\) |
| 23 | 13 from top | At the expense of electrons | Due to the capture of electrons |
| 23 | 16 from top | Crystals of constants | With a constant of the crystals |
| 28 | 7 from bottom | \(A^{-}A \rightleftarrows^{0}_{\tau}+\overline e\) | \(A^{-}\rightleftarrows A_{\tau}^{0}+\overline e\) |
| 36 | 12 from bottom | Zoumeine | Roumeine |
| 40 | 3 from top | outlet | inlet |
| 44 | 5 from bottom | (11) | (1) |
| 47 | 3 from top | and surrounding | into surrounding |
| 51 | Table 1 | \(\mathrm{NH}^{3+}\) | \(\mathrm{NH}_{3}^{+}\) |
| 51 | Table 1 | \(\mathrm{HCl}_{37}^{+}\) | \(\mathrm{HCl}^{37+}\) |
| 54 | Fig. 2 | \(t\) (sec) | \(\lg t\) (sec) |
| 64 | 5 from top | in crystals makes it possible to obtain with a controlled surface value |
in crystals with a controlled surface value makes it possible to obtain |
| 69 | 8 from top and 13 from bottom | PP–Sh | PP–III |
| 70 | Table 1 | \(0,99+1,06\cdot 10^{13}\) | \(0,99+1,06\cdot 10^{13}\) |
| 71 | 3 and 6 from bottom | A. D. Yoffe L. A. Zakharov \(0,5\%\) |
A. D. Yoffe Yu. A. Zakharov \(0,05\%\) |
| 74 | Caption under Fig. 4 | \(\lg\delta\) \(\mathrm{N}_{3}^{--}\cdots\rightarrow \mathrm{N}_{3}^{0}+1\) |
\(\lg\sigma/\gamma\) \(\mathrm{N}_{3}^{-}\cdots\rightarrow \mathrm{N}_{3}^{0}+e\) |
| 77 | Caption under Figs. 1 and 2 | HO ClO |
\(\mathrm{H}_{0}\) \(\mathrm{ClO}_{3}^{-}\) |
| 79 | 5 and 6 from top | \(\mathrm{Cl}_{4}^{--}\cdots\rightarrow \mathrm{Cl}_{4},1,[\mathrm{ClO}_{4}^{-}]^{*}\) | \(\mathrm{ClO}_{4}^{-}\cdots\rightarrow \mathrm{ClO}_{4},e,[\mathrm{ClO}_{4}^{-}]^{*}\) |
| 81 | 17 from bottom | % 1168 | No. 1168 |
| 88 | 8 from top | \(\mathrm{NH}_{3}\) | \({}^{15}\mathrm{NH}_{3}\) |
| 91 | 2 from bottom | \(I_{18}\) | \(I_{18}\) |
| 91 | 11 from bottom | \({}^{14}\mathrm{N}_{15}\mathrm{N}^{+},{}^{12}\mathrm{C}_{16}\mathrm{O}^{+}\) | \({}^{12}\mathrm{C}_{16}\mathrm{O}^{+},{}^{14}\mathrm{N}_{15}\mathrm{N}^{+}\) |
| 111. | 1 from bottom | Kadelatsy | Kadelatsi |
| 126 | 7 from top | Kj | Kl |
| 128 | 1 from bottom | \(G=g+J\) | \(G=g+\gamma\) |
| 132 | 11 from top | \(V\) | \(V_{k}\) |
| 146 | 5 from bottom | spectrometry | spectroscopy |