Double-Membrane Sampling System in a Mass Spectrometer for the Study of Exhaled Air

Technical Physics - A double-membrane sample-introduction system is described that enables mass spectrometric determination of volatile organic compounds in air, while ensuring their detection...     

Ion source with electron ionization for a portable mass spectrometer

An ion source with electron ionization is considered. The charged-particle flow at the exit from this source has a cross section of ∼0.1 × 0.1 mm, an angle spread of 2° × 2°, a relative energy spread of <0.5%, and an energy range of 0.5–3.0 keV. This ion source is intended for systems where an ion beam is focused in two mutually perpendicular directions. The ion source design makes it possible to ionize a sample locally (in a volume of ∼10 mm³), where the concentration of the particles under study exceeds the concentration averaged over the volume of the vacuum chamber of the mass spectrometer by two to three orders of magnitude. The ion-optical properties of the source are numerically simulated, and the optimum parameters of the source are chosen. Examples of the application of the ion source are given for the mass-spectrometric determination of metal salts in aqueous solutions and of gases and volatile compounds in samples in various phase states.     

Multistop analyzer for time-of-flight measurements at a resolution of ±5 ns

A multichannel multistop time analyzer that provides the measurement of the time intervals between start and stop pulses and the accumulation of their time distribution in the memory of its unit is described. The time of arrival of a stop signal is recorded at a resolution of ±5 ns and a dead time of 30 ns. The number of stops per start can achieve 6000. The number of channels is 131072 (2¹⁷). The time analyzer is based on a CAMAC unit and can be used to design measurement-information systems for solving problems in neutron spectrometry and mass spectrometry by time-of-flight methods and for studying the time characteristics of luminescence radiation.     

Setup for taking the radiation spectra of wideband semiconductors

A setup is developed for measuring the spectra of wideband semiconductors (III nitrides) and related heterostructures. The setup makes it possible to trace the time distribution of the luminescence intensity at a fixed wavelength with a resolution of ±5 ns and a sampling rate of up to 10 MHz in the time interval from several microseconds to several hundreds of microseconds. Also, it plots the integral intensity of luminescence versus the wavelength. Precision measurement conditions are provided.     

Statistical estimation in the scheme of continuous Markov random walks

A constructive method of obtaining unbiased estimates of the unknown parameters and characteristics of a continuous finite Markow chain (CMC) ν(t), t≥0, with states 1, 2, ..., k and constant transition intensitiesλ _i,j<∞, i≠j, i, j=1, 2,..., k; $$\lambda _{i,i} = 0,\quad q_i = \sum\limits_{j = 1}^k {\lambda _{i,j} } ,\quad i = 1, 2,..., k,$$ is considered in the present paper for a wide class of stopping rules.     

Asymptotic behavior of the first arrival time in Markovian random walks

The article examines the asymptotic behavior of the first arrival time for homogeneous Markov random walks with a fixed stopping boundary. Conditions of convergence to exponential and gamma distributions are established. The results are applied to solve one problem of statistical control.Translated from Statisticheskie Metody, pp. 183–189, 1982.