SU115144A1 - Non-Magnetic Pulsed Mass Spectrometer - Google Patents

Description

The general principle of non-magnetic dynamic mass spectrometers is that of an initial ion beam having the same energy; a system of different-frequency filters releases ions having the same velocities r, -.

At a given energy E, the velocity: of the ions is unambiguously related to the mass M, which is the basis of mass analysis.

At a CONSTANT distance between the radio frequency filters, measuring the speed is reduced to measuring the time of flight by comparing it with a known radio frequency.

The proposed mass spectrometer is based on a known type of magnetic mass spectrometer with an ion source, which, under the influence of pulses of an electric accelerating field, creates particles that have the same amount of motion.

A distinctive feature of the proposed device is that, in contrast to the known devices, in which the separation of particles of equal energy is carried out according to the time of the flight, in it the release of ions of a certain energy, and consequently, mass, is achieved using an electrostatic analyzer.

This provides the possibility of a significant increase in the aperture ratio of the proposed mass spectrometer, since its resolution is not dependent on the pulse frequency that can be created very large.

Dignity:. The device is also independent, in the first approximation, of its resolving power from its length, which makes it possible to make the device small-sized.

M Y2E -

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No. 115144-2 -

FIG. 1 is a schematic diagram of the proposed mass spectrometer; in fig. 2 is a diagram of an electrostatic apalizauri, which provides for the release of ions of a certain energy.

The generator G of pulses produces pulses /, -, with a frequency of s. L1 impinging Tj, which are received on two rectifying cells, one of which transmits positive pulses, and the other // negative. Positive pulses are sent to the electronically controlled electron beam and unlocked the electron beam.

Negative pulses are applied to the grids a and b and create an accelerating voltage E. Thus, positive pulses create ions, negative -, they are told the same amount of motion.

Sine waves can also be used. After the rectifier cells, one half-wave arrives} ia electron gun, the other on the accelerating grids. The use of sipusoidal oscillations imposes only some limitations on the length of the ion packet.

The extraction of iops of a certain energy, and, consequently, mass, is carried out using an electrostatic analyzer, which extracts ions from the beam with energies in the range from E to f + Af (Fig. 2). Between grids c and d, a main delay field bz is created. Between the grid r and the inclined grid d an additional delay field D is created (, between the grids d e is a small accelerating field.

Ions with energies smaller than L, are trapped between grids a and b, while ions with energies greater than f / pass through all grids.

Ions, whose energies are between U. 6, + TO, are reflected from an electrostatic "mirror between the grids of the VL and the receiver.

The resolution of the proposed mass-spectrometer is limited by those factors that cause the scatter of energies of ions of the same mass and, therefore, the overlap in energy of ions,

close but to the masses.

The resolution scheme, in particular, is limited to the value, -irb-,

which is caused by the initial spread of the energies E of the ions arising during the ionization of the atoms.

The ion energy of a given mass is determined by the amount of motion P, which they acquire in an accelerating field.

t, P (t) dt ezEt- ,.

The pulses that accelerate the voltage must be sufficiently stable in size and shape.

The condition must be met:

  I 0

 ; + T /

where DM is the least distinguishable mass difference.

Since the analyzers release ions with energies lying in the interval -r / Hz-Af ,, this also limits the resolving power

g value