U.S. patent number 3,600,573 [Application Number 04/864,054] was granted by the patent office on 1971-08-17 for ion beam intensity control with pulsed beam deflection and synchronized ion source blanking.
This patent grant is currently assigned to Nihon Denshi Kabushiki Kaisha. Invention is credited to Eiji Watanabe.
United States Patent |
3,600,573 |
Watanabe |
August 17, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
ION BEAM INTENSITY CONTROL WITH PULSED BEAM DEFLECTION AND
SYNCHRONIZED ION SOURCE BLANKING
Abstract
A method and apparatus for selectively introducing an
intermittent ion beam to an analyzer by passing the intermittent
ion beam through deflection electrodes to which generated pulses
are applied to direct the ion beams in a manner that the
intermittent ion beam does not pass the electrodes at a rising and
falling time of the pulses. The pulses selectively project into the
analyzer the intermittent ion beam in accordance with the amount of
exposure.
Inventors: |
Watanabe; Eiji (Tokyo,
JA) |
Assignee: |
Nihon Denshi Kabushiki Kaisha
(Tokyo, JA)
|
Family
ID: |
13525444 |
Appl.
No.: |
04/864,054 |
Filed: |
October 6, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Oct 9, 1968 [JA] |
|
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43/73690 |
|
Current U.S.
Class: |
250/286; 250/281;
250/426 |
Current CPC
Class: |
H01J
49/322 (20130101); H01J 49/18 (20130101) |
Current International
Class: |
H01J
49/32 (20060101); H01J 49/10 (20060101); H01J
49/26 (20060101); H01J 49/18 (20060101); H01j
039/34 (); H01j 037/34 () |
Field of
Search: |
;250/41.93,41.9 SA/
;250/41.92,41.91,41.9SE |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Church; C. E.
Claims
I claim:
1. A mass spectrometer comprising an ion beam source, a beam
deflecting device and an analyzer for spatially separating said
beam according to the mass to charge ratio of the ions comprising
the beam and a control circuit, said ion source having means for
releasing and directing intermittent ion beam pulses through said
deflecting device to said analyzer, said deflecting device
comprising spaced electrodes through which said intermittent ion
beam passes, said control circuit providing first set of electrical
pulses to direct the ion source to release the ion beam pulses of
substantially uniform pulse width and frequency, said control
circuit providing a second set of electrical pulses to the
electrodes of said deflecting device such that the ion beam pulses
may be selectively directed to said analyzer, the duration of the
pulses in said first and second sets an the synchronization of said
sets such that the ion pulses do not pass the electrodes at the
rising and falling of said second set of pulses.
2. A mass spectrometer according to claim 1 wherein said control
circuit may be adjusted to control the ratio of the frequency of
the first set of pulses to the second set of pulses thereby
controlling the intensity of the beam which is directed to the
analyzer.
3. A mass spectrometer comprising an ion beam source, a deflection
device having spaced electrodes, an analyzer for spatially
separating said beam according to the mass to charge ratio of ions
comprising the beam and a control circuit, said control circuit
comprising a clock pulse generator for generating clock pulse
signals, a first generator for generating a first set of
intermittent signals with a fixed delay time from said clock pulse
signals, said signals controlling the ion source to intermittently
produce ion pulses and for intermittently emitting said pulses, a
second generator for generating a second set of signals having a
pulse width greater than the width of the signals generated by the
first generator and selectively synchronized with said clock pulse
signals, said second set of signals directed to the deflection
electrodes to selectively direct the ion beam pulses to said
analyzer.
4. A mass spectrometer comprising an ion beam source, a deflection
device having spaced electrodes and an analyzer for spatially
separating said ion beam according to the mass to charge ratio and
a control circuit, said control circuit comprising a clock pulse
generator for generating clock pulse signals, a first generator for
generating intermittent high voltage signals with a fixed delay
time from said clock pulse signals, said signals being directed to
the ion source having two spark electrodes, a second generator
generating a second set of signals having a pulse width greater
than that of the signals generated by the first generator and
selectively synchronized with said clock pulse signals, said second
set of signals directed to the deflection electrodes to selectively
direct the ion beam pulses to the analyzer.
Description
This invention relates to mass spectrometers and, more
particularly, to an apparatus for controlling the amount of
exposure of an ion beam at a detector.
In the general analysis of elementary composition by a mass
spectrometer, the mass spectra of the composition represented by
varying amounts of exposure is directed onto a sensitive layer.
Analysis of the elementary composition is made by measuring the
total amount of ions in one spectrum and the blackness degree of
each spectrum line in the respective spectrum. The ratio of
blackness degree between the lightest and darkest spectrum line on
the sensitive layer can vary to a maximum of about 100 times.
Therefore, in order to compare different spectrum lines of the same
blackness degree, the mass spectrum must be detected by changing
the entire exposure of the ion beam over a range of 10.sup..sup.-13
Q to 10.sup..sup.-6 Q. To achieve this, the exposure time must be
varied in order to obtain such a wide exposure ratio.
However, the above method of controlling the exposure is
impractical sine the exposure time must be controlled over a wide
range such as 1.8.times.10.sup..sup.+4 sec to 30 min. In view of
this, in the conventional method, the amounts of ions generated in
the ion source are controlled. For instance, in a spark type ion
source, the amounts of ions generated per unit time are controlled
by changing the spark voltage or spark pulse width or repetition
frequency to be applied to the spark electrodes. However, the
condition of ionization changes in accordance with the change of
either the spark voltage, spark pulse width or repetition
frequency, resulting in a variation in the efficiency of ionization
between the various elements constituting the sample. Therefore,
even though spectra with the same ion exposure are obtained from
the same sample, the ratio of the blackness degree between each
spectrum line is different due to the variation of the ion source
condition. Hence, the measurement is reduced 15 percent to 30
percent and further, it is not uniform.
In order to overcome this defect various methods have been used,
the most typical being to control the exposure of the ions by
chopping the ion beam. In this method, the chopper electrodes are
arranged in front of the electrostatic field to which the chopper
voltage is applied. The ion beam which flows from the ion source to
the analyzer is chopped by the chopper voltage so as to control the
amounts of ions arriving at the detector. In other words, the ion
beam is deflected from its path when the chopper voltage is not
applied, but continues in its path when the chopper voltage is
applied so by reaching the sensitive layer.
However, since the chopper voltage has finite rising and falling
times, the ion beam passing between the chopper electrodes during
these times is focused on the shifted position of the sensitive
layer and, as a result, the spectrum lines become dim and the
resolution is consequently decreased. Moreover, even though the ion
beam is chopped in the lengthwise direction of each spectrum line,
the spectrum becomes dim due to second order aberration when a
spherical electric field is used.
My invention permits an ion beam to be passed between the
deflection electrodes without chopping, yet a clear image can be
focused on the sensitive layer. Furthermore, the intensity of the
ion beam which reaches the magnetic field is controlled without
affecting the focusing of the ion beam.
My invention provides a method and apparatus for selectively
introducing the ion beam to the analyzer so as to obtain the
desired amount of exposure of the intermittent ion bear emitted
from the ion source on the sensitive layer by arranging the
deflection electrodes at a selected point along the ion path. The
pulses are applied to the deflection electrodes so that the rising
time and falling time of the pulses coincide with the period when
the ion beam does not pass through the electrodes.
These and other features and advantages of the present invention
will become apparent after perusing the following specification in
conjunction with the accompanying drawings wherein:
FIG. 1 is a block diagram of a typical double-focusing mass
spectrometer showing one embodiment of the present invention which
is useful for controlling the amount of exposure of an ion beam;
and
FIG. 2 is a waveform diagram showing the wave forms necessary for
explaining the present invention.
Referring now to FIGS. 1 and 2: the specimen to be analyzed is
arranged, on the spark electrodes 1 and is ionized by a spark
generated between said electrodes. The ions thus formed are
accelerated between an accelerating slit 2 and are propelled into
the analyzer tube through an earth slit 3 and a main slit 4.
The spark electrodes 1 are connected to the output terminals of a
high frequency generator 10 through a transformer 9. A clock pulse
generator 11 generates periodic pulses with constant intervals as
shown in FIG. 2(a) which are fed into a delay circuit 12 (such as a
delay cable) and a gate circuit 14. The clock pulse with constant
intervals fed into the delay circuit 12 are delayed by a fixed time
.DELTA.t.sub.1 (for example 5.mu.sec) and are then fed into a first
pulse generator 13 which forms spark pulses with a pulse width
.DELTA.t.sub.1 (for example 20.mu.sec) as shown in FIG. 2 (b). The
spark pulses are then applied to the high frequency generator 10
which generates an intermittent high frequency and, after being
boosted by transformer 9, they are applied to the spark electrodes
1 which generate a spark resulting in the specimen fixed to the
spark electrodes being ionized.
The periodic pulses fed from the clock pulse generator 11 into the
gate circuit 14 are in turn fed into a frequency divider 15 which
is arranged so as to generate one pulse for N number of clock
pulses. N can be widely varied to maximum of 10.sup.4. The pulses
generated by the frequency divider 15 are transferred to a second
pulse generator 16 which generates pulses as shown in FIG. 2(c).
These pulses have a pulse width .DELTA.t.sub.2 (for example
50.mu.sec), that is to say, wider than the spark pulse width
.DELTA.t.sub.1 . These pulses are applied to deflection electrodes
5 so that the intermittent ion beam ionized between spark
electrodes 1 passes between the deflection electrodes 5 only when
the said pulses are applied to the deflection electrodes 5. As a
result, the intermittent ion beam is introduced into the
electrostatic field 6. Each ion reaches the deflection field formed
by the deflection electrodes 5 with a time difference due to the
mass difference of each ion. The time difference persists through
the deflection field also. However, since pulse width
.DELTA.t.sub.2 of the pulses from pulse generator 16 is much larger
than pulse width .DELTA.t.sub.1 of the pulses from pulse generator
13 and is advanced by .DELTA.t from the spark pulse passed through
the delay circuit, ions to be analyzed pass between the deflection
electrodes without any deflection. As a consequence the focusing of
the ion beam is not affected. The ion beam of course is then passed
through a standard electrostatic field 6 and magnetic field 7 and
onto the sensitive layer photographic plate 8.
I have explained my embodiment in the case where one spark pulse is
included in one pulse width .DELTA.t.sub.2 of the pulses to be
applied to the deflection electrodes, but my invention is not so
limited. It is possible to apply some of the spark pulses so that
they are included in one pulse width .DELTA.t.sub.2 of the pulses
to be applied to the deflection electrodes. Furthermore, this
invention can be also applied to the single focusing mass
spectrometer.
As mentioned above, my invention provides a method and apparatus
for controlling the exposure amounts of the ion beam in such a
manner that spark pulses with a fixed delay time delayed from the
clock pulses generated by the clock pulse generator are applied to
the spark electrodes, and the pulses with a width which is much
greater than that of the spark pulses are synchronized with the
clock pulses and applied for the pulse generator 16 to the
deflection electrodes. By doing this, a desired ion beam can be
passed between the deflection electrodes without chopping the ion
beam and a clear image can be focused on a reasonable position of
the sensitive layer. Moreover, by controlling the ratio between the
input pulses to the frequency divider and the output pulses from
the frequency divider, the intensity of the ion beam which reaches
the magnetic field is controlled without adversely affecting
focusing of the ion beam.
* * * * *