U.S. patent number 3,654,457 [Application Number 04/798,363] was granted by the patent office on 1972-04-04 for ion source device equipped with sample heating means for use in mass spectrometer.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Tamotsu Noda, Masayoshi Yano.
United States Patent |
3,654,457 |
Yano , et al. |
April 4, 1972 |
ION SOURCE DEVICE EQUIPPED WITH SAMPLE HEATING MEANS FOR USE IN
MASS SPECTROMETER
Abstract
An ion source for a mass spectrometer having a sample cell
containing a sample, a mesh filament surrounding the sample cell
and a radiant heat shield surrounding the mesh filament, in which
the sample cell is heated to a high temperature by being bombarded
with thermoelectrons emitted from the filament so that the sample
in the cell is vaporized and led toward the ion source to be
ionized. In the device, the sample cell and the radiant heat shield
are maintained at a high potential and a low potential,
respectively, relative to the potential at the filament so that the
thermoelectrons emitted from the filament can be accelerated toward
the sample cell.
Inventors: |
Yano; Masayoshi (Katsuta-shi,
JA), Noda; Tamotsu (Katsuta-shi, JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
11723229 |
Appl.
No.: |
04/798,363 |
Filed: |
February 11, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Feb 12, 1968 [JA] |
|
|
43/9545 |
May 22, 1968 [JA] |
|
|
43/42653 |
Nov 29, 1968 [JA] |
|
|
43/86985 |
|
Current U.S.
Class: |
250/425;
313/231.01; 313/230 |
Current CPC
Class: |
H01J
49/14 (20130101) |
Current International
Class: |
H01J
49/14 (20060101); H01J 49/10 (20060101); H01j
039/34 () |
Field of
Search: |
;13/31 ;219/121EB
;250/41.9S,41.9SB,41.9SR,41.9C ;313/230,231 ;315/111 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Birch; A. L.
Claims
We claim:
1. An ion source device equipped with sample heating means for use
in a mass spectrometer comprising a sample cell for containing
therein a sample, said sample cell having an opening, heating means
disposed to surround said sample cell for emitting thermoelectrons
to heat said sample thereby to vaporize the same, radiant heat
shielding means disposed to surround said heating means so as to
serve as a shield against the radiant heat emanating from said
heating means, first electrical power supply means for supplying a
quantity of electricity to the heating means, second electrical
power supply means for applying a high potential to said sample
cell and a low potential to said radiant heat shielding means
relative to the potential at said heating means in order to
accelerate the thermoelectrons emitted from said heating means
toward said sample cell, and ion source means for ionizing the
sample which is vaporized in said sample cell and passes through
said opening in said sample cell.
2. An ion source device as claimed in claim 1, in which said
electrical power supply means includes potential selecting means
for selectively maintaining said radiant heat shielding means at a
high or a low potential relative to the potential at said heating
means.
3. An ion source device as claimed in claim 1, further comprising
means for supporting said sample cell on a base, and a plurality of
electrically and thermally insulating members for intercepting the
conduction of heat from either one of said sample cell and said
base to the other through said sample cell supporting means and
electrically insulating said base from said sample cell.
4. An ion source device as claimed in claim 1, in which there is
provided means for supporting said sample cell on a base, and a
plurality of electrically and thermally insulating members for
intercepting the conduction of heat from either one of said sample
cell and said base to the other through said sample cell supporting
means and electrically insulating said base from said sample cell,
and said electrical power supply means includes potential selecting
means for selectively maintaining said radiant heat shielding means
at a high or low potential relative to the potential at said
heating means.
5. An ion source device as claimed in claim 3, in which cooling
means is provided to cool at least one of said electrically and
thermally insulating members.
6. An ion source device as claimed in claim 4, in which cooling
means is provided to cool at least one of said electrically and
thermally insulating members.
7. An ion source device as claimed in claim 1, in which there is
provided means for supporting said heating means, and said heating
means comprises a cylindrical filament made by disposing a
multiplicity of metal wires in the form of a grid and welding the
metal wires to each other at their intersections, said cylindrical
filament being fixed at its opposite ends to said supporting
means.
8. An ion source device as claimed in claim 2, in which there is
provided means for supporting said heating means, and said heating
means comprises a cylindrical filament made by disposing a
multiplicity of metal wires in the form of a grid and welding the
metal wires to each other at their intersections, said cylindrical
filament being fixed at its opposite ends to said supporting
means.
9. An ion source device as claimed in claim 1, further comprising a
first chamber for accommodating therein said ion source means, a
second chamber for accommodating therein at least said sample cell,
said heating means and said radiant heat shielding means, a
partition wall for partitioning said first chamber from said second
chamber, said partition wall having an opening of relatively small
diameter for allowing passage therethrough of sample gas flowing
toward said ion source means, a shutter movable to and fro over
said partition wall, said shutter having a sample gas passage
having a small discharge conductance, means for causing the
to-and-fro movement of said shutter over said partition wall, and
means for evacuating said first and second chambers independently
of each other.
10. An ion source device as claimed in claim 2, further comprising
a first chamber for accommodating therein said ion source means, a
second chamber for accommodating therein at least said sample cell,
said heating means and said radiant heat shielding means, a
partition wall for partitioning said first chamber from said second
chamber, said partition wall having an opening of relatively small
diameter for allowing passage therethrough of sample gas flowing
toward said ion source means, a shutter movable to and fro over
said partition wall, said shutter having a sample gas passage
having a small discharge conductance, means for causing the
to-and-fro movement of said shutter over said partition wall, and
means for evacuating said first and second chambers independently
of each other.
11. An ion source device as claimed in claim 9, further comprising
an optical plate provided on said first chamber for observing said
sample cell therethrough, and a shutter of magnetic material
disposed within said first chamber adjacent to said optical plate
so as to be pivotal toward an away from said optical plate, said
shutter being urged to its open and closed position by a magnet
disposed outside of said first chamber.
12. An ion source device as claimed in claim 10, further comprising
an optical plate provided on said first chamber for observing said
sample cell therethrough, and a shutter of magnetic material
disposed within said first chamber adjacent to said optical plate
so as to be pivotal toward and away from said optical plate, said
shutter being urged to its open and closed position by a magnet
disposed outside of said first chamber.
13. An ion source device as claimed in claim 1, in which there is
provided a chamber for accommodating therein said ion source means,
and said ion source means includes an electron generator for
ionizing the sample gas led therein from said sample cell, and a
collimator disposed within said chamber for collimating the
electrons emitted from said electron generator.
14. An ion source device as claimed in claim 2, in which there is
provided a chamber for accommodating therein said ion source means,
and said ion source means includes an electron generator for
ionizing the sample gas led therein from said sample cell, and a
collimator disposed within said chamber for collimating the
electrons emitted from said electron generator.
15. An ion source device as claimed in claim 6, further comprising
means for supporting said heating means, a first chamber for
accommodating therein said ion source means, a second chamber for
accommodating therein said sample cell, said heating means, said
radiant heat shielding means and said electrically and thermally
insulating members, a partition wall for partitioning said first
chamber from said second chamber, said partition wall having an
opening of relatively small diameter for allowing passage
therethrough of sample gas flowing toward said ion source means, a
shutter movable to and fro over said partition wall, said shutter
having a sample gas passage having a small discharge conductance,
means for causing the to-and-fro movement of said shutter over said
partition wall, means for evacuating said first and second chambers
independently of each other, an optical plate provided on said
first chamber for observing said sample cell therethrough, and a
shutter of magnetic material disposed within said first chamber
adjacent to said optical plate so as to be pivotal toward and away
from said optical plate, said shutter being urged to its open and
closed position by a magnet disposed outside of said first chamber,
said heating means comprising a cylindrical filament made by
disposing a multiplicity of metal wires in the form of a grid and
welding the metal wires to each other at their intersections, said
cylindrical filament being fixed at its opposite ends to said
supporting means, said ion source means including an electron
generator for ionizing the sample gas led therein from said sample
cell, a target for collecting the ions emitted from said electron
generator, and a collimator disposed within said first chamber for
collimating the electrons emitted from said electron generator.
Description
BACKGROUND OF THE INVENTION
Field Of The Invention
This invention relates to ion source devices equipped with sample
heating means for use in mass spectrometers and more particularly
to an ion source device of the kind described above in which a
sample cell containing therein a sample is heated by means of
electron bombardment so as to vaporize the sample in the sample
cell and to ionize the vaporized sample.
Description Of The Prior Art
In a mass spectrometer, analysis of a sample such as a solid, a
mixture of a solid and a liquid, or a mixture of a solid and a gas
which would not be vaporized unless heated to a high temperature is
frequently required. The sample may be an inorganic material such
as a metal, alloy, ceramic, graphite or the like. An ion source of
the Knudsen cell type is well known in the art as a device which
satisfies the above requirement. In view of the fact that a sample
in a mass spectrometer must be ionized in a gaseous state and in
order that a sample as described above which would not be vaporized
unless heat is applied thereto can be satisfactorily vaporized by
heating, the ion source of the Knudsen cell type comprises a sample
cell containing a sample therein, a filament for heating the cell,
and a plurality of radiant heat shielding plates for shielding heat
radiated from the sample cell.
Further, in view of the fact that the sample must be heated to a
high temperature, for example, of the order of 2500.degree. C., a
method of emitting thermoelectrons from the filament and bombarding
the sample cell with the electrons is commonly employed in an ion
source of the Knudsen cell type. On account of the necessity for
heating the sample to a high temperature, it is very important in
any ion source of the Knudsen cell type to effectively direct the
thermoelectrons emitted from the filament toward the sample cell
for heating the sample cell to a high temperature and to prevent
the radiant heat shielding plates from being bombarded by the
thermoelectrons during the analysis of the sample.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel and
improved ion source device equipped with sample heating means for
use in a mass spectrometer which satisfies reasonably such
requirements.
In accordance with the present invention, there is provided an ion
source device equipped with sample heating means for use in a mass
spectrometer comprising a sample cell for containing therein a
sample, said sample cell having an opening, heating means disposed
to surround said sample cell for emitting thermoelectrons to heat
said sample thereby to vaporize the same, radiant heat shielding
means disposed to surround said heating means so as to serve as a
shield against the radiant heat emanating from said heating means,
first electrical power supply means for supplying the heating means
with a quantity of electricity, electrical power supply means for
applying a high potential to said sample cell and a low potential
to said radiant heat shielding means relative to the potential at
said heating means in order to accelerate the thermoelectrons
emitted from said heating means toward said sample cell, and ion
source means for ionizing the sample which is vaporized in said
sample cell and passes through said opening in said sample
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of an embodiment of the ion
source device equipped with sample heating means for use in a mass
spectrometer according to the present invention.
FIG. 2 is a sectional view taken on the line II-II' in FIG. 1.
FIG. 3 is a horizontal sectional view taken on the line III-III' in
FIG. 1.
FIG. 4 is a developed view of part of a mesh filament shown in
FIGS. 1 and 2.
FIG. 5 is an electrical circuit diagram of power supply means for
the filament, thermoelectron accelerating means and degassing means
preferably used in the device shown in FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1, 2 and 3, there is shown an embodiment of the
ion source device equipped with sample heating means for use in a
mass spectrometer according to the present invention. The device
includes an ion source section 1, a sample heating section 4
partitioned from the ion source section 1 by means of a partition
plate 2 which has an opening 3 of relatively small diameter bored
in its central portion, a shutter mechanism 5 and sample cell
observing sections 6 and 7. The ion source section 1 comprises an
ion source chamber 8 and an ion source 9 disposed thereinside. The
ion source 9 comprises an ionization chamber 13 having sample beam
passages 10 and 10', an ion beam passage 11, and ionizing electron
passages 12 and 12' bored in the walls thereof, a repeller
electrode 14 mounted within the ionization chamber 13, a lens 15
and a slit plate 16 disposed opposite to the ion beam passage 11, a
filament 17 disposed opposite to the ionizing electron passage 2, a
target 18 disposed opposite to the ionizing electron passage 12' so
as to collect the electrons emitted from the filament 17, and a
magnet 19 for establishing a magnetic field in the advancing
direction of the electrons, which are emitted from the filament 17
toward the target 18 through the ionizing electron passages 12 and
12', so as to collimate the electrons while imparting a gyrating
movement to the electrons. The sample beam passing through the
sample beam passages 10 and 10', the ion beam passing through the
ion beam passage 11 and the ionizing electron beam passing through
the ionizing electron passages 12 and 12' stand at right angles
with respect to one another. The ion source section 1 comprises
further an exit slit plate 20 disposed in the ion source chamber 8
and a telefocusing lens 21 for focusing the beam of ions from the
ion source 9 on the slit of the exit slit plate 20. The lens 21 is
mechanically assembled as a unit with the ion source 9, and the
unit is supported by an ion source supporting member 22 provided on
a suitable portion of the wall of the ion source chamber 8.
Although not shown, there is actually an evacuating pump which
evacuates the interior of the ion source chamber 8 through an
evacuating conduit 23 connected to a suitable portion of the wall
of the ion source chamber 8.
The sample heating section 4 comprises a sample cell chamber 24, a
sample cell assembly 25 disposed within the chamber 24, a filament
assembly 26, and a group of radiant heat shielding cylinders 30
having aligned openings 27 and 28 bored through an upper central
portion and a suitable portion at the side thereof, respectively.
The sample cell assembly 25 comprises a sample cell 31 receiving a
sample thereinside, a sample cell support 32 for mounting the
sample cell 31 thereon, a support base 34 for supporting the cell
support 32 through three support rods 33 (only two of them are
shown in FIG. 1), and a stack of electrical and thermal insulators
35 for supporting the support base 34 thereon. The lower end of the
sample cell chamber 24 is provided with a removable flange 36 which
has a central opening 37. Another flange 55 is detachably fixed to
the flange 36 so as to close the opening 37 of the flange 36. A
double tube 38 extends through the center of the flange 55 and a
cooling medium such as water flows through the double tube 38. The
stack of electrical and thermal insulators 35 is supported on the
top of the double tube 38 through a support block 39. Therefore, it
may be said that the flange 55 serves as a base for supporting the
sample cell assembly 25. The sample cell 31 is constituted by a
cell body 40 and a cap 42 covering the upper end of the cell body
40. The cap 42 has a central opening 41. The stack 35 comprises a
plurality of electrically and thermally insulating members 43, 44
and 45 which are spaced a suitable distance from each other by
spacers 46 and 47 and are securely fixed together by screws 48 and
49. The uppermost electrically and thermally insulating member 43
is fixed to the support base 34 by screws 51 with spacers 50
interposed therebetween so as to maintain a suitable spacing
between the member 43 and the support base 34. The lowermost
electrically and thermally insulating member 45 is fixed to the
support block 39 by screws 56 and is in intimate contact with the
support block 39. Various materials may be employed to form the
elements constituting the sample cell assembly 25. For example,
tantalum which has a high melting point, can easily be machined and
has a low vapor pressure may be employed to form the sample cell
31, and tungsten having a high resistance against heat may be
employed to form the support rods 33, while boron nitride which is
highly resistive to thermal shock, has a high melting point and can
easily be machined may be employed to form the stack 35 of
electrically and thermally insulating members. Further, tantalum
which is resistive to heat may be employed to form the sample cell
support 32 and the support base 34. The number of electrically and
thermally insulating members 43, 44 and 45 may suitably be
increased when required.
The filament assembly 26 comprises a cylindrical lower supporting
member 60 of tantalum, a cylindrical upper supporting member 62 of
tantalum having four large openings 61 bored in the wall thereof
(although only two of them are shown in FIG. 1), a cylindrical mesh
filament 63 whose upper and lower ends are secured to the
respective cylindrical members 62 and 60 by welding, and a
plurality of supporting pillars 65 of stainless steel for
supporting the two cylindrical members 60 and 62 through insulating
blocks 70, 71, 72 and 73 of boron nitride which are electrical and
thermal insulators. These supporting pillars 65 are secured on a
supporting ring 67 of stainless steel which is supported on the
flange 36 through a plurality of spacers 66 of alumina. As best
shown in FIG. 4, the mesh filament 63 is in the form of a mesh of a
multiplicity of tungsten wires 68 having a wire diameter of the
order of 0.15 mm and a spacing between wires of the order of 7 mm.
The wires 68 are spot-welded to each other at their intersections
69.
The radiant heat shielding cylinder group 30 comprises a plurality
of spaced cylindrical shielding members of tantalum. These
cylindrical members are welded at their lower end to a first base
plate 75 of tantalum. The first base plate 75 is supported on a
second base plate 77 through a plurality of supporting rods 76. The
second base plate 77 is supported on a supporting ring 79 through a
plurality of supporting pillars 150. The supporting ring 79 is
supported on the flange 36 through a plurality of spacers 78 of
alumina which are electrical and thermal insulators.
The shutter mechanism 5 is mounted on a portion of the side wall of
the ion source chamber 8. The shutter mechanism 5 comprises a
stationary hollow cylindrical member 81 having a pin 80 extending
into the hollow space thereof, a rotary member 83 which is
internally threaded as at 82 and is received in the hollow space of
the cylindrical member 81 so as to be rotatable about its axis but
not movable in its axial direction, a reciprocating member 86 which
is externally threaded as at 84 at one end thereof for threaded
engagement with the internally threaded portion 82 of the rotary
member 83 and has an axial groove 85 on a portion of its outer
periphery adjacent to the other end thereof so that the pin 80 can
engage the groove 85, a shutter plate 88 which is fixed to the
other end of the reciprocating member 86, which is provided with a
sample beam passage 87 having a small pumping conductance, and
which is slidably positioned on the partition plate 2, a flange 89
to which the stationary hollow cylindrical member 81 is fixed, a
vacuum sealing bellows 90 disposed between the flange 89 and the
reciprocating member 86, and a knob 91 secured to the rotary member
83.
The sample cell observing section 6 is mounted on the upper end of
the ion source section 1 and comprises an optical window plate 92,
and a shutter 94 of magnetic material which is disposed within the
ion source chamber 8 so as to be pivotal about a pivot shaft 93.
The sample cell observing section 7 is mounted in the side wall of
the sample cell chamber 24 and comprises an optical window plate
95, and a shutter 97 of magnetic material which is disposed within
the sample cell chamber 24 so as to be pivotal about a pivot shaft
96. The openings 27, 3 and the passages 10, 10' are designed to
align on the same axis so that the interior of the sample cell 31
can be observed from the optical window plate 92 through the
passages and openings 10', 10, 87, 3, 27 and 41. One of the
openings 61 and the openings 28 align on the same axis so that the
outer surface of the sample cell 31 can be observed from the
optical window plate 95 through the openings 28, one of the
openings 61 and the mesh of the mesh filament 63.
Although not shown, there is actually provided an evacuating pump
which acts to evacuate the interior of the sample cell chamber 24
independently of the ion source chamber 8 through an exhaust
conduit 100 suitably connected to a portion of the side wall of the
sample cell chamber 24.
FIG. 5 is a schematic electrical circuit diagram of power supply
means for the filament, thermoelectron accelerating means and
degassing means in the embodiment of the present invention. The
circuit includes three power sources 101, 250 and 200 and one
change-over switch 103. The negative terminal of the power source
101 is connected with the positive terminal of the power source
200, and an intermediate point 201 therebetween is connected with
the filament 63. The positive terminal of the power source 101 is
connected with the sample cell 31 and also with the change-over
contact 105 of the change-over switch 103, while the negative
terminal of the power source 200 is connected with the other
change-over contact 106 of the change-over switch 103. The common
contact 107 of the change-over switch 103. The common contact 107
of the change-over switch 103 is connected with the radiant heat
shielding cylinder group 30.
The device according to the present invention having a structure as
described above operates in a manner as described below.
At first, it is supposed that the sample cell 31 contains already a
sample which is to be subjected to mass analysis. In the above
state, the evacuating pump means (not shown) is operated to
evacuate the interior of the ion source chamber 8 and the interior
of the sample cell chamber 24 through the exhaust conduits 23 and
100 independently of each other. The mesh filament 63 is heated by
current supplied from the power supply means 250 so as to emit
thermal electrons therefrom. The change-over switch 103 is so set
that its common contact 107 is connected with the contact 105 in
order to maintain the sample cell 31 and the radiant heat shielding
cylinder group 30 at a high potential with respect to the potential
at the filament 63. Practically, the potential at the sample cell
31 and the radiant heat shielding cylinder group 30 is kept by
about 500 to 2000 volts higher than the potential at the filament
63. Therefore, the thermoelectrons emitted from the filament 63 are
accelerated by the electric field to move toward and impinge
against the sample cell 31 and the radiant heat shielding cylinder
group 30. Thus, the sample cell 31 and the structure surrounding
the sample cell 31, that is, the radiant heat shielding cylinder
group 30 are heated by the electrons impinging thereagainst. As a
result, undesirable gas particles deposited on or adsorbed in the
surface of these members are effectively released. The released gas
is discharged through the exhaust conduit 100.
Needless to say, the opening or sample beam passage 3 is closed by
the shutter 88 which is urged to its passage closing position in a
manner as described below. Turning of the knob 91 rotates the
rotary member 83 which is associated with the knob 91. As the
rotary member 83 is rotated, the reciprocating member 86 is moved
in the direction as shown by arrow A due to the fact that the
internal threads 82 provided on the rotary member 83 are in
threaded engagement with the external threads 84 provided on the
reciprocating member 86 and the pin 80 extending from the
stationary hollow cylindrical member 81 engages the axial groove 85
provided on the reciprocating member 86. As the reciprocating
member 86 is moved in the direction of arrow A, the shutter 88
associated with the reciprocating member 86 is moved in the same
direction. Thus, by turning the knob 91 in one direction, it is
possible to move the opening 87 of the shutter 88 away from the
sample beam passage 3 thereby to close the sample beam passage 3 by
the shutter 88. Therefore, the undesirable gas within the sample
cell chamber 24 released by the degassing operation does not enter
the ion source chamber 8 which is thereby continuously maintained
at a predetermined pressure and objectionable fouling of the ion
source 9 with the gas can rationally be avoided.
The shutter mechanism 5 is then manipulated to open the sample beam
passage 3. In other words, the opening 87 of the shutter 88 is
aligned with the sample beam passage 3. In the meantime, the
change-over switch 103 is shifted to a position at which the common
contact 107 is connected with the contact 106, whereby the
potential at the radiant heat shielding cylinder group 30 becomes
lower than the potential at the filament 63 although the potential
at the sample cell 31 is left higher than the potential at the
filament 63. For example, the potential applied to the radiant heat
shielding cylinder group 30 is lower by about 50 volts than the
potential applied to the filament 63. Further, the potential at the
cylindrical member 62 is lower by about a few volts than the
potential at the mesh filament 63 because the positive and negative
sides of the power supply means 250 are connected with the mesh
filament 63 and the cylindrical member 62, respectively.
Accordingly, the thermoelectrons emitted from the filament 63 are
accelerated toward the sample cell 31 to impinge against the sample
cell 31, and at the same time, the thermoelectrons tending to move
toward the cylindrical member 62 and the radiant heat shielding
cylinder group 30 from the filament 63 are repelled back toward the
filament 63 to impinge against the sample cell 31 by the action of
the electric fields established between the filament 63 and the
cylindrical member 62 and between the filament 63 and the radiant
heat shielding cylinder group 30. Thus, the sample cell 31 can very
effectively be heated with a small electric power. Further, by
virtue of the fact that the radiant heat shielding cylinder group
30 is almost free from impingement thereagainst of the electrons
emitted from the filament 63 and tending to move toward the radiant
head shielding cylinder group 30, undesirable release of gas
deposited on or adsorbed in the radiant heat shielding cylinder
group 30 can effectively be avoided during the period other than
the degassing operation, that is, the period when the analysis is
being carried out. The filament 63 is in the form of a cylindrical
mesh screen which comprises a multiplicity of tungsten wires 68
welded to one another at their intersections 69 as shown in FIG. 4
and is secured at its opposite ends to the cylindrical supporting
members 60 and 62, respectively. By virtue of the above structure,
the sample cell 31 can uniformly be heated and heating can very
stably be effected because the filament itself is free from any
thermal deformation.
When the sample cell 31 is heated in the manner described above,
the sample contained therein is vaporized. The vaporized sample
enters in the form of a beam into the ionization chamber 13 through
the aligned openings and passage 41, 27, 3, 87 and 10. The
electrons emitted from the ionizing electron emitting filament 17
and passed through the passages 12 and 12' to be collected by the
target 18 impinge against the vaporized sample, within the
ionization chamber 13 to ionize the latter. The ionizing electrons
are uniformly collimated while being imparted with a gyrating
movement by the magnetic field established by the magnet 19 so that
the sample entering the ionization chamber 13 can effectively be
ionized. The sample which has not been ionized within the
ionization chamber 13 passes out of the chamber 13 by way of the
passage 10'. The ions ionized within the ionization chamber 13 pass
through the passage 11 to be focused on the slit of the slit plate
16 by the action of the lens 15. The ions passed through the slit
of the slit plate 16 are focused on the slit of the slit plate 20
by the action of the telefocusing lens 21. Although not shown, the
ions existing from the slit of the slit plate 20 are led toward an
analysis tube for the sake of analysis.
The magnet 19 may be disposed outside of the ion source chamber 8.
In such a case, however, the ion source section 1 is necessarily
large-sized since the sample heating section 4 must inevitably be
large-sized. Therefore, it is unable to obtain a sufficient
magnetic field strength when the magnet 19 is disposed outside of
the ion source chamber 8. It will be understood that the
disposition of the magnet 19 within the ion source chamber 8 in the
arrangement according to the present invention is so effective that
the magnet 19 may have a relatively small size so as to simply
obtain a predetermined magnetic field strength.
In order that the sample within the sample cell 31 can be heated to
a high temperature of, for example, about 2,500.degree. C. by the
electron bombardment, it is quite important that the radiant heat
from the sample cell 31 as well as the conduction of heat be
shielded as much as possible. Further, in view of the fact that a
high voltage is applied to the sample cell 31, it is quite
important that the sample cell 31 be completely electrically
insulated from the base or flange 55 or the like. To deal with such
a requirement, the radiant heat shielding cylinder group 30 is
especially provided in the present invention so as to prevent the
radiated heat from the sample cell 31 and the filament 63 from
escaping outwardly. Further, in accordance with the present
invention, the stack of electrical and thermal insulators 35 is
especially provided to provide a shield against heat which is
radiated from the sample cell 31 and tends to escape past the
sample cell assembly 25 toward the base or flange 55 or the like by
conduction. Furthermore, the stack 35 consists of a plurality of
electrically and thermally insulating members 43, 44 and 45 which
are suitably spaced from each other. Thus, a perfect shield against
the conducted heat can be provided. Moreover, these electrically
and thermally insulating members 43, 44 and 45 serve also as an
effective electrical insulation against the base or flange 55
supporting the sample cell 31 thereon. A cooling medium such as
water is led into the double tube 38 for cooling the stack of
electrical and thermal insulators 35 so as to rationally prevent
any reduction in the electrically insulating function of the stack
of electrical and thermal insulators 35 due to an undesirable
increase in temperature.
A relatively large amount of vaporized sample gas emerging from the
sample cell 31 flows through the opening 41 of the cell 31 toward
the ion source 9 in a considerably dispersed state. Further,
although the gas attach deposited on or adsorbed in the radiant
heat shielding cylinder group 30 has been released prior to the
analysis, some gas particles still deposited on or adsorbed in the
radiant heat shielding cylinder group 30 may be led through the
opening 3 toward the ion source chamber 8 during analysis. These
gases may foul the ion source 9 and bring forth an objectionable
reduction in the degree of vacuum within the ion source chamber 8.
In order to restrict the flow of vaporized sample gas emerging from
the sample cell 31 to a suitable area so that the unnecessary
sample gas and the deposited or adsorbed gas may not be led toward
the ion source chamber 8, the beam passage 87 of small diameter
having a small pumping conductance is provided in the shutter 88,
and the ion source chamber 8 and the sample cell chamber 24 are
arranged to be evacuated independently of each other. In such an
evacuating system, for example, the pressure within the ion source
chamber 8 may be set at 5 .times. 10.sup..sup.-7 to 10 .times.
10.sup.116 7 Torr and the pressure within the sample cell chamber
24 in the vicinity of the sample cell 31 may be set at 5 .times.
10.sup.116 6 to 10 .times. 10.sup.116 6 Torr.
In accordance with the present invention, the internal temperature
of the sample cell 31 can directly be observed from the sample cell
observing section 6 through the aligned passages and openings 10',
10, 87, 3, 27 and 41 for the purpose of measuring the temperature
of the sample. For the sake of measuring the temperature and
uniformity of the sample cell 31, observation of a plurality of
surface holes (need not be a through holes), not shown, of 1 to 2
mm. in diameter of the sample cell 31 is much more effective than
observation of a single hole of the sample cell 31. To this end,
another sample cell observing section 7 is provided according to
the present invention so that the temperature at each surface hole
of the sample cell 31 can be observed from the optical window plate
94 through the openings 28 and one of the openings 61.
The sample gas, adsorbed gas and the like may deposit to form a
coating on the optical window plates 92 and 95 in the sample cell
observing sections 6 and 7. In order to avoid such trouble, the
shutters 94 and 97 are provided in accordance with the present
invention. These shutters must be opened during the observation of
the sample cell 31 and kept closed except for the observation. The
mechanism for effecting the opening and closure of the shutters may
be realized in a variety of forms. For example, a shutter shaft may
be fitted to the shutter in vacuum and may have a portion thereof
projected to the outside of the device, and this projecting portion
may be manipulated to open or close the shutter. However, a vacuum
seal is required to seal the outwardly projecting portion of the
shutter shaft. When the vacuum seal consists of rubber, the seal
may be damaged by the action of heat. Further, in any of the cases
where the vacuum seal is made of rubber and a metal, a suitable
thermal insulator must be fitted on the projecting portion of the
shutter shaft so that such portion can be contacted manually.
In accordance with the present invention, a magnet is disposed
outside of the ion source chamber 8 opposite to the shutter 94 so
that the force of magnetic attraction can be utilized to close the
shutter 94 by turning it about the pivot shaft 93. Of course, the
shutter 97 is also closed by a mechanism similar to the above. It
will be understood therefore that the above problem can rationally
be solved by the present invention.
While a preferred embodiment of the present invention has been
described in detail with reference to the drawings, it will be
understood that the embodiment is merely exemplary of the present
invention and many changes and modifications may be made therein
without departing from the spirit of the present invention.
* * * * *