Abstract: The accelerator includes a source of an ensemble or bunch of ions and a plurality of relatavistic electron beam stages, each of which generate a high current electron beam which in turn are injected along the accelerator centerline in a timed sequence to accelerate the ion bunch to increasingly high kinetic energy levels. In each relatavistic electron beam stage, a region of high electric charge is created by the discharge of a high current, short duration pulse between a cathode and anode. The electron beam created by the discharge stops a short distance beyond the anode, due to the buildup of its electric charge, thereby creating a region of high charge which accelerates the ion bunch. Each successive relatavistic electron beam stage is timed to fire when the ion bunch arrives at the region of high charge of that stage, and in operation, increases the kinetic energy of the ion bunch by a factor equal to or greater than the kinetic energy of the electron beam.

Abstract: An inverse reflex tetrode (IRT) for producing an intense pulsed beam of i includes a real cathode having a curved or conical surface which is substantially transparent to the ions; first anode and second anode, or grid, which are spaced apart and are at the same potential, the first anode being between the real cathode and the second anode and having a curved or conical surface approximately parallel to the surface of the real cathode, and also being formed from a dielectric material such as polyethylene; a curved or conical hollow anode stalk which supports both anodes; and a virtual cathode which is formed by electrons that are emitted by the real cathode and pass through the first anode. The real cathode and first and second anodes are enclosed in a vacuum chamber and are immersed in an applied external magnetic field. The IRT receives an electrical pulse from a high-voltage pulse generator.

Abstract: A mass spectrometer instrument for chemical analysis. An instrument of this invention is capable of performing cyclic operation repetitively and automatically. Each operation cycle consists of at least one chemical ionization operation mode and one venting operation mode. Furthermore, an instrument of this invention is capable of performing cyclic operation which includes multiple chemical ionization operation modes in which each of a plurality of reagent gases is individually employed for each chemical ionization operation mode. Electron impact ionization can also be conducted during each venting operation mode should it be desired.Positive ion and negative ion spectra are also recorded simultaneously which further improves the efficiency of the cyclic operation.

Abstract: The present invention describes an ion source which is capable of producing relatively high density ion currents. The ion source employs an electrically biased ionic conductor to supply ions from a reservoir of the atomic species.

Abstract: Organic samples from a liquid chromatograph are deposited on a conveyor belt which transports them into a vacuum chamber at the entry end of a mass spectrometer. The samples are ionized directly on the belt by particle bombardment or by means of a laser beam. Ionization is enhanced by applying an oxide layer to the belt, by neutralizing the image force, and by vaporizing alkali atoms on the belt to reduce the ionization potential.

Abstract: A new ion source assembly for calutrons has been provided for the efficient separation of elements having high vapor pressures. The strategic location of cooling pads and improved insulation permits operation of the source at lower temperatures. A vapor valve constructed of graphite and located in a constantly increasing temperature gradient provides reliable control of the vapor flow from the charge bottle to the arc chamber. A pronounced saving in calutron operating time and equipment maintenance has been achieved with the use of the present ion source.

Abstract: An arrangement wherein atoms are ionized by contact with a heated ionizing surface and the ions are accelerated along an acceleration path towards an acceleration electrode, and wherein, in order to achieve high current densities, the heated surface is convexly curved towards the acceleration electrode and has a radius of curvature which is substantially smaller than the length of the acceleration path.

Abstract: A tandem quadrupole-based mass spectrometer including a highly efficient intermediate fragmentation stage. The disclosed fragmentation stage employs collision-induced dissociation (CID), in an electrodynamic focus device, which may be a quadrupole operated in a broad band filter mode. The disclosed CID process occurs at low energy (e.g., less than 1 keV, but preferably 2 eV to 100 eV), and is quite different from the high energy (e.g, greater than 1 keV, and typically 3 keV to 10 keV) CID process in prior tandem instruments such as mass-analyzed ion kinetic energy spectrometry (MIKES) systems. The efficiency of the present CID fragmentation is as high as 65%.

Abstract: Ionization chamber for the chemical ionization of vapors of substances in ion-molecule reactions by means of ionizing primary particles and a reactance gas, having at least one inlet opening for feeding the reaction partners and at least one outlet opening for the reaction products formed in the chamber. As shown, the ionization chamber has an elongated shape. The inlet opening for the ionizing primary particles on the one hand, and the outlet opening for the reaction products on the other hand, are arranged in alignment in opposite end walls of the ionization chamber.

Abstract: An ion source supplying a dense flux of low energy ions containing very few neutral particles. It comprises: a microwave circuit in which an electromagnetic wave propagates along a direction ZZ, the conducting elements forming this circuit being arranged periodically and being ring-shaped, inlet means for a neutral gas at the center of the microwave circuit, this gas being ionized thanks to the energy supplied to it by the microwave, a magnetic field guiding the resulting plasma in the direction ZZ, and means for pumping the unionized atoms in a direction normal to the direction ZZ, all along the microwave circuit.

Abstract: A tandem ion accelerator is disclosed having a charge reversing device for recharging negative ions into positive ions. The recharging is carried out in a matter-free zone and a light source is provided having a high luminous density for recharging the negative ions into positive ions. Preferably a deflecting device is provided for displacing an ion path and the light source is arranged such that a path of the light emitted from the light source coincides at least with a portion of the ion path.

Abstract: A plasma source constituting an ion accelerator operating in the presence of an intense magnetic induction for obtaining plasma of large transverse section and comprising a chamber having an inlet for gas and a device to produce electrical discharge at high frequency in the chamber to form a plasma from the gas. A plurality of parallel channels are disposed in axial extension from the chamber and a magnetic induction coil surrounds the channels for producing the intense magnetic induction in a direction parallel to the channels.

Abstract: The extraction electrode consists of a metallic screen provided with an opening and placed within a vacuum chamber in front of an ion source, the screen being brought to a negative potential with respect to the source. Displacement of the electrode is controlled from the exterior of the chamber by two mechanical systems for independent displacement of the two lateral sides of the screen. Each system comprises a deformable parallelogram pivotally coupled to a member for supporting one side of the screen and to a member which is slidably mounted on a guide column, and a mechanism for controlling the deformation of the parallelogram by means of a link-arm rigidly fixed at one end to a toothed wheel in mesh with an endless screw and control rod which is accessible from the exterior of the chamber. The invention is primarily applicable to the construction of ion implanters, especially for the fabrication of semiconductors.

Abstract: This invention relates to an apparatus in which laser pulses of up to about one nanosecond duration (.about.10.sup.-9 secs) and high intensity, more than 10.sup.11 watts cm.sup.-2, generate energetic (>>10 keV) ions, which can have very high charge states of more than twenty times the charge state of a single electron, from solid or liquid targets using non-liner, electrodynamic forces operating within the target material. In the present invention the energetic, highly charged ions are produced in such a manner that isotopes of a particular element forming the target can be separated into their respective groups travelling at particular velocities and directions, at distances of more than one meter from the irradiated target. In the present invention, the energetic, highly charged ions are generated and accelerated with high efficiency (>25%) within a relatively cold plasma (<1000 eV) generated from the target material.

Abstract: A metal vapor source with a regulatable flow rate comprising an enclosure filled with said vapor, means for heating said enclosure to a first temperature, a tube connected to the enclosure and means for heating said tube to a second regulatable temperature, the first temperature being maintained above the second temperature.An ion analyzer comprising an enclosure in which is disposed a target to be analyzed, a lens for extracting secondary ions whose front face faces the target, an enclosure filled with an alkaline vapor, means for heating said enclosure to a first regulatable temperature, a vapor outflow tube connected to one end of the enclosure, while the other end penetrates the analyzer enclosure, traverses the extraction lens and assumes a position level with the front face of the extraction lens and means for heating said tube to a second regulatable temperature, the first temperature being kept above the second temperature of the outflow tube.

Abstract: A reflex tetrode device for efficiently generating intense, pulsed unidirional ion beams. The device includes two thin, semitransparent anodes spaced from a real cathode which is maintained at ground potential. The first anode is spaced from and faces the real cathode. The second anode is spaced a short distance from the first anode and a virtual cathode is formed beyond the second anode when a sufficiently high electron current flows from the real cathode and through the anodes. The anodes are ring-like or disc-like structures secured to the edges of a support member with their planes perpendicular to the axis of the device between the real and virtual cathodes. The anode structure (i.e., the support member together with the two anodes) is connected to a pulsed high-voltage generator which is operated in positive polarity. Consequently, both anodes are at the same positive potential.

Abstract: An ion extraction system utilizing small hole accel grid (SHAG) optics is disclosed. A screen grid, an accel grid and a decel grid are positioned downstream of a neutral, highly ionized plasma source, and each of these grids have apertures in axial alignment. The accel grid has a relatively small aperture in the range of less than 50% to approximately 10% the size of the aperture of the screen grid. The electric field set up by the screen grid and the accel grid serve to extract an ion beam from the plasma source and focus the ion beam through the accel grid aperture. The small aperture in the accel grid is formed by drilling a relatively large aperture in the accel grid and then securing a thin metallic foil on at least the downstream face of the accel grid to cover the large, drilled aperture.The relatively small aperture is etched in the thin metallic foil by the ion beam.

Abstract: An extended range static eliminator for impinging a stream of ionized air upon light-sensitive articles to be neutralized includes a housing for directing air through an opening therein toward the articles and a plurality of pointed discharge electrodes supported in the housing across the opening and facing opposite the air stream. The electrodes are preferably capacitively coupled to the high side of an A.C. power source to reduce likelihood of arcing while a conductive casing connected to the other side of the power source partially encircles the discharge electrodes to shield the high voltage field at the base of the electrodes from the ions emitted from the points thereof and further shield the sensitive articles from corona developed around the points.

Abstract: An improved arrangement of electrode plates, semiconductor materials, electrode supports, and electrical power supplying circuitry is useful for plasma treatment of semiconductor materials in a reaction tube in the presence of a reaction gas.

Abstract: Organic samples 10 coming from a liquid chromatograph 11 are deposited on a conveyor belt 13 which transports them into a vacuum chamber at the entry end of a mass spectrometer. The samples are ionized directly on the belt by ion bombardment or using a gaseous charge carrier. Ionization is enhanced by applying an oxide layer to the belt, by neutralizing the image force, and by vaporizing alkali atoms on the belt to reduce the ionization potential.

Abstract: An apparatus for ionizing and vaporizing non-volatile or thermally labile molecules of a sample for introduction into a mass spectrometer analyzer which comprises a housing containing an ionization chamber; an ion exit port for the introduction of gaseous ions from said ionization chamber into a mass spectrometer analyzer on the portion of the housing attached to said mass spectrometer analyzer; inlet means for introducing a gaseous reactant into said ionization chamber within said housing; inlet means for admitting high energy radiation into said ionization chamber within said housing to at least partially ionize the molecules of said gaseous reactant; aperture means open into said ionization chamber of said housing for admitting a conductive emitter characterized by having a conductive element of a highly irregular surface upon which is deposited said sample for analysis into said mass spectrometer analyzer; and a vacuum exit aperture in said housing by which the pressure within said ionization chamber can

Abstract: An arrangement for detecting low concentrations of molecular gases. A gaseous sample containing molecules of the gas to be detected is simultaneously subjected to two photon beams which, for example, may be generated by lasers. The wave length of the first photon beam corresponds to the energy separation between the ground electronic state and an excited electronic state of the molecular gas and the second photon beam contains energy in a wave length corresponding to the energy separation between the excited electronic state and the ionization limit of the molecule. Detection of the amount of ionization achieved is a measure of the concentration of the molecular gas in the sample. Simultaneous identification of the particular wave lengths causing the transition of the molecules from the ground energy state to the excited state provides an additional parameter identifying the molecules.

Abstract: Ultrasharp diamond edges and points which are usable as high intensity point sources for the emission of electrons, ions, X-rays, coherent and incoherent light and high frequency electromagnetic radiation are produced by preparing and classifying ultrafine diamond powder having a particle size of 10 to 100 angstroms, placing the powder in a diamond mold defining the ultrasharp edge or point to be produced and applying a pressure of the order of 80 to 90 kb while heating the powder to a temperature of the order of 2440.degree. K. in an ultrahigh vacuum or inert atmosphere after degasing to avoid oxidation of the diamond powder.

Abstract: This invention relates to a device for generating an atomic cloud, the device having a housing in which is housed a cathode and an anode, and with suitable passages or flow directing members to direct flow of a gas outwardly away from or past the cathode discharge surface, so that when a suitable potential is applied across the anode and the cathode a glow discharge occurs between the anode and the cathode. The flow of gas preferably draws atoms that are ejected from the cathode discharge surface away from the cathode to a region beyond the cathode glow region, thereby to generate an atomic cloud having a low value of inherent radiation. The device is further incorporated with an apparatus for spectro-scopically analyzing a substance by fluorescent techniques.

Abstract: The separated ion source combines an ion source and a magnetic mass separator within a single magnetic field geometry. The preferred ion source has a low voltage Penning discharge configuration and produces a charged particle beam in the form of a ribbon with a rectangular cross section.

Abstract: An ion beam apparatus applies an ion beam emitted from a gaseous ion source to a solid material which constitutes a solid ion source. Ions of the solid material are emitted from the solid material as a result of the application of the exciting ion beam and are extracted by an extracting electrode and applied to a specimen.

Abstract: A method and apparatus for monitoring particulates which are borne by a surrounding gaseous medium, such as found in smokestacks or the like, through interception of the particulates by a hot filament having a bias potential in the range of about 100 to 1000 volts whereupon each particulate decomposes into a burst of ions which is collected by a nearby electrode at ground potential, by counting those bursts which produce a predetermined total charge and, at the same time, measuring the DC electric current produced by the bursts and other ion exchange between the hot filament and the electrode. The filament operates at a temperature level wherein infrared and visible radiations are emitted, such radiations being monitored by a phototransistor which receives the radiations.

Abstract: A system for automatic regulation of the density of a given molecular type at a pre-arranged point in an apparatus called a "flux or molecular jet", intended to make epitaxy layers. In a vacuum enclosure a probe for mass spectrometry analysis (electrostatic, four pole apparatus) picks up the types projected by evaporating units, ionizes them, filters and detects them as a function of their respective masses. The heating in each unit is regulated by a servo-control loop which contains means for analyzing the type concerned.

Abstract: Method and apparatus for interfacing a liquid chromatograph column and a mass spectrometer. The ions necessary for analysis by a mass spectrometer are provided by utilizing a conduit held at a high voltage potential to ionize at least a portion of the solute flowing out of the liquid chromatograph column. Chambers held at low pressure are utilized to evaporate substantially all of the un-ionized solvent present with the solute to provide an ion stream consisting essentially of ionized solvent and solute to the mass spectrometer. The mass of the ionized solute is then determined by the mass spectrometer, thus providing an analysis of the components eluted from the liquid chromatograph column.

Abstract: A chemical ionization ion source comprising a firt electrode disposed in a discharge region, a counter electrode disposed to confront the first electrode and having at least one space for introducing electrons generated in the discharge region into an ionization region and means for maintaining the counter electrode at a potential higher than that of the first electrode and applying a direct current voltage between the two electrodes, wherein the discharge region and the ionization region are maintained under substantially the same pressures.

Abstract: A reduced size ion source for on-line use with a cyclotron heavy-ion beam is provided. A sixfold reduction in source volume while operating with similar input power levels results in a 2000.degree. C. operating temperature. A combined target/window normally provides the reaction products for ionization while isolating the ion source plasma from the cyclotron beam line vacuum. A graphite felt catcher stops the recoiling reaction products and releases them into the plasma through diffusion and evaporation. Other target arrangements are also possible. A twenty-four hour lifetime of unattended operation is achieved, and a wider range of elements can be studied than was heretofore possible.

Abstract: A high current ion beam is extracted from an ion plasma by a low perveance ion optical system including a screen electrode, a final electrode and an intermediate electrode therebetween which is shaped to correspond to the extraction voltage equipotentials therebetween. By controlling the voltage of the intermediate electrode with respect to the other two electrodes focusing is accomplished.

Abstract: A field ionization source includes a <110> oriented iridium emitter, the tip of which is initially built up in the <110> direction. A negative voltage is applied to the emitter after the emitter has been heated to approximately 2000.degree. C; thereafter, the emitter is cooled to approximately 1200.degree. C. Crystalline buildup of the pointed iridium tip occurs in the <110> direction. After buildup has occurred, the emitter is cooled sufficiently to "freeze" the tip in the built up configuration. The negative voltage is then removed. A gas containing molecules to be ionized is differentially pumped at relatively high pressure through a tube into a region immediately around the emitter tip enclosed by a cathode cap having an aperture through which the ion beam is accelerated. The iridium emitter is mounted in thermal contact with a liquid nitrogen reservoir, which maintains the emitter at near-cryogenic temperatures.

Abstract: An ion source is described in which a compound of the material of a desired ion is dissociated in a plasma discharge process to provide a beam of charged particles including the desired ions. The proportion of the desired ion in the particle beam is selected by adjustment of the temperature of the plasma, and, for increasing the range of selection of obtainable proportions, various means are described for increasing the plasma temperature beyond that which was previously attainable in ion sources of this type.

Abstract: Ion sources which become coated with insulative materials are rejuvenated by forming the repeller electrode in the ion source of gold and bombarding such repeller electrode with ions to sputter the gold onto the coated surfaces to render them conductive again. Gold sputtering is accomplished by bombarding the gold repeller electrode with inert argon ions.To perform this method, the slit of the extractor plate on the ion source is greatly reduced in cross-sectional area such that the normally higher sputtering pressures may be maintained within the ion source itself. If a direct sample probe is used, it too may be formed of gold and used to provide the gold sputtering source.

Abstract: A duopigatron ion source is modified by replacing the normal oxide-coated wire filament cathode of the ion source with a hot tungsten oven through which hydrogen gas is fed into the arc chamber. The hydrogen gas is predissociated in the hot oven prior to the arc discharge, and the recombination rate is minimized by hot walls inside of the arc chamber. With the use of the above modifications, the atomic H.sub.1.sup.+ ion fraction output can be increased from the normal 50% to greater than 70% with a corresponding decrease in the H.sub.2.sup.+ and H.sub.3.sup.+ molecular ion fraction outputs from the ion source.

Abstract: A collective field accelerator which operates with a vacuum diode and utilizes a grooved cathode and a dielectric anode that operates with a relativistic electron beam with a .nu./.gamma. of .about. 1, and a plurality of dielectric lenses having an axial magnetic field thereabout to focus the collectively accelerated electrons and ions which are ejected from the anode. The anode and lenses operate as unoptimized r-f cavities which modulate and focus the beam.

Abstract: A reflex triode for use in producing ultra-high-current (>10.sup.5 A), ul-high-power (>10.sup.11 W) ion beams includes an improved anode and an improved cathode and has a low inductance design. A cylindrical anode stalk supporting the anode is positioned inside of and closely spaced from a cylindrical cathode shank which supports the cathode. Magnetic insulation allows for a close spacing between the anode stalk and cathode shank which reduces the inductance. The improved cathode is embedded in a cathode mount to reduce divergence of the ion beam. The improved anode consists of conducting concentric rings with thin film in the space between the rings to produce a more uniformly dense ion beam having low divergence.

Abstract: Apparatus and method for separating materials, particularly isotopes of heavy metals. An electrohydrodynamic source of positive ions directed in a beam to a transverse magnetic field which deflects the ions along paths which carry the different mass ions to different collectors. An ion source incorporating a container for molten material, a pressure system for delivering the liquid material to a capillary tube, and a high voltage power supply providing an intense electrostatic field at the tube end for producing ions by field emission.

Abstract: A method and apparatus for implanting radioactive gas in a base material which comprises the steps of conducting radioactive gas received in a reservoir to an ion source for ionization; accelerating said ionized radioactive gas into a high energy form; and implanting said high energy radioactive ion beam in a foil made of, for example, stainless steel, aluminium or copper and received in an ion implantation unit.

Abstract: A source of a tubular beam of ions comprising a cylindrical shell with one butt end having an axial hole in it and the other butt end solid. It is provided with a rod having one end fixed to the solid butt end of the cylindrical shell and arranged coaxially to the latter. The free end of the rod carries a disc placed in the axial hole of the butt end of the cylindrical shell so as to obtain a circular gap confined by the side wall of the hole. A hollow annular shell is arranged coaxially within the cylindrical shell so that a circular gap made in the butt end of the annular shell faces the circular gap in the butt end of the cylindrical shell. An annular cathode and an anode are arranged coaxially inside the annular shell. A thermoelectronic cathode is placed outside the cylindrical shell near to its butt end with the circular gap. An electromagnet coil is arranged coaxially inside the cylindrical shell. A device for ion acceleration is placed on the path of emission of the ions.

Abstract: A grid system for an ion beam generator is provided having a frustoconical shape so that the collimated ion beam converges at a predetermined angle toward the target to provide selective beveled etching.

Abstract: A new interface is interposed between a liquid chromatograph and a mass spectrometer, and it consists of a nebulizer, an evaporator and a cooler. An effluent from the liquid chromatograph is nebulized by the nebulizer. The nebulized effluent is heated by the evaporator, and has only its solvent evaporated. A mixed fluid which consists of the evaporated solvent and the nebulized sample is guided to the cooler, and is cooled therein. At this time, the evaporated solvent is condensed again and is separated from the nebulized sample as a liquid. The nebulized sample left behind is guided to an ion source of the mass spectrometer.

Abstract: A method and apparatus for mass spectrometry employing tandem chemical ionization (CI) and electron impact (EI) ionization chambers with independent ionizing electron sources, both CI and EI ions being produced simultaneously. Through electronic shuttering either the CI or EI ions may be transmitted to the mass spectrometer while the ions of the other type are dispersed and rejected. The shuttering being accomplished very rapidly relative to the mass scan rate, which is in turn fast with respect to temporal variations in sample material composition. The two interwoven ion sequences are demultiplexed and smoothed into independent and effective simultaneous CI and EI mass spectrum channels.

Abstract: A balanced ion emission system for "shockless type" static eliminators (wherein pointed discharge electrodes are capacitively coupled to one side of an A.C. high voltage source) employs pointed needles which are adjacently spaced from at least some of the pointed discharge electrodes and connected by way of a conductive path to the other side of the A.C. high voltage source. The points of the needles are adapted to be adjustably positioned with respect to the discharge electrodes so that an equal number of ions of each polarity are discharged into the atmosphere for impingement upon the articles to be neutralized.

Abstract: An ion microprobe analyzer capable of high-precision analyses, and which provides a beam made up of both ions and neutral particles includes an ion beam deflecting means made up of an aperture which is movable between a position on the ion beam optical axis and a position deviating from the optical axis. At least one first deflector is provided which deflects the ion beam towards the point to be occupied by the aperture situated at the deviating position while leaving the path of the neutral particles unaffected, and at least two second deflectors are provided which deflect the ion beam back towards the ion beam optical axis, so that in the vertical direction the ion beam which has passed through the aperture situated at the deviating position is returned to the optical axis. In this way either the ions or the neutral particles may be selected in accordance with the position of the aperture.

Abstract: A workpiece to be treated by using glow discharge is mounted in a container which contains a corresponding gas or gas mixture. The container and the workpiece are respectively connected to different terminals of an electrical source, and the resulting electrical potential gradient produces ions which are accelerated for a bombardment of the exterior surface of the workpiece for hardening the exterior surface area thereof. In order to measure an equivalent of the temperature of the workpiece, a thermal sensor element is mounted within a testpiece in heat-conducting relationship therewith. The sensor element is operative for generating a signal in dependence upon the temperature detected. Wires are connected with the sensor element for conducting the detected signal from the sensor element towards the exterior of the container. These wires are located remotely from the field so as to prevent undesirable electrical interference between the field and the detected signal.

Abstract: The arrangement is for the mass-spectrometric detection of ions in the presence of a disturbing background, and is of the type including a source of ions, a mass-spectrometric separating system, a detector for the presence of ions, and a focusing device for the ions interposed between the source and the detector. The focusing device comprises an asymmetric electrostatic focusing lens arrangement having semi-cylindrical electrodes defining a lens axis, an ion entrance aperture, and an ion exit aperture. In three embodiments of the electrostatic focusing lens, the ion entrance aperture is eccentric to the axis of the lens. In a fourth embodiment, the ion entrance and exit apertures are coaxial with the lens axis and a pair of intermediate electrodes define an ion aperture which is eccentric relative to the axis of the lens.

Abstract: Methods and apparatus for producing intense megavolt ion beams are disclosed. In one embodiment, a reflex triode-type pulsed ion accelerator is described which produces ion pulses of more than 5 kiloamperes current with a peak energy of 3 MeV. In other embodiments, the device is constructed so as to focus the beam of ions for high concentration and ease of extraction, and magnetic insulation is provided to increase the efficiency of operation.

Abstract: This is an ion-producing source having a distinct chemical ionization configuration and a distinct electron impact configuration. In this source, a hollow chamber including an ion source and a source of sample molecules receives a hollow, slidable cylindrical member having a chemical ionization chamber within it. Orifices in the chamber and the cylindrical member connect the chemical ionization source chamber to the electron source and to the sample molecule source when the cylindrical member is pulled to one position. When the cylindrical member is pulled to another position, the slidable cylindrical member and the inside walls of the chamber define the ionization region to which the electron source and the sample molecule source are directly connected. By moving the cylindrical member, the ionization source can be changed from a chemical ionization source to an electron impact source.