referring to fig1 through 5 , wherein like numbers refer to similar parts , the invention is described . the figures show only schematic representations of a sputter ion source and are illustrative only . those skilled in the art will recognize the relation between the described components in the figures and the specific components in particular realizations of a sputter ion source . components required for an understanding of the invention and its application are represented in the figures , and those skilled in the art recognize how these components are typically arranged within evacuated volumes and supplied with electrical currents and potentials from power supplies , cooling water from circulation pumps , metal vapor from a boiler , and gases from a pressurized cylinder or other storage . cs is the most common metal vapor used in these sputter ion sources and is referred to here as only representative of the potential sputtering primary ions that may include the alkali and alkali - earth metals or the noble gases . the figures are medial views through an otherwise axially symmetric construction with singular instances of power lines ( 134 ) and vapor pipe ( 127 ) extending beyond the orthogonally represented components . this type of ion source is typically connected to a mechanical system ( not shown ) that is capable of sequentially placing one of a plurality of sample holders ( 106 ) into the active position of the ion source demarcated by the illustrated positions of the sample holder ( 106 , 206 , and 406 in fig1 , 2 , 4 , and 5 ). the typical operation of this ion source is described with reference to fig1 , in which a solid sample to be analyzed ( 103 ) is pressed into an electrically conducting sample holder ( 106 ) prior to being placed into the active position of the source , where it is shown . the sample holder in this embodiment is retained in position with springs or ball detents ( 109 ) that provide moderate thermal conduction to the mounting plate 112 that is cooled by circulating water in channels 115 . cesium ( cs ) metal vapor is created in a boiler ( not shown ) and brought to the ion source through tube 127 where it disperses around a distribution ring ( 130 ) and emerges from a series of holes ( 131 ) facing a high temperature hemispherical surface of an ionizer ( 133 ) that is powered through wire 134 . the ionizer is at 1100 ° c . or hotter , causing the cs atoms to thermally lose an electron , becoming positive ions . these positive ions are repelled from the ionizer by the electric field created by holding plate 112 at a “ cathode potential ” that is more electrically negative than plate 136 . the cs ions are accelerated toward the sample ( 103 ) in this electric field that is shaped by the hemispherical surface of the ionizer ( 133 ) and the round opening of a lens ( 118 ). cs ions strike the sample surface , sputtering sample atoms , with the large plurality of the sputtered ions being uncharged neutral atoms . the electrical current of positive cs ions ( typically 1 . 5 ma ) represents 10 16 cs atoms per second striking the sample and sample holder . these ions become neutral atoms on the surfaces of the sample holder ( 106 ) where the surface temperature is sufficient to maintain a vapor pressure of neutral cs in the volume ( 119 ) in front of the sample ( 103 ). neutral sample atoms sputtered from the sample ( 103 ) are negatively ionized by collisions with neutral cs atoms , and even more readily ionized by collisions with cs atoms in excited states . negative sample ions drift at their sputtered velocity into the electric field between the lensing shroud ( 118 ) and the ionizer ( 133 ) where they are accelerated . the opening of the shroud ( 118 ) and the shape of the ionizer ( 133 ) focus these negative ions through the opening ( 139 ) where they may be further accelerated by the potential difference between plate 136 and the extraction electrode ( 142 ). the accelerating components are held in position by insulating spacers ( 145 ). a source of photons may be axially introduced to excite cs or sample atoms ( 150 ). the simplest embodiment of the invention uses the recess volume between the surface of the sample ( 103 ) and the end of the sample holder 106 to trap a portion of the neutral cs vapor as the ionizing volume for neutral atoms sputtered from the sample surface . in that case , the sample 103 is recessed at least one or more hole diameters from the surface of the sample holder and the shroud ( 118 ) is a skeletal support of its lensing aperture for improving vacuum near the sample . in another embodiment , the front of the sample holder extends to the shroud ( 118 ) that is thermally insulated by a ring ( 124 ) from the mounting plate ( 112 ) and is heated by the radiant energy of the ionizer ( 133 ). this heated surface has sufficient temperature to create a significant vapor pressure of cs in the vicinity of the shroud . the heat further acts to drive off any sample atoms that can form a contaminant background signal for subsequent samples . the shroud defines a volume ( 119 ) that can be shaped for optimal retention of neutral cs vapor boiled off the sample holder and shroud for the purpose of negatively ionizing any neutral sample atoms that pass out of the sample . alternatively , another embodiment of the invention is shown in fig2 , in which the sides of the sample holder ( 206 ) are extended in order to incorporate the ionizing volume ( 219 ) within constraining walls that are removed and replaced by the entry of a new sample holder . a differently shaped lensing shroud ( 218 ) mounted on plate 212 and the circular walls of the sample holder ( 206 ) focus both the incident positive cs ions and the emitted negative sample ions in a manner similar to the embodiment shown in fig1 . an embodiment of the invention that also serves to replace the volume of cs vapor during every change of sample holder is shown in fig3 . in this embodiment , the sample holder ( 306 ) is a simple cylinder of metal that has a blind hole into which the sample material ( 303 ) is pressed . this sample holder is then secured by a spring clip ( 312 ) within a cylindrical carrier ( 307 ) that fits within the sample position of the ion source and is capable of being loaded by the sample changing mechanism ( not shown ). the face of the sample holder ( 306 ) is held back from the front of the sample carrier ( 307 ) by a small ridge ( 315 ) to create the volume ( 319 ) in which vaporized cs concentrates for the ionization of neutral atoms sputtered from the sample ( 303 ). a high intensity cs sputter source is adapted for accepting gaseous samples rather than solid samples by introducing the gas through a quartz capillary tube ( 402 ) as shown in fig4 . the gas flows around a metal anvil ( 403 ) incorporated into the sample holder ( 406 ). the cs breaks up molecular gas at or above the surface of the anvil ( 403 ). as with the solid sample , some atoms are ionized at the surface and emerge as negative ions . a larger fraction emerge as neutral atoms that are ionized by neutral cs vapor in front of the anvil in the sample holder and in the volume 419 . the modification of the sample holder ( 206 ) from the embodiment of fig2 is also incorporated in this embodiment for gas analysis for illustration . a variation on the sample holder of fig3 including a capillary gas inlet provides a larger volume of the gas sample to ionize with the trapped cs . another embodiment of this invention allows neutral cesium vapor to emerge from the cesium distribution ring ( 130 ) not only through the holes pointing toward the heater ( 131 ), but also toward the sample ( 103 ) and the volume ( 119 ) in front of the sample holder ( 106 ) such as the shroud ( 118 ) of fig1 or the volumes ( 219 and 419 ) defined by the sample holder ( 206 and 406 ) respectively in fig2 and 4 . yet another embodiment incorporates a separate source of cs or other ionizing vapor to fill a volume in line with the path of neutral atoms from a sample , whether or not that volume is defined by constraining structures . all embodiments of the invention include instances of transforming the ionizing vapor to one or more of its excited states in order to increase the probability of negative ionization and to lower the collision velocity required for ionization . this excitation is accomplished with energetic electrons , energetic positive ions such as the primary cs + ion beam , or photons from lasers ( 150 ) capable of selecting specific excited states within the neutral ionizing vapor . particular embodiments of the invention are described here to suggest multiple methods for creating a volume of neutral ionizing vapor directly in front of a sample for the purpose of negatively ionizing neutral atoms sputtered from the sample material . these embodiments are described with reference to particular drawings of a high intensity cesium sputter ion source . the particular drawings and embodiments are merely illustrative and are not restrictive on the spirit of the invention . those skilled in the art recognize that specific geometries and materials for the various components may vary . the invention specifically incorporates methods of increasing the density of neutral vapor of cs in excited states in a region of low electric fields through which neutral atoms sputtered from a sample pass . nuclear instruments and methods in physics research b north holland publishing , amsterdam “ total cross sections for charge transfer between alkali atoms and halogen molecules ” a . p . m . baede , a . m . c . moutinho , a . e . devreis and j . los ( 1969 ) chem . phys . lett . 3 : 530 . “ ultrasensitive mass spectrometry with accelerators ” a . e . litherland , ( 1980 ) ann . rev . nucl . and particle sci . 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