Abstract: Short pulse neutron generators are described herein. In a general embodiment, the short pulse neutron generator includes a Blumlein structure. The Blumlein structure includes a first conductive plate, a second conductive plate, a third conductive plate, at least one of an inductor or a resistor, a switch, and a dielectric material. The first conductive plate is positioned relative to the second conductive plate such that a gap separates these plates. A vacuum chamber is positioned in the gap, and an ion source is positioned to emit ions in the vacuum chamber. The third conductive plate is electrically grounded, and the switch is operable to electrically connect and disconnect the second conductive plate and the third conductive plate. The at least one of the resistor or the inductor is coupled to the first conductive plate and the second conductive plate.

Abstract: A satellite-based missile defense system includes a neutron beam transmission tube, a beam generator disposed within the neutron beam transmission tube and operable to emit neutron beamlets from a neutron source. A first collimating plate is disposed within the neutron beam transmission tube and downstream from the beam generator. A second collimating plate is disposed within the neutron beam transmission tube and downstream from the first collimating plate. Neutron beams can be used to create gamma radiation and which can in-turn disable electronic equipment, such as that found in enemy aircraft, missile guidance systems, communication systems and/or the like.

Abstract: A low-power, compact piezoelectric particle emitter for emitting particles such as X-rays and neutrons. A piezoelectric transformer crystal receives an input voltage at an input end and generates a higher output voltage at an output electrode disposed at an output end. The emitter is in a vacuum and the output voltage creates an electric field. A charged particle source is positioned relative a target such that charged particles from the charged particle source are accelerated by the electric field toward the target. Interaction between the accelerated charged particles and the target causes one of X-rays and neutrons to be emitted.

Abstract: Illustrative embodiments provide nuclear fission igniters for nuclear fission reactors and methods for their operation. Illustrative embodiments and aspects include, without limitation, a nuclear fission igniter configured to ignite a nuclear fission deflagration wave in nuclear fission fuel material, a nuclear fission deflagration wave reactor with a nuclear fission igniter, a method of igniting a nuclear fission deflagration wave, and the like.

Abstract: A neutron generator includes an ion source disposed in a pressurized environment containing an ionizable gas. The ion source includes a substrate with a bundle of carbon nanotubes extending therefrom. The ends of the nanotubes are spaced from a grid. Ion source voltage supply circuitry supplies a positive voltage potential between the substrate and the grid of the ion source to cause ionization of the ionizable gas and emission of ions through the grid. An ion accelerator section is disposed between the ion source and a target. The ion accelerator section accelerates ions that pass through the grid towards the target such that collisions of the ions with the target cause the target to generate and emit neutrons therefrom. The ion source, accelerator section and target are housed in a sealed tube and preferably the carbon nanotubes of the bundle are highly ordered with at least 106 carbon nanotubes per cm2 that extend in a direction substantially parallel to the central axis of the tube.

Abstract: Biomass (e.g., plant biomass, animal biomass, and municipal waste biomass) is processed to produce useful products, such as fuels. For example, systems can use feedstock materials, such as cellulosic and/or lignocellulosic materials and/or starchy materials, to produce ethanol and/or butanol, e.g., by fermentation.

Abstract: Biomass (e.g., plant biomass, animal biomass, and municipal waste biomass) is processed to produce useful products, such as fuels. For example, systems can use feedstock materials, such as cellulosic and/or lignocellulosic materials and/or starchy materials, to produce ethanol and/or butanol, e.g., by fermentation.

Abstract: An ion source includes a conductive substrate, the substrate including a plurality of conductive nanostructures with free-standing tips formed on the substrate. A conductive catalytic coating is formed on the nanostructures and substrate for dissociation of a molecular species into an atomic species, the molecular species being brought in contact with the catalytic coating. A target electrode placed apart from the substrate, the target electrode being biased relative to the substrate with a first bias voltage to ionize the atomic species in proximity to the free-standing tips and attract the ionized atomic species from the substrate in the direction of the target electrode.

Abstract: A pulsed neutron generator (PNG) includes a sealed tube and a gas reservoir disposed in the sealed tube. The gas reservoir includes dispersed particles of a thermally reversible hydride-adsorptive material therein. The material panicles having adsorbed therein deuterium and/or tritium. A heated cathode disposed in the sealed tube, wherein heat from the cathode transfers indirectly to the gas reservoir. A gas ionizer is disposed in the sealed tube. A target is disposed in the sealed tube. The target including adsorbed deuterium and/or tritium therein. In another aspect, tube is pre-filled with deuterium and/or tritium, the reservoir is omitted, and an ion beam current is controlled by controlling an ionizer grid voltage and/or current.

Abstract: A non-destructive assay of deactivation of the contents of explosives and chemical warfare on-field (and or in lab) is presented with high-energy neutrons at 14, 4 and 2 MeV. The elements and substances present in the munitions are transmuted into passive elements through neutron-alpha nuclear reactions. Deactivating of the explosives on-field is presented with a unique and compact neutron generator fueled with deuterium gas and tritium breeder. Several high explosives and chemical warfare are presented in the transmutation with physical analysis. The present method and technique can be employed on-field as an improvised explosive device and as a precise explosive device in labs and centers.

Abstract: Apparatus for generating thermal neutrons includes an electron accelerator for generating an electron beam and a converter for converting the electron beam into photons. A receiving device is provided for receiving the photons and includes a material which provides a photoneutron target for the photons, for producing high energy neutrons in a photonuclear reaction between the photons and the photoneutron target, and for moderating the high energy neutrons to generate the thermal neutrons. The electron beam has an energy level high enough to produce photons of sufficient energy to exceed the photodissociation threshold of the selected target material, but that is sufficiently low as to enable the material to moderate the high energy neutrons resulting from the photonuclear reaction.

Abstract: A method for operating a pulsed neutron generator includes adjusting a target current of the neutron generator to a preselected value. A parameter related to a neutron output of the neutron generator is measured. A target voltage of the neutron generator is adjusted to maintain the measured parameter within a predetermined range.

Abstract: Gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (>100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. Several elements of the system may be modified, including the configuration of the crystal or crystals, the composition of the surrounding environment and the target, the use of multiple probe tips, and the composition of the probe tip.

Abstract: Disclosed is a radiation logging tool, comprising a tool housing; a compact generator that produces radiation; a power supply coupled to the compact generator; and control circuitry. Embodiments of the compact generator comprise a generator vacuum tube comprising a source generating charged particles, and a target onto which the charged particles are directed; and a high voltage supply comprising a high voltage multiplier ladder located laterally adjacent to the generator vacuum tube. The high voltage supply applies a high voltage between the source and the target to accelerate the charged particles to a predetermined energy level. The compact generator also includes an electrical coupling between an output of the high voltage supply and the target of the generator vacuum tube to accommodate the collocated positions of the generator vacuum tube and the high voltage power supply.

Abstract: Various embodiments for shortening the overall length of a pulsed neutron generator having a high voltage power supply are disclosed, including but not limited to, providing the plurality of stages of a high voltage power supply wrapped circumferentially or helically about a radiation generator tube. Various techniques for reducing voltage differentials and mitigating the risk of arcing in these embodiments are also disclosed.

Abstract: A non-destructive assay of deactivation of the contents of explosives and chemical warfare on-field (and or in lab) is presented with high-energy neutrons at 14, 4 and 2 MeV. The elements and substances present in the munitions are transmuted into passive elements through neutron-alpha nuclear reactions. Deactivating of the explosives on-field is presented with a unique and compact neutron generator fueled with deuterium gas and tritium breeder. Several high explosives and chemical warfare are presented in the transmutation with physical analysis. The present method and technique can be employed on-field as an improvised explosive device and as a precise explosive device in labs and centers.

Abstract: A method for operating a pulsed neutron generator including an ionizer with an electron emitting cathode and a grid wherein the cathode and grid are disposed in a sealed chamber. At least one of the following is applicable to the ionizer; a distance between the cathode and the grid, a cathode current and/or a potential on the grid are selected such that the ionizer operates at most about one-half the space charge limited current for a grid current selected to provide a predetermined amount of neutron production.

Abstract: The present invention provides an apparatus for generating a neutron flux using a plurality of neutron sources. The apparatus comprises a cylindrical holder for holding the plurality of neutron sources, a cylindrical moderator unit for holding a sample material and comprising of neutron moderator material. The apparatus further comprises a housing unit for housing the cylindrical holder and the cylindrical moderator unit. A releasing unit is coupled to the housing unit and connected to the cylindrical moderator unit for positioning a portion of the cylindrical moderator unit within the cylindrical holder. The sample material is irradiated with neutron flux generated.

Abstract: Illustrative embodiments of the present invention are directed to devices and methods for ion generation. One such device includes a substrate. The substrate is disposed within a housing that is configured to contain a gas. The substrate includes an interior surface that at least partially defines an interior volume. The substrate also includes a number of channels with walls. Nano-tips are disposed on the walls of the channels.

Abstract: A neutron generator comprises a cylindrical housing having a target rod concentrically located along a central axis of the cylindrical housing. An array of field ionization nanotips is positioned around an inner surface of the housing, where the array of nanotips extends toward the central axis. A method for logging a formation comprises deploying a logging tool having a neutron generator into a borehole. An array of nanotips is located around an inner cylindrical surface of a cylindrical housing in the neutron generator are energized. An ionizable gas proximate the array of nanotips is ionized. The ions are accelerated radially inward to bombard a titanium layer on an outer diameter of a target rod concentrically located along a central axis of the cylindrical housing to generate neutrons.

Abstract: Gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (>100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. Several elements of the system may be modified, including the configuration of the crystal or crystals, the composition of the surrounding environment and the target, the use of multiple probe tips, and the composition of the probe tip.

Abstract: A neutron generator includes a conductive substrate comprising a plurality of conductive nanostructures with free-standing tips and a source of an atomic species to introduce the atomic species in proximity to the free-standing tips. A target placed apart from the substrate is voltage biased relative to the substrate to ionize and accelerate the ionized atomic species toward the target. The target includes an element capable of a nuclear fusion reaction with the ionized atomic species to produce a one or more neutrons as a reaction by-product.

Abstract: An apparatus for destroying bacteria is provided which includes a neutron generator and a target polymer film which will receive the impact of neutron emissions. Neutrons impacting the target film produce a second emission of high energy protons which are made to move through an electromagnetic field external to the neutron tube thereby accelerating and steering a generated proton spray. This embodiment is well-suited for treating physical locations known to be infected by pathogenic microorganisms.

Abstract: A method and apparatus for rapidly producing a plasma jet on demand. A particular application is the production of such a jet and its injection into a magnetically confined target plasma for the purpose of mitigating an emerging disruption event. The apparatus includes a gas source cartridge having concentric inner and outer electrically nonconductive containment tubes, which contain a solid mixture of titanium hydride and fullerene in the annular cylindrical volume between them. The mixture is resistively heated by application of a high power electrical current to produce a gaseous mixture of hydrogen and fullerene within a few tens of microseconds. The resulting mixture of hydrogen and fullerene is introduced radially into an accelerator tube passing through the gas cartridge, where the gas mixture is ionized, accelerated and injected as a plasma jet into the target plasma.

Abstract: A cyclotron that includes a magnet yoke that has a yoke body that surrounds an acceleration chamber and a magnet assembly. The magnet assembly is configured to produce magnetic fields to direct charged particles along a desired path. The magnet assembly is located in the acceleration chamber. The magnetic fields propagate through the acceleration chamber and within the magnet yoke. A portion of the magnetic fields escape outside of the magnet yoke as stray fields. The magnet yoke is dimensioned such that the stray fields do not exceed 5 Gauss at a distance of 1 meter from an exterior boundary.

Abstract: A portable neutron generator includes a Radio Frequency Quadrupole linear accelerator designed to accelerate charged particles of hydrogen (protons) to energies useful for producing neutrons with the (p,n) reaction on lithium. The ion source is driven by a coaxial feed and a spiral antenna to couple the microwave power into the plasma. The linear accelerator is driven by a 600 MHz pulsed RF power supply. A differential pumping scheme is used to balance the need for a high gas load on the ion source end and good vacuum on the accelerator end.

Abstract: A neutron generator and method of constructing the same. The generator includes a grid configured to produce an ionizable gas when heated by electrons impinging thereon. A cathode emits electrons to heat the grid and to collide with produced ionizable gas atoms to generate ions. Neutrons are generated from a collision of ions impinging on a target in the generator. A tool for subsurface use incorporating the neutron generator.

Abstract: The design of a compact, high-efficiency, high-flux capable compact-accelerator fusion neutron generator (FNG) is discussed. FNG's can be used in a variety of industrial analysis applications to replace the use of radioisotopes which pose higher risks to both the end user and national security. High efficiency, long lifetime, and high power-handling capability are achieved though innovative target materials and ion source technology. The device can be scaled up for neutron radiography applications, or down for borehole analysis or other compact applications. Advanced technologies such as custom neutron output energy spectrum, pulsing, and associated particle imaging can be incorporated.

Abstract: An isotope production system that includes a cyclotron having a magnet yoke that surrounds an acceleration chamber. The cyclotron is configured to direct a particle beam from the acceleration chamber through the magnet yoke. The isotope production system also includes a target system that is located proximate to the magnet yoke. The target system is configured to hold a target material and includes a radiation shield that extends between the magnet yoke and the target location. The radiation shield is sized and shaped to attenuate gamma rays emitted from the target material toward the magnet yoke. The isotope production system also includes a beam passage that extends from the acceleration chamber to the target location. The beam passage is at least partially formed by the magnet yoke and the radiation shield of the target system.

Abstract: An acoustic inertial confinement nuclear fusion device is disclosed. The device includes an enclosure that holds a fluid with dissolved alpha emitters. A generator is coupled to the enclosure, and the generator is configured to harmonically drive the fluid in the enclosure to induce an acoustic standing wave in the fluid. The dissolved alpha emitters nucleate bubble clusters in the fluid as the fluid is driven by the generator. Neutrons, tritium and/or gamma rays, are emitted from the fluid, without or with an external source of neutrons.

Abstract: A novel method and compact neutron source for generating thermal neutrons is described that uses an ion source to emit ions toward a target where neutrons are generated. Surrounding the target is a secondary electron shield, and surrounding the target is a first stage moderator to reduce the energy of generated fast neutrons. Enclosing the first stage moderator is a second stage moderator with a thermal neutron port.

Abstract: A microwave or terahertz and neutron radiation type detector, which uses an orbitron as a radiation source. The detector may have a polarity switching apparatus to enable the orbitron to selectively change from between short wave to neutron emission functions. A highly compact and lightweight identifier of explosives and other chemicals, which may be so small and light as to be hand held, and which is effective at stand-off distances, is thereby provided.

Abstract: A polarized neutron guide for separating neutrons into polarized neutrons while minimizing loss of the neutrons is provided. The polarized neutron guide includes a body, the first space and the second space, and a neutron separation space. The body includes super mirrors coated with a neutron-reflective thin film and the first and second spaces are formed by the first plate inside the body. The neutron separation space is formed by the second plate disposed at the entry of the first space and the third plate disposed at the entry of the second space. Spin-up polarized neutrons and spin-down polarized neutrons are simultaneously separated and transferred in the first and second spaces, respectively. Therefore, with minimum loss of the neutrons, the spin-up polarized neutrons and the spin-down polarized neutrons are effectively separated and collected.

Abstract: A neutron-gamma ray tomography system comprises a source, a detector array, and an image processor. The source illuminates an object with a dual neutron-gamma ray beam. The detector array characterizes neutron and gamma ray attenuation in the object. The image processor generates tomography as a function of the neutron and gamma ray attenuation.

Abstract: A method of producing an ion beam in a tandem accelerator, the method includes the acts of insulating, in a cavity containing an insulating gas under pressure, a beam tube having first and second ends and a terminal situated between the first and second ends; seating, using a load lock valve, the insulating gas under pressure; generating an operating voltage using a first voltage source situated outside the cavity when the operating voltage is less than or equal to a threshold value; generating the operating voltage using a second voltage source situated inside the cavity when the operating voltage is greater than the threshold value; coupling the terminal to the first or second voltage sources; generating, using a particle source, an ion beam; and accelerating the ion beam in a first and second parts of the beam tube.

Abstract: A neutron generating device is described. In one embodiment, the device has a chamber filled with a gas containing deuterium or tritium together with a piezoelectric crystal having a mechanical excitation apparatus proximate thereto. The piezoelectric crystal has first and second metal electrodes located on opposing surfaces. The first metal electrode is in electrical contact with a neutral potential. A field emitter tip is located on the second metal electrode, which emits an electrical field to form deuterium or tritium ions upon the mechanical excitation of the piezoelectric crystal. The deuterium or tritium ions are accelerated by an electric potential differential between the first metal electrode and the second metal electrode into a target containing deuterium or tritium with sufficient energy to form neutrons.

Abstract: A cylindrical neutron generator is formed with a coaxial RF-driven plasma ion source and target. A deuterium (or deuterium and tritium) plasma is produced by RF excitation in a cylindrical plasma ion generator using an RF antenna. A cylindrical neutron generating target is coaxial with the ion generator, separated by plasma and extraction electrodes which contain many slots. The plasma generator emanates ions radially over 360° and the cylindrical target is thus irradiated by ions over its entire circumference. The plasma generator and target may be as long as desired. The plasma generator may be in the center and the neutron target on the outside, or the plasma generator may be on the outside and the target on the inside. In a nested configuration, several concentric targets and plasma generating regions are nested to increase the neutron flux.

Abstract: A neutron tube or generator is based on a RF driven plasma ion source having a quartz or other chamber surrounded by an external RF antenna. A deuterium or mixed deuterium/tritium (or even just a tritium) plasma is generated in the chamber and D or D/T (or T) ions are extracted from the plasma. A neutron generating target is positioned so that the ion beam is incident thereon and loads the target. Incident ions cause D-D or D-T (or T-T) reactions which generate neutrons. Various embodiments differ primarily in size of the chamber and position and shape of the neutron generating target. Some neutron generators are small enough for implantation in the body. The target may be at the end of a catheter-like drift tube. The target may have a tapered or conical surface to increase target surface area.

Abstract: A neutron generator includes a modular arrangement of a high current electron bombardment ion source, providing deuterium(D) and/or tritium(T) ions, a high voltage acceleration stage to accelerate the ions and raise the ion energy to the order of 100 keV, and an occluded reaction target containing T and/or D to produce the nuclear reactions. Neutrons are produced in the target using the D—D and/or D-T reaction. The invention is designed to allow the target to be located at the end of a needle and thereby is useful for treating cancers by the Brachy therapy method. The ion source of the neutron generator is a modified version of the electron bombardment type used in mass spectrometers for gas analysis. This source uses an electron beam running through an ionization chamber to ionize gas molecules that are extracted out of the chamber by electric fields.

Abstract: A cylindrical neutron generator is formed with a coaxial RF-driven plasma ion source and target. A deuterium (or deuterium and tritium) plasma is produced by RF excitation in a cylindrical plasma ion generator using an RF antenna. A cylindrical neutron generating target is coaxial with the ion generator, separated by plasma and extraction electrodes which contain many slots. The plasma generator emanates ions radially over 360° and the cylindrical target is thus irradiated by ions over its entire circumference. The plasma generator and target may be as long as desired. The plasma generator may be in the center and the neutron target on the outside, or the plasma generator may be on the outside and the target on the inside. In a nested configuration, several concentric targets and plasma generating regions are nested to increase the neutron flux.

Abstract: A compact neutron generator has at its outer circumference a toroidal shaped plasma chamber in which a tritium (or other) plasma is generated. A RF antenna is wrapped around the plasma chamber. A plurality of tritium ion beamlets are extracted through spaced extraction apertures of a plasma electrode on the inner surface of the toroidal plasma chamber and directed inwardly toward the center of neutron generator. The beamlets pass through spaced acceleration and focusing electrodes to a neutron generating target at the center of neutron generator. The target is typically made of titanium tubing. Water is flowed through the tubing for cooling. The beam can be pulsed rapidly to achieve ultrashort neutron bursts. The target may be moved rapidly up and down so that the average power deposited on the surface of the target may be kept at a reasonable level. The neutron generator can produce fast neutrons from a T-T reaction which can be used for luggage and cargo interrogation applications.

Abstract: A standard cell architecture with a basic cell that spans multiple rows of the standard cell. This multi-row basic cell may be a dual-height cell that spans two rows, or it may span more than two rows. The multi-row basic cell may be intermixed in a standard cell design with smaller, single-height cells for high-density applications. The single-height cells may be used where possible and higher-drive dual-height basic cells where larger transistors are desired. Other multiple height cells may also be included if even more current is desirable. The power rail may include conductors of varying width.

Abstract: Methods and apparatus for analyzing molecular systems with reconfigurable special-purpose hardware or an ASIC is provided. The present invention provides methods and apparatus to perform a quantum mechanical calculation on a programmable logic device (PLD) integrated circuit (IC) (“single-chip”) or an application specific integrated circuit (ASIC).

Abstract: A system and method for rapidly analyzing elemental abundances in rock or soil samples (14) under field conditions. The system uses a portable neutron source (12) to allow neutron activation analysis of elements having identifiable radioactive decay characteristics. A radiation detector (18) detects radiation released by the sample (14) and provides radiation testing results to an amplifier (26) for computing the concentration of trace elements in the sample with a high degree of accuracy.

Abstract: A sealed neutron tube is provided, in which an insulating structure is designed to be solid to enhance the shock-proof performance thereof, an ion beam drawn out from an ion source is pulsated more rapidly, and the lifetime of a target is increased without substantially increasing the filling amount of the Tritium. The sealed neutron tube (1) includes a metal housing (20), an ion source (5) disposed and sealed within the metal housing for ionizing a Deuterium gas, an accelerating electrode (4) charged with a high voltage, disposed and sealed within the metal housing and facing the ion source, and a target (3) disposed within the accelerating electrode and absorbing Tritium and the like therein. An outer wall (20) is constructed by a metal housing, and a ceramic insulating member (11) is disposed within the metal housing. Since the accelerating electrode is held by this insulating member, the outer wall of the sealed neutron tube has enhanced shock-proof performance.

Abstract: A steady-state source of neutrons is produced within an electrically grounded and temperature controlled chamber confining tritium or deuterium plasma at a predetermined density to effect implantation of ions in the surface of a palladium target rod coated with diffusion barrier material and immersed in such plasma. The rod is enriched with a high concentration of deuterium atoms after a prolonged plasma ion implantation. Collision of the deuterium atoms in the target by impinging ions of the plasma initiates fusion reactions causing emission of neutrons during negative voltage pulses applied to the rod through a high power modulator. The neutrons are so generated at a relatively high dose rate under optimized process conditions.

Abstract: A sealed neutron tube with magnetic confinement of the electrons by permanent magnets. The sealed tube contains a D-T gas mixture under low pressure, fitted with a target, an extraction-acceleration electrode (EAE) and an ion source with 2n Penning cells having anodes in a single cathode cavity and one permanent magnetization system (PMS) per cell. The ions, formed in the ion source, by means of the simultaneous presence of an electric and magnetic field, are accelerated by the EAE and projected onto the target in order to cause emission of neutrons therefrom. In this tube, half (n) of the PMS is magnetized to a nominal value and the other half is weakly magnetized or unmagnetized.

Abstract: A neutron generator employing an electron emitter, an ion source bombarded by the electrons from the electron emitter, a plasma containment zone, and a target situated between the plasma containment zone and the electron emitter.

Abstract: A novel hydrogen ion array acceleration generator and method are presented wherein there is provided along a transversely extending diffusion/emission grid surface and within an evacuated contained environment, an array of hydrogen ions at the interstitial sites of the grid surface; such being electrically accelerated along a longitudinal direction substantially normal to said surface toward a transversely extending lattice surface of a heavy metal of atomic radius between about 1.23 and 1.

Abstract: A neutron generator, comprising:(i) an ion source comprising an anode and a thermionic cathode disposed in an ionizable gas environment (e.g. hydrogen isotope);(ii) means for heating the cathode so that the latter emits electrons which, when colliding with the gas atoms, generate ions;(iii) a target;(iv) an electrical gap to accelerate ions from the ion source towards the target upon impingement of the ions; and(v) control means for applying voltages to the anode, cathode and electrical gap.The cathode is of the dispenser type or volume type, and preferably comprises one block of material comprised of a substrate impregnated with an electron emitting material.