A neutron generator, comprising: a pre-moderator block of moderating material having an upper surface, a lower surface, a first and a second end, first and second side surfaces, a first length, a first width substantially less than the first length, and a first thickness; a cylindrical acceleration chamber having a first diameter substantially the first width of the pre-moderator block, sealed at one end to the upper surface of the pre- moderator block adjacent the first end of the pre-moderator block, with a vertical axis perpendicular to the upper surface, the acceleration chamber having a height and a top cover at a second end away from the pre-moderator block; a vacuum pump engaging the acceleration chamber, evacuating the acceleration chamber to a moderately high vacuum; a plasma ion chamber opening into the acceleration chamber through an ion extraction iris through the top cover of the acceleration chamber on the vertical axis of the acceleration chamber; a gas source providing deuterium gas to the plasma ion chamber; a microwave energy source ionizing the gas in the plasma ion chamber; a cylindrical primary isolation well extending a substantial distance into the pre-moderator block from the upper surface, centered on the vertical axis of the acceleration chamber; a secondary isolation well substantially in a shape of a hollow cylinder surrounding the primary isolation well, to a depth somewhat less than the substantial distance of the primary isolation well, within the first diameter of the acceleration chamber; a water-cooled titanium target disk having a target surface orthogonal to the axis of the acceleration chamber, the target disk having a diameter substantially smaller then a diameter of the isolation well, positioned at a lower extremity of the isolation well, the target disk biased to a substantial negative DC voltage; and electrically grounded metal cladding covering all otherwise exposed surfaces of the pre-moderator block; wherein ions extracted through the ion extraction iris are accelerated to bombard the titanium target at the lower extremity of the primary isolation well, producing energetic neutrons that pass through and are moderated by the pre-moderator block, and wherein any path along a surface of the from the titanium target to an electrically grounded element is necessarily maximized by the primary and secondary isolation wells. a pre-moderator block of moderating material having an upper surface, a lower surface, a first and a second end, first and second side surfaces, a first length, a first width substantially less than the first length, and a first thickness; a cylindrical acceleration chamber having a first diameter substantially the first width of the pre-moderator block, sealed at one end to the upper surface of the pre- moderator block adjacent the first end of the pre-moderator block, with a vertical axis perpendicular to the upper surface, the acceleration chamber having a height and a top cover at a second end away from the pre-moderator block; a vacuum pump engaging the acceleration chamber, evacuating the acceleration chamber to a moderately high vacuum; a plasma ion chamber opening into the acceleration chamber through an ion extraction iris through the top cover of the acceleration chamber on the vertical axis of the acceleration chamber; a gas source providing deuterium gas to the plasma ion chamber; a microwave energy source ionizing the gas in the plasma ion chamber; a cylindrical primary isolation well extending a substantial distance into the pre-moderator block from the upper surface, centered on the vertical axis of the acceleration chamber; a secondary isolation well substantially in a shape of a hollow cylinder surrounding the primary isolation well, to a depth somewhat less than the substantial distance of the primary isolation well, within the first diameter of the acceleration chamber; a water-cooled titanium target disk having a target surface orthogonal to the axis of the acceleration chamber, the target disk having a diameter substantially smaller then a diameter of the isolation well, positioned at a lower extremity of the isolation well, the target disk biased to a substantial negative DC voltage; and electrically grounded metal cladding covering all otherwise exposed surfaces of the pre-moderator block; wherein ions extracted through the ion extraction iris are accelerated to bombard the titanium target at the lower extremity of the primary isolation well, producing energetic neutrons that pass through and are moderated by the pre-moderator block, and wherein any path along a surface of the from the titanium target to an electrically grounded element is necessarily maximized by the primary and secondary isolation wells.