Abstract: A negative ion source placed inside a negatively-charged high voltage electrode emits a beam which is accelerated to moderate energy, approximately 35,000 electron volts, and filtered by a momentum analyzer i.e. an analyzing bending magnet, to remove unwanted ions. Reference ions such as carbon-12 are deflected and measured in an off-axis Faraday cup. Ions of interest, such as carbon ions of mass 14, are accelerated through 300 kV to ground potential and passed through a gas stripper where the ions undergo charge exchange and molecular destruction. The desired isotope, carbon-14 along with fragments of the interfering molecular ions, emerge from the stripper into a momentum analyzer which removes undesirable isotope ions. The ions are further filtered by passing through an electrostatic spherical analyzer to remove ions which have undergone charge exchange. The ions remaining after the spherical analyzer are transmitted to a detector and counted.

Abstract: A negative ion source placed inside a negatively-charged high voltage terminal emits a beam which is accelerated to moderate energy, approximately 35,000 electron volts, and filtered by a momentum analyzer i.e. an analyzing bending magnet, to remove unwanted ions. Reference ions such as carbon-12 are deflected and measured in an off-axis Faraday cup. Ions of interest, such as carbon ions of mass 14, are accelerated through 300 kV to ground potential and passed through a gas stripper where the ions undergo charge exchange and molecular destruction. The desired isotope, carbon-14 along with fragments of the interfering molecular ions, emerge from the stripper into a momentum analyzer which removes undesirable isotope ions. The ions are further filtered by passing through an electrostatic spherical analyzer to remove ions which have undergone charge exchange. The ions remaining after the spherical analyzer are transmitted to a detector and counted.

Abstract: The high voltage electrostatic accelerator of this invention has spark arrester rings which form magnetic shield elements around an acceleration tube and which together with mu-metal rings between accelerator segments shield the electrons being accelerated from stray static and dynamic magnetic fields. The spark arresters surround the accelerating electrodes. The rings between accelerator segments are formed of mu-metal, an alloy of nickel designed for its magnetic shielding properties and consisting of 77 percent nickel, 4.8 percent copper, 1.5 percent chrome and 14.9 percent iron. The mu-metal spark arresters together with the rings between accelerators segments provide an effective magnetic shield in a cost-effective manner. Because mu-metal has a high permeability, magnetic field lines tend to travel about the Mu-metal rings rather than pass through the acceleration tube, where they would influence electrons being accelerated.

Abstract: An impulse valve for an ion source is positioned between an ion source chamber and a gas metering valve. The impulse valve is a two-position solenoid-controlled valve which is closed in its off position. In the off-position, the valve forms a reservoir between the valve stem of the impulse valve and the metering orifice of the metering valve. In the off condition, the gas reservoir fills with gas that over time equilibrates to the pressure of the gas supplied to the metering valve. The volume of the gas reservoir and the pressure of the gas which is supplied to the metering valve are chosen so that when the two-position valve is open, the gas contained in the reservoir is sufficient to pressurize the ion source chamber to a pressure of approximately 0.1 Torr. Thus, when the impulse valve opens, a pulse of gas flows into the ion source chamber, where a plasma discharge is initiated.