Ion Source Chamber Research Articles

A proposal to produce a triton beam using a caesium sputter source

Until recently most accelerator laboratories have avoided accelerating tritons because of the excessive activity involved in handling large volumes of tritium. The caesium sputter source utilizes tritium as titanium titride in a sputter cone which releases gas by sputtering the cone with caesium ions at a rate necessary to produce the required negative ion beam. The efforts at McMaster have been directed in four main areas : reliability of source components, cone loading, contamination problems and safety. Tests on the reliability of source components indicate that a lifetime of 1 000 hours of maintenance free operation is not unreasonable. Procedures have been developed for loading the titanium inserts used in sputter cones with deuterium. These results are not expected to differ substantially for tritium. Pumping and collection of released tritium will be accomplished using a high speed titanium getter pump in conjunction with a small oil diffusion pump. The tritium will be differentially pumped to avoid contamination of the existing large oil diffusion pumps on our ion source chamber. The main areas of safety being studied are the use of a residual gas analyser for vacuum monitoring of released gases and a high sensitivity tritium gas monitor for air monitoring. The program at McMaster should allow us to produce triton beams during the summer of 1977.

Determination of oxygen in semiconductor materials with a cryogenically pumped spark-source mass spectrometer

A liquid helium cryogenic pump, which is mounted directly on to the ion-source chamber of the mass spectrometer, is described. Base pressures down to about 8 × 10–10 torr are rapidly obtained within 1 hour of the commencement of cryogenic pumping and pressures of about 10–8 torr are maintained during the analysis. The analytical blank for oxygen is shown to be directly dependent on the residual gas pressure in the ion-source chamber and with liquid helium cryogenic pumping the blank for the determination of oxygen in germanium is not more than 0·02 p.p.m.a. (parts per million atomic).The quantitative performance of the method has been evaluated by using germanium and silicon samples that had previously been analysed by infrared spectrophotometry. A mean standard deviation of 19 per cent. was obtained from measurements of oxygen present in silicon covering the range 11 to 35 p.p.m.a. The method has also been applied to the determination of oxygen and carbon in indium phosphide, and satisfactory agreement at the 0·1 p.p.m.a. level has been found with results independently obtained by gamma-photon activation analysis.

Mass Spectroscopic Studies on the Mechanism of Ionization of Atoms Formed as a Result of Radioactive Decay Processes. II

Measurements have been made on the charge states of ions produced by the electron capture decay of 109Cd(453d). The apparatus employed was a pulse-counting mode magnetic spectrometer, consisting an ion source chamber, an analyzer tube, a detector and 3-channel pumping systems. The radionuclide, 109Cd, produced by the nuclear reaction, 109Ag(d, 2n) 109Cd, was isolated without an isotopic carrier by the solvent extraction procedure developed by M. Inarida. A HCl solution of carrier-free 109Cd was dropped on the stainless steel meshes, which was later mounted to the ion source chamber. The ions produced by the electron capture decay of 109Cd on the solid surface were pulled out, analyzed by the magnetic field, and counted by a 16-stage Cu-Be electron multiplier. 109Cd decays to first excited state of 109Ag, which has a half life of 40 sec. Emitting 87.7 keV gamma rays, the state deexcites to the ground state of 109Ag. The gamma transition has an internal conversion coefficient larger than unity. The charge spectrum of the ions produced by the decay has shown that the most abundant species is singly-charged ions.

On the asymmetry in the angular distribution of the fragments produced from the collision induced dissociation of HD+ion

The recently observed asymmetry in the forward and backward scattering of the fragments produced from the collision induced dissociation of heteronuclear molecular ions has been explained by considering their dipole moments. For simplicity, the electron impact dissociation of the HD+ ion for the 1s sigma 2 Sigma g+ to 2p sigma 2 Sigma u+ transition has been considered by applying the Born-Oppenheimer approximation. To include the effect of the dipole moment of the molecular ion, exchange scattering has also been considered. The results show that the inclusion of the electron-dipole interaction term in the Hamiltonian cannot explain the observed asymmetries. It is suggested that the asymmetry is due to the preferential orientation of the molecular ions due to the effect of the accelerating field on the dipole moment of the ions in the ion source chamber.

Analysis of Oxygen-18 in Solid Oxides by Spark Source Mass Spectrometry

The spark source mass spectrometry was applied to the analysis of 18O in solid oxides. After some trials such method was adopted successfully that a solid specimen was wound around by gold wire and a pointed gold wire was set as a counter-electrode. After the ion source chamber was evacuated, the specimen was heated for 30 minutes by the use of the heater set in the chamber in order to remove the adsorbed water. As a result of this treatment the influence of the water was erased. The quantitative analysis was performed by comparing the density of the spectrum of 18O+ with that of 16O+. The crater sizes were measured by the microscopy and the depth of sampling was estimated at the order of 5μ. The method stated in this note will be applied validly to determine the 18O distribution in the diffusion couple or the product layer formed by solid state reaction. 2 figs., 3 tables, 2 refs.

Mass Spectroscopic Studies on the Mechanism of Ionization of Atoms Formed as a Result of Radioactive Decay Processe. I

Measurements have been made on the charge states of ions produced by the electron capture decay of 109Cd(453d). The apparatus employed was a pulse-counting mode magnetic spectrometer, consisting an ion source chamber, an analyzer tube, a detector and 3-channel pumping systems. The radionuclide, 109Cd, produced by the nuclear reaction, 109Ag(d, 2n) 109Cd, was isolated without an isotopic carrier by the solvent extraction procedure developed by M. Inarida. A HCl solution of carrier-free 109Cd was dropped on the stainless steel meshes, which was later mounted to the ion source chamber. The ions produced by the electron capture decay of 109Cd on the solid surface were pulled out, analyzed by the magnetic field, and counted by a 16-stage Cu-Be electron multiplier. 109Cd decays to first excited state of 109Ag, which has a half life of 40 sec. Emitting 87.7 keV gamma rays, the state deexcites to the ground state of 109Ag. The gamma transition has an internal conversion coefficient larger than unity. The charge spectrum of the ions produced by the decay has shown that the most abundant species is singly-charged ions.

Ionization Energy Difference between Isotopes and its Effect on Isotope Abundance Measurement by Surface Ionization Method

In mass spectrometric measurement of isotope abundance, it has been assumed that ionization energy is same for isotopes. In this paper the finite nucleus mass effect and finite nucleus volume effect ionization energy are considered. Theoretical calculation and spectroscopic data show that the ionization energy difference between7 Li and6 Li is 1?10-4 eV, and only for Li the isotope effect by ionization energy difference can amount to the same order of magnitude as those mass descriminations evaporation of the sample from the filament, by ion optics in the ion source chamber and so on.

A New Method of Measuring the Ion Current of Mass Spectrometers

In most mass spectrometers the ion current received by the collector is measured by D. C. amplifiers, but it is preferable to use A. C. amplifiers, if possible, because in A. C. amplifiers there is no zero point drift and the number of stages can be easily increased. We have intended to use an A.C. amplifier in mass spectrometer of Nier type. The ion current was made alternating by making the potential of the first slit which pulls out the ions from the ion source to have a rectangular form of -4 volts and +1 volt relative to the ion source chamber. The ion current amplified by a three stage A.C. amplifier of 110 db was rectified and then measured by a D.C. milliammeter of 1 mA full scale. The amplifier operated very stable and the current amplification factor was about 0.7×10 10 , the minimum ion current detectable at the collector being about 1.5×10 -15 amperes.