Henry E. Duckworth

A Large Dempster‐Type Double‐Focusing Mass Spectrograph

A description is given of a large Dempster‐type double‐focusing mass spectrograph. The dispersion of the instrument is 2.3 mm for one percent mass difference. The theoretical resolution for a 0.001‐in. principal slit is 7000 and has been experimentally realized. The performance of the instrument is illustrated by a mass spectrum showing doublets formed by singly‐charged Cu and Zn and triply‐charged Pt.

Vacuum Properties of Synthetic Dielectrics

An experiment has been done to determine the relative vacuum properties of a number of the commercially available synthetic dielectrics. The results show wide differences in vapor pressures and indicate that certain materials are particularly well adapted for use in vacuum systems.

Precise Atomic Mass Differences Involving Isotopes of Nd, Sm, Cd, and Pb

During the past year, certain of our experimental techniques have been re-evaluated and modified. In the course of these investigations, we have re-determined two atomic mass differences involving isotopes of cadmium and one involving isotopes of lead. The new values are consistent with reaction data and with our older measurements. Thirteen mass differences involving isotopes of neodymium and samarium have also been determined, several for the first time. These new results are consistent with reaction data and with other recent mass spectroscopic data, but indicate that our previously-reported mass differences in the neodymium-samarium region are systematically too large by small but real amounts. An unusually concordant situation now exists in this region of the mass table.

Stopping Cross Sections in Boron of Low Atomic Number Atoms with Energies from 15 to 140 keV

The electronic stopping cross sections in boron for atomic projectiles with Z≤ 11 have been determined in the energy interval 15 to 140 keV. Reasonable agreement is found with theory, however the previously observed periodic dependence of Sε on the atomic number of the projectile is also evident. Results for the relative straggling in energy loss are reported for hydrogen projectiles in boron, carbon, and aluminium targets and for helium projectiles in boron and carbon. Theoretical straggling estimates agree reasonably well with the experimental results.

Concerning the Masses of the Stable Zinc Isotopes

The masses of Zn64, Zn66, Zn67 and Zn68 have been studied mass spectroscopically by means of the O216-½-Zn64, ½ Xe132–Zn66, ½ Xe134–Zn67 and ½ Xe136-Zn68 doublets. These studies suggest that the currently accepted masses of Zn64 and Zn66 are too large by ~ 0.4 mMU. If these revisions are made several existing discrepancies between transmutation and mass data disappear.