A NEW TYPE OF SURFACE IONIZATION DETECTOR

The ionization coefficient of a potassium atom impinging on a hot Pt-8% W wire is independent of its energy below 3 eV (3850 m/sec) and dependent on it above 3 eV. This is due to the fact that a high energy atom can reflect from the wire without being ionized. By using a tungsten cylinder as an ionizer and a niobium wire in the middle of it as a collector, incident atoms which are not ionized can be prevented from leaving the cylinder without being detected because subsequent collisions with the wall will take place and result in ionization. By means of this type of standard detector, which has a multiplication factor of about 30, the reflection coefficient of a potassium atom incident on a Pt-8% W wire is determined as a function of its velocity. For a potassium atom with an energy of 23.6 eV (10 800 m/sec) this reflection coefficient is about 16.5%. © 1969 The American Institute of Physics.