Grimm glow discharge X-ray tube

A Grimm glow discharge tube was modified to apply high-voltages of up to 10 kV. For this purpose, the cathode is held by a massive support of PTFE in a new type of glow discharge tube. Consequently, stable high-voltage discharge plasmas were created only in the hollow anode near the cathode under the following discharge conditions: He gas pressures of 10∼100 Pa, and discharge currents of 0.1∼10 mA. Electrons emitted from the cathode surface are accelerated in the cathode fall region. They have high energies corresponding to the applied voltage. X-Rays excited by these high-energy electrons were measured in two different configurations: the end-window transmission mode and the side-window mode. The X-ray transparent thin-film was used as an X-ray window in the end-window transmission mode. The X-ray spectra measured in this mode were very simple because high-energy continuous X-rays were self-absorbed by the thin film itself. However, the X-ray intensities were weak, because a high-discharge current could not be applied in order to protect the thin X-ray window. When using the side-window mode, fast electrons bombarded the target at an incident angle of 45°, and the X-rays emitted from the target surface were observed at the takeoff angle of 45° through a Be window. A higher X-ray emission intensity could be obtained in the case of the side-window by applying higher discharge currents and a cooled target.