Secondary Electron Multiplier as a Detector of Very Feeble Ion Current down to 10^-19 Amperes

Abstract

A 12-stage Cu–Be electron multiplier was constructed for detecting very feeble ion current. General characteristics of the multiplier coupled with a vibrating reed electro-meter were investigated by measuring the output of a high vacuum mass spectrometer. The stability of the multiplier gain was sufficient for the measurement of isotope ratios. For example, the 20Ne/22Ne ratio was found to be 10.563±0.006 (un-corrected for mass discrimination). At an ultimate pressure of 10-8 Torr in this mass spectrometer, background mass spectra up to M/e 150 were recorded, and some hydrocarbon fragment peaks corresponding to 10-16–10-18 amperes were found in C2–C7 groups. Mass peaks below 10-16 amperes fluctuate considerably, but such statistical fluctuations may be smoothed out by using an amplifying system with a sufficiently long time constant and a low scanning speed. Under such conditions, an ion current down to 1×10-19 amperes was distinguishable over the noise level of the amplifying system.

Microstructure and Mechanical Evolution of Cu-2.7Be Sheets via Annealing

“…Copper-beryllium alloys are extensively used as dynodes in electron multipliers and photomultiplier tubes, due to high, stable, and durable secondary electron emission (SEE) properties [1,2]. In 1947, Allen discussed the design and construction of a 13-stage electron multiplier tube.…”

“…The electrodes synthesized from the Cu-2.0Be alloy sheets were applied and the method of activating these surfaces was described [3]. Furthermore, in the 1950s-1980s, the activation process played a key role in the investigation of Cu-2.0Be dynodes [1][2][3][4][5]. However, materials with high SEE properties, such as Ag-3Mg [6], Y 2 O 3 -Mo [7], MgO/Au composite film [8], H-terminated, and Cs-terminated chemical vapor deposition (CVD) diamond [9] have been developed, whereas minimal attention was placed on the Cu-Be dynodes.…”