Photoionization detector with an alumina shell, a beryllium foil window, and a xenon gas fill measures small incident photon fluxes from soft X rays. It has high spectral selectivity and quantum efficiencies, and a long shelf life. It minimizes electrical leakage and recontamination, and will hold a high vacuum

Stober, A. K.

Young, R. M.

English

NASA Technical Reports Server

April 1967
	 Brief 67-10072 
NASA TECH BRIEF 
- ..•_________	 -	 ______	 iiiiiizr	 i:iiiiiiiii _IIiiIiiiiIi 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
An Improved Soft X-Ray Photoionization Detector 
Ceramic Shell 
Silver Solder 
Connector 
and Guard Ring	
Gold Plating 
Anode Pi,? Copper Plating Soft Solder 
Copper Gas Fill
	
Beryllium Tube and Shell	
Window Cathode Connection 	 Window Seat 
The problem: 
To design a compact, rugged gas-filled photoioniza-
tion chamber or detector for measuring very small 
incident photon fluxes from soft X-rays. The detector 
must have high spectral selectivity, relatively high 
quantum efficiencies, and a long shelf life. 
The solution: 
A photoionization detector (overall length, 1.50 
inches; outside diameter, 1.375 inches) incorporating 
a shell of high-density alumina, a beryllium foil 
window, and a xenon (or argon) gas fill. Meticulous 
attention is given to fabrication details to minimize 
electrical leakage between electrodes and photoelec-
tric emission from the chamber walls, to prevent 
recontamination of the filling gas after purification, 
and to provide window and connector seals that will 
hold a high vacuum (better than 10- 6 torr). 
How it's done: 
The ceramic shell of high-density fused alumina 
(available from commercial sources) is sequentially 
coated on most of its interior surface with molyb-
denum—manganese (metalizing), a flash plating of 
nickel, a plating of copper, and a sintered gold plate.
Brazed into the unplated rear face of the shell are a 
central pin anode consisting of a commercially avail-
able glass-sealing alloy (20 percent Ni, 17 percent Co, 
0.2 percent Mn, balance Fe), a guard ring and con-
nector of the same alloy, and a copper gas-fill tube, 
which also provides the electrical connection to the 
cathode formed by the metal plating on the interior 
surface of the shell. 
The window material consists of hot-rolled beryl-
lium foil having a thickness of 0.005 inch and a diam-
eter of 0.860 inch. The periphery of the beryllium 
window disk is electroplated with copper using a 
specially developed procedure and plating bath. The 
disk is then prepared for peripheral bonding to the 
gold plated window seat of a previously prepared 
shell. A 60:40 lead—tin solder is used for bonding the 
two components to form a vacuum-tight window seal. 
The chamber assembly is tested to ensure leak-
free joints and then filled with xenon. The gas-filled 
chamber is valved off from the gas supply system, 
and the stem of the fill tube is sealed with a commer-
cial pinch-off tool and snipped from the system. 
Solder is applied to the stem tip to provide addi-
tional protection against leakage. The completed 
continued orerkol) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000072 2020-03-11T20:21:21+00:00Z
chamber is calibrated before use to determine its 
quantum efficiency or photoionization yield. 
Notes: 
1. Detectors of this design have been successfully used 
in several solar rocket probes. They should be of 
value in laboratories wherever stable photoioniza-
tion detectors are required for measurement of 
soft X-ray radiation. 
2. The design of this detector is patterned after the 
vacuum ultraviolet ion chambers (incorporating 
other window materials and gas fills) previously 
developed at the Goddard Space Flight Center.
3. Inquiries concerning this innovation may be di-
rected to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B67-10072 
Patent status: 
No patent action is contemplated by NASA. 
Source: Robert M. Young and Alfred K. Stober 
(GSFC-540)
. 
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Brief 67-10072	 Category 02


An improved soft X-ray photoionization detector

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