1—TRANSMISSION-TARGET SOURCE 
_- Cavity for 
/3 emitter 
—0.065 in. 
Target (Pb) 
0,003 in. 
Lead target 
—7— thickness a 
——0,0035in. 
0,007 in. 
> Steel 
0.097 in. 
Normalized Intensity 
/0.Ol1in. 
Normalized Intensity 
Energy 
Transmission-target source, with Sr°°-Y°° betas, gives spectra in center for various target thicknesses and at right for bremsstrahlung 
Beta-Ray-Excited 
Low-Energy X-Ray Sources 
Beta-ray excitation provides X-rays in the range below 400 kev where gamma 
emitters are lacking. 
Although present units only yield up to “0 mc of 
X-rays per mc of beta particles, their portability and stability recommend them 
for radiography, thickness determinations, and X-ray fluorescence analysis 
By L. REIFFEL 
Armour Research Foundation of the Illinois Institute of Technology 
Chicago, Illinois 
PROMPTED BY THE LACK of low-energy 
(<400 kev) gamma-emitting nuclides, 
for several years we have been exploring 
the possibility of using beta-ray-ex- 
cited X-ray sources. Such sources are 
constructed using pure beta-ray emit- 
ters to bombard target nuclei much in 
the same fashion that electrons in an 
X-ray tube bombard the anode; the 
two processes are essentially identical 
in the physics involved. Although 
radioactive sources cannot compete 
with electronic X-ray sources where 
very high intensity is required, their 
zero power consumption, small size and 
portability, long-time stability, and 
other advantages would be of value in 
many applications. 
Using Sr%-Y® beta emission, we 
have demonstrated the practicality 
of such sources. This article dis- 
cusses the characteristics of various 
source designs and the possibilities for 
future development. 
These sources are needed because of 
the small number of low-energy-emis- 
sion radioisotopes in the classical 
X-ray region. Among the few useful 
emitters in this region are thulium and 
iron-55. Thulium, which emits 84-kev 
and 52-kev radiation, is available at 
high specific activity but, unfortu- 
nately, has an inconveniently short 
half-life of 129 days. It has been 
developed for radiography* and ab- 
sorptiometry. Iron-55 emits, by 
K-capture, a 6-kev X-ray. It has a 
conveniently long life—2.9 years—but 
its energy is unfortunately somewhat 
*S. Untermyer, Nucueonics 12, No. 5, 
35 (1954). 
141 
