KicKsorTERS with small numbers of 
channels and stepping single-channel 
analyzers serve some industrial applica- 
tions better than more elaborate 
multichannel instruments. Several 
instances in which the simpler instru- 
mentation has been successfully used 
are listed in the box at the right. We 
will discuss its use in simultaneous de- 
termination of mixed natural radio- 
activities and of mixed radiotracers. 
Assay for K, Th, U 
It is often desirable to assay a par- 
ticular radioactive ore for its relative 
content of the naturally occurring ac- 
tivities, thorium, uranium, and potas- 
sium. An example is a core sample 
from an oil well. If daughter products 
of thorium and uranium chains are in 
equilibrium with parents, quantitative 
separation using the total gamma-ray 
spectrum is possible. In this analysis 
one measures three regions of the spec- 
trum simultaneously. The result is a 
set of three linear equations with three 
unknowns (the amount of each activity 
present). Calibration with pure forms 
of the activities determines the coeffi- 
cients, and solution of the equations 
gives the amount of each activity. A 
five-window analyzer can perform such 
an analysis in a single run. 
In experiments on limestone and 
sandstone, a 1!4-in.-dia, 2-in.-long Nal 
crystal surrounded by 300-gm samples 
of the ground shale provided data on 
the concentrations of U, Th, and K toa 
maximum of +30% standard devi- 
ation with 2-hr runs. 
Other Successful Applications 
1. Continuous determination of K, Th, and U in oil-well formations by logging 
with a scintillation spectrometer coupled to a 3-channel discriminator feeding 3 
ratemeters and a 3-channel recorder (9). 
2. Continuous determination of the quantity of selected elements by observing 
their prompt gammas under neutron bombardment. Elements detectable include 
Cl, C, H, O. One can distinguish limestone from sandstone even though they both 
have identical total radiation intensities (9, 10). One can determine the difference 
between salt brine and oil by noting the Cl capture gammas. One can log an out- 
flow well in a water-flooding operation to determine the location and relative volume 
of inflow from several different input wells injection waters of which have been 
tagged with different tracers (9). 
3. Continuous simultaneous determination of the rate of wear of two or more 
parts tagged with different radioisotopes (11, 12). 
4. Neutron irradiation and subsequent use of the spectrometer to determine: 
concentration of Cu and Mn in super-pure aluminum (13); concentration of Cl and 
F in Kel-F (14); concentration of Ca, Al, and Mg in cement-mill feed stocks (15); 
milligram quantities of F and microgram quantities of Br, Cl, and I in aqueous 
solutions (16). 
For more complex analyses, where 
computations become extremely tedi- 
ous, it often is necessary to call on addi- 
tional machinery such as a digital 
computer to perform the actual data 
reduction. In such circumstances the 
automatic output of a single-channel 
analyzer may be of the same formas the 
input to the computer in the form of 
punched cards, punched paper tape, or 
magnetic tape. This simplifies and 
speeds up the over-all operation. A 
special technique has been developed, 
for instance, for resolving complex 
spectra by multiple least-squares analy- 
sis on the resulting data, which is im- 
practical without the use of a computing 
machine (1). If the data are presented 
in a form that can be fed directly into a 
computer, final results can be obtained 
more quickly from a complex spectrum 
FIG. 3. Stepping single-channel analyzer offers auto- 
matic, unattended operation. 
Electric typewriter records 
window number, count, time, and time of day 
16 
than from a single component by hand. 
Simultaneous Tracers 
Use of gamma-emitting radioisotopes 
as tracers in refinery-scale studies of 
mixing, stack loss, and aging of fluid 
cracking catalysts has been published 
recently (2-5). Tracer studies em- 
ploying as little as 0.5 me diluted with 
as much as 850 tons of catalyst have 
been carried out successfully, by use of 
high-sensitivity scintillation counting. 
We will describe here a similar study 
simultaneously employing three cata- 
lysts separately tagged. 
Cracking catalysts age as they are 
used. Their surface area may decrease 
from 600 to 100 m?/gm, and pore vol- 
ume from 0.9 to 0.3 cm’/gm. When 
aging characteristics of several cata- 
lysts are to be compared, one should 
study them simultaneously because of 
day-to-day variation of operating con- 
ditions, feed stocks, etc. 
In a recent study carried out by the 
Shell Development Company, the aging 
and stack-loss of three fresh cracking 
catalysts were followed simultaneously 
over a period of 30 days to find out 
which one had the best aging character- 
istics. The three catalysts were tagged 
with Ce!44/Pr!44, Cr®!, and Se4®, respec- 
tively. Three separate tests without 
the spectrometer would have required 
many months, allowing for reasonable 
decay of the suitable radioisotope of 
shortest half-life before use of the next 
longer-lived isotope. 
These isotopes were chosen for several 
reasons. They adsorb strongly and 
uniformly on a silica-alumina catalyst 
surface and are not volatilized at tem- 
peratures up to 1,000° C. They emit 
gamma radiation of energies suitably 
