2. Plan view 
organic bromine compounds, the re- 
coil-freed bromine is probably present 
in part as hydrogen bromide. It was 
found, however, that if the paper strip 
were rolled up with a second plain strip 
of paper, the resulting contamination 
was negligible. 
One possible application is to the 
analysis of a mixture of the isomers of 
hexachlorocyclohexane, the gamma iso- 
mer of which is a well-known insecti- 
cide. A mixture containing 10 yg of 
the a, B, y, and 6 isomers was chro- 
matographed under the conditions 
used for the DDT analogs (3). The 
chromatogram was then irradiated in 
a flux of 10!! n/cm?/sec for one week 
and scanned a fortnight later. The 
radiochromatogram obtained is shown 
in C, the peaks of which are caused by 
178 
How Automatic 
Scanner Works 
Paper strip O is wound around 5.05-em drum H and 
passes over 5.05-cm idler roller M under tension due to 
100-gm weight Q that is fastened to the free end of strip 
O by means of ‘‘bull-dog’”’ clip P. Each drum possesses 
a 3-mm flange on both sides. The other end is held to 
drum H by spring-steel wire Y passing through drum 
slot K. The wire is anchored to the drum H atJ and 
screwed on the opposite side at Z. Drum H drives an 
eight-bladed escapement wheel D by a 4:1 gear F-R so 
that 1g of 1 revolution of D allows strip O to advance, 
under tension, almost exactly 0.5 cm. The diameter of 
drum H is such that the changing thickness of paper on 
the unwinding drum has a negligible effect on the dis- 
tance the paper moves with each escapement movement. 
The mean value of this distance is exactly 0.5 em for the 
average chromatogram. Roller M is- mounted exactly 
below a 1}g-inch X 0.5-cm slot Z cut in the platform N 
so that a transverse 0.5-cm section of strip O is exposed 
through the slot. 
The over-all effect is that for every escapement move- 
ment consecutive 0.5-cm sections of the paper strip are 
exposed to the thin end-window WI of the Geiger-Miiller 
tube GM which is housed inside the lead castle LC. 
Milled nuts E allow the platform to be removed for 
cleaning purposes, etc. Heavy frame B is screwed to 
the edge of laboratory bench A through which a suitable 
hole is cut for the descending strip O. Drum and roller 
shafts run in phosphor-bronze bearings mounted in 
bearing plate C. 
To date, scanning has been limited to beta counting, 
the Geiger-Miiller tube being relatively insensitive to 
the gamma rays from bromine-82, iodine-131, ete. Plat- 
form N must be sufficiently thick to eliminate all beta 
particles from neighboring but unexposed sections of the 
strip, an important factor in the resolving power of the 
scanner; }¢-inch steel plate has been found to be satis- 
S*5 arising from the chlorine of the not lend itself easily to quantitative 
partly separated isomers by the 
Cl35(n,p)S** reaction. This particu- 
lar application is being investigated 
further. 
Radiometric Scanning 
Having prepared the paper chro- 
matogram so that the resolved com- 
ponents are labeled or associated with 
a suitable radiotracer, the distribu- 
tion of the tracer must be determined 
quantitatively. 
Fink et al. (5) have located [}*1- 
labeled compounds by placing the 
chromatogram against an X-ray plate 
in the dark so that the radioactive 
zones could be located autoradio- 
graphically after fixing and developing 
the exposed plate. This method does 
work, and it is far less sensitive than 
counting techniques. 
It has been estimated (6) that, to 
obtain a reasonable contact autoradio- 
graph of a Br8*-labeled compound, a 
radioactive disintegration density of 
the order of 10° disintegrations per 
cm? (of paper chromatogram, in this 
case) would be required. If this 
figure were obtained, say, in a 24-hour 
exposure, it would correspond initially 
to about 0.5 microcuries of Br®*. One 
hundredth of this activity, or 5 X10-5 
microcuries, could be determined to 
within +5% by Geiger counting for 
one minute using typical apparatus. 
A simple method of scanning a paper 
chromatogram is to cut it up into small 
equal sections and mount them, in 
