G-M 
scanner 
High 
volt- 
age 
5-ma or 
100-mv 
pen 
recorder 
; Seer Register unit 
factory. Platform and frame are stainless steel, the from timer 1003 
drums aluminum. 50-v phase 
Left prong V of escapement rocker U normally engages 
a blade of escapement wheel D under the tension of a 
small spring 7 attached to the rocker and frame. The 
armature of solenoid X momentarily pulls back rocker 
U via connecting rod W against the spring; when rocker 
U returns to normal position, D rotates } of a complete 
revolution but no more. Friction clutch S becomes 
disengaged by relaxing milled nut J so that drum H is 
free of R and, hence, the escapement mechanism. New 
strips can then be wound up by means of handle G. 
Lead castle LC is in two parts to facilitate handling. 
Tube GM is placed exactly over L. The lower half of 
LC is then lowered into position so that prongs PR engage 
the GM flange. The top half of LC is then placed in 
position so that contact disk CD engages anode AN. 
High-voltage and ground connections‘are then made at 
AL and ET. Insulating glass tube GL is flared at the 
lower end to guide AN onto CD. 
Solenoid X is simply the electromechanical register 
unit taken from a type 1003 timing unit which is avail- 
able in many laboratories equipped for beta counting. 
Its operation requires 50-v d-c pulses which can be 
drawn from the timing unit at intervals of 44 or 1 second, 
or 4g or 1 minute. By inserting additional scale-of-two 
units, solenoid X can be made to operate at 2-, 4-, or 
8-minute intervals, ete. The probe unit amplifies pulses 
from tube GM and feeds them to a type 1138A ratemeter. 
The 0-100 mv potential difference across the output 
potentiometer is proportional to the mean rate of count; 
alternatively the ratemeter output may be obtained as a 
0-5-ma current in the same circuit. This output is fed 
to a pen-recording milliammeter or to a self-balancing 
potentiometer. The rate of count is thus automatically 
plotted against distance along the strip. 
Additional 
scales 
of two 
Power 
source 
3. Unit-to-unit connections 
4. Lead castle 
turn, below an end-window Geiger 
tube. This method is very tedious, 
and unless each section is cut exactly 
and mounted precisely, errors will 
result. 
Automatic scanning device. The 
four diagrams and text above show 
the components and working order of a 
device for automatic scanning of 11¢- 
inch unidimensional paper chromato- 
grams. Whatman No. 1 paper is 
conveniently available in rolls of this 
width. Two-dimensional chromato- 
grams are scanned by cutting the 
sheet into the equivalent number of 
strips as described later. 
The advantages of this device are: 
1) The paper chromatogram is auto- 
matically scanned in a geometrically 
uniform manner. 2) The movement 
of the paper is controlled by a simple 
escapement mechanism that is oper- 
ated by conventional timing equip- 
ment. 3) Provision is made for plot- 
ting radiochromatograms automati- 
cally. 4) All parts of the scanning 
unit are easily accessible for cleaning 
purposes, decontamination, etc. 
In our experience, the milliammeter 
recorder was more suitable than the 
self-balancing potentiometer because 
the tendency of the latter to over- 
balance gave rise to fluctuations 
greater than the intrinsic statistical 
fluctuations of particle counting. The 
statistical fluctuations of the ratemeter 
output for a given mean rate of count 
can be modified by the variable capaci- 
tance of the integrating circuit of the 
ratemeter. The corresponding inte- 
grating time must be less than the 
time intervals of the scanner or the 
ratemeter will not be able to keep 
pace. On the other hand, the inte- 
grating time must be sufficiently large 
for the statistical fluctuations in the 
counting rate to be small compared 
to the radioactivity peaks of the 
chromatogram. 
Quantitative Interpretation 
A separated component will nor- 
mally be distributed over several 
sections of the paper chromatogram. 
Ideally, the counting geometry will be 
the same for each section. The weight 
of the component is invariably small 
compared to the weight of the paper, 
so that self-absorption of the beta 
particles assayed will depend only 
179 
