ITR-7
SOUTHWESTERN RADIOLOGICAL, HEALTH LABORATORY
INTRALABORATORY TECHNICAL REPORT
December 8B 1965
AUTOMATED CHAMBER EVACUATOR
Anthony Polito
INTRODUCTION
In the analysis of Ra-226 by the radon emanation technique„ the alpha
emissions of Rn°E22 are counted in a specially designed scintillation
chamber (Diagram 1), The chambers consist of Kovar cups with an
inner coating of phosphor material and a quartz window coated with
tin oxide» With proper carej, these chambers may be used until
the phosphor ma Serial wears out.
In cleaning She chambers for re-use, they are evacuated with a
vacuum purnp8 flushed with aged airs and re = evacuated. This pro=
cedure is repeated until the background has attained a constant
minimum value. In the past, this decontamination has been done
by handc which is time consuming and inefficient. To improve this
cleaning step, an apparatus has been constructed that automatically
decontaminates the chambers. This device does a better job of
cleaning th,2 chambers and requires much less time and attention
on the part of the operator.
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Diagram 1
12/5 O-Ring Joint
\ 2 - Stopcock
1" Copper Tubing
3/8" OD
3" Kovar
Chamber
1. 96" OD
L
I
1/8" Quartz Glass
2" D
Tin Oxide Coating on
Inner Glass Surface
SCINTILLATION CHAMBER
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GENERAL DESCRIPTION OF APPARATUS
The apparatus (see Diagram 2) consists of a wooden rack (A)
built to hold from one to six chambers (B). The individual chambers
are connected, by means of a toggle valve (C) and tubing, to a
common header system (D). The air and vacuum lines are con-
nected to opposite ends of this header system through two solenoid
valves (E).
A 1/5 RPM clock motor (F) is mounted to the rear of the apparatus.
This motor rotates two plastic cams (G) through a chain and sprocket
drive (H). As the cams rotate, they raise and lower two rocker
arms (I) on which are mounted two mercury switches (J), The
mercury switches control the solenoid valves on the air and vacuum
inlets.
Three on-off switches are mounted on a panel at the front of the
apparatus. These switches control power to the clock motor and
the two mercury switches.
The operating cycle of the apparatus consists of the following
steps:
I. For approximately 4. 5 minutes, the rocker arms ride
on the lower portion of the cam. In this position, the
vacuum is on and the air is off,
2. As the cam lobe begins to raise the rocker arms, the
vacuum is switched off and the air comes on. The air
remains on for about 30 seconds while the rocker arms
are raised.
3. The rocker arms drop down the back side of the cam lobe,
turning the air off and the vacuum back on. This
completes the cycle.
3
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Diagram 2
2 Mercury
Switches (J)
Solenoid
(Constant
Open)
1/5 RPM Clock Motor (F)
2 Sprockets and Chain 1:1 Ratio (H)
2 Plastic Cams (G)
- 2 6
2'V
Solenoife
(Constant
Off)
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OPERATING PROCEDURE
1. Mount a chamber on the apparatus using a ball-joint clamp,
2» Turn on air and vacuum lines.
3o Open toggle valve (C) and turn on the three front panel
switches. Allow the chamber to remain on the apparatus
from one to three hours depending on the amount of
contamination* One hour is sufficient for most routine
samples-
4. Close toggle valve (C) and remove chamber. Make
background count to see if all contamination has been
removed,. Any chambers not meeting minimum background
requirements should be returned for further cleaning.
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DISCUSSION
The method of manually decontaminating chambers requires the full
time of the operator and takes about one hour per chamber. The
new apparatus will handle up to six chambers at a time and
requires only a few minutes of the operator's time to load and
unload. While the apparatus is in operation, the operator is free
to do other work.
The use of this new apparatus results in a savings in man hours of
approximately one hour per sample. This is equivalent to about
six man weeks per year under the current sample load.
The apparatus has been proven quite usable and convenient for
routine use-
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115 V
L_
Vacuum
Solenoid
Mercury
Switches
WIRING BLOCiPDIAGRAM
115 V
X
Toggle Switches
X
J
115 V
Air
Solenoid
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APPENDIX
Parts List - Automated Chamber Evacuator
1 Solenoid-Asco, 115 volt, KXSwatts, 1/4 inch pipe -
Constant close for air
1 Solenoid-Asco, 115 volt,, 10,, 5 watts, 1/4 inch pipe -
Constant open for vacuum
1 Electric timer motor, 115 volts, 1/8 inch shaft, 1/5 RPM
1 Gage, 2 inch face, 30 psi to 30 inch Hg0
6 Vacuum toggle valves, Hoke, press helium test+^ 10 torr
3 Switches, toggle, on-off
2 Switches, mercury, glass
1 Sprocket, fine tooth, 1/8 inch shaft hole
1 Sprocket, fine tooth, 1/4 inch shaft hole
1 Steel chain, 14 inch
Pipe and Fitting
5 Brass nipples, 3 inch long, 3/4 inch diameter
8 Brass nipples, short, 1/4 inch diameter
4 Brass nipples, 3 inch, 1/4 inch diameter
6 Brass tees, 3/4 inch diameter
1 Brass tee, 1/4 inch diameter
8 Brass bushing, 3/4 inch male to 1/4 inch female
1 Brass bushing, 1/4 inch female
2 Brass elbows, 1/4 inch diameter
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Material
Rubber vacuum tubing
Plexiglass, 3/4 inch thick
Machine screws
Aluminum rodj, 3/4 inch diameter
Aluminum bar0. 3/4 inch thick
Electrical household wire
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