Ludlum Measurements 43-68 User manual

LUDLUM MODEL 43-68,
43-68/1 AND 43-68/2
GAS PROPORTIONAL DETECTORS
February 2011
Serial Number 159017 and Succeeding
Serial Numbers

LUDLUM MODEL 43-68,
43-68/1 AND 43-68/2
GAS PROPORTIONAL DETECTORS
February 2011
Serial Number 159017 and Succeeding
Serial Numbers
LUDLUM MEASUREMENTS, INC.
501 OAK STREET, P.O. BOX 810
SWEETWATER, TEXAS 79556
325-235-5494, FAX: [phone]

STATEMENT OF WARRANTY
Ludlum Measurements, Inc. warrants the products covered in this manual to be free of
defects due to workmanship, material, and design for a period of twelve months from the
date of delivery. The calibration of a product is warranted to be within its specified
accuracy limits at the time of shipment. In the event of instrument failure, notify Ludlum
Measurements to determine if repair, recalibration, or replacement is required.
This warranty excludes the replacement of photomultiplier tubes, G-M and proportional
tubes, and scintillation crystals which are broken due to excessive physical abuse or used
for purposes other than intended.
There are no warranties, express or implied, including without limitation any implied
warranty of merchantability or fitness, which extend beyond the description of the face
there of. If the product does not perform as warranted herein, purchaser’s sole remedy
shall be repair or replacement, at the option of Ludlum Measurements. In no event will
Ludlum Measurements be liable for damages, lost revenue, lost wages, or any other
incidental or consequential damages, arising from the purchase, use, or inability to use
product.
RETURN OF GOODS TO MANUFACTURER
If equipment needs to be returned to Ludlum Measurements, Inc. for repair or calibration, please send to
the address below. All shipments should include documentation containing return shipping address,
customer name, telephone number, description of service requested, and all other necessary information.
Your cooperation will expedite the return of your equipment.
LUDLUM MEASUREMENTS, INC.
ATTN: REPAIR DEPARTMENT
501 OAK STREET
SWEETWATER, TX 79556
800-622-0828 325-235-5494
FAX [phone]

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. February 2011
Table of Contents
General 1
Specifications 2
Hook-Up 4
Flush 5
Detector Performance 6
Static Operation 6
Recharge 7
Parts List 8
Drawings and Diagrams 9

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 1 February 2011
General
The Ludlum Model 43-68, Model 43-68/1 and Model 43-68/2 are
gas proportional detectors, each having an open window area of
100 cm2. They are designed for alpha and beta survey and are
compatible with a number of counting instruments.
The three models are identical in performance specifications and
vary from each other only in the location of the quick disconnect
gas fittings. Both the Model 43-68 and Model 43-68/1 have the
two fittings “topside.” The Model 43-68 fittings are on the same
end as the cable connector, while the Model 43-68/1 has fittings on
opposite corners. The Model 43-68/2 fittings are on the narrow
side of the end of the detector opposite the handle. The cable
connector is also located there on the Model 43-68/2. (Refer to
individual assembly drawings for details.)
Instructions and procedures in this manual apply to all three
models
NOTE: When changing the Mylar window on a detector, it is not
necessary to recalibrate the instrument as long as a functional
check is performed on the instrument and its readings are
consistent with the readings before the window was replaced.

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 2 February 2011
Specifications
Window Thickness: typically two layers of Mylar 0.8 mg/cm2
),
other thicknesses available
Window Area: typically 126 cm2active, 100 cm2 open
Counting Gas : P-10 (10% methane, 90% argon) is
recommended. Other counting gases are also
acceptable.
•
Gas Recharge: expected time of operation on static charge
with 0.99 m (39 in.) cable:
•
Gross counting mode is 15 hours or longer.
Alpha-beta mode is 5 hours or longer.
Background:
•Alpha is 3 counts per minute (cpm) or less
when operating at alpha-only plauteau region.
•Beta-gamma is typically 350 cpm or less (in a
10µR/hr field.
Efficiency (4π geometry)
•typical values for gross countin: 20%-
:
239Pu;
15%-14C; 30%- 99Tc; 20%-90Sr/90
•yypical values for alpha-beta counting: 17.5%-
Y
239Pu; 20%-90Tc; 20%-90Sr/opY

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 3 February 2011
•Alpha is typically 1100-1400 volts.
Operating Voltage:
•Beta-gamma is typically 1600-1800 volts.
Counter Threshold Setting: typically 2-5 mV for scaler or
gross counting instrument
Size
: 7.4 x 11.7 x 19.8 cm (2.9 x 4.6 x 7.8 in.) (H x W x L)
Weight : 0.9 kg (2 lb)
Gas Connectors: double-end shut-off quick disconnects

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 4 February 2011
Hook-Up
NOTE: Plastic dust caps should always be in place on detector gas
connectors when gas lines are disconnected, except during a fast
flush. Dust caps prevent dust and other materials from interfering
with the function of the check valves and should be in place when
the detector is operating on a static charge.
Connect counting gas output and input lines to detector.
RECOMMENDED EQUIPMENT
(1) Dual-Stage Regulator: allows for better low-pressure
regulation
(2) Needle Valve between second regulator stage and
flowmeter for easier flow adjustment
(3) Flowmeters: range of 0-150 cc/min (cubic
centimeters/minute)
(4) Water Pressure Gauge: (optional) range of 0-25
inches of water

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 5 February 2011
Flush
CAUTION: The Model 43-68 uses double-end shut-off quick
connects. Both the male and female quick connects have to be
connected to allow counting gas to flow through the detector.
Connect output gas line from detector to output flowmeter.
Connect input and gas lines from main supply through the
regulator and input flow meter.
Turn main supply on and flush detector at 100-140 cc/min
or 10. 2 cm (4 in.) of water pressure at 1-2 psi gauge
pressure for 15 minutes.
NOTE: A faster flush time can be realized if the output gas line
(only) is removed at the output flowmeter and the flow rate
maximized. Flush time may be reduced to 5 minutes. (Note that the
quick disconnect fitting should not be removed. With the fitting in
place, gas flows out the connection. With the fitting removed, a
check valve is actuated that prevents output flow.)
CAUTION: The main supply should be reduced to less than 50
cc/min before the output gas line is reconnected.
After flush is complete, set flow to 30-50 cc/min.
Check output flowmeter. Determine detector leakage to be
less than 5 cc/min.

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 6 February 2011
Detector Performance
ALPHA PLATEAU: Determine the plateau region of the
background and alpha source counting curves for the applied
voltage range of 1100-1400 volts. Use 50-volt increments and set
the counting instrument input sensitivity at 4 mV. The operating
voltage should be approximately 1250 volts. The background
count should be 3 cpm or less. The operating voltage will increase
with a higher input sensitivity. Check each quadrant of the detector
face for statistically uniform response; that is, ensure that each
quadrant reading is within ±10% of the average of the readings. If
the count is not statistically uniform, check for light leaks in the
window and repeat flush procedures.
BETA-GAMMA PLATEAU: Determine the plateau region in the
background and beta-gamma source counting curves for the
applied voltage range of 1550 volts to 1900 volts or from 1550
volts to when either the source or background count rate increases
dramatically. Use 50-volt increments and leave the input
sensitivity at 4 mV. The operating voltage should be approximately
1700-1750 volts, with the background count at 350 cpm or less.
Setting instrument input sensitivity greater than 4 mV will increase
the operating voltage.
Static Operation
Check detector for proper operation, for appropriate source
count, and gas leakage.
Disconnect output and input male quick connects.

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 7 February 2011
Turn main supply to OFF.
Check source count before and after static operation. A
decrease in detector efficiency should be less than 10% in
15 hours from when the detector is disconnected from the
main gas supply for gross counting or 5 hours for alpha-
beta counting.
Recharge
Connect input and output quick connects.
Turn main supply to ON at 30-50 cc/min for routine
recharge, or refer to flush procedures for faster flush
time.

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 8 February 2011
Parts List
Description Part Number
Completely Assembled
Model 43-68 Gas Probe
47-2005
Completely Assembled
Model 43-68/1 Gas Probe
47-2013
Completely Assembled
Model 43-68/2 Gas Probe
47-2017
Body – Model 43-68
7342-152
Body – Model 43-68/1
7342-161
Body – Model 43-68/2
7339-138
Cover Plate
7342-156
Hex Screen
7342-157
Reversible Handle
7342-133
Electrode Plate
7342-146
Window Assembly
4342-097
Screw-in "C" Connector
13-7751
Quick Disconnect Fitting
Stem (2 each)
13-7912
Quick Disconnect Fitting
Pipe (2 each)
13-7920
Standoff (8 each)
18-8780
Brass Knurled Nut (2 each)
20-9074
Silicone Cord 1.07 m (3.5 ft)
22-9631

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 9 February 2011
Drawings and Diagrams
Assembly View (Model 43-68), Drawing 342 x 97
Assembly View (Model 43-68), Drawing 339 x 70
Assembly View (Model 43-68/1), Drawing 339 x105
Assembly View (Model 43-68/2), Drawing 339 x 104

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 10 February 2011

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 11 February 2011

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 12 February 2011

Model 43-68, 43-68/1, 43-68/2 Gas Proportional Detector
Ludlum Measurements, Inc. Page 13 February 2011