Ludlum

M3

2022-12-03

• ~$900 new
• + ~$150-300 for a 44-9
• https://ludlums.com/products/all-products/product/model-44-7
• the lnd tubes themselves are around $110ish

M15

Calibrated Ludlum 2241? The 2241 appears to be the same model just generic (switches for detector 1 and 2 instead of G-S and N).

Manual (older)

CONNECTOR: Series "C", 706 U/G, BNC or MHV may also be provided

NEUTRON DETECTOR: Nancy Wood G-10-2 Boron Trifluoride

NEUTRON DETECTOR MODERATOR: 2 INCHES OF POLYETHYLENE SURROUNDING THE DETECTOR; 0.030 INCH THICK CADMIUM THERMAL NEUTRON SHIELD ENCLOSING THE MODERATOR; OUTER SHELL AND FITTINGS OF ALUMINUM; WEIGHT-4 lbs

Use 1000 M meter to measure resistance. Model 500 pulser recommended

Schematics, parts list

Manual (newer)

Model 42-14H Neutron Detector

Model 44-7 GM Detector

unimorph speaker?

 When shipping a Model 44-7 by air, it is necessary to ship the
 tube in a sealed container to avoid sudden atmospheric
 changes, which could rupture the tube.

Maybe this happened during shipping? Wonder if this is theoretical or actual risk

neutron detector: check should read 1275-1350 V

HV Pushbutton Switch: The output resistance of the high-voltage supply is 1.5 megohms with a typical scintillation voltage divider of 100 megohms. The actual detector voltage will be 98.5% of the indicated voltage.

Battery Dependence: instrument calibration changes less than 3% within battery check limits on the meter

Linearity : reading within 10% of true value with detector connected

Input Impedance : 0.1 megohm

Model 42-14H Neutron Detector

• 2 Atm 3 He tube, LND 25185 or equivalent; proportional detector with 7.6 cm (3 in.) diameter, cadmium-lined moderator for fast neutrons (remove detector from moderator for thermal neutrons)
• Neutron Detector Operating Voltage : approximately 1275-1350 Vdc
• Energy Response : count response nonlinear throughout energy spectrum (0.025-12 MeV)
• Neutron Sensitivity typically 55 cpm/mrem/hr ( Am-241 Be fast neutrons)
• Detection Range : thermal to approximately 12 MeV
• Gamma Rejection : typically 10 cpm or less through 10 R/hr (100 mSv/h) ( Cs-137)

Model 44-7 Alpha-Beta- Gamma Detector

• Window : 1.7 ± 0.3 mg/cm mica
• Window Area : active is 6.4 cm (1 in 2 ); open is 5.2 cm 2 (0.8 in 2 )
• Efficiency (4pi geometry) : typically 2% for 14 C, 10% for 90 Sr 90 Y, 7% for Pu, and 7% for Tc
• Alpha-Beta-Gamma Sensitivity : typically 2100 cpm per mR/hr ( 137 Cs gamma)
• Background : typically 40 cpm

McMaster unit

Not working. Was supposed to be working when shipped

Speaker wire loose and shorted to case. Caused battery voltage to drop. Fixing that meter still doesn't read anything although battery voltage reads

Maybe the RES switch is stuck?

Broken HV connector? Measure using voltmeter on B-G setting

• Verified voltage readings
• Accuracy unclear due to HV resistors
• Voltmeter connection registers on needle
• Allowed to verify RES switch works

Damaged B-G detector on N setting?

N detector not working either

Unit

Serial number: 55369

• On newer models its at the bottom of the faceplate
• On mine is on the side
• The oldest manual I've found is the 1999 manual for S/N 149428+

2015-12-18 voltage check (no load)

• B-G: 900 V
• Expect: 900 V
• Pass
• N: 1700 V
• Expect: ~1500 V
• Pass?
• Same reading w/ and w/o detector

GM detector

 LUDLUM
 MEASUREMENTS, INC.
 SWEETWATER, TEXAS
 MODEL 44-7
 SERIAL NO. PR 045985

Neutron detector

 RADIATION DETECTORS
 N. WOOD
 COUNTER LABRATORY, INC.
 Chicago Ill. 60615
 
 MODEL G-10-2
 SERIAL G40610
 PLATEAU 1100-1300
 SPECS 20um B10F
 
 ALL INSULATORS (CENTER SEAL, CONNECTORS,
 ETC.) MUST BE KEPT CLEAN AND DRY FOR
 PROPER OPERATION.  DAMAGE DUE TO OVER
 VOLTAGE, OVERHEATING, ROUGH HANDLING AND
 SOLDERING ON THE TUBE WILL VOID THE TWO YEAR
 GUARANTEE.  FOR QUESTIONS CALL N WOOD
 312/324-1113, OR WRITE, 1525 E. 53rd ST.
 CHICAGO IL 60615