Radiation Detection

Science Summaries

Here is a photo of the schematic diagram I found inside this Civil Defense Victoreen CD V-715 Ionization Chamber nuclear radiation detector.

Also shown is the top of the Model CDV-715, Model 1A, for identification purposes. The schematic is a JPEG, so you can download it, and print it out. I have added a parts list, and test voltage information. Note that the black ink "R" stamp is missing right under the serial number, indicating that the unit has not been retrofitted. Purchased on eBay for $10.

1. Nuclear Radiation Detection Summary - for general information
2. Geiger Counters Summary - for descriptions and pricing
3. Geiger Counter Data Compared - for sensitivity comparisons
4. Ludlum Radiation Product Summary - detection devices and probes
5. Victoreen CDV-700 6B Detector Summary - True Geiger Counter (antique)
6. Victoreen CDV-715 1A Detector Summary - Ion chamber detector (antique)
          1. CD V-715 Photograph
          2. CD V-715 Schematic Diagram
          3. CD V-715 Test Voltages
          4. CD V-715 Parts List
          5. CD V-715 Circuit notes
          6. Evolution of the CD Ion Chamber Survey Meters
          7. Scales and ranges
7. Victoreen CD V-750 5B Dosimeter Charger - Charges CD quartz dosimeters
8. Uranium Ore Summary - common types of radioactive ore

Voltages (from top to bottom on the schematic above)

Nominal

Mine

Nominal

Mine

TP1

50 Volts

47.2 Volts

TP4

-3.8 Volts (2nd check)

-3.8 Volts

TP2

10.5 Volts

9.46 Volts

TP5

1.5 Volts (1st check)

1.58 Volts

TP3

1.7 Volts (3rd check)

1.55 Volts

All voltages referenced to negative battery terminal, NOT ground.
All voltages measured with instrument operating on zero range with zero correctly adjusted.
Voltages may vary ±20% from instrument to instrument.

Transformer inductance measured on 1KC bridge with all other windings open.

I think that I need to do a cleanup job on this unit. After main "zeroing", in order to zero each range, all 4 calibration pots must be turned to the extreme end of their travel (zero resistance). Not good, I surmise. I'll bet everything is OK, but that I have the "dirty high-impedance circuit" syndrome. I'm off to buy a camel's hair brush and a jug of isopropyl alcohol.
No cigar. I cleaned the he|| out of it, and no change. I think my problem is that the unit does not have the "R" next to the serial number - in other words, it has not had the MANDATORY retrofit. It remains a boat anchor for now. If you are going to play with one of these things, make sure it has had the obligatory retrofit.

 Resistors

R1

12K @5%

R9

680K

R2

15K potentiometer (zero)

R10, R10A, R10B, R10C

(4) 50K potentiometer unit

R3

470

R11

9.1K @.5W - 5%

R4

5.6M

R12

220,000,000 Ohms

R5

39K

R13

2,200,000,000 Ohms

R6

68K @5W - 5%

R14

22,000,000,000 Ohms

R7

220K

R15

220,000,000,000 Ohms

R8

390K

R16

2.2K

 Capacitors

C1

0.068µF

C4

0.1µF @200V

C2

0.1µF

C5

0.1µF @75V

C3

0.005µF

C6

0.01µF

 Semiconductors

CR1

Diode

CR3

Diode

CR2

Diode

Q1

GP PNP transistor

 Miscellaneous

T1

Transformer

BT1

1.5V Standard D Cell

S1

Function switch

Tin Can

Ion Chamber, solder sealed

V1

VX86 Tetrode Vacuum Tube

M1

50µA meter movement

K1

Zeroing knob

K2

Function switch knob

Check out those resistors - R12 thru R15
From 2.2x10⁸ = 220 Meg Ohms on the x100 scale
to 2.2x10¹¹ = 220 Gig Ohms on the x0.1 scale
No wonder these things have to be degreased, alcohol washed, desiccated and sealed.
This gives new meaning to the words "high impedance". Really, really high.
Don't breathe on the high-Z area, certainly don't cough on it, and never touch it.

NOTES:
* Geiger counter: Measures intensity of radiation (rate) - Uses Geiger-Mueller tube
* Dosimeter: Measures intensity of radiation (rate) AND accumulated exposure over time (dosage)
* Ion Chamber Detector: Measures intensity of strong radiation (gamma), and beta (CDV-720)


Antiques, but still in use
Some Civil Defense Victoreen antique gamma detectors from the 1960's -
CD V-700 - True Geiger Counter - employs Geiger-Mueller tube

CD V-710 - Ionization Chamber Radiation Detector - Gamma
CD V-715 - Ionization Chamber Radiation Detector - Gamma (subject of this page)
CD V-717 - Ionization Chamber Radiation Detector - Gamma
CD V-720 - Ionization Chamber Radiation Detector - Gamma and beta

Here is a summary of Model Numbers, with corresponding dates of production. Anton, Frary and Clark, Landers, and Lionel Ion Chamber units are included.

M #

Note

1954

1-1.5V, 5-22V

Detects gamma only

Typical eBay Price "As Is" = $15
Typical eBay Price "Working" = $25

Good as showpiece only
Buy for appearance

1-1.5V, 3-22V

1-1.5V, 2-22V

1-1.5V, 1-22V

1-1.5V, 1-22V

1956

1-1.5V, 2-22V

Detects gamma and beta

Typical eBay Price "As Is" = $15
Typical eBay Price "Working" = $25

Good as showpiece only
Buy for appearance

2-1.5V, 1-22V

2-1.5V

2-1.5V

1961

1-1.5V

Rendered V-710 and V-720 obsolete, yet most do NOT detect gamma
MUST be retrofit, with bold "R" stamp on top, right next to the serial number.

eBay Price "As Is" no R = $15
eBay Price "Working" no R = $25

eBay Price "As Is" with R = $25
eBay Price "Working" with R = $40

1963

1 - 1.5V

Remote cable built-in
No retrofits required
Gamma detection only
Typical eBay Price "As Is" = $25
Typical eBay Price "Working" = $40

The R means that the unit has had the MANDATORY retrofit, rendering it more reliable than the original. CD V-715 retrofits began in 1971.

"As Is" means "Probably is Bad"
"Working" means the device currently detects radiation Some people say the device is "working" if the meter works. This is NOT an accurate description.

80

30

60

60

110

300-640

Information provided by Oak Ridge Associated Universities

Here is a summary of the Dial Measurement Range Scales for the CD Survey Meters.

Note

For gamma & beta
GM tube detector
For very low levels

Detects gamma only
For very high levels

For gamma & beta
For very high levels

Detects gamma only
For very high levels
Replaces 710 & 720
Requires retrofit "R"

Detects gamma only
For very high levels
Retrofit not required

80

50

50

50

50

50

50

50

200-640

Information provided by Civil Defense Museum

Although the author has tried to be as accurate as possible, errors are possible.

I could not find an online schematic diagram like the above. So, I made this ionizing radiation detector schematic web page, to help myself understand the technology. I hope that it helps you.

I'm new to this stuff - please email me if you find any errors.

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