The Model 43-20 is very similar to the Model 43-68 which replaced it.  You get these at a slight discount.  A large area gas proportional detector for use in simultaneous alpha/beta surveys as well as alpha or beta survey

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INDICATED USE: Alpha-beta survey
RECOMMENDED COUNTING GAS: P-10 (10% methane, 90% argon)
GAS RECHARGE: Will operate on a static charge for over 15 hours with a 39″ cable
WINDOW: Typically 0.8 mg/cm² aluminized mylar (other thicknesses available)
WINDOW AREA:
Active – 181 cm²
Open – 143 cm²
EFFICIENCY (4pi geometry): Typically 20% – Pu-239; 30% – Tc-99; 15% – C-14; less than 1% – gamma
BACKGROUND:
Alpha – Less than 5 cpm (when operating on the alpha only plateau region)
Beta – Typically 400 cpm or less (10 micriR/hr field)
COMPATIBLE INSTRUMENTS: Model 12, 16, 18, 2000, 2200, 2221, 2224, 2225, 2241, 2350-1
OPERATING VOLTAGE:
Alpha – Typically 1000 – 1500 volts
Beta-gamma – Typically 1600 – 1800 volts
COUNTER THRESHOLD SETTING: Typically 2 – 5 mV
GAS CONNECTORS: Double end quick disconnect
CONNECTOR: Series “C” (others available)
CONSTRUCTION: Anodized aluminum housing
TEMPERATURE RANGE: -4° F(-20° C) to 122° F(50° C)
May be certified for operation from -40° F(-40° C) to 150° F(65° C)
SIZE: 3″(7.6cm)H X 5″(12.7cm)W X 8″(20.3cm)L
WEIGHT: 2 lbs (0.9kg)X