. Conduction of electricity through gases and radio-activity; a text-book with experiments . ends uponthe pressure of the gas. The number of molecules in a givenvolume is proportional to the pressure of the gas and conse-quently the number of molecules to be ionized increases withthe pressure and an increase in ionization with increase ofpressure is to be expected. To measure this experimentally anair-tight ionization chamber will be necessary. A suitable oneis shown in Fig. 37. AB is a brass cylinder about 15 and 30 cm. long, the walls being about 2 mm. end B is closed b
. Conduction of electricity through gases and radio-activity; a text-book with experiments . ends uponthe pressure of the gas. The number of molecules in a givenvolume is proportional to the pressure of the gas and conse-quently the number of molecules to be ionized increases withthe pressure and an increase in ionization with increase ofpressure is to be expected. To measure this experimentally anair-tight ionization chamber will be necessary. A suitable oneis shown in Fig. 37. AB is a brass cylinder about 15 and 30 cm. long, the walls being about 2 mm. end B is closed by a brass plate soldered or brazed to thecylinder. At the other end a heavy brass flange cd about 86 RONTGEN RAYS cm. thick and 3 cm. in width, fitting the cylinder tightly, issoldered to it. An aluminium plate about cm. thick and ofthe same diameter as the flange is made to fit closely on theface of the flange, so it may be bolted firmly to it. These sur-faces should be turned as smooth as possible to obtain a closefit. The central part of this plate is recessed down to a thick-. ness of about 1 mm. over an area of 6 or 8 cm. in diameter soas to allow the rays to pass into the cylinder without beingdiminished too much in intensity in passing through the alu-minium. The joint between the plate and the flange may bemade air-tight by placing a soft lead wire about 1 mm. in diam-eter in a circle on the flange inside the bolts and then placingthe aluminium plate on the wire and bolting it down tightlyuntil the wire is squeezed down to about half its original thick-ness, as described in § 31. T and T are two side tubes 5 and placed diametrically opposite. P and P are a set ofguard-ring plates about 6 cm. apart made of aluminium. 5 andS are two stout brass rods which pass through ebonite plugs inthe ends of the tubes T and T and support the plates P and rods should fit tightly in the ebonite plugs and may bemade to screw into the face of the plates P and P. T
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