Wilson M. Powell

Electromagnetic Deflector for the Beam of the 184‐Inch Cyclotron

The removal of the ion beam of 190‐Mev deuterons from the magnetic field of the 184‐inch cyclotron is complicated by the fact that at large radii the ion increases its radius very little in one revolution. The usual type of deflector did not appear to be usable. Consequently, a pulsed electric deflector was designed that would give an additional radial oscillation to the ions which could be as much as seven centimeters. This permits deflection of the ions outward to a magnetic deflector which is outside the range of the circulating ions. The field is sufficiently reduced inside the magnetic deflector to permit the ions to leave the magnetic field of the 184‐inch cyclotron. Approximately ½ percent of the circulating beam appears in the external beam.

30-INCH PROPANE BUBBLE CHAMBER

A propane bubble chamber with a sensitive volume of 30½ in. by 21½ in. by 6½ in. deep operating in a magnetic field of 14 000 gauss is described. Operating parameters and some engineering details are given. The part of the chamber containing the propane is hydrostatically supported in oil through which the chamber is photographed. This permits the use of small glass windows with a large safety factor.

Thirty‐Six‐Atmosphere Diffusion Cloud Chamber

A 36‐atmosphere diffusion cloud chamber has been constructed for use with the 184‐inch cyclotron and with the bevatron. Minimum‐ionizing particles leave dense, sharp tracks of good contrast with hydrogen filling at design pressure. In the operation described, one event is obtained every 15 minutes for a reaction cross section of 30 mb for negative pions on hydrogen. Among the unique features of the chamber are (a) the high pressure; (b) the high magnetic field; (c) the simple unit preassembly of the chamber and the upper pole piece; (d) the distortion‐free photography afforded by the small camera windows of good optical quality directly in front of the camera lenses and the absence of a large top glass near the sensitive region; (e) the thin window for collimated beams; (f) the supported cast Astrolite windows for illumination; and (g) the satisfactory sensitive layer obtained despite the large height‐diameter ratio of the pressure vessel.

A 22-inch Wilson cloud chamber in a magnetic field of 21,700 gauss.

A Wilson cloud chamber 22 inches in diameter in a magnet producing a magnetic field of 21,700 gauss at the center of the chamber is described. The magnet is pulsed in synchronism with the 184‐inch Berkeley cyclotron and can be operated with a steady field of 10,000 gauss. The use of the instrument for identifying light atoms is discussed briefly.

BRIGHT-FIELD BUBBLE CHAMBER ILLUMINATION USING A BEADED REFLECTIVE SCREEN

Bright‐field illumination using a beaded reflective screen is accomplished in the 30‐in. heavy liquid bubble chamber by using separate light sources for each lens. The resolution obtainable is about four times as great as with dark‐field illumination.

Diffusion Cloud Chamber of Unusually Large Dimensions

A diffusion cloud chamber 8 ft long, 4 ft wide, and 5 in. deep has been built and operated successfully for 540 hrs out of a continuous 720‐hr run. Though the actual area is 32 sq ft, the area photographed was 21 sq ft or approximately 2 sq m. A sensitive layer of good quality extending 2½ to 3 in. above the floor was easily maintained. The coolant temperature was held near −67°C and the air above the glass sheet forming the top was held at 30°C. A clearing field of 30 v (top negative) was found desirable to keep the chamber free from general rain. The chamber contained an air and methyl‐alcohol mixture operated at 1 atmos pressure. Tracks in the sensitive region were photographed through the top with the aid of several mirrors. The chamber was used to study the structure of the cores of cosmic‐ray air showers. It is now being used for studies with the bevatron.