An ALPHA-RAY TRACK APPARATUS A. E. TAYLOR University of Idaho, Southern Branch, Pocatello, Idaho
S
EVERAL types of apparatus which will demonstrate the disintegration of radioactive substances are on the market. Most of these, however, are so costly that many students are never given the opportunity of examining one of them first hand. The construction of a simple fog-track apparatus is well within the capabilities of a freshman student of chemisw or physics, and the results Pitchblende obtained are well worth + ; the / Sealinz wax time involved. A similar apparatus is sold by the - . - _ Central Scientific Co. under the name of "Knipp's AlphaRay Track Apparatus" [U. S. Pat. No. 1,617,3971. The materials needed are as follows: one 200-cc. Erlenmeyer flask with a bottom as flat and free from irregularities as possible; one rubber bulb about two inches in diameter (similar to the type with which small hydrometers are equipped); a very small pinch of finely pulverized pitchblende (a salt of uranium or thorium may be substituted here, but is not quite so efficient); a short piece of 4- or 5-mm. soft-glass tubing; a small piece of red sealing wax. The most difficult procedure in preparing this apparatus is the blowing of a small bulb, on the piece of glass tubing, that is thin enough to permit the passage of alpha particles and yet strong enough to withstand the pressure to which it is to be subjected. This
can be dected by heating the glass tubing and drawing it out to a diameter of about l millimeter. The capGllary should then be broken at the center and the piece selected should be sealed over. While hot it should then be blown out to make a bulb about 4 or 5 mm. in diameter. The finely pulverized pitchblende should then be placed in the bulb before cutting off the excess glass tubing. After this is done the capillary should be sealed off at a distance from the bulb equal to one-half the inside diameter of the bottom of the Erlenmeyer flask (about 3 cm.). The sealed end of the capillary is then fastened to the side of the flask by means of the sealing wax in such a way that the small bulb reaches the center of the flask a t a point about 2 millimeters from the bottom. The flask should then be filled to the neck with water colored with a small amount of methylene blue or other suitable dye to furnish the necessary dark background. The rubber bulb is then slipped over the neck of the flask. The apparatus is best supported on a ring stand by means of a buret clamp. Alternately compressing and releasing the bulb produces the fog tracks. An apparatus made according to the above directions has been used for two years and seems to operate as well as ever. The visibility of the fog tracks may be improved by the use of illumination from the side by means of an enclosed light bulb. With the above apparatus the number of tracks is about ten or twelve during the first half minute that it is used. This gradually decreases, probably because of the accnmulation of ionized gas in the air chamber. If, however, the apparatus is inverted for a few minutes so that the water in the flask covers the glass bulb containing the pitchblende,the activity again reaches its previous value.
E;
