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LIQUID SCINTILLATION DETECTOR Tracer lab's unique CE-1 Liquid Scintillation Detector is designed primarily for counting samples of low energy beta emitters such as C-14 and Tritium, which can be prepared in liquid form. Efficien- cies of approximately 75% for C-14 and 20 to 25% for Tritium can be obtained with this unit. The total sample volume is 50 cc and sample preparation is extremely simple. An extremely low background of only 200 to 250 CPM is obtained by refrigeration of the phototubes, use of a dual-channel coincidence amplifier which passes only pulses which occur at the same time, and an overpulse rejection circuit. The two photomultiplier tubes with preamplifiers and a scintillation cell are mounted inside a lead shield in a small refrigerator. Samples may be stored in the dark be- fore counting and a glove port permits transferring samples -with- out exposure to light. Booklet TL 59 contains complete details and will be sent upon request. Circle No. 34 A on Readers' Service Card, page 37 A 34 A INSTRUMENTATION tration on a logarithmic basis. A strip chart recorder can be connected to this system. The record will be an enlarge- ment of the meter readings (11 inches full scale). For a more precise indication over a very limited concentration range, the arrangement of Figure 3 is to be pre- ferred. At the extreme left is the Sin- clair-Phoenix forward-scattering aerosol and smoke photometer. This is con- nected to the Phoenix electron multiplier photometer and detector which is used in place of the standard logarithmic de- tector and amplifier. At the right is a strip chart recorder, although for cer- tain applications a galvanometer or servo-scale expander may be preferred. The actual value of the mass concen- tration corresponding to the reading of any of these instruments depends upon the type of particulate matter in the atmosphere, its particle size, shape, re- fractive index, and color. Each factor must be determined by the user. There are many possibilities—among them, the weighing of material collected on a suit- able collector. Also, the instrument may be cali- brated in the laboratory by using an aerosol of known size and physical properties. The standard calibra- tion using dioctyl phthalate oil fog of 0.3-micron droplet diameter showed that a mass concentra- tion of 10 ~ 3 y per liter gave the minimum per- ceptible reading of about 3 /e4 inch on the large type indicating meter, while 100 y per liter gave full scale deflection. Calculations based on the theory of light scattering show that the lower limit of concentration corresponds to an atmospheric visibility of 930 miles and the upper limit to 50 feet. Any atmos- pheric pollution such as smoke, dust, or haze, would occur well within this visibility range. The instruments can be expected to prove indispensable in the study, meas- urement, and control of air pollution in and around cities, industrial areas, offices, apartment buildings, plants, mines, and the holds of ships. Perhaps more important is their use in the re- search aspects of pollution problems, where filter design, air wash, and ven- tilation systems can be controlled. In municipal air pollution studies, the continuous sampling and recording will be indispensable and should eliminate much uncertainty characteristic of grab sampling. Such studies represent a small but highly important part of the general problem. One need merely look at the results of mass spectrographic analysis of airborne contaminants to un- derstand the complexity of this problem. There are still bitter discussion, acri- monious claim, and pointless name calling in this business—typical of the preinstrumentation phase of any large scale argument. A large portion of California can jus- tify the extravagant claims of its cham- bers of commerce. But, whatever ab- erration leads its citizens to attempt a fusion of heavy industry and idyllic nat- ural resources, it does not work out and Figur« 2. Photometer for Logarithmic Measuring Figure 3. Arrangement for Precise indication over Limited Concentration Range exodus is attaining alarming proportions. Recently, a distinguished chemist drove to southern California to consider a re- search post on this problem. His family accompanied him for a long overdue va- cation. Their open-mouthed gasp at the beauties of Pasadena and environs was a mistake. They reacted with violent sneezing, coughing, and copious weep- ing. Residents comforted them with the statement that this day's smog was by no means the worst. A good man has been lost to this problem. Man has had a century's experience with the studied design of the industrial slum. In the early days of the industrial revolution, coal smoke was the exclusive contaminant. Less than a quarter of the era can be said to be the chemical age, but it presents contamination possi- bilities, wherein only the fruits, of an atomic era can supply a swift, un- answerable, and irrevocable termination. Automatic instrumentation is the an- swer, in our opinion, precisely because it leaves out, very largely, the human ele- ment, which is the real bottleneck. ANALYTICAL CHEMISTRY Tracerlab-®Inc. UU HIUH i l . , BUSIUN 2030 WRIGHT AVE., RICHMOND. CAL.
