Snap III

On President Eisenhower's desk stood a domed metal gadget about half the size of a derby hat. Current flowing from it spun a small propeller. Named SNAP III (for System for Nuclear Auxiliary Power), the little gadget is an atomic battery small and light enough to go into a satellite and keep its instruments and radio voice going at least ten times as long as any chemical battery that the Russians or the U.S. have yet employed.

SNAP III's heart is a pinpoint one-hundredth of an ounce of radioactive polonium 210 encased in a molybdenum capsule. The polonium's entrapped radiation heats the capsule to above 700DEG F. Arranged around it like the spokes of a wheel are 20 thermocouples made of lead telluride. When their ends are heated by the capsule, a flow of electrons is set up in the thermocouples, producing an electric current. At peak power, SNAP III can turn out five watts. Before most of its polonium (half life: 140 days) is exhausted, SNAP III will generate as much current as 1,450 lbs. of the best chemical batteries available. For instance, the batteries of the Atlas satellite weighed 20 lbs., lasted 18 days, generated a total of 500 watt hours. SNAP III weighs 5 lbs., would generate 11,500 watt hours in 130 days.

SNAP III was developed under a modest $15,000 AEC contract with the Martin Co. of Baltimore working in conjunction with the Minnesota Mining & Manufacturing Co. But the polonium, which is made by radiating bismuth in an atomic pile, costs about $10 per curie. SNAP's charge is the equivalent of 3,000 curies, bringing the price of fuel in the capsule to $30,000. An AEC official explained that some cheaper isotope might later be substituted for polonium. If cerium 144 can be used, the unit cost might be as low as $600 per battery.

One excited AEC spokesman compared SNAP III to the discovery of gasoline as a source of power. Scientists were more restrained. SNAP III is an impressive achievement, they point out, but it is an application of an old principle. It merely converts the energy coming from polonium to its lowest form, heat--the standard process in any atomic power plant--and the production of electricity from heat (by means of thermocouples) is a familiar process. The conversion of nuclear radiation directly into electricity --an exciting possibility that is being vigorously explored in many laboratories --is yet to come.

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