John Aristotle Phillips of Princeton is probably even more rah-rah than the average college senior. On Saturday afternoons he puts on a tiger suit and leads the football cheers. He has danced in the male kickline of the Triangle show. And he helps run a campus pizza business that grosses $1,000 a week. But there is another side to John Aristotle Phillips: he has just designed a homemade atomic bomb.

"I wanted it to be simple, inexpensive and easy to build," says Phillips, 21, the son of a Yale engineering professor. "The idea was not to use any classified information. I wanted to do it with what was available to the public."

Phillips spells out his design in a 40-page physics term paper. According to nuclear physicist Frank Chilton of Palo Alto, Calif., the Princeton student has overcome some of the major pitfalls in building a nuclear device. "He says it's 20 years behind the time," Phillips observes, "but still more sophisticated than the Hiroshima bomb." Phillips hasn't actually built the bomb, but it would be about the size of a beachball and weigh 125 pounds. It would cost about $152,000—of which roughly $150,000 is needed to buy the critical 15 pounds of plutonium necessary to make it explode (with one-half the force of the Hiroshima bomb). Plutonium is, however, for sale only to governments and properly accredited corporations and individuals. "The idea is that you steal it," says Phillips, who advocates stronger safeguards to prevent such thefts.

Page 20 of Phillips' research paper has been withheld from public view: It deals with the key problem of the type of high-explosive component needed to trigger the nuclear blast. Phillips figured out the answer with the aid of nuclear engineering textbooks and two U.S. government publications. Says Phillips: "It's very simple. Any undergraduate physics major could have done what I did." (Last year, for a TV show, an anonymous MIT student did design a low-yield A-bomb.)

Phillips is now working on his senior project, a crash-protection system for motorcyclists. He once rode a Honda 500 east from Berkeley, where he spent his first two college years. He will graduate in June with an engineering degree, and is applying for astronaut training. Right now he's looking forward to Princeton's Nov. 6 football game at Yale. The student who plays the Eli bulldog is Phillips' best friend. "We're going to get together and work out some crazy routines," says Phillips. "That's what I like best about being the tiger. You can do just about anything."