Radioactive Materials

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Radioactive materials in wide use in the United States could be turned into capons of terror that would probably kill few people but would spread panic id produce severe economic damage, scientists told the Senate Foreign stations Committee today.

The materials would not produce nuclear explosions. Rather, they would spread using conventional explosives in so-called dirty bombs. The scientists up testified at the committee's hearing today said such weapons were a textually serious problem.

The most dangerous materials, they said, are bars radioactive cobalt (IS) used to irradiate food, medical devices and other products to sterilize ( $j if ) them.

If turned into fine particles dispersed under the right weather conditions, the cobalt could spread en radiation ...
... to force the abandonment of an area the size of Manhattan, the scientists said. But federal and industry officials said such an action with it.

radioactive cobalt was unlikely because of the intense radiation to which thi person trying to use the weapon would be exposed and because the material ii transported in secret and kept behind tons of lead and other shielding while o$ the road or in use.

Other radioactive materials in tens of thousands of medical and industrial devices could be used to make weapons that would leave wide areas will radiation levels above Environmental Protection Agency limits, possibly leaden| to temporary evacuation and an extremely difficult cleanup.

Scientists at this hearing held to understand these threats and to devise ways of protecting Americans against them also said that they remained concerned that fissionable material - the fuel for nuclear weapons - and the expertise needed to use it could be spreading from the former Soviet Union to terrorist networks, but presented no new evidence of such leakage.

Dr. Richard Me serve, chairman of the Nuclear Regulatory Commission said that all such materials, as well as the much more powerful cobalt rods use in sterilizing food, are tightly controlled. He said that the weaker sources, i dispersed, would cause almost immeasurably small increases in cancer rate among people who were exposed.

Nevertheless, that sort of attack could cause long-term problems because techniques for dealing with radioactive contamination rely largely on destruction and removal, Dr. Henry Kelly president of the Federation of American Scientists, said.

Because limits set b the Environmental Protection Agency for radiation exposure are so low, are? Might have to be evacuated for the long term even when the health risks air relatively slight, he said. Nave cooled slightly in the past few decades.

That has been puzzling, because :he polar regions are thought to be more sensitive to warming trends than the -east of the globe. Even more puzzling, a small portion of Antarctica - the peninsula that stretches north toward South America - defies the cooling rend. It has been warming very rapidly, about five degrees over the past 50 'ears, 10 times the global average.

Writing in today's issue of the journal Science, Dr. David Thompson, a professor of atmospheric science at Colorado State University, and Dr. Susan bloom, a senior scientist at the National Oceanic and Atmospheric administration in Boulder, Colo. , argue that the ozone hole, which has penned up each spring over Antarctica in recent years, may help explain both introductory trends.

A vortex ($EM ) of winds continually blows around Antarctica, tending ) trap cold air at the South Pole. In the new paper, Dr. Thompson and Dr. Dolman show that the winds have strengthened in the past few decades,eping the cold air even more confined. The peninsula, which lies outside the ind vortex, escapes the cooling effect, the scientists said. They say the ozone) le may be the cause of the stronger winds.

Close to the ground, ozone, a molecule consisting of three oxygen atoms, rams a large and unhealthy component of smog. High in the atmosphere, waver, naturally occurring ozone is essential for life, blocking ultraviolet rays at would fatally mangle DNA. However, fewer ozone molecules mean s atmosphere absorbs less ultraviolet radiation. Instead of warming the air, the fs bounce off the snow and ice of Antarctica and reflect back into space.

Scientists already knew that the ozone hole had cooled the upper no sphere. Dr. Thompson and Dr. Solomon show that the troposphere (%$ M), the lowest six miles of the atmosphere, has also cooled.

"It's a lot of and for thought in there," said Dr. John Walsh, a professor of atmospheric once at the University of Illinois and an author of a paper in Science in Mary that indicated Antarctica was cooling. He noted that the ozone hole s usually largest in November or December, but that the greatest cooling had been about six months later.