Halflife.

Radioactive-Schmactive: We'll All Be Dead in Half an Hour," proclaimed Mad magazine during the fallout-shelter craze of my childhood. But when Chernobyl melted down in 1986, 1 was living with my two children in Eastern Europe and I learned what it's like to experience a nuclear disaster.

It had been a hard winter in Berlin. Smog--much of it blown over from East Berlin, where they still burned brown coal--was our most serious environmental concern. Then Chernobyl exploded in the first week of spring. The air was finally clear, but now an invisible horror descended on us from the East.

In the brilliant warm weather that followed, I tried to readjust my image of blue, sunny skies to "radioactively contaminated, deadly air." I listened tensely to the weather report. Scientists told us we'd know the worst after the rain: Only then could they measure the exact levels of contamination in our air, water, soil, and food.

"People are cautioned against ingesting fresh vegetables and milk," they warned. "One should not go out in the rain. Pregnant women and children must stay inside with the windows tightly closed. If one must go out, avoid touching plants and outside surfaces, because of the radioactive dust. Clean your shoes very well before reentering your home."

As the nuclear cloud veered first up to Sweden, then down to Italy, a desperate thirst for information competed with my wish to screen out the overwhelming reports.

Then came the day it rained.

I was furious when my sixteen-year-old daughter, in only typical rebelliousness, disobeyed my instruction to bring her six-year-old brother directly home from school and stay inside that day.

"Oh, Mom's got radiation on the brain," she thought, her mind on more important teenaged things. So she took her brother cruising downtown with her friends while I was at work.

I spent the night of the nuclear rain worrying whether the kids, by being out in it, had already inhaled their deaths. Hot particles of plutonium and ruthenium had been reported in Sweden that day. All around me, the lilac and jasmine bushes burst forth like a night blooming in the desert of Berlin's grim gray buildings. But the lush growth and blossoms were heavy with radioactive raindrops.

The next week, I tried to think of a safe place for my son to play outside. Grassy parks were out: Hot particles had been found clinging to blades of grass in southern Germany. Our neighborhood playground had a chain across the entrance with a sign that said the sand was radioactive and children were particularly at risk.

We walked up to Charlottenburg Schloss, with its formal garden and gravel paths. There I found other mothers talking about the situation in German, Turkish, and English: "Did you hear? You can still drink the water--it takes time for the radiation to reach the groundwater--but you can't swim in the lakes .... You have to give your kids iodine tablets or their thyroids will absorb the radioactive iodine."

I went to all the nearby pharmacies, but they were out of iodine tablets. Only fifty miles away, Poland was handing out the tablets to millions of children.

When we got home, we took our Decontamination Shower, as outlined on the radio: "Remove your clothes outside your apartment door. Tie them inside a plastic bag to be washed. Run to the bathroom and shower thoroughly."

"This is fun," my son said. "Can we do it every day?"

On television we saw footage from Chernobyl, where workers were trying to clean up the red-hot debris. Crews with push brooms, dressed like outer-space janitors, ran across the roof of the reactor, counting to 100, then ran back. They were then transported to another part of the Soviet Union, having received their "lifetime dose" of radiation. We know now that thousands of these cleanup-workers have died of exposure.

I saw produce trucks from Poland turned away at West Berlin checkpoints, having set the radiation monitors clicking madly. Who would eat that food now? Or pay those poor farmers?

But as my international awareness increased, my consumer demands became more selfish. (Let it rain somewhere--that is, on someone--else. I want the best food for my kids.

What could I feed the kids? Suddenly the good-for-you foods were verboten. Health officials told us not to eat from our gardens. My daughter, a budding vegetarian, pooh-poohed the warnings; otherwise, she would have nothing to eat. The safest food was the longest preserved, packaged pre-Chernobyl. Inside the supermarket, I found people pushing and shoving near the long-life milk, looking for cartons dated before the meltdown.

Chernobyl Ist Uberall, graffiti said across West Berlin. Chernobyl is Everywhere. A spokesman for the mayor went on TV and hotly denied it. But Chernobyl had created a new frontier, collapsing all borders, including the Berlin Wall.

Politicians and nuclear-industry spokesmen, without even a week's grace for the dead in the Ukraine, told us nuclear power was safe; the Russians just didn't know how to manage it. The International Atomic Energy Agency accepted the Soviet report that the damage had been limited and contained. They insisted that atomic power, even a meltdown, was still under human control.

When I came home to the United States, I found my friends had no idea about Chernobyl. While Europeans saw terrible pictures of deformed babies and children sick with leukemia in Ukraine and Belarus, the U.S. nuclear industry ran a billion-dollar campaign to rehabilitate the idea of nuclear power.

What will you do if a serious nuclear accident happens near you, or even 900 miles away? You'll do what I finally did. You'll let your kids play outside, and pray they don't inhale a hot particle. You'll hope they aren't among that number--the Government may call it a statistically small percentage of the population--who develop cancer, or die prematurely. You'll feed them food containing a level of radioactivity set by the Government as "safe."

But how high is safe? How radioactive do you want your children's milk to be?

Liz Hirsh, a Boston free-lance writer who lived in eastern Germany from 1986 to 1989, is writing a novel, "Borderline States," about Berlin from the time of Chernobyl to the all of the Wall.