Almost all of the 140 million Americans alive during the nuclear bomb tests of the 1950s were exposed, in some degree, to radioactive fallout. Thirty million have died or are expected to die of cancer. Yet only a tiny fraction of those cases — no more than 16,000 — can be attributed to nuclear fallout, say three researchers from the National Cancer Institute in a study published in January.

That estimate is low, say some fallout victims’ advocates. They worry that the study lends support to a recommendation that would significantly decrease the number of downwinders covered by a federal compensation program.

The study follows a 2005 National Academy of Sciences report that recommended scrapping the geography-based standards of the Radiation Exposure Compensation Act (RECA). That 1990 law provides payments to downwinders suffering from certain cancers who lived in parts of Nevada, Arizona and Utah during the tests. The Academy report said radioactive fallout was likely not a "substantial contributing cause of cancer," and it recommended compensation be based on medical evidence instead of location.

Yet it’s difficult to prove that fallout exposure caused a given case of cancer, downwinders say, and developing new compensation standards could take years. "The government might as well say there is not going to be any more compensation," says Tona Henderson, an activist in Emmett, Idaho, who has lost 10 family members to cancers she believes were induced by fallout.

While Congress debates how to change RECA, Sen. Mike Crapo., R-Idaho, Sen. Larry Craig, R-Idaho, and Sen. Conrad Burns, R-Mont., introduced legislation in December to extend compensation to their states, which have counties that were among the hardest hit by fallout. Downwinders suffering from cancer are running out of time, says Henderson: "They should include us in RECA now and study us later."