Can you please provide some numbers to back that up?
You're assertion that "half are dead before the age of 55" doesn't match with what's available online, which is that 10% of the liquidators are now dead. However, given that the majority of them were between 20 and 45 at the time of the accident, some of them would have been 70 by now.
Average male life expectancy in Ukraine is 63.
To check that this low life expectancy isn't as a result of Chernobyl, I looked at the entire Russian federation and other ex-Soviet states. They are worse. Life expectancy across the entire region nosedived after the collapse of the USSR. Interestingly, only those former states that have joined the EU have higher life expectancy approaching that of western standards - and these were the ones that sent many of the liquidators at the time and they were the ones downwind of the site. Even Belarus, which had 60% of the fallout, has a higher life expectancy.
Professor Gerry Thomas, Chair in Molecular Pathology at the Department of Surgery & Cancer at Imperial College London and Director of the Chernobyl Tissue Bank was on BBC News this morning. She said that the only attributable effect to Chernobyl that has been observed is an increase in thyroid cancer in those who were children at the time, because the Soviet authorities were reluctant to admit there was a problem and distribute iodine tablets. Interestingly, the guy sitting next to me at work is from just across the border in Slovakia. He says they were not told about the accident and not told to take any precautions during the May Day parades a few days later, and as it was warm most people were out in T-shirts.
I have no reason to believe that Professor Thomas is anything but a bona fide and independent academic.