I’ve finally gotten to where I’ve wanted to be in working through Biological Effects of Ionising Radiation (BEIR) VII: capable of evaluating radiation doses at Fukushima in terms of health risk. I would have liked to have been able to evaluate the radiation readings at various places around Japan in terms of health risk, but that is a few steps further still.

It’s too bad that it’s this difficult. For the environmental data, one must go from counts per second (becquerels), to energy absorbed (grays), to biologically effective energy absorbed (sieverts), to cancer risk via BEIR VII. That last step has been most of what I’ve done in this series. So it’s not surprising that this aspect, which is what most citizens are interested in, is dealt with poorly by the media, which present multiples of various radiation standards, not enough to understand health risks. more…

While I do love numbers, it’s important to understand their limitations. Numbers are essential for verifying predictions, but the limitations tell you how much you can rely on the numbers I gave in my previous post.

The biggest limitation of Biological Effects of Ionising Radiation (BEIR) VII, or any other study of radiation effects, is the lack of data. The BEIR VII authors, after analyzing a large number of studies of various populations, conclude that the only studies that meet all their criteria are those of the Japanese atom-bomb survivors. And even those are not perfect: dose was not measured directly, but reconstructed as a function of distance from the blasts. And it’s a one-time dose, not continuing. more…

I really like numbers, and it’s taken me some time to get to them in discussing risk to health from radiation. I also like to know what goes into the numbers, so I’ve taken some time working through Biological Effects of Ionising Radiation (BEIR) VII. Now I’m feeling that I (almost) know what I’m doing, I can start to answer the question: what risk of cancer does a particular exposure to radiation carry?

I’ve considered how radiation standards are developed in two earlier posts. These posts have been among the most difficult I’ve written; it’s no wonder that so many people have a hard time understanding what radiation standards mean. Reporters try to put radiation measurements in perspective by saying that they are some multiple of the standards, sometimes large multiples. But unless we know what sort of harm the standards and increases from them represent, we still lack perspective. That is the relationship I’m trying to illuminate for others and understand better myself. more…

I’ve been looking for numbers. What is the probability of a radiation dose of x millisieverts producing a cancer?

I should have found the BEIR VII report, BEIR standing for Biological Effects of Ionizing Radiation, some time ago. It’s been almost 20 years since BEIR V was a constant background presence at my job, the guide for understanding the radiation that my workers and I might be exposed to, one of the small number of studies used by governments to develop exposure standards. I happened on it quite accidentally, a week or so ago. more…

A commenter requested that I explain the difference between radiation and radioactivity. These two words are often used interchangeably by reporters, but they have different meanings. Confusing them is related to other misunderstandings.

Radioactivity is the phenomenon of energy emission by unstable atoms. Radiation is what is emitted. More generally, Wikipedia defines radiation as:

“a process in which energetic particles or energy or waves travel through a medium or space.” more…

We simply don’t know. There are enough radionuclides in the outflow to the sea and in the water in the plant that it looks like a leak is possible, but there are too many other things that we don’t know. If there is a leak, it is not a big one.

It’s not a big one, because reactor #3 has been pressurized. If you try to blow up a balloon with a big leak, nothing happens. You can blow up a balloon with a pinhole leak, though. The steel reactor containment vessel is equipped with pressure gauges to measure the pressure. With a big enough leak, the pressure wouldn’t rise, but it has been rising as water is pumped in and turns to steam. more…

Radioactive decay is inherently probabilistic. It’s not possible to point at a particular unstable atom and predict when it will decay. Further, some types of unstable atoms have more than one path for decay; it’s also not possible to predict the path of a single atom.

The behaviour of large numbers of atoms, however, is statistical, and we can say some things about their collective radioactive decay: half of the atoms present will decay within a time called the half-life, and the fractions of atoms that take the various paths of decay are predictable. more…

Now that things are happening less rapidly at Fukushima, I’ve been looking less frequently at the status reports. It became obvious early on that the general aftermath of the earthquake, the loss of electrical power and communication, and other factors were leading to erroneous reports and too much instant interpretation. Taking some time helps to sort out the erroneous reports, but conflicting reports and interpretations still exist. more…

The Fukushima Daiichi nuclear power plant has six reactors. It is located on Japan’s northeast coast, close to the earthquake’s epicenter. A tsunami higher than any anticipated took the plant’s generators out of service.

In a nuclear power plant, the core, where the nuclear reactions take place, generates heat, which boils water and further heats the steam, which turns turbines to generate electricity, just as electricity is generated in a coal or natural gas plant. Heat exchangers separate steam that contacts the core and therefore contains radionuclides from clean steam that drives the turbines. more…