The Importance of Time

The ANS Position Statement on LNT

The American Nuclear Society provides statements which reflect the Society's perspectives on issues of public interest that involve various aspects of nuclear science and technology. Position statements are prepared by key members whose relevant experience or publications inform the documents and then the documents are reviewed by ANS committees and divisions. The final position statements are approved by the Board of Directors.[ANS web site]

Time is the fourth dimension of our universe, but in my view it should be listed first. We are immersed in time at least as deeply as we are immersed in space. On a practical level, no one understands this better than doctors and engineers. Medical personnel are constantly glancing at watches and clocks. They talk of the Golden Hour. They carefully fractionate doses. They monitor heart rates and respiratory rates. They rarely make a decision based on a single snapshot of a patient's condition.

Engineers spend most of their time thinking about how things move through time. If for some purpose, we freeze everything, we call it a static analysis. The word is used apologetically, as in: for the sake of producing a number, I'm going to pretend things don't change.

So what are we to make of the American Nuclear Society's position statement on LNT? Officially, it's called Risks of Exposure to Low Level Ionizing Radiation, Position Statement No 41. The Position Statement itself is a two page summary, that concludes we don't know if LNT is an accurate harm model because at low doses the data is "inconclusive" given all the confounding factors.

The two page Position Statement is backed up by a 10 page document entitled Background Information. What's striking about both the Position Statement and the Backgrounder is the absence of the time dimension. In the position paper, the word dose appears 9 times. In all but one case, it's clear the authors are referring to cumulative dose. exposure is used 16 times, While exposure could be more general than total dose, it's pretty clear from the context that we are talking about total dose.

While the ANS admits that LNT is unproven, and claims that LNT should not be used in situations like a nuclear power plant release because "such estimates are not reasonable", the ANS seems to be unaware that, in focusing on cumulative dose and pretty much ignoring the time dimension, it is assuming LNT. Only LNT allows you this focus.

In the Position Statement there is no reference to repair. In the Backgrounder, only one indirect reference to "biological processes". There is no discussion at all of all the work that has been done on DNA repair, nor why we have such effective repair processes. The Position Statement could have been written before the discovery of DNA. The word repair itself occurs nowhere. The carefully reviewed Position Statement is either an astounding or feigned display of ignorance by a professional society, supposedly specialized in radioactive processes.

To determine the validity of LNT, the Position Paper calls for a ``long term low-dose radiation research program". The ANS admits this will be expensive and require many years with no guarantee of definitive results. In fact, low dose radiation may be the most exhaustively studied medical hazard in history. And the results are conclusive. Low dose rate radiation is such a weak carcinogen that the signal to noise ratio is too low to reliably detect significant increases in cancer.

If you wish to test a radiation harm model, you must find (or produce in the lab) situations involving high enough doses and high enough dose rates, so that the impact of radiation is clearly visible. We have such situations, most importantly, the atom bomb survivors and the radium dial painters. LNT does a reasonable job of roughly predicting the harm when the dose is received acutely (over a very short period of time) such as the bomb survivors. But it fails miserably, when the same or much larger doses are incurred more or less evenly over a prolonged period, or chronically, such as the radium dial painters. The reason for that failure is LNT ignores the time dimension, which is critically important given our remarkably effective repair processes.

The dial painter data is backed up by a bunch of other examples, plus a slew of animal studies. We don't need more studies of LNT. We already know it is not just quantitatively wrong; it is qualitatively wrong. And we know why. We just need a professional society which feeds off LNT to admit it.

The Backgrounder defends LNT not on its ability to predict harm, but its success "as evidenced by the low doses incurred by the public and radiation". This assumes minimizing dose is the whole point of exercise. Interestingly, the Position Paper sharply criticizes ALARA for doing exactly that. Come on guys, get it together.

The Backgrounder further defends LNT saying "Crucially, no other alternative model has been clearly defined, proposed for use, and recommended for adoption by national or international radiation protection organizations". The first part of that statement is no longer true. The Sigmoid No Threshold(SNT) harm model has been clearly defined, and is ready to go. And SNT works for both acute and chronic dose rate profiles, because it puts the time dimension and our repair processes front and center.