After looking into the experienced radiation for certain space journeys, I was wondering wether it was correct to state that the amount of biological damage is a function of the exposure time for a certain predetermined radiation amount expressed in mSv.

Where a shorter exposure time would imply higher damage due to the accute deterministic radiation damage as described in: https://parker.bidmc.harvard.edu/BiologicalEffectsRadiation.html

*I understand the stoichiometric damage would increase because the increased chance of e.g. cancer occurs earlier in a specific non-infinite life in the case of a shorter exposure period.

What I am not sure of is, how the pre-determined radiation would influence the actual consistency of the radation; I assumed for this question that the particle mass, charge and velocity would remain constant, where simply the amount of particles/flux would double.

If there are assumptions required to answer this question, or my understanding incorrect, please let me know. And if you care to explain, if true, how that actually happends I'd find it most interesting.

Kind regards,


As your link already points out, the regulatory assumption is that there's a "linear, no-threshold assumption". This means that doubling the time and halving the radiation intensity cancels out.

We know this assumption is wrong. In particular, we know this both empirically (statistically) and theoretically. We know the DNA double helix can be repaired if radiation damages one half, but the linear no threshold model presupposes that no repair can happen.

So, yes, spreading that x Sievert over several years will cause just as much direct DNA damage, but less damage after DNA repair is taken into account.

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    $\begingroup$ The relation is even more complex. IIRC, rapid, strong (near-lethal) doses are less harmful than previously estimated; weak exposure over lifetime (living in ore deposits area) is also nearly harmless. Moderate prolonged exposure (working with radioactives) is more harmful than the model predicts. One interesting example: small amounts of radioactive iodine lead to thyroid cancer by damaging DNA. It's treated with large doses of radioactive iodine, which kill the thyroid (including cancer) cells. $\endgroup$ – SF. Jul 28 '17 at 23:08
  • $\begingroup$ @SF: Agree. Regulatory agencies aren't stupid. They know that their model is wrong, that doesn't mean they have a better model. $\endgroup$ – MSalters Jul 30 '17 at 22:28

The linear no-threshold (LNT) hypothesis is certainly wrong in general, but the details are complicated and sometimes controversial. The following two articles are fairly recent summaries of the science, with conflicting interpretations. (They appeared back to back in the same issue of the same journal.)

Tubiana et al., "The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data," doi: 10.1148/radiol.2511080671, April 2009 Radiology, 251, 13-22.

Little et al., 2009, "Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May Be (Almost) the Best We Can Do," doi: 10.1148/radiol.2511081686, April 2009 Radiology, 251, 6-12.

There is quite a bit of evidence that low doses of radiation are good for various lab animals. This is called radiation hormesis. The empirical evidence in humans is not good enough to say anything about linearity, except in a few special cases (e.g., leukemia, which is clearly nonlinear).


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