absorbed dose etc

[John Futter]

John Morris asked what /why is fatal around 4Sv

As the absorbed dose goes up in the short term, damage is being done to sensitive tissues.
Doses of over 1 Sv start to make tissues like the intestinal lining catastrophicly disintergrate.
other sensitive tissues include the marrow (makes red blood cells) skin, and lymphatic system
So even small doses will affect these tissues but only a few cells being destroyed- the body then of course repairs the damage over time.
However cells that were dividing at the time are vulnerable to DNA strand modification that can and does make some of these cells cancerous.

the ALARA (as Low As Reasonably Achievable) principle is still what is used today
My max dose per 2 month period as a radiation worker is 5mSv ---very big questions are asked if I get anywhere near or go over this threshold.

with all of this distance is your friend the further you stand from the source , the lower the dose by the inverse sqaure law

[John Morris]

Thank you for the response, but this doesn't really answer my question. So you're saying is someone got 4Sv over say half their life, it might be spread out enough that it doesnt kill them at 50? I'm still really curious aroximately what dosage over what time interval is considered lethal.

[prestonbarrows]

To put it simply, ionizing radiation harms you by knocking out sections of DNA strands. DNA naturally repairs itself. It actually works exactly like a RAID array in a computer, each section has a 'mirror' image which can be used to reconstruct any faulty sections. If the DNA heals itself before it is copied, the radiation event has essentially no health effects. If the cell tries to replicate before the DNA is patched or multiple damage events damage both a DNA section and its 'backup' simultaneously, the daughter cells will not form successfully or will include mutations. This is why cells which divide rapidly are most affected by radiation; hair, the gut, bone marrow. It is also why chemotherapy preferentially damages fast-splitting cancer cells.

There are two main categories of health effects due to ionizing radiation, known as stochastic and deterministic.

Stochastic effects are those which are governed by chance and statistical probabilities. These are generally associated with very low doses over extended periods of times like months or years. There is no well-defined dose threshold where effects are guaranteed to be or not be seen. Here, radiation events in DNA happen at a much lower rate then they are repaired. Some small, random, number of cells will duplicate before healing or have both DNA pairs damaged simultaneously leading to some probability of health effects. It is hard to impossible to conclusively say the cause of developing colon cancer when you are 40 to that time you got a chest x-ray when you were 16 or just natural random chance with age. However, looking at a large sample of people, you can build up statistics. For example, cigarettes contain radioisotopes known to increase cancer rates, but you are not guaranteed to develop any cancer even if you smoke 3 packs a day for 50 years.

Deterministic effects have a definite threshold dose and are progressively more severe with increasing dose levels. These are usually due to receiving a large dose in a short period of time. Examples include skin burns, cataracts, destruction of gut lining and bone marrow etc. For example, once you get into the 10 Gy type doses seen near atomic blasts or reactor accidents, you are pretty much guaranteed to die. You die from failure of those fast-replicating cells in the gut, blood, etc which need to be replenished every 24 hours or so.

[Chris Bradley]

A mention might be made of the type of radiation. It is 'absorbed dose' that is relevant. Some radiation zapping into soft bodies is more readily absorbed, some isn't and flies on through, or stops short at the skin. Sv is intended to represent 'biological effect', but it is still an approximation of factors from measured radiation quantities. So 4Sv over a lifetime could mean/be interpreted in different ways.

I suspect [do correct me if I am in error] that folks who go on sub-bathing holidays every year will probably receive Sv worth of UV-radiation to their skin (the largest single organ of the body), but that we have evolved to tolerate this form of irradiation, up to the point of tolerating typical life-time exposures. In fact, AFAIK, the human body can receive higher doses of gamma radiation too, than X-ray radiation, because we have evolved to tolerate a gamma exposure that gets through to ground level but not the lower energy X-ray photons that are absorbed in the atmosphere. Yet a typical calculation of 'Sieverts' from measured ionisation levels may overlook these finer details.

[Carl Willis]

John, the mean (50%) lethal dose for acute whole-body exposure is around 5 Gy and leads to death within a month or two after exposure via death of the hematopoietic (blood-forming) system. This assumes the radiation can penetrate the body and irradiate the bone marrow. There are other awesome ways to die from acute radiation depending on the anatomical target and the dose, but this is generally the most important because of the relatively low doses involved. Radiation damage is repaired in the body eventually. Regarding the endpoint of death by the hematopoietic syndrome, the effects of radiation exposure in the long term (weeks, months, years) are not cumulative. What the "safe" dose rate limit for humans is doesn't seem to be too well established by experience, but in rats, up to 0.45 Gy / day is tolerated by the red blood cell system (Hall, Radiobiology for the Radiologist, 5th ed. chap. 5). To be clear, you'll still have serious health problems if you work in such an environment routinely: sterilization for men is a real possibility, as are cataracts. And, of course, the risk of cancer in the long term skyrockets. In the nuclear hobby, acute radiation syndrome is far down the list of concerns to the point of being a ridiculous preoccupation for most projects, and cancer is at the top of the list. Most of the radiation protection principles (e.g. the ALARA principle) that get mentioned on this forum relate to the risk of cancer, and that is what our people should concern themselves with.

-Carl

[prestonbarrows]

The direct measure of energy that radiation deposits in matter is the Grey (Gy). One joule of energy per kilogram of matter. It is an engineering unit mostly.

The location on the body is also very important. For example, a large dose to your hand will have relatively little harmful effects compared to the same dose to your chest. To take this into account, the 'effective dose' is measured in units of Sieverts (Sv) or rem. This is also in joules per kilogram but is weighted according to effect on body parts. This is more meaningful when talking about health effects.

It can get complicated and hand-wavy pretty fast though since the specific form of radiation (neutron, alpha, gamma etc.) as well as the specific energy spectrum also changes the exact health effects.

A semi-wild guess for the setups I have seen on here is probably about 1-10's of mRem/hr for neutron and photons at closer than a meter from the reactor.
For some perspective, the NRC regulation for annual cumulative dose for radiation workers is 5000 mRem per year maximum.

[Chris Bradley]

It might also be noted, in addition to the comments above, that directing large doses to specific, local parts of a body is also a treatment for cancer, rather than necessarily being a cause. I have no first hand knowledge of these things, but as far as I am aware, up to 36 Gy is a typical radiation therapy dose for lymphoma, delivered in 2 Gy doses. This is the J/kg value, on a specific target, and not a whole-body exposure that would certainly be fatal at these dose concentrations if it represented a whole body dose.

[Richard Hull]

All the above specifics and provisos are sage and true. Each case is its own separate study and specific data would be needed to form a possible or probable outcome. What kind of radiation, whether whole body or targeted, the specific particle energy, whether accute or cumulative over what period with within what the high and lower limits over time are, etc......Its all a crap shoot.

Carl probably put it best. Unless you are working in some whacked out amateur nuclear hobby activity like very high voltage x-ray "play" (very, very bad) or ingest some nuclear material like, god forbid, some stupidly removed radium paint from a self luminous object, you are totally safe from death or even serious injury.

Most amateurs are serious, conscious and mindful of what they are about, have read extensively and arm themselves with a minimal amount of radiation detection gear. By simple experiment in a controlled environment, keeping in mind to limit exposure regardless of how little radiation is about and keeping the blessed friend of distance between you and your efforts. The idea of radiation damage or death is a true non-issue. If you take all the preceeding precautions and do not get involved to the level of many hours of exposure at close range for many days over a number of years, even cancer related radiation effects are so low as to not be considered.

It is good that these sort of recurring discussions occur. The proper respect for radiation and its safety are much like any other hazardous endeavor, like firearm handling and shooting. Death becomes an ever more remote and less likely possibility if you properly train for the endeavor and keep the seriousness of the effort ever to the fore.

Most in this fusor game will rely on this website for information and if very lucky will actually do limited fusion and move on to cars, women and life, in general.

Only the truly stupid, uread and uncaring are capable of the sort of buffoonery needed to really kill themselves.

Richard Hull