The age of the earth and where I have been

Dear Reader,

I suspect that some of my regular readers have noticed that I have not been blogging for a while. The reason why I have stopped blogging for a while is that I am in the process of writing a book. I saw something on UK TV today which is an outrage, it is the idea that the earth is only about 6000 years old.

Now while freedom of thought and speech allows people to hold and express what ever ideas they have, even the outlandish and odd ones ! But the idea that the earth is only 6000 years old is deeply disturbing and clearly wrong !

I heard one of the young earth creationists being told by a geoscientist about radioactive dating of rocks and minerals. The creationist said something to the effect of “how do you know when the clock was zeroed”. I know that in Africa many years ago a natural nuclear reactor operated. Some of the fission products such as Tc-99 have decayed away. This suggests that far more than 6000 years has passed since the reactors were in operation.

I will leave it up to my readers to look up the half life for Tc-99 and work out how long it will take for 90 % of the Tc-99 to decay to Ru-99. Think of it as homework.

Cesium chemistry in Japanese soils

Dear Reader,

After having spent much of sunday in a fruitless search for a storage box for my garden tools, I get the chance to write to my beloved readers another blog entry. Now all along I had been making the prediction that the cesium would stick like glue to the soil and stay in the top layer. Some workers have examined soil samples and in a paper (Takeshi Fujiwara, Takumi Saito, Yusa Muroya, Hiroyuki Sawahata, Yuji Yamashita, Shinya Nagasaki, Koji Okamoto, Hiroyuki Takahashi, Mitsuru Uesaka, Yosuke Katsumura and Satoru Tanaka, Journal of Environmental Radioactivity, 2012, 113, 37-44) an examination of soil samples from the Fukushima area has been reported. In this paper it has been shown that the cesium is concentrated in the top layer of the soil.

Circa 70 % of the cesium is in the top 2 cm in the soil, while the iodine was more mobile. The good news is that the cesium will not enter ground water, further good news is that plants with deep root systems are unlikely to absorb much cesium. The bad news is that the cesium will be in the right part of the soil to enter grass via its shallow roots and the fact that the cesium is in the upper layers of the soil will increase the external threat due to gamma photons.

It is interesting to note that the Japanese may not worked out a sensible way to store the contaminated soil which is removed during the clean up of land. It has been reported that people are being required to store contaminated soil from cleaning up their own gardens on their own land. I think it would be better if industrial estates were used as places to store the contaminated soil while the government find a place to store the soil for the next 300 years.

I have spoken to my legal advisor about human rights, and my advisor told me that the right to have a safe environment could override the right to object to a waste store in a given town. I hold the view that if the waste stores are sited well away from homes and other places where the general public spend a lot of time, then it is OK to raise the dose rate in the waste store. The waste store should be designed to avoid releasing cesium into the environment and the construction of the waste store should be done in such a way that it does not increase the dose rate at the edge of the site. I think that the reference dose rate for the latter point should be the dose rate at the edge of the site before the clean up is done.

If the dose rate at the edge of the site is 2 microSv per hour, then this will give a person a dose per year of 17.5 mSv which is a big dose for the general public. But if the dose rate at the same spot was 2 microSv per hour before the clean up which generated the waste which will go into the store is conducted then the clean up will have a neutral effect at the edge of the waste store but will have a good effect on the majority of the land.

I may do some calculations on the subject if I get time in the near future.

Muons and Fukushima

Dear Reader,

One of the great problems right now is working out where the fuel in the damaged cores and the ponds is, and in what condition the fuel is in. We can take for granted that the fuel which was in units 1, 2 and 3 has been damaged by overheating. But the state of the fuel in the ponds was a bit more of a mystery to us.

After clearing the rubbish out of the pond at unit three it has been possible to inspect the pond, the pond is frankly in a bit of a mess. But the fuel seems to have escaped serious damage. Photographs have been taken of the fuel racks in the pond and it does not look like there has been been any dire melting or explosions in the pond.

I have seen that some samples have been taken from the pond at unit four to allow them to be examined (these were samples of unused fuel which were being stored in the pond at the time of the accident). The work so far suggests that the fuel in the pond is in good condition. This suggests strongly that no nuclear explosion occurred in the pond.

The other great question is the state of the reactors. I saw something interesting recently, it is a sensing system based on cosmic rays (muons). This looks to me like a good method for finding the fuel inside the damaged reactors without having to get up close and personal with the stricken reactors.

Another thing which needs to be done is for society to recover from the accident, I have seen some advice from the IAEA on the subject of remediation of the contaminated land (outside the nuclear reactor park). This document might be of interest to some of my readers. It includes a discussion of the cleaning of different types of areas which include farmland. As I predicted it does include the question of deep ploughing the land.

Palomares and the H-bombs

Dear Reader,

Now some doomsayers may have tried to tell you that once radioactivity appears in soil that you should give up all hope, also on the otherhand some false prophets of insincere reassurance will just tell you to stop worrying and that “everything will be OK”. My advice is not to trust either of these two false friends.

The story of the air crash which involved four H-bombs has popped up again, the BBC report that the local people in Spain are fifty years after the air crash unhappy about what has been done.

The BBC report suggests that the local farmers have a problem getting a good price for their produce at market. I would like to point something out.

The plutonium in the H-bombs would have been in the form of the metal, during the accident this would have been burnt into plutonium dioxide. Now the thing to note about plutonium dioxide is that it is very hard to dissolve in acid, also it is not mobile in soil. Any plutonium which was in a water soluble form is likely to have bonded to the soil minerals thus making it impossible for plants to absorb it via their roots.

M.I. Sheppard and D.H. Thibault, Health Physics, 1990, 59, 471 to 482 gives the binding constants for most metals to the four common soil types. It lists for plutonium the following Kd values.

Sand, 150 L/kg

Loam, 1200 L/kg

Clay, 5100 L/kg

Organic, 1900 L/kg

This means in a bucket containing a mixture of clay type soil and water that the plutonium content of the soil (Bq per kilo) will be 5100 times higher than the plutonium content of the water (Bq per litre).

Hence when 1000 Bq of plutonium is added to a litre of water mixed with a kilo of clay type soil, then the soil will absorb 999.8 Bq of plutonium while 0.2 Bq of plutonium will stay in the water. This calculation is for a static batchwise experiment but it will help experts in the field make predictions about the mobility of plutonium solutions in soil.

Another good bit of news is the fact any plutonium dioxide in the dust will not be well absorbed if it is swallowed (dust on the surface of the food), so orally the plutonium dioxide is not a great threat to life and limb. If you were to swallow a well sintered particle of plutonium dioxide it will pass unchanged through your digestive system.

However plutonium dioxide in the lungs is very dangerous to a persons health, I think that a key thing to do in Spain is to keep the plutonium in the most contaminated soils from entering the air as a dust. I think that the ban on building, farming or walking in the contaminated area is a good idea. But I think that it might be a good idea to pour concrete or asphalt onto the worst hot spots to try to fix the soil to keep it from becoming mobile again.

One of the problems with plutonium is that the colloidal particles of clay can make the plutonium mobile, while the plutonium does not move freely through the soil in aqueous solution the colloidal particles can move through the cracks in the soil. Thus sealing the soil would help to stop the plutonium from reaching the surface again in the form of dust.

Bob and his nuclear “facts”

Dear Reader,

It has come to my attention that a person calling themselves Bob Nichols is publishing “news” on a web site. Being a person with some knowledge and understanding of nuclear matters I thought I would take a look.

Bob as we will call him is making the bold claim that nothing is being done to mitigate the accident or clean up the site. I think that this claim is totally false, I am well aware that waste water on site is being contained, treated and then reused to greatly reduce the amount of radioactivity which is released into the ground and the sea.

Bob has claimed that even industrial robots can not cope with the radiation levels on site, I think that this is deeply wrong. A friend of mine has been on the site and he only got a small dose. I would like to know what location he is talking about. In a normal nuclear plant there are some areas which are off limits to humans for radiation safety reasons during normal operation. After shut down it is possible to enter some of these areas within minutes. There are areas at the Fukushima site (inside the reactor pressure vessels and in some areas of the containments) which might be off limits for humans for many years but I suspect that the vast majority of the plant buildings can be entered by either humans or robots.

He suggests putting the reactor cores under water, this is being done but as some of the reactors have leaks it is not a simple matter. His text suggests that no work has been done to fix the reactors is misleading, while fixing these reactors is not a simple matter the work to fix the site has already started.

He writes about the “evils of uranium”, but I would like to point out that small uranium particles are unlikely to stay in the human body for long. Uranium oxides tend to dissolve in water when oxygen and carbon dioxide are present. The uranium will then be lost via the urine. If he wants to think about any radioisotopes then he should be thinking of the shorter lived beta/gamma fission products which were released back in march 2011.

He also fails to note that the amount of radioactivity in the reactor site is now far less than it was back in march 2011, radioactivity in a nuclear reactor’s fuel tends to decay away greatly after the plant is shut down. He also makes some rather far fetched claims about chernobyl claiming that 30 % of the core was released, trust me only about 3.5 % of the fuel at Chernobyl was able to leave the plant. If Bob had read either an undergraduate text book on nuclear chemistry (I can name two books which would tell him this) or even (dare I saw it) wikipedia then he would have found that the release of radioactivity from a damaged nuclear plant is controlled by the boiling point of the main form of the element.

While iodine, tellurium and cesium are mobile, the real nasties such as plutonium and strontium are much less mobile (thank goodness for small mercies). His suggestion of using atomic bombs to cause a landslide to make the reactor site fall into the sea is very silly. I sincerely hope that nobody ever tries to do this !

Alpha decay part II

Dear Reader,

As I sit typing in a railway carriage on the way home sitting near a young lady who is sporting a ”Nuclear power no thanks” badge, I sit here thinking about nuclear processes hopeful that the young lady does not notice what I am typing.

It is interesting to note that one of the physical effects which regulate the reactions which go on inside the red sun of the “Karnkraft nej tak” badge are the electrostatic forces which oppose fusion. The same forces have an effect on the reverse reactions (alpha emission, fission and all the cluster emissions which come between those two extremes).

Now since I had a rather short hair cut recently I can not demonstrate electrostatic attraction using a comb dragged through my hair. I will let you try that at home, also I do not have a cat to rub on a bit of plastic so I can not use that either.

But back to nuclear processes and electrostatics, to a first approximation the atomic nucleus can be treated as a charged sphere. The size is given by the following equation.

R = R_o (A)^0.3333

Where R_o is equal to 1.2 x 10^-15 m, while A is the total number of nucleons (the sum of the number of protons and neutrons) in the nucleus.

So radius of a plutonium-238 nucleus is 7.44 fm, while its daughter (uranium-234) has a nuclear radius of 7.39 fm while an alpha particle has a radius of 1.90 fm. Using these radii we can calculate the energy required to push the alpha particles from plutonium-238 back inside the nucleus.

To do this we need a few more equations from A-level physics.

As the capacitance of a sphere is given by

C = 4 π ε r

Where ε is equal to the permittivity of free space which is 8.854187817620 × 10⁻¹² F m⁻¹ or just 8.85 × 10⁻¹² F m⁻¹

We can use this to estimate the electrostatic energy required to hold an alpha particle on the surface of the uranium-234 nucleus. As soon as the alpha particle is taken out of the nucleus it is no longer being strongly bonded by the very short ranged but very strong attraction between the protons and neutrons in the nucleus (the strong force). So suddenly only the electrostatic forces apply to the system (the weak force and gravity are far far weaker)

This energy (28.5 MeV) is far greater than the decay energy of the plutonium-238 (5.593 MeV), as a result the alpha particle, what has to happen is that the alpha particle must overcome this energy barrier before it can leave the nucleus of the atom. What happens is that by quantum tunneling the alpha particle leaves the nucleus of the atom and then goes on its merry way. Here is a graph of the electrostatic energy in MeV vs the distance from the centre of the nucleus for both the alpha particle and the carbon-12 nucleus.

Electrostatic energy as a function of distance from the centre of the daughter nucleus

When the calculation is repeated for the loss of a carbon-12 nucleus from plutonium-238 to form radium-226 then I have estimated that the energy barrier is 74.5 MeV, while the decay energy is now higher at 22.5 MeV you now have a bigger barrier and some other things also help slow down the release of C-12 nuclei.

I hope to get onto these things later.

Why does alpha decay occur

Dear Reader,

I bemoan the fact that few text books explain why things happen, many text books are content to tell you what happens when they discuss radioactivity but are not able to or willing to explain how it happens. Now some time ago I explained the driving force behind beta decay, today we are going to start to deal with alpha decay.

Alpha decay is when the nucleus of an atom emits the nucleus of a helium-4 atom, now I am sure that some of the smarter readers will have asked (or be considering) the question of why is it always a helium-4 nucleus. Now I have to tell you that helium-4 has a special high stability.

I know as human beings we like to think of ourselves as more than just the sum total of our parts, while one recent estimate suggests that a human body is only worth $ 4.50 the EPA think that a human life is worth $ 9100000. I do not want to get into a debate about the morals or value of human life but it is clear that if we use the EPA estimate that a human is worth much more than the scrap value of the typical human body.

In the same way a group of neutrons and protons which make up an atomic nucleus has a mass which is often different to the sum of the mass of the free nucleons. This is because when they bind to each other some energy is lost. because energy and mass can be interconverted (E = mc2) this means that the mass is changed slightly. In general the more strongly the particles are bonded to each other the lower the energy of the nucleus and the lower the mass is. Now carbon-12 is used as the zero point for many things, the mole is defined as 12 grams of carbon-12 and also it is used as a zero point these nuclear calculations.

If we look at a graph of the excess energy which is due to the extra mass which is associated with taking protons and neutrons out of a very stable system into a less stable system divided by the number of nucleons in the nucleus against the mass of the nucleus then we get a funny looking graph. It has a general downward trend over the mass range 1 to 30 but there are some masses which are extra stable. For this graph I have used the stable nuclides (stable isotopes) except for two points which we will get onto later.

These are 4, 8, 12, 16, 20 and 24 which are magic numbers. It is important to note that these nuclei have even numbers of protons and neutrons. We will get onto magic numbers again some time in the future. Here is the graph below.

A graph of excess energy (keV) per nucleon against the mass of the nucleus

Now I hope that we should be able to see that the helium-4 nucleus is a very stable small fragment. We will continue soon with alpha decay, but before I go you might find this link useful. It is for some lectures on the nuclear physics of radioactive decay.

Dose estimates

Dear Reader,

I have found an interesting document which is on the subject of the atomic bomb tests done years ago down under in Auz. Now before we get going, I do not want to get dragged into a debate regarding the rights / wrongs of nuclear bombs or the moral issues associated with bombs and their testing. What we will be dealing with here is just the reported facts.

A document has been released some time ago by the Australian government which gives estimates of the radiation doses which Australians were exposed to as a result of the bomb tests there.

What is interesting is that the doses are quite low, if the data in the document is true then the vast majority of the Australians were exposed to low doses of radiation. But before we look at the dose estimates lets look at what the current UK limits are.

The 1999 law (1999 Ionising Radiations Regulations) set the following yearly limits

20 mSv Radiation worker

6 mSv Trainees aged between 16 and 18

1 mSv The general public

While the 1980s Ionising Radiations Regulations set the upper limit for a radiation worker at 50 mSv per year.

If we look at table 7.27 in the report from down under we will see the results.

A. 78.9 % of the people involved had doses which were lower than the current UK limit for the general public (1 mSv). I hold the view that this low dose of less than 1 mSv is nothing to worry about.

B. Only about 4 % of people are in the above 20 mSv group, these are doses which would break current UK law for a radiation worker.

C. Very few people (19 people, 0.2 %) are in the above 50 mSv group. These doses are above the yearly limit in the 1990s for radiation workers.

D. About 6.3 % of the people had unknown doses, in some ways this is the most interesting and more worrisome group. Most of these people were in the Royal Australian Air Force.

What would be very interesting is if an alternative set of dose estimates or measurements exist from the same bomb tests. By the way if dose estimates get you angry, do not get mad at either me (I did not make the dose estimates) or someone else but do feel free to point out other dose estimates which you think are more trustworthy.

The horrors of polonium

Dear Reader,

I read recently how it has been suspected that Yasser Arafat may have been murdered using polonium-210. This claim that polonium-210 has been used for another murder made me think for a moment about radium-226 and its daughters. I can tell you that polonium-210 is one of the radioisotopes which most radiation workers love to hate. Polonium-210 and radon-222 are both alpha emitters which are able to diffuse through rubber and plastics. This makes them more mobile than plutonium is. When you write plutonium you have to be careful to understand that not all plutonium is born equal.

Plutonium-239 is a long lived alpha emitter which has a moderate activity per gram (and emits few gamma photons and neutrons), pellets of plutonium dioxide which have been sintered are solids which are clean to handle inside a glove box. I used to work with a nuclear fuel chemist (John Pecket) who used to make plutonium dioxide fuel, MOX and some very werido fuels. He told me how Pu-239 was a nice radioisotope to work with, while plutonium-238 was a nightmare in comparison. Pellets of plutonium-238 dioxide emit so much heat that they tend to glow red hot, they also tend to emit plenty of radioactive dust. He told me that if you place a Pu-238 pellet in a glove box then within days every surface in the box will be crawling with radioactivity. But even plutonium-238 will not pass through a neoprene glove. Thus at least it will stay inside the glove box, the worst radioisotopes I know are alpha emitters which are very mobile.

You can think of low LET radiations (beta / gamma) as being a bit like a goblin with a big stick. This horrible little monster will chase you around the house before trying to hit you with the stick, it can do you some harm but in some ways there is something worse. For alpha imagine a big bath filled with boiling hot jam, while the bath might not be able to chase you, if you fall in then you are going to get a far worse injury. The alpha is very short ranged but if it does get you then it can go a lot more harm than the beta or gamma.

The super mobile alpha emitters are like a evil goblin armed with a steel bucket of boiling hot jam, this evil goblin is also equipped with running shoes or roller blades so it is able to chase you before throwing the boiling hot jam on you. In short this ones combine the some of worst features of alpha and the more long ranged nasties. The only way to stay safe from this wicked goblin is to lock all the windows and doors of the house and keep him sealed outside, with some luck he will die of old age (become weaker when he decays away) before you have to go outside to mow the grass.

OK time to return from analogyland back to reality

With these mobile alpha emitters special extra precautions are needed to keep them contained, for example with polonium-210 some people have been known to put a glove box inside another glove box to increase the thickness of plastic through which the polonium needs to diffuse. Also for radon-222 some people trap the radon on an absorbent material rather than allow it to wander freely around their glove box.

I feel that many members of the general public have a great misunderstanding of what it is like to work with radioactivity.

I have heard of radiochemists being asked “do you glow in the dark”, the short answer is “no”. While the long answer is that is close to impossible to get sufficient contamination on you to make you glow, the only creditable cases I have heard are of some of the radium dial painters who painted their bodies with the radium based glow in the dark paint.

A paper on the legal battle for compensation can be seen here.

I think that the worst aspect of the radium dial industry was the fact that many workers would lick their brush to get a better shape tip. If you look at this document you will see that radium-228 may have been the real villain rather than radium-226. I hold that the pre 1926 two radium dial painting industry could well be the worst part of the radioactivity sector. It is interesting that it appears that only 20 % of the radium which is taken orally is retained in the human body.

Also according to Norris et. al. as cited in this report the human body is quite good at eliminating radium from its self. Some years ago in America as part of a crazy attempt at curing mental patients some people at Elgin state hospital were injected with radium. Using the data from these medical treatments it was possible in the 1950s to work out a mathematical model for the retention of radium in a human. I have rearranged this equation and used a standard bit of maths which allowed me to calculate a biological half life for radium of only 1.33 days.

This value is rather shocking to me, as a chemist I have always been taught and held the view that radium, strontium and lead are calcium mimics which have very long biological half lives because they become part of the bones. I suspect that if radium is injected or swallowed that only part of the radium which enters the blood stream will end up in the bones. While the biological half life of the radium in the bones may be very long, the biological half life of the radium in other parts of the body will be much shorter.

As a result the half life will appear to change if you consider the whole body after a single intake of radium, I suspected that the biological half life will appear to become longer with increasing time after the intake of the radium. Reading more of the report I found that Norris in 1955 published a mathematical equation which predicts how radium is slowly lost from a human. An article in Nature (March 1969, 221, 1059) suggests that the biological half life for radium in humans (long after the intake) is between 10 and 36 years.

The review of radium in humans points out that Dudley in the 1960s suggested an experiment using short lived radiotracers, the experiment was done using humans and it was found that only 20 % of the radium in a mock dial paint was absorbed when it was taken by mouth while only 0.02 % of the thorium in the dial paint was absorbed.

Another interesting point from the review is the fact that if radium-226 sulfate is deposited in the lungs then 25 % of the radon formed can be exhaled, while if radium-226 is deposited in the bones of a person then 60 to 70 % of the radon can be exhaled. This is an interesting difference, which I suspect is due to the difference in the mobility of radon in bone tissue and radium/barium sulfate. I may well get back to this point later.

Radon and your lungs

Dear Reader,

I suspect that the next post is going to make people hopping mad with me, it is about the idea of using radon-222 as a medical treatment. Now before we go any further I would like to point out that I have no vested interest in the radon industry. Nor do I have a personal grudge against the radon therapy industry.

Now we will begin, I come from a school of thought that holds the view that radon-222 is horrible, this school of thought is the vast collection of people in the radioactivity business who live to hate radium-226 and its daughters. Rather than being a nice playful radioisotope radium-226 is considered to be a nasty so and so. It is an alpha emitter which forms a volatile daughter which also emits an alpha and then attaches its self to dust and smoke particles. In this way it creates a horror of sticky alpha active bits which stick in the lungs and do you a lot of harm.

By comparison plutonium-239 is a much nicer radioisotope to work with, it will not diffuse through gloves or fly through the air with great ease.

Some time ago a student (Hanna) at Chalmers was starting a PhD in radium chemistry, and she had a problem. She needed to work in a glove box. The state regulator were not willing to license the work unless it could be shown that the radon was trapped rather than being dumped up the stack. As an inorganic chemist I got involved, I applied what I know about zeolites and xenon to the problem and I then told the young lady of the joys of silver exchanged zeolite. This then resulted in a paper on radon and silver (Hanna Hedström, Mark Foreman, Christian Ekberg  and Henrik Ramebäck, Radiochimica Acta, 2012, 100(6), 395). We will keep the radon and silver story for another day, back to radon.

I checked the yearly intake limit for radon-222 and for inhalation it is 10 mCi when it is pure, but it is normally encountered with the daughters present. The limit when the daughters are present is 100 μCi (0.1 mCi). For comparison polonium-210 (half life 140 days) has a limit which is lower at 600 nCi per year, I would reason that the longer effective half life of the polonium in a human is likely to be responsible (at least in part) for this difference.

So I went and looked for a short lived noble gas, so I looked at the limit for xenon-133 (5.2 day half life), while there is no ALI for this isotope there is a DAC of 100 nCi (0.1 μCi) per litre. The DAC is a derived air concentration which is the limit for the air which you can breathe for 40 hours a week for one year.

I checked the DAC for radon-222 and it was much lower at 0.00003 μCi per litre (when the daughters are present), which works out as 0.03 nCi per litre or 3 pCi per litre. Now it should be clear to you that the USA’s goverment (NRC) hold the view that radon is very much worse for your health than xenon-133 is.

Even if we use their DAC for radon when the daughters are absent (400 pCi per litre) it is a lot worse than the xenon. We need to ask ourselves why.

Lets start by considering the decay energy, the xenon isotope is a mixed beta / gamma emitter which has an average beta energy of 100 keV. If we ignore skin exposure for a moment and only consider the beta dose to the lungs then 100 nCi (3700 Bq) of xenon-133 in air will deliver 370 MeV of energy into your lungs per second.

The alpha decay energy of the radon is 5489.52 keV, 14.8 Bq (400 pCi) of radon-222 will deliver 81.244896 MeV of energy into your lungs (call that 81.2 MeV) which is less energy. But alpha (α) is a high LET radiation which is considered (on the basis of energy delivered) to be 20 times more harmful to your cells than beta (β) or gamma (γ) radiation. So the effect of the radon on the lungs at the limit will be 4.4 times as harmful as the effect of the beta decay of the xenon.

The biggest problem with the radon is that it forms solid radioactive daughters which emit alpha particles, these daughters can lodge in the lungs where they continue to deliver radiation to the lung tissue. The atoms of radon are likely to come out of you when your breath out (some will diffuse into your blood and then go into the fatty tissues). So as a result you can imagine that radon is considered to be a grave threat to the lungs, it is worst when smoke or dust is present.

I recently spoke with a medical doctor from the Czech republic who runs a radon bath treatment site. He told me that in the Czech Republic that inhalation therapy was banned, he told me that one reason was worker safety. He told me that a patient is immersed in a bath of water (circa 5 kBq per litre) in a air conditioned room. The person is kept very still in the bath, I imagine that by avoiding splashing and stirring of the bath that the rate at which the radon is transferred into the air is reduced.

I also imagine that the Czech treatment room is a damp place which should reduce the number of dust particles per litre of air, this dampness will reduce the likelihood of radioactive dust entering a person’s lungs. I think that a bad environment for radon is always a dry and dusty place, the addition of smoke to radon containing air will always make it even worse. I have horrible visions of a uranium miner having a smoke in the mine while driving a poorly maintained diesel truck in the mine. Both the diesel and the tobacco smoke will increase the harm which the radon will do to his lungs.

A better situation would be the same miner now wearing a dust mask driving a well maintained truck in the mine. While I hold the view that it would be best if the miner gave up smoking totally, if he (or she) abstains from smoking in the mine then it would very good for the worker’s health.

So at least in the Czech Republic some steps have been taken to reduce the amount of lung damage.

Now from what I have read so far it is clear that radon therapy does bring with it a risk. I am sure that the supporters of radon treatment and others will point out that no medical treatment is totally without risk. I agree fully on this point, I have never heard of a medical procedure which is perfectly risk free.

But for a medical procedure to be justified, the benefits must out weigh the risks and costs. I will move onto benefit vs cost later.