Americium

While the general public get both excited and concerned about plutonium, some of the other actinides are equally important. Americium because of its higher stability of the +3 oxidation state has chemistry which is very different to plutonium.

I have seen predictions which suggest that the americium-241 either released from Chernobyl or formed in the environment as a result of the beta decay of the plutonium-241 released by the accident will become the radionuclide of greatest importance near Chernobyl after the cesium-137 has decayed away.

Fukushima will be a different matter as far less of the americium or plutonium in the fuel was released during the accident.

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.

Different reports on the same subject

Dear Reader,

In recent times we have had the first serious nuclear accident of the internet age, I am not sure why it is the internet age. The ‘ages’ were named after the materials used to make typical tools.

Stone age : Stone axes

Bronze age : Bronze swords made of a Cu / Sn alloy

Iron age : Iron ploughs

Then later the industrial age came, then we had the atomic age, the space age and then the internet age. My big problem is that for the majority of tools which we use in our lives we do not use atomic (nuclear), space or internet tools to do things like open cans of dog food or dig our gardens. For opening pet food cans and tending the vegetable patch I still use tools based on iron (steel).

While a nuclear powered digging machine or a space satellite which zaps the weeds might make life a little more easy (assuming you can afford to buy it) I think we will be sticking with steel spades and can openers for the forseeable future.

But I think that we do need to move onto something else. Recently a series of different reports have been published about the Fukushima event in Japan. Greenpeace have published a report as have the Japanese government and also Jon. M. Schwantes et. al. in the journal Environmental Science and Technology (DOI: 10.1021/es300556m) have published a paper in which they use the isotope signature of the accident to probe the event. In common with many things it is not always possible to make a direct measurement from samples which can be taken by hand, instead other measurements were used.

Now before we get going I will saw that it is impossible to have a single report which deals with a complex event in perfect detail. The problem is that if we examine one aspect of an event in great detail (using a state of the art study which includes as many details as possible) then this report is likely to become very large and close to impossible to read. If we then couple together a series of sections with a similar level of detail on all the different aspects of the event then we will end up with a wall of words which is impossible to comprehend.

Greenpeace have written about a recent Japanese report that

“The lethally high levels of radiation still present in the damaged reactors have prevented committee members from conducting a full analysis. They should be given all the time they need to complete their investigation.”

While the Japanese writers of the big government report stated that their mandate was

1. To investigate the direct and indirect causes of the Tokyo Electric Power Company Fukushima nuclear power plant accident that occurred on March 11, 2011 in conjunction with the Great East Japan Earthquake.

2. To investigate the direct and indirect causes of the damage sustained from the above accident.

3. To investigate and verify the emergency response to both the accident and the consequential damage; to verify the sequence of events and actions taken; to assess the effectiveness of the emergency response.

4. To investigate the history of decisions and approval processes regarding existing nuclear policies and other related matters.

5. To recommend measures to prevent nuclear accidents and any consequential damage based on the findings of the above investigations. The recommendations shall include assessments of essential nuclear policies and the structure of related administrative organizations.

6. To conduct the necessary administrative functions necessary for carrying out the above activities.

I have highlighted in bold the part which interests me most as a chemist, the Japanese panel  also stated that they would not undertake a series of actions which included.

“investigations that would require on-site visits to reactors with dangerous levels of radioactivity.“

My understanding is that they have chosen quite wisely to avoid either waiting for a full examination of the reactor sites (which will take decades) or rushing into a dangerous area to gather data. My view is that samples collected from outside the reactor buildings, eye witnesses from the site, data from those sensors inside the plant which continued to work together with details which can be obtained from undamaged BWR plants. I see the problem of the clash of two cultures.

The scientific and engineering communities are seeking to get the best quality report which is correct, the speed of publication of the report is a secondary factor. In these communities it is better to delay the publication of a report if the delay will allow the quality to be improved. Also the answer has to be traceable, the computational methods used, the persons who did the work, the devices used and the samples used all have to be documented clearly in this type of work.

On the other hand the newspapers and many of the green NGOs (like Greenpeace) are aiming for speed of publication as their highest priority. In these reports the things which were used to produce the final answer are often not as traceable. What is interesting is when both the rapid publication of people like Greenpeace agrees with the slower and more thorough investigation which goes into the official reports. I would say that it is important to avoid being caught by statements by “The findings of both these reports match closely with the Lessons
from Fukushima report released by Greenpeace in February” in a trap where you think that both reports are the same.

The Greenpeace report has some similarities with and some differences from the Japanese government report, but I would say that neither report deals at length with the containment chemistry and the radiochemistry of the accident. I am unsure of what Greenpeace would be hoping for in an extended report which might be written in 20 years time when the insides of the containments have been fully explored. I think that a main part of the final purpose of the examination of the reactor buildings will be to determine what chemical and physical effects occurred during and after the accident.

The Greenpeace report is more dominated by photographs which relate loosely to the event, I am unsure why it is important in a report of 52 pages to include devote ten pages to photographs of things like wrecked buildings with very little explanation of what is going on in the photograph. For example on page 28 a whole page is devoted to a person holding a pair of radiation meters in a field. There are a series of important questions which are not answered in the text such as “what level of radioactivity has the person found in the field”, “what is the testing protocol” and “what is the date of the measurement”. I hold the view that the report should be written in a way to make these things clear rather than forcing the reader to dig deeply in a series of documents for the answers.

The Japanese government report is much more text and far fewer pictures in the main body of the text than the Greenpeace report, towards the end a lot of data is presented in appendix in the form of graphs. These graphs include things like the fraction of the public who were aware at a given time of some key events. While graphs might be less eye catching than photographs, I hold the view that a well labeled graph is a better way to communicate an idea to another person than a photograph which has little if any commentary in the caption.

The problem I see is that if I show 100 people a photograph with very little writing in the caption then a danger exists that each of the 100 people will interpret it in a different way, while in recent years there has been a backlash against science made by people like the postmodernists. Some people value their “feelings” above everything else and express the view that a series of different interpretations of the same evidence are equally valid, I have to disagree. Firstly there is no such thing as an impartial observer (Read the section of the Alan Chalmers book “Whats this thing called science” on induction for more details).

Secondly some interpretations of evidence are deeply wrong, for example if I was photographed by an alien (who has no knowledge of pet ownership) while walking my dog in the forest the aliens might think (based on the photograph) that I am some sort of cruel person who enslaves small white animals and chains them up. While this interpretation might fit the evidence in the photograph it is deeply flawed.

As a result I think that a report which is dominated by photographs which do not have a clear set of captions explaining what is going on is not a good report. But a report which uses the same amount of space for graphs and figures which bear captions which explain all the key points does communicate in a better way with the reader.

The comment that Greenpeace made of “The lethally high levels of radiation still present in the damaged reactors have prevented committee members from conducting a full analysis. They should be given all the time they need to complete their investigation.” suggests to me that Greenpeace want the Japanese government report to be a comprehensive report which deals with all aspects of the event. It might even be understood as Greenpeace suggesting that their report is more comprehensive.

I have read both reports and I can say that some rather important things are missing from both reports. Neither report mentions the transfer of cesium from soil to plants and then to humans via the food supply. I hold a view that this is an important issue, depending on the soil chemistry, the biology of the food production system and what countermeasures are taken the cesium in the diet is either going to be a small issue or a large issue. Also neither report gives a detailed list of the radionuclides released from the reactors and the amounts which were in the cores during the accident.

One of the best reports on this issue is the paper by J.M. Schwantes et. al., this paper uses the relative amounts of the different radionuclides in soil samples taken from Japan to work out what happened inside the cores of the damaged units.

This paper concludes

1. Volatility dictated by temperature and reduction potential dictated the fraction of the radioisotopes which were released.

2. All coolant was likely to have evaporated by the time the containments were vented.

3. The damage to the fuel was extensive.

4. The vast majority of the less volatile elements such as plutonium, niobium and strontium were contained within the reactors.

In the paper it has been calculated that the ratio of released cesium to plutonium from the Fukushima event was 100000 : 3 which suggests that the Fukushima event was far closer to a pure cesium / iodine release than the Chernobyl event was. The cesium to plutonium ratio for Chernboyl was about 10 : 1. I had from an early time made this prediction as the Chernobyl and Fukushima events were very different types of accident. One was a power surge while the other was overheating.

The most interesting thing in this paper is the graph of soil activity / reactor inventory against the oxygen potential of the dominate oxide form. This graph suggests that the more thermodynamically stable the oxide is then the less of the element will be emitted. The good news from this graph is that worst elements (plutonium) will not be emitted. The only problem is that the graph has some points which are a long way from the trend line.

More barium was released than this graph suggests while less ruthenium and silver was released than this simple model suggests. I think that I can explain why less ruthenium was released, the most easy ways to release ruthenium are either as fuel particles (which did not happen at Fukushima) or as ruthenium tetoxide which would not form as the reactors stayed under reducing conditions during the accident.

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.

Is fusion safe ? and beryllium chemistry

Dear Reader,

I imagine that you have seen the suggestions by fusion experts that nuclear fusion will give us a cheap, safe, clean and green source of energy which will provide power for the world’s needs. I am currently thinking about how green is fusion, right now I have contacted a fusion expert who I know and I am awaiting his views on the matter.

While we are waiting I think it is important to ask the question of what was is the typical cause of a nuclear accident. Is it a issue with management, an “act of god“ or was it a technical failure ?

In the case of the Windscale fire I have seen suggestions that it was human error, poor design of the reactor or mismanagement of the project. I know that before the 1999 Tokaimura that a criticality accident at the JCO site was considered to be a was considered to “be an unrealistic scenario” according to the UN report on the accident.

I have to ask the question, did a failure in a regulatory body (either the external state regulator or the companies own internal regulation) cause the first step to be taken which lead to the accident in 1999.

One model of how accidents occur is the Swiss cheese model, the idea is that a weakness in a system is like a void in a lump of cheese. Due to some event a void can appear in the organisation, this void can grow in size, shrink, vanish or move around. As long as some solid cheese exists which prevents a path existing from one side of the block of cheese to the other then everyone is “safe”.

But when a series of holes align themselves to create a path through the cheese block then an accident occurs and then the airplane crashes, the core melts or some other horrible outcome occurs. In some ways the most important step is for the plant owner or the management is to recognise that a given type of accident is possible.

This first step of admitting that a given accident type is at least a theoretical possibility enables the company to start to take steps to prevent it occurring. For example the understanding that someone could get a body part caught in the moving parts of a machine lead to the idea of the 19th century UK law which requires where possible all moving parts of machines to be fenced off or guarded.

While it is impossible to fence off some moving parts such as the chain of a chain saw or all the parts of a handheld electric drill, this law does improve safety by greatly reducing the number of moving parts which can cause injury to factory workers. In the same way if a fusion reactor is going to be built we need a good understanding of the possible threats which it poses.

One is the beryllium used in the heat transfer fluid in some designs, I was reading recently about fusion reactor safety and I saw that a mixed lithium / beryllium fluoride has been proposed as a tritium breeding layer and as a heat transfer layer. I can tell you that beryllium is a very nasty element, in some ways it is worse than some of the radioactive elements. As a result special care will be needed if beryllium or its compounds are used in fusion reactors.

I have looked at the crystal structure of Li2BeF4 (J.H. Burns and E.K. Gordon, Acta Crystallographica, 1967, 1, 1948-1923), this is an interesting looking 3D network. But before we get stuck into it we should look at some organic salts of “H2BeF4″. L.A.Gerrard and M.T.Weller (Acta Crystallogr.,Sect.C:Cryst.Struct.Commun., 2002, 58, m407) report a nice and simple tetrahedral BeF4 unit which has protonated DABCO as the counterion. Those of you who know VSEPR should have predicted that one OK. Here is a picture of the anion in the solid.

The tetrahedral BeF4 dianion

If we have less fluorides per beryllium centre (to make the Be:F ratio 2:7) then we need to use one of the fluorides as a bridging ligand to give us four electron pairs (eight electrons) around all the metal centres. Then we get the following dinuclear complex. See S. Aleonard and M.-F. Gorius (C.R.Seances Acad.Sci.,Ser.II, 1989, 309, 683)

The BeF7 trianion

If we go a little further and have a Be:F ratio of 1:3 then we will end up with a dinuclear complex which has two bridging flourides. This is shown below. (B. Neumuller and K. Dehnicke, Z.Anorg.Allg.Chem., 2005,631, 2535)

The Be2F6 dianion, note the SiF6 dianion in the right of the picture

And now for something completely different (sorry no monty python for you today) if we mix lithium and beryllium fluorides with an salt of an amine fluoride to give us Li2Be4F14 in the unit cell (L.A. Gerrard and M.T. Weller, Chem.Commun., 2003, 716 ). This network will have a charge of -4 and it will form long strips of metal atoms which are in a 1D coordination polymer. Here is the picture for you of the metal atoms and flouride anions in the unit cell.

The metal and flourine atoms in one unit cell

How here are two strips of metal atoms side by side.

Two strips side by side, note that there are no interconnections between the strips

Now here is four strips viewed from a different angle.

Four strips viewed from a different angle, note that they do not touch each other

Now if we look at Li2BeF4 we will see it is a complex solid, I have looked and all the metal atoms have tetrahedral environments, here are a series of views of the unit cell to show you what the solid looks like. This is going to be hard, it is a 3D coordination polymer. These 3D coordination polymers can turn out to be what I call “atomic fog” but this one is not too bad, I have seen much worse in my time.

Side view of Li2BeF4 cell showing the bonds going in one dirrection

Now after turning by 10 degrees

Now the end view.

One last thing in case any of my readers are thinking of doing beryllium chemistry, my short answer is “do not do it !“. Beryllium is the most toxic non radioactive element, some forms of it are almost as bad gram for gram as Pu-239. In some ways I would like John Hunt (the voice of the UK’s AIDS advert) to dispense advice to you about beryllium chemistry using the voice of doom, but you just have me right now.

I would suggest that if any chemistry students do not want to turn back and do something else then I suggest they talk to your local friendly radiochemist  and learn how to work with gram amounts of plutonium. Then do the beryllium chemistry in the same way using negative pressure boxes and all the other safety precautions which you would use for large scale Pu work.