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.

Home made nuclear reactor part II

Dear Reader,

I was going to tell you some more about crystals and crystallography but that will have to wait for a while. Instead I am going to tell you some of what I think about garden shed nuclear experiments. In case you have come here hoping to read how to make your own reactor, then I have to apologise and tell you that for a series of reasons (including security reasons and a lack of time/space here) it is not possible for me to give you a how to guide to build a reactor in the space we have today.

The way that David Hahn and the Swede were discovered were very different. David gave himself a fright and then in his panic he attracted the attention of a random policeman, while the Swedish man wrote a letter to SSM asking if it is legal to build nuclear gadgets at home. Before we go any further I would like to stress that almost all nuclear and radioactive activities and equipment are regulated by criminal law in all the countries I have heard of. The IAEA have said publicly that they want the penalty for the illegal possession of some nuclear materials to be as high as murder, so we are dealing with “serious stuff” here!

David Hahn wanted to breed uranium-233 which is fissile from natural thorium-232 which is not fissile but just fertile. Fertile means that an isotope can be converted by a simple nuclear reaction into an isotope which either is (or decays into) a fissile isotope.

What David did was to burn up a large number of gas mantles to obtain thorium oxide; he then cut up a large number of lithium batteries to get the lithium. Then using the lithium he converted the thorium into the metal. I think that this was never needed, many reactors using metal oxides as fuels or as targets for radioisotope production. While neutrons can react with oxygen to form radioisotopes such as nitrogen-16 (by a np reaction) this is normally not a major problem.

David then tried to bombard his thorium with neutrons which were from a homemade neutron source. He used a combination of radium-226 and beryllium. This is a horrible mixture; the radium is properly one of the most radiotoxic isotopes in the world while the beryllium is the most toxic non-radioactive element. It causes a series of horrible diseases including a horrible lung rotting disease!

Radium-226; Properly the nastiest radioisotope in the world!

When David was doing his experiment he noticed that the radioactivity level of the thorium target was increasing, this increase in radioactivity prompted him to get into a bit of a panic. What was likely to be happening was during the pyrochemical processing of the thorium dioxide he would have separated the radium-228 and radium-224 from the thorium. These two radioisotopes would have then started to reappear because of the alpha decay of the thorium-232 and thorium-228.

When I get around to it I will plot some graphs of the radioactivity levels as a function of time in a sample of thorium which has been purified. But that will have to wait for another day.

The Swede was spotted in a different way, he wrote a letter to SSM asking for legal advice regarding his home made reactor. I have read the reactor builder’s blog and he does seem to be having some trouble with some concepts.

I am doubtful that even if he had been left to get on with his experiments that he would ever have managed to get his reactor to work. From the little information I have obtained from his blog it looks like he was trying to build a similar gadget to David’s one. It looks like he wanted to build a subcritical reactor which would be driven by an external neutron source.

He describes how he wanted to dissolve radium in 96% sulphuric acid, I think that this was a bad idea for several reasons. Firstly radium is horrible and radiotoxic, while secondly radium sulphate is very insoluble. One of the classic ways to extract uranium is to boil up uranium ore in sulphuric acid, the uranium dissolves while the radium together with the barium will form an insoluble sulphate. For those of you reading in America sulphate = sulfate, and sulphuric acid = sulfuric acid.

I have written some more about barium and radium sulphate, if you want to read about how it applies to this case then go here.

Then the mixed barium/radium sulphate is dissolved, I think in the interests of public safety I will not tell you how to do it here!

So the choice of reagents for the dissolution of the radium was a poor choice, I have also noticed that an ash tray was close to the cooker. I know that you all know that smoking is a dirty habit but smoking anywhere near radium is a very dirty habit. The problem is that in a radium contaminated environment such as an old uranium mine that the air contains radon-222. This ‘evil creeping death gas’ might be able to diffuse through rocks into caves and houses. But the real villain is the polonium-218 and the other radon daughters. These tend to stick to dust and smoke particles.

If you were to breathe radon contaminated but totally dust free air then it would not be good for you but compared with smoke mixed radon daughters the dust free radon air is positively health giving! What happens with tobacco smoke is that the particles get coated with the radon daughters and then they stick in the lungs. The smoke thus acts like glue to stick these nasty alpha emitters into the lungs. As a result a combination of smoke and radon has a far greater baneful effect on the lungs than the sum total of the two if they are done separately in time and space.

Before you are inclined to feel sorry for the Swede bear in mind that while he did stop to ask if home made reactors were legal, he did not think to ask until he had already started his experiments. I suspect that if a random person in Sweden was to write a letter to SSM asking if it was legal to build a nuclear reactor in the basement, then they would get investigated. But if the person had neither acquired nuclear/radioactive materials nor had started to try to build a reactor then they might at worst get their home searched, but I think that after a stern warning that SSM would send him on their merry way.

I do not quite know what the text of the warning would be but maybe the following might be a good one

“The unauthorised construction and use of nuclear reactors in the home is dangerous and may result in a large fine or lengthy imprisonment. I strongly suggest you take up some alternative recreational activity such as …………..”

I once had my lab inspected by a team of UN inspectors who wanted to check that I was not doing some undisclosed nuclear activity in my lab. I found the UN inspectors to be a courteous and professional group of men. What they did was to look in my lab at what sort of equipment I had, they wanted to ask me what sort of chemistry I was doing and to take a gamma spectrum to check what sort of radioisotopes were present in my lab (They found nothing as I have next to no radioactivity in the lab).

While I have no experience of being investigated for illegal back street nuclear reactor operation, I suspect that SSM might use similar tools such as the portable gamma spectrometer to check what radioisotopes were present in the man’s flat. I would also expect them to take some samples in the form of wipe samples to allow for different tests to be done later. One option would be to use an alpha/beta scintillation type contamination meter to search the surfaces in the man’s flat for hot spots of activity. When a hot spot is found it would be logical to sample it and then use a more sensitive and selective counting method to evaluate the sample.

Coal and radioactivity

Dear Reader,

Unless you have been asleep or hiding in a hole you will be aware that in the last few months that a serious nuclear reactor accident has occurred in Japan. After this event people are now asking the questions of “do we need nuclear power” and “should we have nuclear power”. These are perfectly good questions but I say that before you answer them it is important to get all the facts and then think, to make an answer to such an important question when you do not have all the required facts (or to answer without thinking) is plain stupid and reckless.

For those of you who do not know about it I would like to bring your attention to the little known fact that coal can be very radioactive. The problem is that coal often contains uranium, radium and a series of other natural radioisotopes. The level of the radium-226 in coal ash can be very high, the ash from some coal power stations is very radioactive.

Too radioactive for making house bricks for example. It all depends on the coal which was used to fire the boiler. Some coal is clean while other coals are full of radioactivity.

I know that the idea of a vital force which makes natural nice and good exists despite the efforts of  Friedrich Wöhler who showed that a man made sample of a chemical is identical to a natural sample. Some people like to think that if it is natural then it is good while if it is man made then it is nasty and bad. I can think of plenty of nasty natural things, for example cocaine.

Cocaine is a natural drug harvested from a plant, I would challenge anyone to stand up and say that cocaine is good for either the user or society. On the other hand bread is a man made product which is a good form of food, other than a few people who have a medical condition which prevent them eating bread it is a substance which is close to harmless. (Have you ever seen a loaf of bread hanging on a tree growing there ?)

But back to coal and radioactivity, the majority of the radioactivity from the Fukuashima accident is beta/gamma. Most man made radioisotopes from a nuclear power plant are beta emitters. Beta emitters are not good for you, but as anyone who works with radioactivity can tell you “internal contamination with a beta emitter is not normally as serious as having an alpha emitter inside you”.

So as the majority of the radioactivity from the accident is beta and the main isotopes of concern have short half lives of days or at worst 30 years we have some good news.

The radioactivity will go away even if we do not lift a finger to act, and the isotopes released in large amounts are not the worst of the worst radioisotopes.

On the other hand a lot of natural radioactivity is associated with radium-226 and its decay chain, radium-226 is a nasty alpha emitter which decays to an alpha emitting gas (radon-222). The radioactive daughters of radon-222 includes plenty of alpha emitters which can stick in your lungs and give you cancer (not nice). Also the half life of radium-226 is long (1600 years), so the radium will not decay away in my lifetime. Already almost half the cesium-137 from Chernobyl has decayed away, but almost none of the radium isolated by Marie Curie will have had time to decay by now. Radium-226 is in many ways a horror isotope which refuses to lay down and die.

Coal ash can have a lot of radium-226, so as a result the burning of coal can pose a nasty radioactive threat to both plant workers and the general public. Please if you are considering a switch from nuclear to coal then consider this radium problem.

Keeping the dust down

The events inJapanand the way in which the clean up team are dealing with the problem lead me to think about polyacrylamide. It is important from the off set to understand that polyacrylamide and acrylamide are different substances with very different properties. While polyacrylamide is made from acrylamide, good well made polyacrylamide is free of acrylamide. So it is unreasonable in my view to want to outlaw the use of polyacrylamide because the monomer (acrylamide) is toxic.

In the same way, nylon-6,6 (the stuff used for a lady’s tights) is made using cyanide. Hydrogen cyanide is reacted using a nickel catalyst with butadiene to make 1,4-dicyanobutane which is used as a feed stock for making nylon. But I do not think that wearing nylon tights (or a more macho green nylon safety belt as used by people who climb radiomasts or towers) will expose the wearer to any danger of cyanide poisoning.

Sadly some years ago in Swedena tunnel (Hallandsås Tunnel) was being dug, a rock glue which contains acrylamide was used during the construction process. Rhoca-Gil is a rock glue which contains acrylamide and a related substance (N-methylacrylamide). Sadly the monomer leaked out, it caused the deaths of fish and farmyard animals. In addition it was responsible for causing human disease in this case. (http://www.rpaltd.co.uk/documents/acrylamiderrs.pdf)

I hold the view that many monomers are nasty chemicals, and of these acrylamide is one of the nastiest ones (It is a carcinogen and a neurotoxin). But the good news is that the polymer is not able to harm you in the same way as the monomer.

In Japanat the site of the damaged nuclear plant workers have been spraying an antidust agent to stop dust becoming mobile. I have been informed by Prof Ryu Hayano (A Japanese physicist) that kuricoat (http://www.kurita.co.jp/products/kuricoat.html) is being used. One lady inJapan has kindly examined the web site for me and it appears that this product is a water based spray which gives between six and twelve months of dust suppression. Based on these details I suspect that it may be a polyacrylamide product. Such a product is soluble in water and it is known that polyacrylamide does biodegrade.

We need to ask ourselves if keeping the dust suppressed is good for the workforce, one school of thought when dealing with radioactive contamination is to immobilise and fix it. One plutonium chemist I know fromEnglandalways expressed the view that the best thing to do with plutonium contamination in the lab is to paint over it. My reasoning is the greatest threat from plutonium is the internal threat, so fixing it with paint may be the best thing to do. This is the “let sleeping dogs lie” school of thought, I would say that in many cases in chemistry that it is best to let sleeping dogs lie but it is important to take steps to make sure nobody else “wakes the dog”. For example if you find a bottle of a nasty chemical hidden behind a cupboard under the sink (I once made such a discovery) it is best not to open it without finding out how to handle it.

The paint over the plutonium is a method of giving the dog a nice comfortable bed to encourage it to go to sleep. But it is not a final solution to the problem, on the other hand if a bench is contaminated with ³²P then painting and then laying a thick sheet of plastic over the bench does offer a solution as this radioisotope has a short half life.

Another use of paint to control radioactivity is the use of paint to stop radon entering a basement if your home is in a high radon area, one of the best things to do to prevent radon entering the house is to paint all the concrete surfaces in the basement and house. The paint film on the concrete will need to be renewed when the paint starts to age. Here the paint is used to provide a barrier which the radon is slow to diffuse through. The radon is given more time to decay in the walls and floor so less enters the air of the house.

But fixing radioactive dust can be an important part of the management of the contamination, by fixing radioactive dust it can provide the workers with more time to take a further action which will prevent the radioactive dust from becoming a threat to the general public and themselves.

A further reason to fix the dust in the site is to prevent non radioactive dust becoming a means for the transport of the radioactivity. If non radioactive dust enters a radioactively contaminated area then the radioactivity can become bonded onto the normal dust. This now radioactive dust could now blow around in the wind and be a threat to society.

A classic example of this is smoking and radon, I know that smoking is a horrible habit which is harmful to health. So is breathing air which contains high levels of radon, while it is not a socially horrible habit it is harmful to health. But smoking in a radon infested place is much much worse for your health, what happens is that the radioactive daughters of radon stick to the smoke particles in the cigarette smoke. These then enter the lungs and stick to your insides. Thus gluing radioactivity into your lungs. So if you live inCornwallthis is another reason to give up smoking or at least making a point of going out of the house before lighting up.