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Uranium at the Grand Canyon II

Dear Reader,

The story continues, now I am not going to pretend that uranium ore is harmless but at the same time we should not exaggerate how bad it is. One of the problems is that there is a shortage of information on the subject of what was present in the museum building, and also I have no idea of the shape, size and other properties of the museum.

Now I hold the view that the main threat posed by uranium ore in a bucket is the release of radon from the ore. I would like to point out that uranium is not a very toxic substance. Uranium if it is inhaled by a human will be able to dissolve, form a substance that can be excreted with ease via the urine.

So I think that if a person had inhaled some uranium radioactivity then in terms of damage done per Bq inhaled it is less than what something which forms a much less soluble oxide (such as plutonium) would be able to do.

I imagine that the uranium ore was being stored dry, while dry solids tend to form more dust than wet solids in some ways this may have reduced the radiological risk posed by the uranium. The main risk of uranium ore is from the radon which is generated by the radium in the ore.

What will happen is that the uranium (238U) will decay according to the following decay chain.

238U → 234Th → 234Pa → 234U → 230Th → 226Ra → 222Rn → 218Po → 214Pb → 214Bi → 214Po → 210Pb → 210Bi → 210Po → 206Pb

I have chosen to ignore the small amount of 235U as this decays by a pathway which goes via a very short lived radon (219Rn) which due to its very short half life is unable to escape as a gas from the rocks and then deliver an alpha dose to the lungs of the people. In the following diagram I am showing the decay chain of the minor isotope of uranium, I have chosen to ignore any branch which is less than 1 % of the decay chain. The diagonal arrows are alpha decays while the vertical arrows are beta decays.

u235 chain

When a radium containing mineral sample is stored dry the emission of radon from the solid is less than when it is stored wet. A good example of this can be seen in the paper by A. Sakoda, Y. Ishimori, K.Hanamotoa, T. Kataokaa, A. Kawabea and K. Yamaoka (Radiation Measurements, Volume 45, Issue 2, February 2010, Pages 204-210). In this paper the effect of changing the size of the particles was not very clear.

What has to happen for radon to be released from a mineral grain is for the radon atom to be close to the surface of the grain or in the air space between two grains. The radium starts off in the solid grains, when it undergoes an alpha decay the recoil from the emission of the alpha particle will make the atom jump backwards. This recoil can help to liberate the radon atom from the solid.

If the recoil does not bring the radon to the top layers of the grain (a) then it will be trapped so long inside the grain that it will decay. If it recoils into the air gap (b) and the air gap is nice and large then it will slow down in the air gap and find itself floating about in the air gap. However if the air gap is very thin and the recoiling atom strikes the surface of another grain then it can hop between grains. It is possible if it strikes the other grain with sufficient energy that it will bury itself (c) in the other grain where it will decay harmlessly without being able to fly off into the air.

radon recoils

When the ore is wet the gaps between the grains are filled with water, this will reduce the distance the recoils taking path c can take. This can prevent the radon atoms hitting the other grain as they fly along path c. This is because the recoiling nuclei will lose more energy per unit distance of travel when they are flying through water instead of air. The radon can then transfer from the water into the air with ease.

I imagine that the ore was in the form of large lumps, this is a good thing. The reason is that the radon is being generated at an equal rate throughout the whole of the volume of the ore. After being generated it has to diffuse out of the lumps before it can enter the air. The radon has a half life of about 3 days.

To escape from the rock lump it must first be free from the grains and in the air spaces. It then has to diffuse out through the cracks and large pores in the lump to the surface of the rock. One method of reducing the emission of radon from the rock lump would be to paint the outer surface of the rock. But I doubt if they will do that in the museum as it would spoil the appearance of the rock lumps. Another method is to put the rock lumps in a sealed container, if the sealed container delays the escape of the radon by a few weeks then it will make a large difference as the radon will decay inside the container rather than in the air of the room.

If the ore had been crushed to a fine solid then the distance that the radon must migrate is smaller than if the ore is left in large lumps.

Now the next thing which needs to happen for the radon to deliver a dose to people is it has to get into the lungs and stay there. Now if you inhale radon gas then if it is 222Rn from the decay of natural uranium then it is unlikely to decay inside your lungs. You are more likely to exhale the radon before it has had a chance to decay. Even if the radon is adsorbed into your blood in your lungs it still has a good chance of being rereleased again from your body.

The bigger problem is if the radon decays in the air to form a radon daughter such as 218Po, this short-lived polonium can absorb onto dust and smoke particles. These are much more able to lodge in the lungs than the radon gas. One method of greatly reducing the alpha dose to lungs due to radon is to wear a dust mask. This will stop the dust and smoke particles from getting to the lungs. It is well known that uranium miners who are smokers are more susceptible to the induction of lung cancer by radon than non smoking miners. This is thought to be due to the smoke effect.

I am of the view that as smoking is banned in US goverment buildings, as long as the building is clean and free of smoke the radon is less dangerous than it would be in a smoky place. The escape of radon from the building as a result of ventillation will lower the lung dose caused by the radon. I am unable to make a dose estimate due to the fact that I am not privy to the full facts of the case. For my british readers who are able to read between the lines the meaning of the phrase “I am not privy to the full facts of the case” will be very clear. For those of my readers who do not understand british understatement, this means I am missing so many important details about he situation in the museum that it is clearly impossible to make a meaningful dose estimate or prediction of what will happen next.

But at least I can explain some of the things which are important in this case.

I have seen that the US goverment will be investigating what was going on in the museum, this will include dose reconstruction. Rather than jumping to any conclusions I think it will be better to wait for the report from the experts which should appear in about 90 day.+åps0

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Uranium at the museum

Dear Reader

It has come to my attention that in the USA that some buckets of uranium ore were found in a museum site at the Grand Canyon.

Now it is claimed that where the buckets were that the dose rate was 13.9 milliREM per hour, this in european units translates into 139 microSv per hour. I find it interesting that at 5 feet from the buckets the dose rate was zero. A common error is to use a radiation meter which is senstive to beta particles to estimate the gamma dose rate without protecting the detector from the beta particles. This will cause the meter to over read.

Depending on the conditions and the meter in question the over estimate can be small or it can be large.

The problem with a bucket of uranium ore is that the self adsorption of gamma rays can be very large. The late John Pecket told me a funny story about this sort of thing. He had a kilo of plutonium in a glove box as the dioxide. This was in a bottle of dry powder, he pulled a small amount out and dissolved it in acid.

When he changed the geometry and spread it out by dissolving it the dose rate in the glove box went up.

As a result of the self adsorption problem it is hard to make an estimate of the dose rate. It will take me a lot of effort to calculate the dose rate in a room which has thick tiles of uranium dioxide on the walls. This will be a lot more effort than if the room had been painted with a uniform coating of something with a much greater radioactivity put unit volume.

I will have a go at making an estimate for a 5 gallon (25 litre) bucket. If we assume that bucket has a diammeter of 300 mm, it will be 350 mm high and it is a perfect cylinder then we can calculate some things.

If we consider the radiation dose at 1 meter from the end of the cylinder of uranium along the axis we can reduce the problem to a series of disks. Lets for example treat the bucket as a stack of 350 disks. We can consider first the top layer. If we assume that it is pure uranium dioxide which has reached a radioactive equilibrium with its daughters.

The volume of a 1 mm thick slice of the cylinder will be 70.7 cubic cm, as the relative density of uranium dioxide is 11, this means that in the 1 mm slide we will have 777.5 grams of uranium dioxide.

This is 2.88 moles of uranium atoms, this is 1.734E+24 atoms, we will have 8.53 MBq of activity of each nuclide in the decay chain in this slice. So the dose rate due to the top slice will be 1.29 microSv hr-1 at one meter from this slice. If we had no self adsorption then the dose rate at one meter from the cylinder would be about 450 microSv per hour which would be a jolly high dose rate. This is a dose rate which would under almost any circumstances cause me to back away from the source quickly. Well it is not the worst I have heard of, I have heard of a radioactivity worker who on arrival at a possible accident scene in Israel who encountered a radiation field of 500 mSv per hour, he very quickly retreated away from it. If I was to spend one minute in such a place then I would get a 8.33 mSv dose which is almost half my yearly limit as a nuclear worker in Sweden.

I think that when you encounter an unexpected radiation field of 500 mSv per hour the correct procedure is to turn and run (This could be a live saving act), if possible run around a corner in the hope that you can put some concrete between you and the source. So run around the corner and quickly check your dose rate meter before hissing some colourful language, getting to a place of safety, handing in your dosemeter for emergency rapid evaluation, going for a blood test (biological dosemetry), handing over any sugar cubes in your pockets to your radiation protection officer (For ESR dosemetry) and filling in an accident report. The swearing is optional but I will not have a problem with you if you let out some technicolour rant of dirty words which will turn the air blue.

I think that it is very hard to come up with a situation in which you could have a radiation field of 500 mSv per hour (500 mGy per hour). I estimate that you would need to have a point source of 36.5 curies of cobalt-60 at one meter. This is a very large source. Some radiographic sources might be in this range.

But as a result of self adsorption it will be much lower in our case of the uranium cylinder. If we use the NIST data for uranium, as I did and treat the uranium as a series of point sources along the axis of the cylinder. Then I got a value of 9.06 microSv per hour, this will work out at 0.9 milliREM per hour.

While the dose rate of 9 microSv per hour is higher than an area that the general public can legally have access to in Europe (2.5 microSv hr-1) it is not a dose rate which is superhigh. If we assume that a child goes to the museum each weekend and spends 1 hour 1 meter from the uranium bucket then they will get a dose of 453 microSv. This is half of what a member of the public (children are never allowed to be radiation workers so they will always be “members of the general public”).

So I do not think it is likely that any visitor has had a gamma ray dose which is anything to worry about.

 

 

I daniel blake

Dear Reader,

I recently viewed the film “I daniel blake”, I have to admit that this is a rather shocking film. It is in some ways a bit like “Threads” which was a science fiction about nuclear warfare. While on a few occasions a scenario like threads came rather close to occurring, thankfully threads remained science fiction rather than science fact.

Sadly while Daniel Blake is likely to not be a real man, the events shown in the film are based on fact. While it is perfectly reasonable that these events have occurred, it is not reasonable that these events should have been allowed to occur in real life.

I have to warn you that like Threads the film is a gloomy film which I think is equally sad. While watching threads I was hoping to be able to dismiss it as exaggeration but in that case as a radiation worker I could not find a major fault in it with which to dismiss it. On the other hand “On the Beach” is riddled with nonsense, but we can save that for another day.

In the film “I Daniel Blake” we see a hardworking man who is forced to down tools because of a serious health issue. Despite the fact that several doctors declare him unfit for work he is told by DWP (Department for Work and Pensions) that he is fit for work.

We also see a woman being forced into prostitution by poverty, this is also clearly not the sort of thing which should be happening in society.

Now while some people might want to ignore or mock this film, I think it is a rather unpleasant but important wake up call for society. I have heard that the UK government are exceptionally displeased about the film, sadly sometimes the news that people need to hear is not the news that they want to hear !

I hold the view that a safety net should exist for those who have fallen on hard times, despite what some people might say, think, or think that they know this safety net is not a comfortable hammock. I also find it interesting that in society a large series of hue and crys have existed against the benefits cheat while adverts suggesting that people should try to turn in tax cheats are much more rare. It is noteworthy that a typical tax cheat costs society more than one of the rare benefits cheats.

VNA

Dear Reader,

Today I got the VNA which I purchased recently out of the box, and set up the software. This VNA is intended for use in my chemistry lab where it will be used to help unlock the very secrets of the ionic liquids and the deep eutectic solvents. When there are some results I will share with you the results.

Mikhail is now a doctor

Dear Reader,

I am glad to tell you that Mikhail S. Tyumentsev passed his final PhD defense at the end of November. He wrote a PhD on the subject of the solvent extraction of lanthanides by amides.

What he did was to react a malonamide with ortho-dibromomethylbenzene to form a tetraamide. The malonamide in question was not a particularly good lanthanide extraction agent. But the new molecule (The octopus) was a far better extraction agent. Rather than trying to make a series of molecules without understanding them, Mikhail after making his octopus he did a large number of experiments to get a good understanding of the molecule.

These experiments should also help us understand the malonamides better as well. One of the methods which was used was X-ray crystallography, here is a pluto plot of a neodynium complex in which two octopus molecules bond to the metal.

octopus binding to a neodynium

While here is a picture of Mikhail in the final hour of his PhD work presenting his work.

Mikhail presenting

Mikhail has published a series of papers on different topics, before he came to Chalmers he worked on uranium and neptunium chemistry. This work resulted in a paper entitled.

Synergistic effect in heterogeneously catalyzed reduction of U(VI) and Np(V) and decomposition of hydrazine and oxalic acid with bimetallic Pt-Ru catalysts

Which was in Doklady Physical Chemistry, 2013, volume 450, pages 142-145.

While he has been at Chalmers he has published a series of papers on a range of topics.

The solvent extraction of rare earth elements from nitrate media with novel polyamides containing malonamide groups, Hydrometallurgy, 2016, 164, pages 24-30.

Disassembly of old radium sources and conversion of radium sulfate into radium carbonate for subsequent dissolution in acid, Journal of Radioanayltical and Nuclear Chemistry, 2016, 310, 589-595.

Crystal structure and identification of resonance forms of diethyl 2-(3-oxoiso-1,3-dihydrobenzo-furan-1-ylidene)malonate, Acta Crystallographica Section E-Crystallographic Communications, 2017, 73, 1576.

Coordination of Trivalent Lanthanides with Bismalonamide Ligands: Implications for Liquid-Liquid Extraction, European Journal of Inorganic Chemistry, 2017, 37, 4285-4298.

A comparison of two methods of recovering cobalt from a deep eutectic solvent: Implications for battery recycling, Journal of Cleaner Production, 2017, 167, 806-814.

Activity coefficients in deep eutectic solvents: implications for the solvent extraction of metals, New Journal of Chemistry, 2018, 42, 2006-2012.

Temperature effect on the distribution of lanthanides(III) in the perchlorate-malonamide-methyl isobutyl ketone systems, Journal of Chemical Thermodynamics, 2019, 131, 133-148.

Resistor polyhedra

Dear Reader,

Those of you who want to work out your brains might be interested in the resistor polyhedra contest article which I wrote for RadCom. This has been designed to be a challenge which will both tax the minds of very bright people with years of experience in physics / electronics and also offer the new commer some easier problems to allow them to get their feet wet.

I have made a lot of funny networks out of 1000 ohm metal film resistors, my trusty 25 W Antex iron has been very handy for this task. I tend to like to use a iron jacketed 25 W Antex iron for most soldering work. I bought the Antex back in 1992 and it is still going strong. I used to use a 25 W Weller (from the late 1980s) with a copper tip but I found that that the tips were dissolving in the solder too much for my liking. I have to confess that I worked a lot with the Weller, the Weller had coated tips but they did slowly age and dissolve. So what I used to do with that iron was to use 1970s solid copper tips from another older iron I used to own as a lad. I used to have to file the copper tips once in a while to get the shape right.

I have found that a 50 W temperture controlled Weller with a modern tip to be a nice iron. I think that it is a better iron for large items than the 25 W Antex. But I think if you want the best value for money the 25 W Antex is hard to beat. I used that in my youth to build quite a few things.

RadCom is the magazine of the RSGB (Radio Society of Great Britain). Sadly due to an error in the production process it did not publish a closing date. The closing date is 08:30 GMT on the 7th of Jan 2019. To have a chance an entry must have reached the RadCom office by that time / date.

The contest is in RadCom in the december issue at around page 40

The rules by which I will be judging the contest are

Rule 1.

If one person has calculated or measured correctly more networks than any other person, then this person shall be the winner. Any person who gets within 2 % of the correct value will be judged to have got it correct. The networks made by Mark Foreman are to be used to referee what the correct values of the networks are. If the RadCom office or other RSGB workers were to create their own versions of the networks then the average of the values measured from the networks will be used.

Rule 2.

If under rule 1 no single winner can be identified, then Mark Foreman will judge the method used to determine the values of the networks. Mark Foreman normally favers methods which use the bare minimum of advanced mathematics. Thus if the solution requires exotic things like Laplace transformations, matrix operations and the like he will disfavour. Mark Foreman reserves the right to consult other people when judging methods which use advanced maths.

Rule 3.

If under rules 1 and 2 no single winner can be identified, then the first most correct and elegant answer to arrive at the radcom office will be the winner.

Rule 4.

If under rules 1, 2 and 3 no single winner can be identified, then the winner will be randomly selected. The possible winners will be assigned numbers such as 1, 2, 3 and 4. Then Mark will use a measurement of the background radiation in his office or lab as a random number generator. The least significant digit in the total count numbers (number of events detected) will be used to decide the winner.

Bridge in Genoa (Italy)

Dear Reader,

I strongly suspect that some of you will be aware that a bridge in Italy has fallen down resulting in a considerable loss of human life. Now some of you might be wondering what caused it to happen.

At this time I do not know for sure exactly what caused the bridge to fall down, there are reports that a lightning bolt hit the bridge shortly before the bridge came crashing down. The bridge was a suspension bridge (cable stayed bridge) which had reinforced concrete elements which go from the tops of the towers to the part of the bridge which the people / cars travel over.

Now years ago in the senior common room at Reading it was explained to me that there are two types of suspension bridge. There is the true suspension bridge where a long cable which has a shape similar to a washing line exists between two towers. From this cable a series of vertical elements are connected. At the bottom end of the vertical elements are connected to the road way on which the people, cars etc travel over. The other design is a cable stayed bridge in which straight elements which are under tension go from the tower to the road.

For the suspension bridge it is impossible to change the main cable (the one with the washing line shape) but for the cable stayed bridge it is possible to replace a cable.

One big problem is tension, now it is important to understand that concrete is very weak in tension but strong in compression. This is why reinforced concrete is so good a material. The strength of a concrete object can be sometimes increased further by stressing the structure by putting the concrete under additional compression. This can be done by having a hole going through the concrete, the concrete is poured and allowed to set. Afterwards a steel rope in the hole is then put under tension, this then subjects the concrete to compression. One way of doing this would be to have a long bolt passing through the hole with large washers on both ends. By putting a nut on this bolt and tightening it up then the bolt will be under tension and the concrete under compression.

post stressed concrete

Another method would be to use prestressing where the rebar is put under tension before the concrete is poured. It is important to note that when carbon steel is placed in concrete made from ordinary portland cement (OPC) that the pore water in the cement is slightly alkaline. This is good for the steel, under these conditions the steel does not corrode quickly. The steel is in a chemical environment in which the corrosion is very slow.

Corrosion or rusting of rebar is a very big problem, the volume occupied by the rust is greater than that of the steel rebar. As a result if rusting occurs then not only does the rebar lose its strength but also it tends to cause concrete to spall off from the structure. This expansion from within tends to make more holes in it.

However there are two main problems, if the concrete becomes contaminated with chloride salts from sea spray or deicing salts used on the road then the rebar can start to corrode more quickly. Also if as a result of cracking carbon dioxide from the air can enter the concrete then the pore water will become less alkaline. The steel will then be exposed to a new chemical environment in which it will corrode more quickly. All concretes will slowly be carbonated by the air, but in the ideal world only the very outer layer will be carbonated.

If the concrete becomes cracked due to vandalism, a changing mechanical load or even due to corrosion then the rate of carbonation tends to increase. This is due to the fact that the air has greater access to the inner part of the concrete object.

The last main thing which we should be aware of is that some corrosion modes such as stress corrosion cracking are worse when the object is placed under tension such as in the cable of the suspension or cable stayed bridge.

What I think that one of the things the investigators should be doing is to check the chemistry of the concrete used in the reinforced concrete cables used to connect the towers to the deck of the bridge. There are two simple chemical tests which can be used.

The first one is to drill a hole into the concrete and apply a solution of phenolphthalein to the surface. This is an acid/base indicator. When it is acidic it is colourless but when it is alkaline it is intense pink. What you then do is to measure how far the colourless reagion extends into the concrete object. This will give an indication of how bad the carbonation effect was at the point where the hole was drilled. As the bridge has fallen down this test can be used without having to worry so much about plugging up the holes made in the test if you were to examine the fallen lumps of concrete.

Another simple test is to grind up a sample of concrete, then to make this into a paste with a known amount of water. If this paste is then examined by either ion chromatography or a chloride test strip (based on the reaction of silver nitrate with sodium chloride to form insoluble silver chloride) then it is possible to determine how much chloride contamination was present in the concrete.

It would be interesting to know if the people responsible for the bridge were using these tests and some other corrosion tests before the bridge fell down. Now I think that the wreckage from the bridge should be subject to these tests and some other tests to try to work out what has happened. I will try to write more about the bridge and steel corrosion when I get the chance.

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