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Trinitite II

Dear Reader,

I have reexamined the gamma spectrum from the trinitite, and I have some news for my loyal readers. What I did was to look at someone else’s gamma spectrum of trinitite and then try to match peaks.

Here is the spectrum

trinitite9

Gamma spectrum of trinitite

What we can now see are two peaks (51.7 and 129.3 keV) which are due to the gamma emissions from plutonium-239. Also we can see a set of three lines due to uranium L lines X-rays.

We might ask why are we seeing uranium x-rays coming from a sample which contains so little uranium. One explanation which I think is very reasonable is that the alpha decay of the plutonium-239 forms uranium-235 which is formed in an electronically excited state. The uranium-235 then undergoes a rearrangement of the electrons to form the X-rays. This has been observed by others during XRF studies on plutonium metal.

This is further evidence that the sample contains the radionuclides which should be expected from the trinitiy test. So now I have managed to prove that the sample contains plutonium.

As the sample also contains americium-241 I think it would be reasonable to next make an attempt to find the lines for neptunium X-rays. These could be a further sign that the sample contains americium. I can not think of any other alpha emitters which will be present in large / moderate or even less than tiny amounts in the trinitite.

I will have to think further about the sample.

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Trinitite

Dear Reader,

Recently I purchased off eBay a small lump of trinitite, now I had been warned that a lot of fake trinitite is being offered for sale. So I choose to take the step of examining the sample with gamma ray spectroscopy.

In less than a minute I had been a peak at 668 keV which could either be due to either 214Bi (665 keV from the beta branch) or 137Cs (662 keV from 137mBa) was seen. This peak suggested that some radioactivity was present in the sample. I did a quick check at 609 keV. The line at 665 is emitted during a small fraction (1.46) of beta decays of 214Bi, while the 609 keV photons are emitted by 46.1 of all decays. As a result it is clear that the sample contains some man made radioactivity.

trinitite1a

Next I looked at the low energy end of the spectrum, here is a log log view to allow you to see this part of the spectrum better. I found a strong peak at 66 keV. I suspect that this is 59.5 keV peak for americium, keep in mind that the energy calibration of the detector is a little off. It was over reporting the energy of the 137mBa, so it is not totally unreasonable for it to over report the energy of the 241Am. As americium is associated with plutonium this is a good sign that the rock is a true lump of trinitite.

trinitite2

I then looked for some of the other lines of this americum nuclide, I looked for 99 and 103 keV photons. I found peaks at 99, 101 and 105 keV. This suggests that some peaks were in this expected range. Maybe it could be americium present. At 81 keV we should expect a peak for 133Ba, in our spectrum we see peaks at 81.7, 83.8 and 87.7 keV.

Also at 128 keV the spectrum contains a peak which could be due to the 122 keV line from 152Eu.

trinitite3

The spectrum also contains at 1414 keV a line which could be due to the 1408 keV emission from 152Eu. Also this nuclide will emit at 964, 444 and 245 keV. In the high energy part of the spectrum we can also see a line at 1466 keV which corresponds to the 1461 keV emission of 40K (decaying into 40Ar).

trinitite5

In our spectrum we see a line at 969 keV which can be matched with the 964 keV emission of 152Eu.

trinitite6

We can go further into the problem, in the range of 400 to 500 keV it is hard to decide if a peak is present. The signal to noise ratio is too bad in this range.

trinitite7

Now if we try again in the range of 200 to 300 keV range, we can see a line at 251 keV which is a possible match to the 245 keV.

trinitite8

The section of the spectrum between 300 and 400 keV shows peaks at 358 and 362 keV one of which could be the 356 keV line for 133Ba.

trinitite4

I think that after seeing this evidence that we can come to the conclusion that the rock sample came from a place where a nuclear fission event occurred, so it is likely to be real trinitite.

We will come back to this later, what I hope to do next is to try to estimate the way in which the efficiency of the detector changes as a function of photon energy. We will try to match the different lines from different radionuclides to the graph.

New gamma camera design

Dear Reader,

Having an academic interest in nuclear accident chemistry I search the literature every now and then for articles which mention “Fukushima”, I saw one which caught my interest it was about an idea which I think is truly interesting. It is about the age old problem of how do we see radiation.

Now two easy to imagine gamma camera’s exist, these are the pin hole type and the gamma camera with lots of holes, each hole has a well collimated detector at the bottom of it. These gamma cameras will require plenty of heavy lead shielding to operate and collect nice pictures. When the gamma energy is low (such as Am-241 or I-131) it will be possible to make these machines but when the gamma energy is much higher (Cs-137 or Co-60) it will be very hard to build these gadgets as the gamma rays need thick layers of lead to stop them.

Here is the most simple design the pin hole camera which uses a small hole to make the image appear.

Pin hole camera

Pin hole camera

The second design is the array of holes, this will work as long as the holes are much longer than their diameter. Also it will work better with low energy gamma emitters as they are easier to stop in the shielding. If the maker of the camera is clever there are some things that they can do to improve the image such as moving the camera around to reduce the effect of the grid of holes on the picture. In the following diagram it should be clear that while the red gamma ray can reach the thick black detector plate the blue and purple rays are blocked by the lead in the shielding / holes array.

Gamma camera design two

Gamma camera design two

The Compton effect camera works in a different and much smarter way, it uses something known as Compton scattering of gamma rays and two detector arrays. The idea is that when a gamma ray scatters off an electron it changes direction and at the same time loses some energy. At a bare minimum what is needed is an energy dispersive detector at the back of the camera and an ordinary detector at the front of the camera.

The geometry of the Compton camera

The geometry of the Compton camera

The classic formula for Compton scattering is

λ’ – λ = (h/mec).(1- cos θ)

We can rearrange and alter it a little to get

cos θ = 1 – [(c2 me)/E’] + [(c2 me)/E]

cos θ – 1 = [(c2 me)/E] – [(c2 me)/E’]

(cos θ – 1) / (c2 me) = 1/E – 1/E’

(c2 me) / (cos θ – 1) = E – E’

(c2 me/h) / (cos θ – 1) = v – v’

(cos θ – 1)(h / c2 me)  = (1/v) – (1/v’)

(cos θ – 1)(h / c me)  = (c/v) – (c/v’) = λ’ – λ

(cos θ – 1)  = (λ’ – λ)/(h / c me)

cos θ = 1 + (λ’ – λ)/(h / c me)

θ = cos-1 {1 + (λ’ – λ)/(h / c me)}

θ = cos-1 {1 + (λ’ – λ)/(h / c me)}

Now that algebra was fun, to digress the other day I speculated what would happen in a world where children were banned from doing maths and were forced to play video games and do facebook all day at school. I suspected that some children would rebel by forming illegal underground maths clubs where at clandestine meetings they would study geometry and calculus. Maybe they would pass around maths textbooks behind the bike shed or in the woods, some lads might hide a cache of maths books in their bed rooms out of reach and sight of their mothers. Just imagine the shock and horror of a woman when she discovers her 15 year old son is hanging around fully clothed with an immoral maths freak girl who is doing Laplace transformations, or maybe her son has fallen in with the bad of the bad Fourier transformers.

But back to the real world

If we assume that we have a monochromatic gamma source such as the 137mBa formed from 137Cs then we will have a original gamma energy (E) of 662 keV (1.0606 x 10-13 J), as we know the electron rest mass and the speed of light we can from the energy of the photon after scattering work out the angle it was scattered through.

If the Compton camera is used to image when the background is high or when the source emits photons with several different energies then the front detector also needs to be an energy dispersive detector. For example if we were to image a X-ray source or 192Ir source then we would need both detectors to be energy dispersive. We also have the advantage if both detectors are energy dispersive that we will also get a gamma spectrum from the object. This could be an advantage if two different sources are present in the field of view of the camera.

Here is a graph of the energy of the product photon as a function of the scattering angle.

Scattered photon energy as a function of scattering angle

Scattered photon energy as a function of scattering angle

For those of you who like log scales here is the graph with a log scale for the y axis

Graph of energy of scattered photon as a function of scattering angle for four different original gamma photons

Graph of energy of scattered photon as a function of scattering angle for four different original gamma photons

What happens in Compton scattering is that the photon scatters off an electron, the electron gains some of the energy of the photon. As the gamma photons have much more energy than the electrons it can be regarded as gamma photons bouncing off stationary electrons. As the electron takes some of the energy away from the photon the scattered photons have lower energies than the original photons.

What happens in the camera is that by measurement of the energies of the events in the two detectors the angle change of the photon in the first detector is measured. Then as we know the relative positions of the two events in the two detectors we know the angle of the scattered photon. This allows us to create a cone which will include the location of the original source. Here is a crude sketch I have made of the operation of the Compton camera.

The Compton camera is in operation

The Compton camera is in operation

What happens is that the camera will have a computer in it which trys to recreate the original image, it will for each photon event create a curved shape. By adding the data for different events it will be able to establish what the original image (where the gamma source was). This type of camera can be used for a range of tasks which include medical and industrial applications.

Thorium fueled reactors

Dear Reader,

It has come to my attention that the thorium based fuel cycle is being discussed in magazines such as “Chemistry World” which is the magazine of the Royal Society of Chemistry. As with all technology it is important that we have a honest and reasonable debate about it.

One attractive thing about the thorium fuel cycle is that it tends to form less of the transuranium elements such as plutonium, one idea for a nuclear fuel would be to make a mixture of thorium and plutonium dioxides. The idea is that the plutonium will provide the seed fuel while new fuel can be made from the thorium. Natural thorium  (232Th) can be converted by thermal neutrons into  233Th which will decay via  233Pa into  233U.

In many ways a thermal reactor is better than a fast one, I assume that many of my readers have heard of the term “fast breeder”, the idea of a fast breeder reactor is that it uses fast neutrons to make more fuel than it consumes. Commonly a fast breeder is fueled with a mixture of  238U and something fissile such as  235U or  239Pu. The reason why a fast neutron spectrum is better is that thermal neutrons can cause fission of 239Pu but the fission to capture ratio for fast neutrons is more favoring fission than capture. The capture (nγ reaction) of neutrons with 239Pu tends to form a neutron poison (240Pu) which is activated further to form 241Pu which undergoes beta decay to form minor actinides such as 241Am and even curium. These minor actinides can be a right royal pain. Another problem is that in a thermal reactor the formation of 236U by the nγ reaction of 235U can occur, the 236U is long lived and can be activated further to make short-lived 237U which can decay into 237Np. The 237Np can then form by another capture reaction 238Np which does a beta decay into the house of horror bugbear isotope of plutonium (238Pu). It is interesting that while the greens complain about the “evils of plutonium” they never seem to mention the fact that a lot of plutonium formed in power reactors is more alpha active than pure 239Pu. They seem to be trapped in their thinking by the long half life of the nicest plutonium isotope, 239Pu is not very radioactive gram for gram when compared with many other things such as radium.

As the 239Pu undergoes less activation and more fission in a fast reactor it is a logical choice for making and using plutonium, but on the other hand a fast reactor is bad for the thorium based fuel cycle. Here the desired outcome is neutron capture by natural thorium. The intended reactions are the neutron activation of 232Th to form 233Th (t½ 22 min) which decays by beta decay to 233Pa (t½ 27 days) which in turn undergoes a beta decay to 233U (t½ 159200 years). While 233U can be used for both reactor fuel and bombs, it is interesting to note that it is normally contaminated with some 232U. The decay of 232U forms high energy gamma emitters which will increase the dose rate near the 233U, this could make bomb and fuel fabrication more difficult.

The unwanted reaction in the thorium containing reactor is the n,2n reaction on 232Th to form 231Th, the 231Th then does a beta decay to get to long lived 231Pa. The next neutron capture then forms 232Pa which decays into 232U.

Some of the daughters of 232U (208Tl and 212Bi) emit very high energy gamma rays (up to 2.6 MeV) which will be much more troublesome than the gamma rays from 241Am which is commonly found in plutonium which has been allowed to age for some years. The majority of the gamma rays from 241Am are much lower in energy (60 and 33 keV) are much lower in energy and thus can be shielded against with a lead apron (circa 1 mm Pb) or a sheet of glass attached to a glove box. To attenuate the 208Tl gamma rays a very thick layer of shielding would be required making glovebox work impossible unless the glove box worker is willing to incur a large hand dose and happens to look rather like Mr Tickle of the Mr Men.

The key thing to understand is that a slow or thermal neutron has too little energy to do the n,2n reaction on the natural thorium. While a thermal neutron is able to do the neutron capture which we want. With some luck we can consider some reactor designs which reduce the formation of 232U.

Cobalt-60 theft in Mexico

Dear Reader,

It has come to my attention that a truck containing a radioactive cargo from a hospital (A used cancer treatment unit) was stolen recently in Mexico. You will be glad to know that the radioactive cargo has been found. A short comment on the case (made at an early time) by the IAEA can be seen here.

Currently it is unknown why the truck and the radioactive cargo was stolen. I do not know if it was a simple truck theft where they wanted the truck, a scrap metal theft or something more sinister such the theft of radioactivity by someone with the intention of causing harm with it (dirty bombers ?).

I hope when I get some time soon to be able to comment further on this case and on cobalt-60 in general. One report claims that circa 3000 curies of cobalt-60 was inside the machine when it was stolen. From my own personal experience I can tell you that this is a large amount of radioactivity, I would expect that the outside of the shielding could feel warm if that amount of radioactivity is inside. The warmth is due to heat being created in the shielding by the absorption of the beta and gamma rays from the cobalt-60, this heat production (decay heat) is perfectly normal.

We can do some fun calculations with decay heat, but I want to save those for later.

The problem with radioactivity units is that two units for activity exist, the old one (curie) was defined as the amount of radioactivity which is equal in terms of decays per unit time as one gram of radium-226. This is a very large amount of radioactivity, one curie is 37,000,000,000 radioactive decay events per second. Or as I would write it 37 x 109 events per second. On the other hand the modern (SI) unit for radioactivity is the Becquerel which is named after the discoverer of radioactivity. This is defined as one radioactive event per second.

The problem with the  Becquerel is that it is very small and for most applications, event things like expressing how much natural radioactivity is in a person, a kilo of earth from my garden [As far as I know there has never been a radioactive soil contamination problem in the town where I live in Sweden] or a packet of coffee) you need to write a large number.

The great problem I see with the curie and the  Becquerel is that both units are very different to each other in size, the  Becquerel can be thought of being like expressing the weight of a car in grams while the curie can be thought of as like expressing the weight of my dog in terms of equivalents of blue whales.

Cherry picking

Dear Reader,

It was interesting that Sarah Phillips choose to accuse me of “Cherry Picking”, for those of you who do not know what “Cherry Picking” is it is when a person uses a very small amount of data either while deliberately ignoring a large amount of data or while being too lazy to obtain more data.

The problem with a cherry picker is if their argument is reasonable and based on something which truly exists then their use of a far too small amount of data weakens their own argument. For example if I count the blue tits in my garden over one minutes then I might see if I am lucky in summer one blue tit.

If we assume that the area of garden outside my window where I am gazing has two states (free of blue tits or contains a blue tit) then we can use the same ideas as are used for counting radioactive events. The estimated standard deviation (no that is not some sort of sexual matter) of the number of blue tits counted is the square root of the number counted.

So if I look out of the window and see during my observation of the garden that one blue tit is present during the one minute observation time then the estimated standard deviation (ESD) based on the number of observations of the blue tits is 1. This means we have an ESD which is the same size as the average number of blue tits seen per minute.

If during my one minute observation of my garden I see one blue tit and if during a similar observation of the next door’s garden I see no blue tits then it is unlikely that a real difference exists between our gardens.

On the other hand if I observe my garden for one whole hour and see 60 sightings of blue tits while in the garden next door I only see 6 sightings. Then the ESD on my garden is 7.75 blue tits while the ESD on the observation of next door’s garden is 2.44.

The difference between the numbers of blue tit sightings in the two gardens is 56 which is 5.5 times larger than the sum of the ESDs of the two measurements. Thus the likelihood that the gardens are different is far more than 99%.

While bluetits are important to me, their appearance in the garden is a source of joy to me the significance of their numbers is less important than the incidence of adverse health effects in the human population. Now unless you have been hiding in a hole in the ground and making a point of never reading a newspaper, blog or even “yahoo news” you should be aware of the fact that a great debate exists regarding the question of “should we use nuclear power to make our electricity ?”.

After the Fukushima debacle the question of how likely is a nuclear power accident to harm a member of the general public has become important to many members of the public. The problem is that no matter what energy system we choose to make our electricity a finite risk exists that someone will be harmed.

For your information a series of adverse events associated with energy systems are listed below, to qualify as a death it must occur within one year of the event. A worker is a person working at the energy production site during the accident.

Energy   system Location Worker   deaths Non   worker deaths
Coal London   (Great Smog, 1952) 0 12000
Hydropower Vajont Dam (1963) 0 Circa 2000
Coal Courrières mine (France) 1099 0
Natural   gas Ufa train disaster (USSR) 0 575
Natural   gas New London School (Texas) 0 Circa 300 children
Hydropower Dale Dike Reservoir (1864) 0 244
Natural   gas Piper   Alpha (1988) 167 0
Coal Aberfan   (1966) 0 28   adults 116 children
Nuclear Chernobyl   (1986) 31 0
Biomass Boston Molasses Flood (USA) 0 21
Nuclear SL-1 (Idaho, USA) 3 0
Nuclear Fukushima   (Japan) 0 0

Now we should be able to see that in terms of short term human deaths that both Fukushima and Chernobyl are small compared with many of the other energy accidents which have occurred in the 20th century. While it was a small scale accident for pure gross out the Boston molasses accident is one which is etched into my mind, it was an event which condemned people to a truly sticky end.

We should also be aware of the fact that in England (London) and Japan the burning of fossil fuels has lead to clear adverse health effects, even if others are rushing to ban one energy system (nuclear) we should not ignore the fact the many energy systems do have the potential during accidents or in normal operation to harm people.

While I strongly hold the view that we should improve health and safety standards in the nuclear sector, it is clear that great room for improvement exists in the non nuclear sector. I was at a recent meeting on nuclear safety during which one of the speakers did consider the Bhopal event, I held (and expressed) the view that the international scale for radiological accidents should be expanded to consider non nuclear events. The Bhopal event is at least as serious as Chernobyl, the Chernobyl accident was not able to wipe out a whole town in the same was as the MIC gas was able to gas to death a vast number of members of the general public.

One way to put it is “why should other sectors of industry be held to a lower standard than the nuclear industry ?” which I think is a better attitude than “why can not the nuclear industry be held to the same lower standard as other sectors of industry are held to”.

While some people might think it is monstrous we need to ask ourselves the questions of.

  1. Which electricity generation method kills the least people per kilowatt hour ?
  2. Which energy system does the least amount of environmental damage per kilowatt hour ?
  3. Where can society make the largest reduction in death and human suffering for a given expenditure ?

Then based on the answers to these questions we should choose which energy systems to use rather on some philosophical or emotion based reason such as “coal is the devil’s fuel as it is found underground”, “biomass is good because it comes from nature” or “nuclear power is evil as some of the technology was invented during weapons research”.

I know that a lot of people choose their preferred energy system for emotional reasons rather than rational reasons, I would like to know how many of them would choose a health care provider based on emotional reasons such as

“that doctor must be good as he comes from my home town”,

“that doctor is no good as he comes from my home town”,

“that doctor is (good / no good) because the doctor is (Tall / Short / Male / Female / Irish / English / Swedish / An arab / Jewish / Buddhist / Muslim / Hindu / Black / White / insert some other type if you are not happy with the selection offered)”

or

“That doctor is good he always prescribes pills with nice colours”

I am more interested in questions such as

“Is the doctor sober when on duty”

“Does the doctor pay attention to my health issue or not”

“Does this doctor’s care give good outcomes for the patient”

“Does this doctor’s bedside manner rub me up the wrong way”

While a single incidence of finding the doctor drunk in his surgery, smoking weed beside the hospital entrance or snorting drugs off his desk or a single case of a lazy medic would make me go elsewhere the mere fact that one of the doctors patients had an adverse outcome (maybe he was unable to cure a person) or maybe the doctor seemed to annoy me once (properly because he/she failed to fix me as quickly as I wanted to be fixed with zero pain or effort on my part) does not mean a doctor is no good.

Even the best doctor has cases where he/she fails to cure a person, the doctor who only takes on easy to cure cases is deeply unethical. Also the doctor who I do not instantly feel is my best friend can still be a perfectly good doctor.

Rather than using a single observation of the doctor it is better to look at what has happened to a large number of patients. For example in the case of Harold he might have seemed like the perfect family doctor who was willing to visit the frail old lady if you made a single observation of him. But for those of you who do not know of this disgusting felon the local undertakers were aware that a large fraction of his patients were dying in an unusual manner. Harold Shipman the GP from hell was poisoning his patients for his own depraved amusement; an examination of a large dataset was needed to identify this nefarious fiend to enable the evidence which sent him to jail to be collected.

In the same way as you should choose a doctor based on rational reasons, you should choose your energy supply system on rational reasons AND using a data which can be trusted.

Now after seeing the value of using a large pool of data, I have to ask why does the anthropologist use such small samples of people to prove her points in her papers about Fukushima and Chernobyl ?

Regarding Chernobyl Dr Phillips (lets get her name and title right) uses a single case of a man who had brittle bones and died of lung cancer as evidence that radiation exposure is exceptionally bad for your health.

While I hold the view that radiation is bad for my health we need to consider the degree of risk of an adverse outcome, also we need to consider if some effects require a dose above a threshold to exert a malign effect on our bodies. Sadly she has failed to gather or otherwise obtain the evidence required.

She wrote about the alleged radiation induced ill health of a man who worked as a construction worker building housing in a contaminated area (1986 to 1987), this man also was said to have been catching fish from lakes in the restricted areas. While it impossible for me to estimate his internal exposure from the fish, I was able to look in a UN report and see what external exposure level construction workers who were classed as liquidators were subject to. On average a construction worker in 1986 would have had 86 mSv while in 1987 the average dose was 25 mSv. The total average dose would have been 111 mSv which a dose which will have a 0.56 % chance of inducing a cancer, while this is a non trivial dose it is not one which is able to cause the acute radiation syndrome (radiation sickness).

The problem is that the man died of lung cancer and was known to be a smoker, already because the nature of his cancer we have a very reasonable and likely alternative cause of the cancer. Also the sample size was very small. Furthermore a link exists between smoking and the bone disease (Osteoporosis) which further undermines her argument that the Chernobyl event was the cause of the man’s ill health. The fact that ICRP118 indicates that at least 50 Gy is needed to cause rib fractures, also undermines Dr Phillips report of broken bones being associated with Chernobyl. I strongly hold the view that the man would never have been able to get a whole body dose of 50 Gy and live for years after the exposure.

If we look at the UN report on the effects of Chernobyl then we can see some interesting things. Many people were considered as “accident witnesses” who were on the Chernobyl site at the moment when the accident occurred and the emergency workers who were on site at 8 AM the next day then you have a population of 820 people where almost everyone had a dose of at least 500 mSv. The vast majority of these people survived the accident. At first one might reason that surely if in any population brittle bones and cancer would be observed then this population might seem to be the best place to start looking for these effects. If we assume that all the 820 people had a dose of 500 mSv then we would be looking at a collective dose of 410 manSv. This would be expected to induce 21 extra cancers (We assume a 5% additional risk of cancer per Sv for a single person and one cancer case per 20 manSv).

But the problem with this group is that it is small, quite a few who had the higher doses died off early and their exposure is very varied.

I think a better group to look at are the military men who worked in 1986, their average external dose was 110 mSv and the population was 61762 people. This gave a collective dose of 6800 manSv, I would expect this to induce a total of 340 cancers. The great problem is that the natural background for cancers in the human population is high. If we assume that 20 % of the population die of cancer and that 80 % of cancers are fatal then in this population of military personal then 15441 will have get cancer over their lifetime regardless of their exposure at Chernobyl.

So we would be looking at a population with a total of 15781 cases of cancer, the ESD on this will be 125. If we were to take a population of 61762 unexposed men then we can expect 15441 cases of cancer (ESD on this number is 124). Now the sum of the two ESDs is about 249 which is smaller than the expected difference between the two populations, so I would conclude that it might be possible over their lifetimes to see a difference in the cancer rates between the military who worked at Chernobyl in 1986 and members of the military who were stationed elsewhere.

It will be important to use a control group which is well matched to the exposed group in terms of smoking habits, diet, social back ground, drinking habits, sexual habits and other things. If you were to expose a bunch of hard drinking smoking womanizing soldiers to radiation then it would be wrong to compare them with a group of teetotal non smoking monks as a control group.

Already a large group exists in which a health effect caused by Chernobyl can be seen, this is thyroid cancer in children. If we consider two areas of Belarus (Gomel and Mogilev) then we can see a difference. In Gomel the thyroid doses of children which occurred back in 1986 were estimated to be larger than they were in Mogilev. From the UN report I have seen data for 27463 children from Gomel and 4548 from the less exposed Mogilev area.

In the years 1986 to 1989 then Gomel had nine cases of childhood thyroid cancer (the ESD on this is 3, and it was about 6 cases per year per million children. While the Mogilev area had no cases of this disease. However over the time 1991 to 1994 there were 138 cases in Gomel (ESD 11.7 and it was about 140 cases per year per million children). So it is clear that the condition has become more common.

However the data for Mogilev for 1991 to 1994 suggests that only 16 cases occur per year per million children which shows that the higher the thyroid dose the greater the health effect is. This dose response dose makes the hypothesis that the radioactive iodine from Chernobyl causes thyroid cancer to be more convincing.

These reliable statistics do allow an intelligent discussion of how safe an energy system is, these are far better than using a single case in which it is not clear what was the cause of the observed effect. I have not included data for all energy systems, to do so would require me to work for weeks on end on a single blog entry. One adverse outcome from the use of coal / oil and gas which is being considered as length is climatic change.

I think that the Chernobyl accident is at the top of the scale of what can happen, I think that the passive and active features of better reactor designs will limit the consequences of reactor accident to a smaller accident, I am involved in work which is designed to reduce further the consequences of a reactor accident. I would also say that with better designs than a RBMK1000 the likelihood of serious core damage is lower which also makes a reactor safer.

In the case of the thyroid cancer this effect can be designed out of a plant, it is noteworthy that the release of iodine to the outside world can be suppressed by the use of a sodium thiosulfate filled scrubber, this safety feature is fitted to all power reactors in Sweden. Like a Volvo a Swedish nuclear plant is designed to be crash worthy. One of these days I may well blog about the scrubber of a light water reactor.

It is important to judge a technology based on the modern product or system which is being offered rather than making your choice based on yesteryear’s model, I note that the Fukushima boiling water reactors were very old models (The Ford model T of the nuclear world) so it is not reasonable to judge the latest power reactor designs based on the old designs. I would also say that a need exists to retrofit old units or replace them to improve their crash worthiness, the first major modification I would add would be a wet scrubber between the containment and the stack.

I would have also included passive hydrogen recombiners in the containments and reactor buildings at Fukushima. While these do not slow down the core damage or the radioactivity release into the containment, they do improve worker safety during the reactor accident. The likelihood of a hydrogen explosion or fire is reduced which eliminates one threat to the workers and also helps to keep buildings in a good condition.

BNCT a great way to cure cancer

Dear Reader,

Recently I looked into the core of a nuclear reactor for the first time in my life, the closest I had been before then was looking through the door in the inner shielding at the top cap of a defunct reactor which had been shut down decades ago.

I was standing in the operating position above the water pool of a 250 kW reactor which is used for research, training and for treating cancer; the reactor was not running while I was visiting. Apparently in that location the dose rate is about 400 microsievert per hour when the reactor is running, while this dose rate is no where near the level which would cause an injury or death. As the 1970s LD50 dose for radiation was about 3.5 grays, it would take 8750 hours there to reach this dose. The 365 days required to get this dose would mean that the self repair mechanisms in my body would reduce the baneful effect on my body. I do not think that it would make me fall down dead, but within a week or so I would be hitting my yearly limit, so that I would not want to linger in that spot while the reactor is running.

It was an interesting view looking down through a 6 meter pool of water at the core of the reactor; this reactor is a type which is not designed to make electric power. Instead it is designed to make neutrons for radioisotope production, for training and for the treatment of cancer. Almost twenty years ago the reactor was modified to allow it to be used as a neutron source for the treatment of cancer by the boron capture method.

Now I know that some elements in society are very antinuclear but I would ask even the most antinuclear people to stop, read this and think for a while. Frankly I would like it if you shared my point of view but even if you do not come away from reading this with my point of view I accept that people are free to choose what they like to believe.

Now if you have the misfortune to get cancer then one of the treatment methods is radiation, now the problem is that it is best to give the cancer cells one heck of a going over with one almighty dose of radiation while only giving the healthy tissue a very small dose. This is the ideal but sadly with many radiation treatments it is not quite possible to do this.

The most common method seems to be either X-rays or gamma rays delivered from a source outside the patient. The problem with these treatments is that the beam of radiation damages all tissue that it passes through. One solution to try to spare the healthy tissue is to aim beams of radiation into the person from different angles so that the paths of all the different directions converge on the spot where the nasty tumour is. This is not a perfect way of doing things, no matter how good the radiation expert is they will damage some healthy tissue.

The next step up in controlled and localised dose is to implant a source into the person; it is possible to implant a small but intensely radioactive source right at the spot where the cancer is. This can be used to treat a range of different cancers which include cancer of the cervix, breast and prostate. As radiation obeys an inverse square law this treatment is often very good at sparing the healthy tissues.

If you double the distance from the source you make the dose four times lower, while if you triple the distance from the source then the dose is nine times smaller. I hope that you can now see that the effect should be very well localised in one part of the body. With the right choice of photon and beta particle energy you can make the dose even shorter ranged thus allowing you to wipe the smile off the cancer’s ugly face, send it away with its tail between its legs while leaving the vast majority of the person undamaged.

Sounds great doesn’t it! But there is a fly in the ointment. Today for some applications some of the greens are yelling that we need to stop using nuclear reactors. The problem is that for the generation of the radioactive sources often the only thing which will do the job is a nuclear reactor which has been optimised for a high neutron flux. To do this you need to make the core nice and compact and run the reactor with a highly enriched fuel. Here is one of the best arguments for keeping radioisotope production reactors, while they might not fit in with some people’s idea of what is green they do provide an affordable and reliable supply of lifesaving diagnostic and curative medical products.

Now some people might be yelling at the screen that we should ditch the old fashioned radioactive sources for medical use and use modern particle accelerators like LINACs. I would like to point out that the treatment systems based on radioactive sources are simpler and there is much less to go wrong. Using no more than a sheet of graph paper it is possible to predict the strength of a radioactive source on day X, while accelerators are more complex. I am aware of radiotherapy accidents in both Poland and the USA where accelerators have failed to behave as expected. Both cases caused some ugly overexposures of people.

Also to deliver the radiation just where it is needed to some where like the cervix or the prostrate it is not possible to do it with a typical medical accelerator. The way that the LINACs typically work is by whipping up electrons to very high speeds and then slamming them into a metal target. The change in velocity (deceleration) of the electrons cause them to emit very high energy gamma rays. An alternative second method is to use a gadget called a betatron. Both the betatron and the LINAC are suitable as replacements for the cobalt-60 based teletheraphy units which used radioactive sources to make beams of gamma rays, but they are not able to replace the treatments based on radioactive sources which are placed right in the tumours.

Now while brachytherapy is all very well, there is something even better. One of the problems with cancer is the oxygen effect. If tissue is nice and well oxygenated then low LET radiation like gamma and X-rays are good at causing harm. But when the tissue is poorly oxygenated then it has much less effect. While the surface layers of a tumour are often well oxygenated, the core of a tumour is often poorly oxygenated. What can happen is that when a tumour is given a dose of radiation the inner less oxygenated cells survive and then continue to grow thus making the tumour reappear.

But a high LET radiation such as alpha particles still works even if the oxygen content of the tissue is low. If boron is subjected to neutron bombardment then it forms alpha particles which are able to then do immense damage to the cancer while leaving the healthy tissue alone. The reason that this works is that the person is given a dose of a boron containing drug which mainly absorbs into the cancer cells. The drug used in Finland for this treatment is L-para-Boronophenylalanine, this is an amino acid bearing a B(OH)2 group.

The boron-10 reacts with the neutrons to form alpha particles and lithium-7.

10B + n → 4He + 5Li

The helium and lithium-7 ions then damage the cancer cells, as the boron concentration in the healthy cells are low the healthy tissue gets a far lower dose. Here is a picture of the boron compound which is used for the treatment.

A molecule of the amino acid which bears the B(OH)2 group required for the BNCT

Now some of those of you reading this blog might not be the greatest enthusiasts of the nuclear sector, but I would like to caution the “antinuclear brigade” against throwing the baby out with the bath water.

While I am well aware that it is possible to make bombs using some nuclear technology, I would like to point out that Patrick Moore pointed out that the fact that car bombs made with ANFO (Ammonium Nitrate Fuel Oil) are bad. Frankly I have to say I strongly agree that ANFO based car bombs are perfectly horrible.

But he wrote that the fact that you can make a nasty large bomb out of a car, some ammonium nitrate fertilizer and some diesel fuel is not a good reason to ban any of these three items.

I would like to also point out that the nuclear equipment in the form of a radiotherapy reactor is not in a form which is suitable for use as a weapon, I think that the only weapon I had access to at the reactor site were some lead bricks in the radiochemical lab and the bright yellow extra long tongs. I think I can get some weapons which are more suitable for mindless violence from a typical garden centre !

I have to explain something to you, it is possible to use many objects as weapons but the fact that it is possible to employ or adapt an object into a weapon is never a valid reason for banning an object. I will give you an example, in Mr Archer’s prison diary it explains how one person once took a toilet brush, they cut off the bristles and then sharpened it into a sword. The fact that someone managed to adapt a toilet brush into a sword should not be used as an excuse to ban the things !

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