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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