It has come to my attention that a hot debate was erupted involving anti-contamination pills and radioisotope tests being offered for use in Japan. You can read some of this story on the guardian’s web site.
Here are my thoughts on the matter.
It is claimed that cesium will cause cardiac damage in children. I would like to consider the physics and chemistry of this for a moment.
- The physics,
Cesium-137 is a beta emitter with a decay energy of 1176 keV. I emits electrons with an average energy of 174 keV (max energy of 514 keV). So I assume that about 340 keV of the energy will be lost when the neutrino flys away. As neutrinos fly through thick lead sheets they will not interact with human tissue.
Of each decay 662 keV is lost when the excited barium (137mBa) de-excites by emitting a 662 keV photon. Most of these photons will be able to escape from the heart which leaves typically only the short ranged beta behind. This beta has an average energy of 174 keV per decay. This energy is part way between the low energy beta of 14C which does not pass very far into a human body (typically very few beta particles would pass through a glass jam jar) and the high energy beta of 32P which needs thick plastic blocks to stop the radiation. So I would expect only a small fraction of energy to be deposited in the heart even if the heart absorbed all the cesium in the human body. So cesium-137 is not likely to be a radioisotope which can selective give the heart a radiation dose. If the cesium is able to damage the heart then I would also expect to see some effects in the lungs and other parts of the body.
- The chemistry
At high doses stable cesium can cause heart rhythm abnormalities, it requires an intake of grams per day to do this. I doubt if anyone in Japan has had such a large uptake of cesium from the Fukushima accident as one which would cause the same chemical effects as have been seen in people who have swallowed large amounts of cesium salts in an attempt to cure their cancers.
The fission yields of the cesium isotopes made in a reactor is listed below in this table. I have used data for 235U with thermal neutrons for the table.
|Cesium isotope||Fission yield|
|134 (2.06 year half life)||Zero|
|135 (2300000 year half life)||0.06533|
|136 (13 days)||Zero|
|137 (30 years)||0.06286|
Now if we make things simple by ignoring the activation of 133Cs to form 134Cs we can make a simple estimate of the radioactivity of a gram of fission product cesium. A gram of reactor cesium will be roughly 33 % (w/w) cesium-137.
As the activity is given by the equation
A = Nλ = λmNa/ (atomic mass)
As the half life of cesium-137 is 946728000 seconds, then the decay constant (λ) will be 7,322 x 10-10 s-1, and as Na (number of atoms in a mole) is 6.02214179 × 1023 then we can estimate the radioactivity per gram of fission cesium.
A = 7.322 x 10-10 s-1 x 0.333 g x 6.02214179 × 1023 atoms mole-1/ 137 g mole-1 = 1.07 TBq
Now I have to tell you that 1.07 TBq of Cs-137 is a lot of radioactivity, in old units this is about 29 curies. Now when I go to ye olde manual of all things radioactive (the 1966 radiochemical manual published in the UK) it states that at one meter from 1 curie of cesium-137 the dose rate will be 0.32 rads per hour.
Now if we were to stay at one meter from 29 curies of cesium-137 then in one hour we would get a very noticeable dose of 9.3 rads per hour. This in modern units would work out as 93 mGy per hour. In one week a person walking around with a whole gram of reactor cesium one meter from their body would get a dose of 16 grays (likely to be a fatal case of ARS). Now as it takes a daily dose of about grams of cesium to cause heart problems, so I think that it will be impossible to reach this level of chemical contamination without dropping dead of the normal acute radiation illness. So far in Japan there have been no reports of anyone displaying the symptoms of ARS, not even in the team of people who were working on the reactors during the worst parts of the accident.
So I think it is safe to rule out heart disease induced by a normal chemical toxicity of the cesium from the Chernobyl or Fukushima. What those who claim that radioactive cesium damages the hearts of children need to do is to show a different mechanism to show how this cesium damages the hearts of children.
I have seen a paper in which it proves that an acute or semi-acute large dose of gamma rays (circa 5 gray) can induce heart disease in women, I suspect that the exposure level of both workers and members of the general public in Japan is far too low to see these effects. The limit for gamma rays for children in Japan has been set at milligrays per year. I also hold the view that if I was to get a moderate dose to my heart each year (how about 500 mGy) that the self repair processes would fix all the damage and that my heart would remain healthy. I may write another day more about gamma rays and heart disease.
My thoughts on the claims that cesium-137 has caused heart trouble in people is that a degree of common sense is needed, if you are shown data from the Ukraine then always ask if poor diet and other social conditions which relate to the fall of the soviet union have been taken into account. While a possible link between radiation and heart disease in nuclear workers has been reported by some workers, the link between low levels of radiation and heart disease has not been clearly shown to exist. The typical health effect seen in radiation workers who have been over exposed at work is cancer and not heart disease. I think that it be better to looking at the relationship between cancer and low levels of radiation.