Food contamination

Dear Reader,

I want to tell you about some simple agricultural countermeasures, these are the ways in which farmers can change the way they behave to lower the level of the radioactive contamination in the food which they make. I imagine that a lot of farm workers in Japan are normal men and women who want to earn a honest living and that the events right now are a deep source of worry to them. They may be asking themselves if they are going to be forced to give up their way of life because of this accident.

I have read on the BBC that radioactive iodine has been found in food stuffs in Japan. This is not a good thing to have happened. The IAEA site stated that it was radioactive iodine. I have no idea how much radioactive iodine has appeared in the food or what the limit is in Japan for radioactivity in milk.

The iodine could pose some threat to health, the Japanese government have introduced rules controlling the sale of food from the affected area.

My advice now to food producers is not to panic, even if the food is not fit for human consumption now it may be possible to improve the radiological quality of the food in the following way. If the milk only contaminated with radioactive iodine then it could be converted into cheese. The cheese if it was stored for 80 days would then have 1000 times less radioactive iodine in it as a result of radioactive decay.

If you are a dairy farmer in an affected area my advice is ask the authorities in your area before you start cheese making. While it is one method the authority might rather a different method is used to protect the public’s health.

http://www.iaea.org/Publications/Magazines/Bulletin/Bull383/richards.html

If the accident gets worse and cesium is released then while cesium contamination is a more long lived problem. But there is a way out of the problem, Prussian Blue is a cheap non toxic chemical which can be fed to farmyard animals and humans. What it does is to increase the rate at which the radioactive cesium is lost from the animal or human. If you do want to use prussian blue then make sure that you get the right grade, the pigment grade used in paint is not as good as the special medical grade.

Another method for protecting dairy farming is to deeply plough the grass fields where the cows graze. This is a method which should not be done now while the nuclear accident is still occurring. After the nuclear accident is over and the cesium has stopped being deposited onto the land, then if you do choose to deeply plough then this should start.

The reason why deep ploughing works is this, the cesium is very immobile in most soils so it stays in the top layer where the roots of the grass is. If the soil is deeply ploughed up to mixed the different layers up then the majority of the cesium is then buried below the point to which the grass roots can grow. As a result because the grass roots are now in soil which has a lower average radioactive cesium content in terms of Bq per litre the grass which now grows on the land will be less radioactive.

If the grass is less radioactive then the cows which eat the grass will be less radioactive, and finally the milk and meat will be less radioactive.

In some cases a farmer might want to consider changing from growing food to growing a non food crop. This may help some farmers to containue to earn a living.

The water cannon and the inverse square law

News has come from Japan that the police have delivered water cannon to the reactor site.

Now I am sure that no rioting will be occurring at the plant, while some radioisotopes are nasty they are not criminals.

I think that the water cannon are wanted as they increase the distance between the humans and radioactive objects. For a point source of radiation the following rule is true.

Dose rate = k / distance²

k is a constant

So by doubling the distance the dose rate goes down by a factor of four.

The following table can be calculated for a radioactive source which gives a dose rate of 1 Gy per hour at one meter. It is clear that by increasing the distance between the source and the person that the radiation level will go down.

Distance (meters)	Dose rate (Gy hr-1)
0.5	4
1	1
2	0.25
3	0.11
4	0.0625
5	0.0400
10	0.0100
20	0.0025
40	0.000625

 I expect that the water cannon will be used if the workers at the site need to spray water at a radioactive object or a building which is emitting lots of radiation.

Radiation levels in Japan

Dear All

Here is a link to a site which gives details of the radiological situation in Japan

http://www.slideshare.net/iaea/technical-briefing-on-theradiological-situation-in-japan-renate-czarwinski-18th-march-2011

Ido not think that the radiation level in the cities is not able to cause the so called ”radiation sickness”, the dose rates in the cities is higher than normal but it is not an immediate threat to life.

Most of the time in Ibaragi (120 km SW of the plant), Togichi (140 km SW of the plant), Chiba (218 km SW of the plant), Tokyo (230 km SW of the plant) the dose rate has been below 0.3 micro sievert per hour, even if the dose rate was to stay at 1 micro sievert per hour for ever then it would take about 42 days for the dose experienced by the general public to reach their UK occupational limits for one year. But going over the UK occupational limit for the general public does not condemn a person to a certain horrible death.

It would take 2 years and 100 days at that dose rate to reach the one year occupational limit (20 mSv) for a radiation worker. This is a dose which would not cause a serious short term injury or disease. The risk of getting cancer from a 20 mSv dose is 0.1 %. This is not a large chance of cancer. This is based on the assumption that a person has a 5% chance of getting cancer as a result of a 1 sievert dose.

I have checked the details for the reactor site, the radiation level close to the edge of the site is higher than normal. The dose rate close to the fence does in my view justify the evacuation of the general public.

Radioactive decay of iodine

Dear Reader,

There is some good news and some bad news.

The good news is that some of the most horrible of the radioisotopes have decayed away. This means that the reactors are now less able to harm the general public. A further release of radioactivity from the reactors would still be bad if it occurs, but if it does then each day which goes by will make it less harmful.

As Japan’s nuclear safety authority has started to advise the public from the 20 km area around the reactor site to take stable iodine (KI, potassium iodide) I assume that some of the iodine from inside the reactors has escaped. I do not have any idea currently of how much iodine has escaped. But just becuase some iodine has escaped does not mean it has all got out of the reactors, even at Chernobyl much of the radioactive iodine failed to escape from the plant.

It is also important to bear in mind that a serious accident in a used fuel pond will not release any of these shortlived radioactive iodines. So if something occurs in one of the ponds then at least you can not be exposed to the shortlived iodines.

The isotopes which caused the greatest harm at Chernobyl to the general public were the shortlived radioactive iodines.

Iodine has a series of shortlived radioisotopes I-131 (half life 8 days), I-132 (2 hours), I-133 (20 hours), I-134 (53 minutes), I-135 (6.6 hours), I-136 (83 seconds) and some more neutron rich ones which are even more shortlived.

Due to the very short half lives of I-134 and I-136 these isotopes have decayed away totally now, I do not think it is likely that the general public could ever be exposed to these isotopes. The plants in Japan were held in a safe state by the back up power for about ten hours after their were shutdown. During this time the amounts of these very short lived iodines would have decayed to almost zero.

As one week has gone by since the reactors were shut down the amount of I-135 will have decayed to a very low level. The 25 half lives will have lowered the I-135 by a factor of 33554432 (33.6 x 10^6) which means to me that this isotope has gone from the cores.

The I-133 will also have decayed a lot, now after one week it has declined by a factor of more than 256, each day which goes by more than halfs the amount of this radioactive iodine so rapidly this isotope is vanishing from the cores.

The I-131 still has the potential to be a problem, it has a half life of 8 days so the reactors still contain about half as much of this isotope as they did at the moment of shutdown.

While I-132 has a short half life, it is constantly formed by the beta decay of Te-132 (half life 3.2 days) so the half life to watch here is that of the tellurium parent. The good news is that we have had over seven days since the reactors were shut down. Each week of time lowers the threat posed by both Te-132 and I-132 by a factor of 4.

Whatever happens now that so much time has gone by between the shutdown of the reactors and now means that even if something horrible happened in the reactors now then the iodine release would be smaller than what it could have been on day one.

I want to enpower you, rather than letting you sit there and stew as a passive person I want to give you the ability to do radioactive decay calculations. Rather than having to wait for someone else to do it, if you have a pocket calculator you will be able to do it for yourself.

If you want to make your own calculations on the decay of the radioisotopes then go to http://atom.kaeri.re.kr/, here you can get the half life of almost any isotope. The only isotopes missing from the data here are super exotic ones which are only seen in a few rare research labs which are devoted to the study of super shortlived isotopes.

Use the following maths

Activity now (A) = Activity at zero time (Ao) ^{e- lambda t}

Lambda = ln 2 / half life = 0.693 / half life

t is the time in the same units as the half life.

To make it more easy for you I have calculated lambda (decay constants) for the iodines

I-131, lambda = 0.086 days^-1

I-132, lambda = 7.25 days^-1

Te-132, lambda = 0.216 days^-1

I-133, lambda = 0.80 days^-1

I-134, lambda = 19 days^-1

I-135, lambda = 2.5 days^-1

I-136, lambda = 718 days^-1

The bad news is that the radioactivity of the fuel in the ponds will not decay away as quickly as the iodine in the reactor cores. The other bit of bad news is that late this week the level of the accident has gone up from 4 to 5 on the international nuclear accident scale. This means that the accident has changed from an “Accident with local consequences” to an “Accident with wider consequences“. This puts the accident in the same level of accident as the Windscale reactor fire and the Three Mile Island core melt.