Fieldwork 1: ずくなしの冷や水

2014年04月13日

Fieldwork 1

As far as my understanding goes, health damage is already serious over a vast area in Japan. My current concern is: how much more serious can this become?

What about the alpha and beta sources?
There is a fair amount of public data available on gamma radiation air dose rate, though not enough. Nowadays, gamma rays can also be easily measured with Geiger-Mueller counters by individuals. But when it comes to alpha and beta particles, we are still pretty much in the dark about the truth.

So I went out to do some fieldwork
I fear that the contamination by these two radiation sources will be the critical factor in the long run. Wanting to get even just a slight idea of the possible state of such contamination I decided to ask my pretty old survey meter to do one last job before its retirement and headed out. I went to an area where I always find a high air dose rate when I go walking. To begin with I measured the air dose rate at more than 1m above the ground. The counts per minute were high.

Off scale
In order to measure the beta sources with my survey meter I need to approach the end of its tube-shaped sensor to within touching distance of the target area (the sensitivity has gone down with age and anyway that's the design).
So I put the end of the sensor to within touching distance of the ground just to test for beta radiation sources which have a short flying distance (to avoid contamination of the sensor, I had covered the totality of it with a thin plastic bag).
The counts jumped up instantly and went off the scale. Because of its age, my survey meter is extremely sensitive to differences in temperature. Thinking that the wind might have cooled it down suddenly, I raised the range of the scale, reset it and waited for it to settle.

Second measurement: It went off the scale again. So I raised the range for the second time and re-measured. Off the scale yet again. One of the photos of the day shows the scale limit at 3kcpm. So the dose rate was above 3kcpm.

I moved elsewhere and put the sensor next to the ground to check if it was just my survey meter acting old. The sensor only reacted sharply when it was within the red circle of the following photo. The dark patch on the ground is my shadow.



I acknowledge that the figures of my survey meter are not totally reliable. As I said its sensitivity is down and it has never been calibrated either. However, I repeat that the phenomenon of going off the scale happened only within this red circle, and it happened on each of the 4 or 5 times that I measured. When I moved away, the dose rate was around 30cpm at 50cm above the ground. Back at home, the dose rate was in the normal range.

I didn't stay long in this hot spot because I was terrified by the noise that my survey meter gave out. It wasn't like the usual low pitched sound but beeping noisily. I am starting to think though that perhaps I should go back and get a sample of the soil and grass of this spot.

Coincidence or ?
I admit that it wasn’t the first time that the readings of this old survey meter went off the scale. It had happened a few times before. Twice it was due to a sudden change in temperature. The other time it happened when a gardener in a park was using a blower and the dust was blown towards me. I imagined that it must be a really rare case to find such a hot spot so easily. It was the first place I tried to measure and without even moving around I just landed on it.

But then at the same time, a scary thought comes to my mind: Maybe there are micro hot spots like this one all over. I had this area in my mind because of the constant high air dose rate but this is not the only spot where I find high air dose rates when I am walking.

I also had the suspicion that this area might have beta radiation sources that do not originate from the Fukushima Daiichi accident: namely the uranium from the depleted uranium storage facility next to Cosmo Oil Refinery (Chiba prefecture) that burned after the earthquake on March 11th. Looking it up I read that uranium 238 has the specific activity of 14.8 Bq/mg. In order to influence the readings of a survey meter that has a background radiation of 30cpm, I would need about 10mg of uranium 238, which would be a huge amount of particles.

I hence conclude that the radioactive particles in the red circle cannot be uranium 238. If you consider that the air dose rate is relatively high in the whole area around the spot it is more natural to think that various different radioactive particles from Fukushima Daiichi fell on the ground and stuck here.

The problem is that this area is not a particularly highly contaminated area according to the air measurement map by MEXT (Ministry of Education, Culture, Sports, Science and Technology). If in even a moderately contaminated area you find micro hot spots like this, there could be numerous other micro hot spots in the whole Kanto region.

N.B. it didn't rain here on March 15th, but it did on March 21st 2011.

This reminded me of a soil survey that had been conducted by the US where various samples with high gross-alpha and gross-beta radioactivity were found across Kanto and Tohoku regions. When I saw it I was surprised by the frequency of those hot samples but maybe it is not such a big surprise after all. One should understand that even randomly chosen, you can find hot samples from the soil in Kanto and Tohoku.



We need reliable information
There is a lot of conflicting information published on alpha and beta radiation sources which makes it difficult for individuals to get an accurate idea of the contamination. For instance, I once learned that some soil samples in Kanagawa prefecture had a high dose of strontium, but this was denied later. Since it is technically difficult the government should collect samples and conduct the measurements, but I haven’t heard of anything of that nature being done.

I guess that they just don't want to do it. For it will likely lead to a big scandal if they do.
posted by ZUKUNASHI at 19:39| Comment(0) | 福島原発事故
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