Activity of hot particles
There is a lot of talk about hot particles at the moment. Seemingly traditionally these are mostly particles of alpha/beta emitters (uranium, etc), but here it seems we are mostly talking about cesium (and maybe strontium) particles.
Let's take a single cesium hot particle, assume for simplicity it is a cube with each side 0.5um (a conservatively small value - if much smaller it wouldn't get picked up by HEPA filters), so has a volume of 1.25e-13 cm^3.
The density of cesium at room temperature is 1.93 grams/cm^3, so the particle's mass is 2.41e-13 grams.
The activity of Cesium-137 is apparently 3.25e12 Bq/gram, so the activity of the one particle is 0.784 Bq. (i.e. it emits a beta article every 1.27 seconds).
If we look at tap (or sea) water radiation measurements of Cesium (e.g. from MEXT in Japan), we see the minimum detectability is around 0.7 Bg/liter, or a bit better. So if there is less than 1 hot particle per liter (what volume is actually tested?), it wouldn'd be detected.
For atmospheric measurements, it's more difficult to consider because measurements are dose rates. However considering Geiger counters may use conversion factor around 5 Bq/uSv/h (depending on many factors), this would correspond to dose rate measurement of 0.2 uSv/h if the decays from one hot particle were constantly being counted by the meter. In most parts of Japan, values around 1/3 of this are seen, and much of this is probably background radiation.
This leads to a few questions:
- are hot particles of this size small enough to be absorbed into the bloodstream and transported to organs? (where the distance between the particle and cells could become very small)
- what could the biological impact of consuming one or "a few" hot particles per day be? (imagining worst case of hot particle level being just under detectable limit for water)?
- give that cesium is solid at room temperature, if it is not in the form of hot particles, what is its form? (smaller particles? oxides with different crystalline structure?)
Thanks in advance for any comments on the above.
"If we look at tap (or sea)
"If we look at tap (or sea) water radiation measurements of Cesium (e.g. from MEXT in Japan), we see the minimum detectability is around 0.7 Bg/liter, or a bit better."
Where did you get your numbers? For tap water in Tokyo, the minimum detected seems to be around 0.2 Bq/l.
http://monitoring.tokyo-eiken.go.jp/monitoring/w-past_data.html
But anyway, in BRAWM air monitoring you have detection limits around 1.5e-09 Bq/l.
what does it mean?
So I live in Tokyo and have a geiger counter. As you say above, the lowest readings I get are around .06 uSv/h (ie regular background radiation) but it is not uncommon to run into .2 or .25 (what you express above as likely to be "1 active particle."
some areas, like kashiwa-city in neighboring chiba show readings of up to .5 uSv/h. this reading is an air reading about one meter up and is in a park frequented by children.
in kashiwa city, the highest reading are in the low parts of the city where water collected after the rains of march 21 (forgive me if i am wrong on that date). for some reason! they refuse to publish the readings for the first day of rain but the subsequent day they reported nearly 1 uSv/h. Two months later we are left with celsium 137 and .3 to .5 air readings in some areas.
is .3 to .5 uSv/hr dangerous when it comes from celsium 137? for children? i think so but am looking for some sort of dosage calculator or method of calculation.
thank you