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Bananas (K-40)
Dear Radsafers,
Inspired by the recent discussion we had about BBq (bananabecquerels) I
wonder if you could help me with a calculation. Going back to the data,
bananas should contain about 100 Bq (K-40) per kilo. My mind then went
to boat transports of bananas. A boat for Sweden may typically come with
6000 tons of bananas in one transport.
The reason for this reflection is that we presently have a political
"discussion" (in a few newspapers) about Bq:s on the surface of
containers with nuclear fuel waste – containers that should have less
than 4 Bq/cm2 -these are shipped by boats – I don’t know what kind of
Bq:s there typically are but according to a couple of sources, 2% of
surface tests were recently above 4 Bq/cm2 and at least one spot had 40
Bq/cm2 (scenario: touch it – pick your nose and get 40 Bq). The
containers are 6.15 m high and have a diameter of 1.95 m (cylindrical
shape) in case somebody wants to play with numbers there.
Now, Swedes eat about 135 million kilos of bananas per year (almost 9
million people, 15 kg/capita, side topic – not necessary info. for my
question below). BTW: After joining the European market – our banana
consumption has fallen by 25%. This is probably bad health news
considering vitamins, tryptophan and other essentials that bananas
contain.
My question concerns the K-40 related dose rate for someone working
close to the bananas on the boat. The bananas come in boxes so for
simplicity, I think one can assume that the "critical group/person" is
standing 1 meter from the wall of a "cube" or "rectangular superbox"
with bananas (symmetrical position – same distance to the right as to
the left corner). I realize that some assumptions must be made here
about density, self-absorption etc –but I still ask: Can anyone simplify
the problem and give me a realistic estimate of the K-40 dose rate? I
don't expect any megadoses to come out from this - it is more of
curiosity in the question.
(And then the cylinder above, with say 4 "equal" Bq:s/cm2 on a 1 m
distance could be a perhaps more complex task. The cylinders are made
out of steel and lead – from preliminary info – one can assume that the
contribution outside from the spent fuel is zero).
I may mention that the 40 Bq/cm2 have been reported to the police by a
member of our green party. After the Chernobyl accident she drove by car
at least 200 km to buy "becquerel free" milk (she has at least six
children – I am thinking about the high responsibility to stay alive as
a parent – that factor should be sixfold).
These lines reflect my most personal considerations and thoughts that
others may not necessarily share.
Bjorn
bjorn_cedervall@hotmail.com
Depts. Medical Radiation Biology and Medical Radiation Physics,
Karolinska Institutet, Box 260,
S-171 76 Stockholm, Sweden
Ph/fax: Int + 468 343525 (Med. Radiation Physics)
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