[ RadSafe ] Mistake on the UMRC web site
rhelbig at california.com
Sun Mar 12 07:14:57 CST 2006
To: du-list at yahoogroups.com
> From: "marktwain403" <marktwain403 at yahoo.com>
> Date: Sat, 11 Mar 2006 06:05:55 -0000
> Subject: [du-list] A mistake on the UMRC web site
> Just for the fun of it, I was looking at the UMRC http://www.umrc.net/default.aspx web site tonight and found a very signicant mistake. They have a page > titled "Radiation and the human body" http://www.umrc.net/radiation_and_the_human_body.aspx which contains the following text quoted below. But before I present the quoted text, I will comment on the mistake. They say that a tiny pellet of uranium emits
> approximately 37 alpha particles per year and from that they calculate a
> dose of 17 rads per year, far above federal guidelines. I checked their
> calculations and did not get exactly the same number of alphas but
> the number was close to their calculation at about 15 alphas per year.
> "Close" in this context means in the same ball park. But it seems
> that their dose calculation from those alphas is over estimated by a
> factor of 10 million or so.
> They get a dose of 17 rads per year. I get a dose of
> 1.25 times ten to the negative 8 power, in other words a very
> insignificant dose. I don't think I am mistaken because a single alpha
> particle produces a very insignicant dose and here we have, even by
> their own count, only 37 alpha particles. There is no way that 37 alpha
> particles is going create a significant dose. I am traveling now and my
> calculations must be considered preliminary as I just now did them and
> have not checked the calculations carefully but I believe this is
> correct. If the UMRC is wrong, as I think they are, you have to wonder
> about their expertise. I think any average scientist in
> radiation protection would not make such a mistake. I wonder who made it?
Here is the text from the UMRC web site:
>>Each particle emitted has a certain amount of energy. The
> energy multiplied by the total number of particles
> gives the total amount of "uninvited" energy released in the body.
> To illustrate this point, consider the number of alpha particles
> emitted by a single spherical pellet of uranium oxide (UO2) 0.0001 inch
> or 2.5 microns in diameter (equivalent to 1/40th the width of a human
> hair) and the dose rate it produces.
> Tiny as it is, the 2.5 micron depleted uranium oxide
> pellet contains 210 billion atoms (2.1 x 10 to the power of 11) of
> U238. Each year, the pellet will emit an average 32.3 alpha
> particles. It also contains U234, 235, 236 which together yield an additional
> 5.3 alpha particles per year. Thus a single pellet of depleted UO2 will
> produce a total of 37.6 alpha particles per year.
> The 37.6 alpha particles will deliver a radiation
> dose of 17 rads/year. With an RBE (Relative Biological
> Effectiveness) factor of 10, the dose rate is 170 rem/year for the
> surrounding body tissue. In the US, the Code of Federal Regulations regarding
> energy specifies an annual limit of 0.17 rem/year and a specific limit
> of 0.5 rem/year for an individual in the general population.
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