AW: [ RadSafe ] Re: Positive predictive value of dirty bomb screening (was Cell phone automatic radiation detection)

Franz Schönhofer franz.schoenhofer at
Sat Feb 2 10:03:00 CST 2008

Clayton and RADSAFErs,

Remembering my very first lectures in "radioactivity" decades ago in school
and later at university I still remember that there are basically and most
common alpha, beta and gamma rays. (I hope this is still valid.....)

I also remember that months up to a few years ago, there was talk in the USA
about a dirty bomb, containing plutonium ("the most poisonous, highly
radioactive and deadly substance in this world" - RADSAFErs should already
be used to that nonsensical antinuclear propaganda). I could also imagine
theoretically pure beta-emitters like Sr-90 to be used in dirty bombs. Both
kinds of bombs might not be very effective to rise chaos, because of the
analytical problems associated with the radionuclides. Gamma-emitting
radionuclides can be detected much more easily and would ensure fast spread
of horror stories.

So what? Hopefully nobody from DHS reads this, otherwise money will be
allocated to equip cellphones with alpha- and beta- detectors and everybody
using a cellphone will have to be obliged by law to bow to the ground every
10 meters (sorry, every 30 feet) and to approach any passer-bys extremely
close to measure possible alpha- and beta- radiation. In the last case they
may be authorized to take off the other persons coat (clothes?), because it
would shield alpha-radiation. 

For a ridiculous proposal a ridiculing comment!


Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna

-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at [mailto:radsafe-bounces at] Im Auftrag
von Clayton Bradt
Gesendet: Samstag, 02. Februar 2008 16:32
An: radsafe at; FloodJR at
Betreff: [ RadSafe ] Re: Positive predictive value of dirty bomb screening
(was Cell phone automatic radiation detection)

John Flood wrote:

               'Am I missing something 
or oversimplifying?  This seems to me 
to be doomed to failure because of 
nuclear medicine.  Patients moving 
around a city in essentially random 
patterns would make it impossible to 
identify one detected source as hostile 
amongst a large array of detected 
sources that are medical in nature.  
And the number of these patients will 
increase substantially as the baby-
boomer generation ages.  Discrimination 
based on photon energy won't help, 
either. '

I did a quick and dirty calculation of 
the positive predictive value of such a 
screening program for "dirty bombs" in 
NYC.  Assuming that the police pager-
type detectors are 100% sensitive to 
both dirty bomb material and nuc med 
patients, and that on any given day 
there is one dirty bomb being 
transported through the streets of NYC, 
the PPV comes out to around 10-4 to10-

For all intents and purposes, every 
hit is guaranteed to be a false 
positive.  What kind of strategy is 

It is pretty clear that either no 
forethought went into designing this 
dirty-bomb screening program, or that 
the "deciders" in charge have no 
concern about how effective it will be 
so long as it makes it appear that they 
are doing something.

BTW, if I can figure this out, so can 

Clayton Bradt

Clayton J. Bradt
dutchbradt at
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