"Harmless" radiography source

["Doty, Patrick" <fpdoty@SANDIA.GOV>]

Radsafers,



Below is a BBC article on the intriguing idea of using the cosmic background

for radiography.  This method has been demonstrated by Los Alamos, and has

recently captured media attention because of the something-for-nothing

aspect of making radiographic images "without a source".  To me, this method

shows graphically (literally) that background radiation is in fact quite a

significant source, something of an epiphany for most of folks outside of

this circle.  And its harmless, another epiphany.



By the way, William Priedhorsky, the chief scientist of non-proliferation

and international security at Los Alamos, will be giving an invited talk on

this topic at the SPIE annual meeting August 3-8 in San Diego.

http://spie.org/Conferences/Programs/03/am/  I hope to see some of you

there.  



Patrick.



F. P. Doty, Ph. D.

Principal Member of Technical Staff

Sandia National Labs

7011 East Avenue

Livermore, CA



Cosmic rays find uranium

http://news.bbc.co.uk/1/hi/sci/tech/2868041.stm

Naturally occurring particles, generated by cosmic rays, could be used to

detect concealed nuclear material. 

US scientists have shown that an inexpensive and harmless technique

exploiting these subatomic particles could detect a small block of uranium

concealed, for example, inside a truck full of sheep. 

The International Atomic Energy Agency has become increasingly concerned

about smuggled nuclear material. 

William Priedhorsky, one of the scientists involved in the muon work, agreed

that illegal nuclear shipments were potentially a very serious problem and

that new methods to track them down needed to be developed. 

Harmless technique 

Currently, X-rays are used to try to spot material like plutonium and

uranium, but they cannot always penetrate dense objects, such as cars or

containers, where nuclear material might be hidden. 

Now researchers at the Los Alamos National Laboratory in New Mexico have

shown in principle that they can detect a small block of uranium hidden in a

truck full of animals using tiny particles called muons. 

These shower down on the Earth all the time as cosmic rays interact with the

upper atmosphere. 

Muons are completely harmless to humans; millions pass through the body

every day. 

When they meet an object, the muons leave it at an angle that depends on the

material - the denser the material, the bigger the angle. 

This highly predictable scatter pattern is what would form the basis of a

new type of detector. 

The device could be laid out as a platform that trucks could drive on to for

testing, or even a kind of conveyor belt for large shipping containers, the

researchers said. 

The Los Alamos team built a test bench, comprising two upper trackers, to

record the path of the muons as they arrived from the upper atmosphere, and

two lower trackers, to record the path then made by the muons after passing

through a test object. 

Practical applications 

The technique is obviously safer than using X-rays. Fewer "images" would

also be required to confirm the presence of a suspect object. 

The main drawback is that such a muon detector would be slow. X-ray

detectors can scan large trucks in seconds; the muon detector would take

minutes, the researchers said. 

Nevertheless, the researchers are confident the technique can be improved. 

"We conclude that cosmic-ray muons show promise as an inexpensive, harmless

probe for radiography of medium-to-large objects, such as commercial trucks,

passenger cars or sea containers," they write in the journal Nature 

"[Our] method is suitable for a range of practical applications in which

radiography of dense objects with low radiation dose is required - for

example, in surveillance for cross-border transport of nuclear materials." 

Hiroshima bomb 

William Priedhorsky, the chief scientist of non-proliferation and

international security at Los Alamos, told BBC News Online that there was

every possibility the problem of illegal nuclear shipments was growing. 

Only 25 kilograms of nuclear material is needed to make a Hiroshima-sized

bomb. 

He said: "The total amount of material that has been caught in nuclear

smuggling totals about half a critical mass - half the amount that makes a

nuclear bomb. 

"And if we assume that only a small fraction of that that has been smuggled

has been caught, there could be bomb quantities of nuclear material loose

already, which would be a great danger to the world. 

"If a tiny fraction of this nuclear material got into the wrong hands, the

danger is staggering." 







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