RE: shielding of a accelerator facility

[Gerald.P.Lahti@ucm.com]

The layered shielding strategy for nuclear reactors is as follows.  High-Z
material first, then low-Z [hydrogenous] material.  The rationale:  The
high-Z material inelastically scatters the incoming MeV neutrons to keV
energies where the hydrogen elastic scattering cross-section in the next
layer is large enough to complete the thermalization and final capture.   If
the high-Z material is last, MeV neutrons stream thru the hydrogenous
material because of the small cross-section, then are inelastically
scattered by the high-Z final layer transmitting keV neutrons.

My favorite combination (from my NASA space nuclear power reactor shielding
days) was tungsten or depleted uranium followed by lithium hydride
(preferably lithium-6 hydride).  Don't try this one at home.   :-)

* * * * * * * * * * * * * * * * * *
Jerry Lahti
Radiological Safety Specialist
ComEd - Downers Grove
(630) 663-6659
gerald.p.lahti@ucm.com
* * * * * * * * * * * * * * * * * * 

> -----Original Message-----
> From:	CCONTE@correu.gencat.es [SMTP:CCONTE@correu.gencat.es]
> Sent:	Friday, April 07, 2000 4:14 AM
> To:	Multiple recipients of list
> Subject:	shielding of a accelerator facility
> 
> Hello,
> 
> Does anybody know of any problem in having a 18MV accelerator for
> radiotherapy treatments in a bunker (shielded room) whose walls are
> made of lead + concrete?. That is, neutrons get first to the lead shield
> and then to the concrete, and not the other way round, which is most
> common among shielded bunker doors (in fact neutrons and fotons get
> first to a paraffin layer and then to the lead).
> 
> Thanks in advance.
> 
> Carmen Conte
> cconte@correu.gencat.es
> ************************************************************************
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> information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html


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