[Phys-L] Re: lead vest

[Bernard Cleyet <bernardcleyet@REDSHIFT.COM>]

I just returned from a friend's trial in the federal court in Santa
Barbara.  As the marshal said, it's just like at the airport, shoes
X-rayed in addition to carry on, whoops carry in bags, etc.  I didn't
look closely at the screen, but from a distance I notices it was in
bright technicolor, just like superman's X-ray vision w/ the objects
easily identifiable.   The old lady must have struck fear in them, as
there were four police cars parked in front and much police in addition
to armed marshals, just for crossing the "green line" at Vandenberg.  A
crew of about 20 in front demo'ed, and then filled the audience
seating.  Ellsberg is supposed to testify in March.

My dentist still uses the old technology, film.  They are backed w/ I
think a very thin sheet of lead - don't know why.  I get reserved
seating next week;  if I remember I'll have the answer.

Important is the Al filter on the X-ray generator.  This effectively
removes the low energy tail that will cause skin damage w/o even getting
to the tooth, while passing the energy of interest (>50 KeV).


Data (Ch. 25, Evans, the Atomic Nucleus):

Only quickly available is water for flesh.  At 10 KeV the linear
attenuation coefficient is 4 cm^-1 and at 60 KeV drops to about 0.2

Half thicknesses then are, respectively,  1.7 mm and 3.5 cm  so
conveniently in the region useful for tooth imaging the cheek is ~
transparent, while at lower energies absorbs w/ concomitant damage.

Al data:   at 10 KeV   67 cm^-1;  60 KeV   0.68 cm^-1   corresponding
half thicknesses:  0.1 mm and  one cm    Again conveniently, an
effective filter.

For the Pb apron:  from zero to 25 KeV the linear attenuate coefficient
is > 454 cm^-1;   at 60 KeV about 34 and the corresponding half
thicknesses:  0.015 mm and 0.2 mm


Putting a number for MDE's (3 mm AL) apron:  I obtain 3.7 E-05.  (60
KeV).  Yes very knocked out.


bc, hopes no arithmetical errors.

p.s. attenuation is for interaction(s);  absorption is less.



Anthony Lapinski wrote:

> Forum for Physics Educators <PHYS-L@list1.ucc.nau.edu> on Thursday,
> January 19, 2006 at 6:18 PM -0500 wrote:
>
>
> > Typical dental x-ray energy runs between 60 and 70 keV.
> >
> > x-rays of this energy and below are pretty much knocked out even with 1
> > mm of lead sheet, so I would think a 3 mm apron would be extremely
> > effective.
> >
> > I would certainly expect anyone using a lead vest on their body or in
> > their luggage would immediately be subjected to a hand search.  Blocking
> > the airport x-rays does not make you invisible; it's just the opposite.
> > You would effectively be shouting to the security personnel, "I'm hiding
> > something!  Better search me!"
>
> I was thinking more about someone concealing something in a carry-on bag,
> rather
> than on one's self. It would then appear "very dark" on the x-ray TV
> monitor. Right?
> I assume this would be a "red flag" to those watching as most objects are
> 'transparent"
> to some degree when zapped with x-rays. Yes?
>
>
> > Michael D. Edmiston, Ph.D.
> > Professor of Physics and Chemistry
> > Bluffton University
> > Bluffton, OH 45817
> > (419)-358-3270
> > edmiston@bluffton.edu
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