Dave Hinz wrote:



Right, it's got a _big_ field, but it's not as _strong_ of a field.
A static charge from walking across carpet on a dry day can be thousands
of volts, but there's no current behind it.

Yeah? Try explaining that to the cat who's nose you touched after
doing that walk.
jk

"Dave Hinz" wrote in message
...
These weren't iron, they were chrome-plated rare earth magnets of some
sort.

Well yeah, but near the saturation limit of silicon steel. I.e. a pole
piece the same cross section as the magnet would be sort of saturated. I
think.

Strong enough that they held strong through my hand. Hint:
don't let 'em go around and hit each other, because blood blisters will
result (based on a sample of one).

Yeah, they are a lot of fun, ain't they?

Yes, there's an inner coil and a counter-wound outer coil.

Would that be the RF coil? What makes the field precession and stuff
mentioned in the link Joe posted? (Thx BTW.)

How is the gradient made? Less amperage in one of the helmholtz coils?

Yes, the GE magnets have 18 "shim coils", first, second, and third-order
corrections. The simplest is just X/Y/Z; get the overall gradient
from say front to back the same.

Necessary for the natural tapering and fringing of the field...

Second-order does opposing corners,
third order starts getting strange. Some delightful math to calculate
how to get the shims in order, as they all interact heavily.

I bet. Damn that Maxwell...

Well, the protons in them, but yes,

Ok.

Well, there are gradient aplifiers which make the RF pulse only resonate
one location cleanly (this is wrong but close enough to make the point).

That's what I'm not getting, how do you change the field to take a slice?
Fields don't much like shear...

The echo is detected with the same RF coil (goes from transmit to receive
very quickly), which gets fed into a 2-dimensional Fast Fourier Transform,
breaks it into frequencies which tells you a number of things, and then
does it again with more lines of data (each of which also came from a
FFT),
and FFT's _that_ into the image. Sort of.

Yes, all very complex.

D'ya suppose it would be possible to make a cheapassed water-cooled tubing
coil of 0.5 to 2T (I'll have to look at the equation to see what's
reasonable), plus some other coils and whatnot, hook it up to a power supply
and signal generator and do a sort of radar-like trick to it (bad
comparison, but works for me, I mean you're sending a pulse then recieving
it) and actually observe NMRI?

Right. It's usually localized to, say, the arms where they're
closest to the coil. A person inside an antenna acts as an RF "slug"
(heh) and both lowers the frequency of, and widens the peak of, how the
antenna is tuned.

Hm, flesh is diamagnetic... would that decrease, rather than increase (as
ferromagnetism, and I presume, paramagnetism do) inductance?

It's neat seeing how these scanners are made. There are guys on
the manufacturing floor using technology that hasn't changed in
generations, or even centuries. Mix that with superconductors chilled
with liquid helium, and there's a ton of interesting stuff going on.

Heheh.

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

"Dave Hinz" wrote in message
...
On Tue, 15 Mar 2005 23:03:38 GMT, yourname wrote:
Dave Hinz wrote:
On Tue, 15 Mar 2005 03:53:53 GMT, yourname wrote:
On Mon, 14 Mar 2005 20:19:05 +0000, Dave Hinz wrote:
Nah, it won't take out a metal sliver, they're too small to have
much pull on them even with that large of a magnet. You have
_stronger_
magnets in your computer's hard drive, by the way.

this is bull**** go down to the hospital and try.

I worked on MRI scanners for a dozen years. I have direct personal
experience and a verifyable resume. You, are ".
Thank you for sharing your thoughts, I will give them all the
consideration
they are due.

And when the guy with the MD after his name tells be i gotta get an
xray before they let me in the MRI machine
I think I will listen to him before you, giving your thoughts all the
consideration they are due.

You seem to have confused "won't take out a metal sliver" with "safe to
have metal in your eyes during an MRI scan". Thanks for playing,
though.


I just had an MRI done on my head and they took a bunch of X-rays first. It
still made my eyes do strange things and the rings on my fingers did a wierd
twitchy thing even though they are gold. Seemed like it was inducing a
current in the rings and that current was making like a magnet. I really
didn't expect to feel anything but normal vibrations but it caused several
places on my face to pull and twitch. Not painful but certainly got my
attention
Glenn

On Tue, 15 Mar 2005 23:24:30 -0800, the inscrutable "Glenn"
spake:

I just had an MRI done on my head and they took a bunch of X-rays first. It
still made my eyes do strange things and the rings on my fingers did a wierd
twitchy thing even though they are gold. Seemed like it was inducing a
current in the rings and that current was making like a magnet. I really
didn't expect to feel anything but normal vibrations but it caused several
places on my face to pull and twitch. Not painful but certainly got my
attention

I understand that it's such a powerful magnetic force that it hits
every molecule of steel impurity in fillings and rings. That HAS
to be an eerie feeling.

Want some fun? Get a CAT scan and Myelogram. Lay on a pillow with
your spine humped up while they inject a horse-sized needle full of
radioactive dye (contrast material) into it. Loverly!


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com

In article , Tim Williams says...

D'ya suppose it would be possible to make a cheapassed water-cooled tubing
coil of 0.5 to 2T (I'll have to look at the equation to see what's
reasonable), plus some other coils and whatnot, hook it up to a power supply
and signal generator and do a sort of radar-like trick to it (bad
comparison, but works for me, I mean you're sending a pulse then recieving
it) and actually observe NMRI?

NMR. That's what they used to call it before it became MRI. They
didn't like the "N" word, made folks freaky when they went into that
thing.

C. L. Stong's book (Amateur Scientist) has a section on building
a demo NMR setup, IIRC.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On Tue, 15 Mar 2005 23:24:30 -0800, "Glenn"
wrote:


"Dave Hinz" wrote in message
...
On Tue, 15 Mar 2005 23:03:38 GMT, yourname wrote:
Dave Hinz wrote:
On Tue, 15 Mar 2005 03:53:53 GMT, yourname wrote:
On Mon, 14 Mar 2005 20:19:05 +0000, Dave Hinz wrote:
Nah, it won't take out a metal sliver, they're too small to have
much pull on them even with that large of a magnet. You have
_stronger_
magnets in your computer's hard drive, by the way.

this is bull**** go down to the hospital and try.

I worked on MRI scanners for a dozen years. I have direct personal
experience and a verifyable resume. You, are ".
Thank you for sharing your thoughts, I will give them all the
consideration
they are due.

And when the guy with the MD after his name tells be i gotta get an
xray before they let me in the MRI machine
I think I will listen to him before you, giving your thoughts all the
consideration they are due.

You seem to have confused "won't take out a metal sliver" with "safe to
have metal in your eyes during an MRI scan". Thanks for playing,
though.


I just had an MRI done on my head and they took a bunch of X-rays first. It
still made my eyes do strange things and the rings on my fingers did a wierd
twitchy thing even though they are gold. Seemed like it was inducing a
current in the rings and that current was making like a magnet. I really
didn't expect to feel anything but normal vibrations but it caused several
places on my face to pull and twitch. Not painful but certainly got my
attention
Glenn

I noticed that ring thing when I had an MRI years ago. But recently I
had another and now there's a bunch of stainless and titanium in me. I
guess because it's all screwed in place there was no discernable
vibration.
ERS

On Tue, 15 Mar 2005 23:52:27 -0600, Tim Williams wrote:
"Dave Hinz" wrote in message
...
These weren't iron, they were chrome-plated rare earth magnets of some
sort.

Well yeah, but near the saturation limit of silicon steel. I.e. a pole
piece the same cross section as the magnet would be sort of saturated. I
think.

Could be, all I know is it was off the measurable scale, and I'm quite
sure that's the same magnetometer used in the 4T system bays.

Strong enough that they held strong through my hand. Hint:
don't let 'em go around and hit each other, because blood blisters will
result (based on a sample of one).

Yeah, they are a lot of fun, ain't they?

Until you get the pinch, yes. Then, not so much.

Yes, there's an inner coil and a counter-wound outer coil.

Would that be the RF coil? What makes the field precession and stuff
mentioned in the link Joe posted? (Thx BTW.)

Lots of coils. From outermost to closest to patient:
1. Outer "Bucking" coil to contain and shape the main field
2. Main field coil.
3. Shim coils (18 of 'em in different places/areas) to further even field,
(field "shim" is measured accurate into the parts per billion)
4. Outer gradient coils, in the X, Y, and Z direction to counter external
forces on the,
5. Inner gradient coils, in the X, Y, and Z direction, to actually provide
the dynamic magnetic field within the scan area. These operate with very
high current, in audio frequencies, inside a big magnet. This is why
MRI scanners are, by their nature, loud.
6. RF coil (birdcage array if that means anything to you) that transmits
the RF pulse, and picks up the echo from the patient. Usually.

How is the gradient made? Less amperage in one of the helmholtz coils?

Nope, those are constant and superconducting. Park 'em once, and you don't
need to do anything unless (a) someone quenches the magnet (rare), or
(b) you need to ramp it down for some reason (rare). Ramp up times of
years aren't unusual.

Yes, the GE magnets have 18 "shim coils", first, second, and third-order
corrections. The simplest is just X/Y/Z; get the overall gradient
from say front to back the same.

Necessary for the natural tapering and fringing of the field...

Right. The outer Heimholz coils help with keeping the flux lines
close to aligned for the length of the imaging area, but the shim coils
give you excellent control within the "sweet spot".

Second-order does opposing corners,
third order starts getting strange. Some delightful math to calculate
how to get the shims in order, as they all interact heavily.

I bet. Damn that Maxwell...

If you were there for a while and paid attention, you could actually
supercon shim in a magnet faster by tweaking it initially by hand.
At least get the first-order shim in, so the later ones didn't try to
compensate for first order by doing several second-order and so on.
You'd end up in a good place either way, but you could cut a dozen
iterations down to 5 or 6 if you started well.

Well, there are gradient aplifiers which make the RF pulse only resonate
one location cleanly (this is wrong but close enough to make the point).

That's what I'm not getting, how do you change the field to take a slice?
Fields don't much like shear...

The resonant frequency of a proton, in a magnetic field of exactly 1.5T,
is 63.86 MHz. Let's just use a Z gradient. Apply current, and the field
at your head is 1.51T, at your feet it's 1.49T. At exactly 1.50T is,
say, a slice through your belly. That's the only slice that a 63.86MHz
pulse will resonate. It'll _hit_ all of 'em, but only the one at 1.5T
will give an echo at that same frequency.

The other gradients then get you the raw data for horizontal and vertical
within that slice. (see "sort of", "this is wrong but close enough", and
"2D-FFT" below).

Yes, all very complex.

D'ya suppose it would be possible to make a cheapassed water-cooled tubing
coil of 0.5 to 2T (I'll have to look at the equation to see what's
reasonable), plus some other coils and whatnot, hook it up to a power supply
and signal generator and do a sort of radar-like trick to it (bad
comparison, but works for me, I mean you're sending a pulse then recieving
it) and actually observe NMRI?

You could get an echo, sure. A magnetometer is just a transmit coil, a
sample, and a receive coil. The external field makes the resonance happen.
Add a field to a magnetometer, and you could do a pulse/echo. If you're
anywhere near Waukesha Wisconsin, I could talk to some guys and get you
a tour, I think.

Right. It's usually localized to, say, the arms where they're
closest to the coil. A person inside an antenna acts as an RF "slug"
(heh) and both lowers the frequency of, and widens the peak of, how the
antenna is tuned.

Hm, flesh is diamagnetic... would that decrease, rather than increase (as
ferromagnetism, and I presume, paramagnetism do) inductance?

You just passed my area of confidence so I'm not going to speculate.
The analogy I was taught with was of screwing the tuning slug into
an inductor to increase the inductance. Maybe it was flawed, but I
do know that there's a nice sharp RF peak without a tuning slug
(big-ass carboy) in the bore, and it gets fatter and lower in height
and frequency with the tuning slug in the bore.

It's neat seeing how these scanners are made. There are guys on
the manufacturing floor using technology that hasn't changed in
generations, or even centuries. Mix that with superconductors chilled
with liquid helium, and there's a ton of interesting stuff going on.

Heheh.

Actually, I think the most fun was cryogen fills. Liquid helium goes
in at 4.7 Kelvin (-473 Farenheit, I think), and we vent off the gasses
at the top of the magnet. The vent tubing goes from nearly that temperature
closest to the cryostat, and nearly room temperature at the end. Along
the pipe, you can see what temperature it's at by what element is condensing
out of the atmosphere at that point. Liquid oxygen is slightly blue-ish,
CO2 snow over here, liquid nitrogen over further, and so on. Fun stuff.

On Tue, 15 Mar 2005 23:24:30 -0800, Glenn wrote:

I just had an MRI done on my head and they took a bunch of X-rays first.

Yup, it's a CYA as much as anything else. You don't want someone forgetting
they have some sort of implant, or metal in their eyes.

It
still made my eyes do strange things

Purple swirls and splotches, by any chance?

and the rings on my fingers did a wierd
twitchy thing even though they are gold. Seemed like it was inducing a
current in the rings and that current was making like a magnet.

Yes, even non-ferrous metals will get induced eddy currents. If you take
a quarter into the bore and line it up so it's across the bore, and tip it,
it takes several seconds to fall over. An aluminum soda can takes maybe
10 seconds. As it cuts the flux lines, eddy currents are induced in the
conductive metal which cause it to resist moving. Soda can is the best
example because it's large and light.

I really
didn't expect to feel anything but normal vibrations but it caused several
places on my face to pull and twitch. Not painful but certainly got my
attention

That, I can't explain. Could have been physical vibration from the gradients,
maybe?

Dave Hinz

On Wed, 16 Mar 2005 07:37:24 -0800, the inscrutable Eric R Snow
spake:

I noticed that ring thing when I had an MRI years ago. But recently I
had another and now there's a bunch of stainless and titanium in me. I
guess because it's all screwed in place there was no discernable
vibration.

You might be the person to ask about this, Eric. I have a new neighbor
who has a titanium hip and ball joint. His left leg is 2.5" shorter
than the right, and he's on his FIFTH hip. Is there any reason you can
think of (other than lousy doctors) which would make frequent
replacement necessary?


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com

On Tue, 15 Mar 2005 04:35:12 +0000 (UTC), () wrote:


Really interesting was that mid way through Chapter 9 we find:

Another frightening story was of a law enforcement officer being allowed
to go near a magnet with a loaded firearm. The handgun was pulled out of
its holster, and into the magnet. The force of the impact with the magnet
caused the gun to discharge. Luckily, no one was injured in this incident.
In addition to the damage to the MRI and the bullet lodged in the scan
room wall, the gun was magnetized.


I wonder what would happen if the bullet went through the coil causing it to
go open. Can anyone figure out how large the energy dump
would and damage it could have caused?

--

Boris Mohar

On Wed, 16 Mar 2005 10:04:29 -0800, Larry Jaques
wrote:

On Wed, 16 Mar 2005 07:37:24 -0800, the inscrutable Eric R Snow
spake:

I noticed that ring thing when I had an MRI years ago. But recently I
had another and now there's a bunch of stainless and titanium in me. I
guess because it's all screwed in place there was no discernable
vibration.

You might be the person to ask about this, Eric. I have a new neighbor
who has a titanium hip and ball joint. His left leg is 2.5" shorter
than the right, and he's on his FIFTH hip. Is there any reason you can
think of (other than lousy doctors) which would make frequent
replacement necessary?


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com
Yes, I studied implants and their effects on the human body.
Specifically wrists, but the hips act the same. Here's what happens:
No matter what the implants are made of and how non-allergenic the
materials are small particles are shed from wear. There are cells
called osteoclasts and osteoblasts. The osteoblasts build up bone and
the osteoclasts destroy bone. These cells must work in concert to keep
renewing bone. The small particles cause inflamation, an immune
response, just because of their size. This causes the osteoclasts to
be more active than the osteoblasts and bone will be lost in the area
where the implant is anchored in the bone. This causes the implant to
loosen which makes things worse. Surgery to correct the problem works
by removing bad bone and setting a new, larger implant in an enlarged
socket. I imagine if the femur is too wallowed out the only way to get
to good bone is by removing some length as well as opening up the
socket. This could happen because the socket is tapered, at least they
were in the ones I've seen. Hope that explains it. I can be long
winded.
Eric

On Wed, 16 Mar 2005 05:20:30 -0800, Larry Jaques wrote:


Want some fun? Get a CAT scan and Myelogram. Lay on a pillow with
your spine humped up while they inject a horse-sized needle full of
radioactive dye (contrast material) into it. Loverly!




More fun - after your radiation treatment, wander around setting off nuke
detectors.

http://www.signonsandiego.com/news/n...mi2detect.html

Poor guy probably has some nasty disease, and "they" think he's a
terrorist.

-Ron

On Wed, 16 Mar 2005 16:43:10 -0800, the inscrutable Eric R Snow
spake:

Yes, I studied implants and their effects on the human body.
Specifically wrists, but the hips act the same. Here's what happens:
No matter what the implants are made of and how non-allergenic the
materials are small particles are shed from wear. There are cells
called osteoclasts and osteoblasts. The osteoblasts build up bone and
the osteoclasts destroy bone. These cells must work in concert to keep
renewing bone. The small particles cause inflamation, an immune
response, just because of their size. This causes the osteoclasts to
be more active than the osteoblasts and bone will be lost in the area
where the implant is anchored in the bone. This causes the implant to
loosen which makes things worse. Surgery to correct the problem works
by removing bad bone and setting a new, larger implant in an enlarged
socket. I imagine if the femur is too wallowed out the only way to get
to good bone is by removing some length as well as opening up the
socket. This could happen because the socket is tapered, at least they
were in the ones I've seen. Hope that explains it. I can be long
winded.

Thanks.


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com

On Thu, 17 Mar 2005 02:36:16 GMT, the inscrutable Ron DeBlock
spake:

On Wed, 16 Mar 2005 05:20:30 -0800, Larry Jaques wrote:


Want some fun? Get a CAT scan and Myelogram. Lay on a pillow with
your spine humped up while they inject a horse-sized needle full of
radioactive dye (contrast material) into it. Loverly!

More fun - after your radiation treatment, wander around setting off nuke
detectors.

http://www.signonsandiego.com/news/n...mi2detect.html

Poor guy probably has some nasty disease, and "they" think he's a
terrorist.

Man, that just wasn't his day, was it? I'll bet he gets a nice fat
file in the DHS records room as a result, too.


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com

It took three hours to power down the
magnet and free the weapon.

I've worked in mnay labs with large superconducting magnets and there
are interesting stories to tell.

One day a grad student started yelling from the vicinity of the magnet.
We run in and see that Kenny had carried in a regular steel toolbox
which was now stuck to the side of the magnet. He was still yelling
and screaming about being stuck. We knew what was holding the toolbox
to the magnet, but we couldn't figure out what was holding Kenny to the
toolbox :-).

Maybe you had to know Kenny to appreciate the story. The point is,
folks who don't work around big magnets a lot don't really understand
at a gut level what happens (despite many years of schooling as to
electromagnetism...)

Tim.

On Wed, 16 Mar 2005 18:48:02 -0500, Boris Mohar wrote:
On Tue, 15 Mar 2005 04:35:12 +0000 (UTC), () wrote:


Really interesting was that mid way through Chapter 9 we find:

Another frightening story was of a law enforcement officer being allowed
to go near a magnet with a loaded firearm. The handgun was pulled out of
its holster, and into the magnet. The force of the impact with the magnet
caused the gun to discharge. Luckily, no one was injured in this incident.
In addition to the damage to the MRI and the bullet lodged in the scan
room wall, the gun was magnetized.

I wonder what would happen if the bullet went through the coil causing it to
go open.

Couldn't get to it, LOTS of stainless steel between where you are and
where the coil is.

Can anyone figure out how large the energy dump
would and damage it could have caused?

Well, it'd cause a "quench". If any part of the coil goes from superconducting
to resistive, it generates heat. Which boils off the helium (4.7 kelvin is
pretty darn cold), and that helium can't keep the coil cool, so it goes
resistive, which makes more heat, which boils off more helium...etc.

The cryostat (cold part of the magnet) has a carbon burst disk at the top,
calibrated for a fairly low pressure. When enough helium boils that it
makes the internal pressure higher than the few PSI that the burst disk is
set for, it, well bursts, and the helium is released into the vent stack
(8" diameter stainless, typically). The heat is carried away by boiling the
helium; it's calculated that there's enough helium to handle it.

Calculating the joules involved is tricky, because the math doesn't work
so easy when the voltage on the coil is zero (superconducting). There's
700+ amps of current, but no voltage once you're done ramping it up.

On 17 Mar 2005 06:18:20 -0800, Tim Shoppa wrote:

I've worked in mnay labs with large superconducting magnets and there
are interesting stories to tell.

Invisible force tends to be forgotten, yes.

One day a grad student started yelling from the vicinity of the magnet.
We run in and see that Kenny had carried in a regular steel toolbox
which was now stuck to the side of the magnet. He was still yelling
and screaming about being stuck. We knew what was holding the toolbox
to the magnet, but we couldn't figure out what was holding Kenny to the
toolbox :-).

?

Maybe you had to know Kenny to appreciate the story. The point is,
folks who don't work around big magnets a lot don't really understand
at a gut level what happens (despite many years of schooling as to
electromagnetism...)

We had an agency tech who we called "Wild Bill", because if you heard
3 words from him in a week, you wondered what got him so chatty all of
the sudden. Great tech, nice guy, just liked working and not socializing.
Well,...he came over to me, looking at his shoes, and said "I just did
something really dumb." 6 words. 2 weeks worth of communication, all
at once, which of course got my attention.

Seems that he was doing some up-close and personal work on a new magnet.
We had those library-type stools, which roll when you're not on 'em, and
don't roll when you're on 'em, and for the magnet areas, we used fiberglass
ones. Well, somehow one of the steel ones from the component build areas
got into the magnet part of the building, and of course that's the one he
grabbed. Took 4 people to get it off the magnet.

In article , Boris Mohar says...

I wonder what would happen if the bullet went through the coil causing it to
go open.

The real excitement happens when the round penetrates the vacuum
jacket for the heilum dewar. Those are thin, a 9mm round would
go through. At that point all the liquid in the dewar rapidly
changes to gas, one liter of liquid turns into a suprisingly
large volume of STP helium gas....

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

\ one liter of liquid turns into a suprisingly
large volume of STP helium gas....

Jim



people be talkin funny for a week,well at least the ones wiht a little
O2 left

On Thu, 17 Mar 2005 05:58:25 -0800, Larry Jaques
wrote:

On Thu, 17 Mar 2005 02:36:16 GMT, the inscrutable Ron DeBlock
spake:

On Wed, 16 Mar 2005 05:20:30 -0800, Larry Jaques wrote:


Want some fun? Get a CAT scan and Myelogram. Lay on a pillow with
your spine humped up while they inject a horse-sized needle full of
radioactive dye (contrast material) into it. Loverly!

More fun - after your radiation treatment, wander around setting off nuke
detectors.

http://www.signonsandiego.com/news/n...mi2detect.html

Poor guy probably has some nasty disease, and "they" think he's a
terrorist.

Man, that just wasn't his day, was it? I'll bet he gets a nice fat
file in the DHS records room as a result, too.


Happened recently in Bakersfield also. Local welder went to scrap yard
for metal..set off the radiation detectors after some medical
procedure the day before.

Gunner


-
Yea, though I walk through the valley of Minwax, I shall stain no Cherry.
http://diversify.com

Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.
H. L. Mencken

In article , yourname says...

\ one liter of liquid turns into a suprisingly
large volume of STP helium gas....

people be talkin funny for a week,well at least the ones wiht a little
O2 left

If you do this wrong, you can overpressure the dewar enough
to burst it.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On 17 Mar 2005 08:50:08 -0800, jim rozen wrote:
In article , Boris Mohar says...

I wonder what would happen if the bullet went through the coil causing it to
go open.

The real excitement happens when the round penetrates the vacuum
jacket for the heilum dewar. Those are thin, a 9mm round would
go through. At that point all the liquid in the dewar rapidly
changes to gas, one liter of liquid turns into a suprisingly
large volume of STP helium gas....

It'd come out as a "flame", looks _just_ like, say, a propane
flame, but it's white rather than blue. Inner cone & outer
zone and everything. Similar hazards, too.

When you fill a superconducting magnet, you need the inner cone (where it's
still liquid) to be into the fillport, you do not want to put a bubble
of warm helium into the bottom of the cryostat...

On Thu, 17 Mar 2005 18:12:39 GMT, the inscrutable Gunner
spake:

On Thu, 17 Mar 2005 05:58:25 -0800, Larry Jaques
wrote:

On Thu, 17 Mar 2005 02:36:16 GMT, the inscrutable Ron DeBlock
spake:

http://www.signonsandiego.com/news/n...mi2detect.html

Poor guy probably has some nasty disease, and "they" think he's a
terrorist.

Man, that just wasn't his day, was it? I'll bet he gets a nice fat
file in the DHS records room as a result, too.

Happened recently in Bakersfield also. Local welder went to scrap yard
for metal..set off the radiation detectors after some medical
procedure the day before.

'Tis a sad sign of the times that firemen and scrap metal dealers have
to use rad monitors on a daily basis, isn't it?


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In article , Dave Hinz says...

The real excitement happens when the round penetrates the vacuum
jacket for the heilum dewar. Those are thin, a 9mm round would
go through. At that point all the liquid in the dewar rapidly
changes to gas, one liter of liquid turns into a suprisingly
large volume of STP helium gas....

It'd come out as a "flame", looks _just_ like, say, a propane
flame, but it's white rather than blue. Inner cone & outer
zone and everything. Similar hazards, too.

The best story I heard happened at Brookhaven when they were
testing SSC magnets. They were running them in a vertical
dewar that went down into the floor about 30 feet deep.

The magnets were wound on steel laminations and were about a
foot in diameter.

To test them they were hung from fiberglass straps down into the
bath, off of a top plate.

They were removing one of the magnets when the crane operator
jerked the load, and all of the fiberglass straps parted,
dropping the entire magnet assembly back into the bath.

The blow-off from that setup ran out into a buffer volume in
the parking lot which was a large tank about the size of
a RR tank car, via a 6-inch line. Apparently the line
frosted up all the way out to the tank, and frosted up the
tank too.

They had two liquifiers there for this testing, we were
piggybacking on their system. They were delivering helium
to us in 1000 liter tanks. The boil-off was reclaimed
and then liquified again, it was a closed system - or
at least was supposed to be.

Their helium gas storage consisted of surplus tanks from Lakehurst
which had been brought on site. Because they were in somewhat
rough shape they had been de-rated down to about 500 psi
IIRC. But they had about 20 of them stacked up, each one
was about 3 ft in diameter and about 25 feet long.

Jim


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On 17 Mar 2005 12:48:39 -0800, jim rozen wrote:
In article , Dave Hinz says...

The real excitement happens when the round penetrates the vacuum
jacket for the heilum dewar. Those are thin, a 9mm round would
go through. At that point all the liquid in the dewar rapidly
changes to gas, one liter of liquid turns into a suprisingly
large volume of STP helium gas....

It'd come out as a "flame", looks _just_ like, say, a propane
flame, but it's white rather than blue. Inner cone & outer
zone and everything. Similar hazards, too.

The best story I heard happened at Brookhaven when they were
testing SSC magnets. They were running them in a vertical
dewar that went down into the floor about 30 feet deep.

Ah, so before they're put "in the can". Vats of liquid cryogen.
Sounds like fun.

The magnets were wound on steel laminations and were about a
foot in diameter.

To test them they were hung from fiberglass straps down into the
bath, off of a top plate.

Gotcha,

They were removing one of the magnets when the crane operator
jerked the load, and all of the fiberglass straps parted,
dropping the entire magnet assembly back into the bath.

Sounds expensive in cryogens as well as parts.

The blow-off from that setup ran out into a buffer volume in
the parking lot which was a large tank about the size of
a RR tank car, via a 6-inch line. Apparently the line
frosted up all the way out to the tank, and frosted up the
tank too.

At GE Medical (Sorry, "GE Healthcare" now), they have an AirProducts
distribution center on/in the back of the MR building. In the loft above the
main work area is a huge rubber bladder, to get the helium that vents
from the dozens of magnets in the building. They do whatever they do to
it and then re-liquify it. Lots cheaper to catch it than to get it any
other way.

They had two liquifiers there for this testing, we were
piggybacking on their system. They were delivering helium
to us in 1000 liter tanks. The boil-off was reclaimed
and then liquified again, it was a closed system - or
at least was supposed to be.

It's the logical way to do it, unless you put too much into the "closed"
system...

Their helium gas storage consisted of surplus tanks from Lakehurst
which had been brought on site. Because they were in somewhat
rough shape they had been de-rated down to about 500 psi
IIRC. But they had about 20 of them stacked up, each one
was about 3 ft in diameter and about 25 feet long.

Ah, so you stored it at high pressure then. The rubber bladder in
question was very low pressure; they compressed it on site as needed.

In article , Dave Hinz says...

Their helium gas storage consisted of surplus tanks from Lakehurst
which had been brought on site. Because they were in somewhat
rough shape they had been de-rated down to about 500 psi
IIRC. But they had about 20 of them stacked up, each one
was about 3 ft in diameter and about 25 feet long.

Ah, so you stored it at high pressure then. The rubber bladder in
question was very low pressure; they compressed it on site as needed.

There was a low-pressure storage like that too. They ran a compressor
to pump to the hp tanks.

The main compressors for the liquifer were rotary-screw type.
They were driven with 500 hp motors IIRC. Nobody was allowed
in the compressor shed when they were running.

We were just doing an experiment there, but I got to know the
cryogenics group a bit and helped out some there. Very smart
folks.

Jim


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