Tensioned Metastable Fluid Detector (TMFD)

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Dan Knapp
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Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Sun Oct 22, 2017 8:59 pm

I just returned from the 19th US-Japan IEC Workshop in Osaka (now called the Workshop on Fusion Neutron Sources and Applications), where I got to actually see a working tensioned metastable fluid detector (TMFD). (I’ll post a link when the presentations from the meeting are available online.) I have previously discussed this neutron detector as one that an amateur could conceivably build as an alternative to using the bubble detectors which have a short lifetime (viewtopic.php?f=47&t=10405&p=69223&hili ... tor#p69223). The first photo below shows a diagram of a TMFD. The fluid (decafluoropentane in this example) is tensioned by centrifugal force by spinning the tube assembly around the vertical axis with a variable speed motor. The second photo shows the TMFD while spinning. The flower decorated container next to it contains a Cf252 neutron source. The fluid in the bottom center chamber is put into a superheated state due to this tension, and a neutron passing through it initiates bubble formation. The detector in the photo has an infrared detector at the bottom to detect the bubble formation. The bubble formation is almost “explosive” and easily detected visually, but the IR detector enables automate counting and resetting the detector. The TMFD can only detect one neutron, after which the tension must be released (by interrupting the spinning) to reset it. A significant advantage of this detector is that the neutron energy threshold for detection can be set by adjusting the spinning speed.
The TMFD shown at the meeting is being used by Kai Masuda’s group at Kyoto University in a detection system for “special nuclear materials” being developed for the Tokyo Olympic Games. They are using a portable fusor with a 17 cm diameter water cooled chamber operated at 120 kV to generate 5 X 10e7 neutrons per second to actively interrogate suspicious objects. Secondary neutron production is detected by an array of three TMFD’s with energy threshold set to exclude the probe neutrons (i.e. they only detect the higher energy fission product neutrons). The TMFD is ideally suited for this application in that it can be set to only detect neutrons above a given energy threshold. Disadvantages are that the spinning rotor arrangement is a bit “Rube Goldbergish” and not exactly “robust” for a portable application. It is also limited in its count rate capability in that it has to be reset after each detection event. The company developing the TMFD (Sagamore/Adams Laboratories LLC) also has an acoustically tensioned TMFD, but it is not threshold settable like the centrifugal version.
As noted previously, an amateur could build a TMFD. The decafluoropentane fluid is used a degreasing solvent, so it should be obtainable (it is even listed on Amazon, but currently “not presently available”). Many other fluids have been used also as listed in the TMFD publications and patent. It would be interesting to see if fluid from defunct bubble detectors could be used. An enterprising amateur might also devise an alternative mechanism to apply the tension. Building one of these is on my very long list of future projects (which exceeds my expected lifespan at this point).
Attachments
TMFD1.JPG
diagram of a TMFD
TMFD2a.JPG
spinning TMFD

Silviu Tamasdan
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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Silviu Tamasdan » Sun Oct 22, 2017 10:54 pm

Interesting. So essentially the fluid is made superheated by applying a variable negative pressure (which lowers its boiling point). Then a neutron causes the superheated fluid to boil. It should be doable to replace the spinning rotor arrangement with a hydraulic piston to apply the negative pressure. And the DFP was probably chosen primarily because its boiling point is just above any reasonable room temperature, so it's easy to make it superheated.
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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Andrew Seltzman » Mon Oct 23, 2017 4:37 am

Dan,

Do you have a link to the conference website?
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Rich Feldman
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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Rich Feldman » Mon Oct 23, 2017 8:18 am

Very interesting.

Silviu, maybe pistons aren't a practical way to get negative hydrostatic pressure. Any existing bubble of air or vapor would simply expand. After taking measures to eliminate bubbles, it might be hard to eliminate nucleation sites associated with close-fitting pistons and sliding seals. The patent probably talks about it.

How 'bout a glass tube closed at the top, with working fluid (MF) filling the space above a column of mercury? Well, as Torricelli discovered, mercury any higher than what's supported by outside air pressure is happy to separate from the glass, leaving a vacuum space. Why would it not separate from the MF, or the MF separate from the glass -- no boiling required? The same issues apply to the centrifugal TMFD. Maybe surface forces between the fluid and the enclosure are important. In further reading, I saw tension magnitudes of 10 bar mentioned!

On my desk at work is a quart-size can of a dense fluid that's mostly decafluoropentane. Some proprietary mixture for vapor degreasers -- I think they're now using a different fluid in the degreaser at work. Someday before I die, in fact before I retire, I want to try floating an aluminum foil boat on the air/vapor boundary, like we've seen done in open buckets of SF6.

[edit] Yay for Internet search engines, in fact non-Google search engines! Yahoo just pointed me to:

A paywalled paper from 2009, about work at Purdue in ATMFD and CTMFD systems. http://proceedings.asmedigitalcollectio ... id=1629732

And this honestly-readable-for-free paper from 2016:
https://neup.inl.gov/SiteAssets/Final Reports/FY 2012/12-3367 NEUP Final Report.pdf
tmfd.JPG
Many co-authors' names are on both papers.
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Dan Knapp
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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Mon Oct 23, 2017 9:03 am

There was no web site for the meeting this year. The meeting was hosted by Professor Yamamoto in Osaka. I’ll check with him on whether he plans to post the presentations on the web. The meeting is not a regular open meeting; for a variety of reasons, participation is by invitation only. In the past the presentations have been posted on the web. If and when they are posted, I’ll post a link on this site.

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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Silviu Tamasdan » Mon Oct 23, 2017 12:18 pm

Rich Feldman wrote:
Mon Oct 23, 2017 8:18 am
Silviu, maybe pistons aren't a practical way to get negative hydrostatic pressure. Any existing bubble of air or vapor would simply expand. After taking measures to eliminate bubbles, it might be hard to eliminate nucleation sites associated with close-fitting pistons and sliding seals. The patent probably talks about it.

How 'bout a glass tube closed at the top, with working fluid (MF) filling the space above a column of mercury? Well, as Torricelli discovered, mercury any higher than what's supported by outside air pressure is happy to separate from the glass, leaving a vacuum space. Why would it not separate from the MF, or the MF separate from the glass -- no boiling required? The same issues apply to the centrifugal TMFD. Maybe surface forces between the fluid and the enclosure are important. In further reading, I saw tension magnitudes of 10 bar mentioned!
Fair point about nucleation sites. It would be difficult to make the system clean enough.
As for the mercury, I can think of one way to find out if it works or not. :) Except I don't have any mercury. It might be worth considering other liquid metals with different surface tension and adhesion properties, like galinstan.
There _is_ madness to my method.

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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Rex Allers » Mon Oct 23, 2017 10:44 pm

Thanks, Dan, for posting. Interesting stuff.

And Rich, for finding the paper. I had some trouble getting the link to work. If others do too, you can get there by going to top level of the site:
https://neup.inl.gov
and put this in the search field there
"12-3367 NEUP Final Report.pdf"

From that I found this patent on the method
US20030074010
https://www.google.com/patents/US20030074010

And this later one that shows the apparatus in the picture Dan shared
US20090296871
https://www.google.com/patents/US20090296871

One small thing from reading parts of it.
The first paper mentions this, "... under modest sub-vacuum conditions (e.g., -5 bar) at room temperature."
Maybe I'm dense but I don't understand what -5 bar means. Can someone tell me how to translate that to Torr?
Rex Allers

Dan Knapp
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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Dan Knapp » Mon Oct 23, 2017 11:38 pm

The -5 bar means the tension force on the fluid is the equivalent of negative five atmospheres, i.e. less than 0 Torr, so you cannot achieve this tension by simply exposing the fluid to vacuum; you have to apply a force actually pulling on the liquid (i.e. pushing it apart). As such, it would not appear that any piston or other volume expansion apparatus would work. In the centrifugal TMSD, there is a force pushing the liquid away from the axis making a tension on the axial chamber. In the acoustic TMSD, there is a force alternately pushing the fluid in opposite directions. I've racked my brain trying to think of another way to apply the required force, but so far I have come up empty. We can assume that Taleyarkhan has been thinking the same thing for a lot of years on how else to do this and apparently hasn't come up with another method.
In the bubble detector, which is also another type of TMFD, the force is just a relaxation of applied pressure. The force is the intermolecular repulsion in a compressed liquid. It would be of interest to know what is the failure mechanism when bubble tubes go bad. The only thing apparent in the ones I've had is that they just started to leak. Does anyone know anything further about the failure mechanism in dead bubble tubes?

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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Rex Allers » Tue Oct 24, 2017 1:22 am

Thanks Dan. It wasn't intuitive, at least to me, that the pressure (or negative force) in the liquid could get below 0 Torr. I think I'm starting to get it now. So you can't pull the liquid from the outside or you'll just create a vacuum space around it like a barometer. The force can be generated in the liquid itself by centrifugal force.

Still not quite obvious in my mind why the liquid doesn't just open voids, but I guess that's why the detector works. I'll just have to accept it.

I have nothing to offer on the bubble detectors.
Rex Allers

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Re: Tensioned Metastable Fluid Detector (TMFD)

Post by Silviu Tamasdan » Tue Oct 24, 2017 9:44 am

How about applying a (positive) pressure on the fluid and then suddenly releasing it? That might create sufficient moment in the fluid mass to simulate at least briefly a negative pressure. I think that the piezoelectric system above does exactly that. But it could be done by other means. And by varying the amount of pressure and the frequency of the pressure/release cycles you might be able to vary the sensitivity of the system.
There _is_ madness to my method.

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