[Fast-Neutrons] characterization of fast neutron setups

Michael Taylor Michael.Taylor at phoenixwi.com
Wed Dec 18 17:46:42 CET 2019


Dear Pavel,

I agree that a Fourier Ring Correlation is a great tool, and imageJ actually has a plug in for it so the work is mainly already done. However, I think we'll need to standardize a way that we can all measure it the same way with a tool that is useful for all.  As I mentioned, I will purchase and test the MTF on our detector for various materials of interest, but I think we might want to put some effort into an appropriate Siemens star, perhaps based on my measurements?

Best regards,
Michael
________________________________
From: Trtik Pavel (PSI) <pavel.trtik at psi.ch>
Sent: Wednesday, December 18, 2019 10:06 AM
To: Lehmann Eberhard (PSI) <eberhard.lehmann at psi.ch>; Michael Taylor <Michael.Taylor at phoenixwi.com>; Alan Hewat <alan.hewat at neutronoptics.com>
Cc: fast-neutrons at neutronsources.org <fast-neutrons at neutronsources.org>
Subject: RE: characterization of fast neutron setups


Dear all,



just to add to the resolution discussion here, if I may.



I am not sure if my email from Nov 19 has reached the recipients. If it did and the option of FRC assessment is considered unsuitable for fast neutrons, then I apologize for bringing it here again. Please see the email below.



Further, one may also consider production of 3D test objects. For that, may I draw your attention to my attempt for such an object for combined synchrotron/neutron imaging experiment that I reported at NIUS 2012. Please see the slide attached.



Wishing everybody Merry Christmas and all the best in 2020.



Kind regards



Pavel

-------------------------------------------

From: Trtik Pavel (PSI)
Sent: Dienstag, 19. November 2019 16:43
To: 'Michael Taylor' <Michael.Taylor at phoenixwi.com>; fast-neutrons at neutronsources.org
Subject: RE: First fast neutron images at Phoenix



Hi Michael, hi everybody



very nice, congratulations!



Regarding the resolution assessment, may I suggest you also try Fourier Ring Correlation (FRC) for resolution assessment. It has got the advantage that it does not require a test pattern, one just needs to have 2 corresponding images of the given object, so here you can use 2 x 7 projections from the original stock.



FRC has been created for the cases of imaging modalities for which the provision of perfect imaging test objects/patterns is difficult (such as for TEM), which seems to be the case here as well.



With best regards



Pavel





__________________________________________
Paul Scherrer Institut
Pavel Trtik
WBBA/107
Forschungsstrasse 111
5232 Villigen PSI
Schweiz

Telefon: +41 56 310 55 79
E-Mail: pavel.trtik at psi.ch

From: fast-neutrons-bounces at neutronsources.org <fast-neutrons-bounces at neutronsources.org> On Behalf Of Lehmann Eberhard (PSI)
Sent: Dienstag, 17. Dezember 2019 10:49
To: Michael Taylor <Michael.Taylor at phoenixwi.com>; Alan Hewat <alan.hewat at neutronoptics.com>
Cc: fast-neutrons at neutronsources.org
Subject: [Fast-Neutrons] characterization of fast neutron setups



Dear all again,



when we want to judge best for a given setup: beam, detector, sample

we have to agree for the following conditions:



1.       test material (here is discussion about hydrogen – and W therefore

seems to be better)

2.       test device geometry: Siemens start seems to be useful because

already the “image” provides a feature or impression about the

resolution: but how to analyze it more quantitatively.

3.       Therefore edges or gaps seems to be easier and straightforward

to quantify.



Gamma radiation in the beam and by sample interaction

have to be handled separately because the signal depends on the

detector response for it and the amount of gammas.

This signal has to be kept as low as possible. It should not strongly

influence the aspect of spatial resolution of the neutron setup.



I hope for nice tests at NECTAR in spring of 2020 … to answer some

of these questions.



Best regards to all



Eberhard



__________________________________________
Paul Scherrer Institut
Dr. Eberhard H. Lehmann
WBBA/122
Forschungsstrasse 111
5232 Villigen PSI
Schweiz

Telefon: +41 56 310 29 63
E-Mail: eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>



Von: fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org> <fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org>> Im Auftrag von Michael Taylor
Gesendet: Montag, 16. Dezember 2019 21:01
An: Alan Hewat <alan.hewat at neutronoptics.com<mailto:alan.hewat at neutronoptics.com>>
Cc: fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>
Betreff: Re: [Fast-Neutrons] Fast-Neutrons Digest, Vol 6, Issue 1



Alan, that's a good idea.  I shouldn't say we don't produce a lot of gammas, we just shield them out pretty well.  Our neutron to gamma ratio is quite high. I will try to use an Xray detector as well as a fast neutron one to quantify this better.



Our images are even better than what I've shown before.  We've been taking category I ASTM film images (75 minute exposure) and the resolution is down to around 40um now and they look very smooth and have nice contrast.  I'm scanning some soon that I can send out as an example.



Cheers,

Michael

________________________________

From: Alan Hewat <alan.hewat at neutronoptics.com<mailto:alan.hewat at neutronoptics.com>>
Sent: Monday, December 16, 2019 1:53 PM
To: Michael Taylor <Michael.Taylor at phoenixwi.com<mailto:Michael.Taylor at phoenixwi.com>>
Cc: fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org> <fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>>
Subject: Re: [Fast-Neutrons] Fast-Neutrons Digest, Vol 6, Issue 1



I'm happy to hear that Michael's hot neutron source doesn't produce much gamma. Still it would be good if when you took a fast neutron image you could also take a similar image with an x-ray scintillator or image plate. And if you think that gamma produced by fast neutrons scattered from a hydrogenous sample might be a problem, you could easily test that with an image.

Again, very impressed with your thermal neutron images. Great stuff !



Cheers, Alan

______________________________________________________
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
                               from my telephone
<Alan.Hewat at NeutronOptics.com<mailto:Alan.Hewat at NeutronOptics.com>> +33.476.98.41.68
        http://www.NeutronOptics.com/hewat<https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fwww.NeutronOptics.com%2fhewat&c=E,1,liRVuPCZos4Nap8CdQ8I0FHAi4kzaNATgQvRwhWAyDsWrioLQNqu-ykY_6MOxGu2Tl2YoSPYGiaxGXDPvouNyr-DBCk7YjbMUpkUen2hzZWLGWFIGSbE&typo=1>
______________________________________________________



On Mon, 16 Dec 2019, 19:08 Michael Taylor, <Michael.Taylor at phoenixwi.com<mailto:Michael.Taylor at phoenixwi.com>> wrote:

Our source does not produce much for gammas, it’s the gammas produced in the walls of the shielding that are then filtered by 3” of lead. If you’re using a polymer near the detector, that will generate a large number of 2.2MeV gammas from the hydrogen that will be background noise on the detector itself (using an aSi DDA), so that could be an issue as well.

——————————————————

Michael Taylor Ph.D.

Neutron Radiography Product Manager

Phoenix LLC

2555 Industrial Drive

Monona, WI 53713

608-210-3060 office

608-515-3214 mobile



On Dec 16, 2019, at 09:53, Alan Hewat <alan.hewat at neutronoptics.com<mailto:alan.hewat at neutronoptics.com>> wrote:



I disagree with Eberhard :-) that my polymer Siemens star should not be used with fast neutrons because it is complex and the resulting thermalised neutrons are easier to detect. Hot neutron scintillators (PP/ZnS) are not very sensitive to low energy neutrons. But ZnS is quite sensitive to x-rays and gammas, which are produced in far greater quantities from a DD/DT source. As Eberhard showed at Garching, the cross section for gammas and fast neutrons is similar for many materials, so unless you are sure to reduce the hard x-ray flux well below that of hot neutrons, your heavy metal image may have an important gamma component. Gammas, unlike thermal neutrons, are difficult to filter out, but a polymer Siemens star will be transparent to them. Siemens stars are commonly used for thermal neutrons and x-rays, and are not as complicated as real objects.



In fact, I suspect you should try to determine the resolution from your real object, which will contain some edges that can be analyzed, but also small features that can be used to estimate resolution. And use different scintillators to try to separate different beam components.



Alan.



On Mon, 16 Dec 2019 at 11:51, Lehmann Eberhard (PSI) <eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>> wrote:

Dear all fast neutron imagers,



as you might know, the blurring in fast neutron images

are caused by at least three parameters:



1.       beam collimation

2.       inherent detector blurring, mainly by the scintillator

3.       scattering of the sample, even a test pattern



It is difficult to separate them with only one measurement.



To exclude the beam effects, studies with test samples close

to the detector might help. BUT: when the test pattern has to

be thick enough (see below), some beam blurring cannot be

avoided.



The topic of test samples has been discussed by Michael, Alan

and Robert in some details. I completely agree, NOT to have a

complicated structure like Siemens stars, but edges of highly

attenuating materials.



As you can see in the attached slides (from my Garching presentation)

there are some high Z materials with values around 0.5 cm-1.

Because Os, Ir, Re are exotic and expensive, the best choice would be

W. However, a 1 cm layer will attenuate only by 40%, 2 cm by 64%.

There are no “black absorbers” like Gd, Cd or B-10 around for thermal

neutrons.



In conclusion, I agree with Robert to have well manufactured W

edges of 1 to 2 cm thickness, well aligned in beam direction

(by means of a holder structure).

In order to make the resolution more visible, two parallel plates

can be used while the gap can be set variable by a mechanical

equipment.

Such structure can be placed at arbitrary positions in the open beam

to analyze the different beam collimation features.



I would avoid samples of hydrogenous material because of possible

moderation effects which bring neutrons to energies where the can be

detected more efficiently.



Any better/other idea is welcome for further consideration and testing.



Best regards



Eberhard

__________________________________________
Paul Scherrer Institut
Dr. Eberhard H. Lehmann
WBBA/122
Forschungsstrasse 111
5232 Villigen PSI
Schweiz

Telefon: +41 56 310 29 63
E-Mail: eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>



Von: fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org> <fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org>> Im Auftrag von Michael Taylor
Gesendet: Freitag, 13. Dezember 2019 20:22
An: Alan Hewat <alan.hewat at neutronoptics.com<mailto:alan.hewat at neutronoptics.com>>
Cc: fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>; Elizabeth .Hewat <liz.hewat at gmail.com<mailto:liz.hewat at gmail.com>>
Betreff: Re: [Fast-Neutrons] Fast-Neutrons Digest, Vol 6, Issue 1



Alan, we have a decent plastics printer here at Phoenix but if there’s a reason that the seimans star template would not be good for doing this test I don’t wanna bother making the star. I think this work needs development between many different people to figure out a good solution for everybody to do it the same way between facilities and make it repeatable. I’d be very happy to start that conversation now so that we can get a good solution in place in the future.

——————————————————

Michael Taylor Ph.D.

Neutron Radiography Product Manager

Phoenix LLC

2555 Industrial Drive

Monona, WI 53713

608-210-3060 office

608-515-3214 mobile



On Dec 13, 2019, at 12:59, Alan Hewat <alan.hewat at neutronoptics.com<mailto:alan.hewat at neutronoptics.com>> wrote:



Yes, Robert makes a lot of good points. I suppose the best you can say for a printed Siemens star is that it can provide a graphic representation of the resolution. The resolution limit that Robert mentions probably can't be obtained anyway with your hot neutron scintillator and collimation. You should be able to find a local company that will print a polymer star for you. You can even buy suitable printers on Amazon for a few hundred dollars. If you can't find a local supplier and really want one, we have such things. If you were local (EU), we could lend you one, but taxes and shipping back and forth to the US make that less attractive than simply buying it for €150. For a photo, see:

http://neutronoptics.com/downloads/Manual-NeutronOptics-Hot-Neutron-Camera.pdf<https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fneutronoptics.com%2fdownloads%2fManual-NeutronOptics-Hot-Neutron-Camera.pdf&c=E,1,Ojm42aZ5NqLU8ppaotRi6f_VJGljg6LCVEA1oSACfKZzVssKLs7ZAFlJyzaL2dz2QNTrmtDLfYLI_siCgzaUr1UpOGXqM8sLC78VOVA9&typo=1>



Regards Alan

______________________________________________________
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
                               from my telephone
<Alan.Hewat at NeutronOptics.com<mailto:Alan.Hewat at NeutronOptics.com>> +33.476.98.41.68
        http://www.NeutronOptics.com/hewat<https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fwww.NeutronOptics.com%2fhewat&c=E,1,HyVplmih2rSx7XCaGPqmFyBYlwJanQjd8wmcyx8hDDaHPkXDnkmNwcJtdUFIkEDetaiKV0SMyfnSzx5qhmQTvjE2ns0u3LUGpTVawIh2GKUKtA,,&typo=1>
______________________________________________________



On Fri, 13 Dec 2019, 19:11 Michael Taylor, <Michael.Taylor at phoenixwi.com<mailto:Michael.Taylor at phoenixwi.com>> wrote:

Hi Robert,



Thank you for the message, you point out lots of good information in there! I have our machinist working on a couple edges for simple flat and square pieces currently using steel and aluminum to start with. I had hoped a printed Siemens star would come out pretty nicely but perhaps after reading your description it wouldn’t be the best.  Since we don’t have any standard methods to perform this measurement, anything is fair game, except for aligning to the pixel row as you mention, that’s just cheating! I am hopeful we, as a group, can come up with some standard ways to measure the resolution, L/D, etc, just like we have for ASTM thermal neutron imaging.  Once I get some shots taken I will send out the data and see what the group thinks is a good way to process it.



Best regards,

Michael



——————————————————

Michael Taylor Ph.D.

Neutron Radiography Product Manager

Phoenix LLC

2555 Industrial Drive

Monona, WI 53713

608-210-3060 office

608-515-3214 mobile



On Dec 13, 2019, at 06:25, Robert Adams <adams at lke.mavt.ethz.ch<mailto:adams at lke.mavt.ethz.ch>> wrote:



Hello Michael,



I can offer my thoughts on this topic, for whatever they are worth:



To evaluate the resolution of your radiography system, I don't think a Siemens star makes much sense because it should be reasonably thick (unlike e.g. thermal neutrons or X-rays, where a very thin structure can be used and still obtain a decent attenuation), which means the center of the star will have some rounded edges depending on how it's manufactured... e.g. if you make a Siemens star out of some metal or plastic with waterjet, machining, wire erosion, etc., always the cut-out will have some curvature on the order of 0.5-1 mm at the inner "corner", on the same order as what I guess the system will achieve, so it will not give valuable information. One way around this might be cutting wedges individually, then placing them together, but then alignment is tricky. There might be ways around this to get something satisfactory, but in the end I don't see much value above a good old-fashioned edge measurement. A line pair structure is also a possibility, but like the wedge probably cannot be satisfactorily machined monolithically, and does not add a lot of value to an edge in this case in my opinion.



For an edge, it should only be carefully machined to have properly parallel/perpendicular faces, but that's pretty easy. Just make sure the machinist doesn't break or chamfer the corners significantly. Machinable tungsten alloys are readily available and are a good choice for attenuating fast neutrons. Could do alu or steel as well to get some variety. Plastic is also fine but sometimes more annoying to get precise, clean edges and corners compared to metal. I think on the order of 1 cm or so is sufficiently thick to get an easily measured amount of attenuation in the image, without suffering too much from some kind of penumbra blur effect. To be sure that this penumbra is not affecting you, you can do several thicknesses (e.g. 5, 10, 20 mm) and check that they agree. The thickness-direction edge should of course be as parallel as possible with the beam, and it should be placed close to the detector surface if you want to characterize only the detector and minimize effects from the source emitting spot size. You can change the distance to be further away from the detector surface, and then the difference in result will indicate the effect of your source emitting spot or collimation or whatever. More effort, but to check the penumbra effect in more detail you can also put it on a little rotary stage and take a series of measurements from what you consider "edge aligned", and +/- few degrees in small steps, then compare results. If the system is pixelated, the edge should not run palallel to the pixel edge direction, as that can potentially make the measurement suggest a resolution better than it actually is, i.e. put it at 10 degrees from vertical or something like that.

For processing you can get each grayscale value as a function of distance from the edge (defined by a manually selected line segment), for all pixels along some length of the edge (e.g. couple cm) and some distance away, then put that all together on one plot. Then make, for example, an error function fit to that data. Then take the derivative of that fit to get a line spread function, and from that the FWHM is an indication of resolution. Or, process the data a bit further and get an MTF. Or, of course, the edge data could be processed many other ways.



If you want you can to send me image data and I can try apply some scripts I already have to it to give you an example of some of what I'm describing. I expect with some simple edge measurements you can get a robust idea of how your imaging system is performing.



Best regards,
Robert




Robert Adams, Dr. sc.
IET-LKE ML K19

ETH Zürich

Sonneggstrasse 3

8092 Zürich, Switzerland
Office: +41 (0) 44 632 49 01
Mobile: +41 (0) 78 611 39 39





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Today's Topics:

   1. Re: Congrats! Re: First fast neutron      images  at      Phoenix
      (Michael Taylor)


----------------------------------------------------------------------

Message: 1
Date: Thu, 12 Dec 2019 20:49:30 +0000
From: Michael Taylor <Michael.Taylor at phoenixwi.com<mailto:Michael.Taylor at phoenixwi.com>>
To: "Lehmann Eberhard (PSI)" <eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>>, Alan
        <alan.hewat at gmail.com<mailto:alan.hewat at gmail.com>>, "fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>"
        <fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>>
Subject: Re: [Fast-Neutrons] Congrats! Re: First fast neutron   images
        at      Phoenix
Message-ID:
        <SN6PR04MB4477696A12CFD23A4EC47D2892550 at SN6PR04MB4477.namprd04.prod.outlook.com<mailto:SN6PR04MB4477696A12CFD23A4EC47D2892550 at SN6PR04MB4477.namprd04.prod.outlook.com>>

Content-Type: text/plain; charset="windows-1252"

Hello all,

Does anyone already have a printed Siemens star they'd be willing to ship to me for testing?  Has anyone come up with another method for measuring resolution for fast neutron imaging?  We are otherwise going to image an edge on different pieces of material: Fe, W, Cu, Al, HDPE to see how they compare.

Best regards,
Michael
________________________________
From: fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org> <fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org>> on behalf of Lehmann Eberhard (PSI) <eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>>
Sent: Monday, November 18, 2019 4:52 AM
To: Alan <alan.hewat at gmail.com<mailto:alan.hewat at gmail.com>>; fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org> <fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>>
Subject: Re: [Fast-Neutrons] Congrats! Re: First fast neutron images at Phoenix


I disagree with Alan about the n-sensitive imaging plates: they are

made by Fuji on a commercial base adding Gd to the X-ray sensitive

material. Therefore the efficiency is not bad and much better than

film methods ?



Regards



Eberhard



__________________________________________
Paul Scherrer Institut
Dr. Eberhard H. Lehmann
WBBA/122
Forschungsstrasse 111
5232 Villigen PSI
Schweiz

Telefon: +41 56 310 29 63
E-Mail: eberhard.lehmann at psi.ch<mailto:eberhard.lehmann at psi.ch>



Von: fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org> <fast-neutrons-bounces at neutronsources.org<mailto:fast-neutrons-bounces at neutronsources.org>> Im Auftrag von Alan
Gesendet: Montag, 18. November 2019 10:43
An: fast-neutrons at neutronsources.org<mailto:fast-neutrons at neutronsources.org>
Betreff: Re: [Fast-Neutrons] Congrats! Re: First fast neutron images at Phoenix



Hello Michael, Burkhard and Eberhard.



Thank you Michael for these nice images. I too am impressed by the resolution of your thermal images with an L/D of only 35, and agree that it would be good to take thermal images with a camera rather than a neutron image plate. The ordinary Fuji n-plates are just x-ray plates with extra 6LiF and I think only ~10% efficient. ~20 years ago Fuji made special n-plates for ILL that were ~25% efficient but they are no longer available (?). You should be able to reduce the exposure well below 20 minutes with a camera and a good 6LiF/ZnS thermal neutron scintillator even with only 10**4 n.cm-2.s-1. See the images Robert Zboray showed in Sydney from a very low flux Triga reactor, one of which I reproduced in my Munich talk.



It would also be good to compare your fast neutron image with a thermal neutron image using the same detector and L/D (with different scintillators). With such small objects, that can be put close to the scintillator, it would be interesting to see if fast neutrons still have some advantage for imaging such defects.



I also found Burkard's and Eberhard's comments about the best material and thickness for a fast neutron Siemens star interesting. It would be good to see images with these different resolution objects. I also printed a plastic Siemens star, but 40 mm thick, which I have not yet been able to test. A final trivial point; please don't use exponent e4 instead of 10**4 for flux; e has a different meaning for mathematicians.

Thanks again for sharing. Alan

______________________________________________________
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
                               from my telephone
<Alan.Hewat at NeutronOptics.com<mailto:Alan.Hewat at NeutronOptics.com<mailto:Alan.Hewat at NeutronOptics.com>>> +33.476.98.41.68
        http://www.NeutronOptics.com/hewat<https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fwww.NeutronOptics.com%2fhewat&c=E,1,trfayPibiE37z2ho-7D5TpNVA7TTpp4CAOi_NfafXtcFw-fUnzbSjE2ptPnJmF5-qQS9y7dPRHLSRqoAE2rdQFeZnqKjxaNGstiBHAH27FHyUe1fXfiVzZdaICQ,&typo=1><https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fwww.NeutronOptics.com%2fhewat&c=E,1,nsRpj7Ep0HI2dnJQS9mLWP7NTTRFa_A1rnHdA_hwLcr1LAK7nQ2-Td0N6b_DO9Ja1638KxTpmGVeliGNkSNhx7t1hvZbcROb-wXGKiiSSd4b_OlHxdBS0EA,&typo=1>
______________________________________________________



On Mon, 18 Nov 2019, 08:42 Burkhard Schillinger, <Burkhard.Schillinger at frm2.tum.de<mailto:Burkhard.Schillinger at frm2.tum.de><mailto:Burkhard.Schillinger at frm2.tum.de<mailto:Burkhard.Schillinger at frm2.tum.de>>> wrote:

Hello Michael,

congratulations for these nice images!
For a fast neutron image, that resolution is pretty good. Probably
better than ours - which shows that a high collimation is also
important for fast neutrons if you have large samples.

I am also surprised again by your thermal image at L/D of only 35 -
but that's what you get when you can put the samples up close to the
detector.


For an edge - about everything scatters fast neutrons, but I have
tried with a 10 mm thick polyethylen pattern (Siemens Star) that was
3D printed at our lab. When putting it directly on the detector, it
was a good measure to test the screen. The 1.5 mm thickness screen was
much better than the 2.4 mm.
Not sure what really happens if you take it further away - I assume
that 10 mm thickness is a good compromise between attenuation and
scattering blur. You might try 10 mm steel as well, but iron is also a
diffuse scatterer.
A perfect edge does not exist.

Good luck with your new 'toys', and Happy Holidays!

Burkhard




> Good day to all,
>
> I am happy to announce that we've taken our first fast neutron
> images at the Phoenix facility in Wisconsin, USA!  Our source is
> operational now with a source strength of approximately 1.5e12 n/s
> and an L/D of 450 to achieve a flux at the image plane of
> approximately 5e5 n/cm^2-s.  Over the next few weeks, we will be
> increasing our beam current and changing our target to a different
> material.  We expect to get to full power and have a source strength
> of 3e13 n/s and a flux at the image plane of approximately 1e7
> n/cm^2-s.
>
> The image attached was taken using a Varex XRD 1621 digital detector
> array and a PP:ZnS(Cu) screen provided by RCTritec.  The
> scintillator field of view is 310mm x 310mm, but we plan to use the
> full field of view of the detector eventually, which is 430mm x
> 430mm.  The image was taken last night and acquired with 15 frames
> at 20 seconds each.  The frames were then added and the offsets were
> applied for background corrections.  The sample is a simulated M982
> military round.  It is 155mm in diameter.  The outside casing is
> 1/8" steel and the inside simulant is an HMX equivalent, 6% 6656
> binder (simulated with 204 epoxy). Chemically it is similar to HMX
> and RDX but with much less nitrogen.  I have outlined some of the
> defects of interest that we want to see.
>
> We would like to measure the resolution of the system next so I
> would like to ask if anyone has advice on what material to use as an
> edge and how thick it should be?  We do not yet have any kind of
> standard measurement technique for this that I'm aware of, so I
> would like to know what others are doing.
>
> I've also attached a new image we acquired using thermal neutrons of
> several different military grade .50 caliber ammunition.  We took an
> X-ray image for comparison and that is shown as well.  The X-ray was
> done at 350kV but I don't recall the current.  The neutron image was
> acquired using our thermal neutron generator with heavy water
> moderator, the L/D was 35 and the flux was approximately 1e4
> n/cm^2-s.  The exposure time on a neutron sensitive image plate was
> 20 minutes.
>
> I hope everyone is well, it was great to meet so many of you in
> Garching last month and I wish you all happy holidays as they
> approach us soon.
>
> Best regards,
> Michael
>
> Michael Taylor Ph.D.
> Neutron Radiography Product Manager
> Phoenix LLC
> 2555 Industrial Drive
> Madison, WI 53717
> 608-515-3214



--
Dr. Burkhard Schillinger
Technische Universit?t M?nchen - FRM II
Heinz Maier-Leibnitz Zentrum
Lichtenbergstr.1
D-85748 Garching
Germany
Tel. +49 89 289-12185

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--

______________________________________________

   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE

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