[Halld-tagger] [EXTERNAL] notes from tagger working group meeting this morning

[Malte Albrecht]

Hi Beni, all,

I remembered that Luxium Solutions (formerly Saint Gobin Crystals) produces custom arrays (1D or 2D) of small scintillation crystals for various applications. The whole development is driven by the medical industry, but it was investigated for LHC detectors as well. If the material proves to be useful for us, one could imagine ordering pre-fabricated linear arrays instead of individual little crystals. Here is some more info: https://luxiumsolutions.com/radiation-detector-assemblies/pixellated-arrays 
I also looked for the radiation hardness: For larger LYSO(Ce) crystals, a test at Caltech for SLHC showed a loss of light yield of about 10% at 1MRad (see http://www.its.caltech.edu/~rzhu/talks/marat_091029_slhc.pdf )

Of course the decay time of the pulse is crucial for us. I checked Alex Barnes dissertation - the current scintillators have a decay time of 2.7ns, so the LYSO would be about a factor 10 worse. That means, at high rates we will have pile-up, that may or may not be recoverable.


Another option I came across: Apparently there is a more radiation-hard variant of the scintillating fibers we are using now. Luxium advertises the ones we have now (BCF-20) as well as a slightly slower (7ns decay time), but more radiation hard variant called BCF-60XL. Probably these are not available in a square cross section, but nevertheless worth investigating:
https://luxiumsolutions.com/radiation-detection-scintillators/fibers 

Best,
Malte


> On Oct 10, 2025, at 4:42 PM, zihlmann via Halld-tagger <halld-tagger at jlab.org> wrote:
> 
> Hi Justin, and All,
> 
> yes a "two path" approach may give us the most value. 
> The LYSO may not be the best solution either. The advantage is that the geometry is very well defined 
> like the cross section of 2mm by 2mm has a very high accuracy of 0.02mm the potential disadvantages,
> as pointed out by Eugene, is the potential shower effects as the radiation length of this material is 1.1cm
> so a 10mm long crystal may be a better choice. Secondly the signal decay time of order 35ns which may
> be too long at the high rates we can expect in GlueX III.
> 
> cheers,
> Beni
> 
> 
> 
> On 10/10/25 15:40, Justin Stevens wrote:
>> Hi Beni, All, 
>> 
>> Thanks for the information about the crystals.  I like the idea to replace some of the scintillators directly in the “production” microscope for the experiment if we’re convinced it will produce usable signals so that we don’t create a loss of acceptance in some region of the tagger.  We would learn more about the radiation hardness there than we would in the PS area.
>> 
>> A test setup in the PS area would have the advantage that it could be more flexible to evaluate different couplings procedures or other scintillator options which are more speculative, with easier access to adjust the geometry or setup without moving the full microscope.  If we have any spare material from the original scintillator from Saint-Gobain, we could also have a control sample to compare with (before radiation).   
>> 
>> Maybe we want to do both of these tests in 2026?
>> 
>> -Justin
>> 
>>> On Oct 10, 2025, at 10:15 AM, zihlmann via Halld-tagger <halld-tagger at jlab.org> wrote:
>>> 
>>> Hi All,
>>> 
>>> regarding scintillator alternatives (proposed by Malte, Arshak, ...) I am investigating several paths to obtain LYSO crystals 
>>> with 2mm by 2mm cross section and a length of 20mm or thereabouts. I think the length is not that important but the cross section 
>>> is to fit the current geometry. I contacted two companies in the US and waiting responses. There is a company in China where one 
>>> could buy online such crystals right away with a cost of 39$ per piece (excluding taxes and tarifs). So my hope is that we could 
>>> get our hands on some such crystals on a rather short time scale.
>>> 
>>> My basic idea is to equip the last "bundle" (most downstream), 3 columns with 5 scintillators each, with such crystals
>>> (the coupling has not yet been evaluated) till February and run with that in the next run period. If that is possible we would learn
>>> likely quite a lot about the usefulness of such crystals and hopefully a path forward to "upgrade" the full microscope.
>>> 
>>> cheers,
>>> Beni 
>>> 
>>> On 10/10/25 08:36, Justin Stevens via Halld-tagger wrote:
>>>> Hi Richard, All,
>>>> 
>>>> Thanks for the summary of yesterday’s discussion and sorry I had to leave a bit early for the DNP practice talks.  While we continue to investigate the exact reason for the loss of light yield, I suggest we begin planning a test that can be performed in 2026 to evaluate the options for potential replacement of the scintillating fibers before GlueX-III.  
>>>> 
>>>> One possibility would be a small test setup on one of the PS arms with candidates for the 2x2 mm scintillators that can be tested with real signals from energy-tagged electrons.  We would need an equivalent readout to the existing TAGM bundles, but most of the electronics infrastructure: f250 and f1TDC boards, crates, LV, etc. should already be available in that area for the PS/ST/TPOL readout.  So, I believe we would need the TAGM preamp boards with SiPMs and light guide fibers to couple to the candidate scintillators we want to evaluate.  Do we have spares of those items that could be used for such a test starting in early 2026?
>>>> 
>>>> There is also the potentially more important question of what are the options for replacement scintillators with the appropriate shape that may be more radiation resistant and how can we test that radiation hardness?  I understood from Malte that there may be some LYSO crystals with an appropriate profile and Eljen https://eljentechnology.com/products/fibers may have some appropriate fibers, but we should consider procuring these and other options soon if we aim to test them next year.
>>>> 
>>>> More thoughts, suggestions, corrections are welcome.  I just think we need to keep brainstorming on this to keep up the momentum towards finding a solution for GlueX-III.
>>>> 
>>>> -Justin
>>>> 
>>>>> On Oct 9, 2025, at 2:20 PM, Richard T. Jones via Halld-tagger <halld-tagger at jlab.org> wrote:
>>>>> 
>>>>> Hello all, 
>>>>> 
>>>>> We had a special meeting this morning at 10:00 devoted to a review of everything we know regarding the degrading response of the tagger microscope over the last few run periods. A new logbook entry has been added containing a historical record of the photon yield and other calibration constants for the TAGM which presents clear evidence of significant loss of scintillation photon yields over the past 5 years, with most of the loss occurring in the rows that saw the greatest flux of electrons.
>>>>>     • gain and photon yield history of the tagger microscope
>>>>> Ideas to further investigate the exact reasons for the decrease, as well as ideas for recovering and sustaining good performance during Phase 3 running are still in process, with follow-up to happen in the next Photon Beam working group mtg next week.
>>>>> 
>>>>> -Richard Jones
>>>>> _______________________________________________
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>>>>> Halld-tagger at jlab.org
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>>>> 
>>>> 
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