Light Yield measurements o n Kuraray scintillating fibres with different WLS concentrations

1. Light Yield measurements on Kuraray scintillating fibres with different WLS concentrations C. Joram, C. Alfieri, T. Schneider Thanks to M. v. Stenis, F. Garnier, C. David and R. Kristic for mechanical work. 20.08.2014

2. Motivation 1) As part of the general fibre QA, monitoring the scintillation yield from ionizing radiation is a must (e.g. batch-wise). It complements the measurement of the attenuation length. 2) Measurement of the scintillation yield allows to compare fibres with different compositions, e.g. different WLS concentrations. We have samples with 500, 1000, 2000 and 5000 ppm. Simulation by Mirco Deckenhoff (April 2014) The concentration of the WLS should have an impact on the Light Yield and possibly also on the attenuation length. What's the optimum WLS concentration ? Standard Kuraray SCSF-78 fibres contain 1000 ppm of TPB.

3. Attenuation Length vs WLS Concentration Higher WLS concentration->Lower AttLength, but still in a range of good values (≈3m) Typical value is ~300 cm

4. Principle and (improved) set-up for LY measurements • 4 scintillating fibres, vertically aligned • Two trigger fibres, 1 on top, 1 below, separated by an opaque membrane (not shown) • Readout by Hamamatsu PMTs (H7826) Trigger PMTs T2 T1 Signal PMT S1 reads combined signal of all 4 fibres Signal integration on scope  charge Q. e-gun (e- of ~1 MeV) Trigger

6. 3 mm

7. Comments: • The electrons passing the trigger fibres have wide energy loss distributions (geometry, Landau).  We can’t expect sharp peaks! Optical separations (180 mu tape) wall wall • Manually manipulating and mechanically aligning Ø250 mm fibres is non-trivial. There is always a risk of (un-detected) damage to the fibres. • The whole exercise would be more or less trivial with Ø1 mm fibres! ~ 270 mm

8. Integration range for Centre-of-Gravity calculation Q in Vs We approximate distribution under pedestal by a straight line Q in Vs

9. 1 pe calibration 1 pe = 35 pVs Q (Vs)

10. Preliminary results ! (status 7 August) 60 cm 90 cm 120 cm 150 cm Sorry, the data was plotted at slightly wrong x-positions. 1000 ppm appears to give the highest light yield. To be confirmed by more data! Coming week(s).

11. Measurements completed. Set-up unchanged. Discontinuity between 1.25 and 1.3 m (1 of 4 fibres damaged)

12. Prel. conclusions: 1000 ppm (DO fibre) gives highest LY, followed by 500, 2000 and 5000 ppm. Bicron clearly lower LY.

13. A new set of data was measured, with a slightly improved set-up. Black tape replaced by 40 mu thick yellow tape. This is significant as it reduced the distance of the trigger fibres by 280 mu. • Damaged 500 ppm fibres replaced. • 1 damaged trigger fibre replaced. • New 1000 ppm from batch 14080801 also measured. Optical separations (40 mu tape) wall wall ~ 270 mm

14. !!!

15. In the meantime…. • S. Ponomarenko agreed to negotiate with Kuraray about making the new NOL (NanoOrgano-Silicon Luminophore) material available for producing fibre test samples. • Kuraray and Ponomarenko are now in direct contact. • Osamu Shinji from Kuraray: based on our experience we expect the process to develop NOL fibres to be 'not easy', in particular the optimisation of purity and concentration. • Concerning radiation hardness: S.P. has more concerns about polystyrene than the NOL material, but specific tests of NOL have not been done yet.