1. Scintillator testing in Prague (update from Aussois)
Testing station upgrade – vacuum, deltaE, electronics, magnetic properties
Scintillator testing results
V. Vorobel, SuperNEMO meeting, Caen

2. Observed spectra puzzle
Reminder from Aussois
Distorted 207Bi spectrum is observed while electron beam spectra look normal.
207Bi
Pedestal = 20-30% of entries
Electron beam 1 MeV
Pedestal = 2% of entries
Careful check of trigger system
Delta-E design improved
Ruben visited Prague with alternative data acquisition
No malfunction found
Possible explanation
Electrons interacting in the 207Bi source or somewhere else contribute to the spectrum background and to a pedestal.
Conclusion: It is understandable physics effect. We can live with it.
V. Vorobel, SuperNEMO meeting, Caen

3. Station upgrade – update from Aussois
Vacuum
Better and shorter hoses used (instead of previous “garden” type).
Vacuum improved from 7 Pa to 1 Pa. Today, it degrades to 4 Pa - maintenance needed.
No effect of vacuum improvement on spectra is observed -> the vacuum is sufficient
Delta-E
New Delta-E detector made without use of light-guide. The scintillator foil is fixed directly to PMTs with elastic glue RTV615. More light is collected (3x) – more reliable trigger signal. Absence of the light-guide prevents undesirable electron scatterings. PMTs support is black painted to minimize possible light reflections.
V. Vorobel, SuperNEMO meeting, Caen

4. Station upgrade – update from Aussois
Magnetic shielding
The magnetic electron source is covered into a m-metal box (thickness 1mm) to avoid magnetic field impact on PMTs performance.
V. Vorobel, SuperNEMO meeting, Caen

5. Station upgrade – update from Aussois
Electronics
Current source for the magnet equipped with a polarity switch to allow the magnet de-gaussing.
New PMT HV modules installed with PC control.
VME crate supply repaired.
Signal attenuators purchased for work with higher PMT HV.
V. Vorobel, SuperNEMO meeting, Caen

6. Hysteresis measurement
de-gaussing using max. 3 A.
virgin_1: 0 -> +4A
series_1: +4A -> -4A, -4A -> +4A
series_2: +4A -> -4A, -4A -> +4A
De-gaussing using max. 3 A.
virgin_2: 0 -> +4A
Conclusion: de-gaussing using max. 3A is sufficient. We decided to use max. 4A to be safe in future.
De-gaussing procedure
V. Vorobel, SuperNEMO meeting, Caen

7. Magnetic shielding efficiency
“Spectrometer” is installed inside of mu-metallic box.
Magnetic field sensor placed instead of PMT at a point between photo-cathode and first dynode, oriented parallel to B-lines.
Conclusions:
Measurements without shielding cylinder (blue lines) –> B generated by the spectrometer is of the order as natural B.
Measurements with mu-metallic cylinder (green lines) -> remaining spectrometer mag. field as well as natural mag. field is eliminated.
V. Vorobel, SuperNEMO meeting, Caen

8. V. Vorobel, SuperNEMO meeting, Caen
Testing chronology
HV modules change
Ch#1 broken
VME crate change
Station Upgrade
Attenuators installed
V. Vorobel, SuperNEMO meeting, Caen

9. Scintillators production quality
2014
The blocks produced in 2014 have better light yield and energy resolution then the ones from 2011.
2014 production is visually much better - no black specs or other visible pollution, no yellowing in contrast to the 2011 production.
Remaining 8 X-wall blocks will be delivered from ENVINET this week, tested at Prague lab and send to UCL the next week.
V. Vorobel, SuperNEMO meeting, Caen

10. V. Vorobel, SuperNEMO meeting, Caen
Summary
Extensive upgrade of the station done.
De-gaussing procedure elaborated. Magnetic shielding improved and tested.
New optimization of the apparatus settings and calibration done.
Charactrization of X-wall blocks done, remaining 8 blocks next week.
Measurement of reference block(s) in other laboratory(s) is desired. (Bordeaux, UCL)
V. Vorobel, SuperNEMO meeting, Caen

11. V. Vorobel, SuperNEMO meeting, Caen
Backup
V. Vorobel, SuperNEMO meeting, Caen

12. V. Vorobel, SuperNEMO meeting, Caen
Stability of Testing
HV modules change
Ch#1 broken
VME crate change
Station Upgrade
Attenuators installed
V. Vorobel, SuperNEMO meeting, Caen

13. V. Vorobel, SuperNEMO meeting, Caen
Vacuum system upgrade
Vacuum probe installed.
Spectrometer sealed – vacuum improved from 300 Pa to 7 Pa.
We have to change a hoose for further improvement.
Efect of sealing on spectra is significant.
V. Vorobel, SuperNEMO meeting, Caen

14. V. Vorobel, SuperNEMO meeting, Caen
Testing station setup
V. Vorobel, SuperNEMO meeting, Caen

15. Typical signal conditions
DE left
scint. block
DE right
Counts per 10 s
deltaE left
deltaE right
Scint block
coincidence
1439
2096 -
324
1401
405
311
2085
416
335
V. Vorobel, SuperNEMO meeting, Caen