General Meeting Summary 8/21/14
- Prototype cosmic tests with 2cm x 2cm blocks of PbWO4 and two 5 x 10 cm2 scintillator counters
- All blocks are wrapped on the long, but not on the short ends (one end has PMT attached and the other end has the curing/monitoring system attached)
- Runs have been taken with different orientations of the trigger orientations and with and without lead shielding.
- Detector works stable, but a few issues need to be resolved: possible base problem, possible cross talk between channels
- Accuracy of transmittance measurement: ~1%
- Uncertainties on the transmittance measurement were estimated by measuring at the same points several times and evaluating the mean and RMS values of the distributions. Estimates were made at distances 1cm and 5cm from the radition edge. For all following studies the estimate at 5cm will be used.
- Discussion about most recent results of PbWO4 crystal radiation tests - one of the goals of these tests is to test the efficiency of curing
- 3x3x16 cm^3 crystals were irradiated by an additional 84 krad dose. The total accumulated dose is thus 271 krad. Transmittance measurements were made in the transverse direction (with current crystals samples cannot do measurements in longitudinal direction) at distances ranging from 2 mm to 150 mm from the radiated edge and for wavelengths >350 nm. Significant point-to-point variation was observed in that range. The expected depth of radiation dose of 3-5 cm seems consistent with this observation.
- Comparison with measurements at total accumulated dose of 187 krad seems to suggest that there is an effect on the transmittance. The transmittance seems to be reduced at the larger accumulated dose of 271 krad, but the effect is still relatively small (~10%).
- Crystals were examined for surface damage, which may make the measurement less reliable in these places. Locations of surface damage are indicated in Fig. 8 by the gray-shaded bands. Point-to-point variations in transmittance are observed in both locations with and without surface damage.
- Discussion about the path forward with crystal radiation studies
- Accumulated dose of 271 krad is small compared to what is expected in experiments. Adding more radiation limited by slow radiation method (~100 krad/2 weeks, point radiation source radiated from one edge)
- In long term need to identify faster radiation source (Idaho, Duke, BNL?). Need to check administrative requirements, timescale, service cost.
- Observed effect on transmittance at accumulated dose 271 krad seems relatively small (~10%). However, in experiment light has to travel 20 cm in longitudinal direction and the effect may be larger. PbWO4 has radiation length ~ 1cm.
- Curing irradiated crystals would be a good test
- To check reproducibility of curing apply another small dose after curing, e.g., 55 krad, and then measure again
- NSF MRI results from discussions with program officer were not yet available during the meeting - meeting was scheduled 8/22. Details will be discussed in the next NPS meeting, but short summary is that the advice is to re-submit the NPS proposal in January clarifying a few points.
- EIC R&D proposal received funding
- First step is to figure out how to receive the funds - check with BNL on that
ITEMS FOR NEXT MEETING:
- NPS prototype and PWO studies
- NSF MRI summary of discussions with NSF program officer
- Next collaboration meeting
NEXT MEETING: THUR, 18 SEPTEMBER at 9:00 AM (EST)