1. Antineutrino Detector
Outline
Requirements
Overall Design
Mechanics
Liquid Scintillator
PMTs
Electronics
Calibration
Performance
Steve Kettell
BNL
US Daya Bay Project
Chief Scientist
Director’s Review, BNL 9/28/06

2. Antineutrino Detector
I will discuss the overall detector design, including some discussion of electronics and calibrations
Bob will show the results of the studies of the systematic uncertainties
Director’s Review, BNL 9/28/06

3. Antineutrino Detector Requirements
High statistics  large, homogeneous detectors
Identical detectors  precise, redundant measurements
Clean inverse -decay signature with good background separation  Gd-loaded liquid scintillator (LS) (8 MeV/n-capture and 30ms capture time with 0.1% Gd)
Well determined fiducial mass and hydrogen density  precise measurement of Gd-LS volume and mass (no need for vertex cut)
Low threshold to detect e+ at rest  low single g rate
Well-defined neutron detection efficiency  g-catcher, energy scale calibration, identical detectors
Good energy resolution for energy scale, spectral distortion  high scintillation output, long Lattn, good photocathode coverage
Enable transport and swapping in a reasonable tunnel size (easy to build multiple modules), manageable muon flux  moderate size
Director’s Review, BNL 9/28/06

4. Antineutrino Detector Design
Cylindrical three-Zone Structure:
I. Target: 0.1% Gd-loaded liquid scintillator
II. g-catcher: liquid scintillator, 45cm
III. Buffer shielding: mineral oil, ~45cm
20 t
Gd-LS
With 224 PMT’s on circumference
and diffuse reflector on ends:
12.2%
13cm
Oil buffer thickness LS
Rate from PMT glass
oil
Isotopes
(from PMT)
Purity
(ppb)
20cm
(Hz)
25cm (Hz)
30cm
40cm
238U(>1MeV) 40
2.2
1.6
1.1
0.6
232Th(>1MeV)
1.0
0.7
0.3
40K(>1MeV) 25
4.5
3.3
2.3
1.2
Total
7.7
5.6
4.0
2.1
92%
g Catcher thickness
A 45cm buffer provides ~20cm of shielding against PMT glass
Director’s Review, BNL 9/28/06
g-catcher thickness (cm)

5. Antineutrino Target Mass
4 x 20 tons target mass at far site
Sensitivity after 3 years.
Director’s Review, BNL 9/28/06

6. Three zone detector 40 ton 20 ton
2-zones implies simpler design/construction, some cost reduction but with increased risk to systematic effects (neutron e and E spectrum)
3-zones provides increased confidence in systematic uncert. associated with detection efficiency and fiducial volume, but smaller volume
n capture on Gd yields 8 MeV with 3-4 g’s
cut
3-ZONE
2-ZONE
Uncertainty ~ 0.2%
Uncertainty ~ 0.4%
40 ton
20 ton
4 MeV cut can reduce the error by x2, but residual radioactivity in LS volume does not allow us to do so
Director’s Review, BNL 9/28/06

7. Rates spectrum from Aberdeen: same granite as Daya Bay
Fast neutron spectrum
from MC simulation
Director’s Review, BNL 9/28/06

8. Rates are per antineutrino detector module
Source
Units DB LA
far
1) Antineutrino signal
(day-1)
930
760 90
2) Radioactivity
(Hz) 31
Rock 4
PMT glass 8
other materials (steel) 18
Gd contamination 1
3) Muons 24 14
Tagged single neutron
480
320 45
Tagged fast neutron 20 13 2
b emitters (6-10 MeV)
210
140 15
12B
400
270 28
8He+9Li 3
Rates are per antineutrino detector module
Director’s Review, BNL 9/28/06

9. Mechanical Design Gd-LS Target: 3.2m () x 3.2m (L)  ~20 tons
LS g-catcher: 4.1m () x 4.1m (L)  ~20 tons
Mineral oil buffer: 5m () x 5m (L)  ~40 tons
Director’s Review, BNL 9/28/06

10. Detector Vessel Structure
Steel tank
Outer acrylic tank
Inner acrylic tank
PMT
Acrylic transparency
Dimensions inner outer steel
Diameter (mm):
Height (mm):
Wall thickness (mm):
Weight (ton):
Water
Director’s Review, BNL 9/28/06

11. Finite Element Analysis for Steel Tank
Load condition: tank structure filled with liquids
Constraint condition: bottom annular surface was constrained
The max. stress: MPa
The max. deformation: 2.8 mm
Stress result
Unit:Pa
Deformation result
Unit:m
Director’s Review, BNL 9/28/06

12. considered in one of the civil conceptual design reports
Moving the Detector
Moving 100t over 0.5% tunnel grade
Down 10% grade when empty (20t)
Lifting 100t into water pool
Bridge crane option
considered in one of the civil conceptual design reports
Director’s Review, BNL 9/28/06

13. Detector Instrumentation
Monitoring Goals: - mechanical stability during filling, transport, and movement
- liquid levels during filling
- acrylic vessel positions
mass flow
volume flow
temperature
density
CCD camera
Laser reflection for in-situ measurement of:
attenuation length
acrylic vessel movement and position during transport
level sensors
tilt sensors
load sensors
Liquid Scintillator sampling
Director’s Review, BNL 9/28/06

14. Detectors are filled in pairs from common storage tanks
Filling the Detector
Detectors are filled in pairs from common storage tanks
I. Target: 0.1% Gd-loaded liquid scintillator
II. g-catcher: liquid scintillator, 45cm
III. Buffer shielding: mineral oil, ~45cm
Three Liquids:
Mass Measurements: mass + volume flow
load sensors
Example: Coriolis Mass Flow Measurements
Gd-LS LS
oil
Possible mass flow rates of 1g/hr kg/hr with 0.1% repeatability.
Flowmeters – 0.02% repeatability
Baseline = 0.2%
Goal = 0.02%
Director’s Review, BNL 9/28/06

15. Require stable Gd-loaded liquid scintillator with
Gd loading significantly increases the energy of the neutron signal and increases the number of neutron captures (within a given time window) and thereby reduces background
Require stable Gd-loaded liquid scintillator with
high light yield
long attenuation length
Director’s Review, BNL 9/28/06

16. Gd-Liquid Scintillator Optical Attenuation: Stable ~700 days
Gd (carboxylate ligands) in pseudocumene (PC) and dodecane
stable for ~2 years
- attenuation Length >15m
- promising alternative scintillator: Linear Alkyl Benzene (LAB)
Director’s Review, BNL 9/28/06

17. Determination of H/C and Gd in LS
Combustion Analysis
Gd-LS decomposition in O2:
LS: CxHy + (x + y/4).O2  x. CO2 + y/2.H2O
Gd: 2.Gd +(3/2).O2  Gd2O3
Potential of measuring C, H and Gd simultaneously with good precision.
Samples were measured by certified, commercial laboratory; achieved C/H measurements at 0.3%. This precision can be improved further.
Determination of number
of Hydrogen antineutrino
targets in the scintillator
Director’s Review, BNL 9/28/06

18. Prompt Gamma Activation Analysis
Determine H and Gd in LS
Prompt Gamma Activation Analysis
Measure 2.2-MeV  from H; 0.18-MeV and other ’s from Gd after thermal neutron capture.
Samples were measured by the Institute of Isotopes, HAS; achieved Gd and H measurement at 1%; the precision needs to be improved.
Director’s Review, BNL 9/28/06

19. Performance of Gd in PC and LAB
Optical Spectra
Light Output Spectra
Absorbance over 10 cm
Events/nm PC
Lab
 (nm)
 (nm)
Have produced ~1% Gd in LAB and in pseudocumene (PC).
(Will dilute to ~0.1% Gd in Daya Bay experiment.)
LAB has lower optical absorption (longer attenuation length).
LAB has better chemical and ESH properties.
LAB and PC have very similar light output efficiency.
Director’s Review, BNL 9/28/06

20. Low-radioactivity glass Two candidates
PMTs
224 8” PMTs in 7 rings of 32
Low-radioactivity glass
Two candidates
Hamamatsu R5912
Electron Tubes 9354KB
Magnetic shielding under investigation
Director’s Review, BNL 9/28/06

21. Electronics (Front-End)
Charge Specifications:
Dynamic range: PE
Noise: < 0.1photoelecton (PE)
Shaping time: ns
Sampling freq.: 40 MHz
Time Specifications:
Resolution < 500 ps
Signal split two ways for ADC & TDC
Director’s Review, BNL 9/28/06

22. Electronics (Trigger)
Primary Physics Triggers:
Esum: 0.7 MeV
Emult: 10 PMTs
Trigger rate per module:
g < 50 Hz
m = 24 Hz (DB), 14 Hz (LA), 1 Hz (F)
Other triggers:
LED
Radioactive source
Clock
Minbias
Muon system
Director’s Review, BNL 9/28/06

23. Electronics (DAQ) Entire detector is readout on all physics triggers
Each detector system at each
site is readout independently (8
antineutrino streams and 9 muon
streams. An event builder
reassembles the streams
Every e+, neutron or m+ will
independently trigger a readout
Primary Physics Triggers:
Antineutrino Detector
Esum: 0.7 MeV
Emult: 10 PMTs
Muon System
Water Pool
Water Tracker
RPC
Director’s Review, BNL 9/28/06

24. Calibration
Load sensors, level sensors, thermometers, flow meters, mass flow meters
LED
Radioactive sources: 68Ge (1.022 MeV), 60Co (2.5 MeV), 252Cf
3-4 locations (with full z travel)
Data (12B, neutrons, Michel electrons)
Determine/maintain energy scale to 1% at 6 MeV throughout detector volume (=> neutron detection efficiency known to 0.2%).
Director’s Review, BNL 9/28/06

25. More details in Bob McKeown’s talk
Source Calibration
More details in Bob McKeown’s talk
Determination of attenuation length from 2 techniques:
Neutron captures throughout volume relative to center (left)
60Co source in corner relative to center (right)
Director’s Review, BNL 9/28/06

26. LED Calibration Calibration Goal: PMT gains
Director’s Review, BNL 9/28/06

27. Detector Performance 224 PMTs with 12% effective photocathode coverage
GEANT simulations
Photoelectron yield vs. radius, no mineral oil
Energy resolution
224 PMTs with 12% effective photocathode coverage
~100 photoelectron/MeV: 12.2%/E
Director’s Review, BNL 9/28/06

28. Prototype Performance (1)
0.5 ton prototype at IHEP (currently unloaded liquid scintillator)
45 8” EMI PMTs with 14% effective photocathode coverage
~240 photoelectron/MeV and 9%/E
Linearity
Energy Resolution
Director’s Review, BNL 9/28/06

29. Prototype Performance (2)
Comparison of data and MC
0.5ton IHEP prototype
L=1.0m, =0.9m
137Cs
137Cs
60Co
Director’s Review, BNL 9/28/06

30. Conceptual design of the antineutrino detector is well advanced
Summary
Conceptual design of the antineutrino detector is well advanced
Simulation of the detector response is well developed (Geant3), including several calibration studies (Geant4)
Detailed engineering of the vessels, supports and calibration system is underway
Prototype operational at IHEP, a 2nd prototype to be built at Aberdeen, studies underway of PMTs, electronics, calibration system and LS
Director’s Review, BNL 9/28/06

31. Backup
Director’s Review, BNL 9/28/06

32. Chooz Data
Director’s Review, BNL 9/28/06