1. CHANDLER
(Carbon Hydrogen Anti-Neutrino Detector with a Lithium Enhanced ROL)
Update on R&D
Sumanta Pal
Center for Neutrino Physics, Virginia Tech.
AAP2016, 1 Dec 2016
CHANDLER : update on R&D

2. The CHANDLER detector concept
Neutron
Capture
Positron (e+)
ν 𝑒 e+
Detected Light p n 3H
4He
Time
6Li
200 ns
Geant4 Simulation of light transport by total- internal-reflection
10 ns
~50 μs
6Li sheet
Optimal light collection from ROL lattice.
Energy and spatial resolution (critical to reduce the random coincident and fast neutron backgrounds). Cube dimension (62 ×62 ×62) 𝑚𝑚 3 .
Good neutron tagging efficiency.
Cubes: WLS plastic scintillator
Sheets: Li6 loaded ZnS for thermal neutron detection
Photon Ray Tracing in GEANT4
S. Pal, Virginia Tech

3. Research and Development Effort
Cube String Studies have been used to study light production, light collection, light attenuation, energy resolution and wavelength shifter concentration.
MicroCHANDLER is a 3×3×3 prototype which we are using to test our full electronics chain, develop the data acquisition system, study neutron capture identification and measure background rates.
Fully commissioned by the end of the year
MiniCHANDLER is a fully funded system test (8×8×5) which is now being commissioned and will be deployed at North Anna Nuclear Power Plant, Virginia.
S. Pal, Virginia Tech

4. Fully functioning MicroCHANDLER
MicroCHANDLER R&D
Fully functioning MicroCHANDLER
Light guide used with HAMAMATSU PMTs
Old : 2 inch PMT (xp2202)
New : Hamamatsu (R ), 2 inch diameter, high Q.E. and linearity over large dynamic range.
Readout resolution of two types of PMTs are being tested in this set up.
Easy access to PMTs. No possibility of over heating the PMT bases.
No hassle to put the radioactive source on top of the box.
No light leakage observed.
Light tight mechanical set up of the MicroCHANDLER
S. Pal, Virginia Tech

5. MicroCHANDLER : Compton edge study
Compton edge for
1.27 MeV gamma
Compton edge for 511 keV gamma
Compton edge for
1.27 MeV gamma
Compton edge for 511 keV gamma
Old PMTs x y
New PMTs
22Na gamma source : MeV and MeV gamma lines.
Collimated source was placed approximately at the center of each cube on the top layer.
The spectrum shows : 1 𝐴𝐷𝐶 ≈5 −8 𝑘𝑒𝑉.
Threshold used for neutron runs : ~ 10 ADC.
New PMTs show better resolution.
S. Pal, Virginia Tech

6. Mechanical design of MiniCHANDLER
Goal of the MicroCHANDLER mechanical set up was to test the light tightness of the box.
After successful operation of the MicroCHANDLER, same mechanical set up has been prepared for the MiniCHANDLER.
Explain how design came from MicroCHANDLER
S. Pal, Virginia Tech

7. Mechanical design of MiniCHANDLER
Use of O-ring, ring spacer and PMT O-ring clamp plate is to make the box light tight.
Easy access to any PMT channels as before.
Light tightness using Oring, spacer and clamp plate though PMTS are projected out.
S. Pal, Virginia Tech

8. Commissioning of MiniCHANDLER
Assembling WLS scintillator cubes
Assembling PMTs
Li sheets (white) are also visible between layers.
Goal: scale up the technology of the MicroCHANDLER towards CHANDLER.
S. Pal, Virginia Tech

9. Electronics & DAQ set up
Readout Electronics
Anode
2 inch PMTs.
MicroCHANDLER : xp2202 PMTs (9) + R PMTs (9)
MiniCHANDLER : xp2202 PMTs (80)
CHANDLER : R
VME 16 channel shaper (charge integrating):
Analog Preamp and Shaper circuit (VT + CREMAT)
VME digitizer : 64 channels, 16 ns, 12 bit (CAEN V1740)
PreAmp
VME shaper module
(16 channels)
Gain x 2
Shaper (25ns)
Readout Software
VT customized DAQ readout.
Each digitizer connected by dedicated single optical link to the computer (80 MB/s).
Multi-Board readout tested on MicroCHANDLER and successfully working.
Trigger scheme : trigger on a plane.
Apply zero suppression before writing to the disk.
Data streams are combined and sorted to identify events via event builder process running on raw data.
Digitizer (16ns)
Show a real picture
External Trigger
Data
Storage
DAQ system
Scalable set up : successfully tested in MicroCHANDLER. MiniCHANDLER will use same set up.
S. Pal, Virginia Tech

10. Electronics & DAQ set up
Dual
Timer
Shaper
Board
Digitizer
Linear FIFO
CAEN SY527 HV Mainframe
&
CAEN A734N HV cards
S. Pal, Virginia Tech

11. MicroCHANDLER DAQ performance
Trigger rate: highly depends up on the trigger threshold; still optimization is required.
Data rate: with a very low threshold we get 26 GB/h with the 18 channels of MicroCHANDLER and that clearly state that we can readout MiniCHANDLER with some safe margin.
Data rate with zero suppression: 2.6 GB/ h
Multi board DAQ was tested all summer with the multi board readout and a preliminary scheme for merging event offline.
Muon lifetime was computed using the output of the event builder to verify that we understand the time of the system and we got 2.15±0.04 𝜇𝑠 that shows that the event merging scheme that we have works fine.
External Trigger: useful to synchronize events between boards; ensure no data loss.
Digitizer: we have revised few firmware versions with the help of CAEN.
Introduced a register to identify the source of the trigger (External vs Internal).
Baselines can be aligned to identical level for all channels of the digitizer.
PMTs (80) all tested and pre-calibrated using a picoquant LED laser where the light intensity has been tuned to the amount of light register by one cube in microCHANDLER. HV pre-values have been identified.
All cables tested and labelled.
Cross-talk quantified and offline corrections are almost ready.
S. Pal, Virginia Tech

12. MicroCHANDLER : preliminary calibration scheme
Use muons, simple and they are present in the detector, avoiding complicated calibration scheme (not so effective in past experiments while considering the complication of the calibration system and of the risk of the deployment.
Amplitude of pulse
Landau +
Exponential m
Landau +
Polynomial
Each PMT has an individual HV channel.
Better for gain calibration and optimization.
S. Pal, Virginia Tech

13. Neutron and positron Pulse shape
129*16 = 2064 ns = us,
Based on the pulse shape we define neutron PSD variable as
𝐴𝑟𝑒𝑎 𝑢𝑛𝑑𝑒𝑟 𝑡ℎ𝑒 𝑝𝑢𝑙𝑠𝑒 𝐴𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑢𝑙𝑠𝑒
S. Pal, Virginia Tech

14. Neutron PSD : area over amplitude
Front view of the detector
Neutron Source
Cosmic Source
6Li sheet
A clear indication of neutron signal in the detector was presented before.
Neutron like events (left plot) in absence of neutron source are most likely from cosmic background. Can we identify that ?
S. Pal, Virginia Tech

15. Improved neutron selection
Positron/gamma like
Neutron like
Neutron like events : Lower amplitude and larger area under pulse relative to positron like events.
The different classes of events are clearly separated into distinct bands.
In the overlap region positron like events clearly out numbers neutron candidates.
Is there any way to recover those neutrons ?
S. Pal, Virginia Tech

16. Resolving neutron position to a specific sheet
In CHANDLER we can see lights from both sides of the sheets.
So, we can use that light to determine which sheet tag the neutron.
When a good neutron is tagged in the middle layer (above both red lines), we looked at the signals from the top and bottom layers.
Neutron like events selected in the middle layer
Neutron like
The sheet is determined from the layer of larger amplitude.
S. Pal, Virginia Tech

17. The Other Layer Distributions
When a good neutron is tagged in the middle layer (above both red lines), we looked at the signals from the top and bottom layers.
We see a clear neutron band extending into the overlap region.
So, neutrons in the overlapping regions can be recovered by looking into the other sides.
S. Pal, Virginia Tech

18. What is the background to the neutron signal?
Cosmic Background
6Li-free sheet
6Li sheet ?
Front view of the detector
If we see neutron in the middle layer, it should come from middle-bottom 6Li sheet.
We collected large number events over the period of 4012 min (66.87 hr = 2.78 days).
Number of triggers obtained: 62M
Are neutron like events coming really from cosmogenic neutrons ?
To investigate that we use a combination of Li and Li free scintillating sheets to obtain clear neutron PSD.
S. Pal, Virginia Tech

19. Neutron misidentification
1.6% of events w.r.t. the middle layer
89.3% of events w.r.t. the middle layer
6Li-free sheet
6Li sheet
6Li-free sheet
6Li sheet
89/5638 = , 5036/5638=0.8932
When neutron candidates are first identified in the middle layer, we see very few neutron like events in the top layer coming from the Li free sheet.
Cosmogenic neutrons out number fake neutrons by more than 50 to 1 when we compare events between middle-top and middle-bottom layers.
So, the neutron tag is extraordinarily pure in this detector.
S. Pal, Virginia Tech

20. Neutron misidentification
2.4% of events w.r.t. the middle layer
97.6% of events w.r.t. the middle layer
6Li-free sheet
6Li sheet
6Li-free sheet
6Li sheet
28 events
5501/5638=97.57, 137/5638=2.43
28 events are pedestal fluctuation where sheet is assigned incorrectly.
Less than 1% of time we choose wrong sheet in this method.
S. Pal, Virginia Tech

21. Future plan : Deployment at the reactor site
North Anna Nuclear Power Plant, Virginia
Around 4 hours drive from the Virginia Tech.
MiniCHANDLER will be placed inside this trailer at the power plant.
S. Pal, Virginia Tech

22. Summary Chandler R&D is on track:
Read out and DAQ fully designed and tested.
Demonstration of a highly pure neutron tag.
Demonstration of significant gain in energy resolution with light guides and high Q.E phototubes.
MiniCHANDLER construction is complete and commissioning is ongoing.
Fully funded plan for the deployment at the North Anna Nuclear Power plant.
Expected to see IBD events by AAP2017.
S. Pal, Virginia Tech

23. Backup
S. Pal, Virginia Tech

24. MicroCHANDLER : DAQ : offline Event builder
Linux Time Stamp
Board 1
Master
Board 2
Slave
evt1
evt2
evt3
evt4
evt5
evt6
evt7
evt8
evt9
Identify trigger pattern : external or PMTs.
Linux time stamp has been written into the data stream when external trigger fires. External trigger freq. 1 Hz.
Identify external trigger into the data,
Match Linux time stamp between boards,
Estimate time offset between boards ( slave – master ). [All timings are global time in each board]
Correct time in the slave board.
Event merging :
Identify coincidence data between boards (time window 40 ns): merge the data.
If no coincidence found, save data as separate events.
backup
S. Pal, Virginia Tech