# Presentation: 477799

## Neutron detection in LHe(HMI run 2004)

- R.Golub, E. Korobkina, J. Zou
- M. Hayden, G. Archibold
- J. Boissevain, W.S.Wilburn
- C. Gould

## Layout  of the neutron beam

- <date/time>

- Cross section of the full beam was 1 cm2,  intensity ≈ 106 n/cm2/s before Bi
- The distance from the polarizer to the light window was ≈ 120 cm

- Polarizer

- Lead shield

- Collimator, Li

- Light guide  33 cm

- Bi filter

- Lead shield

-  Li Beam stop
- when needed

- Beam
- monitor

- Beam
- stop

- Chopper and neutron guide of SANS

- Li shield

- Guide

## Layout  of the cell and light collecting system

- <date/time>

- OD of the cell =5 cm, ID = 4.4 cm
- The distance from the neutron beam to the light window, L, was L≈2 OD

- PMT C2

- 300K

- 77K

- Light guide  33 cm

- 4K

- Al wall, 2 mm thick

- Neutron beam

- Light window
- of the cell

- Acrylic    cell 22 cm

- Cell Cross section

- Reflector -
- Al foil

## View looking `upstream’ (toward the reactor)

- Beam Stop

- Cryostat

## Collimation

- neutrons

- PMT

- PMT

- light guides

- cell

- delay line

- oscilloscope

## Cell, as viewed through PMT window

- free liquid surface

## Slide 7

## What was studied

- <date/time>

**We have studied at different temperatures**
**Empty cell and Neutron guide hall background    **
**2. Cell filled with Natural He - 90 mK, 300 mK, 700 mK, 1400 mK**
**	****Full beam opened and closed with Li.**
**3. Cell with additional He-3 (about 100 ppm)**
**90 mK, 300 mK, 500 mK, 650 mK, 1500 mK,                                         Full beam opened and closed with Li**.
**Small beam opened, 90 mK, 120 mK, 300 mK, 500 mK, 1500 mK, 1900 mK, 90 mK with and without coincidence, 10 mV LDL and 15 mV LDL**
**Ultra Small beam opened,  90 mK, 1500 mK, 1900 mK **
-  **Data were taken in two modes **
**	****- Count Rate, where 10 ms intervals were recorded, time scale = 10 or 1 ns/point**
- 	- **Sequence, where only coincided events and after pulses during 20 mks were recorded, time scale = 1 ns/point**
**We have used LeCroy oscilloscope with a time scale down to 125 ps per point **
**	**

## Count Rate data evaluation

- <date/time>

**Our data allowed us to compare  Count Rate data evaluation with and without coincidence.**
**Without coincidence is a real count rate of the detectors that is a sum of the background from acrylic light guides and the cell’s signals. **
**Coincidence mode is a great tool to get read of the background  pulses from the light guides.**
**	**

## Empty cell, no coincidence  

- <date/time>

- Empty cell, no coincidence

**First big run; cell is empty, PMT HV=2kV, time scale 1 ns/point  to see small pulses. A single photon (SP) peak  and gamma  are well separated. Gamma peak = 3 SP.**

## Empty cell, coincidence  

- <date/time>

- Empty cell, coincidence

## Beam On, Li in the beam

- <date/time>

- PMT pulse area spectra  at different temperatures when the beam is stopped by Li rubber .
- Left - PMT C2, 500 mK, 300 mK with He-3 and 98 mK, Natural Helium
- Right - PMT C4, 500 mK, 1500 mK with He-3 and 98 mK, Natural Helium

## Full beam and Small beam

- <date/time>

- Full beam shows too high intensity of single pulses.
- We made the beam smaller
- Count Rate over the neutron peak range
- ***************************************************
- C4 Small	 4906
- C4 Li            	 1733
- C2 Small	 4632
- C2 Li 		 1472
- 		Neutrons  3000 sec-1
- ***************************************************
- C4 Full	 19067
- C4  Nat He 	4710.8
- C2 Full	 18605
- C2 Nat He	 4134.41  Hz
-  		Neutrons  14 000 sec-1
- ***************************************************

## Small and Ultra Small beams

- <date/time>

- The main set of data was taken for the Small Beam.
- In addition, we took several runs with a beam even smaller to get more close to EDM conditions
- Ultra Small Beam
- Count Rate over the neutron peak range
- ***********************************************
- C4 USB	 2927
- C4 Li            	 1733
- C2 USB	 2714
- C2 Li 		 1472
- 		Neutrons  1000 sec-1
- ***********************************************
- Ratio      Gamma’s/Neutrons  3/2

## Full Beam, temperatures

- <date/time>

- PMT spectra at different temperatures.
- 90 mk
- 350 mK
- 630 mK
- 1500 mK
- 90 mK were measured at two slightly
-  different  vertical scales.
- Setup 1 was
-  used for all Natural He runs
- Setup 4 - for all He-3 runs

## Count Rate in coincidence, Nat.He

- <date/time>

- Here count rates for channels C2 and C4 were evaluated  in coincidence. Note that here the Low Discrimination Level (LDL) is below a Single Photon  amplitude. Practically, here only presence of any pulse is a trigger. From 0.2 nVsec up to 1.5 nVsec  count rate is:
- C2 ,C4 Nat He, Full beam 	~ 2200 Hz
- C2,C4 Nat He Full beam Li	 ~ 550 Hz

## Beam with Li and Full beam in Natural He

- <date/time>

- Beam with Li and Full beam in Natural He

- Count Rate (s-1) integrated over the neutron peak range [0.2,1.5] nVs
- C2 Li 	 1471
- C2 Nat He	 4134.41
- C4 Li            	1733
- C4  Nat He 	4710.8
- High energy tail is result of the beam entering the cell

## He-3 in the cell, Full Beam with Li,  no coincidence  

- <date/time>

- He-3 in the cell, Full Beam with Li,  no coincidence

**PMT HV=1.9kV, time scale 10 ns/point (for count rate mode)  to see larger neutron’s pulses. A single photon (SP) peak  and gamma  are not separated.  Gamma spectra show no temperature dependence. Count rate is very stable. **

## Neutron Peak, C2 and C4 

- <date/time>

- Neutron Peak, C2 and C4

- Neutron peak  estimated from the Full beam data

## Count Rate in coincidence, He-3, Ultra Small beam   &  Full Beam, Nat.He

- <date/time>

- Count Rate in coincidence, He-3, Ultra Small beam   &  Full Beam, Nat.He

## Neutron Peak in coincidence, He-3, Ultra Small beam   - Full Beam with Li, Nat.HeCount rate is close to expected one for EDM

- <date/time>

- Neutron Peak in coincidence, He-3, Ultra Small beam   - Full Beam with Li, Nat.HeCount rate is close to expected one for EDM

## He-3, Ultra Small beam - spectrum evolution  of a single PMT

- <date/time>

## C2+C4, LDL=15 mV - the same conditions as in the sequence mode 

- <date/time>

- C2+C4, LDL=15 mV - the same conditions as in the sequence mode

## Sequence data evaluation

- <date/time>

**Sequence data were recorded with LDL = 15 mV and coincidence time ********= 20 ns, during 20 mks after a trigger. The trigger position was 1.5 mks.**
**For 2D plot (presented here) we have integrated area of the main pulse (over 100 ns) and counted after pulses during 6 mks after the main pulse. The  first 1 mks and last 10 mks were used to estimate the afterpulse background.**
**We used  sum of pulse areas and numbers of afterpulses of both PMT : C2 and C4 ****	**

## 2D temperature dependence

- <date/time>

- 300 mK

- 1900 mK

## 2D Small beam & Full Beam with Li

- <date/time>

## Rough Comparison with the NIST cell

- <date/time>

- Our position is at about 50% of the light collection efficiency. The far end of EDM cell of proposal is at about 30% that implies a neutron peak position at 0.6 nVs 0r  12 single photons (at HMI we have the neutron peak at 20 SP )

**HMI beam position **

**Position of a far end of the cell from the EDM proposal**

- Light Guide

## EDM cell

- <date/time>

**Probably, light collection can be made from both sides. **
**One side with higher efficiency than another **

**If no light collection from the opposite side, at least, the light guide must be split into 2 parts**

## Summary

- <date/time>

**Our data allowed us to compare  Count Rate data evaluation with and without coincidence.**
**We see that coincidence mode is a great tool to get read of the background  pulses from the light guides.**
**In coincidence we can see clear 400 Hz peak of neutrons  with the beam ********10****4 ****n/sec in the cell in 1D plot. **
**2D plot with afterpulses shows even better separation while not as good as at  higher  temperatures.**
**The single PMT amplitude of the neutron beam is ******** 20 single photons even under our not very optimized conditions(cell mis alignment! ). **
**Our data can be used to simulate quite precisely EDM data.**
**This is only start of our data evaluation!**

## Slide 30