Neutron detection in LHe(HMI run 2004)

R.Golub, E. Korobkina, J. ZouM. Hayden, G. Archibold J. Boissevain, W.S.Wilburn

C. Gould

Layout of the neutron beam

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 stopwhen needed

Beam monitor

Beam stop

Chopper and neutron guide of SANS

Li shield

Guide

Layout of the cell and light collecting system

OD of the cell =5 cm, ID = 4.4 cmThe 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 windowof the cell

Acrylic cell 22 cm

Cell Cross section

Reflector -Al foil

Beam

Stop

Cryostat

View looking

`upstream’ (toward the

reactor)

Collimation

neutrons

PMT

PMT

light guides

cell

delay line

oscilloscope

Cell, as viewed through PMT window

free liquid surface

What was studied

We have studied at different temperatures

1. Empty cell and Neutron guide hall background

2. Cell filled with Natural He - 90 mK, 300 mK, 700 mK, 1400 mKFull 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

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

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.

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1009/ Background 1000 files

C2 C4

Empty cell, coincidence

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1009/ BackgrndNoCollimation Coinc 1000 filesC2+C4 , 200 bins, PMT HV=2kV

areaCountRateCoinC4 areaCountRateCoinC2

Beam On, Li in the beam

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

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Beam On Li, 500 mK, C4 500 mK, He3 98 mK, Nat He 1500 mK, He3

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Beam On Li, 500 mK, C2 500 mK, He3 300 mK, He3 98mK, Nat He

Full beam and Small beam

• 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

***************************************************

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C4,300 mK Full beam, Natural He Full beam, He-3 Small beam, He-3 Beam with Li, He-3

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C2, 300 mK Full beam, Natural He Full beam, He-3 Small beam, He-3 Beam with Li, He-3

Small and Ultra Small beams

• 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

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C2, 300 mK Small beam, He-3 Ultra Small Beam, He-3 Li, Full beam, He-3

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C2, 300 mK Small beam, He-3 Ultra Small Beam, He-3 Li, Full beam, He-3

Full Beam, temperatures

PMT spectra at different temperatures.

90 mk350 mK630 mK1500 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

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pulse area

PMT C2, Full beam, 10 ppm of He-3 in the cell 90 mK, setup1 90 mK, setup4 350 mK, setup4 630 mK, setup4 1500 mK, setup4

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pulse area

PMT C4, Full beam, 10 ppm of He-3 in the cell 90 mK, setup1 90 mK, setup4 350 mK, setup4 630 mK, setup4 1500 mK, setup4

Count Rate in coincidence, Nat.He

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

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Natural He, 300 mK, Full beam C2 C4

Natural He, 98 mK, Full beam with Li C2 C4

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

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root:CR_NatHe_FullBeam:CRNatHeBeamOn300mKC2:

root:CR_NatHe_Li:CRateNatHeBeamOnLi_98mKC2:

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root:CR_NatHe_FullBeam:CRNatHeBeamOn300mKC4:

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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.

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Count Rate: Full Beam with Li, 100 ppm of He-3200 bins, no coincidence

90 mK 300 mK 500 mK 1500 mK

Neutron Peak, C2 and C4 60

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root:CR_FullBeam800bins:CR3HeFullBeam90mKSetup4C4: areaHistSm areaGamma neutronPeak

Neutron Counts Rate = 12498 fit_neutronPeak

x0 = 9.3012e-10 ± 2.12e-12

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root:CR_FullBeam800bins:CR3HeFullBeam90mKSetup1C4:

areaHistSm areaGamma neutronPeak

Neutron Counts Rate = 10401.1 fit_neutronPeak

x0 = 8.9975e-10 ± 2.05e-12

• Neutron peak estimated from the Full beam data

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

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Count rate, C2 in Coincidence with C4 C2, Full Beam , Nat He C4, Full Beam , Nat He C2, Ultra Small Beam, 100 ppm He-3 C4, Ultra Small Beam, 100 ppm He-3

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

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Ultra Small Beam2, 1500mK neutronPeakC2 neutronPeakC4 fit_neutronPeakC2 fit_neutronPeakC4

Fit of C2 x0 = 7.9e-10 ± 7.7e-12 width = 3.8e-10 ± 2.0e-11Neutron Count Rate 380 Hz

Fit of C4 x0 = 9.7e-10 ± 7.6e-12 width = 4.2e-10 ± 2.5e-11 Neutron Count Rate 370 Hz

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

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2509/ CountRate3He1900mKUSB2 C2 2000 files

No coincidence Coincidence, tau=20 ns, LDL=2 mV, Coincidence, tau=20 ns, LDL=15 mV,

C2+C4, LDL=15 mV - the same conditions

as in the sequence mode

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2509/ CountRate3He1900mKUSB2 Coinc 2000 files C2+C4

C2+C4, tau=20ns, LDL=2 mVC2+C4, tau=20ns, LDL=15 mV

Sequence data evaluation

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

Single Photon Peak

300 mK

1900 mK

2D Small beam & Full Beam with Li

Single Photon Peak

Rough Comparison with the NIST cell

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

• 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• 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 104 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!