MARS detector technology and the SOLiD experiment A. Vacheret, A. - - PowerPoint PPT Presentation

MARS detector technology and the SOLiD experiment

• A. Vacheret, A. Weber, Y. Shitov, P

. Scovell University of Oxford

Talk overview

• Introduction to the MARS technology
• MARS neutron portal project
• MARS antineutrino detector system
• Search for Oscillation with Lithium-6 detector : The SOLiD experiment

2

Introduction to the MARS project

• MARS technology is being developed as an alternative for neutron and antineutrino detection
• high performance replacement to Helium-3 tubes used in various applications (border security,

nonproliferation, Science, dosimetry, etc...)

• Novelty in how (old and new) components are combined to give better capability
• handheld to very large area of detector surface
• MARS IP is protected : patent GB2012052097 (PCT phase)
• One of main goals is also applications of antineutrino detection at reactors
• Develop whole solution with electronics and data processing
• technology can be extended with new materials and components (choice of neutron absorber,

progress in organic and inorganic scintillators, photosensors, electronics etc...)

3

Where it all started

• Confidence in technology come from successful large scale use of plastic scintillator based detectors with

embedded WLS fibre read out by solid state photosensors

• design, construction and assembly is simplified and system has very good uniformity. System is reliable and

requires low maintenance.

• Combined high performance required by Science with easier operation (strong point for applications).
• Long experience in calibration and operation accumulated in MINOS and T2K experiments

4 Multi-anode PMT

Extruded PS scint. 4.1 x 1 cm WLS fiber Clear Fiber cables

2.54 cm Fe

U V planes

MINOS detector plane Construction of T2K calorimeter module (~ 3000 channels)

4m 0.5m

PS planes MPPC

Photosensors: compact readout solution

1.3 mm x 1.3 mm (T2K device) 667 pixels (50um pitch) Nominal gain : 7.5x10E5 PDE (500 nm) ~ 30% Timing resolution ~ 200-600 ps Noise 1 MHz/mm2 at 25ºC Cross-talk and after-pulsing ~ 15% 70 V operation voltage Larger area possible Recent improvement on noise level and crosstalk

5 Connector design for P0D/ECAL/MRD WLS Fibre Ferrule MPPC spring foam connector PCB board Shroud

50 um pixel pitch 60-65% active area 1.3mm 50μm Multi-Pixel Photon counters MPPC

MPPC characterisation and model development

• Characterisation of MPPC response
• Use data from measurements to predict behaviour

6

Response to photon signal

70.59 V @ T=22C 70.81 V @ T=22C 71.06 V @ T=22C

Characterization of the 1.3 mm x 1.3 mm MPPC for the T2K near detectors.

• A. Vacheret et al.

NIM.A, doi:10.1016/j.nima.2010.02.195

Electronics development for T2K

• 64 Hi/Lo gain ADC channel

timestamping

• Individual MPPC HV trim (8 bit, 5V

range)

• On board charge injection circuit
• Temperature sensors

7

POWER 5V 3.3V 2.5v 1.2V MINIATURE COAX CONNECTORS DATA TRIG ADC EXTERNAL I2C CALIBRATION CHARGE INJECTION SWITCHES LV POWER REGULATORS HV SWITCH 16 cm 9 cm ADC

High Voltage trim DACs (8 altogether) Trip-t Trip-t Trip-t Trip-t Xilinx Spartan 3 FPGA PROM GAIN SPLITTING COMPONENTS TEMPERATURE AND VOLTAGE MONITORING

Channel cal. test pulse Voltage trim +5V range MPPC Bias voltage ~ 70 V

MPPC connection and channel division

The front end readout system for the T2K-ND280 detectors Vacheret, A.; Greenwood, S.; Noy, M.; Raymond, M.; Weber, A. doi:10.1109/NSSMIC.2007.4436543

MARS neutron portal project

MARS technology : neutron portal project

• Large scale neutron portal system based on solid scintillator

technology

• Active element : transparent bars with embedded WLS fibres

with 6LiF:ZnS layers

• 6 months project completed this summer
• Develop optimised and compact system with in-house

electronics front-end

9

2000.0 mm 1600.0 mm 1700.0 mm

active detector stack with 16 bars

electronics boards 1 data readout to digitiser electronics boards 2 HV, LV in

Neutron detector construction

• Easy construction and assembly

10

MARS neutron system performance

11

MIX - PSD comparison MIX - PSD comparison

60Co 252Cf

• 7

• 6

• 5

• 4

• 3

• 2

• 1

• We demonstrated cost-effective

replacement of 3He tubes in portal

• validated performance at NPL
• > 70% neutron detection efficiency
• Meet security industry standards
• gamma rejection better than

1:1,000,000 level

• efficiency of neutron not

affected by large gamma flux

• First neutron detector based on read
• ut with solid state photosensors

(publication in preparation)

• Development of other type of neutron

system under investigation

10-6

Loss in Effn (%)

MARS antineutrino detector

MARS antineutrino detector

• Based on requirement to develop compact and low maintenance detector system for reactor

monitoring

• rate and spectral measurement towards use in safeguards applications
• robust to backgrounds by design
• Clear signature for neutron : Use of 6LiF:ZnS(Ag)
• good level of segmentation for accurate determination of interaction point
• fully active : target detector used as veto
• flexible and scalable design
• compact system with photosensor read out

13

MARS antineutrino detector element

Cast scintillator cubes (PVT EJ-200)

• large scintillator signal to increase sensitivity

and good energy resolution

• threshold energy down to around 100 keV
• σ(E)/E ~ 0.25 @ 2 MeV
• Easy to manufacture in large quantity

LiF:Zns(Ag)

• 6Li has large cross-section on thermal neutrons

14

X read out Y read out 5 cm 5 cm

~ 60 PE (both ends) Ethres 150 keV Eres 0.13

cosmics muon light yield in 5cm cube

Principle of antineutrino detection

Detect antineutrino via well known inverse neutron decay Detect neutron via reaction on Lithium-6 Time coincidence and 3D localisation of interaction

15

e+ n

¯ νe + p → e+ + n

n + 6Li → 3H + α + 4.78 MeV

e+ n

Δt ~ 1-150 us

MC MC MC

Detector layout

Detector active stack : 1m x 1m x 1m

• 1 ton fiducial mass
• 20 x 20 cells per plane ~ 10k cells and 2k read out

channels

• 3D position reconstruction using X and Y coordinates

Detector footprint ~ 1.5m

16

Y view

νe νe νe νe

Active volume stack

Integrated Charge - All events + Neutron events Integrated Charge - All events + Neutron events

Neutron detection

High capture efficiency on Lithium-6

• signal detection efficiency > 70%
• comparable to Helium-3
• localised signal

Very high discrimination between neutron and γ

• simple charge cut and pulse properties
• very good handle on background γ

εγ < 10-4

• Use neutron signal to trigger detector

read out (simple charge trigger or via digital pulse processing)

17

X channel Y channel

1 10

10

10 Summed Integrated Charge (NPE) 50 100 150 200 250 300 350 400 450 500 Number Of Peaks 5 10 15 20 25 30

AmBe neutron signal EM signal AmBe

Samples

18

Electronics development

Main features

• signal sampling : 80MS/s 12 ADC bit cADC
• dead-timeless
• n board digital processing : pedestal

suppression, readout threshold, PSD etc..

• 32 Channels per board
• charge injection system
• MPPC HV fine control per channel
• Use neutron signal features to trigger on IBD event

19

Digitiser Board 10-20 us FPGA virtec 6 LV HV

signal out

Development of digital pulse processing methods

• Use current Mars neutron system to study various

methods to be implemented in front-end electronics

• first studies made by student
• charge based
• template matching (Normalised cross-

correlation)

• Development and validation to be done
• robustness and reliability is key

20

Positron imaging capability

Large E deposit with additional activity from annihilation γs

• signal within 15 cm around high hit
• topology cut to increase selection purity

21

Cubes X 5 6 7 8 9 10 11 12 13 14 15 16 Cubes Y 7 8 9 10 11 12 13 14

Positron - Face 1

Cubes X 5 6 7 8 9 10 11 12 13 14 15 16 Cubes Y 7 8 9 10 11 12 13 14

Positron - Face 2

γ γ γ e+ e+ MC MC

Antineutrino event selection

neutron trigger look for positron signal

• simple E cut > 600 KeV or topological

100-150us time window within 15-20 cm radius of neutron interaction efficiency is ~50%(~20%) with simple energy cut (positron cut)

• 150-300 events per day @ 7.5m of a ~57 MW reactor

22

e+ signal n signal

MC MC MC

Cosmic muons tracking

good tracking capability for muons

• use for calibration
• active veto reduces further

size of shielding

23

Searching for Oscillation with Lithium-6 Detector

soLi∂

Experimental set up

short baseline < 10 m to probe Δm2 ~ 1 eV2 small size reactor but high thermal power

• access higher value of Δm2 and large statistics

source and event localisation < 0.5 m extension max

• requires good energy and position resolution

use ratio of spectra at two distances from the reactor

• cover same solid angle
• no assumption on shape of spectrum : only look at

differences

• need flexible baseline for optimisation
• increase sensitivity using detector granularity

studying feasibility of absolute measurement

• using MARS neutron low cost system

25

L1 L2

core

concrete

D1 D2

Δm2=2.35, sin22θee = 0.165

Twin Detector set up at ILL

• Reactor is pure 235U core (93%)
• LoI submitted to ILL Science council
• Location for detector in discussion. Need to measure

background

Source ILL RR Power (MW) 57.1 Core size (m) 0.4(D) x 0.8 (H) Baseline (m) 6.0 and 7.5 m Detectors size m3 1 Energy resolution 0.3/Sqrt(E) Vertex resolution cm < 5 IBD/day/Ton ~600 IBD Efficiency (%) 50(20)

Reactor core Detector rooms ?

26

1 2 3

Preliminary sensitivity

Shape only analysis ILL reactor characteristics

• 57 MW, 40 x 80 cm core

baseline : 6.0 m and 7.5 m

• uses full stat of each detector not yet full

granularity

2x 1Ton detector mass

• 50% detection efficiency
• energy resolution : 0.3 at 1 MeV
• 2 years running (200days/year)
• signal to backgrounds ratio = 5 (~10 mwe)

27

new

) θ (2

2

sin

• 2

10

• 1

10 1

2

/ eV

new 2

m Δ

• 2

10

• 1

10 1 10

95 % C.L. 99 % C.L.

Backgrounds

Reactor backgrounds

• high gamma flux from concrete walls
• thermal neutrons

Cosmics background

• nucleonic component : fast neutrons
• muon background (induce spallation neutrons)

Intrinsic radioactivity Main concern is neutron background

• shield reactor neutrons
• need overburden (> 8 mwe)
• affects rate of accidentals

First look at background in simulation

• being currently reproduced with newly implemented

G4 simulation detector response

Need careful measurement at ILL site

28

n γ

2 cm PE

Detector Shielding

0.5 cm Boron Layer 13 cm Borated PE

Cosmics muon simulation

cosmic muons interact in detector and generate spallation neutron

• good rejection with IBD cluster

selection : expect ~3 events/day

• n surface
• shielding with Lead increase

significantly the level of false IBD events

• need good overburden and veto

muon to limit impact

• reduce Lead shielding if possible

29

1,E-12 1,E-11 1,E-10 1,E-09 1,E-08 1,E-07 1,E-06 1,E-05 1,E-04 1,E-03 1,E-02 0,1 1 10 100 1000 10000 differential rate, muons/cm2/sr/s/(GeV/c) muon energy, GeV/c

Muon flux at sea level (Rastin 1984)

PE/B+PE shielding only with Lead shielding

Cosmic neutrons

Main background at shallow

• verburden
• ~20k n/day on surface

background shape (no energy smearing in MC)

• from 4.4 and 8 MeV excitation on

Carbon

• verburden > 8 m.w.e. would

be ideal

• main correlated background of

experiment

30

1,E-13 1,E-12 1,E-11 1,E-10 1,E-09 1,E-08 1,E-07 1,E-06 1,E-05 1,E-04 1,E-03 1,E+00 1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 differential rate, neutrons/cm2/s/MeV neutron energy, MeV

Neutrons from atmospheric muons

(Gordon 2004)

Reactor neutron and γ background

High flux of γ from reactor (MHz rate on detector surface)

• High discrimination with LiF:ZnS
• if needed effective discrimination with

positron topology cut

Timing and spatial cut efficient at reducing accidentals

• expect only a few 10 events/ton/day

reactor neutrons shielded

high signal to noise ratio without minimum shielding possible

31

false IBD from neutrons 10%

Cost and milestones

Total cost of building two detectors :

• ~ £800k for 2x 1m3 detector (1 build in UK and one in France)
• Cost dominated by bulk scintillator, electronics and neutron absorber material
• UK cost is £1.2M (equipment and salaries for 2 years construction phase)

Milestones : 2013

• Full design of detector and development of electronics
• Detector construction starts fall 2013

2014

• Assembly of detector modules and test with calibrated source
• Installation and commissioning of systems during the summer
• Data taking starting in September

32

Conclusion

MARS scintillator technology is well suited for antineutrino detection

• validated for neutron detection
• unique handles on rejecting background and selecting antineutrino interactions
• highly segmented : good localisation of interaction
• efficient and compact detector system
• Scalable design with detector elements easy to produce

The SOLiD experiment can achieve very good sensitivity to reactor anomaly

• high potential for a definitive experiment
• great opportunity for developing further a technology that has potential for many other

applications

33

Reactor monitoring: a first practical use of antineutrinos ?

ν-technology for safeguard purposes :

• antineutrinos can’t be shielded. Can be detected

non-intrusively. Monitoring can be done remotely.

• IAEA engaged with scientific community since

2003

• antineutrino workshop in 2008 on application to

Safeguards (IAEA report STR-361)

• had-hoc working group on antineutrino detection

formed in late 2010. Meet every year at IAEA

• headquarter. Coordination also through ESARDA.
• technology need demonstration
• challenge is to keep high efficiency and meet

IAEA practicality criteria.

Oxford CNRS-Subatech collaboration to develop reactor monitoring code to predict rate at monitor

34 νe νe νe νe νe νe νe νe νe