Outline Background History Physical Design Performance Test Prospects

Outline • Background & History • Physical Design • Performance Test • Prospects 散裂中子源进展汇报 12 December 2021 Page 2

Development of Neutron Source Reactor Spallation CSNS 热 中 子 通 量 年份 散裂中子源进展汇报 12 December 2021 Page 3

China Spallation Neutron Source (CSNS) CSNS, with the power of 100 k. W and the pulse repetition frequency of 25 Hz, is scheduled to begin operation in September, 2016. 散裂中子源进展汇报 12 December 2021 Page 4

Neutron Beam Monitor Sample Neutron Guide Neutron Beam Monitor Neutron Detector • Intensity fluctuations of the incident beam due to the accelerator or reactor power changes • Need beam monitor to correct the experimental data of each neutron scattering instrument • Requirements to meet the need of new generation neutron facilities – Timing resolution(~1μs) – Spatial resolution(~1 mm) Wavelength resolution More accurate corrections – High transmission(>95%) & low efficiency(~1‰) – Gamma to neutron separation(<10 -6) – High counting rate(~106 Hz) 散裂中子源进展汇报 12 December 2021 least perturbation γ insensitivity High intensity (>108 n/ cm 2� s) Page 5

History Year Where Style Stanford University BF 3 ionization chamber GE BF 3 Ionization chamber EG&G Ortec Si surface -barrier with 6 Li 1942 1970 s 1980 s 1990 s 2000 s Spatial Resolution Counting rate Performance Stable in practice NO Slow Radiation damage IPNS, Argorme 3 He gas proportional counter unknown composition plated on the anode ISIS GS 20 glass Sensitive to gamma, in practice Ordela, Canberra, Mirrotron 3 He gas proportional counter No 10 k. Hz well in practice ISIS 3 He σ=0. 1 mm ~100 k. Hz Well in development CERN Micomegas with 235 U、10 B <50μm ~1 MHz Excellent in development SNS Micomegas with 10 B ~1 MHz Excellent in development J-PARC GEM with 10 B 1 MHz Excellent in development 散裂中子源进展汇报 12 December 2021 MSGD ~1 mm Page 6

Why GEM? • Fast signal: ~100 ns • High counting rate: 10 MHz • Flexible readout: pad, strip, CCD • Convenient to use neutron convertor • Spatial resolution: ~1 mm • γ insensitivity: <10 -6 • Radiation endurance • Long life • Cost less • Safety compared with Micomegas 散裂中子源进展汇报 12 December 2021 Page 7

The same work in KEK firstly Requirement Measurement Neutron sensitivity ~0. 1% 0. 042 0. 002% Data transfer rate ~1 MHz ~1. 1 MHz Position resolution ~1 mm (FWHM) ~1. 3 mm (FWHM) Wavelength separation capability Required OK Active area ~50 mm 100 mm 散裂中子源进展汇报 12 December 2021 H. Ohshita et al, KEK, 2009 Page 8

Physical Design 散裂中子源进展汇报 12 December 2021 Page 9

Object for Detection • Beam monitor for Spallation or Reactor Neutron Source • Size of Beam: ~4 cm*4 cm • Flux at Guide Exit CSNS: ~108 n/cm 2. s(MS, HIPD), ~107 n/cm 2. s(SANS) Reactor: ~ 107 n/cm 2. s • Repeated Pulse ~ms, CSNS 40 ms • Wavelength Cutoff with Choppers, Velocity Selector Custom Extent: SANS 0. 4~8 angstrom HIPD 0. 3~4. 8 angstrom 散裂中子源进展汇报 12 December 2021 MS 1. 9~6. 2 angstrom Page 10

Structure neutron Gas ： Ar/CO 2 = 70: 30 n+10 B α+7 Li+2. 79 Me. V 7% Eα=1. 78 Me. V ELi=1. 0 Me. V n+10 B α+7 Li* + 2. 31 Me. V 93% τ=73 fs Cathode plane coated with 10 B α+ 7 Li+γ+2. 31 Me. V Eα=1. 47 Me. V ELi=0. 84 Me. V 7 Li Drift or α -e 10 B: easy to get, cost less, chemical stability Gain: ~103 Charge input: 0. 1~1 p. C Pulse: ~100 ns wide GEM 1 With the thin conversion layer, the time and the location of the emitted α or 7 Li can be just treated as those of incident neutron. Transfer GEM 2 Induction Active area: 50 mm*50 mm 散裂中子源进展汇报 12 December 2021 Readout pad: 4 mm*4 mm, 1 mm gap Page 11

Neutron Convertor--10 B 7 Li Neutron Due to the multiple Coulomb scattering: 1) Range of 1. 47 Me. V α : 3. 6μm Range of 1 Me. V 7 Li : 2μm (SRIM) Al cathode plate 2) Maximum efficiency (~5%) for thermal neutrons: ~2. 5 μm Low efficiency 5‰: ~0. 1 μm coated on Al using evaporation or sputtering techniques. 3) Energy of charged particles is extended down. Thin foil can improve capacity of γ discrimination 4) Cone emission or α 10 B 99% α or 7 Li 0. 1μm Geant 4 Simulation for Thermal Neutron 散裂中子源进展汇报 12 December 2021 η=5. 2‰ 10 B 1μm 10 B η=3. 7% Page 12

GEM detector 1) Operation in flow mode with Ar/CO 2 (70/30) mixtures at atmospheric pressure to avoid ageing effects. 2) Range of 1. 47 Me. V α in the mixture gas is 6. 7 mm and that of 1. 78 Me. V α is 9 mm calculated by SRIM. CERN Standard GEM: 50 µm Kapton 5 µm Copper 70 µm holes at 140 µm pitch 散裂中子源进展汇报 12 December 2021 3) If the drift gap is chosen corresponding to the range of the ions so as to energy deposited completely in the drift gas volume, the neutron can be detected with maximal pulse-height related to good γ discrimination. 4) Track of ions and emission angle determine spatial resolution. Page 13

Readout electronics • Pad readout In order to fulfill counting rate 1 MHz/cm 2 for fast readout, an array of pads is used and the special electronics is being designed in IHEP, each channel of which is independent completely. • Electronics & DAQ FPGA DAC Pad Preamplifier +Shaper Counting individually Ethernet &USB Discriminator DAQ PC Timing counting All channel • The best solution is ASIC 散裂中子源进展汇报 12 December 2021 Page 14

Readout PCB 散裂中子源进展汇报 12 December 2021 Page 15

Shielding & Background • Shielding – Al shell electromagnetism – Boron-rich plastic and Cd absorbing neutrons • Background – Due to low-Z materials used, counting gas with low density and thin low probability – Hardly secondary charged particles – Al without neutron activation – High energy of charged conversion products: α and 7 Li – Insensitive to γ background 散裂中子源进展汇报 12 December 2021 Page 16

Efficiency Linearity : Flux of incident neutron, : Reaction rate, η: Conversion efficiency S : energy spectrum of incident neutron σ(E) : Cross section with energy Energy Linearity: n : Atomic density of 10 B, d: Thickness of 10 B Spatial Linearity: Cathode plate d 10 B △d Uniform d: if energy spectrum S(E) is uniform in 2 dimensional cross section, Conversion η is constant. Intensity Linearity: Determined by counting rate of detector and散裂中子源进展汇报 readout speed of electronics 12 December 2021 Page 17

Performance Test 散裂中子源进展汇报 12 December 2021 Page 18

Prototype Chamber Active area 100 mm*100 mm 散裂中子源进展汇报 12 December 2021 The enrichment 92% of boron-10 (mass thickness 1 mg/cm 2) is coated on one surface of aluminum cathode plate as the neutron convertor with electrophoresis in Beijing 261 Factory so as to obtain the maximum conversion efficiency for irradiation tests. The signal collection plane is a printed circuit board with 96 square pads with each area 8 mm× 8 mm. Page 19

Irradiation tests • Neutron signal ~1. 5μs 241 Am(Be) 散裂中子源进展汇报 12 December 2021 A channel directly connected to charge sensitive amplifier (made in IHEP) with sensitivity 500 m. V/pc. The majority of amplitude is about 100 m. V. The minority is above 200 m. V. Noise <3 mv Page 20

Signal induced by α • 239 Pu α source (1. 0× 106 Bq , 5. 2 Me. V α-ray) ~150 ns One channel with a current preamplifier (FBPANIK). pulse ~150 ns wide. noise <30 m. V. 散裂中子源进展汇报 12 December 2021 Page 21

Image Test by scanning 239 Pu source Pad Pre-amplifier Discriminator Scaler CAMAC DAQ PC A block of 3 mm thick steel with a hole of diameter 2 mm is used to collimate the emitted α. It is hoped that the spatial resolution about 10 mm (FWHM) can be obtained easily with each pad 4 mm× 4 mm 散裂中子源进展汇报 12 December 2021 Page 22

New Prototype Chamber 散裂中子源进展汇报 12 December 2021 Page 23

HV supply 1、 Resistance HV 2、 R-C Filter HV 散裂中子源进展汇报 12 December 2021 Page 24

Prospects Ⅰ • GEM Monitor – Spatial resolution: ~1 mm – Active area: custom size. 100 mm*100 mm, >104 channels – ASIC readout – Insensitive to γ – Calibration for energy, intensity and location – Stable for long time – Native GEM, THGEM 散裂中子源进展汇报 12 December 2021 Page 25

Prospects Ⅱ Efficiency(1. 8 A) : 50%, resolution~1 mm 12 December 2021 M. 散裂中子源进展汇报 Klein, University of Heidelberg, 2004 Efficiency(1. 8 A) : 30%, resolution~1 mm S. Uno, KEK, 2007 Page 26

THANKS! 散裂中子源进展汇报 12 December 2021 Page 27