GEM 中子束监测器的研制进展周健荣, 孙志嘉 [email protected] 中国科学院 “ 核探测技术与核电子学 ” 重点实验室中国科学院高能物理研究所,

GEM 中子束监测器的研制进展

周健荣 , 孙志嘉[email protected]

中国科学院“核探测技术与核电子学”重点实验室中国科学院高能物理研究所 , CSNS 探测器组

2010 年 8 月 17 日

Page散裂中子源进展汇报 April 19, 2023 2

Outline

• Background & History

• Physical Design

• Performance Test

• Prospects


CSNS

Development of Neutron Source

热中子通量

年份

Reactor Spallation

Page散裂中子源进展汇报 April 19, 2023

China Spallation Neutron Source (CSNS)

4

CSNS, with the power of 100kW and the pulse repetition frequency of 25Hz, is scheduled to begin operation in September, 2016.


Neutron Beam Monitor

• 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) Wavelength resolution

– Spatial resolution(~1mm) More accurate corrections

– High transmission(>95%) & low efficiency(~1‰) least perturbation

– Gamma to neutron separation(<10-6) γ insensitivity

– High counting rate(~106Hz) High intensity (>108n/ cm2﹒s) 5

Neutron Guide Neutron Beam Monitor

Sample

Neutron Detector

Neutron Beam


HistoryYear Where Style Spatial

ResolutionCounting rate Performance

1942Stanford University BF3 ionization

chamber

NO Slow1970s1980s

GE BF3 Ionization chamber

Stablein practice

EG&G Ortec Si surface -barrier with 6Li Radiation damage

IPNS, Argorme 3He gasproportional counter

unknown composition plated onthe anode

ISIS GS20 glass Sensitive to gamma, in practice

1990s2000s

Ordela, Canberra,Mirrotron

3He gasproportional counter

No 10kHz wellin practice

ISIS 3He MSGD σ=0.1mm ~100kHz Well in development

CERN Micomegas with 235U 、 10B

<50μm ~1MHz Excellentin development

SNS Micomegas with 10B ~1MHz Excellentin development

J-PARC GEM with 10B ~1mm 1MHz Excellentin development

6


Why GEM?

• Fast signal: ~100ns

• High counting rate: 10MHz

• Flexible readout: pad, strip, CCD

• Convenient to use neutron convertor

• Spatial resolution: ~1mm

• γ insensitivity: <10-6

• Radiation endurance

• Long life

• Cost less

• Safety compared with Micomegas7


The same work in KEK firstly

8

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 ~50 mm 100 mm 100 mm

H. Ohshita et al, KEK, 2009


Physical Design

9


Object for Detection

• Beam monitor for Spallation or Reactor Neutron Source

• Size of Beam: ~4cm*4cm

• Flux at Guide Exit

CSNS: ~108n/cm2.s(MS, HIPD), ~107n/cm2.s(SANS)

Reactor: ~ 107n/cm2.s

• Repeated Pulse

~ms, CSNS 40ms

• Wavelength Cutoff with Choppers, Velocity Selector

Custom Extent: SANS 0.4~8 angstrom

HIPD 0.3~4.8 angstrom MS 1.9~6.2 angstrom 10


neutron

7Li or α

Drift

Transfer

Induction

n+10Bα+7Li+2.79MeV 7% Eα=1.78MeV ELi=1.0MeV

n+10Bα+7Li* + 2.31MeV 93% τ=73fs

α+7Li+γ+2.31MeV Eα=1.47MeV ELi=0.84MeV

GEM1

GEM2

Readout pad: 4mm*4mm, 1mm gap

Gas ：Ar/CO2 = 70:30

Cathode plane coated with 10B

-e

Structure

10B: easy to get, cost less, chemical stability

Gain: ~103 Charge input: 0.1~1 pC

Pulse: ~100ns wide

With the thin conversion layer, the time and the location of the emitted α or 7Li can be just treated as those of incident neutron.

Active area: 50mm*50mm


Neutron Convertor--10B

12

Due to the multiple Coulomb scattering:1) Range of 1.47 MeV α : 3.6μm Range of 1 MeV 7Li : 2μm (SRIM)

2)Maximum efficiency (~5%) for thermal neutrons: ~2.5 μm Low efficiency5‰: ~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 emissionα or 7Li

10B 99%

Al cathode plate

7Li or α

0.1μm 10B 1μm 10B

η=5.2‰ η=3.7%Geant4 Simulation for Thermal Neutron

Neutron


GEM detector

13

CERN Standard GEM: 50 µm Kapton 5 µm Copper 70 µm holes at 140 µm pitch

1) Operation in flow mode with Ar/CO2 (70/30) mixtures at atmospheric pressure to avoid ageing effects .

2) Range of 1.47 MeV α in the mixture gas is 6.7mm and that of 1.78MeV α is 9mm calculated by SRIM.

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.


• Pad readout

In order to fulfill counting rate 1MHz/cm2 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

• The best solution is ASIC

Readout electronics

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Pad Preamplifier

+Shaper

Counting individually

Discriminator

Timing counting

Ethernet&USB

DAC

All channel

FPGA

Pad Preamplifier

+Shaper

Counting individually

Discriminator

Timing counting

DAQPC

DAC

All channel


Readout PCB

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 7Li

– Insensitive to γ background16


Efficiency Linearity

17

dEetyxEStyxSyxd

dEetyxEStyxtyx

yxdEn

yxdEn

),()(

0

),()(0

),,,(1)],,(),,([

)),,,(1)(,,(),,(

S : energy spectrum of incident neutron

σ(E) : Cross section with energy

: Flux of incident neutron, 0

: Reaction rate, η: Conversion efficiency

n : Atomic density of 10B, d: Thickness of 10B

Energy Linearity:

Uniform d: if energy spectrum S(E) is uniform in 2-dimensional cross section, Conversion η is

constant.

10B△ d

d

Cathode plate

Spatial Linearity:

5nm :roughness Surface

%5 ,5 ,1.0 ,

:)(

)(),,(),(),( ,0

nmdmdd

d

ESUniform

dEEnyxESyxdyxd

Intensity Linearity:Determined by counting rate of detector

and readout speed of electronics


Performance Test

18


Prototype Chamber

19

The enrichment 92% of boron-10 (mass thickness 1mg/cm2) 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 8mm×8 mm.

Active area 100mm*100mm


Irradiation tests

• Neutron signal

20

241Am(Be)

A channel directly connected to charge sensitive amplifier (made in IHEP) with sensitivity 500mV/pc.The majority of amplitude is about 100mV. The minority is above 200mV. Noise <3mv

~1.5μs


Signal induced by α

• 239Pu α source (1.0×106 Bq , 5.2 MeV α-ray)

21

One channel with a current preamplifier (FBPANIK). pulse ~150ns wide. noise <30mV.

~150ns


Image Test by scanning 239Pu source

22

A block of 3mm thick steel with a hole of diameter 2mm is used to collimate the emitted α.It is hoped that the spatial resolution about 10mm (FWHM) can be obtained easily with each pad 4mm×4mm

Pad Pre-amplifier Scaler CAMAC DAQ PCDiscriminator


New Prototype Chamber


HV supply

24

1 、 Resistance

HV

2 、 R-C Filter

HV


Prospects Ⅰ

• GEM Monitor

– Spatial resolution: ~1mm

– Active area: custom size. 100mm*100mm, >104channels

– ASIC readout

– Insensitive to γ

– Calibration for energy, intensity and location

– Stable for long time

– Native GEM, THGEM

25


Prospects Ⅱ

26

Efficiency(1.8A) : 30%, resolution~1mm

S. Uno, KEK, 2007

Efficiency(1.8A) : 50%, resolution~1mm

M. Klein, University of Heidelberg,2004


THANKS!

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Documents

GEM 中子束监测器的研制进展 周健荣, 孙志嘉 [email protected] 中国科学院 “ 核探测技术与核电子学 ” 重点实验室 中国科学院高能物理研究所,

GEM 中子束监测器的研制进展周健荣, 孙志嘉 [email protected] 中国科学院 “ 核探测技术与核电子学 ” 重点实验室中国科学院高能物理研究所,