Neutron Imaging with a Novel - PowerPoint Presentation

Slide1

Neutron Imaging with a Novel Position-Sensitive MCP detector

Personnel : Mr. Blake Wiggins (graduate student), Davinder Siwal, RdS (PI), Indiana University

Whether detecting photons, neutrons, or ions ultimately one is inevitably dealing with electrons.

Goal: Develop a detector with single electron sensitivity that has sub-millimeter position resolution, sub-nanosecond time resolution and the capability of resolving two spatially separated, simultaneous electrons.

Individual gunpowder grains inside a bullet

A motorcycle engine

Good position and time resolution are necessary in high quality imaging!

Neutron

imaging

Courtesy of PSI

A.S.

Tremsin

et al., NIM A652 400 (2011)

National Nuclear Security Association Award

No. DE-NA0002012 Slide2

Millions of leaded glass tubes 2-10

μm in diameter act as secondary electron emittersApplied voltage results in an electron producing an avalanche with typical amplification of approximately103 per plateSensitive to electrons, photons, ions

Commercially available PS-MCP technologies

CMOS Timepix detector (state-of-art)

While this approach achieves a resolution of 45-55 m FWHM, it has the disadvantages of:

Complex readout electronics (ASICs) – charge integrating approach

Limited size (tile 22 mm x 22 mm active area using 4 chips)

High power consumption (~1W/chip)

Helical delay line ; Resolution (FWHM): 60 µm; Cons: Fragile

Resistive anode; Resolution (FWHM) : 100-200 µm; Cons: Rate limit 100 kHz, double-hits

D

ue to its large amplification and sub-nanosecond time response the

microchannel

plate detector is an ideal tool for amplifying the original signal.

Hamamatsu Photonics K. K.,

Photomultiplier Tubes Basics and Applications 3

rd

ed

(2007).

Principle of OperationSlide3

Fast signal

Simple readoutMulti-hit capabilityLow power consumptionSenses (does not collect) the electron cloud

Introduction

to the Induced Signal

Approach

R. T.

deSouza

et al

, Rev. Sci.

Instrum.

83

, 053305 (2012). A single electron is amplified to

a cloud of 107

-108

electrons

and sensed

by 2 orthogonal wire

planes.

Wires in a sense wire plane have a 1 mm pitch and are connected to taps

o

n a delay line.

Position is related to the time difference between the signals arriving at the ends of the delay line.

Resolution (

m)

unoptimized

~ 500

Optimize bias, grounding

~240

Improve

zero crossing extraction

~115Slide4

Testing the Induced

Signal

Approach

By digitizing the signals at 10 GS/s and utilizing digital signal processing techniques, a position resolution of

95 m (FWHM) has been obtained

.

With the basic characteristics of the detector determined we turn to neutron detection …

S

ingle alpha particle incident on aluminized

mylar

foil ejects 2-7 electrons

Electrons are accelerated by an electrostatic field towards the position sensitive MCP

Following amplification by the MCP, signals from either end of the delay line are amplified by x30 and the waveforms are digitizedInsertion of a mask just in front of MCP allows determination of the position resolution

Resolution at (near) the single electron limit!Slide5

Low Energy Neutron Source (LENS) at Indiana University

13 MeV proton linac driver9Be(p,n) to produce neutrons

Thermalization (polyethylene, solid CH4

@ 6.5K)100 n/(ms.cm2)

20 Hz repetition rate

XY

Anode

Cd Mask*

* 2mm

Wide

Slits,

Horiz

.

Oriented, 5mm Pitch

σ(thermal) for

113

Cd = 19,820 b

10

B + n (25

meV

)

7

Li +

4

He

σ

= 3840 b

By inserting a neutron sensitive MCP (B-doped) in front of the Z-stack MCP, the detector becomes sensitive to thermal neutrons.

Slow Neutron Radiography

Efficiency for detection of thermal neutrons 20-50%Slide6

Detector setup

25 mm diameter Boron doped MCP (Nova Scientific) in front of a 40 mm diameter detection grade Z-stack MCP (

Photonis

)

Detector housed in ISO200 6-way cross

Dedicated oil free pumping P=2 x 10

-7

torr

NIM bin for HVPS, amplifiers, and trigger

Setup is compact and transportableSlide7

First Neutron images (Dec. 2016)

Count

rate (cps)

radiogenic decays i.e. bkg.

101

slow neutrons + bkg.

172

S/B = 0.7

Outline of 40 mm Z-stack and 25 mm B-doped MCP visible

Three horizontal slits clearly visible (limited by 15 mm diameter beam)

Unexpected intensity modulation in the x-direction

LENS at 10% power

Using VME based DAQ Caen V1729A (

max rate 300 Hz

)

2 mm wide horizontal slits spaced by 5 mmSlide8

Resolution of first Neutron images (Dec. 2016)

The measured resolution is a convolution of the intrinsic resolution of the detector with the finite slit width.

We represented the finite slit width as a step function with a 2 mm width and the intrinsic resolution as a Gaussian with an intrinsic width.

By varying the intrinsic width, the impact of the finite slit width can be determined.

Peak

Slit Width

FWHM

(mm)Instrinsic Rs

FWHM (mm)A2.130.906 B

1.810.770

C2.13

0.906

Fundamental limitation is S/B!To improve the S/B we need a higher neutron flux which requires a faster DAQ !

Average intrinsic resolution is 860 µm for the 2 mm slitsSlide9

Development of a high speed Neutron DAQ

AlazarTech

ATS9373 Waveform Digitizer:

2 Channels

2 GS/s sampling for 2 channels and 4 GS/s sampling for 1 channel

12 bit resolutionFixed +/- 400 mV Range

6.8 GB/s

PCIe x8 Gen 3 interface1.0 GHz analog bandwidth

Variable frequency external clockingSlide10

Characterizing the

nDAQ

Re-triggering capability and neutron pileup

Re-arm window

(system inhibited)

t = 128 ns

Digitization window

t = 128 ns

Max rate achieved with

pulser

:

200 kHz (includes recording to disk)

4 waveforms/event

400 MB/s (at ~ SSD limit)

1.1 MHz (w/o

recording

i.e. attainable with FPGA processing)

T= 20K

D= 10m

Slow n

The digitization and re-arm window result in a time interval during which neutron pile-up can occur

For 256 ns the pileup probability is 1 in 10

5

Even when it occurs, it can be distinguished by the multi-hit capability of the detector.Slide11

Alpha testing with

nDAQ

(asynchronous data)

Max rate of 9 x 103

cps measured. This rate is limited by source intensity (10 µCi

241Am)

Slits in mask (355 µm wide, 2 mm pitch) are clearly visible along with 1mm diameter holes

A relatively uniform background is observed for the MCP detectors

3.5 mm slits; 4mm pitchSlide12

Discussion of Results

Projection of slit spectrum indicates a measured spatial resolution of 603 µm (FWHM)

Deconvolution

of finite slit width yields an intrinsic resolution of 551 µm (FWHM)

This ”intrinsic” resolution includes the influence of slit scattering at the slit edges.

Maximum non-linearity

~1.4%;

average non-linearity ~0.6%

The increased intensity at the intersections where there are a lot of edges indicates that slit scattering significantly impacts the resolution.Slide13

Designed and realized a position sensitive neutron detector

Measured first neutron 2D image using induced signal approach. Initial resolution : ~860 µm (FWHM) with S/B of just 0.7Developed fast PCIe based DAQ (200 kHz/4 waveforms; 128 ns); ~103 speed-up

Spatial resolution (alphas) improved to 551 µm (FWHM

) with good linearity without optimization

Accomplishments/Summary

Outlook

Test with neutrons (LENS at full power) in summer 2017 using new

nDAQ

Develop multi-hit TDC for time-stamping for dynamics (underway)

Implement DSP routines in FPGA to achieve higher data rates

Propose run at LANSCE in 2018 (discretionary time earlier?)

Improved the intrinsic resolution for electrons: 115 um

to

95

um

Submitted

manuscript on PS

ExB

detector

for beam

imaging at RIB

facilities

Slow neutron imaging

I

maging