High resolution imaging with MCP detectors using delay line anodes

Ottmar Jagutzki, Uwe Spillmann, Achim Czasch

Horst Schmidt-Böcking, Reinhard Dörner, …

In collaboration with

Volker Dangendorf from PTB Braunschweig, Neutron Radiography group

The helical wire delay-line anode

Fast timing electronics high rate, multi-hit 5(7) electronic channels only easy read-outCenter-of-mass averaging high position resolution

time resolution: < 1 ns

Sobottka and Williams 1988

DLD40

80 mm “Hexanode” delay-line detector (patented)

Our typical resolution: 40-50 μm rms

Electronic readout:

Time-to-Digital-Converter:

- (old) Wilkinson-type analog-digital conversion (like a TAC): high resolution but a slow digital conversion

- “counter”-type fast (no!) conversion: resolution limited by clock rate Pretty high resolution and fast read-out

TDC8HP: PC-controlled multi-hit TDC with 8 channels, 25 psec LSB, stableread-out speed: 400 kHz now, up to 2 MHz planned (< 10 ns dead-time between hits)

“TDCHP” chip developed by CERN

How to detect visible/near-UV photons with that ?

Photek 75 mm image intensifier with RoentDek DL80 anode

NASA test mask

0.15 mm FWHM

0.075 mm pixel (rms)

Now: < 40 micron rms

5 mm grid constant, 1 mm obstacle

Counting/Imaging near-UV and visible photons with delay-line read-out

DL40-PMT

Quartz windowPhoto cathode

MCP stack

DL40 anode(or bigger)

works fine, but

- difficult to build- not very robust (?)

- size up to 150 mm possible?

Counting/Imaging near-UV and visible photons with delay-line read-out

via image charge pick-up: the RS-PMT

Quartz windowPhoto cathode

MCP stack

Resistive screen

pickup electrode(e.g. delay-line)

Patented technique

- easy, robust design of detector head- size up to 40 mm, may be bigger- standard (multi-layer) PCB pickup electrodes

Image charge read-out: Battistoni et al. 1982

Counting/Imaging near-UV and visible photons with reconfigurable read-out

Quartz windowPhoto cathode

MCP stack

Resistive screen

otherpickup electrodes:

Wedge&Strip, Pixel,…

Patented technique

Read-out technique can easily be reconfigured using the same detector head.

Counting/Imaging VUV photons or particles with reconfigurable read-out

“open RS-PMT”

MCP stack

Resistive screen

pickup electrodes:

Delay-line, Wedge&Strip, Pixel,…

Patented technique

Image charge read-out has some advantages over charge collection for some anodes: Beneficial even for open-face detectors

Delay-line read-out of RS-PMT:

Multilayer PCB

Front and rear side “antennas” (Eland 1994)

connected to delay-line:

(Berkeley group) LC-delay-line

LC-DL50 on open RS-PMT40, irradiated with α – particles, mesh obstacle 80 micron

LC-DL50 on open RS-PMT40, irradiated by ions with 500 kHz, mesh obstacle 80 micron

LC-DL50 on open RS-PMT40, irradiated by ions with 500 kHz, mesh obstacle 80 micron

8 x 8 mm linear scale log scale

50 mm LC Hex-DL on a 4-layer PCB

Hexanode for RS-PMT:

- multi-hit (simultaneous photon pair detection is possible): Compton telescope?- intrinsic linearity correction (no test mask necessary): 3 combination for determining x- and y-coordinates from u, v, w coordinate system

Example for x-layer: x = u = - (v + w) (over-determination) (vector addition)

u

v w

x = u

y =

(w

- v

)/√3

But how can this help correcting non-linearity ?

Linearity correction of LC-delay-line: (no mask needed)

of RS-PMT: 16 18 20 220

20

40

60

80

100

120

140

rela

tive

char

ge /

%

position / mm

Experiment 4 (d=1.0 mm)

Gauss Fit X

c=18.9 mm

=0.86 mm

2,0 mm

Summary:

- Large (open-face) MCP delay-line detector with up to 3000x3000 pixel

- Resistive screen PMT or open MCP detector for counting photons (might qualify for space)

- redundant triple-layer delay-line anode read-out with intrinsic linearity correction

- read-out anodes can easily by swapped

work to be done:

- position resolution needs to be improved for the 40 mm and 25 mm formats

- no experience with flight mission

- not much experience with photon counting at all !

Applications:- FLIM (fluorescence life-time microscopy) - NEURRAD (element sensitive neutron radiography) in cooperation with Volker Dangendorf, PTB Braunschweig

Thanks to Jürgen Barnstedt from Tübingen for borrowing us his RS-PMT!

Obj

ect

Projection of grid mask 70/600micron, resolution 35 micron (1:700)

Results of Barnstedt et al. (1998)

25mm RS-PMT (Proxitronic) - bi-alkali photo-cathode - 4-jaw Wedge&Strip anode