Gas-based Thermal Neutron Detectors - Stanford University · ~1 Mcps Good ~ 0.5-2mm Single pressure vessel ~1 sq.m. Good Ionization chamber with strips or pixels Unity (no avalanche

Gas-based Thermal Neutron Detectors

Veljko Radeka

for the BNL neutron detector team:

G.C. Smith, J. Fried, G. DeGeronimo, G.J. Mahler, D.S.

Makowiecki, J.A. Mead, V. Radeka, N.A.Schaknowski, E.

Vernon and B. Yu

OUTLINE:

• Introduction&Background: Basics and why 3He and not BF3?

• State-of-the-art

• Needs at the facilities

• R&D areas

• Summary

V. Radeka, DOE BES Neutron&Photon Detector Workshop, Aug 1-3, 2012 2

Neutron Capture Cross-Sections


Thermal Neutron Conversion Efficiency in 3He

v 400 m/s v 2km/s v 14 km/s


Thermal Neutron Detection in 3He and Position Resolution Limit

FWHM ~ 0.8 x proton range (~4mm in 1 atm. Propane / CF4)

n + 3He p + 3H + 764 keV ~25000 electron-ion pairs

V. Radeka, DOE BES Neutron&Photon Detector Workshop, Aug 1-3, 2012

5

Proton Range in Common Stopping Gases




8

Neutron Spectrum vs Gas Gain

Energy resolution degrades as the gas gain increases in a MWPC.

Consequences: degraded gamma rejection, detection efficiency, stability and longevity.

n + 3He p + 3H + 764 keV ~25000 electron-ion pairs


OUTLINE:

• Introduction&Background

• State-of-the-art: 3 generations of 3He detector technology with progressively decreasing gas gain


• R&D areas

• Summary


3 directions of 3He detector technology

Gas gain

Counting

rate

Pos.

resolutio

n

Geome-

try

n-peak

resolution

Linear

position

sensitive

with

charge

division

High: ~100-

250

~50 kcps

Medium

~5-10

mm

Tubes

~1 m in

(large)

arrays

Degraded

MWPC

with

Multi-

node

charge

division

Low:

~30-50

~1 Mcps

Good

~ 0.5-

2mm

Single

pressure

vessel

~1 sq.m.

Good

Ionization

chamber

with

strips or

pixels

Unity

(no

avalanche

multiplicati-

on)

~10^8 cps

Medium

~2-5 mm

Single

pressure

vessel

~1 sq.m.

Excellent


Position Sensitive Proportional Counter Tube with 3He

•Modular design, capable of covering very large areas, commercially available

Position resolution using resistive charge division:

1 2

2.35FWHM ENC

L Q Q

(1 ) 1 , 2

100 1%

2 3

agas gain s L FWHM for mtube R kohm

for position resolution

Actual gas gainis times higher

----------------

More on charge division:

J.L. Alberi and V. Radeka, IEEE Trans. Nucl. Sci. NS-23 (1976) 251 V. Radeka and P. Rehak, IEEE Trans. Nucl. Sci. NS-26 (1979) 73 J. Harder, et al.,


12

Array of 192 tubes, 1m long, 8mm

in diameter, spacing 11mm. Two

layers of 96 tubes each, displaced by

half the tube spacing. Mechanical

constraints prevent lateral movement

of cathode tube and potential

breakdown between anode and

cathode. Anode wire resistance is a

few k, with preamplifier at end of

each anode. Tube # determines X-

coordinate, charge division along an

anode wire determines Y-coordinate.

General Electric (Reuter-Stokes) 192-tube

Detector for SANS Beam-line at HFIR),

ORNL

Position resolution along the

tube: FWHM ~ 7mm at 1pc

Max. counting rate/tube

limited by charge collection

(~1-2µs) to ~50 kcps


Large Area, Linear Detector with MSGC

410cm (~154˚) x 15cm, 3.1 bars of 3He + 0.8 bar CF4. 5.3cm gas depth.

48 MSGC plates with 32 cells each. 50 kcps/cell (Ref. B. Gerard)


14

Position Encoding with Interpolating Cathode Strips Multi-node Charge Division

J.L. Alberi and V. Radeka, IEEE Trans. Nucl. Sci. NS-23 (1976) 251 V. Radeka and R.A. Boie, Nucl. Instrum. & Meth. 178 (1980) 543-554


Detector for a Spallation Source

Electronic Block DiagramElectronics

Multi-Node Centroid Readout


Multi-node Charge Division: node samples vs position


BNL’s Neutron Imager Series based on Multi-node Charge Division

5cm×5cm

20cm×20cm 50cm×50cm

150cm×20cm

Detectors of this type have been in operation for a

number of years at the SNS magnetism and liquids

reflectometers, NIST, LANSCE and ANSTO


18

High Precision 5cm×5cm Detector

• Developed for fluid dynamics, radiography

• 8 atm. 3He + 6 atm. propane

• Best neutron position resolution to date in a 3He gas detector

Multi-node charge

division readout


19

120º Detector Installed at PCS at Los Alamos 8 multi-wire segments in common gas volume, 70 cm radius, 1.5m by 20cm sensitive area

Neutron

Beam

Sample


Front Covers from Work at LANSCE’s PCS About the 120° detector:

Uninterrupted operation since

installation in 2002

Position resolution ~ 1·2 mm

(FWHM)

Global rate ~ 500kcps

Sensitive area: 150cm 20cm

Radius of curvature: 70cm

Picture elements: 2 106

Resolution elements: 250 k

Low Gas Gain ~ 50

Absolute position stability (

50m)

Long term elec. stability (10yrs

so far)

Typical diffraction

spectrum from

detector system

21

Wombat Instrument at ANSTO’s Opal Reactor

(HIPD: High Intensity Powder Diffractometer)

120° detector installed in 2007

Has operated very stably,

without interruption, for these

last 5 years

Prolific publication output

One of the most powerful high intensity powder

diffractometers in the world

rapid crystal structure determination for phase

transitions, chemical reactions and rapid kinetic

measurements

Analysis of very small samples (down to 10mg)

Complex sample environments, e.g. pressure cells


OUTLINE:



• Needs at the facilities: Time of flight, geometry, position resolution, stability, counting rate, detector size (area) and configuration

• R&D areas

• Summary


Muscle Studies using SANS Importance of Position and Counting Stability of Detector System

Total neutron scattered counts (raw data) from muscle sample in relaxed state (cross-bridges unattached) and in tensioned state (cross-bridges attached).

Subtraction of raw data for attached state from that for unattached state. Note small absolute value of difference.

Oscillatory behavior of the subtracted curve permits biophysical interpretation of cross-bridge motion, between myosin and actin filaments, when muscle is tensioned.

Data from D. Schneider [email protected]


Diffraction Studies of Coenzyme of Vitamin B12

Diffraction data collected from cobalamine (II) in a small area of the detector. The data have been summed along one of the spatial dimensions so that it can be represented as an isometric view with the TOF axis in the horizontal position and the remaining spatial axis pointing into the page. The slowly varying background scattering is due mostly to unwanted incoherent scattering from hydrogen and reflects the distribution of neutron wavelengths in the incident-beam spectrum. The sharp peaks that sit on the background are the desired Bragg diffraction peaks from the crystal.

From: http://lansce.lanl.gov/

0 ms 33 ms


25

OUTLINE:




• R&D areas: Unity-gain detectors with microelectronics; conservation of He3 - transfer systems

• Summary


Future Direction: 2D Pixel Readout in Ionization Mode

Weighting field of a small circular pixel:

• Ultra high count rate capability: ~105 /s per pixel, >108 /s per detector

• No gas amplification:

– No aging effect

– Stability and reliability

• Flexible geometry:

– Pixel dimension: ~ 1 – 5mm

– Parallax reduction

– Large area, complex geometry possible

• Made possible by development of low noise ASICs


Two-Dimensional, Pixel Detector for Neutrons

d

Weighting potentials of a single pad in a parallel plate geometry

Operation in ionization mode, i.e. unity gas gain, with electronics channel on every pad

ASIC side

(Application Specific Integrated Circuit)

Pad side

24 cm 24 cm anode pad board, with 5mm 5mm →2304 pixels

Neutrons

a

Anode

Pad

Plane


< 5 cts / hr / pad background

3He + n 3H + p (+764 keV)

Completely

assembled

detector

Readout ASICs

in the vessel;

power

dissipation

<10W total

Intensity response to

illumination with point

source of neutrons.

Boundaries in green

represent pads read

out by one 64 channel

ASIC - there are 36

ASICs in total, 2304

pads.

Pulse height response from one pad

Thermal Neutron Response, Pixel Detector

Window

24 cm

24 cm

Neutron

Pulser @ 5 fC

(25- 30k electrons, or 5 fC)


Neutron Pad Detector:

Thermal Neutron Energy Spectrum from One Pad

n + 3He p + 3H + 764 keV


30

One-Dimensional Ionization Chamber for Crystal Backscattering Experiment


Large Pixel detector Data Flow Diagram

Full-size detector for SANS (1m 1m , 40,000 pads),

being planned for ANSTO


The Gas Transfer System is equipment that facilitates almost complete transfer of gas

from a “Drain” receptacle to a “Fill” receptacle, maintaining purity at or close to research

grade. It is also used for initial filling of a new detector from two or more cylinders on

the multi-port manifold.

BNL’s application has been for transferring 3He, 4He, and C3H8, either individually or as

mixtures, for a program of advanced, position sensitive, thermal neutron detector

development.

Diaphragm Compressor: Maximum pressure 12 bar gauge;

Full System is Transportable: Dimensions: 46” x38” x17” ;Weight: ~250 lbs

Typically we can carry extraction and refill with loss of <1% of gas

System is very clean – no leaks, or contamination of gas

We are evaluating recovery of 3He from “punctured” commercial counters contained in a

vacuum enclosure

How to conserve 3He? → Gas Transfer System

Gas Transfer System was designed jointly by BNL and Spectra Gases,

and fabricated by Spectra Gases.


Front View of Gas Transfer System (coupled to Detector and Storage Cylinder)

Detector

Storage

Cylinder

Fill (Drain)

Drain

(Fill)

Multi-valve

manifold


3He Thermal Neutron Detectors: Summary State-of-the-art:

3He represents the “gold standard” for neutron detection in terms of low sensitivity to background, position resolution, stability of response and flexibility of design geometry.

Three electrode configurations with different readout concepts provide design

freedom to cover a broad range of needs at neutron scattering facilities:

1. Proportional tube arrays with charge division can cover very large areas with ~1cm

position resolution;

2. Two-dimensional, multi-wire arrays with multi-node readout operating at low gain and

provide accurate, very stable operation with position resolution in the 1mm range.

3. The newest generation, pixel ionization chambers (unity gas gain), enabled by

microelectronics, makes possible high count rate capability, 105 /s per pixel, >108 /s per

detector, flexible geometry, absence of ageing effects, extraordinary stability and reliability, the

narrowest neutron signal peak.

Proposed R&D:

• pixel ionization chambers with integrated electronics

• stopping -gas mixtures

• 3He conservation – gas transfer systems


35

Documents

Gas-based Thermal Neutron Detectors - Stanford University · ~1 Mcps Good ~ 0.5-2mm Single pressure vessel ~1 sq.m. Good Ionization chamber with strips or pixels Unity (no avalanche