Sensing the Position of a Single Electron Using Induced Signals

R.T. de Souza, S. Hudan, J. Huston, V. Singh, T.K. Steinbach, J. Vadas, B. B. Wiggins Indiana University, Department of Chemistry and Center for Exploration of Energy and Matter

Goal: Development of a position-sensitive microchannel plate (MCP) detector using the induced signal approach.

Applications of Position-Sensitive MCP Detectors Existing Position-Sensitive MCP Technologies

Jacoby, M. Chem. Eng. News, 2014, 92, 11-14. https://str.llnl.gov/str/Dec06/Barty.html

W.B. Feller, “MCP Detector Development.” Neutron and Photon Detection Workshop, Gaithersburg, MD (2012).

Z. S. Browning et al., J. Fish Dis. 36, 911-919 (2013).

Imaging is a powerful tool used in applications ranging from the interdiction of nuclear material to medical diagnostics. High amplification and sub-nanosecond timing make microchannel plate (MCP) detectors excellent devices for the detection of photons, electrons, and ions. MCP detectors can also provide spatial resolution, thus making them useful in several imaging techniques. Such techniques include neutron radiography, 3D atom probe tomography, and positron emission tomography.

MCPs are composed of millions of leaded glass tubes, 2-10 μm in diameter, that can detect electrons, ions, and photons. Each channel acts as an independent secondary electron emitter with a typical amplification of ~103.

The scope of this work is to develop a detector with: a) single-electron sensitivity, b) sub-millimeter spatial resolution, c) sub-nanosecond time resolution, and d) the capability of resolving two simultaneous, but spatially separated electrons. In our test setup, an ejected electron from a secondary-emission foil is accelerated onto the surface a Z-Stack MCP and subsequently amplified to 107 - 108 electrons. The electron cloud is accelerated past a wire plane (1 mm pitch), where the induced signal is sensed, before it is collected on a metal anode. The induced signals have the expected bipolar shape where the zero-crossing point corresponds to the passage of the charge cloud past the sense wire plane.

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Open Questions and Outlook

Prof. R.T. de Souza: desouza@indiana.edu Group Website: http://nuchem.iucf.indiana.edu/

Publications: Ø Using induced signals to sense position from a microchannel plate

detector, R. T. deSouza, Z. Q. Gosser, and S. Hudan, Rev. Sci. Instrum. 83, 053305 (2012).

Ø Optimizing the position resolution of a Z-stack microchannel plate resistive anode detector for low intensity signals, B.B. Wiggins, E. Richardson, D. Siwal, S. Hudan, R.T. deSouza, Rev. Sci. Instrum. 86, 083303 (2015).

Ø Using pulse shape analysis to improve the position resolution of a resistive anode microchannel plate detector, D. Siwal, B. B. Wiggins, R.T. deSouza, Nucl. Instr. Meth. In Phys. Res. A804, 144 (2015).

Ø Sensing an electron cloud emanating from a microchannel plate stack, R.T. deSouza, B. B. Wiggins, D. Siwal, (Accepted in IEEE Proceedings of NSS-MIC 2015).

For More Information

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50 μm wide slits with 900 μm pitch

By extracting the zero-crossing point of the induced signal for each end of the delay line relative to the anode signal, an initial spatial resolution of 466 μm FWHM was achieved. To improve the spatial resolution of the induced signal method, we explored the use of digital signal processing. By extracting the zero-crossing time of the induced signal and anode signal by using the derivative of the signals, a spatial resolution of 115 μm FWHM was achieved.

according to their trophic-level classification, therewere still no significant differences. In addition,SUV values for neither omnivorous nor herbivo-rous fish were significantly different from humanvalues reported in the literature. However, fish

classified as carnivores (red drum and bass species)displayed greater variability in SUV measurementsthan omnivorous and herbivorous fish. This vari-ability suggests that carnivorous fish may be lesssuitable as model species for use with FDG-PET/CT than their omnivorous and herbivorous coun-terparts. The greater variability may be partiallyexplained by the proposal that carnivorous fish are‘glucose intolerant’ (L!opez-Olmeda, Egea-!Alvarez& S!anchez-V!azquez 2009), with the longer timesrequired to clear a glucose load in more carnivo-rous fish (Moon 2001; Rawles, Smith & Gatlin2008; Polakof, !Alvarez & Soengas 2010) contrib-uting to variability in glucose uptake.Imaging with PET/CT generally utilizes larger

animals such as dogs; however, with microPET, itis also possible to use mice. When comparinghuman SUV values to those of dogs or mice,there is a high degree of difference in selectedorgans including heart, liver, brain and kidney.These results suggest that fish could actually pro-vide a useful alternative model for the pathogene-sis of neoplasia using this technique because theFDG uptake in fish species is not significantly dif-ferent from human FDG uptake across all organsystems. In addition, the 95% confidence intervalsfor fish and humans overlapped in all ROIs(Fig. 1). A possible explanation for this similarityis the elimination of the mammalian variability inblood glucose uptake caused by insulin regulation.In mammals, FDG uptake into cells, like glucose,is primarily facilitated by insulin (Landau et al.

Figure 1 FDG-PET/CT image of a tilapia 30-min post-injection. Anatomical landmarks are indicated. The coloured areas reflect

glucose uptake rates, with red being the greatest followed by yellow, green and blue. Organ ROIs were drawn manually on the

transverse or sagittal images, and 3D position was confirmed on the axial images. All ROIs were drawn to include the largest area of

the region or organ in the individual image. SUV analysis is performed in three dimensions, eliminating superimposition of organs

apparent on this static, 2D image.

Figure 2 FDG-PET/CT image of a red drum 30-min post-

injection. The drum were imaged as a group in a single scan with

no increase in scan time. Apparent, intraspecific variability on

this image arises partly from size variation, as fish are viewed in

different planes when imaged as a group. Although there is some

intraspecific variability, it is not as significant as it appears on this

static, 2D image. Three-dimensional technology and individual

analysis eliminate this artefact.

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Journal of Fish Diseases 2013, 36, 911–919 Z S Browning et al. PET/CT imaging in fish

! 2013John Wiley & Sons Ltd

Tomographic Reconstruction: MCP Neutron Imager, ~1 µs time resolution (ICON beamline at PSI, 2009)

NOVA Scientific, Inc. August 1, 2012 16

DOE STTR: Nova Scientific / UCal-Berkeley #DOE DE-FG02-07ER86322

Cold neutrons L/D 350:1, ~107 flux MCP/Timepix readout 55 µm pixels 201 projections/150 sec

Existing Position-Sensitive MCP Technologies

Disadvantages

Multi-Anode Cost of readout electronics, Crosstalk between anodes

Resistive Anode Limited to count rates <100kHz, Cannot distinguish multi-hits

Helical Delay Line Fragility of single wound wire Cross Strip Anode Cost of readout electronics,

High power consumption

Characterization of the Induced Signals

The spatial resolution achieved with the induced signal approach relies solely on the extraction of the zero-crossing point of the induced signal. However, the entire signal shape contains useful information. To further improve the resolution, a position sensitive anode will be used to characterize the dependence of the detailed shape of the induced signal on position.

With joint use of pulse shape and amplitude information, we were able to achieve a spatial resolution of 64 μm FWHM for the RA. This resolution is competitive with more complex MCP arrangements that have a significantly higher signal-to-background than our test setup. However, insertion of a sense wire plane prior to the RA resulted in large coupling between the RA and wire plane making it unfeasible to use the RA to characterize the induced signals.

A spatial resolution of 94 μm FWHM has been demonstrated with our custom multi-strip anode board. The coupling associated with the insertion of the RA is not present with insertion of the multi-anode. As a result, we will be able to use the position on the multi-anode board as a tool to understand the detailed shape of the induced signals.

� Implementation of a resistive anode (RA): � Implementation of a multi-anode:

Neutron Imaging

Courtesy of Paul Scherrer Institut

Romualdo T. deSouza, Indiana University

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Appendix 4: Facilities and other resources

As a member of both the Department of Chemistry and the Center for Exploration of Matter and Energy (CEEM) I have access to several resources pertinent to this project. Most notably, I have access to an excellent machine shop as well as electronic engineers in both locations. The machine shop with a total of seven machinists has CNC mills and lathes, as well as wire EDM capabilities. The shop has produced numerous ultra-high vacuum systems over the past decade. The two electronic shops together consist of a total of seven electronic engineers and two technicians. The engineers possess expertise in both analog and digital electronics. They have access to the necessary electronic design and layout tools necessary for the project. In the recent past they have developed electronics for the STAR detector as well as state-of-the-art mass spectrometry research systems. Our data acquisition needs are presently met by outsourcing to Mr. Ron Fox, Michigan State University as he is the developer of the PC based VME-DAQ system that we presently use. We also have access to standard information technology and network support on campus. Testing will be conducted in laboratory space that is dedicated to the research group of the PI. CEEM will provide adequate office space for both the graduate student and postdoctoral student.

The Low Energy Neutron Source (LENS)

The LENS facility (floor plan shown in Fig. 17) has two target stations with three conventional scattering instruments (SANS, fast/thermal Radiography, and Spin- Echo Scattering Angle Measurement, or SESAME), as well as a test instrument for detector development and neutronics research (the Moderator Imaging Station, or MIS), and a station for irradiating electronics with fast neutrons. Construction of the facility began in the Fall of 2003, and it has been producing cold neutrons, conducting materials research and serving as a center for innovation in neutron instrumentation since April 2005.

Fig. 17: The LENS floor plan. The 13 MeV accelerator (lower left) is powered by thee 1MW klystrons operating at 425MHz and feeds a proton beam onto a beryllium target in one of two target stations (green circle on the right).

SESAME

SANS

MIS

Radiography

We intend to utilize the detector in the area of neutron imaging with both slow and fast neutrons. The measurements will be carried out at the Low Energy Neutron Source (LENS) facility at Indiana University. Characteristics of LENS include: Ø  13 MeV proton linac driver Ø  9Be(p,n) reaction to produce neutrons Ø  thermalization (polyethylene, solid CH4 at 6.5K) Ø  100 n/(ms.cm2) neutron flux

Position-Sensitive MCP Detector Spatial Resolution FWHM (μm)

Multi-Anode 94 Resistive Anode- Charge Division (CD)

157

Resistive Anode- CD + Risetime Analysis

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First Generation Induced Signal 466 Induced Signal with DSP 115

Ø  How does the shape of the induced signal depend on the position and size of the charge cloud?

Ø  Will the use of differential readout implemented in

a second generation prototype improve the present position resolution?

Ø  How well can the detector spatially resolve

multiple particles simultaneously incident upon it?

Low Energy Neutron Source (LENS)

A: 241Am source B: scintillator with PMT readout C: secondary electron-emission foil D: accelerating wire harp

E: mask F: Z-stack MCP G: resistive anode

Sensing Position with Induced Signals

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