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A Solid-state Hand-held Neutron Radiation Sensor. Jennifer I. Brand*, Susan Hallbeck † , and Peter Dowben ◊ *College of Engineering and Technology, † Department of Industrial Management and Systems Engineering, ◊ Department of Physics and Astronomy, University of Nebraska-Lincoln.

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A solid state hand held neutron radiation sensor l.jpg

A Solid-state Hand-held Neutron Radiation Sensor

Jennifer I. Brand*, Susan Hallbeck†, and Peter Dowben◊

*College of Engineering and Technology,

†Department of Industrial Management and Systems Engineering,

◊Department of Physics and Astronomy,

University of Nebraska-Lincoln

Kevin Osberg, Nathan Schemm, and Sina Balkir

Department of Electrical Engineering,

University of Nebraska-Lincoln

Outline l.jpg

  • Overview of the boron carbide diode for neutron detection

  • Hand-held neutron detector

    • Integrated front-end circuitry

    • Hand-held device

  • Experimental results

  • Ongoing work and conclusion

The boron carbide diode as a neutron detection sensor l.jpg
The Boron Carbide Diode as a Neutron Detection Sensor

  • Uses a specific isotope of boron, 10B, to detect neutrons

Thin neutron detectors l.jpg
Thin Neutron Detectors

Semiconducting boron-carbide

Conversion layer

Neutron capture here yields no signal

No electrical charges generated here by neutron capture

Boron-10 + n


Neutron capture that causes electrical charge generation

Electrical charges generated by neutron capture products


Thick neutron detectors l.jpg
Thick Neutron Detectors

Semiconducting boron-carbide

Conversion layer

Neutron capture here yields no signal

No electrical charges generated here by neutron capture

Boron-10 + n


Neutron capture that causes electrical charge generation

Electrical charges generated by neutron capture products


History l.jpg

Position paper on the device possibilities of a “theoretical” boron carbide semiconductor published jointly by the AEC and AFOSR 1958

Semiconducting Boron Deposition, by PECVD 1989

[J. Vac. Sci. Technol. A 7 (1989) 2796]

Semiconducting Boron Carbide First Fabricated 1991

[Mat. Res. Soc. Symp. Proc. 190 (1991) 101–106]

1st BxCy U.S. Patent, Number 4,957,773 issued September 18th, 1990

Direct writing (single step CVD) of boron on a semiconductor substrate demonstrated 1991

[Applied Physics Lett.58 (1991) 607–609; chosen as a Synchrotron Radiation Center Highlight of 1992]

First Boron Carbide/Silicon heterojunction diodes fabricated; 1992

boron carbide demonstrated to be an indirect adjustable band

gap semiconductor material (0.7 eV < Eg < 1.9 eV)

[Journ. Appl. Phys. 72 (1992) 4925–4933; Appl. Phys. A 58 (1994) 223–227]

First boron carbide heterojunction fabricated by direct writing 1994

[Applied Phys. Lett.64 (1994) 1968–1970]

2nd BxCy US Patent, Number 5,468,978 issued Nov. 21, 1995

Slide8 l.jpg

  • First boron carbide transistor fabricated 1996

  • [Appl. Phys. Lett.68 (1996) 1495-1497]

  • First Boron Carbide Esaki tunnel diode

  • [J. Vac. Sci. Technol. B 14 (1996) 2957-2960] 1996

  • First Boron Carbide Homojunction diode, stability of devices demonstrated to 220 °C

  • [Appl. Phys. Lett.70 (1997) 1028-1030] 1997

  • 3rd BxCy US Patent, Number 5,658,834 issued Aug. 19, 1997

  • 4th BxCy US Patent, Number 6,025,611, issued Feb. 15, 2000

  • First Boron Carbide/silicon carbide heterojunction, stability of devices demonstrated to 350 °C

  • [Appl. Phys. Lett.79 (2001) 4357-4359] 2001

  • First Boron Carbide neutron detector

  • [Appl. Phys. Lett.80 (2002) 3644-3646] 2001

  • 5th BxCy US Patent, Number 6,440,786, issued August 27, 2002

  • 6th BxCy US Patent, Number 6,600,177, issued July 29, 2003

  • First Heteroisomeric Diode and all boron carbide neutron detectors

  • [J. Phys. Cond. Matter16 (2004) L139-L146; Mat. Sci. Eng. B 135 (2006) 129] 2004

  • First Neutronvoltaic 2004

  • 7th BxCy US Patent, Number 6,771,730, issued August 3, 2004

  • 8th BxCy US Patent, Number 6,774,013, issued August 10, 2004

  • First All Solid State Hand Held Neutron Detector Prototype 2006

  • [IEEE Sensors Journal6 (2006) 1531-1538]

New source molecules for boron rich semiconductors l.jpg
New Source Molecules for Boron Rich Semiconductors: 1996

J. Vac. Sci. Technol. A 10 (1992) 881


most important strutural element of the boron-rich solids

The boron carbide diode l.jpg
The Boron Carbide Diode 1996

  • Semiconducting boron carbide used to create a neutron sensitive diode

  • p and n type layers formed from molecules identical in formula but different in arrangement

  • Reverse bias applied to the diode sweeps charges out of depletion region, creating detectable current pulses through the diode

The boron carbide diode11 l.jpg
The Boron Carbide Diode 1996

  • The diodes create a detectable, real-time response to a neutron capture

  • Resulting current pulses are in the range of hundreds of nanoamps for durations of 10 to 40 μsec, so the charge content is in the hundreds to thousands of fC

Charge sensitive amplifier l.jpg
Charge Sensitive Amplifier 1996

  • Charge sensitive amplifier converts current pulses to voltage pulses

  • Acts as a lossy integrator with RC feedback network, and gain of ~|1/Cf|

  • Cf realized by on-chip poly1/poly2 capacitors

  • Transistor MF controls the resistive feedback to change time constant

Charge sensitive amplifier14 l.jpg
Charge Sensitive Amplifier 1996

Simulated diode pulses Charge amplifier output

Charge sensitive amplifier15 l.jpg
Charge Sensitive Amplifier 1996

  • In this application, the charge amplifier does suffer from non-linear gain

  • For large width and/or low charge content pulses, the resistive feedback interferes with the charge to voltage conversion

  • Example: A 3000fC charge transfer in 1μsec, and a 3000fC charge transfer in 10 μ sec

Charge sensitive amplifier18 l.jpg
Charge Sensitive Amplifier 1996

  • AMI 1.5 micron Standard CMOS Technology (1mm x 1mm die area)

  • Digitally selectable charge amplifier gain

  • Programmable bias voltages for tuning integrator time constant

Hand held unit l.jpg
Hand-Held Unit 1996

  • The hand-held was designed around an Atmel microcontroller

  • Microcontroller samples charge amplifier output at 1.3 Msamples/sec with 12-bit resolution

  • Custom software modules allow for real-time processing of the waveform to determine resulting charge transfer per neutron

Hand held unit20 l.jpg
Hand-Held Unit 1996

  • USB interface allows the hand-held to operate with computer for remote control and data capture

  • LCD display and rechargeable battery with a continuous operation time of 10 hours

  • Bias voltages for front-end can be controlled with 2mV of accuracy

Experimental results l.jpg
Experimental Results 1996

  • Operation of front-end tested with RC differentiator circuit to model boron carbide diode

  • 5pF feedback capacitor gives ideal gain of 200μV/fC

  • Measured gain based on RC circuit simulation gives a gain of ~170μV/fC

Experimental results22 l.jpg
Experimental Results 1996

  • Neutron testing was conducted with a paraffin moderated plutonium-beryllium source

  • Estimations of the source approximate the flux rate at 20 neutrons/msec over a 1cm2 area

Experimental results24 l.jpg
Experimental Results 1996

  • In this example, there are approximately 10 counts observed above a 1V threshold in 10msec

  • Based on the estimated flux rate, this gives a detection efficiency of 5%

  • If the threshold is reduced to 0.9V, the efficiency approaches 20%

Experimental results25 l.jpg
Experimental Results 1996

  • A typical measurement of particle detection applications is the pulse height spectra

  • Energy levels are quantized as channels, and each detected particle is assigned to a channel based on it’s energy

  • The number of events in each channel is then plotted versus the number of channels

  • The energy of the capture products is proportional to the amplitude of the resulting voltage pulse

Experimental results26 l.jpg
Experimental Results 1996

  • The blue curve is the pulse height spectra measured by the hand-held detector

  • The bottom curve is the predicted spectra based on the boron carbide diode detection characteristics

  • The red curve was measured when neutrons were blocked from the diode

Conclusions l.jpg
Conclusions 1996

  • Presented the complete design of a compact hand-held neutron detector

  • Experimental results verify the design approach and functionality

  • Real-time processing of the charge amplifier output agrees closely with predicted results

Ongoing work l.jpg
Ongoing Work 1996

  • 0.5μm version of the integrated front-end designed using Cadence

  • Includes externally configurable filter to bandlimit output signal

Ongoing work30 l.jpg
Ongoing Work 1996

  • Second generation hand-held detector using the 0.5 μm chip

Slide31 l.jpg

Next Generation Application 1996: Sensor Network Paradigm for Nuclear Proliferation Detection

An Example 3-D Deployment of the Sensor Nodes as a Network: Cargo Container Inspection









: Sensing diode

Proposed Sensor Node

  • Objectives of Proposed Research:

    • The design, fabrication, and test of sensor node components: Sensing Module, Processing Module, Wireless Transmitter/Receiver

    • The design, fabrication, and test of a base station transmitter/receiver and the associated wireless sensor network protocol

  • Outcomes and Deliverables:

    • A neutron detection sensor network with low-power sensor nodes for nuclear proliferation detection

    • Physical dimensions of a single sensor node are similar to those of a business card for easy deployment

    • 3-D sensor node configurations that allow for neutron detection with directionality

    • Detection of fast neutrons (in addition to thermalized ones) by creating multiple wireless detection layers separated with moderators (such as paraffin) to slow down and capture certain fast neutrons (neutron spectroscopy application).