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RadInspectorRadioisotope Identification and MeasurementAMAN KATARIA(EE), JOHNNY KLARENBEEK(EE), DEAN SULLIVAN(EE),DAVID VALENTINE(EE)

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2Design Goals and Motivation

Goal: Portable

Small , light weight, and compact LCD touch display, rechargeable and power efficient

Low Cost Robust

Motivation: The involvement and integration of multiple electrical engineering

disciplines The challenge; foreseen difficulty of research, design, and implementation

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3Specifications

Operating conditions: Low power consumption (< 2W) Long battery life (2+ hrs) Room temperature (25°C)

Energy resolution: < 10% FWHM @ 0.611 MeV (137Cs)

Data collection: Plot spectrum and perform real-time dosimetry Adjustable energy range (400 keV 800 keV 1.2 MeV)

Low cost < $500.00

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4Project Overview

ADC µC

SD F LASH STORAGE

PREAMPLIFIER CIRCUIT

PULSE SHAPING CIRCUIT

ANALOG

DIGITAL

DETECTOR

LITHIUM-ION BATTERYHV SUPPLY CHARGE

CONTROLLER POWER

REGULATION

Semiconductor

USB IN TERF ACE

LCD TOUCH DISPLAY PIEZO BUZZER

POWER

GAMMA TEST SOURCE

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5Detector Design Goals

High stopping ability Increases with increasing Z

High probability of photoelectric interaction Increasing probability with increasing Z (

Charge generation should be linear Determined experimentally and then calibrated

High Q.E. and responsivity 100% Both improve with increasing density

Good resolution Charge generation would resemble dirac-delta pulse

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6Germanium Silicon CZT

Atomic # 32 14 49Band Gap Energy (eV)

0.66 1.12 1.44

Density (g/cm3) 5.3 2.33 6.0Resolution:% FWHM @ 662 keV

0.2 unknown 3.2

Efficiency % (photoelectric)

0.1 unknown 0.47

Dimensions:Area (cm2) x Thick. (cm)

5 cm2 x 1.5 cm(or larger)

1 (cm2) x 0.5 cm(largest)

2.3 (cm2) x 1.5 cm(largest)

Cost > $10,000.00 < $ 300.00 > $2,500.00

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7Probability of Photoelectric Interaction

Calculated Quantum Efficiency

Ideal Resolution Generated Photocurrent

CadmiumZinc

Telluride

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10 mm10 mm

5 mm

► Cost: $90.00► 100 mm2 active area

and 5 mm thick► Trading resolution for

efficiency► Issues

► Charge trapping► Lack of material

uniformity► Microphonic

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9CZT

Atomic # 49

Band Gap Energy (eV) 1.44

Activation Energy (eV) ~5.0

Density (g/cm3) 6.0

Resolution:% FWHM @ 662 keV

3.2

Efficiency % (photoelectric) 0.47

Electron/Hole Mobility (cm2/Vs)

1350/120

taue/taup(µs) 1/0.05

Breakdown Voltage (V) < 350

Images courtesy of Amptek

Charge Collection Efficiency vs. Depth for CZT

𝑒𝑓𝑓 (¿100𝑒𝑉 )=3×106 ∙𝐸 h𝑝− 2.302

• Efficiency• Corrected efficiency

Charge Trapping Effects

characteristic tailing

attenuation

Efficiency Correction

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Ideal response is a single sided exponential decay (RC) Detector charge pulse charges capacitor according to Pulse decays with time constant

Charge Sensitive Preamplifier

𝐼𝐷

𝑉𝑜 (𝑠 )𝐼𝐷 (𝑠 )

=𝑅 𝑓

1+𝑅𝑓 𝐶𝑓 𝑠

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Test circuit with OPA827, Cf = 1pF, Rf = 1Gohm using BPW34 Si photodiode Signal is noisy

Low energy rays close to noise floor Detector is only efficient at low energies, need to maximize SNR

Which components to optimize? Noise Analysis:

Detector contribution Opamp current/voltage noise Thermal noise

Charge Sensitive Preamplifier

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Detector has shunt resistance and capacitance Thermal noise and shot noise modelled

Opamp current noise and voltage noise modelled Flatband and 1/f

Thermal noise (Rf typ. ~ 100M-1G) Find transfer function for each source

Obtain output referred noise

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Charge Sensitive Preamplifier Noise Analysis

Detector (current)

Opamp (current + voltage)

Feedback Resistor (voltage)

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NXP BF862 N-channel JFET

Current noise is a major source of noise► Lower voltage noise op amps typically have higher current noise

► Hybrid implementation: buffer current noise with JFET, select low voltage noise opamp

► Op amp current noise now negligible with respect to detector current noise

► Negligible increase in voltage noise from JFET

► Cost: $0.49► Equivalent noise input

voltage = 0.8 nV/√Hz► Operating temp. as low as

- 65° C if TEC is needed2.5 mm

3.0 mm

100M-1G

1k

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14Charge Sensitive Preamplifier Noise Analysis

* =

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Observations:• Current noise dominates• To reduce noise:

• Lower to reduce gain peaking • Lower 1/f corner freq• Minimize bandwidth with

and GBWP• Lower will reduce current

noise but increase BW• Reduce detector contribution. Lower

dark current (temp)

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16Noise Analysis Verification

OPA827, BPW34 photodiode, NXP BF862 JFET, Rf = 1Gohm, Cf = 1pF Dark current = 5nA @ 10V reverse bias Cin = Cd + Cgs = 15pF + 10pF = 25pF Integrate under the area of each curve to find

that component’s RMS contribution Total RMS noise is root of sum of squares Using these specs we get: 2.67mV (RMS) Experimental measurement yields 1.78mV (RMS)

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17Opamp Noise Calculations

Comments:• Current noise

dominant, so at room temp the difference between opamps is minor.

• Can cool down the detector / feedback resistor to lower current and thermal noise. Picking the right opamp for this application is important!

Opamp 1/f Corner Freq (Hz)

Flat Band Vn (nV/RtHz) Ao (dB) GBWP (Mhz) Vno RMS (mV)

@ T = 298KVno RMS (mV)

@ T = 230K

OPA1612 10.5 1.2 130 40 2.63 0.46

OPA827 11 4 126 22 2.66 0.46

OPA2209 40 2.2 132 18 2.62 0.47

AD8622 5 10.2 137 0.6 2.40 0.47

LMP7721 300 6.5 120 17 2.78 0.47

LT1028 3.5 0.85 150 75 2.54 0.85

AD8397 11 4.5 88 69 3.10 0.96

OPA211 10 1.1 130 80 2.59 0.97

LME49990 30 0.9 135 110 2.61 0.97

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18Analog Pulse Shaping

Charge is integrated into a pulse with exponential decay (RC) Initial “step” contains all the information we need, but preamp signal is

noisy. Charge amplifier pulse magnitude: ~1 – 10mV. Pulses close to noise floor. Reduce signal bandwidth to limit noise and improve SNR

CZT ADC MCA

DetectorCharge

AmplifierAnalog Pulse

Shaper Signal Sampling Spectrum Processing Data Readout

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19Noisy Charge Amplifier Data

CR-3RC Filtered

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20Analog Pulse Shaper Implementation

Flexible 4 stage implementation using quad opamp PCB design includes extra pads for each stage

Reconfigurable: integrator, inverting amplifier Configure for analog pulse shaping or signal conditioning (DSP)

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21Analog Issue: Baseline Shift

Dependent on differentiator , pulse repetition period

Amplitude measured is lower than what it should be

Exaggerated by higher order low pass filter

Analog baseline restoration relatively complex

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22Digital Pulse Shaping

Replace analog pulse shaper with signal conditioning (antialiasing + gain)

Implement DPP using IIR or FIR filters, custom filters (trapezoidal, MWD) Extremely flexible. Accuracy only limited by ADC and floating point precision

CZT DSP MCAADC

DetectorCharge Amplifier + Signal Conditioning Digital Pulse

ProcessingSpectrum Processing Data Readout

Signal Sampling

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Digital Pulse ProcessingFIR filter: 12th order low pass,

0 200 400 600 800 1000 1200 1400 16000

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08133Ba ADC Data

Ampl

itude

Sample

0 200 400 600 800 1000 1200 1400 16000

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08133Ba Data (FIR LPF)

Ampl

itude

Sample

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Digital Pulse ProcessingMWD signal integration:Separate pulses in “pile-up” region -> improve count rate and smooth peaks

0 200 400 600 800 1000 1200 1400 1600 1800 20000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

X: 1275Y: 0.0997

133Ba Data (FIR LPF)

Ampl

itude

Sample

0 200 400 600 800 1000 1200 1400 1600 1800 20000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4133Ba Data (MWD)

Ampl

itude

Sample

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25Digital Peripherals

µC Parallel LCD

SPI SD CardTouch

USBPC

Power Management

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26Microcontroller• The ARM Cortex M4 based STMicro STM32F303VCT6

microcontroller• High speed (72MHz), large flash (256K), and large RAM (48K)• Integrated hardware floating point unit (FPU)• High speed ADC peripheral

• Up to 5Msps• 100 GPIO pins • Cheap development board available

• STM Discovery F3 @ $9

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27LCD• SainSmart 3.2" TFT LCD

Display+Touch Panel+PCB adapter SD Slot

• Standard widely used LCD controller (SSD1289)

• Standard interface controller (SPI interface)

• Inexpensive• Size • Parallel interface 20 GPIO

pins• 16 for data and 4 for

control

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28Microcontroller

STM32F303VCT6 microcontroller schematic

LCD DATA

LCD DATA

LCD CONTROLUSB

SPI

DEBUGGING INTERFACE

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29MCU Program Flow

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30Signal Acquisition

ADC Comparator

DMA Controller

1234...

ADC Buffer (Ring Buffer)

12...

Main Loop[Wait For Input]

Signa l Processing

MCA

SD Card Read / Write

USB Tra nsfer

Process User Input Update LCD

SD Card

Touchsc reen

USBStore Sample

If Signal > Threshold

Interrupt [Pulse Detec ted]

Interrupt [Pulse Detected]

Interrupt[Pulse Detected]

DMA transfers detected pulse

from ring buffer to sample buffer

Continuous Sample & Store (Ring Buffer) Check if ADC Input > Threshold

Copy Detected Pulse

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31Power Management Overview

Regulation IC’s/Ckt’s

Charge ControllerUSB

µC

Preamp & Pulse Shaping

Circuitry

High Voltage Bias

Digital Peripherals

RechargeableBattery

5 Volts500 mA

3.3 Volts30 mA

3.3 Volts30 mA

90 Volts15 µ A

5 Volts25 mA

Charging Delivering

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32Battery Technologies

Specifications Lead acid

Ni-Cd Ni-MH Liquid Li-Ion

Polymer Li Ion

Nominal Voltage (V) 2 1.2 1.2 3.6 3.6

Specific Energy Density (Wh/kg)

35 50 80 125 170

Cycle life (times) 300 500 500 800 1000

Fast-charge time (hours)

8-16 1 2-4 <1 <1

Self-Discharge(%/month)

0 25-30 30-35 6-9 2-5

Overcharge Tolerance High Moderate Low Low Low

Circuit Safety Requirements

Thermally stable

Thermally stable, fuse protection

commonProtection circuitry

mandatory

Lithium Ion Battery Popular for portable electronic design Little to no memory effect Fast charging and high energy density per

cell

2- Cell Series Configuration Utilize the higher voltage for linear step-

down regulation

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33Charging Methodology

Host permission?

Charge Controller

Yes500 mA

NOSUSPEND

DECISION

7.4-8.2 V 2-Cell Li-Ion

Battery

Soft Start

GNDIDD-D+VBUS

GNDGND

VDD

USB_DMUSB_DP

V5V

R28 1.5k

R27 100kR33 22R32 22

V5V V_CHGPMV160UPQ2

Q42N7002

CHG_CTRL

R19 100k

R21 1k

R23 330 R25 100k

C51 3.9uF

GND

GND

V_CHG

CHG_CTRL

C36 22uF

L3ASRF0703-4R7M

R14 270

C30 0.1uF

C34 0.22uF

R15 39

R16 0.05

R11 41.2K

C14 22uF

C15 22uF

VBATC21 4.7uFD7

SSB44 E3/52T

L3BSRF0703-4R7M

R7228K

JP1

BAT

1234

GNDVC IFB

S/S

VIN VSW

VFB1

23

57

6

4

LT1513

GND

USB

µC

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34Power Regulation

µC 3.3 V Regulator

8.2 V 2-Cell Li-Ion

Battery

High Voltage Bias IC/Ckt.

+5 V Regulator

-5 V Regulator

+ Analog Supply

- Analog Supply

On/Off Command

Digital Peripherals

INSENSESHDNBYPNCNCGNDGND

GND

LT1962

C29 0.1uF

C31 10uF

VBAT OUT

GND

C33 10uF

C32 1uF

VDD

8253674

1

2

3

1

76

4

C27 10uF

C201nF

GND

5

8VBAT

VREG_SHDN

VIN_2VIN

SHDNCDELAYADJGND PWRGD

VOUT

MAX5091 C26 100uF

C25 10uF

C23 1uF

C24 0.1uF

+5V

GND

VINSHDN

VOUT

SWGND

LBOUT

LBIN

IPGM

1

2

3

4

5

6

7 8

LTC1174

R2 280k

R6 43k

C10 10uF

C11 1uF

C9 0.1uF

GND

C7 1uF

C6 10uF

C5 10uF

VBAT

GND

D5MBRS130LT

3

L1LB3218T470K

C4 100uF

VREG_SHDN

-5V

GND

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High Voltage Bias• Achieve high voltage to

bias the semiconductor detector• Larger electric field will

sweep more charges to the preamplifier

• Utilization of the LT1930 boost converter IC with external voltage multiplier configuration• 90 volts output at just a

few µAmps

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VIN

FB

SHDN

GND

SW

R8 1k

R10 1k

R12 35.7k R9 35.7k

C22 0.15uF

C28 0.15uF

1% 1%GND

GND

GND

GND

C8 0.15uF

C3 0.15uF

C16 1uF

C12 1uF

C2 1uF

R3 47k

C1 0.1uF

R1 100

GND

GND

GND

5

3

41

2

L22.2uH

R410

R510

D1 CMDSH2

D2 CMDSH2

D3 CMDSH2

D4 CMDSH2

D6 CMDSH2

VBIAS

D8 CMDSH2

LT1930D9

CMDSH2

C16 4.7uF

VREG_SHDN

High Voltage Bias IC/Ckt.

+5 Volt Regulator Detector C rystal

Next: Plot Spectrum

Perform system calibration: Energy: ADC amplitude (channel) -> energy (keV) Absorption efficiency of CZT Correct for CZT charge trapping defects

Plotting procedure: Bin samples according to amplitude. Plot histogram of energy vs counts

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Americium-241 Energy Peaks

Bin 3463

Bin 2716

Bin 851Ba-133Na-22Cs-137

channels energy

Ba-133Na-22Cs-137

88 keV

511 keV

662 keV

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37Experimental Energy Calibration

E = m(ch)+b

Spectral fitting: Cd-109

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88 keV peak clearly identified

centroid

FWHM

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛=𝐹𝑊𝐻𝑀

𝐻0=0.22

Cs-137

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662keV peak clearly identified

Compton edge

Compton back-scatter

centroid FWHM

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛=𝐹𝑊𝐻𝑀

𝐻0=0.12

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40RadInspector Schematic

Main PCBStats:• 1420 Traces• 298 Vias / through holes• 189 Components• 546 SMD PADS

• Most resistors / caps are 0603

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42Budget & Finance

$200

$90 $79

$100

PartsCZT DetectorPCB ManufacturingMiscellaneous

Total: $469.25

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Detector & PreAmp Digital Power Pulse ShaperJohnny Klarenbeek x x x xDean Sullivan x x xDavid Valentine x xAman Kataria x x

Work Distribution

Issues

Semiconductor detector Funding

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45QUESTIONS?