Gammaray’detection’&’ imaging’in’the’digital’world’iop/PTC/PDFs/Gamma-Ray-Detection.pdf · Gammaray’detection’&’ imaging’in’the’digital’world ... •

Dr Laura Harkness-‐Brennan

Liverpool Physics’ Teachers Conference 2014

Gamma-‐ray detection &

imaging in the digital world

•  Gamma-‐ray detec,on and spectroscopy

•  Going digital

•  Gamma-‐ray imaging

•  in medical physics

•  in nuclear security and decomissioning

Outline

Radiation Detection

•  Is there any radia,on?

•  What type is it?

•  What is the ac,vity or dose rate?

•  What material does it come

from?

•  Where is it located?

By measuring the energies of gamma-‐rays, can understand what material they were emi>ed from

Gamma-‐ray Spectroscopy

511keV

1274keV

662keV

137Cs and 22Na fingerprints •  Characteris,c energies •  Probability of emission

Gamma-‐ray Detection Demo

Incident Radia,on

Photoelectron Dynodes Anode

Output Voltage Interac,on point

•  Gamma-‐rays interact in scin,lla,on detector •  Scin,lla,on light is produced (which is propor,onal to how much

energy has been deposited) •  Light is converted into an electrical signal and amplified in a Photo

Mul,plier Tube (PMT) •  Output signals are processed into an energy spectrum

•  Digital electronics offer enhanced func5onality for flexible teaching

and research

•  Compact – can plug directly into computer or laptop

•  Teaching systems easier to use

•  Complex analogue experiments made simpler with digital readout

Going Digital: Teaching

•  Central teaching labs have

43 fully digital systems

(semiconductor, scin,lla,on

and gas detectors), all on

one network

•  Standard commercial products

•  1-‐box spectroscopy

•  Usually 1-‐2 channels

•  Provides low and high voltage

•  “User-‐friendly” so[ware

•  Usually records only energy and ,ming


•  Gamma-‐ray spectroscopy with

scin,llator and semiconductor

detectors

•  Coun,ng sta,s,cs

•  Gamma-‐ray a>enua,on in

ma>er

•  Compton sca>ering

•  Half-‐life measurement

•  Coincidence coun,ng

•  Positron annihila,on


•  Research grade

•  Mul, channel – modular

•  Records detector signals

•  Custom so[ware

Going Digital: Research

•  Informa,on about the

interac,on is o[en

contained in the detector

signal shape

•  Algorithms process the

detector signals

•  Posi5on of interac5on

within the detector

Going Digital: Research Pulse Shape Analysis

Essen5al in imaging applica5ons and gamma-‐ray spectroscopy

Aim: To improve the sensi,vity of germanium gamma-‐ray detectors for measurement of low ac,vity nuclear waste Methods: High-‐precision experimental measurements in lab, modeling and in-‐situ measurements

Enhanced Nuclear Waste Assay Industrial Partner: Nuclear Decommissioning Authority (NDA)

Improved Sensitivity

Experimental Data

Simulated Data Algorithm

Development

Performance Evaluation

MDA = (2.71+ 4.65x B)εtk

B: background counts ε: efficiency t: measurement 8me k: correc8on factor

Objec5ves: 1)  To experimentally assess the response of

detectors for known posi,ons of single gamma-‐ray interac,ons

2)  To use the database to validate a detector modelling code

3)  To op,mise pulse shape analysis algorithms for detectors of differing geometry


4)  To conduct realis,c industrial performance tests at Canberra (Harwell) using their facili,es that include waste drum analogues and at the NNL Central Laboratory

NDA

•  Gamma-‐ray source collimated into beam, suspended above the detector

•  Detector signal stored and processed by digital electronics

•  Collimator moved across surface, using an automated x-‐y posi,oning table

•  Calculate average pulse shapes

•  Pulse shape varia,on -‐ posi,on of interac,on sensi,vity

Time (ns)0 100 200 300 400 500 600

Nor

mal

ised

Pul

se H

eigh

t

0

0.2

0.4

0.6

0.8

1 0mm8mm16mm24mm


•  Technique used to detect sources of gamma

radia,on

•  Iden5fy what the source is: gamma-‐ray

spectroscopy

•  Locate radia,on: imaging methods

Compton Imaging

•  Wide range of fields of view– in a lorry, in a room and in a body

•  Security, nuclear decommissioning and nuclear medicine

•  Gamma rays interact in two detectors

•  The path of each gamma ray is

reconstructed as a cone

•  Source of radia,on located at max cone

overlap

Compton Imaging

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

01

2 111cosEE

cmeϑθ

θ (E, X,Y,Z)2

(E, X,Y,Z)2

Source E0





overlap

Compton Imaging

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

01

2 111cosEE

cmeϑθ

θ (E, X,Y,Z)2

(E, X,Y,Z)2

Source E0





overlap

Compton Imaging

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

01

2 111cosEE

cmeϑθ

θ (E, X,Y,Z)2

(E, X,Y,Z)2

Source E0





overlap

Compton Imaging

⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

01

2 111cosEE

cmeϑθ

θ (E, X,Y,Z)2

(E, X,Y,Z)2

Source E0

Medical Physics -‐ SPECT

•  Single Photon Emission Computed Tomography

(SPECT)

•  Diagnosis/monitoring of cancer and neurological

condi,ons

•  Biological informa,on complements MRI structural

informa,on

•  Mechanical collimator 1 x 10 -‐4

•  Scin,llator detector with photomul,plier tubes

Pa,ent injected with radiopharmaceu,cal

Radiopharmaceu,cal accumulates in organ

of interest

Gamma-‐rays emi>ed from organ and detected outside body by gamma camera

Medical Imaging SPECT: Single Photon Emission Computed Tomography

•  £1.1 million project

•  Prototype system

•  High-‐sensi,vity alterna,ve to

SPECT

•  Different method of imaging the

gamma radia,on

•  Semiconductor detectors

Medical Physics -‐ SPECT Medical Imaging SPECT: Single Photon Emission Computed Tomography

Conventional SPECT

•  Use 1 gamma ray in every 3000

•  Incompa,ble with MRI

ProSPECTus

•  Use 1 gamma ray in every 30 •  Compa,ble with MRI •  Mul,-‐isotope imaging Lower dose

to pa,ent or shorter data acquisi,on ,mes

θ

θ (E, X,Y,Z)2

(E, X,Y,Z)2

Source E0

Medical Physics -‐ SPECT Medical Imaging ProSPECTus: Next Generation SPECT

Criteria •  Prototype system for use with current

medical radionuclides •  High sensi,vity •  Excellent image quality •  MRI compa,bility

Final Design •  Op,mised for imaging gamma rays

from 99mTc •  Si(Li) sca>er detector and a HPGe

absorber detector •  Custom –built cryostat •  Digital electronics


•  Planar Si(Li) (60 x 60 x 9) mm detector

•  16 strips on each face, 4mm pitch

Photo

Courtesy of Semikon

•  Planar HPGe (60 x 60 x 20) mm detector

•  12 strips on each face, 5mm pitch

Photo

Courtesy of ORTEC



•  Preclinical trials in progress

•  Compara,ve imaging of phantoms against clinical scanners

Medical Physics -‐ SPECT Nuclear Security and Decomissioning Industrial Partner: National Nuclear Laboratory (NNL)

•  Radia,on map of source •  Op,cal image •  Stereoscopic image “3D”

•  Nuclear decommissioning •  Remote response

•  High sensi,vity and good image quality essen,al

•  2 semiconductor detectors, which

measure posi,on and energy of

gamma-‐ray interac,ons

Medical Physics -‐ SPECT Nuclear Security and Decomissioning PorGamRays: Portable Gamma-‐ray Spectroscopy

•  PorGamRays – room temperature, small

area, semiconductor detectors portable for

“in the field” measurements

•  Pixelated CZT detectors with ASIC readout

•  Imaging demonstrated: e.g. 133Ba source

located at 100 mm then 120 mm

Medical Physics -‐ SPECT Nuclear Security and Decomissioning Industrial Partner: AWE

•  Compton imaging data acquired at

Liverpool using various gamma-‐ray sources

•  Successful trials AWE to iden,fy “unknown”

sources, at rela,vely far stand off distance

and when “concealed” by various absorbing

materials

57Co 122keV 137Cs 662keV 137Cs 662keV

•  Useful to iden,fy specific materials, e.g. drugs and explosives

•  Research at UoL Physics Dept: Detec,on of gamma-‐rays from neutron

ac,vated materials

•  Can both form an image and produce a gamma-‐ray spectrum

•  The peaks in the gamma-‐ray spectrum contain elemental informa,on:

what is inside?

•  Explosives and drugs contain combina,ons of light elements e.g.

Oxygen (6.1 MeV), carbon, (4.4 MeV)

nitrogen (1.64, 2.31, 5.11 MeV)

* * *

* *

Medical Physics -‐ SPECT Nuclear Security DISTINGUISH

14MeV pulsed neutrons.

Inelastic scattering.

Characteristic gamma rays emitted

Detection & imaging (Compton Camera)

Neutron detector

Neutron generator

Medical Physics -‐ SPECT Nuclear Security DISTINGUISH

•  Gamma-‐ray detec,on and spectroscopy

•  Going digital

•  Gamma-‐ray imaging

•  in medical physics

•  in nuclear security

Summary

Contact: [email protected]

Documents

Gammaray’detection’&’ imaging’in’the’digital’world’iop/PTC/PDFs/Gamma-Ray-Detection.pdf · Gammaray’detection’&’ imaging’in’the’digital’world ... •