compound semiconductors and digital pulse processing ... · “compound semiconductors and digital...

University of Palermo

Dipartimento di Fisica e Chimica

Compound Semiconductors and

Digital Pulse Processing Techniques

for Radiation Detection

Leonardo Abbene

[email protected]

“Compound Semiconductors and Digital Pulse Processing Techniques for Radiation Detection’’

Outline

General principles on radiation detection

X-ray and gamma ray spectroscopy

General characteristics of spectrometers

X-ray and gamma ray interactions with matter

Demands from modern spectrometers

Technological detection improvements: new materials

and new electronics

New semiconductor materials (CdTe, CdZnTe)

Digital Pulse Processing (DPP) Electronics


Radiation detection (1)

Ionizing radiation….

Charged radiation

Uncharged radiation

• Electrons e Positrons

• Heavy charged particles (alpha,

protons, fission products,…)

• Neutrons

• Electromagnetic radiation

(X-rays, gamma rays)

We will focus our attention on X-ray and gamma ray detection!!!



Interaction with matter….

Charged radiation

Main processes

Loss of energy Deflection from its incident direction

• Inelastic collision with atomic electrons

• Elastic scattering from nuclei

• Cherenkov radiation

• Bremsstrahlung

• Nuclear reactions



Interaction with matter….

Uncharged radiation

Main processes

• Photoelectric Absorption

• Compton Scattering

• Pair production

. Rayleigh scattering

• Thompson scattering

• Nuclear scattering

• Delbruck scattering

Neutrons

• Elastic and Inelastic scattering

• Neutron capture

• Nuclear reactions

• Fission

• Hadron showers

Photons



Types of detectors….

We will focus on Spectrometers !!!

· position sensing (tracking)

· energy measurement (spectrometers, calorimeters)

· timing

· particle identification


GOAL

Energy Input Counting Rate

Spectrometer Requirements

Total absorption of radiation

Capability to produce electrical signals

Electrical signals proportional to incident photon energy

X-ray and gamma ray spectroscopy (1)



Main functions of spectrometers….Detector and Electronics

1. Radiation deposits energy in a detecting medium

• The absorbing medium will be chosen to optimize energy loss (high density, high Z).

• Ionization produces a given charge in the absorbing medium

ion-electron pairs in gas electron-hole pairs in semiconductors

In a spectrometer, the charge must be proportional to the absorbed energy !!!


Direct conversion:

Radiation ionizes atoms in

absorber, creating mobile charges

(ionization chambers).


2. Energy is converted into an electrical signal,

either directly or indirectly.


Indirect conversion:

Radiation excites atomic/molecular

states that decay by emission of light,

which in a second step is converted

into charge. (scintillation detectors)



Main functions of spectrometers….

3. Amplification of electrical signals

a) by electronics

b) secondary multiplication within the detectors (proportional

chambers, photomultipliers)

4. Shaping of electrical signals

Shortening the pulses and filtering to enhance the signal-to-noise ratio

5. Digitizing the pulse height

By using ADCs to create energy histograms (energy spectra)



Typical detection system for X-ray spectroscopy

Induced current

Integration and

Amplification Filtering and

Amplification

Pulse Height

histogram

(energy spectrum)

Direct detection…..


X-ray and gamma ray interactions with matter (1)

Interaction of photons in matter is dramatically different from that of

charged particles :

1) X rays and gamma rays are many times more penetrating than charged

particles

2) A beam of photons is NOT degraded in energy but only attenuated in intensity

Beer’s law:

I(x) = Ioexp [-μ(E). x]

Intensity of a photon beam decreases with

distance into material, but the energy of

individual photons remains the same.

μ is the linear attenuation coefficient



100 5 101 5 10210-1

100

101

102

103

104

photon energy, keV

/,

cm

²/g

Calcio Ferro Piombo

30 keV photons

Calcium: μ/ρ = 4 cm2/g

Iron: μ/ρ = 8 cm2/g

Lead: μ/ρ = 30 cm2/g

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.00

100

200

300

400

500

600

700

800

900

1000

1100

I (x

)

Thickness (mm)

Calcium

Iron

Lead

30 keV



Main interaction processes….

• Photoelectric Absorption

• Compton Scattering

• Pair production

Less important processes

• Rayleigh scattering

• Thompson scattering

• Delbruck scattering



Photoelectric Absorption …..

35,4 ,μ EZricphotoelect

Photoelectric absorption involves the

interaction of an incident photon with an

inner shell electron in the absorbing atom

that has a binding energy similar to but

less than the energy of the incident

photon. The incident x-ray photon

transfers its energy to the electron and

results in the ejection of the electron from

its shell (usually the K shell) with a kinetic

energy equal to the difference of the

incident photon energy and the electron

shell binding energy.

Ek = h - We



Compton Scattering…..

1,μ EZCompton

Compton scattering is an inelastic interaction

between an x-ray photon of energy that is

much greater than the binding energy of an

atomic electron (in this situation, the electron

is essentially regarded as “free” and

unbound).

Partial energy transfer to the electron causes

a recoil and removal from the atom at an

angle. The remainder of the energy, is

transferred to a scattered x-ray photon with a

trajectory of angle relative to the trajectory

of the incident photon.

cos1/1

cos1/2

2

'

cmh

cmhhhhE

e

e

e

)cos1(1

h'h

2

mc

h



Pair production…..

Photon energy greater than 1.02 MeV

interacts with nucleus and conversion of

energy to e+ e- charged particles; e+

subsequently annihilates into two 511-keV

photons

22 cmhEE eee

2Zpair

Probability of interaction increases with increasing energy, unlike other processes



Rayleigh scattering….

Photon interacts with bound atomic

electron without ionization; photon is

released in different direction without loss

of energy

No energy absorption occurs;

photons mainly scattered in forward

direction


100 5 101 5 102 5 103 5 104 510-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

photon energy, keV

/,

cm

²/g

Rayleigh Fotoelettrico Compton Pair Totale

Iron

PairComptonphotRayleigh tot




Relative importance of the three interaction processes:

Z and Energy dependence


General characteristics of spectrometers (1)

Sensitivity

Capability to produce a useful signal for a given type of radiation

Detector Response

In spectrometers, is defined as the relation between the radiation energy and

the charge collected.

A linear detector response is needed in spectrometers.

Efficiency

Fraction of events emitted by a source which is registered by the detector

(intrinsic and geometrical efficiency)

To characterize a spectrometer….

e.g. generating a signal charge major than that of noise.

Choosing the proper detecting material to ensure sufficient counts in the

spectra



Mode of Operation

All spectrometers operate in pulse mode. Detector is designed to record each

photon that interacts in its absorption medium.

Each photon generates a

given amount of electric

charge within the active

volume

A current will flow for a

time equal to the

collection time. The area

is the generated charge.

Detectors in pulse mode operation will analyze each current pulse.


General characteristics of spectrometers (2b)

Why integration of each current pulse?

The magnitude and duration of each current pulse may vary depending on the

depth of interaction of photons.

Current pulses generated by

photons with the same

energy:

• Different heights of the

current pulses

• But..same area (charge)


40 60 800

500

1000

1500

2000

Co

nte

gg

i

Energia (keV)

IDEAL

Spectrum

Monoenergetic

photons

Dirac delta

function

40 60 800

500

1000

1500

2000

Co

nte

gg

i

Energia (keV)

Gaussian

function

REAL

Spectrum

The function mainly depends on:

• interaction mechanisms

• detector material and geometry

• electronic noise


Response function



Response function

Changes from interaction mechanisms …..

Photoelectric Compton

Pair Absorption medium should

enhance photoelectric

interaction!!


A. The Full-energy photopeak. This

peak represents the heights of the

pulses that arise from photoelectric

interactions in the detection

medium.


Response function

A realistic example…..

B. Compton Background Continuum.

These pulses come from interactions

involving only partial photon energy

loss in the detecting medium.

C. The Compton Edge. This is the region of the spectrum

that represents the maximum energy loss by the incident

photon through Compton scattering. This corresponds to

a collision between the photon and the electron, where

the electron moves forward and the gamma-ray scatters

backward through 180°

D. Backscatter Peak. This peak is

caused by gamma rays that have

interacted by Compton scattering in

one of the materials surrounding the

detector.



Energy resolution

It is the most important parameter for a spectrometer, that quantifies the broadening

of the photopeak for a monoenergetic source.

It represents the detector capability to resolve the energy photopeaks in the energy

spectra.

40 60 800

500

1000

1500

2000

Co

nte

gg

i

Energia (keV)

FWHM

(Full Width at Half Maximum)

355.22ln22GaussE



Energy resolution

2222

elettrraccstattot EEEE

Fluctuation of the

number of ionizations

(Statistic noise)

Fluctuations due to

incomplete charge

collection

Fluctuations due

electronic noise

energyionizationmeanw

wEw

EwFWHM

w

ENPoisson

w

EN

Stat

355.2355.2

;

For Spectrometers

(full absorption)

Fano correction is needed

wEFw

EFwFWHM Stat

355.2355.2



Energy resolution

2222

elettrraccstattot EEEE



Energy resolution

Typical values

Indirect Detection

Direct Detection



Dead Time

The minimum time that must separate two events in order to record them as two

separate pulses. The time that a system is busy processing a pulse.

Dead Time Distortions

The measured output

counting rate (OCR) is

lower than the Input

counting rate (ICR)

The typical counting

statistics (Poisson) is

distorted



Dead Time Models

Generally, dead times are classified into two main categories…..

m = measured rate in the spectrum

n = true rate

= dead time

ablenonparalyzn

nm ;

1

Non-Paralyzable

Non-paralyzable dead time (also known as non-extendable, non-cumulative or

type I) is produced at each time an event is recorded and any arrival event from

the recorded time to the dead time period will not be recorded.



m = measured rate in the spectrum

n = true input rate

= dead time

Non-Paralyzable

n

m

m/n is generally termed throughput of a system

throughput curves



Paralyzable

eparalyzablnnm ;exp

In the paralyzable case, dead periods

are not always of fixed length

In paralyzable model (also known as extendable, cumulative or type II), each

arrival event, whether recorded or not, produces a dead time and any new

arrival event with a delay less than the dead time from the previous arrival

event will not be recorded.



Dead Time

To avoid ambiguity (paralyzable case), it is important to maintain a maximun

throughput of 40% (m/n*100). The maximum of the blue curve is at n= 1/


Modern Spectrometers

Demands…..

• Near room temperature operation (energy resolution < 10 % 60 keV and

high detection efficiency)

• High rate capabilities (> 100 kcps)

• Multi-parameter analysis, i.e. a system should provide, besides ICR and energy

spectrum, additional experimental parameters for each event:

(i) the event arrival time (e.g. for coincidence/anticoincidence measurements and dead

time correction)

(ii) the pulse shape, i.e. the peaking time (e.g. for detector performance enhancements,

photon tracking or particle identification)


Technological Solutions

Materials…..

• Compound Semiconductors.

Compound semiconductors were first investigated as radiation detectors in 1945 by Van

Heerden, who used AgCl crystals for detection of alpha particles. The great advantage of

compound semiconductors is the possibility to produce materials with a wide range of

physical properties (band gap, atomic number, density), making them suitable to several

applications.

Electronics…..

• Digital Pulse Processing (DPP) approaches.

Digital systems are based on the direct digitizing and processing of detector signals.


Materials

Semiconductor Detectors…….

• 3 eV for semiconductors

• 30 eV for gas

• 300 eV for scintillators coupled to photomultipliers

Small mean ionization energy w

wEFw

EFwFWHM Stat

355.2355.2 Better energy resolution !!!

High density

Development of compact systems!!!

Semiconductors with high Z and wide bad gap

Development of room temperature systems !!!

Detection of hard X-rays (> 15 keV)


Silicon detectors

Among the semiconductor devices, silicon (Si) detectors are the key

detectors in the soft x-ray band (<15 keV). Si–PIN diode detectors and

silicon drift detectors (SDDs), operated with moderate cooling by means of

small Peltier cells, show excellent spectroscopic performance and good

detection efficiency below 15 keV.


Germanium detectors

Germanium (Ge) detectors are unsurpassed for high resolution

spectroscopy in the hard X-ray energy band (>15 keV) and gamma energy

band (> 200 keV) and will continue to be the first choice for laboratory-

based high-performance spectrometers.


New semiconductor materials


There has been a continuing desire for the development of room temperature detectors with

compact structure having the portability and convenience of a scintillator but with a

significant improvement in energy resolution. To this end, numerous high-Z and wide band gap

compound semiconductors have been exploited. Compound semiconductors are generally

derived from elements of groups III and V (e.g. GaAs) and groups II and VI (e.g. CdTe) of the

periodic table. Besides binary compounds, ternary materials have been also produced, e.g.

CdZnTe and CdMnTe.

Compound Semiconductor Detectors

materiale Si Ge

density ( g/cm3 ) 2.33 5.33 5.32 6.20 5.78 6.40

GaAs CdTe Cd0.9Zn0.1Te HgI2

atomic number (max) 14 32 33 52 52 80

band-gap ( eV ) 1.12 0.67 1.43 1.44 1.57 2.15

w ( eV ) 3.62 2.96 4.20 4.43 4.64 6.50

τe (cm2 / V ) > 1 > 1 8 · 10-5 3 · 10-3 3 · 10-3 3 · 10-4

τh (cm2 / V ) 1 > 1 4 · 10-5 10-4 10-4 4 · 10-5

resistivity ( · cm) 104 50 107 109 1010 1013


CdTe and CdZnTe (1)

Among the compound semiconductors, Cadmium Telluride (CdTe) and Cadmium Zinc

Telluride (CdZnTe) attracted growing interests in the development of x-ray detectors.

Due to their high atomic number, high density, and the wide band gap, CdTe and CdZnTe

detectors ensure high detection efficiency, good room temperature performance and are very

attractive for x-ray and g ray applications.

Difficulties in producing detector-grade materials and in growing chemically pure and

structurally perfect crystals are the critical issues of CdTe and CdZnTe detectors.

CZT are usually grown by using the high pressure

Bridgman (HPB), low pressure Bridgman (LPB),

vertical Bridgman and THM methods. The supply

of spectrometer grade CdZnTe is limited to a small

number of companies: eV Products (USA), Imarad

(Israel), Eurorad (France) and Redlen

Technologies (Canada).

CdTe are usually grown by the THM method and

doped with Cl to compensate background

impurities and defects, resulting in high resistivity

p- type materials. Supplies of spectrometer grade

CdTe crystals are offered by a few companies:

Imarad (Israel), Eurorad (France) and Acrorad

(Japan).


materiale Si Ge

density ( g/cm3 ) 2.33 5.33 5.32 6.20 5.78 6.40



band-gap ( eV ) 1.12 0.67 1.43 1.44 1.57 2.15

w ( eV ) 3.62 2.96 4.20 4.43 4.64 6.50

τe (cm2 / V ) > 1 > 1 8 · 10-5 3 · 10-3 3 · 10-3 3 · 10-4

τh (cm2 / V ) 1 > 1 4 · 10-5 10-4 10-4 4 · 10

resistivity ( · cm) 104 50 107 109 1010 1013

CdTe and CdZnTe (2)

Advantages…….high Z

High detection efficiency and high photoelectric

interaction probability high Z


Compton

Photoelectric

CdTe and CdZnTe (3)

Del Sordo et al... Sensors 9, (2009) 3491.

Linear attenuation coefficients for photoelectric absorption and Compton

scattering of CdTe, Si, HgI2, NaI and BGO


CdTe and CdZnTe (4)

L. Abbene et al... CdTe detectors, in Comprehensive Biomedical Physics, (2014) Elsevier.

Total and photoelectric efficiency for 1-mm-thick CdTe detector compared

with Si and Ge.


CdTe and CdZnTe (5)

Efficiency of CdTe detectors as function of detector thickness at various

photon energies.

Del Sordo et al... Sensors 9, (2009) 3491.


materiale Si Ge

density ( g/cm3 ) 2.33 5.33 5.32 6.20 5.78 6.40


band-gap ( eV ) 1.12 0.67 1.43 1.44 1.57 2.15

w ( eV ) 3.62 2.96 4.20 4.43 4.64 6.50

τe (cm2 / V ) > 1 > 1 8 · 10-5 3 · 10-3 3 · 10-3 3 · 10-4

τh (cm2 / V ) 1 > 1 4 · 10-5 10-4 10-4 4 · 10

resistivity ( · cm) 104 50 107 109 1010 1013

CdTe and CdZnTe (6)

Advantages…….wide band-gap

Low leakage current even a room temperature ( < nA) Wide band-gap



-200 -150 -100 -50 0 50 100 150 200-5.0x10

-10

-4.0x10-10

-3.0x10-10

-2.0x10-10

-1.0x10-10

0.0

1.0x10-10

2.0x10-10

3.0x10-10

4.0x10-10

5.0x10-10

Cu

rre

nt

(A)

Cathode Bias Voltage (V)

T = 25 ° CCZT detector

Au/CZT/Au

0.5 mm thick

CdTe and CdZnTe (7)

CZT detectors with quasi-ohmic contacts

ensure very low leakage currents even a room

temperature ( < nA)


Drawbacks…defects

CdTe and CdZnTe (8)

Presence of defects and impurities in the crystals acting as trapping

centers


drawbacks

CdTe and CdZnTe (9)

Position of the ionization energy levels of native defects, impurities, and

defect complexes in semi-insulating CdZnTe.


drawbacks

CdTe and CdZnTe (10)

The major processes that determine the electron and hole trapping,

detrapping, and recombination lifetimes.


materiale Si Ge

density ( g/cm3 ) 2.33 5.33 5.32 6.20 5.78 6.40


Z (max) 14 32 33 52 52 80

band-gap ( eV ) 1.12 0.67 1.43 1.44 1.57 2.15

w ( eV ) 3.62 2.96 4.20 4.43 4.64 6.50

τe (cm2 / V ) > 1 > 1 8 · 10-5 10-3 10-3 3 · 10-4

τh (cm2 / V ) 1 > 1 4 · 10-5 10-4 10-4 4 · 10-5

resistivity ( · cm) 104 50 107 109 1010 1013

Poor mobility lifetime products Reduction of the charge collection efficiency

Drawbacks……poor charge transport properties.



materiale Si Ge GaAs CdTe Cd0.9Zn0.1Te HgI2

band-gap ( eV ) 1.12 0.67 1.43 1.44 1.57 2.15

w ( eV ) 3.62 2.96 4.20 4.43 4.64 6.50

τe (cm2 / V ) > 1 > 1 8 · 10-5 10-3 10-2 -10-3 3 · 10-4

τh (cm2 / V ) 1 > 1 4 · 10-5 10-4 10-4 4 · 10-5

resistivity ( · cm) 104 50 107 109 1010 1013

Difference between the transport

properties of the holes and the electrons Distortions in the spectra (hole tailing)

Drawbacks……..poor hole transport properties


density ( g/cm3 ) 2.33 5.33 5.32 6.20 5.78 6.40

Z (max) 14 32 33 52 52 80


Drawbacks…hole tailing



Generated charge ……Planar detectors

CdTe: Photons of 60 keV

Charge (E/w)·e = q

Charge ~ 2· 10-15 C

1 2

Typical response function of CdTe/CZT detectors (1)


+ + + + +

+ + +

-q

Q1

Q2

Vo +

i2(t)

(1)

(2) dQ2

Induced Charge│Q1│+│Q2│= q

Positive charge + q (holes) Negative charge – q (electrons)

Generated Charge (E/w)·e = q

+ q

Q1

Q2

Vo +

i1(t)

dQ1

(1)

(2)

x

P L

- - -

- - -

Anode

Anode

Cathode Cathode


Generated charge ……Planar detectors


Induced Charge on the electrodes???

Shockley-Ramo Theorem…and

the concept of a weighting potential.

)()( 00 if xxqQ

The weighting potential is defined as the potential that would exist in the detector

with the collecting electrode held at unitary potential, while holding all other

electrodes at zero potential.

The weighting potential is for a specific electrode is obtained by setting the

potential of the electrode to 1 and setting all other electrodes to potential 0.

Note that the electric field and the weighting field are distinctly different.

· The electric field determines the charge trajectory and velocity

· The weighting field only depends on geometry and determines how charge

motion couples to a specific electrode. Only in 2-electrode configurations are the

electric field and the weighting field of the same form (planar detectors).



Weighting Potential

L

xz 1z00 zz


Induced charge ……Planar detectors




Induced Charge (no trapping) )()()( ,, tQtQtQ eindhindind

hr

h

hr

hind

ttxL

Ne

E

xttxtx

L

Ne

tQ

,0

0,0

,

])([

)(

er

e

er

eind

ttxLL

Ne

E

xLttxtx

L

Ne

tQ

,0

0,0

,

][

])([

)(

Electron contribute

Hole contribute




tr,h= x0/ hE

Qe=N·e·(L-x0)/L

Qh=N·e·(x0/L)

t

N·e

tr,e=(L-x0)/ eE

)(tQind

NezNezNeQ )1)(()0)((

holes

electrons (t > tr,h e t > tr,e )

Induced Charge (no trapping)



Induced charge ……TRAPPING

E

xL

eeE

x

hheindhindind

eehh eL

Ee

L

EeNQQQ

00

11,,

eNQQQ eindhindind ,,

Hecht Equation

IDEAL Induced charge will only depend on N and therefore on the photon energy.

The charge also depends on the incoming photon interaction position!!!

t

eQtQ

0)(REAL: Uniform Trapping


In/CdTe/Pt planar

2x2x1 mm3

(Amptek, USA)

LOW-RATE SPECTROSCOPIC PERFORMANCE

Energy (keV)

22.1 59.5 122.1

Energy

resolution

FWHM (%)

T = - 20 °C

2.5 1.3 1.6



The output signals from charge sensitive preamplifiers (i.e. CSP

waveform) are sampled and digitized by ADC and then processed by using

digital algorithms (DPP firmware).

Digital Electronics (1)


As widely recognized, the digital approach gives many benefits against

the analog one, among which:

(i) possibility to implement custom filters and procedures, which are

challenging to realize in the analog approach

(ii) stability and reproducibility (insensitivity to pick-up noise as soon

as the signals are digitized)

(iii) the possibility to perform multi-parameter analysis for detector

performance enhancements and new applications.



• L. Abbene, G. Gerardi. NIM A 654 (2011) 340. • L. Abbene, et al., JINST 8 (2013) P07019

General purpose method for both Real-Time and Off-Line analysis !!

• G. Gerardi, L. Abbene,. NIM A 768 (2014) 46. • L. Abbene, et al. NIM A 730 (2013) 124.


Custom DPP system


Digital Electronics (3a)

Digitized Preamplifier Waveform (red) and Pulses after

digital shaping (black)



Arrival time of the events….

Experimental measurement of the Time-Interval Distribution (TID)

of the events

0.0 5.0x10-7

1.0x10-6

1.5x10-6

2.0x10-6

2.5x10-6

3.0x10-6

3.5x10-6

4.0x10-6

e7

e8

e9

e10

e11

e12

e13

e14

ICR = 2.2 Mcps

calculated from exponential fitting

Ag-target X-ray source

30 kV

Ln

[C

ou

nts

]

Time (s)

0 10 20 30 40 50 60 70 800

500000

1000000

1500000

2000000

2500000

3000000

Ag-target X-ray source

30 kV

ICR from TID

Ph

oto

n C

ou

nti

ng

Ra

te (

cp

s)

Tube Current (A)

Poisson Process Non- linearity is less than 0.5%


Pulse shape analysis …..reduction of trapping effects…..

Bi-parametric techniques (Pulse Height and Peaking time)

Since both peaking time and pulse height

are correlated with the depth of

interaction, one can use these

measurements to improve spectroscopic

performance. Such methods are termed

bi-parametric. In practice, it is achieved

by plotting peaking time as a function of

pulse height, from which one can

generate a set of correction factors.



Reduction of trapping effects…..

Bi-parametric techniques

(Pulse Height and Peaking time)

L. Abbene et al…. NIM A 654 (2011) 340–348.




Bi-parametric techniques (Pulse shape discrimination)


Spectral improvements

but with a reduction of

the counts in the

spectra (> 90%)!!!!!




Bi-parametric techniques (Pulse shape correction)





Bi-parametric techniques (Pulse shape correction)


no reduction of photon

counts!!!!



Reduction of pile-up effects…..

Pile-up rejection


Pulse shape discrimination can also be used to

minimize peak pile-up events, i.e. overlapped

preamplified pulses within the peaking time. Because

the shape (peaking time)of a peak pile-up pulse differs

from that of a pulse not affected by pile-up, analyzing

the measured spectra at different peaking time regions

(PTRs) in the peaking time distribution is helpful to

reduce peak pile-up.



Reduction of pile-up effects…..

Pile-up rejection


Results by using digital

techniques



Applications (1)

Focal plane detectors for

X-ray telescopes (1 - 100 keV)

Portable systems for mammographic

X-ray spectroscopy (1- 40 keV)

astrophysics

medical physics

PET (511 keV)

gamma camera (140 keV)

energy resolved detectors for

diagnostic medicine (1-140 keV)

Detectors for radioactive

isotopes

Homeland security

XRF, Compton techniques

cultural heritage


Applications (2)

X-ray colour imaging in diagnostic medicine (1 -140 keV)

High contrast

Quantitative analysis (the gray-scale pixel

values in traditional X-ray images are not

quantitative but qualitative)

Reduction of patient dose


References

-G. F. Knoll, Radiation Detection and Measurement, 3rd Edition, Wiley 2000.

- K. Debertin and R.T. Helmer - “Gamma and X-Ray Spectrometry with

Semiconductor Detectors ” – North Holland Publishers (Amsterdam 1988).

- Del Sordo S., Abbene L., Caroli E., Mancini A. M., Zappettini A., Ubertini P. “Progress in the Development of CdTe and CdZnTe Semiconductor Radiation

Detectors for Astrophysical and Medical Applications ’’ Sensors, 9, pp. 3491-

3525, (2009)

- Abbene L. and Del Sordo S. “CdTe detectors ’’ Comprehensive Biomedical

Physics, Elsevier (2014).

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