VARIATIONS IN CVD
DIAMOND DETECTOR’S
RESPONSE TO RADIATIONS
WITH THE CRYSTAL’S
DEFECTS COMPARED WITH
CALCULATED VALUES FROM
MC code(PENELOPE) AT LOW
ENERGY MAMMOGRAPHY XRAY RANGE
Y.I Zakari, R.D. Mavunda, T.L Nam
and R.J Keddy
YI Zakari* RD Mavunda, TL Nam and RJ
keddy
DST/NRF Centre of Excellence in Strong
Materials and School of Physics,University
of the witwatersrand, Private Bag 3, PO wits
2050, Johannesburg, Republic of South
Africa
*Post Doctoral fellow from Ahmadu Bello
University, Zaria, Nigeria
INTRODUCTION
• CVD DIAMOND DETECTOR AS
THE ‘STATE OF THE ART’ FOR
FUTURE TECHNOLOGY
• Motivation: Breast cancer reported to
be the highest source of mortality in
women (next to lung cancer) and
that at present X-ray mammography
screening may also induce cancer
AIM
CHARACTERIZATION OF CVD
DETECTORS
TO EVALUATE CVD DIAMOND
RESPONSE TO ALPHA LOW
ENERGY X-RAY
ALPHA SPECTROCOPY
MC CODE(PENELOPE) OF
MAMMOGRAPHIC X-RAY RANGE
INSTRUMENTS FOR
CHARACTERISATION
BRUKER MICROWAVE BRIDGE ESP
380-1010
VARIAN CARY 500 UV-Vis-NIR
SPECTROMETER
JOBIN-YVON T64000 RAMAN
SPECTROMETER
TOLEDO 654 TLD UNIT
KEITHLEY 237 FOR i-v
CHARACTERISTICS
CVD
MATERIALS
SINGLE CRYSTAL CVD
DIAMOND
POLYCRYSTALS: DETECTOR
GRADE AND OPTICAL GRADE
CVD DIAMOND
METALIZED CVD DIAMOND
EXPERIMENTAL SETUP-1
SPECIALLY CONSTRUCTED AMPLIFIER
CUM HIGH VOLTAGE SYSTEM
COUPLED TO PC
Am-241 ALPHA SOURCE +PRE-AMP. IN
VACUUM.
ACQUISITION OF DATA USING APTEC
SOFTWARE
EXPERIMENTAL SETUP-2
 SENOGRAPHE 500T MAMMOGRAPHY X-RAY
UNIT.
 PTW DIADOS 11003-1121 REFERENCE
DETECTOR
 SAMPLE HOLDER WITH APPLIED FIELD
ACROSS SAMPLE AND DIADOS DETECTOR
 RECORDINGS FROM WELLHOFER
DOSIMETRIE CU500 CONTROL COMPUTER
232C-A
 DATA ACQUISITION SOFTWARE PACKAGE
WP600 VERSION 4.26C
RESULTS-1
Sample
Raman spectral
broadening
FWHM (cm-1)
TL
response
(arbt.unit)
ESR: single
substitution
nitrogen
(ppm)
UV
absorption
(cm-1)
Total
alpha
counts
(cps)
absolute
Efficiency
%
energy
peak
Efficiency
%
Alpha
FWHM (keV)
DG1
2.64±0.17
1147
3.5
0.51±0.06
32969
68
80
1010.59±27.03
DG2
2.57±0.17
881
4
1.93±0.13
31327
65
80
693.41±11.16
DG3
2.63±0.15
2024
5
1.03±0.08
29834
62
81
64.14±0.8
DG4
2.55±0.16
814
5.3
1.9±0.05
32732
68
80
672.55±5.46
OG1
2.59±0.15
155
42.9
3.86±0.05
50314
104
60
7465.39±90.4
OG2
2.78±0.24
83
71
3.52±0.09-
49010
101
60
5975.00±34.99
OG3
2.76±0.24
141
53.6
3.48±0.11
49397
103
60
7050.34±124.8
OG4
2.81±0.22
93
62.5
3.59±0.11
39046
81
60
7245.66±60.48
SC
2.32±0.03
25
<1
0.88±0.02
25401
52
80
85.28±0.9
VARIATION OF TOTAL ALPHA COUNTS WITH UV(/cm) Absorption
for detector and optical grade CVD
55000
50000
OG
Alpha counts per sec
45000
DG
40000
35000
30000
25000
SC
20000
15000
10000
5000
0
0.5
1
1.5
2
2.5
UV absorption (cm-1)
3
3.5
4
4.5
Variation of total alpha counts with the single
substitution nitrogen concentration (ESR) of optical
grade CVD diamond
Alpha counts per second (cps)
32500
30500
28500
26500
24500
22500
3
3.5
4
4.5
Single substitutional nitrogen (ppm)
5
5.5
Variation of total alpha counts with single substitution
nitrogen concentration for detector grade CVD
diamonds
4
3.9
UV absorption (cm-1)
3.8
3.7
3.6
3.5
3.4
3.3
3.2
3.1
3
40
45
50
55
60
Single substitutional nitrogen (ppm)
65
70
75
Variation of total alpha counts with the Raman
broadening (FWHM) for optical grade CVD diamonds
Alpha counts per second (cps)
60000
50000
40000
30000
20000
10000
0
2.55
2.6
2.65
2.7
2.75
Raman Broadening (FWHM in cm-1)
2.8
2.85
Variation of TL response with single substitutional nitrogen
concentration (ESR) for detector and optical grade CVD diamonds
2500
TL response (arbt.unit)
DG
2000
1500
1000
OG
500
0
0
10
20
30
40
50
Single substitutional nitrogen (ppm)
60
70
80
Variation of TL emission with Raman broadening for
optical grade CVD diamonds
170
TL (arb. unit) emissin
150
130
110
90
70
50
2.55
2.6
2.65
2.7
2.75
Raman broadening (FWHM in cm-1)
2.8
2.85
Variation of Alpha FWHM counts with averaged UV absorption
values for both detector and optical grade and single crystal CVD
diamonds
8000
OG
7000
Alpha FWHM (keV)
6000
5000
4000
3000
2000
SC
1000
DG
0
-1000
0.6
1.1
1.6
2.1
2.6
UV absorption (cm-1)
3.1
3.6
4.1
Variation of FWHM of total count with averaged Raman broadening
values for both detector and optical grade and single crystal CVD
diamonds
10000
OG
Alpha FWHM (keV)
1000
SC
DG
100
10
1
2.28
2.38
2.48
2.58
Raman broadening (FWHM in cm-1)
2.68
2.78
Variation of alpha FWHM with single substitutional nitrogen
concentration (ESR) for detector and optical grade CVD diamonds
9000
8000
Alpha FWHM (keV)
7000
OG
6000
5000
4000
3000
2000
1000
DG
0
-1000
0
10
20
30
40
50
Single substitutional nitrogen (ppm)
60
70
80
Variation of experimental alpha count rate with energy
for optical grade (DG) CVD diamonds
80
70
Count rate (cps)
60
50
40
30
20
10
0
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
energy (keV)
Variation of experimental alpha count rate w ith energy f or optical grade (OG) CVD
diamonds
20000
A typical optical grade CVD diamond spectrum before (upper curve)
and after (Lower curve) background subtraction
250
Total alpha counts
200
150
100
50
0
0
5000
10000
Energy (keV)
15000
20000
Alpha spectrum from OG4 polycrystalline and single crystal (SC)
CVD diamond samples showing energy peak.
180
160
OG4
Total alpha counts
140
120
100
SC
80
60
40
20
0
0
2000
4000
6000
8000
Energy (keV)
10000
12000
14000
Alpha spectrum from detector grade DG3 and DG4
CVD diamonds showing the characteristic energy peak
120
Total alpha counts
100
80
DG4
60
40
DG3
20
0
0
2000
4000
6000
8000
Energy (keV)
10000
12000
14000
Summary1 of observations on Alpha
interaction with defects in CVD
 Consistent trend of alpha counts having +ve
gradient with UV absorption and TL emission but
a –ve gradient to the Raman broadening and
and Ns.
 Relatively high total alpha counts from OG CVD
diamond may be associated with UV related
defects and build-up effect.
 Ns. in CVD diamond is seen to act as a
recombination center due to the observed higher
sensitivity (counting efficiency) with lower
Ns.concentration
Summary2 of observations on
Alpha interaction with defects in
CVD
 For reasonable alpha spectroscopy, the
values of nitrogen concentration, UV
absorption and Raman broadening be as
low as possible, but TL value must be
highest.
 In General for alpha spectroscopy the SC is
the choice material or DG grade as
substitute.
 Otherwise for a detector with higher
sensitivity and less expensive the OG CVD
material could serve
The alpha spectrum stripping methodology
for a comparative evaluation of inherent
spectrometric performance of CVD diamond
• Level of defects in CVD diamond wafers affects
their response to radiation( Nam et al 1991; Davies, 1994;
Iakoubovski et al, 2002; Nebel, 2003 Mavunda ,2008)
• Alpha interaction( primary and secondary) with the detector
material to cause excitation and ionization of the electrons
into e-hole pairs
• Deceleration of the e-hole pairs produced in the field of
alpha produces bremsstrahlung that interacts by Compton
scattering to cause the observed fluctuations in the
spectrum
• The sensitivity of the optical grades results in the observed
skewedness and deviation of the spectrum peak.
• Electronic and statistical factors were also considered
Formulation of stripping equation
using the Bragg-Kleeman rule.
  A
RD i  R Ai  A  D -------------------------------------------------------(1)
  D  AA
where R Ai (cm)  0.325 Ei
3
2
( MeV ) (Lamarsh,1997)
The specific ionization I(Ei) defined as
I E i

Ei (eV )
/cm
ions
WR Di
2
2 Ei
E c E i  
(keV )
2 Ei  1022
f pi 

I E i   I ci E c 
I E i 
I ci Ec   I Ei  Ec 
I pi  I o Ei   ( I o Ei   f Ei  2 I o Ei   f Ei )

f Ei  1  f pi
Variation in peak efficiency with energy
1.2
1
Peak efficiency
0.8
0.6
0.4
0.2
0
0
5000
10000
15000
Energy (keV)
Fig. 1 Variation in peak ef f iciency w ith energy
20000
25000
Variation in alpha count rate s with energy for an
Optical grade CVD diamond (OG1)
Fig.2 Variation in Alpha count rates with Energy
for an Optical grade CVD diamond (OG1)
250
Alpha count rate (cps)
Exptal counts
Exptal (Baseline subtracted)
Stripped counts
200
150
100
50
0
0
5000
10000
Energy (KeV)
15000
20000
Variation in alpha count rate with energy for an optical
grade CVD diamond (OG2)
F1g.3 Variation in alpha count rate with energy
for an Optical grade CVD diamond (OG2)
300
Alpha count rate (cps)
250
Exptal counts
Exptal (Baseline subtracted)
Stripped counts
200
150
100
50
0
-2000
0
2000
4000
6000
8000 10000 12000 14000 16000 18000
Energy (KeV)
Variation of Alpha count rate with energy for a detector
grade CVD diamond (DG1)
Fig.6 Variation in Alpha count rate with Energy
for a detector grade CVD diamond (DG1)
80
Alpha count rate (cps)
70
Exptal counts
Exptal (Baseline subtracted)
Stripped counts
60
50
40
30
20
10
0
-2000
0
2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Energy (KeV)
Variation in Alpha count rate with energy for a
particular detector grade CVd diamond (DG3)
Fig.8 Variation in Alpha count rate with energy
for a detector grade CVD diamond (DG3)
20000
18000
Alpha count rate (cps)
16000
14000
12000
Exptal Counts
Stripped counts
10000
8000
6000
4000
2000
0
-1000
0
1000
2000
3000
4000
Energy (KeV)
5000
6000
7000
8000
Variation in Alpha count rate with energy for a single
crystal CVD diamond
Fig.10 Variation in Alpha count rate with Energy
for a Single Crystal CVD diamond (SC)
3500
3000
Total Counts
2500
Experimental Counts
Corrected Counts
2000
1500
1000
500
0
-500
-2000
0
2000
4000
6000
8000
Energy (keV)
10000
12000
14000
16000
Table 1: Spectral Analysis of accumulated alpha spectra from the three grades of
CVD diamonds (The energy of the impinging alpha particles being 5.47MeV)
Alpha counts
%Absolute
Stripped
Peak
% peak
(cps)
Efficiency
spectrum
Resolution
Efficiency
FWHM
Detector
Type
DG1
DG2
DG3
DG4
OG1
OG2
OG3
OG4
SC
EXPT
32969
31327
29834
32732
50314
49010
49397
39046
25401
ANALT
35245
39150
40623
37225
45355
46531
46288
43787
34172
EXPT
68
65
62
68
104
101
103
81
52
ANALT
73
81
84
77
94
96
96
91
71
AREA
28504
63228
1031800
40622
318840
631500
858870
364760
285470
Height
25.1
88.3
13352
54..2
73.8
125.6
161.4
104.4
2693
(keV)
907.8
571.7
61.7
622.5
3447.6
4041.8
4245
4564
84.58
ANALT
EXPT
stripped
0.185±
0.166±
0.001
0.0008
0.125±
0.105±
0.0023
0.0034
0.012±
0.011±
0.0018
0.0016
0.124±
0.114±
0.0030
0.0092
1.365±
0.630±
0.0089
0.0064
1.092±
0.739±
0.004
0.0045
1.289±
0.776±
0.0048
0.0040
1.325±
0.834±
0.0046
0.0049
0.016±
0.015±
0.0056
0.0055
ANALT
EXPT
stripped
80
80
80
80
82
82
80
80
60
60
60
60
60
60
60
60
80
80
Summary of spectrometric analysis
Stripping method used was observed to have
improved the detector peak resolution but
without any effect on the peak efficiency of the
detector.
The technique has more effect on the OG CVD
diamond detectors than the DG and SC CVD
detectors. The observed absolute efficiency above
100% due to build-up effect and fluctuation were
stripped off to have a more realistic value
At the peak energy of 5.48 MeV a range of 90μm
was calculated indicating the interaction is on the
surface.
A mass stopping power of 0.281 MeV/mgcm-2
and a leakage current of betwn 5.2pA and 54.2
pA observed could classify these detectors as
semiconducting
An average full energy peak efficiency of 80%
both experimentally and analytically indicates
CVD detector’s responses with crystal defects at low energy
mammographic X-ray range
 Aim: To determine the effects of impurities
in diamond on its performance as a
mammographic X-ray detector.
To assay the I-V characteristics
Use the MC code to model the
experimental set up carbon in place of
diamond
Current-voltage characteristics for DG, OG and SC
diamond detectors
Current (amps)
Voltage
Setting (volts)
SC
OG
DG
30
2.10E-13
6.50E-12
1.50E-12
50
8.00E-13
9.30E-12
9.00E-12
80
1.60E-12
1.65E-11
2.00E-12
120
3.00E-12
2.50E-11
1.80E-12
200
5.80E-12
4.80E-11
1.17E-11
300
9.10E-12
8.80E-11
3.68E-11
500
1.64E-11
1.86E-10
8.80E-11
800
2.50E-11
1000
3.50E-11
Characterization results of CVD diamod as earlier
reported Mavunda et al,2008)
Sample
Raman spectral
broadening
FWHM (cm-1)
TL response
(arbt.unit)
ESR: single
substitution
nitrogen (ppm)
UV
absorption
(cm-1)
DG1
2.64±0.17
1147
3.5
0.51±0.06
DG2
2.57±0.17
881
4
1.93±0.13
DG3
2.63±0.15
2024
5
1.03±0.08
DG4
2.55±0.16
814
5.3
1.9±0.05
OG1
2.59±0.15
155
42.9
3.86±0.05
OG2
2.78±0.24
83
71
3.52±0.09-
OG3
2.76±0.24
141
53.6
3.48±0.11
OG4
2.81±0.22
93
62.5
3.59±0.11
SC
2.32±0.03
25
<1
0.88±0.02
X-ray response rate at 200V bias for DG, OG
and SC diamonds
X-ray response (cps) at 200V bias
Raman
FWHM (cm-1)
TL
(arbt.
Unit)
ESR
(ppm)
DG1
2.64
1146.8
DG2
2.57
DG3
Detector
Type
UV (cm-1)
22
kVp
23
kVp
24
kVp
25
kVp
26
kVp
27
kVp
3.5
0.51
1.52
1.64
1.72
1.95
2.18
2.35
881.2
4
1.93
1.62
1.96
2.41
2.56
2.78
3.01
2.63
2023.7
5
1.03
1.72
2.46
3.07
3.46
4.08
4.56
DG4
2.55
813.8
5.3
1.9
1.65
2.28
2.53
2.64
2.76
3.03
OG1
2.59
154.5
42.9
3.86
1.29
1.57
1.76
1.95
2.1
2.2
OG2
2.78
83.2
71
3.52
1.22
1.54
1.88
2.15
2.24
2.4
OG3
2.76
140.5
53.6
3.48
1.2
1.55
1.96
2.12
2.4
2.21
OG4
2.81
93.2
62.5
3.59
1.25
1.54
1.64
1.91
2.05
2.19
SC
2.32
25
1
0.88
1.35
1.74
1.86
2.1
2.21
2.42
X-ray response rate at 300V bias for DG, OG and SC diamonds
X-ray response (cps) at 300V bias
Raman
Detector FWHM
-1
Type (cm )
DG1
2.64
DG2
2.57
DG3
2.63
DG4
2.55
OG1
2.59
OG2
2.78
OG3
2.76
OG4
2.81
SC
2.32
TL
(arbt.
Unit)
1146.8
881.2
2023.7
813.8
154.5
83.2
140.5
93.2
25
ESR
(ppm)
3.5
4
5
5.3
42.9
71
53.6
62.5
1
UV
-1
(cm )
0.51
1.93
1.03
1.9
3.86
3.52
3.48
3.59
0.88
22
kVp
23
kVp
24
kVp
25
kVp
26
kVp
27
kVp
1.92
2.38
3.15
3.87
4.5
4.98
2.18
2.73
3.67
4.14
4.6
5.25
2.45
2.92
3.71
5.26
5.62
6.15
2.26
2.76
3.41
3.76
4.55
4.86
1.78
2.22
3.05
3.14
3.22
3.34
1.89
2.26
2.8
3.54
3.72
3.81
1.91
2.38
2.9
3.1
3.4
3.5
1.82
2.31
2.84
3.15
3.37
3.52
2.13
2.59
2.75
2.95
3.34
3.56
X-ray response rate at 400V bias for DG,
OG and SC diamonds
X-ray response (cps) at 400V bias
Raman
Detector FWHM
-1
Type
(cm )
DG1
DG2
DG3
DG4
OG1
OG2
OG3
OG4
SC
2.64
2.57
2.63
2.55
2.59
2.78
2.76
2.81
2.32
TL
(arbt.
Unit)
ESR
(ppm)
UV
-1
(cm )
22
kVp
23
kVp
24
kVp
25
kVp
26
kVp
27
kVp
1146.8
881.2
2023.7
813.8
154.5
83.2
140.5
93.2
25
3.5
4
5
5.3
42.9
71
53.6
62.5
1
0.51
1.93
1.03
1.9
3.86
3.52
3.48
3.59
0.88
2.31
2.87
3.26
3.94
4.64
5.07
2.42
2.98
3.72
4.08
4.78
5.41
3.31
3.74
4.48
5.38
5.71
6.29
2.59
2.92
3.54
3.88
5.61
5.46
2.19
2.27
3.09
3.32
3.5
3.72
2.26
2.42
3.17
3.58
3.84
3.92
2.14
2.34
3.2
3.29
3.57
3.66
2.16
2.61
2.88
3.23
3.41
3.62
3.68
4.29
4.79
5.07
5.34
5.9
Averaged CVD diamond response to X-ray in
calculated dose (Gy) values
Detector
Type
DG1
GD2
DG3
DG4
OG1
OG2
OG3
OG4
SC
X-ray Dose (Gy) values calculated from CVD diamond response at 200v bias
22kVp
23kVp
24kVp
25kVp
26kVp
27kVp
1.62E-09
2.22E-09 3.32E-09 3.32E-09
4.06E-09
4.58E-09
1.54E-09
2.22E-09 3.09E-09 3.66E-09
4.22E-09
5.01E-09
1.48E-09
1.76E-09 2.01E-09 2.58E-09
3.02E-09
3.67E-09
1.71E-09
2.4E-09 2.82E-09 3.56E-09
4.48E-09
4.96E-09
1.49E-09
1.76E-09 2.86E-09 3.35E-09
3.97E-09
4.33E-09
1.6E-09
2E-09 2.59E-09 3.51E-09
4.15E-09
4.81E-09
1.46E-09
1.66E-09 2.37E-09 2.69E-09
3.07E-09
4.26E-09
1.51E-09
1.96E-09 2.52E-09 2.91E-09
3.24E-09
3.5E-09
2.09E-09
2.95E-09 3.29E-09 4.2E-09
4.82E-09
5.86E-09
Variation of current with bias voltage for DG, OG and
SC diamonds
4.00E-10
C urrent (am pere)
3.50E-10
OG
3.00E-10
2.50E-10
2.00E-10
DG
1.50E-10
1.00E-10
5.00E-11
SC
0.00E+00
-5.00E-11
0
200
400
600
V oltage (V )
800
1000
1200
Variation of sensitivity with bias voltage for DG, OG
and SC diamonds
Sensitivity (response kVp-1)
0.9
DG3
0.8
0.7
0.6
0.5
SC
0.4
0.3
0.2
OG1
0.1
0
180
230
280
330
Bias Voltage (V)
380
430
Variation of sensitivity with UV absorption for DG and
SC CVD diamond at 200V bias
Sensitivity (response.kVp -1)
0.6
0.5
0.4
0.3
0.2
sc
0.1
0
0
0.5
1
1.5
UV absorption (cm-1)
2
2.5
Sensitivity (response.kVp -1)
Variation of sensitivity with single substitutional nitrogen
concentration for DG CVD diamonds at 200V bias
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
3
3.5
4
4.5
Single substitutional nitrogen (ppm)
5
5.5
Variation of X-ray response rate with TL emission for
DG and OG CVD diamond detectors
2
X-ray response rate (cps)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
500
1000
1500
TL emission (arb. unit)
2000
2500
variation of X-ray response rate with Raman
broadening for DG and OG CVD diamond detectors
X-ray response rate (cps)
1.8
DG
1.7
1.6
1.5
OG
1.4
1.3
1.2
1.1
1
2.5
2.55
2.6
2.65
2.7
2.75
Raman broadening FWHM (cm-1)
2.8
2.85
Variation of X-ray response rate with single substitution nitrogen
concentration for DG and OG CVD diamond detectors
2
X-ray response rate (cps)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
Single substitution nitrogen (ppm)
60
70
80
Variation of X-ray response rate with UV absorption for OG CVD
diamond detectors
at voltage peak of 22 kVp and 200V bias
X-ray response rate (cps)
1.3
1.28
1.26
1.24
1.22
1.2
1.18
3.4
3.5
3.6
3.7
UV absorption (cm-1)
3.8
3.9
5.6 Variation of X-ray response rate with UV absorption for DG CVD
diamond detectors at voltage peak voltage peak of 22kVp and 300
V bias
X-ray response rate (cps)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
0.2
0.7
1.2
UV absorption (cm-1)
1.7
2.2
Monte Carlo
(PENELOPE) for
evaluation of Filtered
mammographic X-ray
energy Range
6.1 Variation of X-ray response rate with energy for DG1, OG1 and
SC CVD diamond detectors and absorbed dose of a simulated
plane and metallized diamond, with platinum, titanium and gold
contacts
Energy
KeV
DG1
OG1
SC
Simulated
and
metalized
diamond
22
1.52
1.29
1.35
1.114
1.0521
0.0160
0.0044
0.0618
23
1.64
1.57
1.74
1.100
1.0357
0.0162
0.0044
0.0641
24
1.72
1.76
1.86
1.084
1.0186
0.0164
0.0045
0.0662
25
1.95
1.95
2.1
1.074
1.0067
0.0164
0.0046
0.0676
26
2.18
2.1
2.21
1.058
0.9894
0.0165
0.0047
0.0697
27
2.35
2.2
2.42
1.049
0.9797
0.0166
0.0047
0.0707
Plane
Diamon
d
Platinum Titanium
Gold
Variation of absorbed dose with X-ray peak energy for
Monte Carlo simulation on
platinum, titanium and gold
arb. unit
gold
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Platinum
Titanium
21
22
23
24
25
Energy (keV)
26
27
28
Arb. unit
Variation of absorbed dose with X-rap peak energy for
Monte Carlo simulation on
plane and metallized diamond
1.14
1.12
1.1
1.08
1.06
1.04
1.02
1
0.98
0.96
Metalized diamond
Plane diamond
21
22
23
24
25
Energy (keV)
26
27
28
Comparison of actual responses with peak voltage for DG, OG and SC at
200V bias with that of simulated response for a pure diamond using Monte
Carlo
code PENELOPE
3
SC
DG
2.5
Arb. Unit
2
OG
1.5
1
Simulated
0.5
0
21
22
23
24
25
Peak voltage (kVp)
26
27
28
Discussion
1 The sensitivity of all CVD diamond types (DG, OG and SC) increase in applied
electric field

2 Generally CVD diamond saturates with increase peak voltage and is related to
defects and impurities in CVD diamond

3 The difference in resistivity is also related to difference response rate of CVD to Xrays

4 The presence of defects and impurities explain sensitivity and linearity of the
detector i.e low defects and impurities, the higher the response to X-rays by DG and SC
5 The Detector and Single Crystals CVD diamond are better in performance as X-ray
probe in terms of linearity and sensitivity than the Optical Grade CVD diamond
wafers.

6 The relatively low performance of OG CVD diamond to X-rays could be ascribed to
the higher presence of single substitutional nitrogen concentration and larger
concentration of grain boundary related defects depicted by Raman broadening.

7 For the choice of X-ray dosimetry, The specimen must have a higher TL emission
and UV absorption but a low Raman broadening and single substitutional nitrogen
concentration.

8 Comparison of the results of measured deposited energy in CVD diamond detector
with the energy deposited on simulated pure diamond using PENELOPE, showed
different trends with increase peak voltage that could be related to concentration of
impurity/defect in the detectors. The difference in Detector Grade can also be related
to their different performance, not only in sensitivity but also the linearity as
observed with the detector grades and single crystal CVD diamond wafers, and in
comparison with the simulated pure diamond performing negatively to
mammography X-rays.


Suggestion for future work




An investigation into a possible use of CVD
diamond as X-ray spectrometer for low energy Xrays in the mammographic energy range is
suggested as an area for further research. The
observed linearity and sensitivity of the
Detector Grade and Single Crystal CVD diamond
to low energy mammography X-rays hint at their
possible use in X-ray spectroscopy.
The limitations of the MC code (PENELOPE) with
regard to the study of a detector under the
application of electric field across opposite
surfaces coupled with the presence of added
impurities to detector matrix, prevented an exact
modeling of the research under taken.
An improvement in the Code could make it an
invaluable validatory and design tool if all such
parameters (electric field, voltage and impurity
concentrations) could be taken into account as
this study has shown their presence affect the
simulation of actual experiment.
Acknowledgement
 The Authors would like to extend a special
thanks to all the people who assisted in this
work: Dr.J.A Wyk (ESR studies).
 Mr R.B Erasmus (Raman and UV Expts).
 Prof M Hayes (Ohmic contacts to Sample).
 Mr K Grobellar (deisgned Amplifier and power
supply.
 Mr Mpo Mofokeng( contributes to computer
related problems.
 Mr M Rebak for polishing and cleaning samples.
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