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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 X-RAY RANGE. Y.I Zakari, R.D. Mavunda, T.L Nam and R.J Keddy. YI Zakari* RD Mavunda, TL Nam and RJ keddy. - PowerPoint PPT Presentation
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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 X-RAY 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
INTRODUCTIONINTRODUCTION
•CVD DIAMOND DETECTOR AS CVD DIAMOND DETECTOR AS THE ‘STATE OF THE ART’ FOR THE ‘STATE OF THE ART’ FOR
FUTURE TECHNOLOGYFUTURE TECHNOLOGY•MotivationMotivation:: Breast cancer reported Breast cancer reported
to be the highest source of to be the highest source of mortality in women (next to lung mortality in women (next to lung cancer) and that at present X-ray cancer) and that at present X-ray
mammography screening may mammography screening may also induce cancer also induce cancer
AIM
CHARACTERIZATION OF CVD DETECTORS
TO EVALUATE CVD DIAMOND RESPONSE TO ALPHA LOW ENERGY X-RAY
ALPHA SPECTROCOPYMC 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 UNITKEITHLEY 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
ESR: single Total energy
Sample
Raman spectral broadening
FWHM (cm-1)
TL response
(arbt.unit)
substitution nitrogen (ppm)
UV absorption
(cm-1)
alpha counts (cps)
absolute Efficiency
%
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
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
UV absorption (cm-1)
Alp
ha c
ounts
per
sec
OG
DG
SC
Variation of total alpha counts with the single substitution nitrogen concentration (ESR) of optical grade CVD diamond
22500
24500
26500
28500
30500
32500
3 3.5 4 4.5 5 5.5
Single substitutional nitrogen (ppm)
Alp
ha c
ounts
per
second (
cps)
Variation of total alpha counts with single substitution nitrogen concentration for detector grade CVD diamonds
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4
40 45 50 55 60 65 70 75
Single substitutional nitrogen (ppm)
UV
absorp
tion (
cm-1
)
Variation of total alpha counts with the Raman broadening (FWHM) for optical grade CVD diamonds
0
10000
20000
30000
40000
50000
60000
2.55 2.6 2.65 2.7 2.75 2.8 2.85
Raman Broadening (FWHM in cm-1)
Alp
ha c
ounts
per
second (
cps)
Variation of TL response with single substitutional nitrogen concentration (ESR) for detector and optical grade CVD diamonds
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80
Single substitutional nitrogen (ppm)
TL r
esponse (
arb
t.unit)
DG
OG
Variation of TL emission with Raman broadening for optical grade CVD diamonds
50
70
90
110
130
150
170
2.55 2.6 2.65 2.7 2.75 2.8 2.85
Raman broadening (FWHM in cm-1)
TL (
arb
. unit)
em
issin
Variation of Alpha FWHM counts with averaged UV absorption values for both detector and optical grade and single crystal CVD diamonds
-1000
0
1000
2000
3000
4000
5000
6000
7000
8000
0.6 1.1 1.6 2.1 2.6 3.1 3.6 4.1
UV absorption (cm-1)
Alp
ha F
WH
M (
keV
)
SCDG
OG
Variation of FWHM of total count with averaged Raman broadening values for both detector and optical grade and single crystal CVD diamonds
1
10
100
1000
10000
2.28 2.38 2.48 2.58 2.68 2.78
Raman broadening (FWHM in cm-1)
Alp
ha F
WH
M (
keV
)
OG
DGSC
Variation of alpha FWHM with single substitutional nitrogen concentration (ESR) for detector and optical grade CVD diamonds
-1000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 10 20 30 40 50 60 70 80
Single substitutional nitrogen (ppm)
Alp
ha F
WH
M (
keV
)
DG
OG
DG
Variation of experimental alpha count rate with energy for optical grade (DG) CVD diamonds
Variation of experimental alpha count rate w ith energy for optical grade (OG) CVD diamonds
0
10
20
30
40
50
60
70
80
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
energy (keV)
Count ra
te (
cps)
A typical optical grade CVD diamond spectrum before (upper curve) and after (Lower curve) background subtraction
0
50
100
150
200
250
0 5000 10000 15000 20000
Energy (keV)
Tota
l alp
ha c
ounts
Alpha spectrum from OG4 polycrystalline and single crystal (SC) CVD diamond samples showing energy peak.
0
20
40
60
80
100
120
140
160
180
0 2000 4000 6000 8000 10000 12000 14000
Energy (keV)
Tota
l alp
ha c
ounts
SC
OG4
Alpha spectrum from detector grade DG3 and DG4 CVD diamonds showing the characteristic energy peak
0
20
40
60
80
100
120
0 2000 4000 6000 8000 10000 12000 14000
Energy (keV)
Tota
l alp
ha c
ounts
DG3
DG4
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 The alpha spectrum stripping methodology for a comparative evaluation of inherent for a comparative evaluation of inherent
spectrometric performance of CVD diamondspectrometric 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 equationusing the Bragg-Kleeman rule.
A
D
D
AAiiD A
ARR
-------------------------------------------------------(1)
where )(325.0)( 23
MeVEcmR iAi (Lamarsh,1997)
The specific ionization I(Ei) defined as
ionsWR
eVEEI
Di
ii
)( /cm
)(10222
2 2
keVE
EEE
i
iic
i
ccii
pi EI
EIEIf
cicci EEIEI
)2( EiioEiioiopi fEIfEIEII piEi ff 1
Variation in peak efficiency with energy
Fig. 1 Variation in peak eff iciency w ith energy
0
0.2
0.4
0.6
0.8
1
1.2
0 5000 10000 15000 20000 25000
Energy (keV)
Peak e
ffic
iency
Variation in alpha count rate s with energy for an Optical grade CVD diamond (OG1)
0 5000 10000 15000 200000
50
100
150
200
250
Fig.2 Variation in Alpha count rates with Energy for an Optical grade CVD diamond (OG1)
Alp
ha
co
un
t ra
te (
cp
s)
Energy (KeV)
Exptal counts Exptal (Baseline subtracted) Stripped counts
Variation in alpha count rate with energy for an optical grade CVD diamond (OG2)
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000 180000
50
100
150
200
250
300
F1g.3 Variation in alpha count rate with energy for an Optical grade CVD diamond (OG2)
Alp
ha c
ount ra
te (
cps)
Energy (KeV)
Exptal counts Exptal (Baseline subtracted) Stripped counts
Variation of Alpha count rate with energy for a detector grade CVD diamond (DG1)
-2000 0 2000 4000 6000 8000 1000012000140001600018000200000
10
20
30
40
50
60
70
80
Fig.6 Variation in Alpha count rate with Energy for a detector grade CVD diamond (DG1)
Alp
ha c
ount ra
te (
cps)
Energy (KeV)
Exptal counts Exptal (Baseline subtracted) Stripped counts
Variation in Alpha count rate with energy for a particular detector grade CVd diamond (DG3)
-1000 0 1000 2000 3000 4000 5000 6000 7000 80000
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
Fig.8 Variation in Alpha count rate with energy for a detector grade CVD diamond (DG3)
Alp
ha
co
unt ra
te (
cps)
Energy (KeV)
Exptal Counts Stripped counts
Variation in Alpha count rate with energy for a single crystal CVD diamond
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000-500
0
500
1000
1500
2000
2500
3000
3500
Fig.10 Variation in Alpha count rate with Energy for a Single Crystal CVD diamond (SC)
To
tal C
ou
nts
Energy (keV)
Experimental Counts Corrected Counts
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
(cps)
%Absolute
Efficiency
Stripped
spectrum
Peak
Resolution
% peak
Efficiency
Detector
Type
EXPT
ANALT
EXPT
ANALT
AREA
Height
FWHM
(keV)
EXPT
ANALT
stripped
EXPT
ANALT
stripped
DG1
32969
35245
68
73
28504
25.1
907.8
0.185±
0.001
0.166±
0.0008
80
80
DG2
31327
39150
65
81
63228
88.3
571.7
0.125±
0.0023
0.105±
0.0034
80
80
DG3
29834
40623
62
84
1031800
13352
61.7
0.012±
0.0018
0.011±
0.0016
82
82
DG4
32732
37225
68
77
40622
54..2
622.5
0.124±
0.0030
0.114±
0.0092
80
80
OG1
50314
45355
104
94
318840
73.8
3447.6
1.365±
0.0089
0.630±
0.0064
60
60
OG2
49010
46531
101
96
631500
125.6
4041.8
1.092±
0.004
0.739±
0.0045
60
60
OG3
49397
46288
103
96
858870
161.4
4245
1.289±
0.0048
0.776±
0.0040
60
60
OG4
39046
43787
81
91
364760
104.4
4564
1.325±
0.0046
0.834±
0.0049
60
60
SC
25401
34172
52
71
285470
2693
84.58
0.016±
0.0056
0.015±
0.0055
80
80
Summary of spectrometric analysisSummary of spectrometric analysisStripping method used was observed to have Stripping method used was observed to have improved the detector peak resolution but without any improved the detector peak resolution but without any effect on the peak efficiency of the detector.effect on the peak efficiency of the detector.The technique has more effect on the OG CVD The technique has more effect on the OG CVD diamond detectors than the DG and SC CVD detectors. diamond detectors than the DG and SC CVD detectors. The observed absolute efficiency above 100% due to The observed absolute efficiency above 100% due to build-up effect and fluctuation were stripped off to build-up effect and fluctuation were stripped off to have a more realistic valuehave a more realistic value
At the peak energy of 5.48 MeV a range of 90At the peak energy of 5.48 MeV a range of 90μμm was m was calculated indicating the interaction is on the surface.calculated indicating the interaction is on the surface.A mass stopping power of 0.281 MeV/mgcmA mass stopping power of 0.281 MeV/mgcm-2-2 and a and a leakage current of betwn 5.2pA and 54.2 pA observed leakage current of betwn 5.2pA and 54.2 pA observed could classify these detectors as semiconductingcould classify these detectors as semiconductingAn average full energy peak efficiency of 80% both An average full energy peak efficiency of 80% both experimentally and analytically indicates that the experimentally and analytically indicates that the stripping formular validate and improves the stripping formular validate and improves the experimental data without any effect on the detectors experimental data without any effect on the detectors inherent characteristic performance inherent characteristic performance
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 characteristicsUse the MC code to model the
experimental set up carbon in place of diamond
3.50E-111000
2.50E-11800
8.80E-111.86E-101.64E-11500
3.68E-118.80E-119.10E-12300
1.17E-114.80E-115.80E-12200
1.80E-122.50E-113.00E-12120
2.00E-121.65E-111.60E-1280
9.00E-129.30E-128.00E-1350
1.50E-126.50E-122.10E-1330
DGOGSC
Current (amps)Voltage
Setting (volts)
3.50E-111000
2.50E-11800
8.80E-111.86E-101.64E-11500
3.68E-118.80E-119.10E-12300
1.17E-114.80E-115.80E-12200
1.80E-122.50E-113.00E-12120
2.00E-121.65E-111.60E-1280
9.00E-129.30E-128.00E-1350
1.50E-126.50E-122.10E-1330
DGOGSC
Current (amps)Voltage
Setting (volts)
Current-voltage characteristics for DG, OG and SC diamond detectors
0.88±0.02<1252.32±0.03SC
3.59±0.1162.5932.81±0.22OG4
3.48±0.1153.61412.76±0.24OG3
3.52±0.09-71832.78±0.24OG2
3.86±0.0542.91552.59±0.15OG1
1.9±0.055.38142.55±0.16DG4
1.03±0.08520242.63±0.15DG3
1.93±0.1348812.57±0.17DG2
0.51±0.063.511472.64±0.17DG1
UV absorption
(cm-1)
ESR: single substitution
nitrogen (ppm)TL response (arbt.unit)
Raman spectral broadening
FWHM (cm-1)Sample
0.88±0.02<1252.32±0.03SC
3.59±0.1162.5932.81±0.22OG4
3.48±0.1153.61412.76±0.24OG3
3.52±0.09-71832.78±0.24OG2
3.86±0.0542.91552.59±0.15OG1
1.9±0.055.38142.55±0.16DG4
1.03±0.08520242.63±0.15DG3
1.93±0.1348812.57±0.17DG2
0.51±0.063.511472.64±0.17DG1
UV absorption
(cm-1)
ESR: single substitution
nitrogen (ppm)TL response (arbt.unit)
Raman spectral broadening
FWHM (cm-1)Sample
Characterization results of CVD diamod as earlier reported Mavunda et al,2008)
2.422.212.11.861.741.350.881252.32SC
2.192.051.911.641.541.253.5962.593.22.81OG4
2.212.42.121.961.551.23.4853.6140.52.76OG3
2.42.242.151.881.541.223.527183.22.78OG2
2.22.11.951.761.571.293.8642.9154.52.59OG1
3.032.762.642.532.281.651.95.3813.82.55DG4
4.564.083.463.072.461.721.0352023.72.63DG3
3.012.782.562.411.961.621.934881.22.57DG2
2.352.181.951.721.641.520.513.51146.82.64DG1
27kVp
26kVp
25kVp
24kVp
23kVp
22kVp
X-ray response (cps) at 200V bias
UV (cm-1)ESR
(ppm)
TL(arbt. Unit)
RamanFWHM (cm-1)
DetectorType
2.422.212.11.861.741.350.881252.32SC
2.192.051.911.641.541.253.5962.593.22.81OG4
2.212.42.121.961.551.23.4853.6140.52.76OG3
2.42.242.151.881.541.223.527183.22.78OG2
2.22.11.951.761.571.293.8642.9154.52.59OG1
3.032.762.642.532.281.651.95.3813.82.55DG4
4.564.083.463.072.461.721.0352023.72.63DG3
3.012.782.562.411.961.621.934881.22.57DG2
2.352.181.951.721.641.520.513.51146.82.64DG1
27kVp
26kVp
25kVp
24kVp
23kVp
22kVp
X-ray response (cps) at 200V bias
UV (cm-1)ESR
(ppm)
TL(arbt. Unit)
RamanFWHM (cm-1)
DetectorType
X-ray response rate at 200V bias for DG, OG and SC diamonds
X-ray response rate at 300V bias for DG, OG and SC diamonds
X-ray response (cps) at 300V bias
Detector Type
Raman FWHM (cm-1)
TL (arbt. Unit)
ESR (ppm)
UV (cm-1)
22 kVp
23 kVp
24 kVp
25 kVp
26 kVp
27 kVp
DG1 2.64 1146.8 3.5 0.51 1.92 2.38 3.15 3.87 4.5 4.98
DG2 2.57 881.2 4 1.93 2.18 2.73 3.67 4.14 4.6 5.25
DG3 2.63 2023.7 5 1.03 2.45 2.92 3.71 5.26 5.62 6.15
DG4 2.55 813.8 5.3 1.9 2.26 2.76 3.41 3.76 4.55 4.86
OG1 2.59 154.5 42.9 3.86 1.78 2.22 3.05 3.14 3.22 3.34
OG2 2.78 83.2 71 3.52 1.89 2.26 2.8 3.54 3.72 3.81
OG3 2.76 140.5 53.6 3.48 1.91 2.38 2.9 3.1 3.4 3.5
OG4 2.81 93.2 62.5 3.59 1.82 2.31 2.84 3.15 3.37 3.52
SC 2.32 25 1 0.88 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
Detector Type
Raman FWHM (cm-1)
TL (arbt. Unit)
ESR (ppm)
UV (cm-1)
22 kVp
23 kVp
24 kVp
25 kVp
26 kVp
27 kVp
DG1 2.64 1146.8 3.5 0.51 2.31 2.87 3.26 3.94 4.64 5.07
DG2 2.57 881.2 4 1.93 2.42 2.98 3.72 4.08 4.78 5.41
DG3 2.63 2023.7 5 1.03 3.31 3.74 4.48 5.38 5.71 6.29
DG4 2.55 813.8 5.3 1.9 2.59 2.92 3.54 3.88 5.61 5.46
OG1 2.59 154.5 42.9 3.86 2.19 2.27 3.09 3.32 3.5 3.72
OG2 2.78 83.2 71 3.52 2.26 2.42 3.17 3.58 3.84 3.92
OG3 2.76 140.5 53.6 3.48 2.14 2.34 3.2 3.29 3.57 3.66
OG4 2.81 93.2 62.5 3.59 2.16 2.61 2.88 3.23 3.41 3.62
SC 2.32 25 1 0.88 3.68 4.29 4.79 5.07 5.34 5.9
Averaged CVD diamond response to X-ray in calculated dose (Gy) values
X-ray Dose (Gy) values calculated from CVD diamond response at 200v bias Detector Type 22kVp 23kVp 24kVp 25kVp 26kVp 27kVp DG1 1.62E-09 2.22E-09 3.32E-09 3.32E-09 4.06E-09 4.58E-09 GD2 1.54E-09 2.22E-09 3.09E-09 3.66E-09 4.22E-09 5.01E-09 DG3 1.48E-09 1.76E-09 2.01E-09 2.58E-09 3.02E-09 3.67E-09 DG4 1.71E-09 2.4E-09 2.82E-09 3.56E-09 4.48E-09 4.96E-09 OG1 1.49E-09 1.76E-09 2.86E-09 3.35E-09 3.97E-09 4.33E-09 OG2 1.6E-09 2E-09 2.59E-09 3.51E-09 4.15E-09 4.81E-09 OG3 1.46E-09 1.66E-09 2.37E-09 2.69E-09 3.07E-09 4.26E-09 OG4 1.51E-09 1.96E-09 2.52E-09 2.91E-09 3.24E-09 3.5E-09 SC 2.09E-09 2.95E-09 3.29E-09 4.2E-09 4.82E-09 5.86E-09
-5.00E-11
0.00E+00
5.00E-11
1.00E-10
1.50E-10
2.00E-10
2.50E-10
3.00E-10
3.50E-10
4.00E-10
0 200 400 600 800 1000 1200
V oltage (V )
Cur
rent
(am
pere
)
OG
DG
SC
Variation of current with bias voltage for DG, OG and SC diamonds
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
180 230 280 330 380 430
Bias Voltage (V)
Se
nsi
tivity
(re
spo
nse
kV
p-1
)
DG3
SC
OG1
Variation of sensitivity with bias voltage for DG, OG and SC diamonds
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.5 1 1.5 2 2.5
UV absorption (cm-1)
Sen
sitiv
ity (
resp
onse
.kV
p-1)
sc
Variation of sensitivity with UV absorption for DG and SC CVD diamond at 200V bias
00.050.1
0.150.2
0.250.3
0.350.4
0.450.5
3 3.5 4 4.5 5 5.5
Single substitutional nitrogen (ppm)
Sen
sitiv
ity (
resp
onse
.kV
p-1)
Variation of sensitivity with single substitutional nitrogen
concentration for DG CVD diamonds at 200V bias
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 500 1000 1500 2000 2500
TL emission (arb. unit)
X-r
ay r
espo
nse
rate
(cp
s)
Variation of X-ray response rate with TL emission for DG and OG CVD diamond detectors
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85
Raman broadening FWHM (cm-1)
X-r
ay r
espo
nse
rate
(cp
s)
DG
OG
variation of X-ray response rate with Raman broadening for DG and OG CVD diamond detectors
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 10 20 30 40 50 60 70 80
Single substitution nitrogen (ppm)
X-r
ay r
espo
nse
rate
(cp
s)
Variation of X-ray response rate with single substitution nitrogen concentration for DG and OG CVD diamond detectors
1.18
1.2
1.22
1.24
1.26
1.28
1.3
3.4 3.5 3.6 3.7 3.8 3.9
UV absorption (cm-1)
X-r
ay r
espo
nse
rate
(cp
s)
Variation of X-ray response rate with UV absorption for OG CVD diamond detectorsat voltage peak of 22 kVp and 200V bias
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0.2 0.7 1.2 1.7 2.2
UV absorption (cm-1)
X-r
ay r
espo
nse
rate
(cp
s)
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
Monte Carlo (PENELOPE) for evaluation of Filtered mammographic X-ray
energy Range
0.07070.00470.01660.97971.0492.422.22.3527
0.06970.00470.01650.98941.0582.212.12.1826
0.06760.00460.01641.00671.0742.11.951.9525
0.06620.00450.01641.01861.0841.861.761.7224
0.06410.00440.01621.03571.1001.741.571.6423
0.06180.00440.01601.05211.1141.351.291.5222
GoldTitaniumPlatinum
Plane Diamon
d
Simulated and
metalizeddiamondSCOG1DG1
Energy KeV
0.07070.00470.01660.97971.0492.422.22.3527
0.06970.00470.01650.98941.0582.212.12.1826
0.06760.00460.01641.00671.0742.11.951.9525
0.06620.00450.01641.01861.0841.861.761.7224
0.06410.00440.01621.03571.1001.741.571.6423
0.06180.00440.01601.05211.1141.351.291.5222
GoldTitaniumPlatinum
Plane Diamon
d
Simulated and
metalizeddiamondSCOG1DG1
Energy KeV
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
0
0.010.02
0.03
0.04
0.050.06
0.07
0.08
21 22 23 24 25 26 27 28
Energy (keV)
arb.
uni
t
Titanium Platinum
gold
Variation of absorbed dose with X-ray peak energy for Monte Carlo simulation onplatinum, titanium and gold
0.96
0.98
1
1.02
1.04
1.06
1.08
1.1
1.12
1.14
21 22 23 24 25 26 27 28
Energy (keV)
Arb
. un
it
Metalized diamond
Plane diamond
Variation of absorbed dose with X-rap peak energy for Monte Carlo simulation onplane and metallized diamond
0
0.5
1
1.5
2
2.5
3
21 22 23 24 25 26 27 28
Peak voltage (kVp)
Arb
. Uni
t
SCDG
OG
Simulated
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 Carlocode PENELOPE
1 The sensitivity of all CVD diamond types (DG, OG and SC) increase in applied 1 The sensitivity of all CVD diamond types (DG, OG and SC) increase in applied electric fieldelectric field
2 Generally CVD diamond saturates with increase peak voltage and is related to 2 Generally CVD diamond saturates with increase peak voltage and is related to defects and impurities in CVD diamonddefects and impurities in CVD diamond
3 The difference in resistivity is also related to difference response rate of CVD to 3 The difference in resistivity is also related to difference response rate of CVD to X-raysX-rays
4 The presence of defects and impurities explain sensitivity and linearity of the 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 detector i.e low defects and impurities, the higher the response to X-rays by DG and
SCSC 5 The Detector and Single Crystals CVD diamond are better in performance as X-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 ray probe in terms of linearity and sensitivity than the Optical Grade CVD diamond wafers.wafers.
6 The relatively low performance of OG CVD diamond to X-rays could be ascribed 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 to the higher presence of single substitutional nitrogen concentration and larger concentration of grain boundary related defects depicted by Raman broadening.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 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 and UV absorption but a low Raman broadening and single substitutional nitrogen concentration.concentration.
8 Comparison of the results of measured deposited energy in CVD diamond 8 Comparison of the results of measured deposited energy in CVD diamond detector with the energy deposited on simulated pure diamond using PENELOPE, detector with the energy deposited on simulated pure diamond using PENELOPE, showed different trends with increase peak voltage that could be related to showed different trends with increase peak voltage that could be related to concentration of impurity/defect in the detectors. The difference in Detector Grade 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 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 the linearity as observed with the detector grades and single crystal CVD diamond wafers, and in comparison with the simulated pure diamond performing wafers, and in comparison with the simulated pure diamond performing negatively to mammography X-rays. negatively to mammography X-rays.
DiscussionDiscussion
Suggestion for future workSuggestion for future work
An investigation into a possible use of CVD An investigation into a possible use of CVD diamond as X-ray spectrometer for low energy X-diamond as X-ray spectrometer for low energy X-rays in the mammographic energy range is rays in the mammographic energy range is suggested as an area for further research. The suggested as an area for further research. The
observed linearity and sensitivity of the Detector observed linearity and sensitivity of the Detector Grade and Single Crystal CVD diamond to low Grade and Single Crystal CVD diamond to low energy mammography X-rays hint at their possible energy mammography X-rays hint at their possible use in X-ray spectroscopy. use in X-ray spectroscopy.
The limitations of the MC code (PENELOPE) with The limitations of the MC code (PENELOPE) with regard to the study of a detector under the regard to the study of a detector under the application of electric field across opposite surfaces application of electric field across opposite surfaces coupled with the presence of added impurities to coupled with the presence of added impurities to detector matrix, prevented an exact modeling of detector matrix, prevented an exact modeling of the research under taken. the research under taken.
An improvement in the Code could make it an An improvement in the Code could make it an invaluable validatory and design tool if all such invaluable validatory and design tool if all such parameters (electric field, voltage and impurity parameters (electric field, voltage and impurity concentrations) could be taken into account as this concentrations) could be taken into account as this study has shown their presence affect the study has shown their presence affect the simulation of actual experiment.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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