NATURAL AND CVD TYPE DIAMOND DETECTORS AS DOSIMETERS IN HADROTHERAPY APPLI CATIONS Cirrone G.A.P., Cuttone G., Raffaele L., Sabini M.G., De Angelis C.,

NATURAL AND CVD TYPE DIAMOND

DETECTORS

AS DOSIMETERS IN HADROTHERAPY APPLI

CATIONS Cirrone G.A.P., Cuttone G., Raffaele L., Sabini M.G.,

De Angelis C., Onori S., Pacilio M.,

Bucciolini M., Bruzzi M., Sciortino S.

INFN-Laboratori Nazionali del Sud, Catania

CATANA - Italian Center for Prothontherapy

Istituto Superiore di Sanità, Roma

Dipartimento di Fisiopatologia Clinica Università di Firenze, Firenze

Dipartimento di Energetica, Università di Firenze, Firenze

Diamond is potentially a very suitable material for use as radiation dosimeter

Wide band gapLow dark current and

low sensitivity to visible light

High carrier mobility Fast response

Tissue equivalentNo correction on the dose

determination

Strong bonds

High sensitivitySmall dimensions and then high

resolution

High Radiation Hardness

....moreover

It is particularly indicated for measurements in regions of high

radiation field gradient

Proton beams... IMRT....IMPT

•PTW NATURAL DIAMOND

•DE BEERS CVD DIAMOND FILM

Irradiation with 62 AMeV proton beams from a superconducting cyclotron used for the treatment of ocular melanoma : CATANA facility

Nominal current [nA] 4

Dose rate range [Gy/min] 2 - 15

Dose range [Gy] 2 - 20

Our attention has been placed towards two different diamond detectors

20 mm20 mm

7.3mm7.3mm

•Sensitive area: 4.3/4.5 mm2

•Sensitive volume: 1.3/1.4 mm3

•Thickness of sensitive volume: 0.30/0.31 mm

•Operating bias: 100 V

In photon and electron beams the relative differences have been studied and already published (see De Angelis C et al. Med. Phys. 2002; 29(2): 248-254.)

In proton beams the measured repeatability is 0.1%

PTW NATURAL DIAMOND

100Dark current [pA]

16Sensitive surface [mm2]

6,4Sensitive volume [mm3]

0,4Thickness of sensitive volume [mm]

Operating bias [V] 400

DE BEER CVD DIAMOND

Charge and current measurements from four

electrodes

Vsens is 1,6 mm3

For the characterization of each detector has been paid attention to:

I – V characteristic

Preirradiation Effects

Dose linearity

Dose rate effects

LET Dependence

Relative dose distribution measurements

DARK CURRENT AT 100 V

Specific resistance 2,7 * 1014 cm

Specific resistance 11,3 * 1014 cm

CVD diamond 9 pA

Natural diamond 2,5 pA

SIGNAL TO NOISE RATIO AT 100 V

CVD diamond 5000

Natural diamond 1000

I – V CHARACTERISTICS

-200.0

-150.0

-100.0

-50.0

0.0

50.0

100.0

150.0

200.0

-500 -400 -300 -200 -100 0 100 200 300 400 500

Bias [V]

Cu

rre

nt

[nA

]

CVD

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-150 -100 -50 0 50 100 150

Bias [V]

Cu

rren

t [n

A]

Natural

CURRENT RESPONSE AND PREIRRADIATION (PUMPING EFFECTS)

0

0,5

1

1,5

2

2,5

0 10 20 30 40 50

Dose [Gy]

Nor

mal

ized

col

lect

ed c

harg

e

Natural diamond

CVD diamond

3,5% after 15 Gy

and 50 % increase

0,1 % after 15 Gy

and 8 % fall off

DOSE LINEARITY

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 5 10 15 20 25

Dose Assorbita [Gy]

Car

ica

[uC

]

Specific sensitivity7,5 nC/CGy*mm3

CVD

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20Absorbed dose [Gy]

Co

llec

ted

ch

arg

e [u

C]

Specific sensitivity 0,64 nC/CGy*mm3

Natural

DOSE RATE EFFECTS

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16

Dose rate [Gy/min]

Cu

rren

t [n

A]

CVD

Decrease:

4 % for natural

13 % for CVD

0.8

0.85

0.9

0.95

1

1.05

0 5 10 15

Dose rate [Gy/min]

Norm

aliz

ed c

urre

nt

Natural diamond

CVD diamond

Fower describes the dose rate linearity as

DOSE RATE EFFECTS

eL

V

w

VolDI r

2exp

From which

VeF

IL exp2 Recombination time

decreases with dose rate

Number of electron-hole pairs inside the material

F

IF WE EXPRESS THE INDUCED CONDUCTIVITY AS

rD

rDe 1110 = 0.5 is expected for a pure material with no traps or for high excitation rate

meDr

1110 = 1 for low excitation rate

So for high recombination rate we expect < 1 due to the lower recombination time

DOSE RATE EFFECTS

rfondo DAII

Fitting our experimental data with the semi-empirical formula:

6 MV Photon

250 kV X-Ray

62 AMeV proton

62 AMeV proton

DOSE RATE EFFECTS

THE RECOMBINATION TIME RESULTS

=5,9 ns For the CVD diamond

=1 ns For the natural diamond

And this justifies the higher sensitivity of CVD detector

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

0,0 5,0 10,0 15,0 20,0 25,0 30,0 35,0 40,0

Depth in water [mm]

No

rma

lize

d d

ose

[u

.a.]

Camera Markus

Diamante CVD

Diamante naturale

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

0,0 5,0 10,0 15,0 20,0 25,0 30,0

Depth in water [mm]

No

rma

lize

d d

ose

[a

.u.]

Natural diamond

Markus Ionization chamber

DEPTH DOSE PROFILES

‘Pure’ Bragg peak

SOBP

0,00

20,00

40,00

60,00

80,00

100,00

120,00

-20 -10 0 10 20

Distance from axis [mm]

No

rma

lize

d d

ose

[a

.u.]

Natural diamond

Silicon diode

Lateral Penumbra 1mm

90/50 Ratio 0.89

TRANSVERSAL PROFILES

CONCLUSION

Preirradiation

LET and Dose-rate dependence(to investigate deeper)

Good linearity with absorbed dose

Good radiation hardness

High sensitivity for the CVD

LOW response time (rise time of 2 s)