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Development and characterisation of a new fibre optic dosimeter

C. Gaedtke1, G. V. M. Williams1, S. G. Raymond2, J. Donaldson3, L. Greig3, and J. Steel3

• Materials: fluoroperovskites • Photoluminescence measurements• Optically stimulated luminescence• Radioluminescence studies• Fibre optic dosimeter• Characterization of dosimeter

1 SCPS, Victoria University, PO Box 600, Wellington 6140, New Zealand2 Industrial Research Limited, PO Box 31310, Lower Hutt 5040, New Zealand

3 Blood and Cancer Centre, Wellington Hospital, Private Bag 7902, Wellington, New Zealand

Materials – Fluoroperovskites • Motivation: Searching for new materials

that have good transparency, high sensitivity, and with a response to radiation that is comparable to that of tissue.

• NaMgF3:Eu2+, NaMgF3:Mn2+, Rb:MgF3:Eu2+, RbCdF3:Mn2+

Zeff = 7.6 for tissue

Zeff = 10.43 for 0.1 % Mn2+ in NaMgF3

Zeff = 12.33 for 0.05 % Eu2+ in NaMgF3

Zeff = 31.5 for 0.2 % Eu2+ in RbMgF3

Zeff characterizes a materials response to low

energy x-rays (α Z4/E3 for photoelectric effect)

• Transparent polycrystalline samples are made by mixing the starting materials in stoichiometric ratio in a glassy carbon crucible

• samples were heated slightly above the melting temperature and then slow cooling down to below the melting point

Orthorhombic fluoroperovskite structure

Materials – Fluoroperovskites

Optically stimulated luminescence (OSL) and radioluminescence (RL) measurements

X-irradiation

conduction band

valence band

A+

electronX-rays

A0

(A0)*

hole

F

photostimulated luminescence

photo-stimulation

A0

(A0)*

OSL emissionIrradiation, trapping and RL

Photoluminescence measurements

8S7/2

6P7/2

6P5/2

4f65d(Eg)

Wav

enum

ber

Q

Eu2+ configurational coordinate diagram in NaMgF3:Eu2+

NaMgF3:Eu2+

PL excitation and emission from NaMgF3: 0.2% Eu2+ bulk material in phosphorescence mode

Photoluminescence measurements

Eu2+ configurational coordinate diagram in RbMgF3:Eu2+

RbMgF3:Eu2+

PL excitation and emission from RbMgF3: 0.2% Eu2+ in phosphorescence mode

Photoluminescence measurements

Energy levels of Mn2+ in a crystal field 10Dq

PL excitation and emission in phosphorescence mode

NaMgF3: 1% Mn

RbMgF3: 5% Mn

Optically stimulated luminescence

OSL measurements of Eu2+ doped samples in phosphorescence mode after 18 hours of irradiation with the 241Am source

RbMgF3: 0.2% Eu2+ NaMgF3: 0.2% Eu2+

Optically stimulated luminescence

OSL measurements of Eu2+ doped samples in phosphorescence mode after 18 hours of irradiation with the 241Am source

RbMgF3: 5% Mn NaMgF3: 1% Mn

Radioluminescence

NaMgF3: 1% Mn2+

irradiation over the weekend RbMgF3: 0.2% Mn2+

irradiation overnight

RL measurements of Mn2+ doped bulk materials during irradiation with the 241Am source

RadioluminescenceRL measurements of Eu2+ doped bulk materials during irradiation with the 241Am source

RbMgF3: 0.2% Eu2+

irradiation overnight NaMgF3: 0.2% Eu2+

irradiation over the weekend

RadioluminescenceRL measurements of Eu2+ doped nano particles (pressed into small pellets) during irradiation with the 241Am source

NaMgF3: 1% Eu2+

irradiation over the weekend

Radioluminescence (RL) and optically stimulated luminescence (OSL) measurments

• Real-time radiation dose and dose rate for radiation protection, non-destructive testing, and in medicine for monitoring radiation dose during radiotherapy or for dose verification and validation

• Advantages of OSL dosimeters: • Retains dose information for a long

time• Higher sensitivity than organic

scintillators • Different shape of materials, can be

made as nano particles, bulk transparent polycrystalline materials or 2D sheets

• Can be nearly tissue equivalent

E.G. Yukihara and S.W.S. Mc Keever, „Optically stimulated luminescence (OSL) dosimetry in medicine“, Phys. Med. Biol., 53, R351, (2008)

Fibre optic dosimeter

Exposure to 10.5 µGy/s 241Am 60 keV γ-rays, then OSL stimulated at 505 nm

We have a patent on the fluoroperovskite materials and a patent application on the device.

Characterization of the fiber optic dosimeter

• Different fluoroperovskite compounds have been attached to the end of an optical fibre. Tested using the 241Am source at IRL and the linear accelerator at Wellington hospital operating at 6MV

• Second set of measurements involved collaboration with the Wellington Hospital medical physicists

• Can be used in different modes:– Total dose readout: will reset the dosimeter– Latest dose readout: when there is a series of irradiation, readout of each irradiation is

possible– Pulsed dose rate monitoring: IR stimulated pulsed OSL– Continual low dose rate monitoring: RL– Continual high dose monitoring: RL and blue stimulation

Characterization of the fiber optic dosimeter

Recent RL measurements at Wellington Hospital with the bulk materials

Setup at Wellington Hospital showing the linear accelerator

Summary

• response to radiation that is comparable to that of tissue• Fluoroperovskites show good PL, OSL and RL response and therefore used

in application • Characterisation in Wellington Hospital showed that bulk materials have a

linear response to dose• Further studies on nano particles as RL signal is dose independent• Characterization of our fluoroperovskites at linear accelerator at

Wellington Hospital