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New high radiation resistant scintillating thin films
Synthetic Metals 138 (2003) 275–279
New high radiation resistant scintillating thin films A. Quarantaa,b, A. Vomieroa,b,*, S. Carturana,c, G. Maggionib, G. Della Meaa,b a
b
Dipartimento di Ingegneria dei Materiali, Universita` di Trento, Via Mesiano 77, 38050 Trento, Italy Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Legnaro, Via Romea 4, 35202 Legnaro, PD, Italy c Dipartimento di Fisica, Universita` di Trento, Via Sommarive 14, 38050 Povo, TN, Italy
Abstract New scintillating thin films with improved radiation hardness were synthesised for applications in the field of radiation monitoring, by dispersing Rhodamine B (RB) dye into a high radiation resistant polymeric matrix (6FDA-DAB polyimide). The radiation hardness and the scintillation efficiency of this new composite material were tested by means of ion beam induced luminescence (IBIL) and compared to thin films of the traditional NE102 plastic scintillator. The samples were irradiated by 2.0 MeV 4 Heþ ion beam at fluences ranging between 1012 and 1015 ions/cm2. IBIL results indicated that the polyimide-based scintillator has a better radiation hardness and a good scintillation efficiency for high doses irradiations. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Plastic scintillators; Dye; Radiation hardness; Ion beam induced luminescence
1. Introduction Thin film plastic scintillators play a crucial role in many fields of radiation detection, such as dosimetry measurements in medicine [1], radiation monitoring in high intensity beams [2,3], simultaneous counting of different radiations [4]. The degradation of the luminescence properties of the detectors, as due to the induced radiation damage, makes the continuous dose monitoring at increasing irradiation fluence a very difficult task. This degradation is particularly pronounced in high radiation environments, where the scintillators undergo high radiation fluxes. For this reason, one of the main goals in the synthesis of the scintillating materials is to obtain enhanced radiation hardness in order to guarantee an accurate light calibration over a wide range of radiation fluence [5]. In the last few years particular interest has been devoted to the characterisation of the scintillation properties of plastic scintillators under high radiation fluxes [6] and a description of the time evolution of the light emission has been attempted. The evolution can give meaningful information both on the damage of the polymeric structure as induced by scission processes and on the growth of new structures owing to the cross-linking of chemically active radicals [7] which are formed during irradiation. In this work the luminescence properties of a new Rhodamine * Corresponding author. Tel.: þ39-049-8068-406; fax: þ39-049-641925. E-mail address: [email protected] (A. Vomiero).
B (RB) doped polyimide thin film were investigated by using ion beam induced luminescence (IBIL) analysis. A comparison with the properties of a standard polyvinyltoluene (PVT) plastic scintillator (NE102 or BC400 from Bicron) was also performed. All the tested samples were irradiated by a 2.0 MeV 4 Heþ beam.
2. Experimental Thin films of pure polyimide 4,40 -hexafluoroisopropylidene diphthalic anhydride-4,40 -diaminobenzophenone (6FDA-DAB), RB doped polyimide (RB-6FDA-DAB), pure PVT and NE102 were deposited on silicon substrates. NE102 and PVT films were obtained by dissolution of bulk plastics into toluene and by spinning the solution onto the substrates (2000 rpm for 20 ). The preparation details of polyimide-based samples are reported elsewhere [8]. Film thickness (ranging from 2 to 6 mm) was measured with a stylus profilometer (TALISTEP). Ion irradiation was performed at the 2.5 MV Van de Graaff accelerator of the INFN Laboratori Nazionali di Legnaro. An 4 Heþ beam (2.0 MeV) was used in IBIL analyses. The beam spot size was about 10 mm2 and the beam current was not higher than 10 nA/mm2 in order to prevent sample heating. Each IBIL spectrum was collected within fluence intervals of about 1012 to 1013 ions/cm2, corresponding to a typical collection time of a few seconds. The study of the time evolution of the light
0379-6779/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(02)01287-0
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A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
emission in the fluence range 1 1014 to 5 1014 ions/cm2 was performed by interposing irradiation steps of about 1 1014 ions/cm2 between two consecutive IBIL spectra. The light emitted from the films was collected during the irradiation by a four silica lenses optical system and focussed on a silica fibre bundle connected to an Acton optical spectrometer. The light was dispersed by a 150 g/mm grating on a nitrogen cooled Princeton CCD detector, equipped with an array of 1340 100 pixels, 20 20 mm2 each one. Every spectrum was corrected taking into account the spectral response of the entire acquisition system.
3. Results and discussion IBIL spectra of 6FDA-DAB (fluence ¼ 4.5E12 ions/cm2) and PVT (fluence ¼ 3E12 ions/cm2) irradiated with 4 Heþ ions are reported in Fig. 1a and b, respectively. The 6FDADAB matrix exhibits a broad band centred at about 550 nm, whose shape does not change during irradiation and whose intensity decreases at increasing fluence. The pure PVT IBIL spectrum shows a very different behaviour: a narrow band centred at about 320 nm is ascribed to the intrinsic luminescence of the PVT, together with a luminescence band centred at about 500 nm. A shoulder appears at lower wavelength in the 500 nm band, which grows up as the fluence increases. The 500 nm band and the related shoulder could be attributed to aggregates of phenyl radicals similar to amorphous hydrogenated carbon clusters, already observed in irradiated polystyrene, whose structure is very similar to PVT [9,10].
The typical RB-6FDA-DAB IBIL spectrum (Fig. 2a, fluence ¼ 4.3E12 ions/cm2) exhibits an intense band centred at 590 nm, a smaller band at about 700 nm and a third broader band at 490 nm. The features at 590 and 700 nm are due to the RB molecules dispersed into the matrix, while the band at 490 nm is the polymer characteristic emission as distorted by the Rhodamine absorption [11], which is peaked at 560 nm. In NE102 films, the typical emission bands of the dye molecules dispersed into PVT are observed: namely the p-T band at 340 nm and the POPOP band at 420 nm (Fig. 2b, fluence ¼ 4.3E12 ions/cm2). As compared to the pure PVT film, the 320 nm band does not appear. This fact can be explained by the good energy transfer between the PVT emission peak and the p-T absorption band. An estimation of the radiation hardness of the plastic films has been obtained by analysing the decay of the intensity of IBIL spectra as a function of the irradiation fluence. In the following, each IBIL spectrum is normalised to the charge collected during its acquisition, which is proportional to the number of impinging ions, and to the intensity of the first spectrum. In this work, we focus our attention on the evolution of the ‘‘intrinsic’’ and dye bands of the composite films, while the behaviour of the 500 nm band and of the related shoulder, due to the formation of new luminescent structures in PVT and NE102 has not been considered. All the bands related to the host intrinsic emission and to the dispersed dye luminescence present a monotonically decreasing trend with the irradiation fluence. The normalised integral of the dye bands (i.e. the sum of p-T at 340 nm and POPOP at 420 nm for NE102, and the RB band for RB6FDA-DAB) is presented in Fig. 3a as a function of the
Fig. 1. IBIL spectra of pure 6FDA-DAB (a) and of pure PVT (b).
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
277
Fig. 2. IBIL spectra of the composite RB-6FDA-DAB (a) and of the traditional NE102 plastic scintillator (b). Arrows mark the scintillation bands characterising the samples.
irradiation fluence. The normalised integral relative to the intrinsic luminescence of PVT and 6FDA-DAB matrix is reported in Fig. 3b. The intensity of both RB and pT þ POPOP bands shows a fast decay at increasing fluence up to 5 1013 ions/cm2, and then a slower decay for higher
irradiation fluences. As can be seen, the relative lowering of the RB band is slower than the decrease of the p-T þ POPOP signal, indicating a greater radiation hardness of the RB6FDA-DAB composite with respect to the NE102 reference material. In particular, when the irradiation fluence is
Fig. 3. Normalised scintillation intensities of the composite films (a) and of the pure matrices (b) as a function of the fluence. The fitting lines are obtained by applying Eq. (1).
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A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
Fig. 4. Relative scintillation intensity of the RB-6FDA-DAB sample with respect to the dye bands of NE102 (~) and to the total NE102 emitted light (*), as a function of the irradiation fluence.
5 1014 ions/cm2, the light emitted from RB dye lowered at 4% of the initial value, and the p-T þ POPOP dye system showed a decrease down to 1% of the initial intensity. The same behaviour is presented by the bands of the PVT and 6FDA-DAB matrices: at the same irradiation fluence the light intensity of pure 6FDA-DAB is the 14% of the initial value, while for PVT it is only 0.4%. The normalised intensities of IBIL spectra as a function of the fluence are well fitted by a second order exponential decay function: IðFÞ ¼ A0 þ Af expðsf FÞ þ As expðss FÞ
(1)
in which A0, Af and As are fitting constants, sf and ss are the ‘‘fast’’ and ‘‘slow’’ damage cross-section (expressed in cm2/ion). The radiation damage cross-sections sf and ss give a quantitative estimation of the radiation hardness of the material. In Table 1, the damage cross-sections are reported. As can be seen, the ‘‘slow’’ radiation damage cross-section of doped and undoped 6FDA-DAB are smaller than the PVT-based systems, indicating a higher radiation hardness Table 1 Damage cross-sections of the irradiated samples, obtained with the fitting function reported in Eq. (1) Sample
PVT 6FDA-DAB NE102 (p-T þ POPOP) RB-6FDA-DAB
of the polyimide-based scintillator. Concerning the ‘‘fast’’ cross-section, all the values are quite similar, with the exception of pure 6FDA-DAB, which is about three times lower than the RB-doped polyimide. From a comparison between the doped and undoped materials, it can be seen that in PVT-based systems, the dye emission seems to decay slower with fluence with respect to pure PVT. The opposite behaviour is observed for doped and undoped 6FDA-DAB. This is probably due to the radiation induced decomposition of RB, whose hardness is considerably lower than the polyimide matrix. To give an indication of the scintillation efficiency of RB-6FDA-DAB with respect to NE102, in Fig. 4 is reported the ratio between the IBIL intensity of RB and p-T þ POPOP dye bands versus fluence, and the ratio between RB and the total light in NE102, which also takes into account the luminescence of the 550 nm band. The intensities are normalised to the collected fluence and to the film thickness. As a consequence of the higher radiation hardness of the RB-6FDA-DAB, its scintillation efficiency relative to NE102 grows at increasing fluence. At a fluence of 5 1014 ions/cm2 a ratio of 33% is reached between RB and the p-T/POPOP dye system, and a ratio of 6.5% between RB and the total light from NE102.
IBIL ss
sf
As
Af
A0
5.0E14 0.4E14 2.9E14 1.1E14
2.63E13 9.3E14 2.17E13 2.56E13
0.28 0.54 0.17 0.23
1.19 0.5 1.24 0.99
0.03 0.05 0.02 0.05
4. Conclusions New radiation resistant thin films were produced and tested. A quantitative measurement of the radiation hardness and of the scintillation efficiency of RB-6FDA-DAB and
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
NE102 traditional scintillating films was performed by means of the IBIL technique. The new material demonstrated its highly enhanced radiation hardness, and its good scintillation efficiency for high irradiation fluences. Two improvements for polyimide-based scintillators can be suggested for further investigations: the enhancement of radiation hardness could be reached by dispersing into the polymer a more radiation resistant dye molecule, while higher scintillation efficiency can be obtained by improving the energy transfer process between the polyimide matrix and the dispersed dye molecule.
Acknowledgements The Fifth Commission of Istituto Nazionale di Fisica Nucleare financially supported this research.
279
References [1] I.J. Yeo, C.-K-C. Wang, S.E. Burch, Phys. Med. Biol. 44 (1999) 3055. [2] L. Torrisi, Nucl. Inst. Meth. B 170 (2000) 523. [3] W. Busjan, K. Wick, T. Zoufal, Nucl. Inst. Meth. B 151 (1999) 434. [4] S. Usuda, Nucl. Inst. Meth. A 356 (1995) 334. [5] V.G. Senchishin, F. Markley, V.N. Lebedev, V.E. Kovtun, V.S. Koba, A.V. Kuznichenko, V.D. Tizkaja, J.A. Budagov, G. Bellettini, V.P. Seminozhenko, I.I. Zalubovsky, I.E. Chirikov-Zorin, Nucl. Inst. Meth. A 364 (1995) 253. [6] W. Busjan, K. Wick, T. Zoufal, Nucl. Inst. Meth. B 151 (1999) 434. [7] E.H. Lee, Nucl. Inst. Meth. B 151 (1999) 29–41. [8] A. Quaranta, S. Carturan, G. Maggioni, P.M. Milazzo, U. Abbondanno, G. Della Mea, F. Gramegna, U. Pieri, IEEE Trans. Nucl. Sci. 48 (2) (2001) 219. [9] L. Calcagno, G. Foti, Nucl. Inst. Meth. B 65 (1992) 413. [10] G. Marletta, Nucl. Inst. Meth. B 46 (1990) 295. [11] A. Quaranta, S. Carturan, G. Maggioni, G. Della Mea, M. Ischia, R. Campostrini, Appl. Phys. A 72 (2001) 671.
New high radiation resistant scintillating thin films A. Quarantaa,b, A. Vomieroa,b,*, S. Carturana,c, G. Maggionib, G. Della Meaa,b a
b
Dipartimento di Ingegneria dei Materiali, Universita` di Trento, Via Mesiano 77, 38050 Trento, Italy Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Legnaro, Via Romea 4, 35202 Legnaro, PD, Italy c Dipartimento di Fisica, Universita` di Trento, Via Sommarive 14, 38050 Povo, TN, Italy
Abstract New scintillating thin films with improved radiation hardness were synthesised for applications in the field of radiation monitoring, by dispersing Rhodamine B (RB) dye into a high radiation resistant polymeric matrix (6FDA-DAB polyimide). The radiation hardness and the scintillation efficiency of this new composite material were tested by means of ion beam induced luminescence (IBIL) and compared to thin films of the traditional NE102 plastic scintillator. The samples were irradiated by 2.0 MeV 4 Heþ ion beam at fluences ranging between 1012 and 1015 ions/cm2. IBIL results indicated that the polyimide-based scintillator has a better radiation hardness and a good scintillation efficiency for high doses irradiations. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Plastic scintillators; Dye; Radiation hardness; Ion beam induced luminescence
1. Introduction Thin film plastic scintillators play a crucial role in many fields of radiation detection, such as dosimetry measurements in medicine [1], radiation monitoring in high intensity beams [2,3], simultaneous counting of different radiations [4]. The degradation of the luminescence properties of the detectors, as due to the induced radiation damage, makes the continuous dose monitoring at increasing irradiation fluence a very difficult task. This degradation is particularly pronounced in high radiation environments, where the scintillators undergo high radiation fluxes. For this reason, one of the main goals in the synthesis of the scintillating materials is to obtain enhanced radiation hardness in order to guarantee an accurate light calibration over a wide range of radiation fluence [5]. In the last few years particular interest has been devoted to the characterisation of the scintillation properties of plastic scintillators under high radiation fluxes [6] and a description of the time evolution of the light emission has been attempted. The evolution can give meaningful information both on the damage of the polymeric structure as induced by scission processes and on the growth of new structures owing to the cross-linking of chemically active radicals [7] which are formed during irradiation. In this work the luminescence properties of a new Rhodamine * Corresponding author. Tel.: þ39-049-8068-406; fax: þ39-049-641925. E-mail address: [email protected] (A. Vomiero).
B (RB) doped polyimide thin film were investigated by using ion beam induced luminescence (IBIL) analysis. A comparison with the properties of a standard polyvinyltoluene (PVT) plastic scintillator (NE102 or BC400 from Bicron) was also performed. All the tested samples were irradiated by a 2.0 MeV 4 Heþ beam.
2. Experimental Thin films of pure polyimide 4,40 -hexafluoroisopropylidene diphthalic anhydride-4,40 -diaminobenzophenone (6FDA-DAB), RB doped polyimide (RB-6FDA-DAB), pure PVT and NE102 were deposited on silicon substrates. NE102 and PVT films were obtained by dissolution of bulk plastics into toluene and by spinning the solution onto the substrates (2000 rpm for 20 ). The preparation details of polyimide-based samples are reported elsewhere [8]. Film thickness (ranging from 2 to 6 mm) was measured with a stylus profilometer (TALISTEP). Ion irradiation was performed at the 2.5 MV Van de Graaff accelerator of the INFN Laboratori Nazionali di Legnaro. An 4 Heþ beam (2.0 MeV) was used in IBIL analyses. The beam spot size was about 10 mm2 and the beam current was not higher than 10 nA/mm2 in order to prevent sample heating. Each IBIL spectrum was collected within fluence intervals of about 1012 to 1013 ions/cm2, corresponding to a typical collection time of a few seconds. The study of the time evolution of the light
0379-6779/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(02)01287-0
276
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
emission in the fluence range 1 1014 to 5 1014 ions/cm2 was performed by interposing irradiation steps of about 1 1014 ions/cm2 between two consecutive IBIL spectra. The light emitted from the films was collected during the irradiation by a four silica lenses optical system and focussed on a silica fibre bundle connected to an Acton optical spectrometer. The light was dispersed by a 150 g/mm grating on a nitrogen cooled Princeton CCD detector, equipped with an array of 1340 100 pixels, 20 20 mm2 each one. Every spectrum was corrected taking into account the spectral response of the entire acquisition system.
3. Results and discussion IBIL spectra of 6FDA-DAB (fluence ¼ 4.5E12 ions/cm2) and PVT (fluence ¼ 3E12 ions/cm2) irradiated with 4 Heþ ions are reported in Fig. 1a and b, respectively. The 6FDADAB matrix exhibits a broad band centred at about 550 nm, whose shape does not change during irradiation and whose intensity decreases at increasing fluence. The pure PVT IBIL spectrum shows a very different behaviour: a narrow band centred at about 320 nm is ascribed to the intrinsic luminescence of the PVT, together with a luminescence band centred at about 500 nm. A shoulder appears at lower wavelength in the 500 nm band, which grows up as the fluence increases. The 500 nm band and the related shoulder could be attributed to aggregates of phenyl radicals similar to amorphous hydrogenated carbon clusters, already observed in irradiated polystyrene, whose structure is very similar to PVT [9,10].
The typical RB-6FDA-DAB IBIL spectrum (Fig. 2a, fluence ¼ 4.3E12 ions/cm2) exhibits an intense band centred at 590 nm, a smaller band at about 700 nm and a third broader band at 490 nm. The features at 590 and 700 nm are due to the RB molecules dispersed into the matrix, while the band at 490 nm is the polymer characteristic emission as distorted by the Rhodamine absorption [11], which is peaked at 560 nm. In NE102 films, the typical emission bands of the dye molecules dispersed into PVT are observed: namely the p-T band at 340 nm and the POPOP band at 420 nm (Fig. 2b, fluence ¼ 4.3E12 ions/cm2). As compared to the pure PVT film, the 320 nm band does not appear. This fact can be explained by the good energy transfer between the PVT emission peak and the p-T absorption band. An estimation of the radiation hardness of the plastic films has been obtained by analysing the decay of the intensity of IBIL spectra as a function of the irradiation fluence. In the following, each IBIL spectrum is normalised to the charge collected during its acquisition, which is proportional to the number of impinging ions, and to the intensity of the first spectrum. In this work, we focus our attention on the evolution of the ‘‘intrinsic’’ and dye bands of the composite films, while the behaviour of the 500 nm band and of the related shoulder, due to the formation of new luminescent structures in PVT and NE102 has not been considered. All the bands related to the host intrinsic emission and to the dispersed dye luminescence present a monotonically decreasing trend with the irradiation fluence. The normalised integral of the dye bands (i.e. the sum of p-T at 340 nm and POPOP at 420 nm for NE102, and the RB band for RB6FDA-DAB) is presented in Fig. 3a as a function of the
Fig. 1. IBIL spectra of pure 6FDA-DAB (a) and of pure PVT (b).
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
277
Fig. 2. IBIL spectra of the composite RB-6FDA-DAB (a) and of the traditional NE102 plastic scintillator (b). Arrows mark the scintillation bands characterising the samples.
irradiation fluence. The normalised integral relative to the intrinsic luminescence of PVT and 6FDA-DAB matrix is reported in Fig. 3b. The intensity of both RB and pT þ POPOP bands shows a fast decay at increasing fluence up to 5 1013 ions/cm2, and then a slower decay for higher
irradiation fluences. As can be seen, the relative lowering of the RB band is slower than the decrease of the p-T þ POPOP signal, indicating a greater radiation hardness of the RB6FDA-DAB composite with respect to the NE102 reference material. In particular, when the irradiation fluence is
Fig. 3. Normalised scintillation intensities of the composite films (a) and of the pure matrices (b) as a function of the fluence. The fitting lines are obtained by applying Eq. (1).
278
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
Fig. 4. Relative scintillation intensity of the RB-6FDA-DAB sample with respect to the dye bands of NE102 (~) and to the total NE102 emitted light (*), as a function of the irradiation fluence.
5 1014 ions/cm2, the light emitted from RB dye lowered at 4% of the initial value, and the p-T þ POPOP dye system showed a decrease down to 1% of the initial intensity. The same behaviour is presented by the bands of the PVT and 6FDA-DAB matrices: at the same irradiation fluence the light intensity of pure 6FDA-DAB is the 14% of the initial value, while for PVT it is only 0.4%. The normalised intensities of IBIL spectra as a function of the fluence are well fitted by a second order exponential decay function: IðFÞ ¼ A0 þ Af expðsf FÞ þ As expðss FÞ
(1)
in which A0, Af and As are fitting constants, sf and ss are the ‘‘fast’’ and ‘‘slow’’ damage cross-section (expressed in cm2/ion). The radiation damage cross-sections sf and ss give a quantitative estimation of the radiation hardness of the material. In Table 1, the damage cross-sections are reported. As can be seen, the ‘‘slow’’ radiation damage cross-section of doped and undoped 6FDA-DAB are smaller than the PVT-based systems, indicating a higher radiation hardness Table 1 Damage cross-sections of the irradiated samples, obtained with the fitting function reported in Eq. (1) Sample
PVT 6FDA-DAB NE102 (p-T þ POPOP) RB-6FDA-DAB
of the polyimide-based scintillator. Concerning the ‘‘fast’’ cross-section, all the values are quite similar, with the exception of pure 6FDA-DAB, which is about three times lower than the RB-doped polyimide. From a comparison between the doped and undoped materials, it can be seen that in PVT-based systems, the dye emission seems to decay slower with fluence with respect to pure PVT. The opposite behaviour is observed for doped and undoped 6FDA-DAB. This is probably due to the radiation induced decomposition of RB, whose hardness is considerably lower than the polyimide matrix. To give an indication of the scintillation efficiency of RB-6FDA-DAB with respect to NE102, in Fig. 4 is reported the ratio between the IBIL intensity of RB and p-T þ POPOP dye bands versus fluence, and the ratio between RB and the total light in NE102, which also takes into account the luminescence of the 550 nm band. The intensities are normalised to the collected fluence and to the film thickness. As a consequence of the higher radiation hardness of the RB-6FDA-DAB, its scintillation efficiency relative to NE102 grows at increasing fluence. At a fluence of 5 1014 ions/cm2 a ratio of 33% is reached between RB and the p-T/POPOP dye system, and a ratio of 6.5% between RB and the total light from NE102.
IBIL ss
sf
As
Af
A0
5.0E14 0.4E14 2.9E14 1.1E14
2.63E13 9.3E14 2.17E13 2.56E13
0.28 0.54 0.17 0.23
1.19 0.5 1.24 0.99
0.03 0.05 0.02 0.05
4. Conclusions New radiation resistant thin films were produced and tested. A quantitative measurement of the radiation hardness and of the scintillation efficiency of RB-6FDA-DAB and
A. Quaranta et al. / Synthetic Metals 138 (2003) 275–279
NE102 traditional scintillating films was performed by means of the IBIL technique. The new material demonstrated its highly enhanced radiation hardness, and its good scintillation efficiency for high irradiation fluences. Two improvements for polyimide-based scintillators can be suggested for further investigations: the enhancement of radiation hardness could be reached by dispersing into the polymer a more radiation resistant dye molecule, while higher scintillation efficiency can be obtained by improving the energy transfer process between the polyimide matrix and the dispersed dye molecule.
Acknowledgements The Fifth Commission of Istituto Nazionale di Fisica Nucleare financially supported this research.
279
References [1] I.J. Yeo, C.-K-C. Wang, S.E. Burch, Phys. Med. Biol. 44 (1999) 3055. [2] L. Torrisi, Nucl. Inst. Meth. B 170 (2000) 523. [3] W. Busjan, K. Wick, T. Zoufal, Nucl. Inst. Meth. B 151 (1999) 434. [4] S. Usuda, Nucl. Inst. Meth. A 356 (1995) 334. [5] V.G. Senchishin, F. Markley, V.N. Lebedev, V.E. Kovtun, V.S. Koba, A.V. Kuznichenko, V.D. Tizkaja, J.A. Budagov, G. Bellettini, V.P. Seminozhenko, I.I. Zalubovsky, I.E. Chirikov-Zorin, Nucl. Inst. Meth. A 364 (1995) 253. [6] W. Busjan, K. Wick, T. Zoufal, Nucl. Inst. Meth. B 151 (1999) 434. [7] E.H. Lee, Nucl. Inst. Meth. B 151 (1999) 29–41. [8] A. Quaranta, S. Carturan, G. Maggioni, P.M. Milazzo, U. Abbondanno, G. Della Mea, F. Gramegna, U. Pieri, IEEE Trans. Nucl. Sci. 48 (2) (2001) 219. [9] L. Calcagno, G. Foti, Nucl. Inst. Meth. B 65 (1992) 413. [10] G. Marletta, Nucl. Inst. Meth. B 46 (1990) 295. [11] A. Quaranta, S. Carturan, G. Maggioni, G. Della Mea, M. Ischia, R. Campostrini, Appl. Phys. A 72 (2001) 671.