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Scintillation characteristics of LiB3O5 and β-BaB2O4 single crystals
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553 www.elsevier.com/locate/nima
Scintillation characteristics of LiB3O5 and b-BaB2O4 single crystals B.P. Nazarenkoa, V.Yu. Pedashb, A.N. Shekhovtsova,, V.A. Tarasovb, O.V. Zelenskayab a
Institute for Single Crystals, NAS of Ukraine, Lenin Ave. 60, Kharkov, Ukraine, 61001 Institute for Scintillation Materials, NAS of Ukraine, Lenin Ave. 60, Kharkov, Ukraine, 61001
b
Received 28 October 2005; received in revised form 29 November 2005; accepted 1 December 2005 Available online 27 December 2005
Abstract LiB3O5 and b-BaB2O4 single crystals have been grown by the top seeded solution growth technique. The optical characteristics and scintillation parameters of the grown single crystals have been tested and discussed. r 2005 Elsevier B.V. All rights reserved. PACS: 29.40.M Keywords: Borate single crystal; Scintillator
1. Introduction Borate single crystals are attractive, mainly for neutron detectors because of the great number of boron atoms per unit cell, the large thermal neutron capture cross-section of 10 B isotope and the high-energy release per absorbed neutron (10B(n,a)7Li reaction). The presence of Li atoms in the borate matrices makes possible, also to use the reaction 6 Li(n,a)T neutron recording. We can use the resonant absorption of neutron by some nuclei of Ba for neutron detection too (for example: there are a number of neutron absorption resonances of 136Ba beginning from 3 102 eV). This paper continues the scintillation characteristic investigations of boron containing crystals [1]. The scintillation characteristics of LiB3O5 (LTB) and b-BaB2O4 (BBO) single crystals were measured and discussed.
2. Experimental Li2CO3, BaCO3 and H3BO3 (99.99% purity grade) were used as the initial components. LTB and BBO single crystals were grown by the top seeded solution growth technique in platinum crucibles under air. The growth of LTB and BBO single crystals was carried out from Corresponding author. Tel./fax: +38 057 340 9343.
E-mail address: [email protected] (A.N. Shekhovtsov). 0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.12.001
Li2O–B2O3 (10–90%) and BaB2O4–Na2O (80–20%) melts, respectively. To relax the thermoelatic stresses the crystals were held over the melt and then cooled down slowly to the room temperature within the furnace. The temperature in the operating zone was controlled within 70.5 K. The main crystallographic parameters of the crystals corresponded to the data on LTB [2] and BBO [3]. The polished 7(dia.) 2 mm3 LTB and BBO samples were prepared for optical and scintillation characteristic measurements. The scintillation parameters of the single crystals, namely, light yield S and amplitude resolution R were determined using a standard spectrophotometric setup consisting of a BUS2-94 preamplifier, a BUI-3K linear amplifier and an AMA-03-F multichannel pulse amplitude analyzer. A HAMAMATSU R1307 photomultiplier with 3 in. photocathode diameter was used as the photoreceiver. To excite the scintillations, a 238Pu (E a ¼ 5:5 MeV) radiation source was used with a multihole collimator to avoid the side emission effect. The profiles of decay components were measured by the single photon method (delayed coincidence method [4]) under scintillation excitation by annihilation g-quanta from a 22Na source. 3. Results and discussion The long-wave edge of LTB crystal fundamental absorption is located at l ¼ 160 nm. Under excitation in
ARTICLE IN PRESS 552
B.P. Nazarenko et al. / Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553
Fig. 1. Normalized X-ray luminescence spectra of (1) LiB3O5 and (2) bBaB2O4 single crystals.
this region, LTB crystals exhibit luminescence with a maximum at l ¼ 280 nm (Fig. 1, curve 1). The detail description of LTB emission nature is given in Ref. [5]. It was considered that a ‘‘molecular type’’ exciton exists due to transitions between different molecular orbitals of the anionic group, which forms the top of valence band and bottom of conductive band. The relaxation, self-trapping and dissociation of excitons were already studied in Ref. [5]. We observed LTB crystal radioluminescence decay with to10 ns emission at room temperature. It is in consistency with the data of [5] (t ¼ 8:8 ns). The light yield for LTB single crystals is about 700 photons/MeV. The pulse amplitude spectrum for LTB crystals obtained under excitation by 5.5 MeV a-particles from a 238Pu source is presented in Fig. 2. The resolution Ra is 33%. The long-wave edge of BBO crystal fundamental absorption is located at l ¼ 190 nm. At X-ray excitation BBO crystals show luminescence with a maximum at l ¼ 400 nm (Fig. 1, curve 2). Unfortunately, the structure of optic centres in BBO crystals is unknown. Authors of Ref. [6] were supposed that BBO crystal emission is connected to radiative relaxation of ‘‘exciton like’’ excitations. It is quite likely self-trapped excitons. The observed emission at room temperature is characterized by a fast component lying at to10 ns. The light yield for BBO crystals is low (approximately 50 photons/MeV). The pulse amplitude spectrum for BBO crystals obtained under excitation by 5.5 MeV a-particles from a 238Pu source is presented in Fig. 3. The characteristics of LTB and BBO single crystals are presented in Table 1. Both LTB and BBO crystals have not shown high Va/Vg value (the ratio of pulse amplitudes normalized to the excitation energy) what is typical for borate crystals [1]. Some features of the studied crystals are worth to be noted. LTB crystals own low density r, and Zeff values, thus their sensitivity to g-quanta is rather low and close one
Fig. 2. Pulse (E a ¼ 5:5 MeV,
amplitude spectrum Pu; Ra ¼ 33%).
of
LiB3O5
single
crystals
b-BaB2O4
single
crystals
238
Fig. 3. Pulse amplitude (E a ¼ 5:5 MeV, 238Pu).
spectrum
of
for Li2B4O7:Cu crystal. However, light yield of Li2B4O7:Cu crystal is lower (about 500 photons/MeV) and the scintillation pulse decay consists of few slow components defining the main part of the light yield and lying at t410 ms range [1]. Moreover, both LTB and BBO crystals are not hygroscopic. 4. Conclusions The scintillation characteristics of LTB and BBO single crystals were tested and discussed. The light yield of LTB and BBO crystals is not high and equals 700 and 50 photons/MeV, respectively. The emission decay for both LTB and BBO crystals is characterised by a fast component less than 10 ns.
ARTICLE IN PRESS B.P. Nazarenko et al. / Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553
553
Table 1 Characteristics of LiB3O5 and b-BaB2O4 single crystals
LiB3O5 b-BaB2O4
lem (nm)
S (photon/MeV)
t (ns)
Va/Vg
Zeff
r (g/cm3)
Hygroscopicity
280 400
700 50
o10 o10
0.3 0.3
7.3 47
2.47 3.83
No No
References [1] V.V. Chernikov, M.F. Dubovik, V.P. Gavrylyuk, et al., Nucl. Instr. and Meth. A498 (2003) 424. [2] J. Krogh-Moe, Acta Cryst. B 24 (1962) 179. [3] D. Eimerl, L. Davis, S. Velsko, et al., J. Appl. Phys. 62 (1987) 1968.
[4] N.Z. Galunov, I.V. Kopina, L.I. Mitsay, Yu.A. Tsyrlin, Pribory Tekhn. Eksper. 4 (1983) 81 (in Russian). [5] I.N. Ogorodnikov, V.A. Pustovarov, M. Kirm, et al., Phys. Solid State 43 (2001) 1396. [6] Ya.A. Valbis, L.I. Ivleva, Yu.S. Kuzminov, et al., Optika i Spectroskopiya 66 (1989) 308 (in Russian).
Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553 www.elsevier.com/locate/nima
Scintillation characteristics of LiB3O5 and b-BaB2O4 single crystals B.P. Nazarenkoa, V.Yu. Pedashb, A.N. Shekhovtsova,, V.A. Tarasovb, O.V. Zelenskayab a
Institute for Single Crystals, NAS of Ukraine, Lenin Ave. 60, Kharkov, Ukraine, 61001 Institute for Scintillation Materials, NAS of Ukraine, Lenin Ave. 60, Kharkov, Ukraine, 61001
b
Received 28 October 2005; received in revised form 29 November 2005; accepted 1 December 2005 Available online 27 December 2005
Abstract LiB3O5 and b-BaB2O4 single crystals have been grown by the top seeded solution growth technique. The optical characteristics and scintillation parameters of the grown single crystals have been tested and discussed. r 2005 Elsevier B.V. All rights reserved. PACS: 29.40.M Keywords: Borate single crystal; Scintillator
1. Introduction Borate single crystals are attractive, mainly for neutron detectors because of the great number of boron atoms per unit cell, the large thermal neutron capture cross-section of 10 B isotope and the high-energy release per absorbed neutron (10B(n,a)7Li reaction). The presence of Li atoms in the borate matrices makes possible, also to use the reaction 6 Li(n,a)T neutron recording. We can use the resonant absorption of neutron by some nuclei of Ba for neutron detection too (for example: there are a number of neutron absorption resonances of 136Ba beginning from 3 102 eV). This paper continues the scintillation characteristic investigations of boron containing crystals [1]. The scintillation characteristics of LiB3O5 (LTB) and b-BaB2O4 (BBO) single crystals were measured and discussed.
2. Experimental Li2CO3, BaCO3 and H3BO3 (99.99% purity grade) were used as the initial components. LTB and BBO single crystals were grown by the top seeded solution growth technique in platinum crucibles under air. The growth of LTB and BBO single crystals was carried out from Corresponding author. Tel./fax: +38 057 340 9343.
E-mail address: [email protected] (A.N. Shekhovtsov). 0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.12.001
Li2O–B2O3 (10–90%) and BaB2O4–Na2O (80–20%) melts, respectively. To relax the thermoelatic stresses the crystals were held over the melt and then cooled down slowly to the room temperature within the furnace. The temperature in the operating zone was controlled within 70.5 K. The main crystallographic parameters of the crystals corresponded to the data on LTB [2] and BBO [3]. The polished 7(dia.) 2 mm3 LTB and BBO samples were prepared for optical and scintillation characteristic measurements. The scintillation parameters of the single crystals, namely, light yield S and amplitude resolution R were determined using a standard spectrophotometric setup consisting of a BUS2-94 preamplifier, a BUI-3K linear amplifier and an AMA-03-F multichannel pulse amplitude analyzer. A HAMAMATSU R1307 photomultiplier with 3 in. photocathode diameter was used as the photoreceiver. To excite the scintillations, a 238Pu (E a ¼ 5:5 MeV) radiation source was used with a multihole collimator to avoid the side emission effect. The profiles of decay components were measured by the single photon method (delayed coincidence method [4]) under scintillation excitation by annihilation g-quanta from a 22Na source. 3. Results and discussion The long-wave edge of LTB crystal fundamental absorption is located at l ¼ 160 nm. Under excitation in
ARTICLE IN PRESS 552
B.P. Nazarenko et al. / Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553
Fig. 1. Normalized X-ray luminescence spectra of (1) LiB3O5 and (2) bBaB2O4 single crystals.
this region, LTB crystals exhibit luminescence with a maximum at l ¼ 280 nm (Fig. 1, curve 1). The detail description of LTB emission nature is given in Ref. [5]. It was considered that a ‘‘molecular type’’ exciton exists due to transitions between different molecular orbitals of the anionic group, which forms the top of valence band and bottom of conductive band. The relaxation, self-trapping and dissociation of excitons were already studied in Ref. [5]. We observed LTB crystal radioluminescence decay with to10 ns emission at room temperature. It is in consistency with the data of [5] (t ¼ 8:8 ns). The light yield for LTB single crystals is about 700 photons/MeV. The pulse amplitude spectrum for LTB crystals obtained under excitation by 5.5 MeV a-particles from a 238Pu source is presented in Fig. 2. The resolution Ra is 33%. The long-wave edge of BBO crystal fundamental absorption is located at l ¼ 190 nm. At X-ray excitation BBO crystals show luminescence with a maximum at l ¼ 400 nm (Fig. 1, curve 2). Unfortunately, the structure of optic centres in BBO crystals is unknown. Authors of Ref. [6] were supposed that BBO crystal emission is connected to radiative relaxation of ‘‘exciton like’’ excitations. It is quite likely self-trapped excitons. The observed emission at room temperature is characterized by a fast component lying at to10 ns. The light yield for BBO crystals is low (approximately 50 photons/MeV). The pulse amplitude spectrum for BBO crystals obtained under excitation by 5.5 MeV a-particles from a 238Pu source is presented in Fig. 3. The characteristics of LTB and BBO single crystals are presented in Table 1. Both LTB and BBO crystals have not shown high Va/Vg value (the ratio of pulse amplitudes normalized to the excitation energy) what is typical for borate crystals [1]. Some features of the studied crystals are worth to be noted. LTB crystals own low density r, and Zeff values, thus their sensitivity to g-quanta is rather low and close one
Fig. 2. Pulse (E a ¼ 5:5 MeV,
amplitude spectrum Pu; Ra ¼ 33%).
of
LiB3O5
single
crystals
b-BaB2O4
single
crystals
238
Fig. 3. Pulse amplitude (E a ¼ 5:5 MeV, 238Pu).
spectrum
of
for Li2B4O7:Cu crystal. However, light yield of Li2B4O7:Cu crystal is lower (about 500 photons/MeV) and the scintillation pulse decay consists of few slow components defining the main part of the light yield and lying at t410 ms range [1]. Moreover, both LTB and BBO crystals are not hygroscopic. 4. Conclusions The scintillation characteristics of LTB and BBO single crystals were tested and discussed. The light yield of LTB and BBO crystals is not high and equals 700 and 50 photons/MeV, respectively. The emission decay for both LTB and BBO crystals is characterised by a fast component less than 10 ns.
ARTICLE IN PRESS B.P. Nazarenko et al. / Nuclear Instruments and Methods in Physics Research A 558 (2006) 551–553
553
Table 1 Characteristics of LiB3O5 and b-BaB2O4 single crystals
LiB3O5 b-BaB2O4
lem (nm)
S (photon/MeV)
t (ns)
Va/Vg
Zeff
r (g/cm3)
Hygroscopicity
280 400
700 50
o10 o10
0.3 0.3
7.3 47
2.47 3.83
No No
References [1] V.V. Chernikov, M.F. Dubovik, V.P. Gavrylyuk, et al., Nucl. Instr. and Meth. A498 (2003) 424. [2] J. Krogh-Moe, Acta Cryst. B 24 (1962) 179. [3] D. Eimerl, L. Davis, S. Velsko, et al., J. Appl. Phys. 62 (1987) 1968.
[4] N.Z. Galunov, I.V. Kopina, L.I. Mitsay, Yu.A. Tsyrlin, Pribory Tekhn. Eksper. 4 (1983) 81 (in Russian). [5] I.N. Ogorodnikov, V.A. Pustovarov, M. Kirm, et al., Phys. Solid State 43 (2001) 1396. [6] Ya.A. Valbis, L.I. Ivleva, Yu.S. Kuzminov, et al., Optika i Spectroskopiya 66 (1989) 308 (in Russian).