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Electroluminescence gas-filled detector with a build-in photocell
ARTICLE IN PRESS Nuclear Instruments and Methods in Physics Research A 603 (2009) 56–57
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Electroluminescence gas-filled detector with a build-in photocell Al.D. Goganov a, D.A. Goganov a,, A.A. Schultz b, A.A. Vazina c,d a
Elion Plus, Ltd./41-A, 11-H Liteiny Ave., 191014 S-Petersburg, Russia Bourevestnik Inc., 68 Malookhtinsky Ave., 195272 S-Petersburg, Russia Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia d Russian Research Center ‘‘Kurchatov Institute’’, Moscow, Russia b c
a r t i c l e in f o
a b s t r a c t
Available online 19 January 2009
The design and features of an experimental model of a GSPC detector—DELG with a build-in photocathode—are described. The energy resolution of 7.5% at 5.9 keV line is achieved. The overall dimensions of the detection unit based on the new developed detector are reduced by two times due to the exclusion of a photomultiplier from the body. It is proposed to test the new detector in experiments with synchrotron radiation both in spectrometric and in current modes. & 2009 Elsevier B.V. All rights reserved.
Keywords: Gas proportional scintillation detector Photocathode Energy resolution
In 1972 Portuguese researchers reported [1] on the creation of a gas-filled detector with the energy resolution almost double that of a proportional counter—500 eV (8.5%) at MnKa-line of radiation (5.9 eV). In the following years various modifications of GSPC (gas-filled proportional scintillation counters) have been designed for application in nuclear physics, cosmos, X-ray fluorescence and diffraction analysis. In particular, we succeeded [2,3] in designing a sealed-off GSPC—DELG (in Russian scientific literature the abbreviation DELG is used—Detector Electro Luminescence Gas-filled)—for use in X-ray fluorescence analysis. The DELG ensures resolution of X-ray radiation lines for Z, Z+2 elements in the Mendeleyev System. A detector with an entrance window of 20 mm in diameter and count rate of 5 104 c 1 has been manufactured by small-scale production at Bourevestnik Inc. Disadvantages of the existing detector unit based on DELG are large overall dimensions and power consumption due to the use of a photomultiplier, as well as complexity and brittleness of the construction itself. In the last years repeated attempts have been made [4] to replace the PMT by another sensitive element, in particular, microstrip plates coated with CsJ, as well as a large (16 mm diameter) avalanche photodiode. In this case a record value of energy resolution has been achieved—7.8% (5.9 eV). It should be noted that in all cases there were flow-type detectors using pure Xe. For the purpose of creating an efficient small-sized DELG we have made an attempt to design an experimental DELG with a build-in photocell. Fig. 1 shows a sketch of the construction of the new electroluminescent detector. The X-rays penetrate the detector’s body through 150 mm thick Be-window. The detector’s body is
Corresponding author. Fax: +7 812 442 60 78.
E-mail address: [email protected] (D.A. Goganov). 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.12.229
made of vacuum-tight ceramic. The Be-window is joined with the detector’s flange by means of thermodiffusion welding. Inside of the detector’s body there are two grid electrodes, which divide the detector’s volume into two functionally different parts—an absorption region (from the window to the first grid) and an electroluminescence region (intergrid space). The absorption region depth is 30 mm, the electroluminescence region depth is 10 mm. On the output of the gas space there is a MgF2-window. The detector’s construction is vacuum-tight and withstands a heating up to 300 1C. There is an outlet in the construction through which pumping-out is performed with subsequent filling of highly purified Xe and sealing of the counter. The principle of operation of the detector is as follows. Primary ionization electrons arising in the process of X-ray quanta detection rush under the action of applied potential to the intergrid space, where the electrical field is by an order of magnitude greater than that in the absorption region. High-speed electrons excite (without ionization) Xe-atoms in the process of collisions. As a result of triple collisions, molecules of Xe+2 arise which emit UV-quanta in the process of dissociation. UV-quanta (173 nm) exit the detector’s body through the MgF2-window. In the conventional design of the detector unit with DELG, the photomultiplier window (in our case usually FEU-39A is used) joins the MgF2-window. In the design described a photocell body (70 mm diameter, 80 mm length) made of stainless steel is welded on to the flange mounting MgF2. In the body there are glass bushings, through one of which the anode rod is introduced, while through the others pumping out of the photocell body and introducing of the photocathode sprayers are performed. Initially DELG and photocell volumes were pumped out up to high vacuum trough the common outlet when heating up to 300 1C, then the DELG volume was detached. In the photocell volume the sputtering of the photocathode was carried out, particularly K-Cs-antimonial cathode was sputtered (Fig. 1, dotted
ARTICLE IN PRESS A.D. Goganov et al. / Nuclear Instruments and Methods in Physics Research A 603 (2009) 56–57
57
- 5700 V Be window
- 4500 V
- 160 V MgF2 Fig. 2. X-ray spectrum of the isotope
0V
Photocell
Fig. 1. Schematic sketch of the DELG detector with a build-in photocathode.
line inside of the photocell volume). The sputtering modes are perfected initially on the test targets. After sputtering the photocell volume was detached from the vacuum system, while in the DELG volume Xe-leak-in was carried out under pressure nearly 1 atm. In the described design of the detector we succeeded in increasing essentially light collection of the DELG electroluminescence when avoiding absorption in air space between the DELG output window and the PMT entrance window, dispersion on the air—quartz boundary as well as absorption (up to 40%) in the entrance quartz window of the PMT. As a result of increased light collection and increasing of the convention factor of the photocathode, a value of charge collected on the photocell anode for any detected X-ray quantum was essentially increased in comparison to the charge falling in the first dynode of the PMT. Furthermore, contribution of the charge value to statistical amplitude spread of output pulses which limit the energy resolution of the detector as a whole was essentially reduced. At the same time, the charge value obtained from the photocell anode was found to be sufficient enough to exceed not less than 10 times the upper background threshold of the preamplifier on the MnK-line (Fig. 2). To measure the detector parameters a set of equipment was used which included a charge-sensitive preamplifier PK 801 (OUTOKUMPU) with a field-effect transistor on the input, high voltage power supply for the DELG, photocell power supply and low voltage power supply units. Special measures were taken to suppress the pulsation and pick-ups of both low voltage power supply of the preamplifier as well as the DELG and the photocell high voltage power supplies and the output pulsation of the high voltage power supply units. Amplification, forming and fixation of signals after preamplifier were performed on the multichannel analyzer LP 4900 (NOKIA). High voltage power supply of negative polarity with potentials 5.6 and 4.8 kV on the entrance window and the first grid accordingly was applied to the DELG. Negative potential of 160 V was applied to the photocell body connected with the second grid, at the same time the photocell anode was connected directly to the gate of the field-effect transistor of the preamplifier.
55
Fe.
Fig. 2 illustrates the spectrum of the Fe55 source (MnKa,b). At the MnKa-line energy resolution of 7.5% was achieved (diameter of the diaphragm on the entrance window is 3 mm, the count rate is 1 103 s 1). There are clear notable and well resolved Xe escape peaks with energies 1.47 and 1.78 keV. Resolution of 4.4% was obtained under the same conditions for AgKa-line (22 keV). In the range from 1.5 to 25 keV an energy linearity of the order of 1% was obtained. The long term stability of the amplitude at the constant count rate came after a one hour pause to approximately 1% within 6.5 hours, that is several times better than in case of using a PMT. Stability of average amplitude of output pulses of the whole detection section (without the use of a special stabilization system, as it is shown in Ref. [2]) of approximately 5% was achieved in the DELG input at multiple rushes of the count rate from 1 103 to 3 104 s 1. The achieved energy resolution level of 7.5% for 5.9 keV energy is limited by the self-resolution of the DELG (approximately 6%) and by noises of the detection section and can be improved in perspective by reduction of preamplifier noises and by increase of light collection in the photocell. An essentially smaller (107 and more times) value of charge collected on the photocell anode in comparison with that on the PMT anode (which operates at the minimum acceptable for spectrometry voltages) allows for a DELG equipped with a photocell to provide measurement of X-ray quanta flux from a synchrotron radiation source up to value 1010 s 1 when operating in the average current mode on the photocell anode. With this it is possible to go into the spectrometry mode with maximum energy resolution performance at the release of the count rate to 5 104 s 1. A small value of charge on the photocell anode and the use of a photocathode coated on a metallic substrate let us expect an increase of amplitude stability on the detector’s output at rushes of count rate in a spectrometry mode, assuming that conversion stability in the electron detection section is achieved. Integration of DELG and a photocell in one body increases vibrational load stability of the detector unit and at the same time reduces its overall dimensions by almost two times. The detector has shown the stable parameters within four years of testing. References [1] A.J.P.L. Policarpo, M.A.F. Alves, M.C.M. Dos Santos, M.J.T. Carvalho, Nucl. Instr. and Meth. 102 (1972) 337. [2] D.A. Goganov, A.A. Schultz, Nucl. Instr. and Meth. 394 (1997) 151. [3] D.A. Goganov, A.A. Schultz, X-ray Spectrom. 35 (2006) 47. [4] J.M.F. Dos Santos, et al., X-ray Spectrom. 30 (2001) 373.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Electroluminescence gas-filled detector with a build-in photocell Al.D. Goganov a, D.A. Goganov a,, A.A. Schultz b, A.A. Vazina c,d a
Elion Plus, Ltd./41-A, 11-H Liteiny Ave., 191014 S-Petersburg, Russia Bourevestnik Inc., 68 Malookhtinsky Ave., 195272 S-Petersburg, Russia Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia d Russian Research Center ‘‘Kurchatov Institute’’, Moscow, Russia b c
a r t i c l e in f o
a b s t r a c t
Available online 19 January 2009
The design and features of an experimental model of a GSPC detector—DELG with a build-in photocathode—are described. The energy resolution of 7.5% at 5.9 keV line is achieved. The overall dimensions of the detection unit based on the new developed detector are reduced by two times due to the exclusion of a photomultiplier from the body. It is proposed to test the new detector in experiments with synchrotron radiation both in spectrometric and in current modes. & 2009 Elsevier B.V. All rights reserved.
Keywords: Gas proportional scintillation detector Photocathode Energy resolution
In 1972 Portuguese researchers reported [1] on the creation of a gas-filled detector with the energy resolution almost double that of a proportional counter—500 eV (8.5%) at MnKa-line of radiation (5.9 eV). In the following years various modifications of GSPC (gas-filled proportional scintillation counters) have been designed for application in nuclear physics, cosmos, X-ray fluorescence and diffraction analysis. In particular, we succeeded [2,3] in designing a sealed-off GSPC—DELG (in Russian scientific literature the abbreviation DELG is used—Detector Electro Luminescence Gas-filled)—for use in X-ray fluorescence analysis. The DELG ensures resolution of X-ray radiation lines for Z, Z+2 elements in the Mendeleyev System. A detector with an entrance window of 20 mm in diameter and count rate of 5 104 c 1 has been manufactured by small-scale production at Bourevestnik Inc. Disadvantages of the existing detector unit based on DELG are large overall dimensions and power consumption due to the use of a photomultiplier, as well as complexity and brittleness of the construction itself. In the last years repeated attempts have been made [4] to replace the PMT by another sensitive element, in particular, microstrip plates coated with CsJ, as well as a large (16 mm diameter) avalanche photodiode. In this case a record value of energy resolution has been achieved—7.8% (5.9 eV). It should be noted that in all cases there were flow-type detectors using pure Xe. For the purpose of creating an efficient small-sized DELG we have made an attempt to design an experimental DELG with a build-in photocell. Fig. 1 shows a sketch of the construction of the new electroluminescent detector. The X-rays penetrate the detector’s body through 150 mm thick Be-window. The detector’s body is
Corresponding author. Fax: +7 812 442 60 78.
E-mail address: [email protected] (D.A. Goganov). 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.12.229
made of vacuum-tight ceramic. The Be-window is joined with the detector’s flange by means of thermodiffusion welding. Inside of the detector’s body there are two grid electrodes, which divide the detector’s volume into two functionally different parts—an absorption region (from the window to the first grid) and an electroluminescence region (intergrid space). The absorption region depth is 30 mm, the electroluminescence region depth is 10 mm. On the output of the gas space there is a MgF2-window. The detector’s construction is vacuum-tight and withstands a heating up to 300 1C. There is an outlet in the construction through which pumping-out is performed with subsequent filling of highly purified Xe and sealing of the counter. The principle of operation of the detector is as follows. Primary ionization electrons arising in the process of X-ray quanta detection rush under the action of applied potential to the intergrid space, where the electrical field is by an order of magnitude greater than that in the absorption region. High-speed electrons excite (without ionization) Xe-atoms in the process of collisions. As a result of triple collisions, molecules of Xe+2 arise which emit UV-quanta in the process of dissociation. UV-quanta (173 nm) exit the detector’s body through the MgF2-window. In the conventional design of the detector unit with DELG, the photomultiplier window (in our case usually FEU-39A is used) joins the MgF2-window. In the design described a photocell body (70 mm diameter, 80 mm length) made of stainless steel is welded on to the flange mounting MgF2. In the body there are glass bushings, through one of which the anode rod is introduced, while through the others pumping out of the photocell body and introducing of the photocathode sprayers are performed. Initially DELG and photocell volumes were pumped out up to high vacuum trough the common outlet when heating up to 300 1C, then the DELG volume was detached. In the photocell volume the sputtering of the photocathode was carried out, particularly K-Cs-antimonial cathode was sputtered (Fig. 1, dotted
ARTICLE IN PRESS A.D. Goganov et al. / Nuclear Instruments and Methods in Physics Research A 603 (2009) 56–57
57
- 5700 V Be window
- 4500 V
- 160 V MgF2 Fig. 2. X-ray spectrum of the isotope
0V
Photocell
Fig. 1. Schematic sketch of the DELG detector with a build-in photocathode.
line inside of the photocell volume). The sputtering modes are perfected initially on the test targets. After sputtering the photocell volume was detached from the vacuum system, while in the DELG volume Xe-leak-in was carried out under pressure nearly 1 atm. In the described design of the detector we succeeded in increasing essentially light collection of the DELG electroluminescence when avoiding absorption in air space between the DELG output window and the PMT entrance window, dispersion on the air—quartz boundary as well as absorption (up to 40%) in the entrance quartz window of the PMT. As a result of increased light collection and increasing of the convention factor of the photocathode, a value of charge collected on the photocell anode for any detected X-ray quantum was essentially increased in comparison to the charge falling in the first dynode of the PMT. Furthermore, contribution of the charge value to statistical amplitude spread of output pulses which limit the energy resolution of the detector as a whole was essentially reduced. At the same time, the charge value obtained from the photocell anode was found to be sufficient enough to exceed not less than 10 times the upper background threshold of the preamplifier on the MnK-line (Fig. 2). To measure the detector parameters a set of equipment was used which included a charge-sensitive preamplifier PK 801 (OUTOKUMPU) with a field-effect transistor on the input, high voltage power supply for the DELG, photocell power supply and low voltage power supply units. Special measures were taken to suppress the pulsation and pick-ups of both low voltage power supply of the preamplifier as well as the DELG and the photocell high voltage power supplies and the output pulsation of the high voltage power supply units. Amplification, forming and fixation of signals after preamplifier were performed on the multichannel analyzer LP 4900 (NOKIA). High voltage power supply of negative polarity with potentials 5.6 and 4.8 kV on the entrance window and the first grid accordingly was applied to the DELG. Negative potential of 160 V was applied to the photocell body connected with the second grid, at the same time the photocell anode was connected directly to the gate of the field-effect transistor of the preamplifier.
55
Fe.
Fig. 2 illustrates the spectrum of the Fe55 source (MnKa,b). At the MnKa-line energy resolution of 7.5% was achieved (diameter of the diaphragm on the entrance window is 3 mm, the count rate is 1 103 s 1). There are clear notable and well resolved Xe escape peaks with energies 1.47 and 1.78 keV. Resolution of 4.4% was obtained under the same conditions for AgKa-line (22 keV). In the range from 1.5 to 25 keV an energy linearity of the order of 1% was obtained. The long term stability of the amplitude at the constant count rate came after a one hour pause to approximately 1% within 6.5 hours, that is several times better than in case of using a PMT. Stability of average amplitude of output pulses of the whole detection section (without the use of a special stabilization system, as it is shown in Ref. [2]) of approximately 5% was achieved in the DELG input at multiple rushes of the count rate from 1 103 to 3 104 s 1. The achieved energy resolution level of 7.5% for 5.9 keV energy is limited by the self-resolution of the DELG (approximately 6%) and by noises of the detection section and can be improved in perspective by reduction of preamplifier noises and by increase of light collection in the photocell. An essentially smaller (107 and more times) value of charge collected on the photocell anode in comparison with that on the PMT anode (which operates at the minimum acceptable for spectrometry voltages) allows for a DELG equipped with a photocell to provide measurement of X-ray quanta flux from a synchrotron radiation source up to value 1010 s 1 when operating in the average current mode on the photocell anode. With this it is possible to go into the spectrometry mode with maximum energy resolution performance at the release of the count rate to 5 104 s 1. A small value of charge on the photocell anode and the use of a photocathode coated on a metallic substrate let us expect an increase of amplitude stability on the detector’s output at rushes of count rate in a spectrometry mode, assuming that conversion stability in the electron detection section is achieved. Integration of DELG and a photocell in one body increases vibrational load stability of the detector unit and at the same time reduces its overall dimensions by almost two times. The detector has shown the stable parameters within four years of testing. References [1] A.J.P.L. Policarpo, M.A.F. Alves, M.C.M. Dos Santos, M.J.T. Carvalho, Nucl. Instr. and Meth. 102 (1972) 337. [2] D.A. Goganov, A.A. Schultz, Nucl. Instr. and Meth. 394 (1997) 151. [3] D.A. Goganov, A.A. Schultz, X-ray Spectrom. 35 (2006) 47. [4] J.M.F. Dos Santos, et al., X-ray Spectrom. 30 (2001) 373.