A Gas Proportional Scintillation Counter based on a dual-cathode Microstrip Plate covered with a CsI film is described. This new dual-cathode technique has the advantage of increasing the VUV sensitive area of the Microstrip Plate. A detailed description of the technique is presented together with a discussion of the performance. The results obtained for a xenon filled Gas Proportional Scintillation Counter show an improvement of the energy resolution for 5.9 keV X-rays from 12.7%, for a single cathode device, to 11.1% for the dual-cathode devic

Freitas, Diogo S. A. P.

Silva, Rui M. Curado da

Mendes, Nuno F. C.

Conde, Carlos A. N.

University Marketing and Communications

Eastern Illinois University

Eastern Illinois UniversityThe Keep1994 Press Releases6-24-199406/24/1994 - EIU Draws Thousands of VisitorsUniversity Marketing and CommunicationsFollow this and additional works at: https://thekeep.eiu.edu/press_releases_1994This Article is brought to you for free and open access by the Press Releases at The Keep. It has been accepted for inclusion in 1994 by an authorizedadministrator of The Keep. For more information, please contact tabruns@eiu.edu.Recommended CitationUniversity Marketing and Communications, "06/24/1994 - EIU Draws Thousands of Visitors" (1994). 1994. 394.https://thekeep.eiu.edu/press_releases_1994/39494-181 June 24, 1994 FOR IMMEDIATE RELEASE: EIU DRAWS THOUSANDS OF VISITORS CHARLESTON -- Eastern Illinois University will host more than 16,000 visitors attending 65 summer camps and conferences now through August. The Civil Air Patrol was at Eastern this past week for its 26th visit. More than 150 cadets were housed at the university while they completed training at the Coles County Airport where they learned how to operate hot-air balloons, gliders and engine planes. Eastern will host the only national percussion camp July 10-16, according to Johnny Lane, EIU music professor and camp founder. The United States Percussion camp will feature music directors from Los Angeles, New York, Miami and Texas who represent nationally-known talent and top university professors of music. The camp attracts more than 300 participants ages 11-18. The Ambassador music camp is new to Eastern this year. Its 115 participants are Illinois' top high school students who were nominated by their school music directors. The honor concert band and choir are holding practices on the EIU campus -more-FILE COPY ADD 1/1/1/1 SUMMER and will conclude their visit with a concert at 7 p.m. Tuesday, June 28 in the Doudna Fine Arts Center Auditorium. The students will then travel to London, Paris, Switzerland and Italy for a European tour. "I am really looking forward to traveling with Illinois' top musical students and watching them perform in Europe," said Bruce Moss, director of bands at Eastern and camp leader. Other groups new to Eastern include D.A.Y., Devotional Associates of Yogischwar, a 400-member youth group which studies the culture and spirituality of India; B.A.M.M.I., Bicycle Across the Magnificent Miles of America; and a State Farm Insurance training camp for 300 sales associates. The Illinois Mathematics and Science Academy (IMSA), the only three-year, residential high school for gifted freshmen and sophomores, will again offer the "Summer 'AD' Ventures II" program in mathematics, science and technology July 6-17. Cosponsored by Eastern's Honors Programs and IMSA, this camp attracts some of the brightest students in the state. The 120 participants are recommended by their schools and chosen from thousands of applicants. "This is a wonderful opportunity for EIU to introduce academically gifted students to scientific thinking and learning. These young people are our nation's future. It is imperative that we invest in them," said Herbert Lasky, director of Eastern's Honors Programs and IMSA campus liaison. -more-ADD 2/2/2/2 SUMMER Partnerships for Excellence, a unique summer program which brings minority freshmen and seniors from 11 high schools around the state, is now in its seventh year. Seniors participating in the program will be at Eastern July 3-Aug. 6 completing college-level courses in mathematics, English and physical education. The freshmen will be on campus July 3-16, taking classes in mathematics, science, speech, creative writing, radio/TV and journalism. Both groups will receive credit-in-escrow for coursework completed. "In addition to the academic preparation the Partnerships for Excellence (PFE) program provides, it also expands students' horizons, offers them different perspectives and improves their social skills. Most importantly, as a result of its reinforcement of participating students' belief in themselves and their abilities, the PFE program plays a role in increasing minority representation in higher education institutions of this state," said John Craft, program director. Other campers include the Universal Cheerleaders, with 500 participants here through June 30 and boys basketball camps through June 26 with 500 attendees. The Showstoppers pom pon camp, during the third week in July, will attract another 450 visitors. Athletic camps in June and July include tennis, girls basketball, volleyball, softball, football, soccer and triathlon, with more than 500 campers. Eastern will again offer Elderhostel, a national program designed to bring older adults to campus for residential, educational experiences. Two one-week sessions will -more-ADD 3/3/3/3 SUMMER be offered July 10-23, with 80 participants expected. Topics covered will include "Big Band Sounds and All That Jazz," "Remembering the Depression," and "Men and Women of the 90s." From the end of July to mid-August, 15 high school marching bands and auxiliary units will hold practices on Eastern's campus. Journalism, art, cosmetology and leadership camps complete the summer schedule with most activities ending in mid-August. -30-

English

06/24/1994 - EIU Draws Thousands of Visitors

The Keep

Estudo Geral

2662 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 55, NO. 5, OCTOBER 2008
Dual-Cathode CsI Covered Microstrip Plate as VUV
High Efficiency Photosensor
Diogo S. A. P. Freitas, Rui M. Curado da Silva, Nuno F. C. Mendes, and Carlos A. N. Conde, Life Member, IEEE
Abstract—A Gas Proportional Scintillation Counter based on a
dual-cathode Microstrip Plate covered with a CsI film is described.
This new dual-cathode technique has the advantage of increasing
the VUV sensitive area of the Microstrip Plate. A detailed descrip-
tion of the technique is presented together with a discussion of the
performance. The results obtained for a xenon filled Gas Propor-
tional Scintillation Counter show an improvement of the energy
resolution for 5.9 keV X-rays from 12.7%, for a single cathode de-
vice, to 11.1% for the dual-cathode device.
Index Terms—Gaseous radiation detectors, microstrip detectors,
photocathodes, X-ray spectroscopy detectors, scintillation detec-
tors.
I. INTRODUCTION
S INGLE Cathode Microstrip Plates (MSP) covered witha CsI film have been used for some time [1] as VUV
photosensors for xenon filled Gas Proportional Scintillation
Counters (GPSC) yielding energy resolutions of 12.7% for 5.9
keV X-rays [2], [3] for equivalent geometry devices as the one
presented herein, although 11.4% resolution has been achieved
with optimised geometry devices [4], which is a resolution not
as good as that for GPSCs instrumented with photomultipliers
(8.0%), but better than that for standard Proportional Counters
(14%).
CsI covered MSP based GPSCs have the advantage of being
much more compact than the photomultiplier based ones.
The schematic of a MSP based GPSC is shown in Fig. 1.
X-rays are absorbed in an absorption region where they produce
primary electrons. These electrons drift towards a fairly strong
electric field region delimited by a
grid and the CsI covered MSP; in this region, the so-called scin-
tillation region, the primary electrons excite the xenon atoms
which in the decay process produce VUV photons in quite large
numbers (typically 500 photons per primary electron). These
photons when absorbed in the CsI film covering the cathodes of
Manuscript received April 11, 2008; revised June 25, 2008. Current version
published December 04, 2008. This work was supported by FEDER through
Project POCTI/FP/FNU/49561/2002 from Fundação para a Ciência e para a
Tecnologia-Portugal, and carried out in Centro de Instrumentação (Unit 217/94),
Departamento de Física da Universidade de Coimbra, Portugal. C.A.N. Conde
acknowledges travel support from Fundação Luso-Americana para o Desen-
volvimento. D. S. A. P. Freitas was supported by a grant from Fundação para a
Ciência e para a Tecnologia-Portugal: SFRH/BD/3244/2000. R. M. Curado da
Silva was supported by a post doctoral grant from Fundação para a Ciência e
para a Tecnologia-Portugal: SFRH/BPD/11670/2002.
The authors are with the Departamento de Física da Universidade de
Coimbra, P-3004-516 Coimbra, Portugal (e-mail: diogo@gian.fis.uc.pt;
ruisilva@saturno.fis.uc.pt; nmendes@gian.fis.uc.pt; canconde@gian.fis.uc.pt).
Digital Object Identifier 10.1109/TNS.2008.2002325
Fig. 1. Schematic of a MSP based gas proportional scintillation counter.
the MSP release photoelectrons which drift towards the anodes
of the MSP where they are charge multiplied by an avalanche
process, leading to a fairly large signal, approximately propor-
tional to the energy of the X-ray photon absorbed in the xenon
gas.
However, as soon as the photo-electrons leave the pho-
tocathode they collide with the xenon atoms and may be
backscattered towards the CsI photocathode itself, and so lost.
This effect reduces the efficiency of the photocathode for the
VUV scintillation.
The study of VUV photoelectric emission of a CsI film in a
gaseous atmosphere has been the subject of both experimental
[5] and theoretical [6] treatments. It was shown that the electric
field intensity at the surface of the CsI film has to be stronger
than about 3 for proper photoelectron extrac-
tion. However, we must point out that this extracting electric
field must have a pointing direction opposed to that of the field
in the scintillation region, which means that if we want to have
improved photoelectron extraction, the electric field intensity in
the scintillation region must be reduced, so reducing the number
of VUV photons and thus the number of photoelectrons.
Fig. 2 shows the electric field lines obtained with Ansoft
Maxwell 2D Field Simulator in the case of a standard MSP
with 80 wide cathodes, 10 wide anodes and 55
anode-cathode gap. For this example, the anodes were biased
at 200 V and the MSP placed in a xenon (800 Torr) scintillation
region with the electric field set at 2500 electric field
0018-9499/$25.00 © 2008 IEEE
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FREITAS et al.: DUAL-CATHODE CsI COVERED MICROSTRIP PLATE AS VUV HIGH EFFICIENCY PHOTOSENSOR 2663
Fig. 2. Calculated electric field lines for a standard MSP.
Fig. 3. Dual-cathode microstrip plate geometry.
intensity (reduced electric field: 3 ). With these
conditions, the electric field calculations show that for 100% of
the photocathode area the electric field intensity is above the
threshold for proper photoelectron extraction.
However, if the scintillation field intensity is increased
up to the optimum value of 5000
, only for a 20 wide region in the
cathode border is the electric field strong enough for complete
photoelectron extraction. In this case, the efficiency of the MSP
based photosensor is reduced by a factor of 50%.
II. THE DUAL-CATHODE MSP PHOTOSENSOR TECHNIQUE
To overcome this problem a new microstrip design was de-
veloped with cathode split into two parts: a central cathode, sur-
rounded by a border cathode, as shown in Fig. 3.
If the central cathode is biased at a few volts more negative
potential than the border cathode, then the electric field at its sur-
face is increased and the opposing effect of the scintillation field,
described before, is compensated. This way the electric field
reaches values above the 3 threshold for pho-
toelectron extraction, not only on the border cathode, but also
on the central cathode, thus increasing the overall efficiency of
the microstrip, even for scintillation fields close to the optimum
Fig. 4. Equipotential curves for a dual-cathode MSP with the anode biased
at 300 V, the border cathode at 0 V, a scintillation region field of about 5000
   , and central cathode at 0 V and  20 V.
value . Fig. 4 shows a plot of the equipo-
tential curves for the dual-cathode MSP used in the present work
(anode width, 10 , central cathode width, 80 , border
cathode width, 35 , on each side, anode-to-border cathode
gap, 50 , border cathode-to-central cathode gap, 5 ). The
plots are for 300 V at the anode, 0 V at the border cathode and
central cathode voltages of 0 V and 20 V. The closer spaced
equipotential curves at the central cathode surface for the 20
V case, indicate a stronger electric field.
III. EXPERIMENTAL SYSTEM
The Gas Proportional Scintillation Counter used for the
present experiments has a drift region 43 mm thick and a scin-
tillation region 10 mm thick. It was filled with xenon at about
800 Torr. The dual-cathode MSP used has anode and cathodes
with the dimensions referred to above, deposited on a 5 cm
5cm wide and 0.5 mm thick glass (Desag D263) plate. It was
covered with a 500 thick CsI film deposited by vacuum
evaporation.
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2664 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 55, NO. 5, OCTOBER 2008
Fig. 5. Variation of the pulse amplitude with the dual cathode MSP anode
voltage for central-to-border cathode voltages of 0 V,  10 V,  15 V,  20 V
and  40 V, where        	

 .
Fig. 6. X-ray spectrum for a 5.9 keV x-rays obtained with the dual-cathode
MSP based gas proportional scintillation counter presenting an energy resolu-
tion of 11.1%.
IV. RESULTS
The performance of this detector for 5.9 keV X-rays from
a radioactive source, was studied for a constant reduced
electric field, in the scintillation region, close to the optimum
value (6 ), and for a variety of MSP central
cathode and anode voltages.
The variation of the pulse amplitude with anode-to-border
cathode voltages for a variety of central cathode negative volt-
ages is plotted in Fig. 5 as shown the pulse amplitude increases
with both the anode voltage and the central-to-border cathode
voltages. This behavior is partly the result of the increased dif-
ference of potential, between central cathode and anode, as we
place at a more negative potential the central cathode.
The experimental results for the performance of the dual-
cathode MSP based GPSC as an X-ray spectrometer are illus-
trated in Fig. 6 which shows an X-ray spectrum for 5.9 keV pre-
senting an energy resolution of 11.1%.
The variation of the energy resolution as a function of the
MSP anode voltage for central-to-border cathode voltages
ranging from 0 to 40 V is plotted in Fig. 7. The lowest value
was obtained for an anode voltage of 290 V and
10 V in the central cathode.
Fig. 7. Variation of the energy resolution of the dual-cathode MSP based gas
proportional scintillation counter, as a function of the anode voltage, for central
cathode voltages of 0 V,  10 V,  15 V,  20 V and  40 V, where    
   	

 .
V. CONCLUSIONS
We have described a new Gas Proportional Scintillation
Counter having integrated as photosensor a dual-cathode Mi-
crostrip Plate covered with CsI.
With this dual-cathode MSP the scintillation detection effi-
ciency is increased and the energy resolution of the GPSC im-
proved.
For the dual-cathode MSP design here described (anode
width, 10 , central cathode width, 80 , border cathode
width, 35 , on each side, anode-to-border cathode gap, 50
, border cathode-to-central cathode gap, 5 ) the energy
resolution obtained for 5.9 keV X-rays was 11.1%.
For a standard single cathode MSP with similar dimensions
(10 anode width, 160 cathode width, 55 anode-to-
cathode gap) the energy resolution obtained [4] was not as good:
12.7%.
As shown in Fig. 5 the relative amplitude increases, for a fixed
anode voltage, as the central cathode becomes more negative,
since then the voltage difference along the path of the photoelec-
trons released from the central cathode in their way to the anode,
also increases. For more negative central cathode voltages the
electric field at its surface also increases and so increases the
photoelectron extraction efficiency. These effects lead to the ob-
served amplitude dependence on the central cathode voltage.
However, unexpectedly, as shown in Fig. 7, the energy resolu-
tion for central cathode voltages of 20 V is slightly worse than
for 10 V. This effect may result from the fact that as the cen-
tral cathode becomes too negative more electric field lines will
end up in the border cathode, rather than in the anode, leading
to the loss of the photoelectrons following these lines.
Although the results here presented for the energy resolution,
are not much better than those for the standard single-cathode
devices, the dual-cathode concept works and has the further ad-
vantage that the best energy resolution is not very much depen-
dent on the anode voltage, as shown in Fig. 7.
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585–587, 1994.
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FREITAS et al.: DUAL-CATHODE CsI COVERED MICROSTRIP PLATE AS VUV HIGH EFFICIENCY PHOTOSENSOR 2665
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