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Fluorescent screens for accelerators
NUCLEAR
INSTRUMENTS
AND
METHODS
FLUORESCENT
41 (1966)
SCREENS
D. COHEN+ Particle Accelerator
1499150;
0 NORTH-HOLLAND
PUBLISHING
co.
FOR ACCELERATORS*
and R. ROMAN
Division, Argonne National Laboratory,
Argonne, Illinois
Received 30 January 1966
often require fluorescent screens and flags to display various beam positions and properties for diagnostic and experimental purposes. A particular display system and phosphor coating technique was developed at the Argonne ZGS and has proven to be reliable over the past several years of operation. The use of this system for beam diagnostic studies has already been reported in the literature’,2) along with photographs of typical illuminations; this present report concerns some details of the system and the coating technique. The completed system consisted of various phosphorcoated flags and “transparent” screens which could be remotely inserted into the beam path at a number of stations along the acceleration complex. The flags and screens were viewed by vidicon television cameras. The camera outputs could be fed directly into control-room monitors or switched into storage units which also fed the monitors. The storage units were able to store one or more television frames so that these “frozen” frames could be displayed and studied for a period of some three or four minutes. The television and storage systems were chosen for high resolution, high light sensitivity and long-range reliability. The over-all system had a IO-MC bandwidth capability, and the RCA 7735-A vidicon tube was chosen over several more sensitive experimental tubes which were found to be unstable and had poor resolution. The storage units were built around two Raytheon QK 685 storage tubes in such a way that any of four cameras could be switched onto all or part of each storage tube, for simultaneous display. Storage produced only negligible loss of resolution, although the gray-tone range was decreased. About fifteen of the most promising commercial and experimental phosphors were tested for radiation damage and efficiency. Our dejinition of eficiency was the relative amount of light emitted per minimumAccelerators
* Work performed
under the auspices of the U.S. Atomic Energy Commission. + Present address: Physics Department, University of Illinois at Chicago Circle, Chicago, Illinois.
149
ionizing bombarding proton per unit area, as measured only with the RCA 7735-A vidicon tube, with the bombardment restricted to less than 1 msec. Tests were made with both 21-MeV deuterons from the Argonne 60” cyclotron and 50-MeV protons from the ZGS injector linac. The highest-efficiency phosphor was found to be Sylvania # 140, which has an average particle size of about 30 pm, long persistence and a chemical composition of (Zn,Cd)S:Cp. In a thick coating, this phosphor produced a barely visible stored image at 1.1 x lo8 equivalent minimum-ionizing bombarding protons per cm2, under the most sensitive operating conditions of the television camera with an f0.95 lens. The next most efficient phosphors were Sylvania # 132 and # 161, which were respectively 45% and 300,; as efficient as # 140. Phosphors # 140 and # 161 were extensively tested for radiation damage. Under prolonged deuteron bombardment, the efficiency of both these phosphors decreased exponentially and reached e-’ of their initial efficiencies after passage of about 2 x 10” equivalent minimum-ionizing protons per cm2. It was necessary to bond the # 140 phosphor onto both screen and foil flags, where the geometric screen transparency was to be greater than 80q/b in order to study multiturn injection in the ZGS ring. It was eventually found that the same bonding technique could be used on fine photo-etched copper screens and foils. The bonding substance needed good vacuum properties, radiation resistence, high-temperature resistence and strong adhesion. The commercial crt coating technique of allowing the phosphor to settle by gravity onto a surface from an aqueous silicate solution was rejected because the coated screen was too easily erased by abrasion and handling. The second method attempted consisted of dusting the phosphor onto an epoxy coated screen just prior to curing the epoxy. Erasure damage was eliminated; however, the epoxy was thermally degraded under the severe deuteron bombardments of the efficiency tests. The coated layer appeared crystallized and charred. Several coating systems were then tried and a commercial silicone resin based coating system
150
D. COHEN
AND
was finally selected. The coating process used is as follows : 1. Thoroughly clean and degrease the screen or foil by solvent washing. 2. Lightly spray-coat (
R. ROMAN
By using a very thin coat of resin, capturing and holding one particle thickness per coat was possible which yielded a layer thickness of 0.0015” or less. For thicker layers and more light intensity, steps 2-4 were repeated, thereby adding more layers in an easily controlled manner. Under deuteron bombardment these resin coatings appeared to suffer less radiation destruction than the phosphors.
References 1) R. L. Martin, IEEE Trans. Nucl. Sci. NS-12, no. 3 (1965) 556. 2) E. A. Crosbie and P. V. Livdahl, IEEE Trans. Nucl. Sci. NS-12, no. 3 (1965) 799.
INSTRUMENTS
AND
METHODS
FLUORESCENT
41 (1966)
SCREENS
D. COHEN+ Particle Accelerator
1499150;
0 NORTH-HOLLAND
PUBLISHING
co.
FOR ACCELERATORS*
and R. ROMAN
Division, Argonne National Laboratory,
Argonne, Illinois
Received 30 January 1966
often require fluorescent screens and flags to display various beam positions and properties for diagnostic and experimental purposes. A particular display system and phosphor coating technique was developed at the Argonne ZGS and has proven to be reliable over the past several years of operation. The use of this system for beam diagnostic studies has already been reported in the literature’,2) along with photographs of typical illuminations; this present report concerns some details of the system and the coating technique. The completed system consisted of various phosphorcoated flags and “transparent” screens which could be remotely inserted into the beam path at a number of stations along the acceleration complex. The flags and screens were viewed by vidicon television cameras. The camera outputs could be fed directly into control-room monitors or switched into storage units which also fed the monitors. The storage units were able to store one or more television frames so that these “frozen” frames could be displayed and studied for a period of some three or four minutes. The television and storage systems were chosen for high resolution, high light sensitivity and long-range reliability. The over-all system had a IO-MC bandwidth capability, and the RCA 7735-A vidicon tube was chosen over several more sensitive experimental tubes which were found to be unstable and had poor resolution. The storage units were built around two Raytheon QK 685 storage tubes in such a way that any of four cameras could be switched onto all or part of each storage tube, for simultaneous display. Storage produced only negligible loss of resolution, although the gray-tone range was decreased. About fifteen of the most promising commercial and experimental phosphors were tested for radiation damage and efficiency. Our dejinition of eficiency was the relative amount of light emitted per minimumAccelerators
* Work performed
under the auspices of the U.S. Atomic Energy Commission. + Present address: Physics Department, University of Illinois at Chicago Circle, Chicago, Illinois.
149
ionizing bombarding proton per unit area, as measured only with the RCA 7735-A vidicon tube, with the bombardment restricted to less than 1 msec. Tests were made with both 21-MeV deuterons from the Argonne 60” cyclotron and 50-MeV protons from the ZGS injector linac. The highest-efficiency phosphor was found to be Sylvania # 140, which has an average particle size of about 30 pm, long persistence and a chemical composition of (Zn,Cd)S:Cp. In a thick coating, this phosphor produced a barely visible stored image at 1.1 x lo8 equivalent minimum-ionizing bombarding protons per cm2, under the most sensitive operating conditions of the television camera with an f0.95 lens. The next most efficient phosphors were Sylvania # 132 and # 161, which were respectively 45% and 300,; as efficient as # 140. Phosphors # 140 and # 161 were extensively tested for radiation damage. Under prolonged deuteron bombardment, the efficiency of both these phosphors decreased exponentially and reached e-’ of their initial efficiencies after passage of about 2 x 10” equivalent minimum-ionizing protons per cm2. It was necessary to bond the # 140 phosphor onto both screen and foil flags, where the geometric screen transparency was to be greater than 80q/b in order to study multiturn injection in the ZGS ring. It was eventually found that the same bonding technique could be used on fine photo-etched copper screens and foils. The bonding substance needed good vacuum properties, radiation resistence, high-temperature resistence and strong adhesion. The commercial crt coating technique of allowing the phosphor to settle by gravity onto a surface from an aqueous silicate solution was rejected because the coated screen was too easily erased by abrasion and handling. The second method attempted consisted of dusting the phosphor onto an epoxy coated screen just prior to curing the epoxy. Erasure damage was eliminated; however, the epoxy was thermally degraded under the severe deuteron bombardments of the efficiency tests. The coated layer appeared crystallized and charred. Several coating systems were then tried and a commercial silicone resin based coating system
150
D. COHEN
AND
was finally selected. The coating process used is as follows : 1. Thoroughly clean and degrease the screen or foil by solvent washing. 2. Lightly spray-coat (
R. ROMAN
By using a very thin coat of resin, capturing and holding one particle thickness per coat was possible which yielded a layer thickness of 0.0015” or less. For thicker layers and more light intensity, steps 2-4 were repeated, thereby adding more layers in an easily controlled manner. Under deuteron bombardment these resin coatings appeared to suffer less radiation destruction than the phosphors.
References 1) R. L. Martin, IEEE Trans. Nucl. Sci. NS-12, no. 3 (1965) 556. 2) E. A. Crosbie and P. V. Livdahl, IEEE Trans. Nucl. Sci. NS-12, no. 3 (1965) 799.