Multi-alkali Cathode Research Articles

Light-controlled pulsed x-ray tube with photocathode* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61901470 and U1931138), the Strategic Pioneer Program on Space Science, Chinese Academy of Sciences (Grant No. XDA15020501-04), the CAS “Light of West China” Program (Grant No. XAB2018A07), and the Foundation of State Key Laboratory of China (Grant No. SKLIPR2021).

Unstable mechanical structure, low energy efficiency, and cooling requirements limit the application of conventional x-ray tubes based on filament as cathode in several academic areas. In this paper, we demonstrate a light-controlled pulsed x-ray tube using multialkali cathode as electron generator. The photocathode active area of the light controlled x-ray tube is 13.2 cm2 (41 mm in diameter), which provides high photoelectron-emitting efficiency up to 0.288 mA/lm in 460-nm LED and 2.37-mA maximum tube current. Furthermore, the modulation ability from 1 kHz to 100 kHz of the x-ray tube is tested. The results suggest that the light-controlled pulsed x-ray tube has easy modulation and short x-ray pulse properties and is promising to be the next generation x-ray tube with wide applications in medical radiationtherapy as well as the calibration for detectors and scintillators.

多碱阴极光电发射理论研究

The spectral reflectivities of Na2KSb film both with and without the activation layer of Cs-Sb were measured.The measurement results show that the spectral reflectivity of these two films within the wavelength range of 200～700nm are substantially the same.So it can be inferred that the refractive index of both films are also substantially the same,and both films are substantially no change in its internal constituent.Because the spectral reflectivity is not changed,and the optical path difference of the two films are substantially the same,it can be inferred that the Cs-Sb layer was coated on the surface of Na2KSb,so the activation process of Na2KSb surface is a surface effect.In addition,Na2KSb(Cs)multi-alkali cathode film was analysis by XPS,the results showed that three elements was existed mainly in addition to Na,K,and Sb,but also the presence of CO2and a small amount of Cs elements.The reason of the presence of C and O on the surface of Na2KSb(Cs)is oxidation in the unsealed process of sample.After 10second time of argon ion etching,Na2KSb(Cs)multi-alkali cathode film was analyzed by XPS,the results show that the energy spectrum of Cs atoms has disappeared.When continued for 600seconds time of the argon ion etching,on Na2KSb(Cs)multi-alkali cathode film surface,the spectrum of the Si atoms in XPS spectroscopy was appeared.This showed that argon ion has already etched to the glass window surface.According to the etching time analysis,the thickness of the multi-alkali cathode film surface Na2KSb(Cs)of Cs atomic layers approximately 3nm,and the Cs atomic layer exists only in the surface of the multi-alkali cathode layer,No deep into the multi-alkali cathode film inside.The fluorescence spectrum of multi-alkali cathode with the Cs-Sb activation and without Cs-Sb activation has been measured.The measurement results showed that the peak wavelength of fluorescence spectrum of sample with Cs activation has shifted toward to short directions,while peak intensity of samples with the Cs-Sb has reduced compared with sample without Cs activation.This phenomenon lustrated that not only quantity of transition electron of Na2KSb multi-alkali cathode with Cs activation has increased,but also the energy level of transition electron has increased.This phenomenon can be defined as "volume effect" during the activation process.So during activation process of Na2KSb multi-alkali cathode,the reason of sensitivity increasing is a kind of surface effect and a kind of"volume effect".Yet this"volume effect"refers to the structure change inside the multi-alkali cathode layer material,rather than surface Cs atoms diffused inside film.

A single-photon sensitive ebCMOS camera: The LUSIPHER prototype

Processing high-definition images with single-photon sensitivity acquired above 500 frames per second (fps) will certainly find ground-breaking applications in scientific and industrial domains such as nano-photonics. However, current technologies for low light imaging suffer limitations above the standard 30fps to keep providing both excellent spatial resolution and signal-over-noise. This paper presents the state of the art on a promising way to answer this challenge, the electron bombarded CMOS (ebCMOS) detector. A large-scale ultra fast single-photon tracker camera prototype produced with an industrial partner is described. The full characterization of the back-thinned CMOS sensor is presented and a method for Point Spread Function measurements is elaborated. Then the study of the ebCMOS performance is presented for two different multi-alkali cathodes, S20 and S25. Point Spread Function measurements carried out on an optical test bench are analysed to extract the PSF of the tube by deconvolution. The resolution of the tube is studied as a function of temperature, high voltage and incident wavelength. Results are discussed for both multi-alkali cathodes as well as a Maxwellian modelization of the radial initial energy of the photo-electrons.

Multiphoton Microscopy for 3-Dimensional Imaging of Lymphocyte Recruitment Into Apolipoprotein-E–Deficient Mouse Carotid Artery

Two recent elegant studies have shown that in apolipoprotein-E–deficient mice, the lamina adventitia is a major site of arterial wall inflammation associated with lymphocyte infiltration into atherosclerotic arteries and with formation of adventitial lymphoid-like tissues.1,2 These results suggest that lymphocyte responses in the lamina adventitia may play a crucial role in atherosclerosis development.1,2 However, in both studies, the detection of immune cells within the artery was limited to conventional analysis systems (flow cytometry, immunohistochemistry), which require the removal, disruption, and processing of tissue at defined time points to give a “snapshot” of the immune response to vascular damage in vivo. For evaluation of atherosclerotic processes and their relationship to immune activation, imaging of 3-dimensional structures in intact vascular tissues and functional aspects of the diseased artery (eg, details of the interactions of immune cell with vessel wall structures) are required. A potential solution to this problem is offered by the development of multiphoton laser-scanning microscopy,3 with the ability to penetrate directly into tissues at sufficient depths to image tissues in situ in the absence of significant phototoxicity. By moving the focal point axially, …

Parameters of photomultipliers with small photocathodes

A description is given of FEU-64 tubes, cathode area 0.2 cm2, for Sb-Cs and multialkali cathodes. The latter can measure fluxes of 2 × 10−15 W in the range 4000–6000 a with a signal-to-noise ratio of 10 in a passband of 1 Hz.

On the Temperature Dependence of Multi-Alkali Photocathodes

Measurements of the temperature dependence of the photoemission from multi-alkali cathodes down to 77.4 °K are described. The general shape of the measured characteristics is compared with curves obtained by other authors for cathodes of different origin. It is found that the properties of the cathodes depend on the preparation method. In all measurements, decrease of photoemission with decreasing temperature is a property common to all cathodes if the trivial case of insufficient transverse conductivity can be eliminated. It is shown that this property may be connected with possible emission from acceptor levels in the long wavelength tail range.

Non-linearities and Discontinuities of the Photoemission from Multi-Alkali Cathodes at Nitrogen Temperatures

An account is given of measurements relating to the temperature dependence of the photo­emission of muhialkali cathodes at temperatures in the region of 80 °K. These measurements show intensity-dependent and spectrally dependent non-linearities with hysteresis in which pronounced discontinuities of the quantum yield of the photoemission occur up to a factor of 2. With a temperature constancy in the region of ±0.01 °K these discontinuities are fully reproducible. Because of the extremely high temperature sensitivity of the effect interesting prospects are afforded when it is used for detecting thermal radiation on the basis of photoelectrons that can be utilized parti­cularly well technically.

Progress on Photomultiplier Tubes and Rage Intensifiers at EMI Electronics Ltd.

The development of photomultiplier tubes for tube counting is discussed, and bias curves are given. The advantages of tubes with multi-alkali cathodes are described. Specific tubes are described, such as those developed for scintillation counting (venetian blind type), for use under vibration conditions, and for detection of ions and soft x rays. A 4-stage magnetically focused intensifier using bialkali cathodes is described briefly. (D.L.C.)

A Wollaston photometer.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Wollaston photometer. Gehrels, Thomas ; Teska, Thomas M. Abstract A photometer of the McDonald Observatory was converted for interchangeable use in either UB V photometry, or in six-color polarization measures. The polarization is analyzed with a Wollaston prism and two multiplier phototubes by simultaneous integration. A complete series on a fairly bright object, at six position angles and in six colors, takes about 60 minutes; this requires 144 integrations as at each angle the tubes are exposed twice, namely with and without a depolarizer in the incoming beam. Neither thin clouds nor poor seeing affect the polarization measures. The effe~tive wave lengths range from 3250 to 9900 A. Two types of tubes are used, namely RCA 7102, having S-I response, and RCA 7265, with multi-alkali cathode. Reductions of the observations are made with the IBM 650 of Indiana University. The internal probable errors are ~2o in position angle, larger when the polarization is very small, and ~0. I in the percentage polarization. Results on the main program of solar system studies are in a separate paper. As a check on this new equipment, eight strongly polarized stars were observed that occur in the lists of Hall and Mikesell and of W. A. Hiltner; in visual light the agreement is close. However, it was found that in the ultraviolet as well as in the infrared the interstellar polarization is less than in visual light. The sunlit blue sky shows approximately the same wavelength dependence. It was found that neither the 82-inch mirror nor the photometer cause depolarization in the ultraviolet; the observations and the depolarization test will be fully reported in another publication. Astronomy Department Indiana University Bloomington, Ind. Publication: The Astronomical Journal Pub Date: 1959 DOI: 10.1086/108029 Bibcode: 1959AJ.....64R.332G full text sources ADS |

Multi-Alkali Photo Cathodes

The quantum efficiency of a photoemitting material is determined by a combination of physical properties. It has been found that the requirements are met best by semiconductors of low work function surfaces. In the light of these general considerations, a short survey is given of the photocathodes available heretofore. A more detailed description will then be given of the new multi-alkali cathodes, particularly those of the composition of Sb-K-Na and Sb-K-Na-Cs. Their advantages for use in scintillation counters are discussed.