Tungsten mesh as positron transmission moderator in a monoenergetic positron beam

Weng, Huihui; Ling, CC; Beling, C. D.; Fung, S.; Cheung, Chun; Kwan, P.; Hui, I.P.

doi:10.1016/j.nimb.2004.05.002

Cited by 13 publications

(13 citation statements)

References 14 publications

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“…The same authors found selfabsorption to be negligible for a NEN source of 10 mCi initial activity. (1985), Brusa et al (1992), and Weng et al (2004) for the unetched foil are, within the scatter of the data, not inconsistent but, as all other previous experimental determinations, they should be considered underestimates since not all the efficiencies discussed in Section II may have been accounted for in these works.…”

Section: Resultsmentioning

confidence: 47%

“…To test the hypothesis that the moderation efficiency could be increased by using meshes with thinner diameter wires, an etching procedure was devised similar to the one used by Weng et al (2004). The mesh (Swallow Metals: 99.99% purity; wire diameter, d ¼ 25 lm; transmission coefficient, t ¼ 81%) was cut into 15 mm diameter circular disks and placed into a sodium hypochlorite solution; d was reduced to $19 lm (t $ 86% transmission) in approximately 20 min at 75 C. The reduction in d was calculated by measuring the mass (m), before (b) and after (a) etching using…”

Section: Experimental Methodsmentioning

confidence: 99%

“…As moderators, meshes are usually stacked together to enhance interception of the b þ particles emitted by the radioactive source (e.g., Zafar et al 1996). Weng et al (2004) expressed the probability of extracting a slow positron from such an arrangement as…”

Section: Experimental Methodsmentioning

confidence: 99%

“…) have more recently been obtained from stacks of meshes which had been electropolished (Saito et al 2002) or etched (Weng et al 2004). The latter authors found the efficiency to depend on the annealing pre-treatments, the duration of the etching and the number of the folding layers.…”

Section: à3mentioning

confidence: 99%

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Moderation and diffusion of positrons in tungsten meshes and foils

Williams

Murtagh

Fayer

et al. 2015

Journal of Applied Physics

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The efficiency of tungsten meshes and thin foils for moderation of fast positrons from 22Na has been investigated in transmission geometry and a fair agreement has been found with previous experimental results where directly comparable. For foils, the dependence on material thickness is found to be similar to the prediction of the Vehanen-Mäkinen diffusion model; however, the magnitude is 5–10 times lower. A broad consensus is observed between experiment and the results of a three-dimensional model developed in this work. For a given thickness, meshes are found to be generally better than foils by around a factor of 10 with a maximum efficiency (∼10−3) comparable to that achieved with thin single crystal foils, in accord with previous measurements and the results of the present model.

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Section: Resultsmentioning

confidence: 47%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Section: à3mentioning

confidence: 99%

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Moderation and diffusion of positrons in tungsten meshes and foils

Williams

Murtagh

Fayer

et al. 2015

Journal of Applied Physics

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“…15 The efficiency (η ++ = slow e + /fast e + ) of these moderators is reported in the range of ∼ 10 −4 − 10 −3 . 28,29 On the other hand, the η ++ of a solid Ne moderator is more than an order of magnitude higher, in the range of ∼ 7 × 10 −3 − 1.4 × 10 −2 with positrons emitted from a 22 Na positron emitter. 30,31 Solid Ne provides much higher efficiency than metallic moderators due to the fact that positron diffusion length (L + ) inside a RGM is much longer than it is inside a metallic moderator, and therefore thermalized positrons may diffuse back to the surface with higher probability before they annihilate inside the material.…”

Section: The Challenges and The Conceptmentioning

confidence: 99%

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

Golge

Vlahović

Wojtsekhowski

2014

Journal of Applied Physics

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We present a conceptual design for a novel continuous wave electron-linac based high-intensity high-brightness slow-positron production source with a projected intensity on the order of 10 10 e + /s. Reaching this intensity in our design relies on the transport of positrons (T + below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. This design progressed through Monte Carlo optimizations of: electron/positron beam energies and converter target thickness, transport of the e + beam from the converter to the moderator, extraction of the e + beam from the magnetic channel, a synchronized raster system, and moderator efficiency calculations. For the extraction of e + from the magnetic channel, a magnetic field terminator plug prototype has been built and experimental results on the effectiveness of the prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

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First positron flux measurements at the Argonne Positron Source (APosS)

Chemerisov

Jonah

Jean

et al. 2007

Phys. Status Solidi (c)

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PACS 23.20.Ra, 41.75.Fr, 78.20.Mb The development of the APosS at the Argonne low-energy linac is discussed. We measured the yields and outline strategies to increase the number of slow positrons. We describe the measurement of the yield of slow positrons as a function of electron-beam energy and compare these results with theoretical calculations.1 Introduction Positron annihilation spectroscopy is an extremely sensitive, non-destructive method to study the nature, concentration and distribution of the defects in materials [1][2][3]. This method has been successfully used for the last forty years, but low positron flux prevents the realization of the full potential of the positron spectroscopy. One of the most promising directions for increase in positron flux is to use an electron linac as a source of fast positrons [4,5]. We are in the process of developing a low-energy positron facility based on the Argonne Chemistry Division High-Current electron Linac [6]. This is an attractive source for the generation of positrons because the linac is capable of producing a relatively high current of electrons (in the present configuration, more than 100 µA average of electrons (6 x 10 14 electrons per second) and with relatively few modifications, greater than 2 milliamp of electrons (1.2 x 10 16 electrons per second) with an energy of 15 MeV. Pulsed accelerators provide a convenient source of positrons. They have the advantage of being able to turn off the source of radiation by simply turning off the accelerator, which is not possible with an isotope source. Because the source of positrons is pulsed, high peak currents of positrons are available, which are well suited for filling positron traps. Traditionally, high-energy electron accelerators (50-100 MeV) have been used as a source of electrons to generate positrons because the yield of positrons per electron will be higher for the higher energy electrons [4,5]. However, when one considers the efficiency of generating positrons for the total beam energy (current times translational beam energy), the increase in efficiency is no longer as clear. Higher energy electron beam produces more positrons per incident electron, but the energy spectrum of the

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Tungsten mesh as positron transmission moderator in a monoenergetic positron beam

Cited by 13 publications

References 14 publications

Moderation and diffusion of positrons in tungsten meshes and foils

Moderation and diffusion of positrons in tungsten meshes and foils

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

First positron flux measurements at the Argonne Positron Source (APosS)

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