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Using a Bent Tube as an Energy Filter for a Positron Beam. Simulations on Determining the Optimum Angle of the Bend

100%

Dinescu D., Djourelov N.

Acta Physica Polonica A

2017

vol. 132

issue 5

1624-1627

One way to perform lifetime measurements at a DC positron beam is to pass positrons through a pulsing device. The compressed e⁺ bunches are accelerated to a desired energy for depth profiling of the studied sample. A fraction of the e⁺ that are backscattered from the sample surface can travel back through the uniform magnetic field that is generated along the central axis of the beam transport lines and reach the accelerator. The backscattered e⁺ that reach the accelerator can be re-accelerated towards the sample and re-implant in it with a delay from the initial implanted e⁺ bunch. These e⁺ that are re-implanted into the sample with a delay cause distortions in the lifetime spectra. A setup which uses a bent tube to act as an energy filter to reduce the effect of the backscattered e⁺ is studied by simulations. The simulations are performed in order to find the optimum geometry for minimum distortions.

Positronium Formation in Nanostructured Metals

76%

Čížek J., Melikhova O., Hruška P., Vlček M., Anwand W., Liedke M., Novotný M., Bulíř J.

Acta Physica Polonica A

2017

vol. 132

issue 5

1579-1584

Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared.

Design of an Acceleration Gap for Brightness Enhancement in a Reactor-Based Slow Positron Beamline

64%

Kuzuya Y., Oshima N., Kinomura A., Yabuuchi A.

Acta Physica Polonica A

2017

vol. 132

issue 5

1620-1623

Design of an acceleration gap using mesh electrodes of the brightness enhancement system for the slow positron beamline of Kyoto University research reactor was studied to improve the performance of brightness enhancement. The transmittance and the increase in the angular divergence of the beam resulting from acceleration with the mesh electrode were estimated by trajectory simulations. The effect of the increase in the beam emittance on the beam radius at the focus point was estimated based on the analytical solution of the beam envelope equation. Using the obtained beam transmittance and beam radius, the beam brightness after remoderation was evaluated. Then, the influence of the mesh electrode configuration on the brightness was investigated.

A Method to Produce Linearly Polarized Positrons and Positronium Atoms with the J-PET Detector

52%

Mohammed M., Białas P., Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Raj J., Rudy Z., Sharma N., Sharma S., Shivani, Skurzok M., Silarski M., Wieczorek A., Wiślicki W., Zgardzińska B., Zieliński M., Moskal P.

Acta Physica Polonica A

2017

vol. 132

issue 5

1486-1489

A method for creating linearly polarized positrons and ortho-positronium (o-Ps) atoms with the J-PET detector is presented. The unique geometry and properties of the J-PET tomography enable one to design a positron source such that the quantization axis for the estimation of the linear polarization of produced o-Ps can be determined on the event by event basis in a direction of the positron motion. We intend to use ²²Na or other β⁺ decay isotopes as a source of polarized positrons. Due to the parity violation in the beta decay, the emitted positrons are longitudinally polarized. The choice of the quantization axis is based on the known position of the positron emitter and the reconstructed position of the positronium annihilation. We show that the J-PET tomography is equipped with all needed components.

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Using a Bent Tube as an Energy Filter for a Positron Beam. Simulations on Determining the Optimum Angle of the Bend

Positronium Formation in Nanostructured Metals

Design of an Acceleration Gap for Brightness Enhancement in a Reactor-Based Slow Positron Beamline

A Method to Produce Linearly Polarized Positrons and Positronium Atoms with the J-PET Detector