1. Obergurgl, 20.06.2004

2. Damian Pliszka *, Grzegorz P. Karwasz, Roberto S. Brusa, Antonio Zecca, Dipartimento di Fisica, Università Degli Studi di Trento, 38050 Povo (TN) Italia * Institute of Physics, Pomeranian Pedagogical University, 76-200 Slupsk, Poland

3. 1. Slow positron apparatus 2. Testing 3. High energy mode 4. Deaccelerating mode 5. Benzene results

4. Schematics INJECTION OPTICS REMODERATOR STAGE FIRST ACCELERATOR DEFLECTOR

5. First accelerator - wide-angle electrostatic optics where slow positron beam is formed from Na 22 source coupled with 1  m W monocrystal

6. 90  electrostatic spherical deflector - used to prevent high-energy positrons from the source reaching the target

7. Remoderator stage – second accelerator equiped with electron gun which allows in situ conditioning Cu remoderator film

8. Injection optics - formed by three aperture electrodes, in focusing conditions a weak longitudinal magnetic field is used, and guides positrons through 10 cm long scattering cell.

9. Beam modelling First accelerator (SIMION simulation) 1515 1 32 190190 30 30 +22 00 V +8 50 V +20 00 V

10. Testing 1. Electrons (focusing effect of magnetic field)

11. 1. Electrons (cross sections)

12. 2. Positrons (focusing effect of magnetic field)

13. 2. Positrons (pass - band of deflector)

14. 2.4 eV Energy correction

15. Benzene results – vs. experiments

16. Benzene results – vs. theory

17. Acknowledgements: EPIC – made it possible! Trento is Rome subnode Marco Bettonte Chiara Perazzolli