Gamma-induced positron lifetime and age-momentum

1. Gamma-induced positron lifetime and age-momentum correlation measurements of water at temperatures between 20 °C and 90 °C

2. Gamma-induced positron lifetime and age-momentum correlation measurements of water at temperatures between 20 °C and 90 °C Content: • Gamma-induced Positron Spectroscopy – GiPS • Simulations using GEANT4 • Positron lifetime spectroscopy at GiPS • Time dependent S parameter – S(t) • Conclusions

3. Gamma-induced Positron Spectroscopy – GiPS Detector setup • ~ 300 cps • 12 hours for 106 counts in AMOC spectrum of water • up to 16 MeV, 0.7 mA • 5 ps bunch width • 38 ns between each bunch • pulsed beam of brems strahlung from superconducting electron LINAC ELBE • 4 coincident setups for Age-MOmentum Correlation (AMOC )

4. Gamma-induced Positron Spectroscopy (GiPS) Positron lifetime measurement • time structure of e- beam maintained for photon beam • accelerator pulse serves as start signal • gate on 511 keV at HPGe and BaF2 t = 5 ps Start Lifetime Stop

5. Gamma-induced Positron Spectroscopy – GiPS Age-MOmentum Correlation – AMOC projection on energy axis projection on time axis energy and timing information of the same annihilation event

6. GEANT4 simulations GEometryANd Tracking – GEANT4 Distribution of positron generation by pair production and annihilation Simulation of particle transport and interaction with matter using Monte Carlo methods beam direction → smearing up to ~ 10 mm in z direction GEANT4: S. Agostinelli et al. Nucl. Instr. Meth. A 506 (2003), 250-303

7. GEANT 4.0 simulations “Source contribution“ and dose rate • no influence of Al caps or • temperature sensor; Kapton • tube can be neglected • dose rate for water at GiPS: • ~ 1 mGy / s • positron generation within 20 • cm³ → effect of radiolysis • can be neglected

8. Positron lifetime spectroscopy at GiPS Fixing second lifetime component • three components fit using PALSfit • analysis by fixing 1 and 2 , and looking for minimum of chi2 → 2 = 400 ps

9. Positron lifetime spectroscopy at GiPS Results • no source correction necessary for fit • good agreement to published data, just intensity of free annihilation is lower Duplâtre – Phys. Status Solidi A, Vol. 6, Issue 11, 2476-2481 (2009) Kotera et al. – Phys. Lett. A, Vol. 345, 184-190 (2005)

10. Positron lifetime spectroscopy at GiPS Influence of oxygen on positron lifetimes • oxygen acts as scavenger for radicals and e-aq Effect on annihilation components: → Ie+ decreases → IPs increases This explains the lower intensity of the free e+ annihilation component

11. Time dependent S parameter – S(t) extracting Doppler curves calculating S parameter for each curve

12. Time dependent S parameter – S(t) Motivation – “quantum beats“ in water T. Hirade (Chemical Physics Letters 480 (2009) 132–135): • spin conversion of ortho-positronium can possibly be detected using AMOC • periodic changes in S(t) parameter = quantum beats Our motivation: • AMOC spectra are part of GiPS • measurements for T = 21 … 90 °C • Can we confirm quantum beats?

13. Time dependent S parameter – S(t) Dependence on temperature • no periodic behaviour of S parameter changes (increases) for temperatures between 50 and 90 °C

14. Time dependent S parameter – S(t) Dependence on statistics differences in curves for different statistics of the S(t) curves no reproducable results of periodic changes in S parameter no quantum beats were found for T = 21… 90 °C using the GiPS setup.

15. Conclusion • GiPS is suitable for the investigation of liquids • radiolysis effects due to the use of bremsstrahlung can be neglected • temperature stabilized sample holder does not influence positron lifetime measurement → no source correction necessary • positron lifetime results fit well to published data • AMOC spectra can be measured within a fraction of usual time (days instead of weeks) • quantum beats could not be verified for temperatures between 20 … 90 °C

16. Many thanks to my collaborators … Wolfgang Anwand, Thomas E. Cowan, Andreas Hartmann, Andreas Wagner and the ELBE crew for always stable beams Helmholtz-Zentrum Dresden-Rossendorf Jörg Haeberle, Marco Jungmann, Reinhard Krause-Rehberg, Arnold Krille Martin-Luther-Universität Halle-Wittenberg … and to you for your attention !

17. GiPS – Gamma-induced Positron Spectroscopy • up to 16 MeV, 0.7 mA • 5 ps bunch width • 38 ns between each bunch • temperature stability ± 0.5 °C • bulky samples, liquids, disperspion, gases, powders, activated samples • Lifetime & Doppler broadening Spectroscopy, Age-Momentum Correlation • user dedicated facility, application for beam time twice a year (14.11.2011)

20. GEANT 4.0 simulations Radiolysis of water Is there any effect on the positron lifetime components?

21. GEANT 4.0 simulations Photon beam hitting the Kapton tube beam direction • bremsstrahlung up to 6 and 16 MeV • calculated with beam diameter = 41 mm

22. GEANT 4.0 simulations Distribution of positron generation by pair production and annihilation beam direction → smearing up to ~ 10 mm in z direction

23. Positron lifetime spectroscopy at GiPS Local variance minimum for 2 = 400 ps for all temperatures

24. Time dependent S parameter – S(t) Peak differences

25. Time dependent S parameter – S(t) Comparison with recently published data • comparable to recently reported data Hirade – Chem. Phys. Lett., Vol. 480, 132–135 (2009 )