Charged particle emission from Ti/TiO 2 :D x system stimulated by e-beam and X-ray radiation

1. Charged particle emission from Ti/TiO2:Dx system stimulated by e-beam and X-ray radiation A.S. Roussetski1*, I.P.Chernov3, Yu.P. Cherdantsev 3, B.F. Lyakhov2, E.I. Saunin2, Yu.I. Tyurin3 1 P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia 2 Tomsk Polytechnic University, Tomsk, 634050 Russia 3 A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 199915, Russia

2. Introduction • Recent ab-initio study of hydrogen desorption from metal hydrides with a high hydrogen solubility [V.M., Silkin, I.P Chernov et. al, Phys. Rev., B 76, 245105 (2007)], showed that excitation of hydrogen subsystem in those deuterides is resulted in plasmon formation leading to generation of strong electric fields (F ~ 108 V/cm) within a lattice parameter scale (a ~ 0.3-0.4 nm). As a result, a mean energy of desorbed protons/deuterons (Ed), escaping from the hydride surface would effectively be increased from kT to the several eV values (Ed = Fa ~ 3-4 eV) or two orders of magnitude, effectively producing “hot” deuterons • Such deuteron acceleration mechanism, alongside with a possible large electron screening in the metal targets with enhanced hydrogen diffusivity could potentially strongly enhance the yield of DD-reaction in metal deuterides, even at extremely low energy of their excitation. • We have started this work with Dr. Andrey Lipson ~5 years ago. Now we are continue the investigations already without him but with his colleagues, and based on Lipson`s ideas.

3. Objectives • To verify the hypothesis on the role of e-beam and X-ray excitation of the hydrogen subsystem in metal deuteridesto enhance DD-reaction yield. • To check feasibility of energetic alpha-particle emission from Ti/TiO2:Dx systemunder e-beam and X-ray irradiation.

4. Experimental: Set up 1Sample-detector holder assemble mounted in the SEM vacuum chamber (p = 10-6 torr) and irradiated by collimated electron beam of EDS electron gun (J = 100-300 nA, E = 30 keV): The desorbed deuterium and generated charged particles reach the detectors from the spot produced by e-beam with dimensions S = 8x6 mm2. The effective distance between the center of the spot and the detectors 1 and 2 is about <Reff> = 12 mm. The Background counts are taken from the rare side of CR-39opposite to that faced to the sample surface. Additional Background measurements were carried out with pure Ti foil at the same conditions. 1,2 and 3 – are the CR-39 detectors covered with the 11 µm Al (1), 25 µm Cu (2) and 33 µm Al (3) foils, respectively, 4 –deuterated sample, 5-manipulator, 6-electron gun, 7- stainless support

5. TiDx sample preparation • The Ti foils of 300 μm thick have been loaded in 1M solution of D2SO4 in D2O during t = 35 hr at J = 30 mA/cm2, in order to dissolve the TiO2 oxide layer at the Ti-surface and to provide D-penetration. • The average loading (x = D/Ti = 0.1 at depth of 2-3 μm) has been determined by weight balance before and after electrolysis. • It was found (by weight balance before and after irradiation) that the D-desorption rate in case of TiD1 irradiation is consistent with the JD ~ 2.0 x 1014 D/s-cm2. • All desorbed deuterons in TiDx has been caused only by irradiation because the compound is absolutely stable at T = 300 K.

6. RBS/ERD profiles of the TiDx samples prior to e-beam bombardment –left; after D-desorption in vacuum during 60 min of e –beam (J=0.6 µA/cm2 U = 30 kV) treatment - right

7. Alpha-sources and Cyclotron alpha beam calibration (2-30 MeV) of CR-39 Tracks from 11.0 MeV -beam @ normal direction with respect to CR-39 (Landauer) surface: image area S= 120x90 µm2

8. CR-39 track diameter vs. charged particle energy (calibration data) for protons (p) and alphas (α) of normal incidence (etching conditions:7h in 6 N NaOH at t = 70C)

9. Vacuum Background: Traces of fast neutron irradiation (recoil protons) at both sides: obtained, apparently, in security facility during air-transportation. (peaks at 8.0 and 8.6 are consistent with alphas from Rn and Th series). No peaks is seen after subtraction of the rear side counts from the front side one. In the track diameter range of interest (4.0<d<8.0 μm) <N(bg)> = 25±10 track/cm2 (normal Background is ~ 10 track/cm2), Etch: 6N NaOH, 70 C, t=7.0 hr.

10. TiDx e-beam stimulation results: total 42 runs of 60 min each: two CR-39 detectors [11 μm All (left) and 25 μm Cu (right)] with the Background (rear side) subtracting Both statistically significant 3 MeV proton (5.2-5.4 µm track diameter) and 11-20 MeV alphas (7.0-7.6 µm track diameter) bands are appeared in the 11 μm Al covered detector (left); bands of 1.5 MeV protons (track diameter 6.0-6.6 μm, consistent with the 3 MeV proton losses in 25 μm Cu foil) and 14 MeV alphas (track diameter near 7.4 μm, consistent with ~ 17 MeV alpha losses in 25 μm Cu foil are detected (right)

11. Averaged by two CR-39 detectors (11 μm All and 25 μm Cu) emission rates for 3 MeV protons and energetic alphas in TiDx during 42 runs in 3 series (t = 2200 min) • For 3 MeV protons: <Np> = (8.4 ± 1.5) x 10-4p/s-cm2 of TiDx sample. (the significance level of the result above the Background is L = 5.6 ). • The yield of DD-reaction in the TiDx target under e-beam bombardment, taken only for movable deuterons) is found to be DD ~ 5x10-18 p/DD-pair (7 orders of magnitude above the “Jones level”). • For 10-20 MeV alphas N =(4.7 ± 1.0) x 10-4 /s-cm2 of the TiDx sample, (the significance is of ~ 4.5 ). The soft component of  (E ~ 11 MeV) is not statistically significant • The non-irradiated by e-beam face of the TiDx sample show no signatures of nuclear emission.

12. Experimental: Set up 2Ti/TiO2:Dx sample is placed between two CR-39 detectors with the 11 µm Al and 25 µm Cu filters and irradiated by X-rays on the air(I = 5 mA, U = 120 kV) 1 – CR-39 detectors, 2 – Ti/TiO2:Dx sample, 3 - 25 µm Cu 4 - 11 µm Al

13. Tracks of protons and alphas emitted from the TiDx sample irradiated by X-raysImage size 130x100 m

14. Tracks of protons and alphas emitted from the TiDx sample irradiated by X-raysImage size 130x100 m

15. TiDx X-ray stimulation results: total 4 runs of 60 min each: two CR-39 detectors [11 μm All (left) and 25 μm Cu (right)] with the Background (rear side) subtracting. Another Background detector (11 μm All filter) was in contact with blank Ti sample

16. Track diameters and energies of protons and alphas, corresponded to distribution of tracks on detector N10 with 25 m Cu filter.Ер, α – detected energy Е0 – energy before filter • N D, m Ер, α, MeV Е0, MeV • 16.0 ± 0.21.2 ± 0.23.0 ± 0.2 • 27.4 ± 0.211.5 ± 0.516.5±0.5 • 38.0 ± 0.27.5 ± 0.513.5±0.5 • 49.4 ± 0.24.4 ± 0.311.7±0.3 • 5 10 ± 0.23.5 ± 0.311.0±0.3 • 611 ± 0.22.4 ± 0.210.5±0.2 • 711.4 ± 0.22.1 ± 0.110.3±0.1 • 812 ± 0.22.0 ± 0.110.2± 0.1

17. Examples of measurement of α-particle energies on the ranges in CR-39 detector and Cu filter 3α-track. Sample – TiDx + X-ray, CR-39 + 25 µm of CuImage size 130x100 µm Eα1= 9.7 MeV, Eα23= 10.6 MeV

18. 3α-track. Sample – TiDx + X-ray, CR-39 + 25 µm of Cu Image size 260x200 µm Eα1= 10.2 MeV, Eα2= 10.7 MeV, Eα3= 14 MeV

19. TiDx X-ray stimulation results:emission rates for 3 MeV protons and energetic alphas in TiDx during 4 runs of X-ray irradiation (texp = 4 h) • For 3 MeV protons: fluxes against and along the X-ray beam are np1(3 MeV) = (1.5 ± 0.3 )10-2andnp2 (3 MeV) = (3.8 ± 0.4 )10-2c-1cm-2into 4π, respectively. The flux along the beam is 2.5 times more than against • For 10-20 MeV alphas: fluxes against and along the X-ray beam are nα1(>10MeV) = (2.2 ± 0.8 )10-3 andnα2(>10MeV) = (5.0 ± 0.3 )10-2c-1cm-2into 4π, respectively. The flux along the beam is 23 (!) times more than against • Thus we have strong anisotropy of charged particle fluxes emitted against and along the X-ray beam • The mean flux of 3-MeV protons for 2 CR-39 detectors are <np(3 MeV)> = (2.7 ± 0.2)10-2c-1cm-2. The results ~2 orders of magnitude more intensive than for e-beam stimulation • The mean flux of 10-20 MeV alphas for 2 CR-39 detectors are <nα(>10 MeV)> = (2.6 ± 0.2)10-2c-1cm-2 . The results are ~2 orders of magnitude more intensive than for e-beam stimulation

20. Reconstruction of charged particle primary energy spectra

21. Alpha particle energy spectra (fine structure)demonstrates few bands in the range 10 – 17 MeV

22. Conclusions • Taking into consideration experiments with e- beam in vacuum and X-ray on air irradiation, we come to conclusion that electron beam (J ~ 100-300 nA, E = 30 keV) and X-ray (I = 5 mA, U = 120 kV) stimulation of the Ti based deuteride targets (cathodes) surface can really to enhance the intensity of the emissions of nuclear charged particles. • Both products of DD-reaction (3 MeV protons) and high energy alphas (10-17 MeV) are clear distinguished in e-beam and X-ray stimulation experiments with the TiDx targets. • The signatures of 3 MeV protons and energetic alphas are appeared simultaneously at the surface of all independent detectors used in the same experiment and provided by metallic foil filters with different stopping ranges/powers. • 3-MeV protons are the DD-reaction products whereas the emission of alpha-particles in energy range 10 – 17 MeV is the result of some unknown nuclear reactions. • Using of X-ray stimulation of the Ti based deuteride provide the charged particle emission, that are ~2 orders of magnitude more intensive than for e-beam stimulation • The results of this work were published in JETP (2011) v.112, p.952