Coatings for neutron conversion for nTOF Wil Vollenberg

Coatings for neutron conversion for n_TOF Wil Vollenberg TE-VSC-SCC VSC Seminar 11 Nov. 2011 Wil Vollenberg

Contents: - introduction - 10 B 4 C coatings for n-TOF - Sulfur coatings for n-TOF (33 S) - conclusion and future work VSC Seminar 11 Nov. 2011 Wil Vollenberg

What is / does n-Tof: neutron time of flight facility Neutrons are produced in a wide range of energies and in very intense beams. Kinetic energy determined by time of flight This allows precise measurements of neutron related processes (neutron cross section) that are relevant for several fields. - Nuclear (astro) physics - Nuclear technology - Archeological and cultural studies - Nuclear Medicine (33 S) VSC Seminar 11 Nov. 2011 Wil Vollenberg

n-Tof Lead Target Proton beam from PS Neutron beam 200 m sample few cm Neutron detector Necessary to measure neutron flux: - measurement upstream of sample position - mass as low as possible to reduce perturbation VSC Seminar 11 Nov. 2011 Wil Vollenberg

Principle of Micromegas for neutron detection Neutron / charged particle convertor * 10 B Ionization of filled gas by charged particles Signal amplification + spatial resolution 10 B + n → 7 Li + 4 He (energy ≤ 100 e. V) 235 U fission VSC Seminar 11 Nov. 2011 (energy ≥ 100 e. V) THIN FILMS Wil Vollenberg

Boron B thin films 4 C thin But how to make this film? Coating by DC magnetron deposition using B 4 C target, enriched 10 B (>96%). (B 4 C is a conductor) Support: Reduce to minimum material to minimize the perturbation Solution: Coatings on thin polymers VSC Seminar 11 Nov. 2011 Wil Vollenberg

DC Magnetron sputtering planar configuration VSC seminar 13 -11 -2009 Wil Vollenberg

B 4 C thin films 10 B 4 C 10 B on Polymer: Bad adherence 4 C on aluminized Mylar foils: - good adherence - problems with heat load: reduce power still stress in foils - Low deposition rate - Still stress → Try other polymer VSC Seminar 11 Nov. 2011 0. 23 µm 10 B 4 C Wil Vollenberg

10 B 4 C coatings for n_TOF Support : Kapton foil 12 µm + 1 µm Cu film 10 B C coating on Cu side of foil 4 Good results in case of: - small samples ( Ø 35 mm – Ø 80 mm)) Ø 35 mm - reduced power - sputter ion cleaning insitu 1. 1 µm 10 B 4 C 2 µm 10 B 4 C Ø 80 mm VSC Seminar 11 Nov. 2011 Wil Vollenberg

10 B 4 C coatings for n_TOF Ø 80 mm Drawings n-Tof Micro Megas (MGAS): Neutron fluence VSC Seminar 11 Nov. 2011 XY Megas : Spatial resolution Wil Vollenberg

10 B 4 C coatings for n_TOF (sulfur project) Most recent: 50 µm Kapton + 10 nm Cr + 200 nm Cu Support: Ø 180 mm Coating on Ø 90 mm: 0. 9 µm B 4 C VSC Seminar 11 Nov. 2011 Wil Vollenberg

10 B 4 C coatings for n_TOF Thickness measurement: CERN: SEM cross section Uni. Sevilla: RBS B 4 C RESULTS IDENTICAL Silicon sample Collaboration with ILL / LIU / ESS: - SEM: Same results - ERDA: 82 % of 10 B in film - HRXRR: density: 2. 41 g/cm 3 VSC Seminar 11 Nov. 2011 Wil Vollenberg

10 B 4 C coatings for neutron detectors Scientific collaboration with ESS /ILL Aim: replace 3 He neutron detectors by “grid” detector with 10 B thin films: Prove effiency increase of 10 B instead of nat. B 2 nd prototype 3 m 2 Large area ≥ 100 m 2 VSC Seminar 11 Nov. 2011 ILL Wil Vollenberg

SULFUR COATINGS Lead Target Proton beam from PS Neutron beam 200 m n-Tof sample few cm Neutron detector VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films (33 S) for cross section measurement For nuclear medicine applications But how to make this film? Thermal Evaporation Sulphur is an extremely volatile and reactive material Deposition is possible by thermal evaporation in vacuum (T~120°C) First tests with nat. S VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films Support: Reduce to minimum material to minimize the perturbation → Polymers However sulphur did not adhere to the substrates (kapton, Mylar, etc. ) which may be acceptable for the experiment. VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films As for B 4 C films: Kapton + Copper film Coating spot but bad adherence After 4 days: coating darker and better adherence VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films From literature: Simple Method for Making Sulfur Targets D. D. Watson ; Rev. Sci. Instrum. 37, 1605 (1966); Ag 2 S formation by sulfur evaporation at 200 ºC and condensation on bulk Ag heated at 150 ºC. Advantages: easy / good adherence / small amount of Sulfur / can be used for isotopes Disadvantage: Aging effect after several months in air VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films Solution: Apply this principle by reacting S while being evaporated with a thin Cu layer deposited onto a thin Kapton foil, to form a stable compound Cu 2 S. VSC Seminar 11 Nov. 2011 Wil Vollenberg

Sulfur thin films Solution: Apply this principle by reacting S while being evaporated with a thin Cu layer deposited onto a thin Kapton foil, to form a stable compound Cu 2 S. Heated Kapton sample With thin Cu 2 film S film Heating tape Boat loaded with Sulfur VSC Seminar 11 Nov. 2011 Wil Vollenberg

Coating optimization The process required a lengthy optimisation. The final coating quality has been found to strongly depend on: The sample reaction temperature. Optimum ~ 60°C. The Cu substrate. -Standard Cu plated kapton foils do not work. -Specially prepared Kapton foils with thin Cu film made by magnetron deposition. The sputtering parameters used for Cu production have an influence on the Cu structure, which in turn has a strong influence on the S-Cu reaction. IN STUDY VSC Seminar 11 Nov. 2011 Wil Vollenberg

Coating optimization The process required a lengthy optimisation. The final coating quality has been found to strongly depend on: The evaporation chamber. -Remaining S from previous evaporation runs condensed on cold surfaces perturbs subsequent runs. -Extensive chemical cleaning after each run is necessary for reproducible results. VSC Seminar 11 Nov. 2011 Wil Vollenberg

Final “recipe”: CERN standard Kapton with Cu coating. Remove chemically Cu. Adhesion Cr layer (25 nm) left in place Sputter coat a 10 nm Ti layer (adhesion) and 200 nm Cu layer with carefully selected parameters. Pump down deposition chamber. Pre-heat the Cu substrate in the evaporation chamber at 60 °C. This has to be done in a clean N 2 atmosphere (for better heat exchange). Evaporate a few mg of S at 120 °C onto the substrate kept at 60 °C Store all produced films in vacuum or N 2 All testing carried out with 32 S. All thickness calibration done by RBS in Sevilla (correlation between the amount of S evaporated and the thickness) VSC Seminar 11 Nov. 2011 Wil Vollenberg

Final coatings with 33 S 15. 7 mg 33 S VSC Seminar 11 Nov. 2011 for 68 µg/cm 2 5. 6 mg 33 S for 24 µg/cm 2 Wil Vollenberg

Conclusions and future work: - Measurements ongoing in n-Tof Future: - Build new system: cleaning / heating / handling - Study needed : aging effects Cu structure effects on Cu 2 S VSC Seminar 11 Nov. 2011 Wil Vollenberg

END Acknowledgments: colleagues SCC section: surface treatement workshop TE-MPE for sample preparation VSC Seminar 11 Nov. 2011 Wil Vollenberg