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

2. Contents: - introduction - 10B4C coatings for n-TOF - Sulfur coatings for n-TOF (33S) - conclusion and future work
VSC Seminar 11 Nov. 2011
Wil Vollenberg

3. 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 (33S)
VSC Seminar 11 Nov. 2011
Wil Vollenberg

4. n-Tof
Neutron beam
Lead Target
sample
200 m
Proton beam from PS
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

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

6. Boron thin films B4C thin films But how to make this film?
Coating by DC magnetron deposition using B4C target, enriched 10B (>96%). (B4C is a conductor)
Support: Reduce to minimum material to minimize the perturbation
Solution: Coatings on thin polymers
VSC Seminar 11 Nov. 2011
Wil Vollenberg

7. DC Magnetron sputtering planar configuration
VSC seminar
Wil Vollenberg

8. B4C thin films 10B4C on Polymer: Bad adherence
10B4C on aluminized Mylar foils:
- good adherence
- problems with heat load: reduce power still stress
in foils
- Low deposition rate
- Still stress
→ Try other polymer
0.23 µm 10B4C
VSC Seminar 11 Nov. 2011
Wil Vollenberg

9. 10B4C coatings for n_TOF Support : Kapton foil 12 µm + 1 µm Cu film
1.1 µm 10B4C
10B4C coating on Cu side of foil
Good results in case of:
small samples
( Ø 35 mm – Ø 80 mm))
reduced power
sputter ion cleaning insitu
Ø 35 mm Ø
2 µm 10B4C
Ø 80 mm
VSC Seminar 11 Nov. 2011
Wil Vollenberg

10. 10B4C coatings for n_TOF Ø 80 mm XY Megas : Micro Megas (MGAS):
Drawings n-Tof
XY Megas :
Spatial resolution
Micro Megas (MGAS):
Neutron fluence
VSC Seminar 11 Nov. 2011
Wil Vollenberg

11. 10B4C coatings for n_TOF (sulfur project)
Most recent: 50 µm Kapton + 10 nm Cr nm Cu
Support: Ø 180 mm
Coating on Ø 90 mm:
0.9 µm B4C Ø
VSC Seminar 11 Nov. 2011
Wil Vollenberg

12. 10B4C coatings for n_TOF Thickness measurement:
CERN: SEM cross section
B4C
Uni. Sevilla: RBS
RESULTS IDENTICAL
Silicon sample Ø
Collaboration with ILL / LIU / ESS:
- SEM: Same results
- ERDA: 82 % of 10B in film
- HRXRR: density: 2.41 g/cm3
VSC Seminar 11 Nov. 2011
Wil Vollenberg

13. 10B4C coatings for neutron detectors Scientific collaboration with ESS /ILL
Aim: replace 3He neutron detectors by “grid” detector with 10B thin films:
Prove effiency increase of 10B instead of natB Ø
2nd prototype 3 m2
Large area ≥ 100 m2
ILL
VSC Seminar 11 Nov. 2011
Wil Vollenberg

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

15. Sulfur thin films (33S) 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 natS
VSC Seminar 11 Nov. 2011
Wil Vollenberg

16. 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

17. Sulfur thin films As for B4C films: Kapton + Copper film
Coating spot but bad adherence
After 4 days: coating darker and better adherence
VSC Seminar 11 Nov. 2011
Wil Vollenberg

18. Sulfur thin films From literature:
Simple Method for Making Sulfur Targets
D. D. Watson ; Rev. Sci. Instrum. 37, 1605 (1966);
Ag2S 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

19. 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 Cu2S.
VSC Seminar 11 Nov. 2011
Wil Vollenberg

20. 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 Cu2S.
Heated Kapton sample
With thin Cu2S film
With thin Cu film
Heating tape
Boat loaded with Sulfur
VSC Seminar 11 Nov. 2011
Wil Vollenberg

21. 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

22. 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

23. 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 N2 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 N2
All testing carried out with 32S.
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

24. Final coatings with 33S 5.6 mg 33S for 24 µg/cm2
VSC Seminar 11 Nov. 2011
Wil Vollenberg

25. Conclusions and future work: - Measurements ongoing in n-Tof Future: - Build new system: cleaning / heating / handling - Study needed : aging effects Cu structure effects on Cu2S
VSC Seminar 11 Nov. 2011
Wil Vollenberg

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