The title of our Project in CRP: “Study of the tritium content in materials of fusion reactors”

1. The title of our Project in CRP: “Study of the tritium content in materials of fusion reactors” S.V. Artemov, Ya.S. Abdullaeva, A.H. Abdurakhmanov, Karakhodzhaev, G.A. Radyuk, V.P. Yakushev, E.A. Zaparov Institute of Nuclear Physics, Tashkent, Uzbekistan.

2. Objectives of the work as a whole • The project was directed to upgrade the NERD (Neutron-induced Elastic Recoil Detection) method, which is developed for definition the content and concentration profiles of tritium and other hydrogen isotopes in materials. • It was supposed that in consequence the modified NERD method will be used for diagnostics the areas of the tritium concentrations (in the frameworks of IAEA Co-ordinated Research Project “Tritium Inventory in Fusion Reactors”).

3. Principle of the Neutron–induced Recoil Detection (NERD) Method • The depth profiles of hydrogen isotopes concentration in materials are obtained from the energy spectra of the recoiled hydrogen nuclei induced by fast monochromatic neutron flux. • The relation between the concentration profile C(x) and the energy spectra N(E) of the recoiler nuclei can be roughly presented as: C(x) ~ N(E)(dE/dx)/nH HerenHis the cross section of the (n,H) elastic scattering and dE/dxis thespecific energy loss.

4. Scheme of Measurement in the NERD Method

5. Fast neutrons source Neutron generator NG-150 Ed=150 keV d+D→3He+n, En≈2.5 MeV d+T→4He+n, En≈14 MeV Solid TiD or TiTtargets

6. In the reported (up to 31 Sept. 2006) year of our Project we planned to do: • To develop and manufacture the telescope of detectors with improved energy resolution; • To develop and manufacture the remote control system to scan the investigated samples; • To make the electronic system for the ∆E-E telescope to sum up the signals from the doublet E-detectors; • To measure the content and concentration profiles of hydrogen isotopes in samples, if available.

7. Increasingthe sensitivity • It was achieved by: • - reducing the background of charged particles (including tritons). The material (graphite) was used for the box of ∆E – E telescope, which do not generate tritons in interaction with the fast (14 MeV) neutrons; • - decreasing the background of random coincidences of pulses from ∆E and E –detectors of the detecting system The random coincidences are conditioned by large intensity of the gamma-quanta from TiT-target of the NG-150. For this purpose some more fast electronics was used. It provides the quick selection (T=0.15 sec) of the analysed signal; • - subtracting the background energy spectrum of tritons which arise in the interaction of fast neutrons with the nuclei of matrix of the analysed sample. For this purpose the additional function in the program of Monte-Carlo simulation has been developed for the background spectrum simulation.

8. ∆E-E -telescope with the reduced charged particle background and improved resolution (detectors “see” only carbon walls of the box and the surface of the analysed sample)

9. Block scheme of the electronics CSPA - charge-sensitive preamplifier with a fast output; FA ( FPA) - fast amplifier (fast post-amplifier); FSCA – fast single-channel analyzer; 23 DL- cable delay line; SA- spectrometric amplifier; ADC- analog-to-digital converter; СC – fast coincidence circuit; LG - linear gate.

10. Principal scheme of the modified fast linear gates.The pedestal under the passed signal is minimal

11. Electronic system for the ∆E-E telescope to sum up the signals from the doublet E-detectors with high energy resolution

12. Increasing the rapidity of analysis • Utilization of the mentioned above fast electronics allows one to use more intensive neutron flux and hence to increase the rapidity of analysis ~ in 3-5 times. • Some upgrade of the NG-150 target cooling system was done.

13. Improvement of the depth resolution • It was achieved due to more monochromatic neutron flux which irradiates the analyzed specimen. • A large amount of metal along the neutrons trajectories from the neutron source to the specimen was excluded. As a result the “geometric” energy resolution and hence the depth resolution was improved ~ in 1.5 times. • E-detectors with high energy resolution were used.

14. Energy spectra of recoiled protons before (a) and after (b) reconstruction of the target flange and entrance window

15. Increasing the reliability of analysis • Is achieved due to using the procedure of comparing the experimental energy spectra of the recoiled tritium nuclei with simulated ones which are calculated via the modified program of spectra simulation (DRIN_M). • This possibility is especially useful for the cases of non-uniform distribution of hydrogen in the analyzed specimen and sufficient contribution of the background reactions.

16. The system for change the analyzed samples and scanning along the surface

17. The characteristics of the upgraded NERD installation were checked using the test samples. The typical energy resolution of the spectrometer is 300 – 400 keV. These values results in the following depths resolutions: • for depths profile of hydrogen ~ 60 mkm • of deuterium ~ 20 mkm • of tritium ~ 10 mkm (up to • 5 mkm using Monte-Carlo simulation) • The depth of analysis (for example, in silicon) is: • for hydrogen – 1200 mkm • for deuterium – 500 mkm • for tritium – 260 mkm

18. Ranges of the hydrogen recoils from 14 MeV neutron elastic scattering

19. Sensitivity of the analysis is limited mainly by the preventing nuclear reactions (n,p), (n,d) and (n,t) on the nuclei of the analyzed materials. • It varies for various materials over a wide range: from ~ 0,1 аt.% to 1 аt.% for deuterium and tritium isotopes; • from ~ 1 аt. % to 10 аt. % for hydrogen (protium) isotope.

20. Rapidity of the analysis The rapidity of the analysis is: • a few hours for small concentrations (close to the sensitivity) • ~ tens minutes for the concentrations ~ 10÷100 аt.%.

21. A few examples of the NERD analysis.Sample: Ti saturated by T (width 5 mkm) on the molybdenum substrate (width ~50 mkm) after irradiation by the deuteron beam • The optimal form of the profile of T concentration is the linear decreasing within ~25 mkm T- difusion to molybdenum plate?

22. The sample with the configuration shown in insertion Green points connected with line is the experimental energy spectrum Violet line is the simulated by Monte-Carlo spectrum.

23. Two-dimensional ∆E-E -spectra for the samples:Left - boron carbide B4C exposed to a low energy (~200 eV/D) and high ion flux (~1021 m-2s-1) D plasma. D atoms diffuse into the bulk at temperatures above 553 K, and are accumulated up to maximum concentration of ~0.2 at.%. Right - CD2(8.3 mkm)-Al(100mkm)-CD2(20mkm)

24. Conclusion • The improved NERD installation and its analogues can be successfully used for diagnostic the elements of the “first wall” of tokamaks and other materials of the nuclear technology on presence and distribution of the hydrogen isotopes. The advantage of the NERD method: large depth of the analysis. The disadvantage: rather small sensitivity.

25. Thank you for the attention!

26. Additional information

27. Choosing of the constructional materials The criteria - minimal cross sections of the (n,n), (n,p), (n,d), (n,t) and (n, ) reactions Total cross-sections of gamma ray generation by neutrons in carbon, aluminum, silicon and iron as a function of neutron energies. Carbon is the best material. Aluminum alloys are preferable for the scattering chamber and metallic elements inside it.

28. Features of the method • Nondestructive measurement; • All hydrogen isotopes are analyzed simultaneously ; • Possibility of the analysis irrespective of the condition of material (gas, liquid, solid); • Depth of the analysis is hundreds mkm (defined by the range of recoil hydrogen nuclei in material); However the method is intended for the analysis of the relatively large hydrogen concentrations!!!

29. Tritium distribution in TiT sample (2) Experimental energy distribution of tritium (measurement #527) and its Monte-Carlo simulation for 3 different thicknesses of the uniform tritium distribution: 20 (green), 25 (red), 30 (blue) microns

30. Results of this work were presented at the International Conferences and in publications: • 1. G.A. Radyuk, S.V. Artemov, A.Kh. Abdurakhmanov, V.P. Yakushev, E.A. Zaparov, “Improvement of the Neutron-Induced Elastic Recoil Detection Spectrometer on Base of Neutron Generator NG-150”. Abstract Book of International Conference “NUCLEUS-2004”, Belgorod, (Russia), June 2004 y., P. 284. • 2.G.A. Radyuk, S.V. Artemov, A.H. Abdurakhmanov, A.A. Karakhodzhaev, L.I. Slusarenko, V.V. Tokarevsky, V.P. Yakushev, E.A. Zaparov “Modified NERD Spectrometer for H –Isotopes Profiling in Various Materials”. Third Eurasian Conference “Nuclear Science and its Application”, Tashkent, Uzbekistan, Oct 5-8, 2004, Abstract book, pp.69-70; • 4. S.V. Artemov, Ya.S. Abdullaeva, A.H. Abdurakhmanov, A.A. Karakhodzhaev, G.A. Radyuk, V.P. Yakushev, E.A. Zaparov. “NERD-method to study profiles of tritium concentration in interior elements of a fusion reactor”. INDC International Nuclear Data Committee, Summary Report of Second IAEA Research Co-ordination Meeting, Tritium Inventory in Fusion Reactors, IAEA Headquarters, Vienna, Austria, 18-19 October 2004.

31. Tritium distribution in TiT sample (1) Experimental energy distribution of tritons in TiT target (measurement #526) and its Monte-Carlo simulation for 3 supposed thicknesses of tritium location: 20 (green), 25 (red), 30 (blue) microns.

32. Restoring the tritons concentration profile The energy spectrum of tritons for the RGT sample (graphite with the boron carbide B4C covering) after plasma irradiation (JET) and the depth profile of the tritons concentration restored. (Reanalysed old data)