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Feasibility of An Ice based Cold Neutron Source

Feasibility of An Ice based Cold Neutron Source. Saibal Basu Solid State Physics Division Bhabha Atomic Research Centre Mumbai 400085, INDIA. Typically, neutrons with energy less than 5 meV or wavelength more than 4 Å are termed as cold neutrons in neutron scattering parlance.

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Feasibility of An Ice based Cold Neutron Source

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  1. Feasibility of An Ice based Cold Neutron Source Saibal Basu Solid State Physics Division Bhabha Atomic Research Centre Mumbai 400085, INDIA Typically, neutrons with energy less than 5 meV or wavelength more than 4 Å are termed as cold neutrons in neutron scattering parlance. A suitably chosen cold moderator placed inside the reactor in a pre-decided location in a research reactor can shift the Maxwellian energy distribution of the neutrons to lower energies and can cause considerable enhancement in cold neutron flux. Broadly this is the underlying principle of a cold neutron source. S. Basu, Hokkaido, July07

  2. 1985 1960 S. Basu, Hokkaido, July07

  3. Neutron Guides Reactor Block Triple axis Mag. Diffrac. FDS Single x-tal Diffr. University-DAE Power Diffr With PSD S. Basu, Hokkaido, July07

  4. Spin Echo + POLSANS SANS MSANS PNR S. Basu, Hokkaido, July07

  5. SANS-I Polarized Neutron Reflectometer Double Crystal SANS S. Basu, Hokkaido, July07

  6. SANS Facility at BARC (SANS-I) collimator: 2 m sample to detector: 2 m * = 2.2Å guide BeO filter as monochromator 1 m long PSD Q range: 0.015 to 0.3 Å-1 mean= 5.2Å S. Basu, Hokkaido, July07 [Aswal et al. Current Science 79, 947 (2000)]

  7. Typical SANS Data at Dhruva Reactor Transmission Data Measuring Time ~ 10 Hrs Scattering Data Scattering Data Most of the samples are measured in time range of 8 to 24 Hrs. Detector S. Basu, Hokkaido, July07 Beam Stop

  8. Polarized Neutron Reflectometer at Dhruva Journal of Neutron Research, 14 , (2006) 109 Monochromator : Si (113) Wavelength : 2.5 Å Polarizer : Co-Fe/Ti-Zr SM Non-Polarizer : Ni-Mo/Ti SM Detector : Linear He3 PSD Flux at sample : 104 n/cm2/s D.C. Flipper efficiency : 92 % S. Basu, Hokkaido, July07

  9. Reflectivity geometry and measurements • Specular reflectivity Scattering length density profile along normal to surface Θi = Θf • Off-Specular (diffuse) reflectivity To study the lateral inhomogeneties and morphology of the interfaces Height-height correlation functions S. Basu, Hokkaido, July07

  10. Refractive Index • The Schrödinger equation for neutron in medium of potential V • The refractive index is defines as For Ni: θc (in deg) = 0.1λ(Å) ≈ 6.0 arc minute per Å Reflection from smooth surface: matrix method S. Basu, Hokkaido, July07

  11. Continuity condition: S. J. Blundell, et al, Phys. Rev. B 46, 3391 (1992). S. K. Sinha, et al, Phys. Rev. B 38, 2297 (1988). When q to 10q, R becomes to 10-4R S. Basu, Hokkaido, July07

  12. Polarized Neutrons • Diffraction from Heusler alloys • Reflection from magnetized multilayers ( supermirrors) • Polarized 3He Nonmagnetic layer Choose Magnetic layer S. Basu, Hokkaido, July07

  13. Fe/Ge Multilayer-Semicond./Mag. : Possible spintronics material (A): Si /Ge(100Å)/[(Fe 20Å/Ge 20Å)]×5/Au 30Å Neutron X-ray Fe layers are crystalline and textured along [110] direction normal to the surface of the substrate. S. Basu, Hokkaido, July07 Ge layers are amorphous Appl. Surf. Sci., 240, (2005) 251

  14. Polarized neutron reflectometry Reduction in magnetic moment of ultra thin Fe layer on Fe/Ge multilayers Reduction in magnetic moment in ultrathin Fe (~17 Å) layer in this multilayer sample.1.45 μB(bulk value is 2.22 μB) S. Basu, Hokkaido, July07 Appl. Surf. Sci., 240, (2005) 251

  15. (B) Si /Ge(100Å)/[(Fe 70Å/Ge 60Å)]×10/Au 30Å Investigation of Interface magnetic moment Polarized neutron reflectometry Physica B, 385-386, (2006) 653 S. Basu, Hokkaido, July07 J. Appl. Phys., 101, ( 2007 ) 33913 Unpolarized Neutron and X-ray reflectivity

  16. Asymmetric ratio Reduction in magnetic moment at interfaces Asymmetric diffusion of Fe on Ge with respect to Ge on Fe. S. Basu, Hokkaido, July07 J. Appl. Phys., 101, ( 2007 ) 33913

  17. Ni/Cu thin films and multilayer • perpendicular magnetic anisotropy (PMA) and used in magneto-optical recording • magnetic moment: thickness dependent, reduction in magnetic moment • alloying at interfaces reduce the magnetic moment of the Ni (a) Ni/Cu Multilayer by sputtering Si (111)/[Ni 90 Å/ Cu 70 Å] × 5. lattice mismatch of about 2.5 % Absence of Ni peak S. Basu, Hokkaido, July07 Solid State Comm., 136, (2005) 400

  18. PNR: Reduction in magnetic moment Solid State Comm., 136, (2005) 400 S. Basu, Hokkaido, July07

  19. (b) Ni/Cu Thin film by electrodeposition XRD: Crystal Structure PNR: reduction in interface magnetic moment The XRD confirms that the film is of polycrystalline nature. layers have not undergone any strain distortion Magnetic moment of Ni atom increases gradually to the bulk value from the interface Ni layer to the deep-seated Ni layer. S. Basu, Hokkaido, July07 Electro. and Solid-State Letters, 9, (2006) J5.

  20. This requires a suite of spectrometers: * * * S. Basu, Hokkaido, July07

  21. World Scenario There are several cold moderator materials used all over the world in major neutron sources (research reactors and spallation neutron sources). These are liquid H2 or D2 at about 20 K, liquid CH4 at about 100 K, and solid CH4 at about 20 K. Liquid CH4 undergoes rapid polymerization under irradiation in a reactor and at present it is not used in any research reactors due to this problem. Its use is limited to spallation neutron sources with powers ranging from tens of watts to few kilowatts. The most commonly used cold moderator is liquid hydrogen around 20 K (e.g. Saclay, BENSC, NIST) or its more expensive variant liquid D2 (ILL Grenoble, FRM II Münich). S. Basu, Hokkaido, July07

  22. Data Collection • The experiment consisted of starting with the Be-filtered neutron counts in the detector for the water moderator at room temperature and then collecting neutron counts after removing the Be filters from the beam • Next the Be filters were placed in front of the detector and the moderator was cooled by flowing liquid nitrogen. While the moderator gets cold, the count in the Be-filtered beam goes up The increase in the counts of Be-filtered neutron beam coming from the cold moderator with respect to the counts from room temperature moderator indicates the shift in the Maxwellian. S. Basu, Hokkaido, July07

  23. Other alternatives Experiments performed in 1960’s clearly demonstrated suitability of D2O ice as cold moderator Till recently a D2O ice-based source at 20 K was operational at NIST, Gaithersburg, USA In the earlier days several D2O based sources were tested at MIT reactor One was operated at now-decommissioned CP-5 reactor at Argonne This moderator is not hazardous at all and may be an attractive option as an inexpensive, safe cold source with modest gain S. Basu, Hokkaido, July07

  24. With this background, we felt that a H2O ice based source maintained at 77K using liquid nitrogen as coolant is worth considering for implementation under the present circumstances at Dhruva. At this temperature water becomes polycrystalline ice Ih. This phase of ice is expected to give good moderation because it has six translational modes at 7.1mev, 13.2mev, 19.0mev, 24.2mev, 28.2mev and 37.7mev; while libration, bending and stretching modes exist at 89, 204 and 406 mev respectively. S. Basu, Hokkaido, July07

  25. S(α, β) for inelastic scattering from light Water ice. Model by Nakahara et. al. in Journal of Nuclear Science and Technology, 5 ( 31), 1968 K. Nünighoff et. al., Investigation of the Neutronic Performance of Advanced Cold Moderators and Validation of New Evaluated S(,) Neutron Scattering kernels, 16th meeting of the International Collaboration on Advanced Neutron Sources (ICANS XVI), May 12-15 2003, Dusseldorf, Germany Energy Spectra for ice measured at JESSICA S. Basu, Hokkaido, July07

  26. one may also estimate the spectrum by measuring the integrated intensity of a Be-filtered beam. Experiment in APSARA reactor A simple experiment was undertaken by us at APSARA reactor to reconfirm the moderating property of ice and to estimate the gain from a H2O ice source cooled by LN2 compared to the room temperature spectrum. One may estimate the gain by measuring the integrated intensity of a Be-filtered ibeam. S. Basu, Hokkaido, July07

  27. A moderator pot for efficiently producing ice in-situ was designed and fabricated. The moderator pot is made from pure aluminum in cylindrical geometry. Diameter of the cylindrical moderator pot was about 200 mm and the thickness of the pot was about 50 mm. It could hold approximately 600 cm3 of water in it. The pot was radially separated into two chambers: the central chamber was meant for holding water and the peripheral chamber is for circulating LN2 to cool the water chamber. S. Basu, Hokkaido, July07

  28. Experimental set up at APSARA The present experiment was performed at the neutron radiography beam line at APSARA reactor. The schematic of the experimental set up is shown in the figure S. Basu, Hokkaido, July07

  29. Results match with COSY results S. Basu, Hokkaido, July07

  30. Proposed Cold Neutron Source for Dhruva Moderator pot will be enclosed in a water cooled vacuum jacket. Liquid nitrogen will circulated within its outer annulus while water will be contained in its central region. Freezing of water will be facilitated by provision of fins projecting inwards from the wall. The tube carrying liquid nitrogen to and from the moderator pot will be thermally isolated by a spacer from the other parts. It will be made of aluminum towards the side of reactor core and made of SS304 outwards. This minimizes heat transfer as well as nuclear heating. The moderator pot will have separate ports for filling and draining water. S. Basu, Hokkaido, July07

  31. Proposed flow diagram S. Basu, Hokkaido, July07

  32. Nitrogen Flow Loop • Liquid nitrogen circulation outside the in-pile assembly will occur through a number of double-walled transfer lines. These will be connected to the liquid nitrogen Dewars. When Dewar is pressurized liquid will flow to the moderator pot and will go to another Dewar which will be vented to atmosphere. When inlet Dewar is empty a liquid level sensor unit will do the flowing things to reverse the flow direaction • closes the pressurization valve of inlet Dewar • opens vent valve of inlet Dewar • opens pressurization valve of outlet Dewar • closes vent of outlet Dewar S. Basu, Hokkaido, July07

  33. Safety Commercial liquid nitrogen will be used as the coolant in this project. It contains certain amount of oxygen. Commercial liquid nitrogen will be used as the coolant in this project. It contains certain amount of oxygen. Nitrogen will be removed continuously so that no oxygen enrichment may occur Mock up test: Presently we have made a loop to simulate the cooling of the moderator under an estimated nuclear heating of 900 W at the moderator pot location in Dhruva reactor and map the temperature profile of ice under heat load and LN2 flow rate S. Basu, Hokkaido, July07

  34. Thank You S. Basu, Hokkaido, July07

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