The Low Energy Neutron Source at IUCF

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1 The Low Energy Neutron Source at IUCF David V. Baxter Indiana University 21 September, 2005 Acknowledgments Mike Snow John Cameron Aslam Lone Paul Sokol Hans Otto Meyer Mark Leuschner Helmut Kaiser Laddie Derenchuk Tom Rinckel Chris Lavelle Nick Remmes Sasha Bogdanov Sasha Klyachko Barbara von Przewoski Many more! OUTLINE Why use neutrons and how do you do it? What is LENS? Early results and plans for the future Conclusions Why Neutrons? Weak non-destructive probe of condensed matter with easily interpretable results. Random n-nucleus n nucleus cross section across the elements -> see light elements amongst heavy. n-h H is very different from n-dn -> > useful for probing polymers, biomaterials, etc. to really see what the hydrogen is doing! Also sensitive to magnetic moments! Versatile probe of the weak interaction Water in Fuel Cells From J Root: Neutron Radiography from NIST 1

2 H on nanotubes Artificial membranes Neutron Reflectometry from NIST CNBT team 2005 From Paul Sokol Protein Interactions (in solution!) JK Krueger et al. Biochem. 37, (1998) Calmodulin and myosin L C Kinase Scattering: Neutron Facilities (traditional) Reactor λ + θ Q ( δλ/λ ) Crystal (<< 1%) Vel. Selector (1-40%) I K I C I CK Spallation Time-of-flight (<1%) (SPSS) From R. Pynn, UCSB From R. Pynn, UCSB ISIS ILL 2

3 Brightness over the years The Spallation Neutron Source (SNS) From Reactor Pulsed Neutron Sources What is LENS? Low Energy Neutron Source: : based on low-energy (p,nx)) reactions (E( p <13MeV) in Be. Applications to Materials Research and Single Event Effects in electronics (NREP( NREP). The source is tightly coupled to a cold moderator (e.g. solid CH 4 at 4K<T<25K). LENS will have a variable pulse width (from <5 μs to more than 1.0 ms). In long-pulse mode, LENS will have a time-averaged cold neutron intensity suitable for materials research with SANS, reflectometry and other techniques. Budget : $13M+ (not including surplus etc.). Missions IUCF 3

4 IUCF LENS at IUCF Distinct Features of LENS Its low proton energy makes LENS ideal for studies of new moderator materials and designs. No high-energy (E>11MeV) neutrons and few γ s allows reduced costs, lower moderator temperature, close-in choppers, etc. Its variable pulse width (<5μs s to 1ms) makes LENS suitable for instrumentation development. Its low cost (both capital and operating) should make such sources accessible to industry and/or smaller nations. Major Applications Neutron moderator development. SANS studies of materials (glassy, magnetic, biological, composite, polymer, etc.). Develop precession instrumentation: SESAME, high- resolution diffraction, and reflectometry studies of materials. Neutron Radiography Education, particularly in the areas of Chemistry, Biology, and industrial applications. LPSS instrumentation development. Some fundamental physics (weak interaction). The Facility Timeline Official NSF project funding started in Sept Phase I (Now: 7MeV, 7mA, 0.3% DF; n/s) Moderator studies: Benchmarking LENS performance, lower T, different materials, Simple diffraction experiments with SANS instrument Initial instrumentation commissioning: Radiography, SANS Phase Ia (Early 2006: 7MeV, 20mA, 2% DF; n/s) Phase II (Fall 2006: 7MeV, 50mA, 5% DF; n/s) SANS studies of complex fluids, nano-materials, clays, Development of Precession instrument, RF spin flippers etc. Neutron Radiation effects (SEE) studies in electronics Eventual power (13MeV, 50mA, 5% DF; n/s) Neutron Yield (n/mc) p + Be Reaction p+be Neutron Production MeV 7 MeV 2006 Yield ~ n/p@ 13 MeV ~ MeV E (MeV) 4

5 LENS Floor Plan-2007 Target Moderator Reflector (TMR) R.F. Systems NREP Accelerator SANS TMR Radiog. SESAME MCNP model of TMR Neutron Flux within the TMR 32kW beam power 5

6 Facility Layout: Fall 2005 Protons into linac: : 15 Dec Neutrons in 2-D 2 D Detector: 15 Dec Celebrations! 15 Dec Moderator Assembly PT-410 Al Polyethylene CH 4 50 cm Water 6

7 Cryostat insertion Cryostat insertion PT-410 Al Polyethylene CH 4 50 cm Water P [torr] first methane cooldown - 06Apr05 vapor pressure curve normalized T3 data First Neutron Spectra T [K] 3 He detector here Activation Foil here Cold Neutrons: 15 Apr First Cold Spectrum (T=3.6K) 7

8 Spectral Analysis: MCNP Moderator Cryogenic Tests T4 T3 Dec P(W) T4 (K) T3(K) * * Estimated thermal load at 32kW SANS Experiment (traditional) Collimation Spin Echo SANS P II + II - II I A k f k i Q=k f -k i Encode momentum info in neutron SPIN! NO COLLIMATION NEEDED! Max length scale probed is set by the maximum B field; 0.1T microns! The measured quantity is the Polarization as a function of magnetic field (B) and λ: P( z) = (1 s) + G( z) P where: G ( z) dq dq S ( Q ) cos( zq + ε ) = y z z o 2 z = Cλ Bcot( θ ) s is the fraction of scattered neutrons and P o is the polarization without a sample. o Conclusions LENS has produced its first cold neutrons and is starting its work on science, education, and technology. The next few years will see a steady increase in the source power, instrument commissioning, etc. The facility provides a unique opportunity for developing cold-moderator technology, novel instrumentation, materials research, and neutron radiation effects. 8