Cold Neutron Chopper Spectrometer

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Cold Neutron Chopper Spectrometer
Paul Sokol The Pennsylvania State University

• Scientific Focus
• Quantum Liquids
• Low Energy Inelastic Scattering
• Quasi-elastic Scattering and Diffusion
• Quantum Tunneling
• Magnetism

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Scientific Focus

• Scientific Focus
• Quantum Liquids, diffusion, magnetism,
• Broad community
• Instrument Requirerments
• Large Q-E range
• Good Resolution
• High S/N ratio
• Flexibility

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Quantum Fluids
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Magnetic Systems

• Dynamics near a Quantum Critical Point
• UCu3.5Pd1.5 at low temperatures
• No Long Range Magnetic Order
• Near antiferromagnet to paramagnet transition
• Spatial and dynamic correlations determined by
  T0 antiferromagnetic transition
• Isolated rare spins dominate
• Random magnets vs 2nd order phase transitions

M.Aronson et al. To be published
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• Cu(NO3)2D2O
• S1/2 AF alternating chain
• One magnon mode observed on IRIS
• Exceptional resolution
• Two magnon mode observed on SPINS
• Relaxed resolution
• Increased intensity
• The SNS Multichopper instrument will be able to
  observe
• One magnon with exceptional resolution
• Two magnon with sufficient intensity

G. Xu et al. PRL 84, 4465 (2000)
D. A. Tennant et al. cond-mat/0005222
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Quasi-elastic Scattering
A Quasi-Elastic and Inelastic Neutron Scattering
Study of H2 in Zeolite   H. Fu, F. Trouw, and
P. E. Sokol

• Diffusion of Water in Cement
• QE tails extends to 2 meV
• Short time librational motion in cage
• Long time relaxation of cage

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Tunneling
INS spectrum of methane in a controlled pore
glass taken with the high resolution chopper
spectrometer MIBEMOL. The excellent energy
resolution was necessary to resolve the peaks at
?77 meV and ?145 meV.
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Inelastic Neutron Scattering
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Instrument Development Team

• Executive Committee
• Paul Sokol Penn State
• Herb Strauss - Berkely 
• Sow-Hsin Chen - MIT
• Meigan Aronson Michigan
• Hak Taub Missouri
• Robert Dimeo NIST
• Instrument Scientist
• Garret Granroth

• Open Membership Policy
• Any interested parties can join.
• Current Membership
• 12 National Labs
• 18 University
• Disciplines
• Physics
• Chemistry
• Nuclear Enginerreing
• Materials Science
• Polymers
• Environmental Studies

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History of the IDT

• 1998 (Laresse et al)
• Tunneling
• Quantuim Liquids
• Adsorbed Films
• Porous Media
• 2000 (Sokol, Trouw et al)
• Enhanced emphasis on magnetism and porous media
• Better signal/noise ratio
• 2001
• Broader scientific emphasis
• Single crystals (magnetism)

• HERMES-I
• Graphite Backscattering
• 15 meV Resolution
• SABER
• Silicon Bacskattering
• 15 meV Resolution
• CNCS
• Disc Chopper
• 10-100 meV Resolution

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Development Plan
Two Phase Project

• Phase 1 - IPNS
• Modified Incident Flight Path
• Horizontal Final Flight Path
• Operational in three years

• Phase 2 SNS
• Full Spectrometer
• True Day 1 instrument

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Benefit Analysis

• Disadvantages
• Additional Cost

• Advantages
• Commissioning and testing in advance of SNS
• Development of analysis techniques
• High Involvement of Academic Community
• Development of new users in advance of SNS

• Milestones
• Periodic Reviews
• Is two phase approach still advantageous

The ultimate goal is to build a world class
spectrometer at the SNS
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Preliminary Cost Estimate
Equipment 6.9 M Personel 3.5 M University
Science/development 1.2 M Phase I Additional
costs 1.0 M Indirect 1.0 M Total 13.6 M
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SDT Structure
Principal InvestigatorP. Sokol(Spokesperson)

• PSU is lead institution
• Instrument Design
• Subcontract to IPNS
• Construction
• Commercial Vendors
• National Labs
• Universities
• Development
• Installation
• National Labs
• Universities

ExecutiveCommittee M. Aronson S.-H. Chen R.
Dimeo H. Strauss H. Taub
SNS/IPNS LiasonTBN
Design IPNS w/input IDT
Sample Environemnt IDT
Procurement PSU Specs from IPNS
Construction IPNS, SNS, IDT Q/A IPNS, PSU
Development IDT, IPNS, SNS
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Conclusions

• Disc Chopper Spectrometer
• Flexible
• Complimentary to Si BS and Fermi Chopper
• Scientific Program
• Broad range of topics and discipline
• Instrument of choice for many problems
• Development Plan
• Build the best spectrometer possible for SNS
• Advantages of a two-phased approach
• Pre-testing for SNS
• Day One instrument
• Build a user community