Small Angle Neutron Scattering (SANS)

Transcription

1 Small Angle Neuton Scatteing (SANS) A DANSE Subpoject DANSE Kick-Off meeting Aug Pasadena CA Paul Butle

2 SANS measues time aveaged stuctue of nm o moe Mesopoous stuctues Biological stuctues (membanes, vesicles, poteins in solution) Polymes Colloids and sufactants Magnetic films and nanopaticles Voids and Pecipitates

3 Anatomy of a SANS instument Sizes of inteest = lage scale stuctues = nm o moe 0.02 < Q ~ 2π/d < 6 Q=4π sinθ / λ 3-5< λ <20A and 0.1 < θ <20 64 cm - 1m Beam attenutato Velocity selecto Neuton Guide 2D detecto Souce Apetue, A 1 sample L 1 L 2 Sample Apetue, A k pixels

4 Incident beam Sample Scatteing Contibution to detecto counts 1) Scatteing fom sample 2) Scatteing fom othe than sample (neutons still go though sample) 3) Stay neutons and electonic noise (neutons don t go though sample) apetue sample ai cell Stay neutons and Electonic noise I meas (i) = Φ ta ε(i) Ω T c+s [(dσ/dω) s (i) d s + (dσ/dω) c (i) d c ]+I bgd t

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6 Small Angle Neuton Scatteing (SANS) Macomolecula stuctues: polymes, micelles,complex fluids, pecipitates,poous media, factal stuctues Measue: Scatteed Intensity => Macoscopic coss section = (Scatteed intensity(q) / Incident intensity) T d dσ dω v [ Q ] S = V S v ρ [] exp[ iq. ] 3-D Fouie Tansfom of scatteing contast 2 nomalized to sample scatteing volume V S v S v d 3 v 2 Recipocity in diffaction: Fouie featues at Q S => size d ~ 2π/Q S Intensity at smalle Q S (angle) => lage stuctues Slide Coutesy of William A. Hamilton

7 Uniqueness of models

8 O1 SANS Model Independent Concepts At lage q: 10 % black 90 % white S/V = specific suface ae

9 Slide 8 O1 Stuctue facto is had to model à pefe to avoid inteactions Invaiant = fo given amount of stuff X integated scatteing ove all Q is fixed Finite size and Guinie egion Repulsive and attactive inteactions Shap intefaces at high Q = Pood (see NR) à specific suface aea ORNL, 6/25/2006

10 SANS moe detailed analysis dσ dω coh ( Q) 2 = φv ρ P( Q) S( Q) p 1 S(Q) = Stuctue facto (inteactions o coelations) o Fouie tansfom of g() P(Q) = fom facto (shape) Q

11 Fouie tansfom P() Fequency = max 0 ) ( ) ( )) ( sin( ) ( 4 ) ( D j i j i j i j i j i o d Q Q P V Q I ρ ρ π Paid Distance Distibution Function PDDF Shape econstuction (ab initio)

12 So.. SANS DATA Analysis.. Let s DANSE At the same time we want: Analytic fom Modeling Fee fom modeling Stuctual modeling Add constaints In 2D.. Fo oiented objects Optimization with data based on some set of paametes Non paticulate (i.e no P(Q) and S(Q) sepaation (e.g. Sponge) G() (inteactions) allowing easy input of new ones impotant Complicated additions based on specific model (e.g. wates of hydation, exchangeable potons Confomational o othe seach MC and MD I(Q) Time esolved (and othe paametic studies AND (of couse) Intuitive and easy to use and extend Gaphical inteface with full 3D visualization Pefeably with automated guidance and idiot guads. Fast (inteactive as much as possible)

13 Choices fo Today s use I Get softwae fom somewhee: IGOR maco package distibuted fom NIST (latest elease last month) Gasp distibuted by ILL (eduction mainly but used fo votex lattices) ATSAS 2.1 distibuted by Dimiti Svegun EMBL (latest elease this yea) An eclectic aay of outines available fom vaious souces (ISIS maintains a site) II Do-it youself (mostly command line fotan baie to doing new stuff) III Minimal Analysis (bigge, smalle, slope of xxx. factal?) 1 Data taken on NG7 6/7/2000 Fit using Coe + shell sphee model\ 1/cm

14 Steps to the DANSE 1. Analytical model fits to 2D data sets and model independent fits 1. Include oientation with espect to beam 2. Include instument esolution 3. Include oientation and esolution coections 4. Include paametic analysis and simultaneous fitting 5. Include intelligent defaults and intelligent help 2. Ab initio (fee fom) modeling and P(R) 1. include most popula appoaches (dummy atom, spheical hamonics, etc) 2. Include intelligent help, and defaults 3. Include limit switches 3. Modeling of abitay shapes (including invesion to P(R)) 1. 3D model building fom simple shapes 2. Coase gain PDB file 3. Invet eal space model to I(Q) 4. MC and MD simulations fo complex inteacting systems 5. Refinements based on constaints 4. Full instument simulation with plug in sample fo expeimental planning

15 Fist step

16 DANSE cad I NIST and ORNL heavily involved -- Fall meeting planned to detemine: Shot tem plan fo collaboation and distibution of analysis softwae How to stuctue the shot tem plan to take advantage of DANSE components as soon as they become available Plan fo smooth long tem tansition to new system Some questions: How do we co-odinate with ATSAS, how to incopoate X-ay, is PDB sufficient o do we need a second standad II Othe inteested facilities US Los Alamos and IPNS Intenational SANS instument scientists inteested: ILL ISIS ANSTO HANARO III Fist contacts with most well known SANS algoithm developes Svegun Glatte Pedeson

17 When the Music Stops: Beyond DANSE The goal is NOT softwae - it is to extact all possible infomation fom the mateial being studied. Neuton scatteing fom the use s point of view is a pocess in which the sample is placed in the machine and the elevant, meaningful infomation comes out the othe end. Good softwae enables that pocess. The DANSE poject is not the end but the beginning. It cannot delive eveything. Rathe it must meet two objectives: 1. Povide baseline softwae that includes: 1. A libay of well documented and tested e-usable components 2. Basic applications with sufficient new value to attact lage numbes of uses 3. A new vision of ease of use as a means of fully utilizing the heavy invetsments in hadwae Fo success must do 3 things: Must povide eveything that is commonly doable with today s packages Must povide new functionality not commonly available with today s packages Must povide an easy famewok fo extension and contibution by the community

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