Egypt, Cairo, Tahrir Square, 25 Jan

Huge lattice for calibration of SANS instrument Ahmed Esmail Shalan Ahmed Kamel Mohamed Ahmed Eid Hamed Hossam Donya supervisor Dr. Alexander Kuklin Pesenter: Hossam Donya, Menoufia university

SANS is a powerful method for condensed matter investigation for objects of sizes between 1 nm to 100 nm – therefore it can be considered a nanoscale procedure. The IBR – 2 reactor at the JINR is adequate for SANS machine. Several applications for SANS exist in the fields of Biology, Chemistry, Polymers, Ferrofluids, etc.

Since the early days of neutron scattering, there has been an insatiable demand for higher neutron fluxes. Neutron sources are based on various processes that liberate excess neutrons in neutron rich nuclei such as Be, W, U, Ta or Pu. Presently, the highest fluxes available are around a few n/cm 2 sec. Even though various neutron sources exist, only a few are actually useful for scattering purposes. These are: 1- Steady-state reactors. 2- pulsed reactors. 3- spallation sources. 4- some other neutron sources.

Universitatea din Bucuresti, Facultatea de Fizica, Septembrie 2008 High energy incoming particle (typically protons) Heavy metal target (Ta, W, U) Neutron cascade >10 neutrons per incident proton low energy load per outgoing neutron (~ 55 MeV) 2.5 neutrons per event 1 neutron consumed in sustaining reaction 0.5 absorbed high energy load per neutron(~ 180 MeV) Spallation Fission

1- possible to measure isotopes and used to measure magnetic materials. 2- Neutrons interact through short-range nuclear interactions. They are very penetrating and do not heat up (i.e., destroy) samples. 3-Neutron energies are comparable to normal mode 3- Neutron energies are comparable to normal mode energies in materials (for example phonons, diffusive energies in materials (for example phonons, diffusive modes). Neutrons are good probes to investigate the modes). Neutrons are good probes to investigate the dynamics of solid state and liquid materials. dynamics of solid state and liquid materials. 4-Neutron wavelengths are comparable to atomic sizes and inter-distance spacing. 4- Neutron wavelengths are comparable to atomic sizes and inter-distance spacing. Advantage of neutron scattering

1-Neutronsources are characterized by relatively low fluxes compared to x-ray sources (synchrotrons) and have limited use in investigations of rapid time dependent processes. 1- Neutron sources are characterized by relatively low fluxes compared to x-ray sources (synchrotrons) and have limited use in investigations of rapid time dependent processes. 2-Relatively large amounts of samples are needed: typically 1 mm-thickness and 1 cm diameter samples are needed for SANS measurements. This is a difficulty when using expensive deuterated samples or precious (hard to make) biology specimens. 2- Relatively large amounts of samples are needed: typically 1 mm-thickness and 1 cm diameter samples are needed for SANS measurements. This is a difficulty when using expensive deuterated samples or precious (hard to make) biology specimens. 3-Neutron sources are more expensive to build and to maintain. 3- Neutron sources are more expensive to build and to maintain. Disadvantage of neutron scattering

Sizes of interest = “large scale structures” = 1 – 300 nm or more Mesoporous structures Biological structures (membranes, vesicles, proteins in solution) Polymers Colloids and surfactants Magnetic films and nanoparticles Voids and Precipitates

SANS PRINCIPLE A typical sans result is a graphic of the Scattering Intensity function of a wavevector Q Q is defined as where Theta = scattering angle Lambda = Wavelength of incident beam The scattering intensity is defined as: Where Phi = density of particles in volume P(Q) = form factor S(Q) = structure factor J. Texeira, Introduction to Small Angle Neutron Scattering Applied to Colloidal Science, Kluwer Academic Publishers, Netherlands, 1992

FORM AND STRUCTURE FACTORS FORM FACTOR Concerns each particle and is related to its nuclear density Usually defined as: Where F(Q) is defined as: Rho is the density of scattering length of the sample It can be calculated using a simple formula (given here for heavy water): Where b is the scattering length of deuterium respectively oxygen STRUCTURE FACTOR Is related to the spatial distribution of the centres of mass Is usually defined as Where R is the position vector of a particle inside the compound

CONTRAST VARIATION METHODS Contrast variation is used when the sample being studied is made up of a series of compounds with close scattering lengths One of the most important advantages of SANS spectroscopy is the ability to change contrast by isotope substitution The most common form of substitution is changing hydrogen compounds with deuterium ones Another interesting situation appears when a mixture of normal and deuterated solvents are obtained in colloidal suspensions in such a way that the background scattering length of the solvent is “erased”. This is called contrast matching We can take as an example a sample containing three compounds and, using contrast matching, we can erase the contrast between two parts allowing us to analyze the third compound

IBR-2 Pulst Fast Reactor

EQUIPMENT IBR – 2 Reactor YuMO Spectrometer: 1 – reflectors; 2- zone of reactor with water moderator; 3 – chopper; 4,6 – collimator; 5- neutron guide(vaccum tube); 7- thermostate; 8 – sample table; 10- Vn-standered; 11,12 – detectors; 13- PSD detector ;14 – direct beam detector Reactor parameters: Mean power 2 MW, in pulse 1500 MW Pulse frequency of 5 Hz Spectrometer parameters: Wavelength 0.5 A to 8 A Size range of object 500 A – 10 A Size of beam on sample 8 – 22 mm 2 Detectors of 3 He (home made) Detector for direct beam of 6 Li (home made)

Silver behenate: is a silver salt of the long-chain fatty acid behenic acid It is a possible low-angle diffraction standard that was characterized using the powder diffraction technique. Diffraction patterns obtained with 1.54 Å synchrotron and Cu Ka radiations showed thirteen regularly spaced (001) peaks in the range °q. Sample example: Silver behenate SANS spectrum from Silver Behenate showing a sharp first peak at Q = 0.01 (d-spacing of Å).

Data Treatment d= 2π/Q o

d= A  Qo = T= 3.55 Qo = 2π/d

The resolution of the device and the quality of the information depend on considering the errors due to wavelength,finite width of the detector cell,finite time of the detector and collimation system. The calibration of delay time is very important in SANS instrument and it can be achieved using data of Ag behenate as a standard sample. Delay time of SANS YuMO instrument was found to be 3.55 m sec. Conclusion

AKNOWLEDGEMENTS The authors would like to acknowledge Dr. Kuklin Alexander and all members of the YuMO Group, Condensed Matter Department. We would also like to extend our regards to the organizers of this Practice and all members of the JINR involved with this project. We would also like to thank the Ambassador of the Arab Republic of Egypt in the Russian Federation and all the members in the embassy for their kind Reception in the Embassy of Egypt.