Neutron reflection real time

However, the low intensity of the neutron beam and the coarse resolution compared to x-rays often result in quite large error bars. The flux of a neutron beam is typically more than 5 orders of magnitude smaller than the photon flux of a synchrotron radiation source with up to 10 photons/sec on an area of (0.2x2)mm. From Eq. 1 it is known that the specularly reflected intensity at least falls with 1/ /. Thus, the low intensity of a neutron beam restricts the acc sible -range (a neutron reflectivity almost never exceeds a -value of qz,muF 0.2A" ). This means a relatively coarse resolution Az in real space via Azoc27i/ niax- In contrast, an x-ray reflectivity easily covers about 9 orders of magnitude which corresponds to a range of 0.7A to l.OA This yields a 4 times better resolution in real space if x-rays are used. 

Neutron reflection has been used to stu die interfaces between the melt phases of ciystallisable polymers as well as real time interdiffusion of polymers and oligomers. Both systems are experimentally demanding and have required the use of specialised cells and data collection procedures. The interfacial widths for a number of polymer systems have been determined and the Flory Huggins interaction parameters obtained. In addition, the interdiffiision process has been followed for a polystyrene-polystyrene system above its Tg and also for a polystyrene-oligostyrene in-situ in real time using very rapid reflectivity scans. 

Table III. The characteristics of the polymers used in real time neutron reflection...

With current neutron sources the times of data collection for each partial reflectivity scan will remain of the order of minutes. However, with the advent of the next generation of high intensity neutron sources being planned or built around the world significant advances can be predicted for these real time measurements. Time will tell as the saying goes. 

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