Nitrogen camera

The X-ray camera is prepared to accept a loop-mounted sample. The X-ray camera should be properly aligned with the X-ray beam and the cold nitrogen cold stream should be aimed at the eucentric point of the X-ray camera. 

Figure 4.4 Procedure for shock-cooling a crystal using a gaseous cryogen. (a) The goniometer head is assembled on the X-ray camera and the cold gaseous nitrogen stream is centred on the eucentric point of the camera, (b) The stream is deflected with some appropriate obstruction.

The most intriguing of Saturn s moons is Titan, larger than the planet Mercury. It is the only moon known to have an atmosphere. Nitrogen and methane gasses shroud Titan with dense clouds which our cameras cannot penetrate. The chemistry of this atmosphere is unlike that of any other. If we could descend to the surface of Titan, we might see ice mountains softly eroded by a persistent rain of complex chemicals, and a deep chemical ocean, a strange parody of the oceans of earth. Titan s atmosphere, like the ancient atmosphere of earth, contains prelife chemicals, but is too cold for life to evolve. 

The aerated stirred vessel is placed in a square vessel that is filled with water to obtain the picture of the bubbles. The impeller is rotated at a fixed rotational speed and the nitrogen gas is fed at a fixed flow rate. After confirming that the flow in the vessel has attained steady state, the images of bubbles are obtained by a video camera. By using these images, the bubble size distribution is estimated by fitting new PSD defined by Eq. (5.18). 

Some nitrogen dioxide was mixed with phosgene to make the clouds visible, so we wanted time lapse photos. I rigged up a windshield wiper with a t riable voltage rheostat source from a battery. This was used to trip a movie camera at voltage dependent intend. We t some good pictures that way. 

The excitation of the t-PL was carried out using a continuous wave NdrYLF laser with a wavelength of 266 nm (hio = 4.66 eV), i.e. a photon energy between the GaN (3.5 eV) and AIN (6.2 eV) band gaps. The laser spot was about 1.5 am in diameter. The density of QDs in our samples is about lO" cm, so about 10 QDs was excited in the experiment. Polarization of radiation from the sample was rotated by a half-wave plate and was analyzed by Gian Thompson polarizer. The p-PL signal was detected by a liquid-nitrogen cooled UV-enhanced CCD camera. 

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