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Sonoluminescence

Introduction

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A sonoluminescing bubble is trapped in a fluid (water is the best) by an intense oscillating acoustic field which forces the bubble to expand and collapse during each acoustic cycle. Typically,  the ambient radius of the bubble is 5 μm, expands to a maximum of 50 μm, and then collapses to a minimum of about 0.5 μm. The last stages of the compression occurs so rapidly that gas temperature in the bubble  is thought to reach as high as 20,000 K at a pressure of about 10,000 atm. A very brief (about 150×10-12 sec) flash of light is emitted just before the bubble reaches the minimum radius. The emission occurs synchronously with the imposed sound field of about 20 KHz. The emission spectrum is broad without any discrete lines and is well represented by a black body radiation spectrum.

It has been found that a small percentage of the noble gas Argon present in air is essential for both the stability and brightness of the bubble in Single Bubble Sonoluminescence (SBSL). 1,2 This phenomenon is explained by the dissociation hypothesis which states that as the bubble collapses the temperature becomes high enough (9,000 K) to dissociate N2 and O2. These N and O radicals react with H radicals from dissociated water vapor forming products which dissolve into the water.3 We aim to investigate the effects of mixing two or more noble gases into Nitrogen gas. During collapse there is a large temperature and pressure gradient within the bubble. It has been theorized that these gradients are sufficient to segregate a noble gas mixture. This causes the species with lower mass to gravitate towards the lower pressure and higher temperature region at center of the bubble.4 Our objective is to measure the effects of segregation on SBSL.
[1] B.P. Barber, R.A. Hiller, R. Lofstedt, S.J. Putterman, and K.R. Weninger, Phys. Rep. 281, 67 (1997)

[2] M.P. Brenner, S. Hilgenfeld and D. Lohse, Rev. of Mod. Phys. 74, 425(2002)

[3] Detlef Lohse, Michael P. Brenner, Todd F. Dupont, Sascha Hilgenfeldt, and Blaine Johnston, Phys. Rev. Lett. 78, 1359 (1997)

[4] B.D. Storey and A.J. Szeri, J. Fluid Mech. 396, 203 (1999)

 
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