<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> With great reluctance, a minor clarification; The solar composition would reflect the composition of the nebula that formed our solar system, and since we know of 'primordial' uranium on earth, logically, there is some U in the sun. Additionally, U in the core of the sun will be exposed to neutron flux from the fusion reactions occurring there. The reaction of the various U isotopes to neutron flux was of considerable interest to the US government (et al) starting in the 1940s and continuing to the present day. IIRC my nuke physics, various U isotopes fission via either fast or slow neutron irradiation. Isotopes in particular, U233, U235, and U238, have found use in various and sundry nuclear devices to date. Also, it would seem that regardless of the energy of the fusion neutrons emitted in various fusion reactions, the presence of low Z isotopes (H, D, T, He3, He4, He5, C, etc.) would moderate even a high energy N flux accordingly. So, grudgingly, we conclude fission occurs in the sun, but at a very low order, and certainly at a drastically reduced rate from 4+ billion years ago. We can also conclude that this was unknown, and unknowable prior to the crucial and historic realization by Lize Meitner, IIRC, ca 1940, and the hard work and insight of many workers in the field since. <br />Posted by vogon13</DIV><br /><br />I think you are forgetting the structure of the sun as defined by michael. As michael has stated many times the sun is mass seperated down to the <em>isotope! </em>That is why the sun appears to be made of primarily hydrogen and helium - these light elements are at the upper layers of the sun. Uranium being a very heavy element would be near the core of the sun. But, as michael has explained the core of the sun is a neutron star, so the uranium would be pulled into the neutron core and not be available to undergo fission. Er somithing like that, I guess....</p><p> </p> <div class="Discussion_UserSignature"> </div>