Tariq Al-Abdullah Hashemite University, Jordan Cairo 2009 Problems and Issues in Nuclear Astrophysics Why nuclear physics in astrophysics? Why indirect measurements of cross sections in nuclear astrophysics? The indirect teqhniques and their applicatoins! Perspectives of the method: RIB and (part,g) reaction Nuclear Physics Research and Education! SUMMARY Nucleosynthesis 1945 : Gamows Hypothesis all of today elements were made during the early BIG BANG of the Universe Questions: When did it start ?? What elements are produced and can we understand the isotopic composition ?? Do parameters of the Early Universe have an influence ?? wrong! Big Bang Nucleosynthesis Wrong for 3 simple reasons oBinding energy of deuteron (2.22 MeV) is too small !! oBinding energy of 4 He is too large (28.3 MeV) !! oThere are no stable isotopes with A=5 and A=8 !! Deuterons are being dissociated until the Universe Has cooled down to 80 keV !!! for further fusion the train has Long left the station !! Universe composition: ~76% H and ~23% 4 He Stellar life cycle energy production energy production stability against collapse synthesis of metals thermonuclearreactions BIRTH gravitational contraction explosion DEATH mixing of interstellar gas Interstellar gasStars abundance distribution The goals of experimental Nuclear Astrophysics are: - study of the origin of the elements or nucleosynthesis - study of the energy generation processes in stars. Courtesy: M. Arnould Experimental nuclear astrophysics Experimental nuclear astrophysics M. Smith & E. Rehm Average Reaction rate per particle pair: In stellar plasma the velocity of particles varies over a wide range Assume (v) is the velocity distribution Thermonuclear reactions in stars: general features Reaction rate: r = N 1 N 2 v (v) ( # reactions Volume -1 Time -1 ) Thermonuclear reactions in stars: general features is a KEY quantity Total reaction rate R 12 = (1+ 12 ) -1 N 1 N 2 12 Energy production rate 12 = R 12 Q 12 to be determined from experiments / theoretical considerations as star evolves, T changes evaluate for each temperature energy production as star evolves - change in abundance of nuclei X NEED ANAYLITICAL EXPRESSION FOR ! Mean lifetime of nuclei X against destruction by nuclei a charged particles Coulomb barrier tunnel effect E kin ~ kT (keV) E Coul ~ Z 1 Z 2 (MeV) nuclear well Coulomb potential V rr0r0 T ~ 15x10 6 K (e.g. our Sun) kT ~ 1 keV T ~ K (Big Bang) kT ~ 1 MeV energy available from thermal motion exp(-2 = GAMOW factor reactions occur by TUNNEL EFFECT tunneling probability P exp(-2 ) during quiescent burnings: kT