Direct measurement of Nuclear Fusion Cross Section at Stars.

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Cross section of ^<12>C+^4He->^<16>O+γ reaction at Ecm = 0.3 MeV plays a crucial role in nuclear synthesis in stars, and measurements of the cross section have been attempted for about 40 years in the world However, the cross section has not measured yet since the experiment is extremely difficult. We have prepared the measurement of ^<12>C+^4He->^<16>O+γ reaction cross section at Kyushu University tandem laboratory for 15 years. In our method, we detect ^<16>O from inverse kinematics 12C+4He >16O+γ reaction at Ecm = 2.4 -0.7 MeV, and extrapolate the cross section down to 0.3 MeV. This is only one method to arrive the goal, but there are many difficulties. In 2004, we first succeeded in detecting ^<16>O from ^<12>C+^4He->^<16>O+γ reaction at Ecm = 2.4 MeV, although absolute value of the cross section could not be obtained.To arrive the goal, we need a)C beam intensity of more than 5 μA, b)He windowless target of 25 Torr x 3cm, c)background(BG)level below 10^<-19>, d)pulsed beam, e)stab … More le RF power supply of 2-6 MHz, f)optimized slit system of a recoil mass separator, and g)extrapolation method. Already we have pulsed the beam. BG level is now 10^<-17>, and remaining BG is to be found below Ecm = 1.2 MeV. In 2007, progress was made in a), b), and e)-g). We succeeded in preparing a He windowless target of 25 Torr x 3cm. The windowless target is 5 times thicker than those in the past. For a) and e)-g), we made concrete plan and 60-80% have been finished in 2007.In 2007, we made system check by measuring ^<12>C+^4He->^<16>O+γ cross section at 2.4 MeV, and found new BG produced by scattering of secondary beam halo at fixed slit in the recoil mass separator. By this trouble, experiment at 1.5 MeV was postponed to 2008. At Ruhr University, Germany, ^<12>C+^4He>^<16>O+y cross section has been measured at Ecm = 5.0-1.9 MeV. Owing to the preparation made in this research project, grant-in-aid, we will be able to make the ^<12>C+^4He->^<16>O+y experiment at Ecm= 1.5-0.7 MeV in 2008-2011, and arrive at the goal. Less