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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Statistical properties of warm nuclei

Awarded: NOK 6.0 mill.

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Level densities and gamma strength function are fundamental properties of the atomic nucleus and important input parameters in reaction cross-section calculations. In Oslo an experimental method to measure both level densities and gamma strength functions has been developed. Normally one uses the extrapolation of the tail of the Giant Electric Dipole Resonance (GEDR) to describe the strength function at low energy. Experiments done in Oslo revealed an enhancement of the gamma-strength function at low ene rgy for several nuclei. The probability to decay with low energy gamma-rays was more than 10 times larger than current theories predict. This forces us to drastically change our view of how the nucleus emits gamma-rays in continuum. There are still no the ories, which can explain these experimental results. The increased probability to decay by low-energy gamma rays has a dramatic effect on cross-sections if it is also present in exotic nuclei and will influence the results of large network calculations of supernova explosions. The enhancement of low energy gamma emission is expected to help understanding the formation of elements in stellar environments, where there today is a discrepancy between the measured and calculated abundances of elements in our s olar system. Since it is for exotic nuclei that the effect on cross-section is the biggest, the main part of this project is to further develop the Oslo method to study exotic neutron rich nuclei. We start by adapting/developing the method for inverse kin ematics and an experiment with stable beam will be done at Berkeley. Then we will propose a pilot experiment using inverse kinematics with exotic beams at HieISOLDE /SPIRAL2.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek