Towards background-free studies of capture reaction in a heavy-ion storage ring

Abstract

Stored and cooled, highly-charged ions offer unprecedented capabilities for precision studies in the realm of atomic, nuclear structure and astrophysics[1]. After the successful investigation of the 96Ru(p,7)97Rh reaction cross section in 2009[2], the first measurement of the 124Xe(p,7)125Cs reaction cross section has been performed with decelerated, fully-ionized 124Xe ions in 2016 at the Experimental Storage Ring (ESR) of GSI[3]. Using a Double Sided Silicon Strip Detector, introduced directly into the ultra-high vacuum environment of a storage ring, the 125Cs proton-capture products have been successfully detected. The cross section has been measured at 5 different energies between 5.5AMeV and 8AMeV, on the high energy tail of the Gamow-window for hot, explosive scenarios such as supernovae and X-ray binaries. The elastic scattering on the H2 gas jet target is the major source of background to count the (p,7) events. Monte Carlo simulations show that an additional slit system in the ESR in combination with the energy information of the Si detector will enable background free measurements of the proton-capture products. The corresponding hardware is being prepared and will increase the sensitivity of the method tremendously.

The status and future of direct nuclear reaction measurements for stellar burning

“…Since the ambitious final goal of the experimental campaign is to measure with radioactive ion beams of limited intensity, a new approach to increase the overall sensitivity of the method has been pursued. The main idea is based on blocking the scattering distribution directly in front of the separating dipole magnet, where the Rutherford cone has already a sizable extension, while the proton-capture products are still on the central orbit of the ring [220]. In accordance with the simulations the preliminary results of a very recent measurement show that this blocking scheme indeed seems to work well and will maximize the sensitivity of the technique as expected.…”

Low-energy nuclear reactions with stored ions: a new era of astrophysical experiments at heavy ion storage rings

“…In fact the signalto-background ratio for proton-capture becomes worse with decreasing beam energy, as one would expect from the divergent behaviour of the declining nuclear and increasing Rutherford cross sections. To anticipate this sensitivity limit of the experimental technique, which is critical for applications inside the Gamow window, an improved method was developed [39,40]. It is based on blocking part of the Rutherford distribution directly in front of the dipole magnet, where the scattering cone is already quite extended while the beamlike (p,γ ) products remain on the storage orbit.…”