Search for isovector M1- and M2-transitions in 17O and 18O by high resolution electron scattering on gas targets

For the high resolution electron scattering facility of the Darmstadt Linear Accelerator a high pressure gas target system was developed. Experiments on the nuclei 17O and 18O with this target system served for the search for magnetic dipole and quadrupole transitions to Tsub(>) states. In 17O the excitation of the states at 11.08 MeV (Jsup(π)=1/2-), 12.47 MeV (Jsup(π)=3/2-), 13.00 MeV (Jsup(π)=5/2-), 14.23 MeV, 14.75 MeV, and 15.10 MeV could be observed. The uptake of fire spectra at momentum transfer between 0.3 fm-1 and 0.5 fm-1 allowed the determination of the magnetic quadrupol strength to the states at 14.23 MeV and 14.75 MeV as B(M2)up = 46+-7 μsub(N)2 fm2 respectively B(M2)up = 27+-9 μsub(N)2 fm2. The transition to 15.10 MeV possesses a magnetic dipol strength of B(M1)up = 0.14+-0.04 μsub(N)2. The studies on 18O were concentrated on the excitation energy range between 16 MeV and 19 MeV. The ten uptaken spectra cover a range of the momentum transfer between 0.3 fm-1 and 0.5 fm-1. Two transitions at Esub(x) = 16.399+-0.005 MeV (Jsup(π)=2-) and Esub(x)=18.871+-0.005 MeV (Jsup(π)=1+) dominate the spectra. The corresponding strengths are B(M2)up = 58+-8 μsub(N)2 fm2 and B(M1)up = 0.28+-0.04 μsub(N)2. (orig./HSI)