Experimental results

Several experimental studies of transfer reactions, to measure spectroscopic information, have now been reported. The reader is referred to the original articles for details. The first example is the experiment by Rehm and coworkers [16], who measured reaction probabilities of astrophysical interest using the reaction ⁵⁶Ni(d,p)⁵⁷Ni in inverse kinematics. The beam of ⁵⁶Ni was obtained using radioactive source material and a tandem accelerator, and was of relatively high optical quality. The protons were detected in an array of silicon strip detectors at backward angles, as can be understood from the above discussion of the kinematics (Method 2). The second example is a study of the structure of the ground state of the halo nucleus ¹¹Be, using the reaction ¹¹Be(p,d)¹⁰Be in inverse kinematics [17,18]. The ¹⁰Be reaction products were detected using a dispersion matched magnetic spectrometer (Method 1). The coincident detection of deuterons was vital in the elimination of background events arising from the carbon in the extended (CH₂) $_{{\rm n}}$ polymer target. A third example is a study of the low-lying levels of the unbound nucleus ¹⁰Li using the reaction ¹¹Be(d,³He)¹⁰Li in inverse kinematics [14,19]. The ³He products were recorded using an array of silicon strip detectors (Method 2), and the Li ions originating from ¹⁰Li breakup were recorded in a scintillator telescope spanning the forward angles. An indication of how gamma-ray coincidences (Method 3) can be expected to improve transfer measurements with radioactive beams is given by the exploratory work of ref. [20]. The ¹¹Be(p,d)¹⁰Be is an interesting example, because the interpretation of the experimental data has led to new theoretical ideas: the coupling between weakly bound nuclear states and the continuum has been extended to include breakup of complex nuclei such as ¹¹Be [21]. The data also highlight the difficulties in extracting spectroscopic data for nuclei in which the single particle orbitals are strongly coupled [18], a situation that was mentioned in section 2. It should be noted, however, that more generally the interpretation can be expected to be more straightforward. The ¹¹Be experiment was aimed at quantitative measurements of spectroscopic factors at the 10% level. A more typical experiment would be seeking to locate states with a largely single particle character and the level of accuracy required in the absolute spectroscopic factors will be relatively modest.