Highest mass capture measurement with radioactive beam
The DRAGON collaboration has recently performed an experiment measuring the strength of the 38K(p, γ)39Ca radiative proton capture reaction. This reaction is significant in oxygen-neon novae and can potentially have significant consequences for the abundances of 38Ar, 39K, and 40Ca. This region of the nuclear chart represents the probable end-point for nucleosynthesis in novae.
In the experiment, the investigators focused on measuring the strengths of three key resonances at center-of-mass energies of 386, 515, and 689 keV. At the highest energy, the experimenters observed a clear signal from 39Ca recoils. At the lower two energies, the team saw no clear sign of recoils, suggesting that the strengths of these resonances are too low to be observed in the approximately two weeks of beam time allotted to the experiment. However, more detailed analysis is required to check for indications of recoils at the lower energies.
The experiment represents a significant technical achievement, setting a new world record as the highest mass radiative capture experiment ever performed with a radioactive beam. Acceleration of the radioactive 38K ions to DRAGON required use of TRIUMF's new charge state booster, the first time this has been utilized for an accelerated beam experiment in the ISAC-I hall. The beam delivery was an astounding success, with approximately 5 × 107 particles per second of 38K delivered to the experiment.
Figure: Plot of time of flight through DRAGON vs. time of flight between the two micro-channel plates located in DRAGON's focal plane. The clustering of events circled in red is indicative of a clear signal from 39Ca recoils.