Study On Cluster Structure In Neutron-Rich Nucleus ¹⁷C

Cluster structure is one of hot subject of active discussion on nuclear physics in the last 40 years.The experimental study of cluster structure has been focused on Be and B isotopes which have two-body clusters.Many people have predicted the existence of triple-? structure of carbon isotopes.And experimental study has shown out the well know holy state of 12 C and the triangle and linear-chain configurations in 14 C.However,the experimental result of 16 C does not find a well-developed cluster structure in its ground state.So the breakup measurement of 17 C can confirm the presence of cluster structure in it.The experiment was carried out at Radioactive Ion Beam Line in Lanzhou?RIBLL?.The energies of the secondary beams,at the physical target 12 C were 44 MeV/nucleon for 17 C.Two Position-sensitive Parallel-plate Avalanche Chambers?PPACs?were used to reconstruct the position and incident angle of the incoming beam at target.And Time of Flight?TOF?with a flight path of 21 m and the energy-loss of the beams in Si-detector??35?E?were used for the secondary beam particle identification.Particle identification by reaction products was achieved using ?E-E telescope detector and momentum of reaction products were also measured.The first part of ?E-E telescopes is a 150 ?m thick Double-sided Silicon Strip Detector?DSSD?with 16 strips each side,which are 48 mm long and 3 mm wide on both the front and the back sides.The calibration of silicon strip were used by ¹⁷C?¹⁵B?¹³B?¹⁰Be secondary beam.And a close packed array of 64,2.5×2.5 cm2,CsI?Tl?scintillators was located behind the strip-detector.It was also calibrated by secondary beam.For the two-body cluster decay of the 17 C nucleus,the excitation energy of the projectile prior to breakup was reconstructed by measuring the relative energy and the angle between the two coincidence fragments.With the coincidence fragments ⁸Li and ⁹Li,the excitation energy spectrum of 17 C were reconstructed.Excited states in 17 C were observed at 25.6±0.71 MeV,27.4±0.73 MeV,28.6±0.95 MeV.Through the detection of coincident fragments ⁶He and 11 Be,the excitation energy spectrum of 17 C were reconstructed and observed one peak at17.9±0.93 MeV.The measurements indicate that 17 C is likely to have well-established cluster structure in the ground state.