Neutron Halos in Excited States of 12B

An experiment was done to search for states with a neutron halo in 12B. The measurements were carried out at the cyclotron of the University of Jyvaskyla (Finland) using Large Scattering Chamber (LSC). The idea of the work was to search for two states with the expected neutron halo, 1 ̄ and 2 ̄. Differential cross sections with excitation of 12B states, including abovementioned states, were observed. The preliminary calculations on halo radii by the method of asymptotic normalization coefficients for the 2 ̄ and 1 ̄ states which are in a discrete spectrum gave following values: 5.6 fm and 7.4 fm, which is much larger than the radius of the valence neutron in the ground state. But strictly the presence of a neutron halo can be confirmed only for 1 ̄ state. The 2 ̄ state can be considered only as candidate for halo. An unexpected result was obtained for the 3 ̄, 3.39 MeV state, which is in continuum 19 keV above the decay threshold 12B → 11B + n, preliminary estimation for its halo radius is ∼ 6.5 fm. This indicates that the halo can be present in this state as well. But strict conditions for neutron halo are not fulfilled in the same way as for 2 ̄ state. Until now, the neutron halo in unbound states has been observed only for the members of the rotational bands.

Development of SuperHRPD, a TOF neutron powder diffractomter at J-PARC

SuperHRPD is one of six time-of-flight neutron powder diffractometers in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). SuperHRPD is looking at a newly developed high resolution moderator which gives narrow & symmetrical neutron pulse with less tails. With using this moderator and lower repetition rate of 25Hz as well as the flight path shorter than 100 m, a high resolution and wide dynamical range is attainable with limited loss of neutrons. The designed highest resolution of SuperHRPD is as high as Δd/d = 0.035 % in the backward bank. Although unplanned shutdown for two years due to the earthquake and the Hadron radiation accident, SuperHRPD has been upgraded repeatedly by the scattering chamber replacement, the increase of detector solid angle, and the improvement of the detector systems, and improvement of resolution. Sample environments cover 4 K – 1000 K, 10GPa and 14 T with up to d = 40 Å. It is emphasized the magnet was designed to detect tiny structural changes precisely as well as magnetic reflections up to 14 T. After three years of operation, we confirmed higher resolution can reduce systematic errors in structural analyses. The current status of SuperHRPD will be reported.