T. N. Massey

Spectroscopy of exotic nuclei with multi-nucleon transfer reactions

Structure investigations of neutronrich helium isotopes and of10Li and11Be have been performed using multi-nucleon transfer reactions. New results have been obtained for7He He, where we have evidence for the observation of the first excited state, i.e. the 1/2-resonance, which is of interest for the spin-orbit splitting in these light neutronrich nuclei. Our results on8He,9He and10He are briefly summarized. Reactions of distinct selectivity have been chosen to study the states of10Li. The structure of the eight states found in these reactions is discussed, as well as their relevance for the decay of11Li resonances. The isotopes10Be and11Be have been investigated to study the a-cluster structure and high-lying states. Nine states of the observed11Be-resonances can be characterized as a molecular rotational band extending up to 25 MeV excitation energy, with a probable maximum spin of 19/2. The reaction mechanism is studied in terms of two-step calculations, where protons are picked-up from the target and neutrons are transferred to the target. Using measured strength amplitudes for the single steps results in a quantitative description of the observed two-step cross sections.

Measurement of the thick-target 9Be(p, n) neutron energy spectra

Abstract The thick-target neutron energy spectra of the 9Be(p,n) reaction were measured at several angles for proton-bombarding energies of 3.0, 3.4, 3.7, 4.0, and 5.0 MeV. Time-of-flight techniques were used to determine the neutron energy spectra and to discriminate against background radiation. By using lithium-loaded glass scintillators and low proton pulse rate frequency, the neutron spectra have been determined at energies as low as 70 keV. The detectors were calibrated for efficiency using the neutron spectrum of the Al(d,n) reaction, which was accurately measured using fission chamber detectors.

Spectroscopy of 10He

Abstract The mass of 10 He has been measured with the double charge exchange reaction 10 Be( 14 C, 14 O) 10 He at E Lab = 334.4 MeV and a mass excess M.E. = 48.81 (7) MeV is obtained. It follows that 10 He is particle unstable against 2 n - emission by S 2n = −1.07(7) MeV . Two excited states are observed: a broad resonance at an excitation energy of E x = 3.24(20) MeV , and a strong resonance at E x = 6.80(7) MeV .

Stud of weakly bound and unbound states of exotic nuclei with binary reactions

Abstract Binary reactions using neutron-rich beams (and targets) give the best approach to study the level structure of exotic nuclei. Systematic cross section dependencies of multi-step transfer reactions are discussed. Some rections, for example the proton-neutron exchange ( 12 C, 12 N) and ( 13 C, 13 N) , have distinct selectivity for the population of unnatural or natural parity states, respectively. This selectivity has been applied to new spectroscopic studies of 10 Li using the 10 Be( 12 C, 12 N) and 9 Be)(P 13 C, 12 N) reactions. The lowest resonance of 10 Li observed at 0.24(6) MeV above the neutron threshold. The results are discussed together with other available data.

Spectroscopy of 13B, 14B, 15B and 16B using multi-nucleon transfer reactions

Abstract: New information has been obtained on excited states of the neutron-rich boron isotopes 14B, 15B and 16B, using the reactions 12C(14C,12N)14B, 13C(14C,12N)15B and 14C(14C,12N)16B at about 24 MeV/A. The mass excess of 16B has been measured for the first time, it is 37.08(6) MeV. This means that 16B is unbound by only 0.04(6) MeV. Furthermore, the nucleus 13B has been investigated with the four reactions 16O(14C,17F), 12C(14C,13N), 12C(13C,12N) and 12C(15N,14O). Choosing different target-projectile combinations, it was possible to populate states with different selectivity. New states are observed in 13B at excitation energies above the threshold for two-neutron decay.

A Measurement of the 27Al (d, n) Spectrum for Use in Neutron Detector Calibration

Calibration of neutron detectors for use in measurements spanning a wide range of neutron energies is normally a challenging task. Use of monoenergetic neutron beams is tedious and not convenient for certain energies. Measurements of a continuous spectrum of neutrons from the {sup 27}Al(d,n) reaction at E{sub d} = 7.44 MeV have been made with a fission chamber. This should allow rapid calibration of neutron detectors in the energy range 0.2 {le} E{sub n} {le} 14.5 MeV.

Spectroscopy of excited states of11Li

The10Be(14C,13N)11 Lireaction and the14C(14C,17F)11 Lireaction have been used to study the levels of11Li. Three excited states have been found, in both reactions, at excitation energies of 2.47(7) MeV, 4.85(7) MeVand 6.22(8) MeV

Study of light neutron-rich nuclei with 14C-induced reactions

Abstract The 14C-beam has been used at HMI to study light neutron-rich nuclei with multi-nucleon transfer reactions. Spectroscopic results about the T=3 nuclei 10He, 14Be and 16B have been obtained, but also 11Li, 7He and the 3n-system have been investigated.

γ-strength functions in 60Ni from two-step cascades following proton capture

The two-step cascade method previously used in neutron-capture experiments is now applied to a proton-capture reaction. The spectrum of two-step cascades populating the first 2{sup +} level of {sup 60}Ni has been measured with the {sup 59}Co(p,2{gamma}){sup 60}Ni reaction. The simulation technique used for the spectrum analysis allows one to reveal the range of possible shapes of both E1 and M1 {gamma}-strength functions. The low-energy enhancement previously observed in {sup 3}He-induced reactions is seen to appear in M1 strength functions of {sup 60}Ni.

Level density of Fe 56 and low-energy enhancement of γ-strength function

The