N.J. Davis

A double-sided silicon strip detector system for proton radioactivity studies

Abstract A new double-sided silicon strip detector has been developed to study the phenomenon of ground-state proton radioactivity. Highly proton-rich fusion-evaporation reaction products are velocity and mass separated using the Daresbury recoil separator before being implanted into the strip detector located at the separator focal plane. The double-sided strip detector has 48 strips per face with a pitch of 335 μm. Front and back strips are orthogonal providing an effective pixel area of 0.09 mm2, enabling correlations between implanted ions and subsequent decays to be clearly established. Test results obtained using the reactions 58 Ni + 92 Mo → 150 Yb ∗ and 58 Ni + 54 Fe → 112 Xe ∗ are reported. In the latter commisioning experiment the proton decay of 109I was unambiguously established using the correlated decay sequence 109I→p108Te→α104Sn.

Study of the threshold anomaly in the scattering of polarized 7Li from 208Pb

Abstract Experimental data on elastic and inelastic analysing powers T 20 and inelastic cross sections for the scattering of polarized 7 Li from a 208 Pb target are presented. The experimental data are analyzed with DWBA and coupled channels calculations, which show the sensitivity of the experimental data to the real and imaginary parts of the nuclear transition form factor. This study reveals the existence of a threshold anomaly for the transition terms of the interaction.

Proton radioactivity from 146Tm. The completion of a sequence of four odd-odd proton emitters

Abstract Proton emission has been observed from the new isotope 146 Tm. Two transitions have been identified at energies of 1119±5 keV and 1189±5 keV corresponding to Q -values of 1127±5 keV and 1197±5 keV respectively. The measured half-lives of 235±27 ms and 72±23 ms are well reproduced by simple WKB calculations assuming proton emission from h 11 2 orbitals. The proton transitions are assigned to a 10 + isomeric state and a low lying 5 − or 6 − level.

208Pb(7Li,6Li)209Pb reaction at 33 MeV and its effect on elastic scattering

Abstract Angular distributions of the differential cross section and the second-rank tensor analysing power T 20 have been measured for the one-neutron transfer reaction induced by polarized 7 Li ions on 208 Pb at 33 MeV leading to five states in 209 Pb. The experimental data were analysed simultaneously with data for elastic and inelastic scattering of 7 Li by means of CCBA and CRC calculations. A strong effect of the transfer channels on the elastic scattering was found. Coupling to the transfer channels cancelled out the effect of projectile excitation on the elastic-scattering cross section but was unable to account fully for the renormalization factor of the double-folding potential found previously in an optical-model analysis of 7 Li+ 208 Pb elastic scattering. The second-rank tensor analysing power for the elastic scattering was strongly affected by the transfer channels.

Alpha decay of the new isotope172Au

The first observation of the extremely neutrondeficient nucleus172Au is reported, produced using the fusion evaporation reaction70Ge+106Cd→176Hg* (Ex≃64 MeV). Mass separated evaporation residues were implanted into a double-sided silicon strip detector, and the energy and time of subsequent decay events were recorded. The alpha decay of172Au was measured with an energy =6860±10 KeV, corresponding to =7020±10 Kev, and a half-life of 4±1 ms. No evidence was seen for a proton decay branch, implying a limit ofbp≤ 2 %.

Quantum-mechanical analysis of analysing powers of the 54Fe(7Li, 6Li)55Fe reaction at 70 MeV

Abstract The differential cross sections, first- and second-rank analysing powers were measured for several states in 55 Fe using the 54 Fe( 7 Li, 6 Li) reaction with a 70 MeV polarised 7 Li beam. Only the T T 20 exhibits a clear j -dependence while most of the T kq s are sensitive to the l -values of the final states. The results were successfully described by complex CCBA calculations involving channel coupling in the entrance partition and spectroscopic properties of the projectile. The quantum-mechanical analysis confirms the reaction dynamics assumed in the semiclassical approach to the nucleon transfer process in heavy-ion collisions.

Analysing powers of the 6Li continuum from the 7Li + 54Fe interaction at 70MeV

Abstract The vector analysing power T T 10 and a full set of second-rank analysing powers were measured for the 6 Li continuum from the 7 Li + 54 Fe interaction at 70 MeV corresponding to a Q -value interval between −23 and −4 MeV and an angular range 12.5° ⩽ θ c.m. ⩽ 35.3°. Main features of the data are well reproduced by a semiclassical model of the analysing powers in transfer reactions considering 6 Li as a spectator. The behaviour of analysing powers determined the choice of the average trajectory as a smooth function of the reaction Q -value.

Tensor analyzing powers for Li induced transfer breakup reactions

The tensor analysing power T/sub 20/ has been measured for the /sup 120/Sn(/sup 7/Li, /sup 8/Be to 2 alpha )/sup 119/In and /sup 120/Sn(/sup 7/Li, /sup 6/Li* to alpha +d)/sup 121/Sn transfer breakup reactions at 70 MeV bombarding energy. Coupled channels and continuum discretized coupled channels calculations, incorporating a detector phase space correction, were found to give good agreement with the data.

A high efficiency 8Be detector

Abstract A very high efficiency 8Be detection system, based on silicon strip-detectors, has been developed. The theoretical performance of the system is evaluated by the use of Monte Carlo simulation methods and the experimental performance is investigated by a study of the reactions 12C, 120Sn(9Be, 8Be).

Tidal symmetry in scattering of polarized 23Na from 208Pb

Abstract The data for differential cross sections and transverse tensor analysing powers in scattering of polarized 23 Na from 208 Pb at 170 MeV were obtained for the ground, first and second excited states of 23 Na. The measurements were performed with the QMG/2 magnetic spectrometer at Daresbury Laboratory. The extracted data were analysed on the basis of the tidal symmetry model and the adiabatic approximation. The ground-state reorientation coupling together with two-channel and three-channel coupling schemes for 23 Na states have been attempted. Both nuclear and Coulomb terms were used in the reorientation and coupling potentials. The differential cross section and the transverse tensor analysing powers in the elastic channel are successfully described in the tidal symmetry model. However, the data in the inelastic channels are only approximately described by this model. Comparison of these results with exact coupled-channel calculations shows the implications of tidal symmetry breaking in the inelastic channels.