K. Lindh

A small size zero-degree spectrometer with germanium detectors

Abstract A small size spectrometer for detecting heavy reaction products emitted at small angles has been developed. It is installed at the synchrotron storage ring CELSIUS in Uppsala. It uses the focussing and bending magnetic elements of the storage ring itself in combination with a detector telescope, made of high-purity germanium, inserted into the ring vacuum. The spectrometer has been used for studies of pion production reactions close to threshold. The spectrometer is described together with results of ray-trace calculations and experimental tests.

Isospin resolved double pion production in the reaction p+d→3He+2π

Abstract Neutral and charged two-pion production in p+d→ 3 He+2 π reactions has been studied at CELSIUS at a proton beam energy of 477 MeV. The total cross section for double pion production is 0.22±0.03 μ b. The ratio of the cross sections for the production of charged pion pairs with isospin T =1 and T =0 was determined to be σ ( π + π − ; T =1)/ σ ( π + π − ; T =0)=1.4±0.4.

The inclusive reaction d + d → 4He + X 29 MeV above the 2π0 threshold☆

Abstract The momentum spectrum of 4 He particles from d + d reactions at E lab = 569 MeV has been measured at zero degrees in the laboratory. The missing-mass spectrum is consistent with a pure phase space behaviour for the isospin zero channel of two pions, corresponding to a total cross section of 43 ± 5 nb.

Pionic fusion to a halo state, the d(α,6Li∗)π0 reaction studied close to threshold

Abstract The d(α,6Li ∗ 3.56 )π0 reaction has been studied at Ec.m.=1.2 and 1.9 MeV above threshold with an alpha-particle beam incident on a deuterium cluster-jet target in CELSIUS. Complete differential cross sections were measured at both energies, integrated to σ=228±6+70 nb and 141±12+42 nb respectively. Observed large anisotropies are discussed in relation to the cluster structure of the 6Li ∗ halo.

Search for double Gamow-Teller strength by heavy-ion double charge exchange

Abstract We have carried out a search for double Gamow-Teller excitations, employing the 24 Mg( 18 O, 18 Ne) 24 Ne reaction at 100 and 76 MeV/nucleon at NSCL-MSU and GANIL, respectively. The cross sections for low-lying excitations are typically a few nb/sr, providing evidence for a strong suppression of double Gamow-Teller excitations in heavy-ion double charge exchange, compared to pion-induced reactions. This result does not give good hope that heavy ions at intermediate energies could be used to probe double Gamow-Teller strength.

Pionic Fusion Study of the Halo Nucleus 6He in the Reaction d + 14N -g 6He + pi+ at CELSIUS

The halo nucleus 6He has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala. The 6He nuclei were produced in reactions with a deuteron beam incident on a 4He jet target 0.9–5.4 MeV above threshold in the center-of-mass frame. The 6He ions were detected in a ΔE-E solid-state detector telescope inserted into the CELSIUS ring. The aim of the experiment was to investigate, in particular, the high-momentum part of the halo wave function by measuring the total and differential cross sections of the reaction d+4He→6He+π+.

Pionic Fusion Study of the halo analogue state6Li

The isobaric analogue state of the ground state of the halo nucleus6He,6Li* has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala, Sweden. This was the first of two proposed experiments with the aim to study the high momentum part of the wave functions of the halo nuclei6He and6Li (0+, T=1). The Li nuclei were produced in inverse kinematics reactions with alpha particles incident on a deuterium cluster jet target. The6Li ions were detected in a zero-degree spectrometer situated in the fourth quadrant of the CELSIUS ring. The measurement was done for three different beam energies corresponding to 5.4, 2.2 and 1.5 MeV above threshold in the c.m. The cross-sections slowly increase with beam energy from 95 nb at the lowest energy to about 250 nb at 5.4 MeV above threshold.

A zero-degree spectrometer in CELSIUS and the d(d, 2π)4 He reaction

For the realization of near threshold studies a small-size spectrometer has been developed by the Nuclear Physics Division at Stockholm University in conjunction with Institut fur Kernphysik in Julich. A particle telescope is mounted inside the CELSIUS vacuum chamber in the bend following the cluster-jet target. It is possible to vary the measuring position within the dipole field to cover different magnetic rigidities which makes it a versatile tool for studies of threshold reactions. The first aim has been to study two-pion production and we present preliminary results from measurements of the d(d, 2π)4 He reaction.