L. Holmberg

Levels in 115In populated in the decay of 115mCd

Abstract The decay of 115mCd to 115In is studied. Gamma intensities are measured with a Ge(Li) detector. Two new transitions are observed and placed in the level scheme. The following γ-γ directional correlations are determined (energies in keV): 484.35–933.6, 158.1–1132.5 and 316.1–1132.5. The M1 strengths are derived for two transitions connecting members of the vibrational multiplet: B( M 1, 1290.5 13 2 + → 1132.5 11 2 + ) = 0.5 ± 0.1 μ 2 0 and B( M 1, 1448.7 9 2 + 1132.5 11 2 + ) = 0.5 ± 0.3 μ 2 0 . The half-life of the 933.6 7 2 + state as measured by the delayed-coincidence technique is T 1 2 = 57 ± 5 ps . The partial half-life of the 933.6 7 2 + → 828.4 3 2 + E2 transition is 55 times less than the Weisskopf estimate. The static quadrupole moment of the 7 2 + and 3 2 + states is evaluated on the assumption that these levels are members of the proposed rotational band: Q0 = 2.7 ± 0.3 b. This is in agreement with the corresponding value for the 864.0 1 2 + → 828.4 3 2 + transition, and the result of a recent direct measurement of the static quadrupole moment of the 828.4 3 2 + state. The suggestion that the 1418.0 9 2 + level is also deformed is supported by the fact that the decay occurs preferentially to the 933.6 7 2 + state, whereas no transition connecting the 1448.7 9 2 + state with the 933.6 7 2 + state is observed.

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.

Gamma-gamma Directional Correlations in 103Rh

Gamma-gamma directional correlations in 103Rh were measured in the decay of 103Ru. No dependence on the chemical composition of the source was observed. The following directional correlation coefficients were determined: A2(557 - 53) = -0.064 ± 0.003, A2(444 - 53) = -0.035 ± 0.013. The lifetime of the 93 keV state was measured as T½ = 1.06 ± 0.05 ns. By use of this value for the lifetime and the rotation in an external magnetic field of the directional correlation pattern, the gyromagnetic factor of the 93 keV state is obtained as g = 1.07 ± 0.17. The properties of 103Rh were calculated on basis of the unified vibrational model. The adequacy of this model for describing the positive-parity states studied in this work is discussed.

Levels and transitions in136Ba

Excited states of136Ba are studied in the beta decay of136Cs. The gamma spectrum is measured with high-resolution and coincidence techniques. Several new transitions are suggested to be connected with two recently reported levels. Gamma-gamma directional correlations are performed in an attempt to determine the characteristics of these levels, and in order to determine mixing ratios. The lifetime of the 2207.5 keV state is remeasured, and the lifetime of the 2140.5 keV state is measured for the first time.

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.

Levels and transitions in126Te

The decay of126Sb to126Te is studied by use of Ge(Li) detectors in singles and coincidence arrangements. The gamma-gamma directional correlations of six cascades are measured. A level scheme is constructed where all transitions observed are located. The characteristics of several of the levels are assigned, on basis of the logft values deduced and the directional correlation results. Mixing ratios are deduced for three transitions. From the comparison of the relative intensities ofE1 andE2 transitions depopulating the same levels, threeE1 transitions are concluded to be strongly retarded.

Sub-nanosecond lifetimes in 126Te

Abstract The half-lives of the 1776.8 keV 6 + level and the 2497.3 keV 7 − level in 126 Te are measured by registering β-γ coincidences in the decay of 126 Sb. The results are T 1 2 (1776.8) = 66±3 ps and T 1 2 (2497.3) = 152±5 ps . The collective strength of the 6 + → 4 + transition depopulating the 1776.8 keV state is estimated. An additional half-life of 0.36±0.06 ns is found but not definitely assigned in the level scheme.

Internal Conversion and Radiative Processes of the 113 keV M1-E2 Transition in 177Hf

Gamma-electron and gamma-gamma correlations of the 208-113 keV cascade in 177Hf are measured. The following ratios between directional distribution coefficients are obtained, A2(K)/A2(γ)= -0.211±0.035, A2(L)/A2(γ)=0.111±0.037. By use of a commonly adopted value for the gamma-gamma directional correlation, and the internal conversion data, the penetration contribution to the M1 component is evaluated, λ= -0.6±2.0. This is in agreement with a theoretical prediction by Reiner, λ ≈ -2. The lifetime of the 113 keV state is determined, T½=0.490±0.015 ns. When this value is used for evaluation of the gyromagnetic ratios gK and gR from a PAC measurement, agreement with theoretical predictions is found.

Transition probabilities in146Eu

Transition probabilities in the odd-odd nucleus146Eu are measured. A recent determination of the lifetime of the 115.6 keV level has indicated a strong retardation of the 115.6 keVM1 transition. In contrast, the present results areT1/2(230.3)≦165 ps,T1/2(115.6)≦160 ps. TheE2 cross-over transitions of 269.5 and 230.3 keV were not found in the Ge(Li) gamma spectrum. All results are in agreement with the single particle model.