D.J. Decman

Electron spectroscopy in coincidence with protons from the (t,p) reaction☆

Abstract An electron spectrometer has been operated in coincidence with a thin annular Si(Au) proton detector to obtain conversion-electron spectra associated with the (t,p) reaction. Electrons are transported from the target to a Si(Li) detector through a solenoidal magnetic field in a two-loop baffle arrangement. Proton detection efficiencies of up to 14% were obtained with a 98 Mo target by optimizing the forward-angle position of the Si(Au) detector.

Electromagnetic decay of 10+ states and yrast isomers in 208Pb

Abstract Gamma decay of the four previously known 10 + states between 4.8 and 5.9 MeV of excitation in 208 Pb, and isomerism of the lowest 10 + [T 1 2 =500(50) ns ] and 8 + [T 1 2 =3.2(5) ns ] states have been established with α - γ coincidence measurements in 209 Bi(t, αγ ) 208 Pb. Wavefunctions for the 10 + states were deduced in the model space involving 1p-1h excitations only. These show that the π h 9 2 h 11 2 −1 strength is nearly evenly distributed among the 10 + states, in disagreement with results from (e, e′) data.

Quadrupole moments of low-energy isomers in 210Po

Abstract The quadrupole interaction frequencies of the 8 + , 11 − , 13 − and 16 + isomers in 210 Po have been measured in a Bi single crystal by the DPAD method with the 209 Bi(t, 2n) 210 Po reaction. The results for the quadrupole moments, normalized to Q (8 + 1 ) = −55.2 (20)fm 2 , are | Q (11 − )| = 86 (11)fm 2 , | Q (13−)| = 90(7)fm 2 and | Q (16 + )| = 129.7 (20) fm 2 . The quadrupole moment of the 0 i 13 2 proton orbital was deduced, and found to be surprisingly small. The results are compared with shell model calculations using the surface delta interaction as residual interaction.

Particle-hole multiplets in146Gd from in-beam studies of non-yrast levels

Non-yrast levels of146Gd have been investigated by in-beamγ-ray and conversion electron spectroscopy following the144Sm(α, 2n) reaction at 25.7 MeV, an energy which was determined to provide optimum population of levels above the yrast line. The detailed146Gd level scheme includes twenty-one newly identified levels, many of which can be characterized in terms of specific proton particle-hole configurations. Several twoparticle-twohole states involving the 3− phonon have also been identified.

The ground state mass of147Gd from single-neutron-transfer reactions and its impact on derived mass values

Using a148Gd radioactive target and the (p,d), (d,t), and (3He,α) single neutron pick-up reactions we have measured the147Gd mass excess as — 75,366(4) keV, which differs by 139(24) keV from the adopted value of the 1983 mass table. From this result, and from recently reported first transfer-reaction mass determinations for145Eu and146Eu, we have recalculated the masses of nuclei above146Gd from a previous shell model analysis of high-spin states.

Collective excitations in148Gd populated in thep p′-reaction on a radioactive target

Collective excitations in the two-particle nucleus148Gd up to 2.9 MeV have been investigated by thepp′-reaction at 25 MeV beam energy, and angular distributions have been analyzed with standard DWBA calculations. It is found that148Gd has larger octupole- than quadrupole collectivity in the energy range investigated. The 3− strength distribution is in quantitative agreement with predicted results for the levels formed by the coupling of two valence particles to the146Gd core octupole phonon.

Occupancy of single-proton orbitals in148Gd

The (3He,d) and (t, α) reactions on a radioactive Z=64148Gd target were used to populate the single-proton states in149Tb and147Eu. In149Tb the data establish the five single-proton states of the 51 to 82 major shell. The proton occupancies deduced from these experiments suggest that in the148Gd ground state there are on average 1.8(3) proton pairs above the Z=64 shell gap.

Decay of the 21/2− isomer in211Bi and structure of thevg 9 2/2 πh9/2 levels

Gamma rays and conversion electrons have been measured in211Bi populated by the209Bi(t,p) reaction, and the near yrast levels were observed up to 21/2−. The 21/2− state is isomeric withT1/2=70(5) ns. No alpha decaying isomer was found in211Bi. ObservedM1 transitions reveal mixing of the210Pb parent states in the levels of211Bi. The levels and transitions are well reproduced by the shell model with experimental matrix elements and pure configurations.

Conversion-Electron Expffiment To Characterize The Decay Of The 237 Np Shape Isomer

Conversion electrons from the decay of low-lying levels of 237Np have been measured to detect the population of these levels by 2i/ gamma-ray decay of the Np shape isomer. Analysis of the 208-keV transition L conversion-electron peak _gives an upper limi3J?f about 17 pb for the population of the 3/2 267-keV level in Np from the shape isomer decay. Model calculations are compared with the measured limit. Improvements are suggested for this experiment.