Robert G. Lanier

Nuclear levels in152Eu

The transitional nucleus152Eu has been studied using the (n, e), (n, γ), (nres,γ), (n, γγ), (d, p), (d, t) and (p, d) reactions. The experiments have been performed at nine different laboratories. A model independent level scheme was established including 95 levels below 510 keV and nearly 900 transitions by combination of low energy transitions and reaction data. More than 20 additional levels result from gamma rays and/or charged particle reactions. The level scheme is interpreted in terms of the Nilsson model indicating that152Eu is a deformed nucleus. Seven rotational bands and Nilsson configurations are established. An additional 27 rotational bands are tentatively or speculatively assugned. Gallagher-Moszkowski splittings are discussed. The neutron binding energy was determined as 6305.2±0.5 keV. The energy of the 9.3 h 0− isomer is 45.599 keV. The lifetimes of four levels were measured.Nuclear Reactions151Eu(n,γ),En=thermal and resonance; measuredEγ,Iγ,Ec.e.,Ic.e.,γγ Coinc.,γγΔt coinc.;151Eu(d, p),E=12MeV and 14MeV;153Eu(d, t),E=12MeV;153Eu(p, d),E =18MeV; deduced level scheme of152Eu,J, π, T1/2,cc, Nilsson configurations. Magnetic electron spectrometer, curved crystal spectrometer, Ge(Li) and Si(Li) detectors, magnetic spectrographs. Enriched targets.

Nuclear levels in 160Tb

Abstract The high energy γ-ray spectrum from thermal neutron capture in natural terbium has been studied over the energy range of 5200 to 6400 keV. Low energy γ-radiation of the same reaction has been observed from 20 to 1230 keV and conversion electrons from 6 to 160 keV. Low energy (n, γγ) coincidences have been measured. A value of 6375.1 ± 0.3 keV has been obtained for the neutron binding energy in 160Tb. The data, when combined with a previous 159Tb (d, p) study, allow a level scheme to be constructed. These levels are assigned to nine rotational bands built on two quasiparticle configurations. The decay of several other levels is discussed. In three cases we have observed both parallel and antiparallel coupled bands with K − = ¦Ω p −Ω n ¦ and K + = Ω p + Ω n , and found the Gallagher-Moszkowski rule to be valid. The energy splitting has been calculated using Nilsson wave functions and a δ-force. Two K = 1 bands with irregular level spacing have been observed.

Composite charged particle detectors with logarithmic energy response for large dynamic range energy measurements

Abstract We have developed an array of detectors to identify charged particles produced in heavy ion reactions. The array, which consists of eight individual detector modules and a forward hodoscope, subtends a solid angle of 0.58π and covers 62% of the reaction plane in laboratory coordinates. Each of the eight identical modules has an active area which extends 13° above and below the array plane with additional limited coverage between 13° and 26°. Each module measures the position, energy and velocity of charged particles over a dynamic range which extends from minimum ionizing protons with energies up to 200 MeV to highly ionizing fission fragments with Coulomb-like energies. Position and time-of-flight are measured with low pressure multiwire proportional counters (MWPC). Total energies for heavier ions are obtained from large ion chambers. Energy and position measurements for more energetic lighter ions which pass through the ion chambers are made with segmented phoswich arrays. The forward angle hodoscope is a 34-element array of phoswich detectors mounted symmetrically around the beam axis. These detectors are sensitive to beam velocity particles ( E / A > 10–40 MeV / A ) and capable of elemental resolution from protons to Z = 23.

The 154Eu(t, p) reaction: Some new systematics in the N = 90 spherical-deformed transition region

A radioactive target of 154Eu(8.3y) has been used to study the 154Eu(t, p)156Eu reaction at an incident energy of 17 MeV. The bandhead and one rotational state of the {;π52[413]; ν112[505]}K = 3− configuration have been identified in 156Eu. The excitation energy of the 3− bandhead is determined to be 448 ± 15 keV. The angular distribution of the first excited rotational state is anamolous and may indicate evidence for a strong two-step component in the reaction mechanism. The energy systematics of the Eu-Sm transition region are also investigated. We find that the systematics of h22I suggest that at N = 87 the 150Eu {π52[413]; ν112[505]}K = 3− excited configurations has a significantly more stable deformed structure than the corresponding 112[505] one-quasiparticle structure in 149Sm.

The 152,154Eu(t, α) reactions: Studies of the 112[505] bands in 151Sm and 153Sm☆☆☆

Radioactive targets of 152Eu(13 y) and 154Eu(8.5 y) have been used to study the 152,154 Eu(t, α)151,153Sm reactions at an incident triton energy of 16 MeV. In these studies, we have identified the bandhead and three excited rotational states of the 112[505] neutron orbital in both the 151,153Sm nuclei The angular distributions and relative intensities for states in this band in both 151,153Sm are reproduced reasonably well by using DWBA calculations and by assuming strongly deformed single-particle wave functions. We have used our results and the results of other studies to determine the equilibrium prolate shapes of both 151,153Sm when the odd-neutron quasiparticle occupies the 112[505] orbital. We estimate β2 ~ 0.26 for 151Sm and β2~ 0.3 for 153Sm.

Nuclear levels in166Ho: Evidence for a large configuration mixing

Fifty-six levels in166Ho have been observed up to an excitation energy of 2,000 keV using the167Er(t,α)166Ho reaction with 17.0-MeV tritons. An anomalously small spectroscopic factor for the states in the [411↑±633↑] configuration has been observed, which has been interpreted as evidence for a large amount of configuration mixing with the states in the [523↑±521↑] configuration. Residual interaction calculations with a finite range central force have failed to account for the large configuration mixing observed. New assignments for 29 rotational states have been proposed. An anomalous singlet-triplet splitting is observed in the [404↓±633↑] configuration.

Observation of a shell gap at N = 152 in the 246 Cm(t, p) 248 Cm reaction☆

Abstract Previous reports of two-neutron stripping reactions in the actinide nuclei have not indicated any excited 0 + strength below an excitation energy of 1.5 MeV. In contrast, the 246 Cm(t,p) 248 Cm reaction shows a relatively strong 0 + state at 1.084 MeV. We believe that this result, coupled with a marked change in ground-state transition strenghts between 246 Cm and 248 Cm targets, indicates a gap in the single-particle orbitals that is larger than the pairing gap.

In-beam study of174Lu isomers

Levels in174Lu have been investigated using the176Yb(p,3n) reaction. Prompt and delayedγ-ray spectra have been observed with a 0.56-cm3 Ge(Li) detector by a multispectrum analysis method. The half-life and decay mode of two isomeric levels, one at 240.8keV (395±15ns) and the other at 365.1keV (145±3ns) have been firmly established. Hindrance factors are discussed. New delayed transitions in175Lu are also noted.

Gaussian polynomial method for spin-dependent level density and new formula for spin distribution

Large-scale combinatorial calculations of level densities were performed for selected nuclei using Gaussian polynomial generating function method (GPM). Contrary to the results of previous combinatorial calculations, we find a good agreement of the combinatorial total level densities and Bethe formula. Combinatorial GPM calculations were performed also for spin-dependent level densities and comparison is made with various algebraic formulas. On the basis of our GPM calculations we propose a new phenomenological spin-dependent level density formula, which in the low-spin limit reduces to the spin-dependent formula of Bethe. The new formula (24) is for all spins factorized into the product of total level density and spin distribution function, where the spin distribution function (25) contains an additional spin correction parameter.

Evidence for a strongly deformed prolate shape at N = 87 from 154Eu and 152Eu(p, t) reactions

Abstract The (p, t) reaction on radioactive targets of 152,154Eu has been used to study rotational states associated with the { p 5 2 [413]; n 11 2 [505]} K=3 − configuration in the transitional odd-odd 152Eu and 150Eu nuclei. Our studies yieldcompelling evidence that this configuration in 150Eu has a prolate structure which is strongly deformed and occurs at excitation energy of 1224 keV.