Conversion Electron Measurements Research Articles

Protonh 2 11/2 and octupole excitations in148 66Dy82 and149 66Dy83

The yrast states of148Dy and149Dy have been studied by γ-ray and conversion electron measurements in (α, xn) and (16O,xn) reactions on enriched152Gd and135Ce targets. Level schemes to above 4 MeV for the two nuclei are reported. The πh211/2 spectrum identified in148Dy and the πh11/2 effective chargeeeff=1.52±0.05e, derived from the measuredE2 transition rate between the (πh211/2) 10+ and 8+ states, are discussed and compared with results for other two-particle nuclei. The yrast cascades in148Dy and149Dy continue above the (πh211/2) 10+ and πh211/2vf7/2) 27/2− states by ∼ 1 MeVE1 transitions de-exciting the lowest members of octupole multiplets built on these states. The energy shifts for the observed members of the πh211/2 × 3− multiplet are analyzed in terms of twoparticle-phonon exchange coupling using an empirical coupling strength extracted from the one valence particle nucleus147Tb. The dominantvf7/2×3− character of low-lying 13/2+ isomers in149Dy and otherN=83 nuclei is emphasized.

Neutron excitations in even mass Sn nuclei

Abstract High-spin neutron quasi-particle excitations in the even-mass 110–118Sn nuclei have been investigated using Cd(α, 2nγ)Sn reactions. The experiments included γ-ray excitation function, γ-γ coincidence, lifetime, γ-ray angular distribution, γ-ray linear polarization and conversion electron measurements. Four new isomeric states were identified, i.e. the Jπ = 6+ state at 2480 keV in 110 Sn(T 1 2 = 8.3±0.4 ns ) , the Jπ = 8− state at 3440 keV in 112 Sn(T 1 2 = 0.58±0.06 ns ) , the Jπ = 8− state at 3190 keV in 114 Sn (T 1 2 = 0.35±0.20 ns ) and the Jπ = 7− state at 2909 keV in 116 Sn (T 1 2 = 0.5±0.3 ns ) . These isomers and in addition several new levels observed in 110–114Sn can be related to neutron quasi-particle excitations. Spin and parity assignments to known levels are firmly established. The data are interpreted within the framework of the broken-pair model, including proton 1p-1h excitations. Excitation energies and static moments are well accounted for by this model. Experimental transitions rates however, are not always well reproduced by the calculations, especially for Eλ decays between excited states of the type J → J - λ. It is argued that in such cases collective two-broken-pair admixtures dominate the transitions.

Level structure in double odd 104Ag

The level structure of the odd-odd 47 104Ag 57 nucleus has been studied using the 103Rh(α,3nγ) 104Ag reaction. The assignment of γ-rays to 104Ag and the construction of the level scheme are based on relative excitation function and γ- γ- Δt coincidence experiments. Spins and parities of levels are proposed on the basis of the angular distribution of γ-rays and conversion electron measurements. Excited states with spin value up to J π = 13 + have been observed. The 212.1 keV; J π = 7 + level was found to decay with T 1 2 = 1.4±0.2 ns while for the 112.6 and 387.0 keV levels upper limits of T 1 2 < 1 ns and T 1 2 ≦ 0.4 ns , respectively, were obtained. A positive-parity band with spin sequence ΔI = 1 based on the J π = 5 + ground state has been identified. This band is interpreted as resulting from the coupling of the π g 9 2 ν g 7 2 proton-neutron configuration to the even-even moderately deformed core. Performed calculations on the basis of the Nilsson model (at deformation ε = 0.15) with Coriolis interaction reproduce well the observed band and the electromagnetic transition probabilities when taking into account attenuation of the Coriolis interaction α = 0.55.

High-spin states in 103Ag and particle-core coupling at intermediate deformation

The 103Ag nucleus has been studied using the 103Rh(α, 4nγ) 103Ag and 103Rh( 3He, 3nγ) 103Ag reactions. A set of standard in-beam measurements involving relative excitation function measurements of γ-rays, γ- γ- Δt coincidences, conversion electron measurements and angular distribution and linear polarization measurements of emitted γ-rays have been performed. Excited states with spin values up to 27 2 are populated in this nucleus. Among these excitations a positive-parity band built on the J π = 7 2 + or 9 2 + state can be distinguished. This band has similar properties as the band observed in 105Ag. The experimental data on the band in 103, 105Ag are compared to the prediction of the Nilsson model with Coriolis coupling at intermediate deformation ε = 0.10−0.15. Energy levels of the positive-parity bands are reproduced satisfactorily by the calculations assuming either a K = 7 2 + [413] or K = 9 2 + [404] band head. However, electromagnetic properties of the levels, branching and mixing ratios, are better reproduced when assuming the K = 7 2 + band head. Attenuation of the Coriolis interaction was introduced in order to improve the fit of the calculated energies of the levels to the experimental values.

Construction and application of a delay line for position read-out of wire chambers

The construction and characteristics of an electromagnetic delay line are described. The materials used in the delay line are selected because of their dielectric and magnetic properties. The effective length of the delay line is 24 cm and the delay 1.4 μs. The rise time of the pulses is 70 ns. The specially designed preamplifiers, based on the principle of “electronic cooling”, and the electronic set up are discussed. The application of the dealy line as a device for position read-out of the avalanches in a proportional chamber, used for the measurement of conversion electrons in a double focusing β-spectrometer, is described.

Details of conversion electron spectroscopy with mini-orange spectrometers

Two mini-orange spectrometers for in-beam measurements of conversion electrons have been built and employed for spin and parity assignments of nuclear states by measuring absolute conversion coefficients. A detailed description of the experimental procedure and data analysis is given. Numerical calculations of transmission curves have been performed in order to achieve precise predictions of the optimal measuring geometry and to design new versions of mini-orange spectrometers. The methods were applied to 70Ge, where spins and parities of 6 − and 7 − were assigned to the levels at 3666.1 and 3954.5 keV, respectively, including the influences of the electron and γ angular distributions.

In-beam electron conversion from high-spin states inPb203

In-beam, time-sorted measurements of internal conversion electrons and ..gamma.. rays are reported for /sup 203/Pb formed by the /sup 204/Hg(..cap alpha..,5n) reaction at E/sub b/ = 53.5 MeV. The multipolarity of the 153 keV transition de-exciting the 29/2/sup -/ isomer is determined to be E3. The 239-keV transition, in the cascade connecting the 23/2/sup +/ and 21/2/sup +/ states, is determined to be M1. The 874-keV transition is found to have and M1/E2 ..gamma.. intensity ratio of 0.4/sup +0.20//sub -0.15/. Thus, the state at 2796 keV is assigned J/sup (/ = 23/2/sup +/ and has a probable configuration p/sub 1/2/ /sup -1/f/sub 5/2/ /sup -3/i/sub 13/2/ /sup -1/ +p/sub 1/2/ /sup -2/f/sub 5/2/ /sup -1/f/sub 7/2/ /sup -1/i/sub 13/2/ /sup -1/. The other measured multipolatities are E2(258 keV), M1(635 keV), E2(839 keV), and M4(1027 keV) with no measurable admixture of multipoles.

Particle plus octupoleM2/E3 isomers and high-spin particle-hole states in147Tb and148Tb

The level structures of theN=82 andN=83 nuclei147Tb and148Tb have been studied by means of (α, 8n) and (α,7n) reactions induced by 68 to 110 MeVα particle bombardments of151Eu targets. In-beam conversion electron measurements have established that isomers withT1/2=4.8(6)ns in147Tb andT1/2=22(1)ns in148Tb decay byM2+E3 transitions to the ground states. The measuredB(E3) values show that the isomeric states arise from the coupling of the valence nucleon(s) to the146Gd core octupole. Particlephonon coupling in these nuclei and in the one-neutron nucleus147Gd is discussed and compared with well known cases involving the208Pb core. The higher lying yrast states in the two Tb nuclei are described as shell-model particle-hole excitations using empirical single particle energies and nucleon-nucleon interactions.

Collective bands in even mass Sn isotopes

Positive parity bands in 112, 114, 116, 118Sn have been excited up to levels with spin and parity J π = 12 + using Cd(α, 2nγ)Sn reactions. The experiments consisted of γ-ray excitation function, γ-γ coincidence, lifetime, γ-ray angular distribution, γ-ray linear polarization and conversion electron measurements. The observed bands show strong resemblances with ground-state bands of transitional nuclei in this mass region. It is pointed out that the J π = 0 + band-heads originate from 2p-2h excitations in the Z = 50 proton shell. The excitation energies of the band-heads are calculated by means of the macroscopic-microscopic renormalization method. Pair correlations between the 2h and 2p configurations are included separately in a phenomenological way by taking into account the pairing energies of the Cd and Te ground states with respect to the Sn ground state.

Internal conversion electron measurements following the decay of 152Eu

Relative intensities of internal conversion electron lines from the decay of 152Eu are measured accurately with a Si(Li) detector. The results thus obtained are presented, clarifying many discrepancies of previous works.

Gamma-gamma coincidences and electron conversion measurement in141La

The gamma rays and conversion electrons following the gamma decay of 141Ba obtained by mass separation of 235U fission products have been measured. The main features of the 141La level scheme were established on the basis of gamma-ray energies and intensities, internal conversion electron measurements and quantitative and qualitative gamma - gamma coincidences. A total of 144 gamma rays have been identified as belonging to the 141Ba decay. Conversion coefficients were determined.

The double focusing iron-core electron-spectrometer “BILL” for high resolution (n, e −) measurements at the high flux reactor in Grenoble

A new high resolution iron-core electron spectrometer (BILL) has been constructed at the High Flux Reactor in Grenoble. It is currently being used for measurements of conversion electrons after thermal neutron capture. An internal target (maximal size 40 cm 2) is irradiated in a thermal neutron flux of 3 × 10 14 n cm −2 sec −1. The electrons pass through a vertical beam tube, 14 m long and 10 cm in diameter, defining the solid angle of 3.4 × 10 −6 / 4π. The spectrometer itself consists of two independent flat electromagnets. Both magnets act as double focusing spectrometers, where the double focusing is achieved by the combination of homogeneous and 1 r fields. The first, a 58° deflecting magnet, forms a 10:1 scaled down intermediate image of the large, 14 m distant target in the reactor hall. The dispersion of this magnet is 94 cm. The second magnet views this reduced image with a very high dispersion of 540 cm. The radius of the optic circle of both magnets is 50 cm. The energy range of the spectrometer is 15 keV < E < 10 000 keV. Multi-wire proportional counters are used as detectors. The best measured momentum resolution has been 8 × 10 −5 at 300 keV with a target of 2 × 100 mm 2. Routine measurements have been carried out with targets of 30 × 100 mm 2 achieving a resolution of Δp/ p = 4 × 10 −4. The momentum precision of the instrument is 1 part in 10 5 and the sensitivity for neutron capture conversion electrons 300 μb at 400 keV.

Band structure and hole-core coupling in 111In

The level structure of 111 In was studied using the 109Ag(α, 2nγ) 111 In reaction. The experiments included γ-ray excitation function, γ-γ coincidence, γ-ray angular distribution and conversion electron measurements. The structure of the cascade of positive-parity states with spins in the range from 9 2 + to 17 2 + is well described by coupling a g 9 2 proton-hole to the quadrupole vibrations of th 112Sn core. Branching and mixing ratios of γ-rays decaying within this band are reproduced satisfactorily by hole-phonon coupling calculations. A calculation of the leading order contributions in the transitional matrix elements shows that in particle-phonon coupling the sign of the mixing ratios is related to the sign of the quadrupole moment of the band head. This is in agreement with the experimental results. The half-life of the isomeric state at 2717 keV (J π = 21 2 +, T 1 2 = 13.8 ns) is related to the half-life of the 6 + isomer in the adjacent 112Sn nucleus. Also the negative-parity states can be interpreted within the hole-core coupling model. No evidence was found for bands based on deformed proton states.

Decay ofTh234to thePa234isomers

The low-energy portion of the photon spectrum for the ..beta.. decay of /sup 2/34Th has been investigated with a carefully calibrated Ge(Li) detection system because of the excessive photon intensity of the M1 73.7-keV transition reported previously. The new photon intensity obtained for this transition relative to other strong transitions is consistent with the most recent conversion electron measurements in the two-step /sup 2/34Pa/sup m/ isomeric transition. The upper energy limit of the unobserved E3 isomeric transition is discussed in terms of total converion coefficients, hindrance factors, and the detection limit of the recent conversion electron measurements.

Properties of the 3? first excited state in the doubly closed shell nucleus146Gd

Conversion electron measurements confirm the 3− assignment recently proposed for the 1579 keV first excited state in146Gd. Fromγγ- ande−γ-coincidence data the half life of that state has been determined asT1/2=1.06±0.12 ns.

Investigation of i [formula omitted] excitations in 197Hg and 191Pt

The level schemes of the odd-neutron nuclei 197Hg and 191Pt have been studied using in-beam spectroscopic methods. Energies, intensities, angular distributions and coincidences of the γ-rays following (α, 2n) reactions were measured. Also conversion electrons and delayed γ-ray spectra were recorded. Most of the levels in both nuclei are de-populated via the 13 2 + isomers. Besides the yrast states, several additional states with spin values between 13 2 and 21 2 were identified. The negative parity of a side band in 197Hg starting with an f = 21 2 state was proved by the conversion electron measurement. The families of positive-parity states were compared with model calculations where the core was described as rigid triaxial rotor or anharmonic vibrator. For 197Hg both models give similarly good results for the energy spectrum and the branching ratios of electromagnetic transitions. Several negative-parity states found in 197Hg are compared with the predictions of a pairing-plus-quadrupole model.

A study of high spin states in 151Gd

States in the transitional nucleus, 151Gd, excited by the (α,2n) reaction have been studied by gamma-ray and conversion electron measurements. Gamma-ray energies, intensities, excitation functions, and γ–γ coincidence measurements were used to establish the levels populated. Angular distributions involving measurements at seven angles from 0° to 90° and K-conversion coefficients have been used to make spin and parity assignments.The El character of the 65, 79, 340, 358, 406, and 462 keV transitions, which in the absence of K-conversion data had been tacitly assumed to be M1 by earlier workers leads to a significant revision of their parity assignments and interpretation of the level structure. The negative parity states at 1210, 1463, 1726, 2004, 2295, 2600, 2915, and 3237 keV form a well-developed rotational band based on the 11/2− [505] state at 1210 keV. The properties of this band in this nucleus are compared with those of the same band in a number of nearby nuclei. Two non-interacting negative parity bands with states at 0(7/2−), 706(11/2−), 1435(15/2−), 2078(19/2−), and 379(9/2−), 902(13/2−), 1511(17/2−), 2297(21/2−), respectively, have been found, as well as a number of other negative parity states of spin 7/2, 9/2, and 13/2. A complex positive band structure involving states at 784(11/2+), 852(13/2+), 1116(13/2+), 1346(17/2+), 1364(15/2+), 1677(17/2+), 1851(19/2+), 1853(21/2+), 2197(21/2+), 2325(23/2+), and 2405(25/2+) has been identified. By using a somewhat unusual set of parameters, we have been able to approach a description for the positive parity states in terms of the triaxial model of Meyer-ter-Vehn.

Structure ofPm141from decay ofN=79Sm141

The 10.2 min $^{141}\mathrm{Sm}^{g}$ decay has been investigated. Positron, $\ensuremath{\gamma}$-ray singles, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$, and ${\ensuremath{\beta}}^{+}\ensuremath{-}\ensuremath{\gamma}$ coincidence as well as conversion electron measurements led to a decay scheme comprising 27 transitions among 12 excited states with deduced ${J}^{\ensuremath{\pi}}$ assignments in $^{141}\mathrm{Pm}$. The ${J}^{\ensuremath{\pi}}=\frac{1}{{2}^{+}}$ for $^{141}\mathrm{Sm}^{g}$ is confirmed. Internal conversion electrons resulting from the decay of 22.6 min $^{141}\mathrm{Sm}^{m}$ have also been measured. The half-life of the $\frac{11}{{2}^{\ensuremath{-}}}$ state at 628.6 keV in $^{141}\mathrm{Pm}$ populated in the latter decay has been measured to be 0.59 \ifmmode\pm\else\textpm\fi{} 0.02 \ensuremath{\mu}s. The ${\ensuremath{\beta}}^{+}$ end-point energy measurements yielded decay energy ${Q}_{\mathrm{EC}}=4.70\ifmmode\pm\else\textpm\fi{}0.06 \mathrm{MeV}\mathrm{and} 4.56\ifmmode\pm\else\textpm\fi{}0.04 \mathrm{MeV}$ for $^{141}\mathrm{Sm}^{m}$ and $^{141}\mathrm{Sm}^{g}$, respectively, and these values are compared with predictions of mass formulas. Systematics of the low-lying states and the $B(M2)$ and $B(E3)$ reduced transition rates in the odd-$A$, $N=80$ isotones are discussed.RADIOACTIVITY $^{141}\mathrm{Sm}^{m,g}$ from $^{144}\mathrm{Sm}(p, p3n)$ and $(p, 4n)^{141}\mathrm{Eu}\ensuremath{\rightarrow}({\ensuremath{\beta}}^{+}, \mathrm{EC})$; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\mathrm{ce}}$, ${E}_{{\ensuremath{\beta}}^{+}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$, ${\ensuremath{\beta}}^{+}\ensuremath{-}\ensuremath{\gamma}$ coin, ${\ensuremath{\beta}}^{+}\ensuremath{-}\ensuremath{\gamma}$ delay, deduced ${Q}_{\mathrm{EC}}$. $^{141}\mathrm{Pm}$ deduced levels, $J$, $\ensuremath{\pi}$, ${T}_{\frac{1}{2}}$, $log\mathrm{ft}$, ICC, $\ensuremath{\gamma}$ multipolarity. Enriched targets, Ge(Li), Si(Li), plastic detectors.

States inN=79Nd139populated in the decay ofPm139

The structure of $^{139}\mathrm{Nd}$ is investigated through the ${\ensuremath{\beta}}^{+}$ decay of $^{139}\mathrm{Pm}$, whose decay half-life is measured to be 4.15 \ifmmode\pm\else\textpm\fi{} 0.05 min. A level scheme comprising 19 excited states and 47 transitions is constructed by means of ${\ensuremath{\beta}}^{+}$, $\ensuremath{\gamma}$-ray, and electron spectroscopy measurements. Using internal conversion electron measurements and the deduced $\ensuremath{\beta}$-decay $\mathrm{ft}$ values, ${J}^{\ensuremath{\pi}}$ assignments are made to states in $^{139}\mathrm{Nd}$ and to the ground state of $^{139}\mathrm{Pm}$. From the $\ensuremath{\beta}$ end-point energy measurements, the total decay energy of $^{139}\mathrm{Pm}$ has been established as 4.45 \ifmmode\pm\else\textpm\fi{} 0.08 MeV. The structure of $^{139}\mathrm{Nd}$ is discussed in terms of the systematics of the odd-$A$, $N=79$ isotones. Decay energy systematics of the odd-$A$, $N=78 \mathrm{and} 80$ isotones are also discussed.RADIOACTIVITY $^{139}\mathrm{Pm}$ from $^{142}\mathrm{Nd}(p, 4n)$; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\mathrm{ce}}$, ${E}_{\ensuremath{\beta}}^{+}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence, deduced ${Q}_{\mathrm{EC}}$. $^{139}\mathrm{Nd}$ deduced levels $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$, ICC, $\ensuremath{\gamma}$ multipolarity. Enriched targets, Ge(Li), Si(Li), plastic, NaI(T1) detectors.

Negative parity bands in 100Ru observed in the 100Mo(α, 4n)100Ru reaction

In the study of the 100Mo(α, 4n)100Ru reaction at Eα = 45 MeV the ground state band of 100Ru was excited up to Jπ = 10+ and a negative parity band up to Jπ = (15)−. In addition, two negative parity bands were observed, one of which probably has even and the other odd spin states. The experiments encompassed γ-ray angular distribution, coincidence, linear polarization and conversion electron measurements. New levels are reported at Ex = 5130, 5165 (Jπ = (13)−), 5280, 5717 and at 6201 keV (Jπ = (15)−). In addition spin or parity assignments were made for the Ex = 2529, 2953, 2965, 3141, 3356, 3505 and 4233 keV levels as Jπ = 5−, 7−, (6)−, 7−, (8)−, 9− and (11)−, respectively. A 3− state is for the first time observed at Ex = 2180 ± 20 keV in the 100Ru(α, α') reaction at Eα = 104 MeV. Multipolarities, conversion coefficients, branching and quadrupole/dipole amplitude mixing ratios have been determined for many transitions in 100Ru. From a detailed comparison of excitation energies and of the properties of many, even weak, transitions with the results of the interacting boson approximation model, it appears that this simple model provides a good overall parametrization. This supports the description of 100Ru as an anharmonic vibrator with quadrupole and octupole bosons as independent but interacting basic excitation modes. A negative parity band in 101Ru, of which a new level at Ex = 3474 keV is a candidate for the 272− member, is well described by coupling the h112 single particle to the 100Ru quadrupole excitation.