Energy levels of the nucleus248Bk

The ambiguities and contradictions in presently available experimental information on the energy levels of the doubly odd deformed nucleus²⁴⁸Bk are sought to be cleared through calculation of the band head energies of the two-particle states based on evaluation of the residualn-p interaction energy for a zero range interaction. The applicability of the Gallagher-Moszkowski rule for the relative ordering of the spin triplet and singlet states is critically examined. It is concluded that the 8^? state from the {7/2⁺[633]p; 9/2^?[734]n configuration is the long lived isomer and forms the ground state of this nucleus. The 1^? state of the same configuration is the short lived isomer and an excited state in accordance with the GM rule and so is the 6⁺ state of the {3/2^?[521]p; 9/2^?[734]n configuration. The expected location of 20 two particle states comprising 10 GM pairs is calculated and compared with the available experimental information.     

Low-lying two-particle states in the nucleus236Np

The ambiguities and the uncertainties about the energy levels of the doubly odd actinide nucleus ₉₃ ²³⁶ Np₁₄₃ are sought to be removed by determination of the bandhead energies of various two-particle configurations expected to appear in the low energy spectrum of this nucleus. The calculations involve quantitative evaluation of the zero range neutron-proton residual interaction energy contribution to the bandhead energy for each configuration. It is concluded that the ground state is the long-lived isomer with spin-parityI ^π=6^- arising from the configuration {5/2⁺[642] _p +7/2^?[743] _n }. Bandhead energies for eight two-particle states appearing upto an excitation energy of 400 keV are presented and the results are discussed in the context of the available and further experiments.     

Der Zerfall des163Tb

The beta and gamma radiations of¹⁶³Tb have been investigated employing scintillation and semiconductor spectrometers and coincidence techniques. The sources were produced by the¹⁶³Dy(n,p)¹⁶³Tb reaction. A half-life of 19.5 min has been measured without evidence for an isomeric state in the half-life range of 2 sec to 7 d; especially a 6.5 h activity previously assigned to¹⁶³Tb could not be confirmed. 76 of the total of 82 gamma-ray transitions, representing 99.6% of the gamma-ray intensity, could be assigned to 23 levels in¹⁶³Dy. From beta and beta-gamma coincidence measurements aQβ-value of 1.7 ± 0.1 MeV has been determined. Spin and parity of 3/2⁺ are deduced for the ground state of¹⁶³Tb with the Nilsson configuration [411↑]. The level at 884 keV is interpreted as aJ ^π=1/2⁺ state with a high contribution of the three-quasiparticle configurationp[411↑]-p[523↑]-n[523↓] because of an allowed unhindered beta-ray transition to this level.     

Nuclear spectroscopic studies of the 23.7 h 248Bk

Main features of the decay of the 23.7 h ²⁴⁸Bk have been determined by spectroscopy with scintillation and semiconductor detectors. The results are as follows: half-life 23.7 ± 0.2 h; branching is (30 ± 5)% to ²⁴⁸Cm (≈ 23% EC decay to 0⁺ ground state and ≈ 7% to first 2⁺ state) and (70 ± 5)%β^? decay to ²⁴⁸Cf(5 % to 592 keV K^π = 2^? state and (65 ± 5)% to the ground-state band). The β^? decay energy, Q_β^?, has been measured to be 860 ± 20 keV, and the electron capture decay energy, Q_EC, has been derived from closed cycle to be 705 ± 25 keV. The deduced logft values of β^? and EC transitions restrict the spin of the ²⁴⁸Bk ground state to 1, with configuration assignment $\text{{}\text{n}\text{[734]}\text{9}\text{2}{}^{\mathrm{?}}$; $\text{p}\text{[633]}\text{7}\text{2}{}^{\mathrm{+}}$. It has also been deduced that the long lived isomer lies 65 ± 40 keV abovethe 23.7h ²⁴⁸Bk ground state.     

Magnetic moment and electric quadrupole moment of the anomalous186Ir ground state

The ground state nuclear moments of¹⁸⁶Ir (j ^π=5⁽⁺⁾) have been determined with NMR on oriented¹⁸⁶Ir in Ni as |μ|=3.80 _?0.02 ^+0.12 μ _n andQ=?3.00 (15)b. The quadrupole moment is consistent with an anamolousj ^π K=5⁺0 or 5⁺1 ground state configuration. The explanation of the magnetic moment in terms of pure 5⁺0 or 5⁺1 configurations would require a high collectiveg _R-factor ofg _R≧0.76. On the other hand the magnetic moment can be explained with a “normal”g _R and a mixed ground state configuration.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

The decays of 21.55 min 162gTm and 24.3 s 162Tm (a new isomer)

The decay of the 21.55 min ground state and of the 24.3 s isomeric state of ¹⁶²Tm was investigated with semiconductor detectors. The γ-ray spectrum was investigated with a Compton-suppression Ge(Li)-NaI(Tl) arrangement. A Si (Li) detector, mounted in an electron transport solenoid, was used to investigate the conversion electron spectrum. Three-dimensional coincidence measurements were performed with large-volume Ge(Li) detectors. The ¹⁶²Tm ground state has spin-parity 1^? and Nilsson assignment p[411]↓?n[521]↑. An allowed β-transition (log ft ≈ 6.4) was observed to a 2^?, 2 octupole vibrational level at 1572.84 keV. The Q-value determined from positon-gamma coincidence measurements is 4705 ± 70keV. The discrepancy of the experimental K /β⁺ ratio with theoretical predictions might possibly be explained by a large number of unobserved weak γ-rays besides the total of 315 stronger ones observed in this study. The average β-strength function was calculated to be 1.2 × 10^?5. Among the 50 levels observed in the decay, the 2⁺, 4⁺ and 6⁺ members of the ground-state band, the 2⁺, 3⁺ and 4⁺ members of the γ-band, several 0⁺ and 2⁺ members of the K = 0 β-bands and 1^?, 2^? and 3^? octupole vibrational levels were identified. Parameter values Z_γ(0) and Z_γ(2) determining the mixing between the γ-band and the ground-state band, allow no conclusive evidence about unequalness of the intrinsic quadrupole moments of the ground states and the γ-band. The Z(0) parameters, determining the mixing between the β-bands and the ground-state band, and X parameters determining the ratio of E0 to E2 transition probabilities, were deduced. A previously unreported 24.3 sec isomer in ¹⁶²Tm was observed to decay in 10% of the cases by an allowed unhindered (log ft = 4.7) β-ray transition to a level at 1712.20 keV in ¹⁶²Er. The Nilsson configurations assigned to the isomeric and 1712.20 keV levels are p[523]↑ + n[521]↑₅₊ and n[523]↓ + n[521]↑₄₊ respectively. The isomeric level decays in 90% of the cases by an E3 transition (E_IT < 125 keV) to a p[404]↓ ?n[521]↑_2? level at 66.90 keV in ¹⁶²Tm, which decays by an (M1+ < 40 % E2) to the 21.55 min ¹⁶²Tm 1^? ground state.     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

The g-factor of the Jπ=12+ isomeric state in188Hg

Using the reaction¹⁷⁵Lu(¹⁹F, 6n) theg-factor of the¹⁸⁸Hg isomeric state (J ^π=12⁺,T _1/2=135 ns) has been measured with the TDPAD method. The experimental value g=?0.168(10) supports the interpretation of an almost pure (vi13/2)^?2 configuration for this isomer.     

Half-life and configuration of the 1/2+ intruder state in203Bi

The decay properties of theJ ^π=1/2⁺,E _exc=1,098 keV state in²⁰³Bi were studied. The state was populated via the²⁰⁴Pb(p, 2n) reaction and the activity was studied with the ion guide isotope separator on-line system IGISOL. The half-life of the 1/2⁺ state was measured to beT _1/2=303 ±5 ms. From this value the partial half-lives of the three depopulating branches 1/2⁺ →7/2^? (E3), 1/2⁺→5/2^? (E3 +M2) and 1/2⁺→9/2 _g.s. ^? (M4) were deduced. Since all the transitions are configuration forbidden in first order, a detailed study of second-order shell-model configuration mixing could be performed.     

Mössbauer study of the hyperfine and magnetic properties of organo-di-iron electron reservoirs containing a polyaromatic bridging ligand

Organo di-iron electron reservoirs Fe(CP^*)₂(Ar) ⁿ⁺ withn=2, 1, 0, where Cp^* is C₅(CH₃)₅ and where Ar are the following bridges: biphenyl, dihydrophenanthrene, triphenylene, have been studied by Mössbauer spectroscopy in the solid state. Complexes withn=2, with 36e^? in the coordination spheres of the metals, exhibit the usual diamagnetic behaviour of 18e^?, Fe^II mono-iron systems. Complexes withn=1, 37e^?, are delocalized mixed valence (Fe^IIFe^I) with a spin 1/2; the magnetic hyperfine interaction, measured under an external field, shows equal delocalization of the 37^th e^? on the two iron centers and the two bridging carbon atoms of the biphenylene. Complexes withn=0, formally with 38e^?, have a practically temperature-independent quadrupole splitting, and isomer shift values which constrast with the expected behaviour of independent Fe^I, 19e^? centers. This indicates that the 37^th and 38^th electrons are mostly located on the polyaromatic bridge. Spectra obtained in an external field show a negligible magnetic hyperfine interaction and support this conclusion. In the case of biphenyl and dihydrophenanthrene bridges, this electron localization can be related to a strong intramolecular chemical coupling, evidenced by other spectroscopic and X-ray data [1].     

A measurement of the branching ratio for the∑ + →pγ decay

We have measured the weak radiative decay branching ratio (∑ ⁺ →pγ)/(∑ ⁺ →pπ⁰). The experiment was carried out at Brookhaven National Laboratory using a low-energy separatedK ^? beam stopping in liquid hydrogen. The∑ ⁺ was tagged by observing the pion fromK ^? K ⁺ p→∑ ⁺π^? in a range telescope, and the gamma was detected in a segmented NaI detector. The result is (2.81±0.39 _?0.43 ^+0.21 )×10^?3, which is consistent with previous measurements. This corresponds to a branching ratio for (∑ ⁺ →pγ)/(∑ ⁺ → all) of (1.45±0.20 _?0.22 ^+0.11 )×10^?3, where the quoted errors are statistical and systematic, respectively. A total of 408 signal events were observed, doubling the previous world total.     

Isomeric state at 945.3 keV in237Np

A new isomeric state in²³⁷Np has been discovered at an excitation energy of (945.3±0.2) keV withT _1/2 =(711±40) ns. Six gamma-ray lines have been measured depopulating the isomeric state to known levels in²³⁷Np. The comparison of the measured absolute gamma-ray transition probabilities with empirical values yields as most probable spinI andK assignmentI=K=13/2 for this isomeric state. It is most likely a 1-proton-2-neutron quasiparticle state 13/2^?π5/2⁺ [642] +ν7/2^? [743] + ν 1/2⁺ [631]. However, a one-quasiparticle 11/2^? [505] configuration for the isomer cannot be excluded.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

Multiphoton mass spectra of XeKr molecules in the range of excited Xe*6<Emphasis Type="Italic">p</Emphasis>[5/2]<Subscript>2, 3</Subscript> atoms

Data on excited states of XeKr molecules in the energy range 78280–77600 cm^?1 are obtained. Using the method of multiphoton laser photoionization of molecules in a supersonic jet, five vibrational progressions of XeKr molecules are obtained, which are attributed to five electronic-vibrational transitions from the ground state of the XeKr molecule of the symmetry 0⁺ to excited states of the symmetry Ω = 0⁺, 1, 2 with the dissociation limit Kr¹ S ₀ + Xe*6p[5/2]₂ and of the symmetry Ω = 1, 2 with the dissociation limit Kr + Xe*6 p [5/2]₃. The molecular constants of the corresponding excited states of the XeKr molecule are estimated.     

A new determination of the capture ratior_c = \frac{{\sum ^ - p \to \sum ^0 n}}{{(\sum ^ - p \to \sum ^0 n) + (\sum ^ - p \to \Lambda ^0 n)}}, the Λ0-lifetime and the ∑−-Λ0 mass difference

The two∑ ^? reactions at rest∑ ^? p→Λ ⁰ n and∑ ^? p→Λ ⁰ n have been studied in order to determine the capture ratio $$r_c = \frac{{\sum ^ - p \to \sum ^0 n}}{{(\sum ^ - p \to \sum ^0 n) + (\sum ^ - p \to \Lambda ^0 n)}}$$ , theΛ ⁰-lifetime and the∑ ^?-Λ ⁰ mass difference. The following results were obtained: $$\begin{gathered} rc = 0.474 \pm 0.016 \hfill \\ \tau _{\Lambda ^0 } = (2.47 \pm 0.08) \times 10^{ - 10} \sec \hfill \\ M_{\sum ^ - } - M_{\sum ^0 } = 81.64 \pm 0.09{{MeV} \mathord{\left/ {\vphantom {{MeV} {c^2 }}} \right. \kern-\nulldelimiterspace} {c^2 }} \hfill \\ \end{gathered} $$ The∑ ^?-mass was determined from the range of the stopping∑ ^?-hyperons,M _∑} =1197.19±0.32 MeV/c ².     

p-n Multiplets and band-like structures in106Ag

The half-life of a 3^? excited state in¹⁰⁶Ag was measured as T_1/2 (364.4 keV)=0.9±0.1 ns using the¹⁰³Rh(α, n)¹⁰⁶Ag reaction. The intramultiplet transition rate B(M1, 3^?→2^?) indicates that the configuration π(g_9/2)₀ ^?2π(p_1/2)^?1 vd_5/2 can be assigned. A low-lying 3⁺ isomer, as known in^108,110Ag, was not found in¹⁰⁶Ag, what is explained by the raising energy of the vd_3/2 shell with decreasing neutron number. For the 6^? bandhead of a rotational-like structure T_1/2 (765.2 keV)< 0.2 ns was derived in contradiction to an earlier prediction (200 ns). Indirect evidence for a negative sign of the magnetic moment of¹⁰⁵Ag (g.s.) is obtained.     

Electroproduction of π+ n, π- p andK + Λ,K + 2211; 0 final states above the resonance region

The reactionsΣ _v p→π⁺ n,K ⁺ Λ,K ⁺ ∑ ⁰ andΣ _v n→π⁺ n were studied at invariant hadronic masses around 2.2. GeV forQ ²=0.06, 0.28, 0.70, and 1.35 GeV². The main results are: At small |t| the π⁺ production is dominated by longitudinally polarized photons and can be described by one pion exchange. At low |t| the transverse (π⁺ n) cross section drops steeply withQ ², but remains roughly constant forQ ²≧0.5 GeV². For |t?≧0.8 GeV², (π⁺ n/dt) is almost independent ofQ ². The integrated cross section (π⁺ n) shows a similarQ ²-dependence asσ _tot (γ _v p) forQ ²≧0.28 GeV². The ratioσ(π^- p)/σ(π⁺ n) atQ ²=0.70 and 1.35 GeV² for |t|≧0.6 GeV² is smaller than in photoproduction and close to 1/4. The ratioσ(K ⁺ ∑ ⁰ decreases steeply withQ ² following roughly the predictions of the quark-parton model.     

Nuclearg-factors of theJ π=21/2+isomer in112In and theJ π=6+ 112Sn

Theg-factor of theJ ^π=21/2⁺ isomeric state in¹¹¹In (T _1/2=13.3 ns) and of theJ ^π=6⁺ isomeric state in¹¹²Sn (T _1/2=13.7 ns) were measured using the spin rotation method. The result obtained for theJ ^π=21/2⁺ level in¹¹¹In,g=+0.47 (2), indicates that this state has an almost pure ((πg _9/2)^?1 νg _7/2 νd _5/2) shell model configuration. The experimental valueg=+0.04 (3) for theJ ^π=6⁺ isomer in¹¹²Sn agrees with the theoretical value calculated within the frame of the BCS model.     

The 235 ns 9+ isomer in 63 148 Eu85

From (p, xn) in-beamγ-ray and electron measurements aT _1/2=235(14) ns isomer at 720 keV was identified in ₆₃ ¹⁴⁸ Eu₈₅ and the levels populated in its decay have been characterized. The results determineI ^π=9⁺ for the isomeric state, and we assign it as the (πh _11/2 j ₀ ^?2 ν f ₇ ^2/3 )9⁺ shell model state, analogous to the configuration of the 235 μs isomer in ₆₃ ¹⁴⁶ Eu₈₃.