Transition probabilities and the structure of some negative-parity states in 126,130Xe and 132Ba

The lifetimes of several negative-parity states in ^126,130Xe and ¹³²Ba have been determined by means of the generalized centroid-shift method. The reactions ^124,128Te(α, 2n) and ¹²²Sn(¹³C, 3n) have been used. Following results were obtained: T_1/2(2758 keV) = 1.3 ± 0.2 ns in ¹²⁶Xe, T_1/2 (2060 keV) = 0.20 ± 0.10 ns, T_1/2 (2104 keV) = 0.50 ± 0.10 ns, T_1/2 (2376 keV) = 0.30 ± 0.10 ns and T_1/2 (2973 keV) = 4.6 ± 0.4 ns in ¹³⁰Xe as well as T _1/2(2120 keV) = 0.40 _?0.10 ^+0.20 ns in ¹³²Ba. A systematics of the B(E2; 7 ₁ ^? ? 5 ₁ ^? ) values in the N = 76 nuclei is presented. Electric dipole and quadrupole transition rates are discussed in terms of octupole and quadrupole collectivity. The structure of the 5 ₁ ^? and 7 ₁ ^? states is considered. Nuclear reactions: ^124,128Te(α, 2n), E = 26 MeV, ¹²²Sn (¹³C, 3n), E = 53 MeV; measured E_{gg}, I_{gg}, γ-r.f. Deduced T_1/2, B(σL) in ^126,130Xe and ¹³²Ba. Ge detectors. Generalized centroid-shift analysis.     

New isomeric states in the stable nucleus 185Re

High-spin states in ¹⁸⁵Re have been studied using the ¹⁷⁶Yb(¹³C,p3n) reaction at 65 MeV. Levels up to spin (37/2) h? at E _x = 4.799 MeV have been identified. Among them two levels were observed with half-lives of 6 ± 2 ns and 123 ± 23 ns.     

Probabilities of muon induced nuclear reactions involving charged particle emission

The probabilities for the reactions (μ^?, p), (μ^?, pn), (μ^?, p2n), (μ^?, p3n) and (μ^?, α) were measured by activation experiments on 18 elements from Na to Bi. The results suggest the following systematics : (i) the probability W of each type of reaction depends on the atomic number of the target and can be described by W = aexp( -bV), where V is the Coulomb barrier of the compound nucleus for the ejected charged particle; (ii) the factor b is the same for all (μ^?, pxn) reactions and not very different for (μ^?, α) reactions; (iii) the relative probabilities for (μ^?, pxn) reactions for a given target vary as 1 :6 :4 :4 for x = 0, 1, 2, 3. The experimental results are compared with a theoretical estimate of the reaction probability and with the corresponding 14 MeV neutron induced reactions.     

Unnatural parity levels populated in the 16O(6Li,d)20Ne reaction

The ¹⁶O(⁶Li, d)²⁰Ne reaction to the 2^?, 4.97 MeV, 3^?, 5.63 MeV, and 4^?, 7.01 MeV members of the K^π = 2^? band has been studied. Angular distributions were measured at 32 MeV from 7.5° to 145° (lab). Excitation functions were measured at 15° (lab) and 145° (lab) from 31 to 33 MeV and 31.75 to 32.5 MeV, respectively. Results of multi-step and compound nuclear calculations are compared to the data. At this incident energy, both mechanisms appear to contribute to the population of the unnatural parity levels.     

Structure of 14C from 12C(t,p)

The reaction ¹²C(t, p)¹⁴C has been investigated with an 18 MeV triton beam. Twenty energy levels of ¹⁴C were identified up to 13 MeV excitation. Angular distributions were measured and compared with DWBA calculations. A previously unreported 0⁺ level at 9.75 MeV was observed; it undoubtedly corresponds to the second predominantly sd shell 0⁺ state in ¹⁴C. Additional spin and parity assignments have been made in the present work: 9.81 MeV, (1^?); 10.43 MeV, 2⁺; 10.50 MeV, (3^?); 10.74 MeV, 4⁺; 11.40 MeV, 1^?; 11.67 MeV, (1^?); 11.73 MeV, (5^?); 12.58 MeV, (2⁺, 3^?); 12.87 MeV. 2⁺, 3^?; and 12.96 MeV, (1^?); none of which had a definite spin and parity assignment previously. Our results confirm the previous information on the level structure of ¹⁴C below 8.5 MeV. The cross section for the unnatural parity state at 7.34 MeV, J^π = 2^?, is well reproduced by a two-step reaction calculation. The results are compared with the predictions of a weak coupling model.     

Die Reaktion7Li (d, α)5He im Energiegebiet von 0,6 bis 2,0 MeV

The excitation function of the reaction⁷Li(d, α)⁵He has been measured between 0.6 and 2.0 MeV in steps of 50 keV. The two resonances at 0.75 and 1.00 MeV corresponding to the levels at 17.28 and 17.48 of the compound nucleus⁹Be were resolved. Angular distribution measurements were performed at 14 different energies mainly near the 1.00 MeV resonance. From the analysis of the data the 17.28 MeV level seems to be a positive parity state (3/2⁺ → 7/2⁺) whilst a negative parity (7/2^? or 9/2^?) is indicated for the 17.48 MeV level. This is contrary to the order of parities as given in the literature.     

In-Beam study of neutron deficient100Cd

The very neutron deficient nucleus¹⁰⁰Cd₅₂ has been identified in the reaction⁴⁶Ti (⁵⁸Ni, 2p2n) and its level scheme was studied up to E_x=4.3 MeV and I ≈12. A T_1/2=40 _?10 ⁺²⁰ ns isomer was found at E_x=2.548 MeV with I^π=(8⁺).     

High spin states in153Er

High spin states in¹⁵³Er have been populated in the¹⁴⁴Sm(¹²C, 3n)¹³³Er reaction. Excitation functions, lifetimes, angular distributions,γ-γ coincidences and internal conversion coefficients were measured. Three isomeric states at 2.75 MeV (T _1/2=400 ns), 2.95 MeV (T _1/2～10 ns) and 5.2 MeV (T _1/2=200 ns) have been observed. A fourth isomer seems to be weakly excited above 6.8 MeV. The level scheme proposed is discussed in term of the nuclear shell model.     

Isomers in the N = 83 nucleus 149Dy

Energy levels in the N = 83 nucleus ¹⁴⁹Dy were studied by the reaction ¹⁵²Gd(α, 7n) at 106 MeV bombarding energy using in-beam γ-ray spectroscopy methods. The measurements identified three isomers in this nucleus, at 1073 keV (13 ± 3 ns), at 2700±150keV (5 μs < T_{$\text{1}\text{2}$} < 0.5 s), and above 3.5 MeV (50 ± 15 ns). The low-lying isomer is interpreted as i_{$\text{13}\text{2}$}. The configuration $\text{27}\text{2}$^?(πh_{$\text{11}\text{2}$}²)₁₀₊ ×vf_{$\text{7}\text{2}$} is suggested for the state at 2.7 MeV.     

Phase shift analysis of elastic proton scattering by12C

Angular distributions of the polarization and cross section in¹²C (p,p)¹²C were measured at 24 energies between 9.95 and 10.90 MeV. A phase shift analysis of the data was carried out. The results show four resonances in¹³N atE _x =11.40, 11.64, 11.67 and 11.82 MeV with spins 5/2⁺, 5/2^?, 3/2^? and 3/2⁺.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in²⁵Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the²⁴Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the²²Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2O d _5/2 — 1s _1/2-O d _3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of²⁵Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of²⁵Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of²⁵Mg in great detail. The prospectiveI ^π=9/2^?, 13/2^?, and 15/2^? members of the established negative-parity,K=1/2 band are found in levels atE _x=7801, 9410, and 8896 keV.     

On the inelastic excitation of 2− state of 16O by α particles

The excitation of the unnatural parity state (2^?, 8.87 MeV) of ¹⁶O by inelastic scattering of 40 MeV α particle is investigated microscopically. The two step excitation mechanism via the 3^? state at 6.13 MeV is found to reproduce the magnitude of the measured cross section of the 2^- excitation. The α-nucleon interaction used for the 2^- excitation also reproduces the 3^- excitation.     

Der radioaktive Zerfall des Fe61

Fe⁶¹(T _1/2=5.95 min) was produced irradiating Ni⁶⁴ and natural nickelfoils with fast neutrons in the reaction Ni⁶⁴(n, α)Fe⁶¹; Fe was chemical seperated. The gamma and beta spectrum were investigated with Ge(Li)-counters, NaJ(Tl) and plastic scintillation spectrometers. Fe⁶¹ emits five gamma rays having the energies and intensities per Fe⁶¹ decay: 121 keV (0.064), 177 keV (0.027), 298 keV (0.293), 1025 keV (0.461), 1202 keV (0.539). Threeγγ-cascades could be identified: 121–177 keV, 121–1202 keV, 298–1025 keV. Inγ β-coincidence measurements the maximal beta energy was determined:E _βmax=2.86 MeV. A decay sceme Fe⁶¹-Co⁶¹ was constructed: Fe⁶¹, spin and parityJ ^π=3/2^?, decays by means of allowed beta decay to three excited states of Co⁶¹: 1323 keV (1/2^?), 1202 keV (3/2^?), 1025 keV (5/2^?). The energies and intensities per Fe⁶¹ decay of the three beta decay modes are: 2.56 MeV (0.367), 2.68 MeV (0.495), 2.86 MeV (0.138). — A 88 keV gamma ray (T_1/2=33 sec) was observed coming from the Co⁶³ decay.     

Structure of the mirror nuclei21Ne and21Na

Theγ-decay of levels in²¹Ne up to 10 MeV excitation energy has been investigated byn — γ coincidence measurements initiated with the¹⁸O(α, nγ) reaction at 12, 13, 14.5 and 15.4 MeV bombarding energies. Spin(-parity) assignments of excited states are obtained by combining then — γ angular correlation measurements performed atE _α=11, 11.82 and 13.6 MeV with a consideration of lifetimes, neutron penetrabilities of the unbound states, and information from the mirror nucleus²¹Na. The resulting values of E_x[keV]?J ^π are as follows: 4525-5⁺, 4686-3⁺, 5431-7⁺, 5549-3⁺, 5819-7^?, 6175-7⁺, 6268-9⁺, 6550-9, 6639-9, 7006-7⁺, 7041-9, 7356-7 or 9, 7422-11^(?), 7648-7⁺, 7981-11 or (7⁺), 8154-9, 8240-11, 8664-9^? or 11 or 13^?, 9401-13^?, 9867-13^? or 15⁺, 9941-13^? or 15 or 17⁺. The assignment of mirror levels in²¹Ne —²¹Na has been extended to the 6175 keV level of²¹Ne. Excitation energies, electromagnetic properties, Gamow?Teller matrix elements and spectroscopic factors of positive parity states are compared with the results of shell-model calculations which employ a unifieds—d shell Hamiltonian and the unrestricted configuration space of the 0d _5/2 —1s _1/2—0d_3/2 shell. Collective properties contained in shell model wave functions are explored up to the termination of bands atJ=17/2 or 19/2. The spectrum of intruder states in²¹Ne is observed to begin with a 5628 keV,J ^π=7/2⁺ state. The 7422, 8664 and 9401 keV levels are assigned as members of previously established negative-parity rotational bands.     

Spins and parities of hole states in25Na and25Mg

Angular distributions of differential cross sections and vector analyzing powers were measured forl=0, 1 and 2 transitions induced by the \(^{26} Mg\left( {\overrightarrow d ,\tau } \right)^{25} Na\) reaction at 52 MeV. The following spins and parities of final states in²⁵Na were deduced:J ^π =1/2⁺ (1.069 MeV), 3/2⁺ (2.202 MeV), 5/2⁺ (2.914 MeV), 1/2^? (3.995 MeV) and 3/2^? (5.190, 5.690, 6.549 and 7.603 MeV). The DWBA analysis of proton and neutron pick-up spectra obtained from a parallel measurement of the²⁶Mg(d, τ)²⁵Na and²⁶Mg(d, t)²⁵Mg reactions allows the identification ofT=3/2 analog states in²⁵Mg. Interpretation in terms of the Nilsson model of energies and spectroscopic factors of the first 1/2^? and 3/2^? hole states observed in proton pick-up reactions from even 1d _5/2- shell nuclei indicates a close correspondence of the final state deformations with those of the first excited 2⁺ states in the target nuclei.     

High spin states in21Ne

States in²¹Ne up to 6.3 MeV have been investigated by means of the¹⁸O(α,nγ)²Ne reaction. The γ-decay of individual levels was studied in coincidence with neutrons by using a neutron time-of-flight spectrometer. Revised branching ratios are given for the states at 5.34, 5.63, 5.82 and 6.03 MeV. Neutron-gamma angular distribution measurements yielded the following J^π assignments: 5.34∶7/2^?, 5/2⁺; 5.63∶(3/2, 7/2); 5.78∶(3/2, 5/2); 6.03∶9/2^?; 6.18∶(5/2,7/2); and 6.27∶(7/2, 9/2). The results are discussed in the frameworkoftheNilsson model.     

Discovery of deeply bound π− states in the208Pb(d,3He) reaction

Narrow lines were observed around 133 MeV excitation energy in the²⁰⁸Pb(d,³He) reaction atT _d=300 MeV/u using the Fragment Separator System at GSI. They are assigned to the deeply boundπ ^??²⁰⁷Pb states with configurations of $\left( {2p} \right)_{\pi ^ - } $ (3p_1/2, 3p_3/2) _n ^?1 .     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

Structure studies of neutron-rich beryllium and carbon isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion induced transfer reactions. A strong sensitivity to the chosen core nucleus is found for the cores of ⁹Be and ¹⁰Be, respectively. With a ⁹Be core, molecular rotational bands up to high excitation energies are observed due to the pronounced 2α-cluster structure, whereas only few states at low excitation energies are populated with a ¹⁰Be core. For ¹¹Be a detailed investigation has been performed for the three states at 3.41 MeV, 3.89 MeV and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2⁺, 5/2^? and 3/2^?, respectively. Furthermore we have studied particlehole states of ¹⁶C using the ¹³C(¹²C,⁹C)¹⁶C reaction and found 14 previously unknown states.