Low-energy excited states in 128I produced by the (p,n) reaction

Gamma spectra produced in the ¹²⁸Te(p, n)¹²⁸I reaction were taken as a function of proton bombarding energy E_p = 2.8 MeV to 5.0 MeV. A level scheme composed of 41 excited states was constructed on the basis of singles γ-spectra and extensive γ-γ coincidence measurements. The coincidence measurements were carried out utilizing a three-parameter Ge(Li)-Ge(Li)-timing system. Upper limits were placed on the lifetime of six levels. The modes of de-excitation of many levels as deduced in the present investigation are significantly different from the results obtained in the (n, γ) reaction. Angular distribution measurements combined with the results from the coincidence counting rates and the population strength of the states by primary transitions in the (n, γ) reaction enabled some spin and parity assignments and tentative assignments for many other levels. The ground state and nine positive-parity states were described in terms of admixed twoquasiparticle multiplets.     

High-resolution study of 0+ and 2+ excitations in 168Er with the (p, t) reaction

Excited states in the deformed nucleus ¹⁶⁸Er have been studied with high energy resolution in the (p, t) reaction, with the Munich Q3D spectrograph. A large number of excited 0⁺ states (25) and 2⁺ states (64) have been assigned up to 4.0-MeV excitation energy. This allows detailed investigations along two directions of current interest: first, an extension of microscopic model interpretations into the region of medium level density above the pairing gap; second, a first analysis of the statistical fluctuation (order/chaos) properties of pure sequences of levels, in one deformed nucleus. Predictions of two models (the quasiparticle-phonon model and the projected shell model) are compared to the data, and it is concluded that, in both cases, mixing of more configurations is required in the wave functions. The text was submitted by the authors in English.     

0+ states near the N = 20 neutron shell from Ar(t,p) reactions

The (t, p) reactions leading to ^38,40,42Ar and ⁴²Ca have been used to study the 0⁺ level spectrum near the N = 20 neutron closed shell. The Ar isotopes show a significant reduction and fragmentation of the L = 0 (t, p) strength relative to Ca. A major change in the structure of the 0⁺ levels thus takes place between Ca and Ar.     

Isobaric analogue states excited in the59Co(p, γ)60Ni reaction

The⁵⁹Co(p, γ)⁶⁰Ni reaction has been investigated in the proton energy regionE _p=1365–2150 keV. Decay schemes and branching ratios have been determined for ten resonances, five of which have been identified as possible analogues or fragments of analogues of the ground state (5⁺) and the 58.6 keV (2⁺), 277.1 keV (4⁺), 288.4 keV (3⁺), and 435.7 keV (5⁺) levels in⁶⁰Co. At eight of the resonances most of the decay seems to go via a group of states with an excitation energy of 5–9 MeV. The investigated analogue states give a Coulomb displacement energy of 9118±7 keV.     

New 0+ states in 146Sm from a (p,t) experiment and the particle-core coupling model

The reaction ¹⁴⁸Sm(p,t)¹⁴⁶Sm was studied at E_p = 26 MeV. Fifty-six excited states in the final N = 84 nucleus were observed below E_exc = 4.2 MeV and their angular distributions were measured at 8 angles. Spin and parity assignments are made for 37 of them, based on the determination of the transferred angular momentum L. Ten excited J^π = 0⁺ states were identified. The emerging excitation energies of the J^π = 0⁺ states and the monopole strength distribution in ¹⁴⁶Sm are compared with those observed in nearby nuclei and with results of calculations done in the framework of the Particle-Core Coupling Model. The main features of the experimental results are interpreted using a superposition of two types of configurations: two-particle states coupled to the collective excitations of the N = 82 core and two holes coupled to the collective excitations of the N = 86 core. Calculations show also that two-phonon⊗two-particle configurations are spread over many states and their identification becomes difficult.     

Study of low-lying 0+ excitations in228Th and232,234,236U in the (p,t) reaction

The (p, t) reaction was studied at 22 MeV proton energy using targets of^230,232Th and^234,236,238U. In²²⁸Th we observed in addition to the 832 keV first-excited 0⁺ level a second-excited 0⁺ level at 939 keV populated with 5% of the ground-state strength. A 0⁺ level proposed recently in²³²U at 927 keV was not observed in the (p, t) reaction, with an upper limit for its excitation of 0.2% of the ground-state strength. In²³⁴U a level at 1045 keV, assigned in the literature as second-excited 0⁺ level, is weakly populated in the (p, t) reaction but does not show the angular distribution characteristic for single-stepL=0 transfer. In²³⁶U we observed a level at 1036 keV with an angular distribution suggesting that it might be a doublet composed of a known 3^? level and a new 0⁺ level. The properties of the first two excited 0⁺ bands in²²⁸Th,²³²U and²³⁴U are compared and discussed.     

Gamma-ray production in the 170Er(p,n)170Tm nuclear reaction

For the first time discrete gamma-rays following the nuclear reaction ¹⁷⁰Er(p,n)¹⁷⁰Tm with enriched target were measured with a high resolution GeHP spectrometer. Protons delivered by the Bucharest FN Tandem Van de Graaff accelerator bombarded a thin self-supporting film of enriched erbium. Measured γ-ray energies (E_γ), their relative intensities (I_γ) and corresponding excitation functions for the beam energy range 2.0–3.6 MeV are reported in the present work. The measured excitation functions were fairly well reproduced by compound nucleus calculations based on the Hauser-Feshbach formalism.     

Pole approximation in the quasi-free t + p scattering and the t(p,d)d reaction via the t + d interaction

The t(p,p)t and t(p,d)d channels have been investigated in an indirect way through the ²H(t,tp)n and ²H(t,dd)n three-body reactions performed at E _t = 35.5?MeV in quasi-free kinematics. The agreement with direct data supports the pole approximation at energies above the Coulomb barrier.     

An investigation of excited states in32S by the31P(p, γ)32S reaction

The³¹P(p, γ)³²S reaction has been studied in the proton energy region 300–1420 keV using Ge(Li)-techniques. Gamma decay schemes of 16 resonances are proposed. The branching ratios of the resonance states and 23 bound states are presented. The spin of theE _x=7116 keV level was found to beJ ^π=2⁺. In addition, the present results are compared with earlier ones.     

Measurement of the 24Mg(p, t)22Mg reaction for the states near the 21Na + p threshold

Differential cross-sections of the ²⁴Mg(p, t)²²Mg reaction were measured at 34.68 MeV for the states near the proton threshold at 5.502 MeV in ²²Mg. Among them, the new states at 5.962, 6.046, 6.246 and 6.323 MeV, which were reported previously, have been confirmed. Angular distributions for these states were analyzed by distorted-wave Born-approximation calculations to deduce the spins and parities. The angular distribution for the 5.714 MeV state, which is considered to be most crucial for the stellar reaction ²¹Na(p, γ)²²Mg, has been found to be consistent with J ^π = 2⁺ assignment. The 6.046 MeV state is newly assigned to have J ^π = 0⁺, and the 5.962 MeV state is tentatively assigned to have J ^π = (1^-). These two states will also play an important role for ²²Mg production in novae. Received: 7 March 2002 / Accepted: 7 May 2002     

The (t,p) reaction on the zinc isotopes

Multichannel spectrograph studies of the (t, p) reaction on the Zn isotopes have provided energy-level data, cross-section measurements and many new spin and parity determinations. The systematics of the energy spectra of the even zinc isotopes are discussed.     

Evidence for excited 0+ states in94Sr

Beta-delayed neutron measurements on⁹⁵Rb have indicated evidence for two heretofore unknown excited O⁺ states in⁹⁴Sr which are not fed by ß -decay from the J^π = 3^? ground state of⁹⁴Rb.     

Investigation of 16O excited states via the 14N(3He,p) reaction

The reaction ¹⁴N(³He, p)¹⁶O has been investigated at a bombarding energy of 15.0 MeV, using a differentially pumped gas target. Angular distributions were measured for 30 levels below 16.5 MeV in excitation. Data were compared with shell-model calculations of Zuker, Buck and McGrory for states whose correspondence with theory is established. Many states are found to possess a large compound-nucleus reaction component. Several previously unreported levels are observed at high excitation. Angular distributions for all except the weakest levels have been compared with DWBA calculations.     

The24Mg(p,t) reaction at 50 MeV

Angular distributions are given for tritons from the ground and first two excited states of the²⁴Mg(p, t)²²Mg reaction. Excitation energies, spins and parities of these levels are given, and a new level also reported.     

Study of excited states in49V with the48Ti (p, γ)49V reaction

In the⁴⁸Ti(p, γ)⁴⁹V reaction gamma decays of thirteen resonances betweenE _p =960 and 1570 keV are investigated. Level energies within ±0.5–±2.0 keV andQ-value 6756.8±1.5 keV are obtained. Branching ratios for the resonance states and strongly populated bound states are given. Gamma-ray angular distribution measurements yield the followingJ(keV) assignments of⁴⁹V bound and resonance states:J(1140)=5/2,J ^π(2235)=5/2^(?),J(2264)=(3/2),J(2308)=3/2,J(3912)=3/2,J(8105,Ep=1374keV)=(1/2) andJ ^π(8289,E _p =1564keV)=3/2^(?). Multipolarity mixing ratios for all measured primary and secondary gamma rays are tabulated. Dopplershift attenuation measurements yield the mean lifetimes τ _m (keV) of the following bound states in⁴⁹V:τ _m (748)=(200± ₁₀₀ ⁴⁰⁰ )fs, τ _m (1140)=(250± ₁₀₀ ⁵⁰⁰ )fs, τ _m (1155)>400 fs, τ _m (1515)=(45± ₂₀ ³⁰ )fs, τ _m (1644)=(55± ₂₀ ³⁰ )fs, τ _m (1661)=(25±5)fs, τ _m (1994)>400 fs, τ _m (2235)=(30± ₁₅ ³⁰ )fs, τ _m (2264)=(45± ₁₅ ³⁰ )fs and τ _m (2308)=(20±10)fs.     

Core-excited states of Fe from the Fe(p, t)Fe reaction at 52 MeV

The perturbation theory for projected states is applied to the two-level pairing force model. Both approximate and exact forms of number projection are considered. The results are compared with the exact ones and with ordinary perturbation theory based on BCS wave functions without projection.     

Study of even-mass Ba nuclei by the (p,t) reaction

The (p, t) reaction on the nuclei ^{134, 136, 138}Ba has been studied at a bombarding energy of 52 MeV. Angular distributions of emitted tritons were obtained between 6° and 60°. The following six negative-parity states were strongly excited by the (p, t) reaction: 5^?(2.121 MeV) and 7^?(2.482 MeV) in ¹³²Ba, 5^?(1.998 MeV) and 7^?(2.274 MeV) in ¹³⁴Ba, and 5^?(2.139 MeV) and 7^?(2.031 MeV) in ¹³⁶Ba. DWBA calculations using the code DWUCK successfully reproduce these angular distributions. The 0⁺ assignment to the 1.761 MeV level in ¹³⁴Ba is confirmed. Intensities of the (p, t) reaction for low-lying states are discussed.     

The (t,p) reaction on the even isotopes of neodymium

The Aldermaston multi-angle magnetic spectrograph and tandem Van de Graaff accelerator have been used to study the (t, p) reactions leading to the neodymium isotopes ^{144,146,148,150, 152}Nd bombarding energy of 13 MeV. The Q-values were measured for final states with excitation energies up to about 3 MeV.     

First excited 0+ states in the germanium isotopes via the Se(d, 6Li) reaction

A systematic study of the even-A germanium isotopes with mass 70 ≦ A ≦ 78 via the Se(d, ⁶Li) reaction has been performed at E_d = 45 MeV. The reaction products were momentum analysed and mass identified with a QMG/2 magnetic spectrograph and the accompanying focal-plane detector system. The main emphasis of this investigation was on the nature of the first excited 0⁺ states. The striking variation in strength from one isotope to the other already observed in the (p, t) reactions to the same final nuclei is also seen for the α-pickup reaction. Previously derived wave functions that assume the excited 0⁺₂ states to be pure proton configuration states can also account for the present results.     

Formation of highly excited states of 6He in the 9Be(π−, tt)t reaction

The hypothesis of a heavy stable quark of the fourth family can provide a nontrivial solution for cosmological dark matter if baryon asymmetry in the fourth family has a negative sign and an excess of ū antiquarks with charge (?2/3) is generated in the early Universe. Excessive ū antiquarks form (ūūū) antibaryons with electric charge ?2, which are all captured by ⁴He and trapped in a [⁴He⁺⁺(ūūū)^??] O-helium OHe “atom” as soon as ⁴He is formed in Big Bang nucleosynthesis. Interaction of O-helium with nuclei opens a new path to the creation of heavy nuclides in Big Bang nucleosynthesis. Due to the large mass of the U quark, OHe “atomic” gas decouples from baryonic matter and plays the role of dark matter in large-scale structure formation with structures on small scales being suppressed. Owing to nuclear interaction with matter, cosmic O-helium from the galactic dark matter halo is slowed in the Earth below the thresholds of underground dark matter detectors. However, an experimental test of this hypothesis is possible in the search for OHe in balloon-borne experiments and for U hadrons in cosmic rays and accelerators. OHe “atoms” might form anomalous isotopes and could cause cold nuclear transformations in matter, offering a possible way to exclude (or prove) their existence.