Nuclear orientation of171Lu and173Lu

The decays of¹⁷¹Lu and¹⁷³Lu have been studied by means of nuclear orientation. External perturbations of two¹⁷¹Yb levels have been observed. Unambiguous spin assignments have been made for several levels in¹⁷¹Yb and mixing ratios of the transitions in¹⁷¹Yb and¹⁷³Yb have been deduced. The properties of the¹⁷¹Yb and¹⁷³Yb rotational bands have been studied using the quasiparticle-phonon model including a Coriolis interaction.     

Time distribution of γ-rays from spontaneous fission of 252Cf at short times

The gross time distribution of γ-rays from spontaneous fission of ²⁵²Cf has been measured in the time range 10^?14?10^?10 s after fission for γ-ray energies greater than 0.15 MeV. The measurements have been made by a new method based upon the solid angle aberration. From the measured correlation between half-lives and γ-ray transition energies it is concluded that the transitions are predominantly E2, single-particle transitions at high energies, and mostly vibrational and rotational transitions at lower energies. Some contribution of E1 transitions and M1-E2 mixtures cannot be excluded, however. It was found that about 30% ofthe γ-rays emitted within 12 ns with energies greater than 0.10 MeV, have half-lives shorter than 1 ps and about 52 % half-lives between 1 and 100 ps. The relative yield of γ -rays and γ-ray energy in the time range 10^?14 to 1.2 × 10^?7 s ater fission is given.     

The spin(6) scheme and electromagnetic transitions in 191Ir and 193Ir

The Coulomb excitation of natural Ir and Pt targets has been measured with protons and α-particles of energies between 5.0 and 6.0 MeV. Accurate γ-ray angular distributions were taken to determine the relative yields of observed γ-rays. Using ¹⁹⁴Pt as standard the reduced electric quadrupole transition probabilities to the ground states from Coulomb excited levels in the Ir and Pt isotopes were determined. Other B(E2) and B(M1) values were determined from the decay schemes obtained and from mixing ratios deduced from γ-ray angular distributions or from previously measured internal conversion coefficients. The detailed sets are compared with calcula- tions based on the Spin(6) scheme, which predicts several symmetries in ¹⁹¹Ir and ¹⁹³Ir. The possible existence of wider supersymmetry multiplets in this region of nuclei is examined on the basis of comparison of electromagnetic properties of Ir nuclei with those of Pt and Os isotopes.     

The reaction 35Cl(n,γ)36Cl studied with non-polarized and polarized thermal neutrons

The γ-radiation following capture of non-polarized and polarized thermal neutrons in ³⁵Cl has been investigated. Of the 420 γ-rays ascribed to the ³⁵Cl(n,γ)³⁶Cl reaction, 236 have been placed in a ³⁶Cl decay scheme. The branching ratios and the excitation energies (with 0.04–0.9 keV errors) of 72 bound states have been determined. Unambiguous spin assignments are given for 11 levels. The multipole mixing ratios for some primary γ-ray transitions have been determined. There exists a significant correlation between (d, p) stripping strengths and (n, γ) reduced primary transition probabilities for transitions to l_n(d, p) = 0 levels.     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

Isomeric γ-ray transitions in 98Tc

Delayed γ-rays from ⁹⁸Tc have been observed following pulsed proton beam bombardment of an enriched ⁹⁸Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.     

Etude du noyau 63Cu par la reaction 60Ni(α, pγ)63Cu

The level structure and the decay properties of low-lying levels in ⁶³Cu have been investigated via the ⁶⁰Ni(α, pγ)⁶³Cu reaction at E_α = 11.7MeV. Using a Ge(Li) detector, the correlations of twenty-five primary γ-rays in coincidence with protons, stopped in an annular detector at approximatively 180° with respect to the beam direction, were measured. From these measurements, branching ratios, γ-ray mixing ratios and spin assignments have been obtained for most of the levels up to 2.4 MeV excitation.     

Low-spin levels in 136Ba studied via the (n,n'γ) reaction

Low-spin levels in ¹³⁶Ba have been studied by means of the (n, n'γ) reaction using reactor fast neutrons. Excited states up to an excitation energy of 2.8 MeV and with spin values up to 7 were found to be populated. Energies, intensities and angular distributions of γ-rays attributed to ¹³⁶Ba have been measured.In addition to the confirmation of known level characteristics the angular distribution data resulted in new unique spin assignments for 7 levels (2 for the levels at 2080.0 keV, 2128.8 keV and 2484.7keV, 3 for those at 2390.8, 2399.8 and 2431.0 keV as well as 0⁺ for the 2141.3 keV level). Furthermore E2/M1 multipole mixing ratios were determined for the most intensive mixed γ-transitions.     

Nuclear orientation of57Co

⁵⁷Co has been oriented in an iron foil at temperatures down to 12.7 m^oK. The⁵⁷Co magnetic moment was measured by taking temperature-dependent⁵⁷Co and⁶⁰Co data, and the result was μ(⁵⁷Co)=4.733±0.023 n.m. The mixing ratios, δ=E2/M1, of the intense 122 keV γ-ray as well as of the weak⁵⁷Fe γ-rays, resulting from the decay of the 707 keV level, were measured. We obtained δ (122)=0.1195±0.0010, ?0.186<δ (230) <0.072 or ?6.99<δ (230)相似文献   

The nuclear structure of 151Pm in the low excitation region < 1 MeV

The level scheme of ¹⁵¹Pm populated by the β-decay of 12 min ¹⁵¹Nd has been studied using Ge(Li) detectors as singles and coincidence γ-ray spectrometers. Most of the new γ-rays have been included in a partial level scheme of ¹⁵¹Pm involving four new levels. Angular correlation measurements on the 170.752–255.678 keV and 170.752–138.882 keV cascades have been made with the result A₂ = 0.088±0.005 and ?0.02 – +0.05, respectively. A PAC measurement on the 170.752–255.678 keV cascade has yielded the g-factor of the 255.676 keV level as g = 1.18 ±0.16. A Nilsson-model calculation including Coriolis coupling has been made and the experimental level energies have been well reproduced by the Nilsson orbitais [413]↓, [411]↑, [420]↑, [532]↑, [541]↑ and [550]↑. Theoretical transition rates, E2/M1 mixing ratios, branching ratios and g-factors are in good agreement with experimental values.     

Exotic nuclei produced by heavy-ions induced fission

About thirty nuclei in theA≈100 mass region have been produced as fission fragments following the fusion-evaporation reactions^28,30Si+¹⁷⁶Yb at 145 MeV bombarding energy. These nuclei have been individually identified from their γ-ray cascades detected with the Eurogam2 array. The level schemes of several stable or neutron-rich nuclei have been extended to higher spins. From cross coincidences between transitions in complementary fragments, γ-rays de-exciting high-spin states of new isotopes can be identified and some aspects of the fission mechanism can be analyzed.     

The decay of 174Tm and mixing of the Kπ = 5− two-quasiparticle states in 174Yb

The decay of 5.4 min ¹⁷⁴Tm has been investigated using Ge(Li) spectrometers in singles and coincidence measurements. A total of 43 γ-ray transitions, 26 of them not reported before, have been observed following the decay of ¹⁷⁴Tm. All transitions could be placed in a level scheme comprising 19 excited states of ¹⁷⁴Yb. The Nilsson model has been used to interpret the level structure. The mixing of two-quasineutron and two-quasiproton states is studied and the experimental mixing matrix element is compared with the results of theoretical calculations.     

Energy levels in 93Mo populated by the 93Nb(p,nγ) reaction

Energy levels of ⁹³Mo have been investigated by means of the ⁹³Nb(p, nγ)⁹³Mo reaction. The excitation functions of the level de-excitation γ-rays were measured with a Ge(Li) detector under proton bombardment in the energy range 3.0 to 5.0 Me V. A detailed γ-ray decay scheme which includes 69 levels and 123 γ-ray lines was constructed from the threshold energies for 64 γ-rays and the γ-ray excitation functions around five isobaric analogue resonances in the ⁹³Nb(p, nγ) reaction. Spin-parity values for 59 levels and favourable values for 8 levels were assigned from the analysis of relative neutron yields via the isobaric analogue resonances of the parent odd-odd nucleus ⁹⁴Nb. The results of the present experiment are compared with shell-model calculations.     

The decay of theI π=8+ isomer in100Cd-neutron particle and proton hole states

The γ-decay and half life of the t_1/2=60(3) ns I^π=8⁺ isomer in¹⁰⁰Cd have been studied with a recoil catcher setup inside the multidetector π-array OSIRIS. Evaporation neutrons and charged particles from the reaction⁵⁸Ni+⁴⁶Ti were measured in coincidence with delayed γ-rays. Six new γ-ray transitions with intensities of 1–10% of the main γ-ray cascade were found, two new states established and firm spin-parity assignments were made to all states below the isomer. The new states were identified as the 4⁺ and 6⁺ members of the proton πg_9/2 ^?2 multiplet.     

Coriolis coupling and electromagnetic properties of rotational bands in odd-a Yb nuclei

Properties of the rotational bands in¹⁶⁷Yb are studied using the quasiparticle-phonon model with the Coriolis interaction included. The level energies,B(E2) andB(M1) values, E2/M1 mixing ratios, and magnetic moments are calculated. In particular, theB(E2) values and the E2/M1 mixing ratios measured by using delay coincidence and nuclear orientation methods, respectively, are well reproduced.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.