Nuclear resonance fluorescence in121Sb

Usingγ quanta from a⁵⁶Co source, resonance fluorescence from a 3,452 keV level in¹²¹Sb was observed. Four deexcitingγ transitions were identified. The profile of theγ emission line, investigated by means of a high speed centrifuge, yields with a novel variety of Doppler shift analysis a lifetime of τ_4,298=(110±50)fs for theγ emitting 4,298 keV level in⁵⁶Fe. The lifetime of the 3,452 keV level was determined to beτ _3,452 =(200±100)fs.     

Lifetime measurements in56Co with the58Ni(d, αγ)56Co reaction

The two-particle pick-up reaction⁵⁸Ni(d, αγ)⁵⁶Co atE _d =7.0 MeV was used to determine mean lifetimes of levels in⁵⁶Co up to 2.73 MeV excitation energy by the Doppler shift attenuation method,γ-rays were observed in a 43 cm³ Ge(Li)-detector at 90° to the beam axis in coincidence withα-particles detected in two 200 μm-silicon surface barrier detectors atΘ _α =±55°. Mean lifetimes for 10 levels in⁵⁶Co and two lifetime limits have been obtained usingF(τ)-curves calculated with the Winterbon theory. The experimental results are compared with the predictions of recent shell model calculations.     

Investigation of excited states in56Co with the54Fe(3He,pγ)56Co reaction

The two-particle stripping reaction⁵⁴Fe(³He,p γ)⁵⁶Co at \(E_{3_{He} } \) =15.15 MeV was used to investigate theγ-ray transitions and to determine branching ratios, possible spin assignments and mean lifetimes of levels in⁵⁶Co up to 5.5 MeV excitation energy. Gamma-rays for both angular correlations and lifetime measurements were observed with a 43 cm³ Ge(Li) detector in coincidence with proton-groups detected at 0°. The level scheme and lifetime values are compared with the predictions of various shell model calculations.     

The lifetime of the 5.14 MeV state in22Ne

Using the delayed coincidence method and the reaction¹⁹F(α, pγ)²²Ne at 10.80 MeV alpha energy, the lifetime of the 5.14 MeV state in²²Ne is determined to beτ=0.84 nsec±10%.     

The decay of 8.7 min237Pa

The beta and gamma radiations of²³⁷Pa have been investigated employing semiconductor and scintillation spectrometers and coincidence techniques. Sources of²³⁷Pa were obtained after bombardments of²³⁸U with bremsstrahlung and 14-MeV neutrons and subsequent chemical separation. From the total of 18γ-rays following the decay of 8.7±0.2 min²³⁷Pa 17 transitions, representing 99.9% of theγ-ray intensity, could be placed in a level scheme of²³⁷U. AQ _β- value of 2.25±0.1 MeV has been determined.     

Properties of excited levels in102Rh by the102Ru(p,nγ) reaction

The level scheme of¹⁰²Rh has been investigated by the¹⁰²Ru(p, nγ) reaction in the proton energy range 3.1 MeV≦E _p≦6 MeV. Excitation functions,γ-γ coincidences and pulsed beam measurements have been performed and a level scheme including 33 excited states up toE _x≈650 keV has been constructed. Theγ-branchings of several levels have also been measured. The lifetimes of 5 excited states have been determined with the centroid-shift method:τ _m(105.2 keV)=(1.3±0.3) ns,τ _m(123.7 keV)=(0.6±0.3) ns,τ _m(178.6 keV)=(1.5±0.3) ns,τ _m(208.7 keV)=(0.5±0.3) ns,τ _m(359.6 keV)=(0.8±0.4) ns. Upper limits have been placed for the lifetimes of 20 other levels.     

Study of the structure of16O above 25 Mev by the reaction13C(τ, α)12C*(γ15.1)

The nucleus¹⁶O has been investigated within the excitation range of 25–32 MeV by means of the reaction¹³C(τ, α)¹²C^* _15.1(γ)¹²C. Excitation functions for the 15.1 MeVγ-rays, taken for bombarding energiesE _τ=2.6–12 MeV at 0? and 90?, exhibit some marked structures with widths of 0.5 to 1 MeV. As the (τ, α)-reaction leads to the 15.1 MeV,T=1 state, levels in¹⁶O underlying these structures should have largeT=1 components. Angular distributions of theα-particles coincident to the 15.1 MeVγ-rays show patterns typical for a direct process and are, therefore, compared with DWBA calculations.     

Gyromagnetic factor of the 9+, 3034 keV State in66Ga

Theg-factor of the 9⁺, 3034 keV state in⁶⁶Ga has been found to beg=0.47±0.10 by means of the integral perturbed angular distribution in an implanted source. The excited states were populated by the reaction⁵⁶Fe(¹²C, pn)⁶⁶Ga atE _C=45 MeV.     

Study of the ground state doublet in57Fe

The⁵⁶Fe(d,p)⁵⁷Fe reaction has been studied at an incident energy of about 10 MeV. The ground state doublet of⁵⁷Fe has been resolved using the Heidelberg Q 3 D magnetic spectrograph and the Minnesota split-pole spectrograph. The ratio of the spectroscopic strengths (2J+1)S for the transitions to the first excited state at 14.4 keV excitation energy (J ^π=3/2^?) and the ground state (J ^π=1/2^?) has been determined to be 5.80±0.5. This number is of special interest with respect to a possible deformation of the nucleus⁵⁷Fe and in connection with the corresponding analogue resonances in⁵⁷Co.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

Spectroscopy of highly excited states in29Si

Particleγ-ray coincidences have been measured in the²⁸Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the²⁶Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the²⁷A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of²⁹Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the²⁸Si (d,pγ) reaction at 6.5 MeV and in the²⁶Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in²⁹Si and²⁹P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK ^π=5/2⁺ band with prolate deformation is discussed.     

Effect of entrance channel parameters on fission fragment angular momentum in medium energy fission

Independent isomeric yield ratios of¹³²I were radiochemically determined in alpha particle induced fission of²³⁸U in the energy range 25–44 MeV. Fission fragment angular momenta were deduced from the measured isomeric yield ratios using spin dependent statistical model analysis. It was seen that angular momentum of¹³²I increases with increase of excitation energy and angular momentum of the fissioning nucleus. Comparison of the present data on¹³²I in²³⁸U(α,f) with the literature data for the same product in²³⁸U(p, f) and²³⁸U(γ, f) at various excitation energies show that fragment angular momentum strongly depends on the input angular momentum in the range of excitation energy considered. Experimental fragment angular momentum at all excitation energies were seen to be in agreement with the theoretical values calculated based on thermal equilibration of the various collective rotational degrees after considering the occurence of multichance fission. Thus, strong effect of input angular momentum as well as the statistical equilibration among the various collective rotational degrees of freedom in medium energy fission is corroborated.     

Energy levels,decay scheme, γ-ray branching ratios and lifetimes in 55Fe from the 55Mn(p,nγ)55Fe reaction

The reaction ⁵⁵Mn(p, nγ)⁵⁵Fe has been studied at E_p = 4.0 and 6.0 MeV using a pulsed beam. From the experiments at 6.0 MeV, the energy levels of ⁵⁵Fe up to an excitation of 3810 keV, their decay scheme and the γ-ray branching ratios have been determined. Levels have been identified for the first time in the (p, nγ) reaction. The results have been compared with those available from the literature. From the 4.0 MeV experiment, the mean lifetime of the 1408 keV level has been determined to be 142.7 ± 6.6 ps by direct timing techniques.     

Investigation of203, 205Hg with the (d,pγ) reaction — Identification of thei 13/2 neutron hole state in205Hg

Low lying levels in²⁰³Hg and²⁰⁵Hg were studied with the (d, p) deuteron break-up reaction atE _d=14 and 18 MeV. Gamma-rays and conversion-electrons were measured in coincidence with protons. In addition delayed spectra were recorded with us and ms beam pulsing. Thei _13/2 neutron hole state was identified in²⁰⁵Hg and confirmed in²⁰³Hg. The known level structure of²⁰⁵Hg below 2 MeV is confirmed and extended. For²⁰³Hg we observe theγ-decay of several levels below 1.5 MeV, which were previously known from transfer reactions.     

Levels in104Ru populated by the β−-decay of104Tc

Theβ ^? — andγ-activities of 18.4 min¹⁰⁴Tc have been studied with singles and coincidence measurements. Sources were prepared by chemical separation of technetium from the fission products of thermal-neutron-induced fission of²³⁵U. A revised level scheme of¹⁰⁴Ru up to an excitation energy of 4.26 MeV is proposed. Fromβ-γ coincidence measurements, aQ _β-value of 5.62±0.07 MeV has been obtained.     

New aspects of the rotational model in25Mg

Spin assignments have been made to the²⁵Mg levels in theE _x=5–6 MeV region fromγ-ray angular distributions measured in the²²Ne(α, n y) reaction atE _α=8.0 and 8.8 MeV and fromp-γ angular correlations measured in the²⁴Mg(d, p γ) reaction atE _d=6 MeV. Unique spin assignments ofJ=7/2, 5/2, 5/2, and 9/2 could be made to the levels atE _x=5005, 5511, 5851, and 5967 keV, respectively. Ambigious assignments have been made to the levels atE _x=5245, 5524, 5785, 6032 keV (J=11/2, 7/2), 5455 keVJ=13/2, 9/2), and 5738 keV (J=3/2, 5/2). The present data confirm previous assignments ofJ=1/2 to the levels atE _x=5108 and 5466 keV, respectively. Lifetime estimates have been obtained, using the Doppler-shift attenuation method, for the levels atE _x=5245 keV (τ=30–60 fs), 5785 keV (τ=50–100 fs), 5967 keV (τ=50–100 fs), and 5455 keV (τ>1ps). All other levels in theE _x=5–6 MeV region haveτ<60 fs. A breakdown of theK-selection rule has been observed in theγ-decay of some high spin states, indicating a deviation from the strong coupling model.     

Resonant and intrastate transitions to the 2+ state in8Be

We have studied resonant, intrastate and non-resonant bremsstrahlungγ-ray transitions leading to the 2⁺ state in⁸Be atE _x=2.94 MeV. We find aγ-width of Γ _γ =0.45 eV for the 4⁺ state in⁸Be, corresponding to anE 2 strength of 19 W.u. For the intrastateγ-ray transition within the 2⁺ resonance we predict a maximum cross section of 2.5 nb atE≈3.3 MeV. An experimental observation of this novel type ofγ-ray emission, however, appears to be difficult due to the dominance of competing resonant and direct capture processes.     

Kernspektroskopische Untersuchungen zu den Termschemata der Kerne56Fe und56Co

Gamma-gamma directional correlations have been investigated for several cascades in⁵⁶Fe formed in the decay of⁵⁶Mn or⁵⁶Co. A combination of NaI(Tl) and Ge(Li) detectors was used for the experiments. It was established that a level at 3601 keV is populated in the decay of⁵⁶Co. Spins given in the paranthesis were assigned to levels at the following energies: 2658(2), 2960(2), 3123(4), 3370(2), 3445(3), 3601(2), 3856(3), 4049(3), 4100(4), 4120(3), 4298(4), 4395(3) and 4459 keV (3,4). Multipole mixing ratios were determined forγ transitions of the following energies: 978, 1038, 1175, 1360, 1772, 1811, 1964, 2015, 2035, 2113, 2213, 2523, 2599, 3010, 3202, 3254, 3273, 3451 and 3548 keV. Theγ-rays from the decay of⁵⁶Co of energies 674.7 and 2657.4 keV have been observed for the first time, and the presence of several other weakγ-rays in the⁵⁶Fe decay has been confirmed. Nine angular correlations in the decay of⁵⁶Ni have been investigated. The spin sequence 4, 3, 2, 0, 1 was unambiguously determined for the levels at 0, 158.2, 970.1, 1450.7 and 1720.0 keV. The multipolarity of theγ-rays of energies 158.2, 749.9 and 811.9 keV was determined as almost pure M1. The results are discussed within the framework of recent shell model calculations.     

Shape coexistence and other aspects of nuclear structure in40Ar

Theγ-decay of⁴⁰Ar has been studied by particle-γ-ray coincidence measurements in the³⁷Cl(α, pγ) reaction at 12 and 13 MeV bombarding energy. Particle-γ-ray angular correlations and linear polarizations ofγ-rays were measured at 12 MeV. A lifetime measurement using the Doppler-shift attenuation method was performed at 11 MeV. The coexistence of spherical and deformed states in⁴⁰Ar could be concluded from the observation of aK ^π=0⁺ rotational band which has itsI ^π=0⁺ through 6⁺ members at 2,121, 2,524, 3,515 and 4,959 KeV excitation energy. The intrinsic quadrupole moment derived fromB(E2) values is ∥Q ₀∥=1,320 _?120 ⁺⁶⁰ mb. Negative-parity states with high spin were observed at 4,858(5^?), 4,494(5^?), 4,226(4^?) and 4,991 KeV(4^?) excitation energy. A complete account of all levels below 5 MeV excitation energy is obtained by a model in which twod _3/2 proton holes couple weakly to the⁴²Ca levels below 4.75 MeV excitation energy.     

NMRON spin echo in a slowly varying magnetic field

Nuclear spin-spin relaxation of⁶⁰Co and⁵⁶Co in iron single crystals has been studied, using the three-pulse NMRON spin echo. A previously reported rapidT ₂ in⁶⁰CoFe is shown to have arisen from a modulation of the echo amplitude, caused by variations in the phase of the Larmor precession relative to the applied rf field. A lower limit ofT ₂∼0.2s is found in⁵⁶Co⁵⁶ Fe. Extension of this result to other CoFe samples is discussed.