Cross sections and isomeric ratios in the photoproduction of 44Sc from heavier nuclei

The yields and isomeric yield ratios in the photoproduction of⁴⁴Sc from ⁴⁵Sc, ⁵⁵Mn, Fe, ⁵⁹Co and ⁷⁵As have been measured by activation methods in the energy region 100–800 MeV. Mean cross sections and isomeric cross-section ratios in the energy region 250–800 MeV have been deduced and the number of valence neutrons available for the (γ, n) reaction estimated. The experimental cross sections are compared both to cascade-evaporation calculations based upon the free-nucleon photopion cross sections and to cross sections calculated with a semi-empirical formula. The isomeric cross-section ratios are compared to calculations based on the statistical formalism by Huizenga and Vandenbosch together with cascade-evaporation theory.     

Cross section of metastable state population in the photoneutron decay of the E1 giant resonance for 110Pd, 112Cd, and 113In nuclei

The cross sections of isomeric state excitation in the ¹¹⁰Pd(γ, n)^109m Pd, ¹¹²Cd(γ, n)^111m Cd, and ¹¹³In(γ, n)^112m In reactions have been investigated. The measurements were performed in the γ-ray energy range 9–18 MeV with a step ΔE = 0.5 MeV. The dependences of the isomeric ratios on the γ-ray energy are obtained. The experimental data are compared with the results of calculations within the cascade-evaporation model.     

Electro- and photoinduced spallation reactions on27Al and51V at intermediate energies

Cross sections for some electro- and photoinduced spallation reactions on²⁷Al and⁵¹V have been measured in the energy region 130–580 MeV with the activation method. The cross sections per photon are compared to Monte-Carlo calculations based on a cascade-evaporation model. The electrodisintegration cross sections are compared to calculations based on the Dalitz formalism for virtual photon spectra.     

Electro- and photoinduced spallation reactions on27Al and51V at intermediate energies

Cross sections for some electro- and photoinduced spallation reactions on²⁷Al and⁵¹V have been measured in the energy region 130–580 MeV with the activation method. The cross sections per photon are compared to Monte-Carlo calculations based on a cascade-evaporation model. The electrodisintegration cross sections are compared to calculations based on the Dalitz formalism for virtual photon spectra.     

The (γ, p n) and (γ, 3p3n) reactions in40Ca at intermediate energies

The yields of the reactions⁴⁰Ca(γ, p n)^38g K and⁴⁰Ca(γ, 3p 3n)^34m Cl have been measured by the activation method in the energy range 80–800 MeV. From the measured yields the cross sections are deduced. The experimental cross sections are compared to calculations with a cascade-evaporation model for photo-induced reactions.     

Isomere Wirkungsquerschnittsverhältnisse beim thermischen Neutroneneinfang im Bereich der 2p 1/2 und 1g 9/2 Schalenmodellzustände

Thermal capture cross sections and isomeric cross section ratios in thermal neutron capture were determined for even-even nuclei in the region of the 2p _1/2-1g _9/2 neutron shell. Capture cross sections for formation of Zn 69 ^m , Zn 71 ^m , Zn 71, Ge 71, Ge 75 ^m , Ge 77 ^m , Se 77 ^m , Se 79 ^m , Se 83 ^m , Se 83, Sr 85 ^m and Sr 87 ^m were measured by the activation method. From these data and additional measurements of cross section ratios the isomeric ratios for thermal capture in Zn 68, Zn 70, Ge 70, Ge 74, Ge 76, Se 76, Se 78, Se 80, Se 82 and Sr 84 were determined. In addition epithermal capture isomer ratios were determined for Zn 68, Ge 74, Ge 76, Se 80 and Sr 84. The isomer ratios are compared with calculations based on the statistical model ofHuizenga andVandenbosch. With the exception of Se 80 the measured ratios can be explained theoretically with reasonable values of the spin-cutoff-factorσ and gamma-ray multiplicityN, however there seems to be unexplained difference in eitherσ orN between the two groups of nuclei leading to either 1/2–7/2 or 1/2–9/2 isomers.     

Isomeric cross section ratio for110Pd(n,2n)109Pd reaction at 14.7 MeV

Reaction¹¹⁰Pd(n, 2n)¹⁰⁹Pd has been investigated at 14.7 MeV neutrons. Cross sections for the formation of^109m Pd and^109g Pd were measured. Experimental value of the isomeric cross section ratio has been compared with the theoretical calculation performed with the Huizenga and Vandenbosch method.     

Isomeric ratios of the cross sections for Sn(p, xpyn)X reactions

In proton-nucleus reactions, the ratios of the cross sections for 18 isomeric pairs were measured by the induced-activity method as functions of the initial-proton energy and of the number of emitted nucleons. The isotopic effect and the cross sections for charge-exchange reactions are discussed. The experimental values of the cross sections for disintegration reactions like (p, xpyn) are compared with the theoretical values calculated on the basis of the cascade-evaporation model.     

Some (γ, π− xn) reactions on197Au at intermediate energies

The yields for some (γ, π ^? xn)-reactions on¹⁹⁷Au have been measured from threshold to 750 MeV by use of the activation method. The experimental mean cross sections are compared to results obtained from other experiments on similar reactions and to cascade-evaporation calculations.     

Isomeric cross sections for the (n, 2n) reaction on 82Se, 81Br,and 45Sc at 15.1 MeV

Activation techniques have been used to measure the cross sections at 15.1 MeV neutron energy for the following reactions: ⁸²Se(n, 2n)^81m+gSe, ⁸¹Br(n, 2n)^80m+gBr, and ⁴⁵Sc(n, 2n) ^44m+gSc. Isomeric cross-section ratios were evaluated by applying the method of least squares to the time behavior of γ-ray activity following the ground-state decay of each isomeric pair. The absolute cross section σ_m for the formation of the metastable state was measured by the mixed-powder method with the ²⁷Al(n, α)²⁴Na reaction as the monitor. The cross section σ_g for the formation of the ground state was then determined by using the isomeric cross-section ratio. The sum of σ_m and σ_g for each reaction is compared with the theoretical value obtained from calculations based on the statistical model for the formation of a compound nucleus and its subsequent emission of neutrons.     

Activation cross sections and isomeric ratios in reactions induced by 14.5 MeV neutrons on152Sm,154Sm and178Hf

Cross sections for the reactions¹⁵²Sm(n, p)^152g,m1,m2 Pm,¹⁵⁴Sm(n, p)^154g,m Pm,¹⁷⁸Hf(n, p)^178m,g Lu,¹⁵⁴Sm(n, d)¹⁵³Pm and¹⁵²Sm(n, α)¹⁴⁹Nd were measured at 14.5 MeV neutron energy by the activation method. On the basis of these cross sections, the associated isomeric ratios in¹⁵⁴Pm,¹⁵²Pm,¹⁷⁸Lu and the comparison with the predictions of different compound and precompound models, conclusions are drawn about the role of the preequilibrium processes in 14.5 MeV neutron induced reactions. Calculations for equal angular momentum removal by equilibrium and preequilibrium emitted particles better reproduced the experimental isomeric ratios, than for higher angular momentum removal in the preequilibrium phase. The isomeric ratios may be used as a source of additional information about the spin of the isomeric states in¹⁵²Pm and¹⁵⁴Pm for which the spectroscopic information is uncertain.     

Isomerenverhältnisse für die Reaktionen107Ag(α,2n)109g,mIn und109Ag(α,2n)111g,mIn

Isomeric cross-section ratios have been measured for the reactions¹⁰⁷Ag(α,2n)^109g,mIn and¹⁰⁹Ag(α, 2n)^111g,mIn for energies of theα-particles between 19 and 40 MeV. The experimental isomeric cross-section ratios are compared with statistical-model calculations. The program ofHafner et al. was extended by including the competition of the (α,n)- and (α, 3n)-reactions and of charged particle emission. Agreement between experiment and theory could be achieved.     

Diffusion model for relativistic heavy-ion collisions

The decay of 2.4 h^117g Cd and 3.4 h^117m Cd has been investigated with the use of high-resolution Si(Li) and Ge(Li) detectors, also in an anti-Compton arrangement. Spectra from the two isomers have been resolved by comparing young reactor-produced¹¹⁷Cd with aged cyclotron-produced¹¹⁷Cd. Ge(Li)-Ge(Li) coincidences have been measured with a multi-parameter analyzer. A hundred observedγ-rays are placed in a level scheme of¹¹⁷In. Possible theoretical interpretations are discussed. The I.T. Branching of¹¹⁷In is (47.1±1.5)%. Only about 1% of 11/2^{? 117m} Cd decays to 1.93 h 1/2^{? 117m} In and 10.9% of 1/2^{+ 117g} Cd decays to the 9/2^{+ 117g} In ground state bypassing the isomeric In state.     

Investigation of the isomeric ratio for 44m, g Sc

The isomeric ratios measured for ^{44m, g} Sc in (γ, n), (p, n), (p, αp3n), and (α, p3n) reactions are presented. The values obtained in this way are compared with the results of calculations within the cascade-evaporation model and with data coming from an investigation of reactions like (n, 2n), and (d, t).     

Fission cross sections of medium-weight and heavy nuclei induced by 1 GeV protons

Coincidence studies performed in 4π geometry with silicon detectors and parallel plate avalanche counters have been used to measure total fission cross sections of²³⁸U,²³²Th,²⁰⁹Bi,²⁰⁸Pb,¹⁹⁷Au,^natYb,^natHo,^natTb,^natSm,^natTe,^natAg and^natNi nuclei induced by 1 GeV protons. The experimental results agree qualitatively with cascade-evaporation calculations.     

Excitation of <Superscript>109</Superscript>Pd and <Superscript>112</Superscript>In nuclear isomers in (γ, <Emphasis Type="Italic">n</Emphasis>) reactions

Dependence of isomeric ratios on maximum photon energy in the reactions ¹¹⁰Pd(γ, n)^{109m, g} Pd and ¹¹³In(γ, n)^{112m, g} In is studied in the energy region of bremsstrahlung 9–18 MeV with the step ΔE = 0.5 MeV. Cross sections of population of the metastable state for ¹⁰⁹Pd and ¹¹²In in (γ, n) reactions were first obtained in the energy region under study. The obtained results are compared with the results of the calculation in the framework of the cascade-evaporation model.     

Wirkungsquerschnitte und Isomerenverhältnis für die Reaktionen89Y(α, 3n)90g Nb und89Y(α, 3n)90m Nb

Absolute cross-sections and isomeric cross-section ratios have been measured for the reactions⁸⁹Y(α, 3n)^{90g, 90m} Nb. The energy of the α-particles was varied between 34 and 54 MeV. The experimental isomeric ratios are compared with statistical-model calculations.     

Mechanism of formation and decay of the compound nuclei150Gd produced by two entrance channels (16O+134Ba) and (40Ar+110Pd)

Excitation functions have been drawn for evaporation residues issued from¹⁵⁰Gd, a compound nucleus produced either by¹⁶O ions on¹³⁴Ba, or by⁴⁰Ar on¹¹⁰Pd. Absolute cross sections were measured for^145–147Gd,^145–147Eu,^141m Sm,^143m Sm,^140m Pm and^139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ _CF=πR _Fuss ² (1?V _Fus/E) whereR _Fus andV _Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σ_CF=πR _cr ² (1?V_cr/E) with the model of critical distanceR _cr and critical potentialV _cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel.     

Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Long-lived isomers of⁸⁷Sr,¹⁰³Rh,¹¹¹Cd,^113,115In,¹¹⁷Sn,¹⁷⁶Lu,¹⁸⁹Os,¹⁹³Ir and¹⁹⁵Pt were produced by means of bremsstrahlung from a 4 MeV endpoint energy 25µA intensity electron beam. Isomeric activities were measured by gamma-spectrometry. Photoexcitation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity¹³⁷Cs,⁶⁰Co,¹⁴²Pr and²⁴Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely differing isomer ratios governed by spin differences between isomeric and ground levels, and likely by differences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n,n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.     

26g,mAl production cross sections from the 23Na(α, n)26Al reaction

Cross sections have been determined for the production of ^{26g, m}Al from the ²³Na(α, n) reaction. Total ²⁶Al production cross sections were obtained from measurements of the thick-target neutron yield. ^26mAl cross sections were measured using an activation technique. ^26gAl cross sections were deduced by subtracting the ^26mAl cross sections from the total (α, n) cross sections. The principle of detailed balance has been applied to the low-energy data to obtain cross sections for the astrophysically interesting ^26gAl(n, α₀)²³Na reaction. These results are compared with the results of Hauser-Feshbach calculations.