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Register a new userEmission patterns of neutral pions in 40 A MeV Ta+Au reactions
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Differential cross sections of neutral pions emitted in 181Ta + 197Au collisions at a beam energy of 39.5A MeV have been measured with the photon spectrometer TAPS. The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.
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Excitation functions for the production of the 181,182m,182g,183,184g,186Re and 183,184Ta radionuclides from proton bombardment on natural tungsten were measured using the stacked-foil activation technique for the proton energies up to 40 MeV. A new data set has been given for the formation of the investigated radionuclides. Results are in good agreement with the earlier reported experimental data and theoretical calculations based on the ALICE-IPPE code. The thick target integral yields were also deduced from the measured excitation functions. The deduced yield values were compared with the directly measured thick target yield (TTY), and found acceptable agreement. The investigated radionuclide 186Re has remarkable applications in the field of nuclear medicine, whereas the data of 183,184gRe and 183Ta have potential applications in thin layer activation analysis and biomedical tracer studies, respectively.
Decay modes of excited nuclei are investigated in $^{78,82}$Kr + $^{40}$Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the $4pi$ INDRA array. Kinetic-energy spectra and angular distributions of fragments with atomic number 3 $le Z le$ 28 indicate a high degree of relaxation and are compatible with a fission-like phenomenon. Persistence of structure effects is evidenced from elemental cross-sections ($sigma_{Z}$) as well as a strong odd-even-staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross-section of the $^{78}$Kr + $^{40}$Ca reaction is slightly higher than the one measured in $^{82}$Kr + $^{40}$Ca reaction. The fission-like component is larger by $sim$ 25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to $Z$ = 14 in their ground states as well as excited states does not account for the main features of $sigma_{Z}$. For both reactions, the transition-state formalism reasonably reproduces the $Z$-distribution of the fragments with charge 12 $le Z le$ 28. However, this model strongly overestimates the light-fragment cross-sections and does not explain the o-e-s of the yields for 6 $le Z le$ 10. The shape of the whole $Z$-distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition between evaporation, fusion-fission and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 $le Z le$ 22 could signal a mechanism in addition to the capture process.
Natural silver targets have been irradiated by using a 50 MeV alpha-particle beam in order to measure the activation cross sections of radioisotopes in the 40-50 MeV energy range. Among the radio-products there are medically important isotopes such as $^{110m}$In and $^{111}$In. For optimizing the production of these radioisotopes and regarding their purity and specific activity the cross section data for every produced radioisotope are important. New data are measured in this energy range and the results of some previous measurements have been confirmed. Physical yield curves have been calculated by using the new cross section data completed with the results from the literature.
Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $gamma pto ppi^0$ for photon energies between 0.85 and 2.50 GeV. The $pi^0$ mesons are observed in their dominant neutral decay mode: $pi^0togammagamma$. For the first time, the differential cross sections cover the very forward region, $theta_{rm c.m.}<60^circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).
A recent analysis of experimental ternary fission fragment yields using a nucleation moderated statistical equilibrium model reproduced observed yields with fairly good accuracy. In the present work, the same approach is applied to neck emission in peripheral and mid-peripheral 124Sn+112,124Sn collisions at 26A MeV. The model can reasonably reproduce the yields of lithium to silicon isotopes with realistic time and temperature values. A comparison is made between equilibrium constants derived from the present data and those previously obtained for ternary fission of 242Pu.
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