Elemental analysis of light constituents in thin plastic films El Masri, Y.; Heitz, Ch; Keutgen, Th ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
04/2009, Letnik:
267, Številka:
7
Journal Article
Recenzirano
Experiments with 1–3
MeV
4He beams and 2.2–3.2
MeV proton beams have been performed in order to develop a precise and highly sensitive method for the detection and analysis of light elements in ...threat or drug materials using simultaneously the RBS and ERDA techniques. Commercially available plastic films have been used as samples. The 1
MeV
4He beam has been found to be inadequate owing to the rapid destruction of the targets. Best results have been obtained using proton beams with energies higher than 3
MeV. For 3.2
MeV proton beams, ERDA has been used for the analysis of the hydrogen constituent.
Clustering in alpha conjugate nuclei Schmidt, K.; Kim, E. J.; Wuenschel, S. ...
EPJ Web of Conferences,
01/2015, Letnik:
88
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Characteristics of the decay of alpha like nuclei produced in various reactions with alpha conjugate nuclei are discussed. We observe a significant number of events in which a large fraction of the ...system breaks up into alpha-conjugate nuclei. Lighter fragments in the various decay channels appear to originate from a neck-like region between 4 and 7 cm/ns whereas the heavier fragments appear to originate from velocities near the beam velocity. This behavior is consistent with a hierarchy effect that cannot be explained by statistical processes.
Identification of α-cluster states analogous to the C 12 Hoyle state in heavier α-conjugate nuclei can provide tests of the existence of α condensates in nuclei. Such states are predicted for O 16 , ...Ne20 , Mg24 , Si28 , etc., at excitation energies slightly above the multi- α-particle decay threshold but have not yet been experimentally identified. The thick target inverse kinematics (TTIK) technique can be used to study the breakup of excited self-conjugate nuclei into many α particles. The reaction Ne20+α was studied using a Ne20 beam at 12 MeV/nucleon from the K150 cyclotron at Texas A&M University. The TTIK method was used to study both single α-particle emission and multiple α-particle decays. Events with α multiplicity up to four were analyzed. The analysis of the three α-particle emission data allowed the identification of the Hoyle state and other C 12 excited states decaying into three α particles. The results are shown and compared with other data available in the literature. Although the statistics for events with α-multiplicity four is low, the data show a structure at about 15.2 MeV that could indicate the existence in O 16 of a state analogous to the C 12 Hoyle state. Moreover, the reconstructed excitation energy of Mg24 for these events peaks at around 34 MeV, very close to the predicted excitation energy for an excited state analogous to the C 12 Hoyle state in Mg24 . The structure is further confirmed by the reanalysis of α-multiplicity-four events from a previous experiment performed at 9.7 MeV/nucleon with a similar, but lower granularity, experimental setup.
Ternary fission of actinides probes the state of the nucleus at scission. Light clusters are produced in space and time very close to the scission point. Within the nonequilibrium statistical ...operator method, a generalized Gibbs distribution is constructed from the information given by the observed yields of isotopes. Using this relevant statistical operator, yields are calculated taking excited states and continuum correlations into account, in accordance with the virial expansion of the equation of state. Clusters with mass number \(A \le 10\) are well described using the nonequilibrium generalizations of temperature and chemical potentials. Improving the virial expansion, in-medium effects may become of importance in determining the contribution of weakly bound states and continuum correlations to the intrinsic partition function. Yields of larger clusters, which fail to reach this quasi-equilibrium form of the relevant distribution, are described by nucleation kinetics, and a saddle-to-scission relaxation time of about 7000 fm/c is inferred. Light charged particle emission, described by reaction kinetics and virial expansions, may therefore be regarded as a very important tool to probe the nonequilibrium time evolution of actinide nuclei during fission.
The 12C+12C sub-barrier fusion cross section is calculated within the framework of a Time Dependent Hartree-Fock (TDHF) based classical model using the Feynman Path Integral Method. The modified ...astrophysical S*-factor is compared to direct and indirect experimental results. A good agreement with the direct data is found. In the lower energy region, where recent analyses of experimental data obtained with the Trojan Horse Method (THM) lead to contrasting results, the model predicts an S* factor half way between those results. Low energy resonances revealed in the THM data are added to the calculation and the relative reaction rate in the Gamow region is calculated. The role of different resonances is discussed in detail and their influence on the reaction rate at temperatures relevant to stellar evolution is investigated.
The yields of light elements (\(Z=1,2\)) obtained from spontaneous ternary fission of \(^{252}\)Cf are treated within a nonequilibrium approach, and the contribution of unstable nuclei and excited ...bound states is taken into account. These light cluster yields may be used to probe dense matter, and to infer in-medium corrections. Continuum correlations are calculated from scattering phase shifts using the Beth-Uhlenbeck formula, and the effect of medium modification is estimated. The relevant distribution is reconstructed from the measured yields of isotopes. This describes the state of the nucleon system at scission and cluster formation, using only three Lagrange parameters which are the nonequilibrium counterparts of the temperature and chemical potentials, as defined in thermodynamic equilibrium. We concluded that a simple nuclear statistical equilibrium model neglecting continuum correlations and medium effects is not able to describe the measured distribution of H and He isotopes. Moreover, the freeze-out concept may serve as an important ingredient to the nonequilibrium approach using the relevant statistical operator concept.
In order to reconstruct the yields of the primary hot fragments at the time of their formation, the neutron multiplicity associated with intermediate mass fragments (IMFs) was determined ...experimentally using the kinematical focusing of light particles emitted along the direction of each IMF. The reaction system 64Zn + 112Sn has been studied at 40 A MeV. IMFs were isotopically identified with Z up to 18. Neutrons were measured at 16 angles around the direction of the IMFs. The exctrated neutron multiplicities are in good agreement with those calculated AMD+Gemini simulations.
In V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612 the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was ...interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. Ad. Raduta et al., Phys. Lett. B 623 (2005) 43 performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy.
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