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Title: Fission and binary fragmentation reactions in {sup 80}Se+{sup 208}Pb and {sup 80}Se+{sup 232}Th systems

Abstract

Fission and binary fragmentation of the excited nuclear systems of Z=116 and 124 were investigated using the reactions induced by {sup 80}Se beams on {sup 208}Pb and {sup 232}Th targets at bombarding energies ranging from 470 to 630 MeV. The mass and kinetic energy of the binary reaction products were reconstructed by measuring their velocities by the time-of-flight method and the angles of emission using multiwire proportional chambers. Total neutron multiplicities were measured in coincidence with the fragments, using an array of neutron detectors. The fragment mass-energy correlation was studied for the two systems. The average total kinetic energy (TKE) of fragments for the {sup 80}Se+{sup 208}Pb system agrees with earlier measurements and with Viola's systematics in the mass symmetric region for compound nucleus fission, whereas for the {sup 80}Se+{sup 232}Th system, the TKE values are significantly lower. This is also consistent with higher values of total neutron multiplicities observed for the case of {sup 80}Se+{sup 232}Th at comparable available energies. From an extrapolation of the measured total neutron multiplicities for the mass symmetric region to zero compound nucleus excitation energy, the average number of prompt neutrons expected to be emitted in the spontaneous fission of the superheavy Z=116 hasmore » been estimated to be {nu}{sub tot}{sup sf}=10{+-}2, which is consistent with the value derived for the same compound nucleus populated in the {sup 56}Fe+{sup 232}Th reaction in an earlier work. In the case of the {sup 80}Se+{sup 232}Th system, similar analysis was carried out by taking the average TKE from Viola's systematics for estimating the available energy for particle emission corresponding to compound nucleus fission. In this way, by extrapolating the observed neutron multiplicities to zero compound nucleus excitation energy, a value of {nu}{sub tot}{sup sf}=15{+-}2 was obtained for the spontaneous fission of the superheavy Z=124 nucleus. The increase in the average number of neutrons emitted in fission as a function of the atomic number of the nucleus in the superheavy mass region was confirmed by comparing the results of the present work with published data.« less

Authors:
; ; ; ;  [1];  [1];  [2];  [3]; ; ; ;  [4]; ; ; ; ; ;  [5]; ; more »;  [6] « less
  1. Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
  2. (India)
  3. Department of Physics, Punjab University, Chandigarh 160014 (India)
  4. INFN Laboratori Nazionali di Legnaro, I-35020 Legnaro (Pd) (Italy)
  5. Dipartimento di Fisica and Sezione INFN Padova, I-35131 Padova (Italy)
  6. Dipartimento Interuniversitario di Fisica and Sezione INFN Bari, I-70100 Bari (Italy) (and others)
Publication Date:
OSTI Identifier:
20991017
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevC.75.024604; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COMPOUND NUCLEI; EMISSION; EXCITATION; EXTRAPOLATION; FRAGMENTATION; IRON 56; KINETIC ENERGY; LEAD 208; MASS; MEV RANGE 100-1000; MULTIPLICITY; MULTIWIRE PROPORTIONAL CHAMBERS; NEUTRON DETECTORS; PROMPT NEUTRONS; SELENIUM 80; SPONTANEOUS FISSION; THORIUM 232; TIME-OF-FLIGHT METHOD

Citation Formats

Thomas, R. G., Saxena, A., Sahu, P. K., Kailas, S., Kapoor, S. S., Choudhury, R. K., Institute of Physics, Bhubaneswar 751005, Govil, I. M., Barbui, M., Cinausero, M., Prete, G., Rizzi, V., Fabris, D., Lunardon, M., Moretto, S., Viesti, G., Nebbia, G., Pesente, S., Dalena, B., D'Erasmo, G., and Fiore, E. M. Fission and binary fragmentation reactions in {sup 80}Se+{sup 208}Pb and {sup 80}Se+{sup 232}Th systems. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.024604.
Thomas, R. G., Saxena, A., Sahu, P. K., Kailas, S., Kapoor, S. S., Choudhury, R. K., Institute of Physics, Bhubaneswar 751005, Govil, I. M., Barbui, M., Cinausero, M., Prete, G., Rizzi, V., Fabris, D., Lunardon, M., Moretto, S., Viesti, G., Nebbia, G., Pesente, S., Dalena, B., D'Erasmo, G., & Fiore, E. M. Fission and binary fragmentation reactions in {sup 80}Se+{sup 208}Pb and {sup 80}Se+{sup 232}Th systems. United States. doi:10.1103/PHYSREVC.75.024604.
Thomas, R. G., Saxena, A., Sahu, P. K., Kailas, S., Kapoor, S. S., Choudhury, R. K., Institute of Physics, Bhubaneswar 751005, Govil, I. M., Barbui, M., Cinausero, M., Prete, G., Rizzi, V., Fabris, D., Lunardon, M., Moretto, S., Viesti, G., Nebbia, G., Pesente, S., Dalena, B., D'Erasmo, G., and Fiore, E. M. Thu . "Fission and binary fragmentation reactions in {sup 80}Se+{sup 208}Pb and {sup 80}Se+{sup 232}Th systems". United States. doi:10.1103/PHYSREVC.75.024604.
@article{osti_20991017,
title = {Fission and binary fragmentation reactions in {sup 80}Se+{sup 208}Pb and {sup 80}Se+{sup 232}Th systems},
author = {Thomas, R. G. and Saxena, A. and Sahu, P. K. and Kailas, S. and Kapoor, S. S. and Choudhury, R. K. and Institute of Physics, Bhubaneswar 751005 and Govil, I. M. and Barbui, M. and Cinausero, M. and Prete, G. and Rizzi, V. and Fabris, D. and Lunardon, M. and Moretto, S. and Viesti, G. and Nebbia, G. and Pesente, S. and Dalena, B. and D'Erasmo, G. and Fiore, E. M.},
abstractNote = {Fission and binary fragmentation of the excited nuclear systems of Z=116 and 124 were investigated using the reactions induced by {sup 80}Se beams on {sup 208}Pb and {sup 232}Th targets at bombarding energies ranging from 470 to 630 MeV. The mass and kinetic energy of the binary reaction products were reconstructed by measuring their velocities by the time-of-flight method and the angles of emission using multiwire proportional chambers. Total neutron multiplicities were measured in coincidence with the fragments, using an array of neutron detectors. The fragment mass-energy correlation was studied for the two systems. The average total kinetic energy (TKE) of fragments for the {sup 80}Se+{sup 208}Pb system agrees with earlier measurements and with Viola's systematics in the mass symmetric region for compound nucleus fission, whereas for the {sup 80}Se+{sup 232}Th system, the TKE values are significantly lower. This is also consistent with higher values of total neutron multiplicities observed for the case of {sup 80}Se+{sup 232}Th at comparable available energies. From an extrapolation of the measured total neutron multiplicities for the mass symmetric region to zero compound nucleus excitation energy, the average number of prompt neutrons expected to be emitted in the spontaneous fission of the superheavy Z=116 has been estimated to be {nu}{sub tot}{sup sf}=10{+-}2, which is consistent with the value derived for the same compound nucleus populated in the {sup 56}Fe+{sup 232}Th reaction in an earlier work. In the case of the {sup 80}Se+{sup 232}Th system, similar analysis was carried out by taking the average TKE from Viola's systematics for estimating the available energy for particle emission corresponding to compound nucleus fission. In this way, by extrapolating the observed neutron multiplicities to zero compound nucleus excitation energy, a value of {nu}{sub tot}{sup sf}=15{+-}2 was obtained for the spontaneous fission of the superheavy Z=124 nucleus. The increase in the average number of neutrons emitted in fission as a function of the atomic number of the nucleus in the superheavy mass region was confirmed by comparing the results of the present work with published data.},
doi = {10.1103/PHYSREVC.75.024604},
journal = {Physical Review. C, Nuclear Physics},
number = 2,
volume = 75,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • Complete energy spectra and angular distributions of charged light particles (Z < or = 2 and A < or = 4) were measured for the bombardment of 80 MeV deuterons on /sup 27/Al and /sup 58/Ni and 70 MeV deuterons on /sup 90/Zr, /sup 208/Pb, and /sup 232/Th. The charged particles were detected by two triple-counter telescopes using combinations of ..delta..E-E and time-of-flight techniques for particle identification. The experimental results are presented in cross sections doubly differential in energy and angle, as well as in angle- and energy-integrated cross sections. For all the nuclei studied, the proton energy spectra showmore » large deuteron-breakup peaks centered at approximately half of the incident deuteron energy at forward angles. The energy spectra for the same type of emitted particle are similar in shape for all nuclei at a given angle except in the region of the low-energy evaporation peak. The magnitude of evaporation peak varies rapidly with target mass. The total nonequilibrium yield of charged light particles is approximately (300 +- 50) A/sup 1/3/mb. The angular distributions for the high-energy particles are strongly forward peaked and are nearly isotropic for the low-energy particles. The deuteron and triton yields increase with A while those for p, /sup 3/He, and ..cap alpha.. particles decrease with A. The total charged light-particle yield is found to be roughly two times the total reaction cross section (sigma/sub R/) for light- and medium-mass nuclei; while it is less than sigma/sub R/ for heavy nuclei. The experimental results were analyzed within the framework of the pre-equilibrium exciton model together with evaporation theory. The pre-equilibrium exciton model using a 3p-1h initial configuration reproduces the experimental angle-integrated energy spectra except for protons. The deuteron-breakup yield was compared with the Serber model. When the breakup yield is added to the pre-equilibrium yield, agreement is obtained for the proton spectra.« less
  • Using the fragment folding angle technique, the complete fusion-fission is separated from the transfer-induced fission. The cross sections of the complete fusion-fission and fragment angular distributions for the systems of [sup 16]O+[sup 232]Th, [sup 19]F+[sup 232]Th, and [sup 16]O+[sup 238]U at near- and sub-barrier energies have been measured. The observed fission excitation functions can be fitted very well by coupled-channels theory calculations. It is found that fragments from complete fusion fission show a smaller angular anisotropy as compared with our previous measurements in which the transfer-induced fission component was not excluded. However, the measured angular anisotropies of complete fusion-fission aremore » obviously greater than expected on the basis of theoretical models in which the effect of prefission neutron emission was taken into account. Also the peak in the variation of the anisotropy with incident energy still persists in the [sup 19]F+[sup 232]Th case.« less
  • As a first application of our fusion model, the dynamical fragmentation process of fusion and subsequent fission is analyzed in the reactions of 4.8--8 MeV/nucleon /sup 208/Pb on /sup 50/Ti, /sup 52/Cr, /sup 58/Fe, and /sup 64/Ni. In this two step model, the colliding nuclei are first shown to be captured in the pockets behind the adiabatic interaction barriers and then the composite systems so formed, being strongly excited, fission adiabatically. The calculated capture cross sections agree reasonably well with the experiments and the mass distributions are systematically symmetric, independent of the choice of relative separation distance R and themore » large structure in the cranking masses. The symmetric mass fragmentation is a (dynamical) liquid drop effect and the peaks or other detailed structure in mass distributions depend on how the temperature would modify the masses and also on the dynamical coupling of mass asymmetry with the relative motion. This demands refined measurements of the fission data for larger mass asymmetry. The calculated critical angular momentum, which refers to the vanishing of the interaction barrier, in these reactions occurs at the incident energy greater than 8 MeV/nucleon. This suggests a possible importance of extending these experiments beyond their present energy limits.« less