We identified gamma transitions in several neutron-rich nuclei near 132Sn produced in the spontan... more We identified gamma transitions in several neutron-rich nuclei near 132Sn produced in the spontaneous fission of 252Cf. These are of interest because they can test shell model calculations. These nuclei are 139Ba, 133,135Te, and 121,123Cd. Excited states in neutron-rich 133Te exhibit four types of particle-hole bands built on the known 334.3 keV isomer in 133Te. The yrast and near yrast
Complete fusion (CF) and incomplete fusion (ICF) reactions were studied with the beams of loosely... more Complete fusion (CF) and incomplete fusion (ICF) reactions were studied with the beams of loosely bound 6He and 6Li bombarding 166Er and 165Ho targets. Experiments were carried out to test an approach exploiting the measured intensities of gamma rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding
ABSTRACT In an experiment carried out at the 4π Ge detector facility Gammasphere the yields of te... more ABSTRACT In an experiment carried out at the 4π Ge detector facility Gammasphere the yields of ternary fission events of 252Cf accompanied by the emission of He, Be and C LCPs were measured. For the first time independent yields were measured for 59 pairs of secondary fragments of the He ternary fission and for many fission fragments detected together with the He, Be and C LCPs. With a reasonable assumption that the detected LCPs predominantly are 4He, 10Be and 14C their yields and the charge distributions of fission fragments were conjointly analyzed in terms of the ``energy cost'' concept first suggested by Halpern.
Submitted for the DNP06 Meeting of The American Physical Society γ-γ Angular Correlations and g-f... more Submitted for the DNP06 Meeting of The American Physical Society γ-γ Angular Correlations and g-factor Measurements from Spontaneous Fission of 252
VME based data acquisition system for the experiments with radioactive ions beams (RIBs) on ACCUL... more VME based data acquisition system for the experiments with radioactive ions beams (RIBs) on ACCULINNA facility at U-400M cyclotron (Dubna Russia, http://aculina.jinr.ru/) is described. The DAQ system includes a RIO-3 processor connected with CAMAC crate via GTB resources, TRIVA-5 master trigger, standard VME units ADC, TDC, QDC (about 250 parameters in total) and various software (Multi Branch System -MBS version 5.0 http://www-win.gsi.de/daq/, based on CERN ROOT http://root.cern.ch/drupal/ Go4 version 4.4.3 http://www-win.gsi.de/go4/ and real time OS LynxOS version 3.3.1). The new system provides flexibility to use new VME modules (registers, digitizers, etc) and possibility to process a triggers rate (~5000 s -1) higher than that of the old system.
High spin excited states in the neutron-rich nucleus ^139Cs were investigated from a study of the... more High spin excited states in the neutron-rich nucleus ^139Cs were investigated from a study of the prompt gamma rays emitted in the spontaneous fission of ^252Cf with the Gammasphere detector array. Ten new excited levels with eighteen new deexciting transitions were observed and the level scheme of ^139Cs was extended up to 4670 keV. Spins and parities of levels in ^139Cs were firmly assigned up to 25/2 ^+ based on measurements of the angular correlations and an internal conversion coefficient. Shell model calculations were performed to interpret the experimental results. A good agreement between theory and experiment was found in the level energies and the mixing ratio of the 595.4 keV transition. This agreement shows the power of the shell model extended to this nucleus with five protons and two neutrons beyond the double magic ^132Sn core. The present experiment has provided further evidence for the similarity of the spectroscopy of the N=84 isotones, which is clearly born out by...
Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loos... more Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loosely bound 6 He and 6 Li projectiles bombarding 166 Er and 165 Ho targets at energy of about 10 MeV/nucleon. Experiments were carried out to test an approach exploiting the measured intensities of γ rays emitted at the transitions between the yrast band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF reactions 165 Ho ( 6 Li, 5n) 166 Yb and 166 Er( 6 He, 6n) 166 Yb as well as ICF 165 Ho ( 6 Li, α3n) 164 Er and 166 Er( 6 He, α4n) 164 Er reaction channels were revealed from the obtained γ ray data. The method of exit channel identification via the triple coincidence (γ1-γ2 light charged particle) was employed for these reactions study.
Fragment angular momenta as a function of neutron multiplicity were extracted for the first time ... more Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252Cf by studying prompt coincident gamma-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large (nutot>5) and small (nutot=0) scission point elongation. These oscillations are excited to the temperature of 2-3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found.
Exploring Fundamental Issues in Nuclear Physics, 2012
ABSTRACT Prompt γ-γ-γ coincidence studies of neutron-rich nuclei populated in the spontaneous fis... more ABSTRACT Prompt γ-γ-γ coincidence studies of neutron-rich nuclei populated in the spontaneous fission of 252Cf led to the discoveries of many important processes like neutron-less binary and ternary fragmentation in spontaneous fission, binary and ternary hot fission modes, hyper-deformation, cluster radioactivity and quasi-molecular states in ternary fission. The high statistics data, 5.7 × 1011 triples and higher folds, opened up discoveries of new band structures and significant extensions of previously known bands. These data were used to measure the angular correlations of cascades of γ-rays from the excited states of neutron-rich fission fragments stopped in an unmagnetized iron foil. By using this γ-γ angular correlation technique, the single particle configurations of the known rotational bands were assigned and confirmed in the present work. In other words, the multipole mixing ratios of ΔI=1 transitions in the rotational bands were measured. These experimental mixing ratios are compred with the theoretical ones of particle and axial-rotor model. The configuration of the ground states in 109,111Ru were, for the first time, assigned. And magnetic g-factors of excited states in even-even neutron-rich nuclei were meaured, too. Two sets of ΔI=1 alternating parity doublets with opposite parities were observed in Ba and Ce isotopes. The B(E1)/B(E2) branching ratios and D0 values may indicate that the octupole correlations are strong in Ba and Ce isotopes because of the Z=56 and N=88 octupole shell gaps. High-spin, even-parity bands in neutron-rich 108,110,112Ru nuclei indicate two-phonon quasi-gamma bands in 110,112Ru.
Fission and Properties of Neutron-Rich Nuclei - Proceedings of the Fourth International Conference, 2008
The structure of Tc nuclei is extended to more neutron-rich regions based on the measurements of ... more The structure of Tc nuclei is extended to more neutron-rich regions based on the measurements of prompt gamma rays from the spontaneous fission of 252 Cf at Gammasphere. The level scheme of N = 67 neutron-rich (Z = 43) 110 Tc is established for the first time and that of 111 Tc is expanded. The ground band of 111 Tc reaches the band-crossing region and the new observation of the weakly populated α = -1/2 member of the band provides important information of signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band-crossing of the ground band of 111 Tc be due to alignment of a pair of h 11/2 neutrons. The best fit to signature splitting, branching ratios and excitations of the ground band of 111 Tc by RTRP model calculations result in a shape of ε 2 = 0.32 and γ = -26 0 for this nucleus. Its triaxiality is larger than that of 107, 109 Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated 'K+2 satellite' band provides strong evidence for the large triaxiality of 111 Tc. In 110 Tc, the four lowest-lying levels observed are very similar to those in 108 Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a ∆I=1 band are observed. This band of 110 Tc is very analogous to the ∆I=1 bands in 106,108 Tc but it has greater and reversal signature splitting at higher spins.
Prompt Γ-Γ-Γ coincidence studies following spontaneous fission of 252Cf were carried out at Gamma... more Prompt Γ-Γ-Γ coincidence studies following spontaneous fission of 252Cf were carried out at Gammasphere first with 36 and later with 72 Ge detectors. Yields and neutron multiplicities were measured directly for Sr-Nd, Zr-Ce Mo-Ba, Ru-Xe, and Pd-Te correlated pairs. A new hot fission mode was discovered going via only 108Mo-144Ba,107Mo-145Ba, and/or 106Mo-146Ba pairs where one or more of 144,145,146Ba are
The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron... more The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron emission from primary fragment pairs) obtained by detecting coincidences between gamma rays following the spontaneous fission of 252Cf have been expanded. Our approach to estimate characteristics of the primary fragments pairs (mass and excitation energy distributions) by unfolding the yields of secondary fragment pairs is discussed. Mew model parameters were introduced and results are presented here. The new results confirmed our old assumption that in case of Mo-Ba charge split the two fission modes differing with average total kinetic energy on ~36 MeV are realized.
Ternary spontaneous fission of 252Cf has been studied in two experiments with the Gammasphere det... more Ternary spontaneous fission of 252Cf has been studied in two experiments with the Gammasphere detector array with light charged particle detectors surrounding the source. From alpha-gamma double gated spectra, neutron multiplicity distribution were determined for related alpha ternary fission pairs. In going from binary to alpha ternary SF for approximately the same mass splittings (A≈104-146) the average neutron multiplicity decreases
We identified gamma transitions in several neutron-rich nuclei near 132Sn produced in the spontan... more We identified gamma transitions in several neutron-rich nuclei near 132Sn produced in the spontaneous fission of 252Cf. These are of interest because they can test shell model calculations. These nuclei are 139Ba, 133,135Te, and 121,123Cd. Excited states in neutron-rich 133Te exhibit four types of particle-hole bands built on the known 334.3 keV isomer in 133Te. The yrast and near yrast
Complete fusion (CF) and incomplete fusion (ICF) reactions were studied with the beams of loosely... more Complete fusion (CF) and incomplete fusion (ICF) reactions were studied with the beams of loosely bound 6He and 6Li bombarding 166Er and 165Ho targets. Experiments were carried out to test an approach exploiting the measured intensities of gamma rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding
ABSTRACT In an experiment carried out at the 4π Ge detector facility Gammasphere the yields of te... more ABSTRACT In an experiment carried out at the 4π Ge detector facility Gammasphere the yields of ternary fission events of 252Cf accompanied by the emission of He, Be and C LCPs were measured. For the first time independent yields were measured for 59 pairs of secondary fragments of the He ternary fission and for many fission fragments detected together with the He, Be and C LCPs. With a reasonable assumption that the detected LCPs predominantly are 4He, 10Be and 14C their yields and the charge distributions of fission fragments were conjointly analyzed in terms of the ``energy cost'' concept first suggested by Halpern.
Submitted for the DNP06 Meeting of The American Physical Society γ-γ Angular Correlations and g-f... more Submitted for the DNP06 Meeting of The American Physical Society γ-γ Angular Correlations and g-factor Measurements from Spontaneous Fission of 252
VME based data acquisition system for the experiments with radioactive ions beams (RIBs) on ACCUL... more VME based data acquisition system for the experiments with radioactive ions beams (RIBs) on ACCULINNA facility at U-400M cyclotron (Dubna Russia, http://aculina.jinr.ru/) is described. The DAQ system includes a RIO-3 processor connected with CAMAC crate via GTB resources, TRIVA-5 master trigger, standard VME units ADC, TDC, QDC (about 250 parameters in total) and various software (Multi Branch System -MBS version 5.0 http://www-win.gsi.de/daq/, based on CERN ROOT http://root.cern.ch/drupal/ Go4 version 4.4.3 http://www-win.gsi.de/go4/ and real time OS LynxOS version 3.3.1). The new system provides flexibility to use new VME modules (registers, digitizers, etc) and possibility to process a triggers rate (~5000 s -1) higher than that of the old system.
High spin excited states in the neutron-rich nucleus ^139Cs were investigated from a study of the... more High spin excited states in the neutron-rich nucleus ^139Cs were investigated from a study of the prompt gamma rays emitted in the spontaneous fission of ^252Cf with the Gammasphere detector array. Ten new excited levels with eighteen new deexciting transitions were observed and the level scheme of ^139Cs was extended up to 4670 keV. Spins and parities of levels in ^139Cs were firmly assigned up to 25/2 ^+ based on measurements of the angular correlations and an internal conversion coefficient. Shell model calculations were performed to interpret the experimental results. A good agreement between theory and experiment was found in the level energies and the mixing ratio of the 595.4 keV transition. This agreement shows the power of the shell model extended to this nucleus with five protons and two neutrons beyond the double magic ^132Sn core. The present experiment has provided further evidence for the similarity of the spectroscopy of the N=84 isotones, which is clearly born out by...
Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loos... more Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loosely bound 6 He and 6 Li projectiles bombarding 166 Er and 165 Ho targets at energy of about 10 MeV/nucleon. Experiments were carried out to test an approach exploiting the measured intensities of γ rays emitted at the transitions between the yrast band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF reactions 165 Ho ( 6 Li, 5n) 166 Yb and 166 Er( 6 He, 6n) 166 Yb as well as ICF 165 Ho ( 6 Li, α3n) 164 Er and 166 Er( 6 He, α4n) 164 Er reaction channels were revealed from the obtained γ ray data. The method of exit channel identification via the triple coincidence (γ1-γ2 light charged particle) was employed for these reactions study.
Fragment angular momenta as a function of neutron multiplicity were extracted for the first time ... more Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252Cf by studying prompt coincident gamma-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large (nutot>5) and small (nutot=0) scission point elongation. These oscillations are excited to the temperature of 2-3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found.
Exploring Fundamental Issues in Nuclear Physics, 2012
ABSTRACT Prompt γ-γ-γ coincidence studies of neutron-rich nuclei populated in the spontaneous fis... more ABSTRACT Prompt γ-γ-γ coincidence studies of neutron-rich nuclei populated in the spontaneous fission of 252Cf led to the discoveries of many important processes like neutron-less binary and ternary fragmentation in spontaneous fission, binary and ternary hot fission modes, hyper-deformation, cluster radioactivity and quasi-molecular states in ternary fission. The high statistics data, 5.7 × 1011 triples and higher folds, opened up discoveries of new band structures and significant extensions of previously known bands. These data were used to measure the angular correlations of cascades of γ-rays from the excited states of neutron-rich fission fragments stopped in an unmagnetized iron foil. By using this γ-γ angular correlation technique, the single particle configurations of the known rotational bands were assigned and confirmed in the present work. In other words, the multipole mixing ratios of ΔI=1 transitions in the rotational bands were measured. These experimental mixing ratios are compred with the theoretical ones of particle and axial-rotor model. The configuration of the ground states in 109,111Ru were, for the first time, assigned. And magnetic g-factors of excited states in even-even neutron-rich nuclei were meaured, too. Two sets of ΔI=1 alternating parity doublets with opposite parities were observed in Ba and Ce isotopes. The B(E1)/B(E2) branching ratios and D0 values may indicate that the octupole correlations are strong in Ba and Ce isotopes because of the Z=56 and N=88 octupole shell gaps. High-spin, even-parity bands in neutron-rich 108,110,112Ru nuclei indicate two-phonon quasi-gamma bands in 110,112Ru.
Fission and Properties of Neutron-Rich Nuclei - Proceedings of the Fourth International Conference, 2008
The structure of Tc nuclei is extended to more neutron-rich regions based on the measurements of ... more The structure of Tc nuclei is extended to more neutron-rich regions based on the measurements of prompt gamma rays from the spontaneous fission of 252 Cf at Gammasphere. The level scheme of N = 67 neutron-rich (Z = 43) 110 Tc is established for the first time and that of 111 Tc is expanded. The ground band of 111 Tc reaches the band-crossing region and the new observation of the weakly populated α = -1/2 member of the band provides important information of signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band-crossing of the ground band of 111 Tc be due to alignment of a pair of h 11/2 neutrons. The best fit to signature splitting, branching ratios and excitations of the ground band of 111 Tc by RTRP model calculations result in a shape of ε 2 = 0.32 and γ = -26 0 for this nucleus. Its triaxiality is larger than that of 107, 109 Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated 'K+2 satellite' band provides strong evidence for the large triaxiality of 111 Tc. In 110 Tc, the four lowest-lying levels observed are very similar to those in 108 Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a ∆I=1 band are observed. This band of 110 Tc is very analogous to the ∆I=1 bands in 106,108 Tc but it has greater and reversal signature splitting at higher spins.
Prompt Γ-Γ-Γ coincidence studies following spontaneous fission of 252Cf were carried out at Gamma... more Prompt Γ-Γ-Γ coincidence studies following spontaneous fission of 252Cf were carried out at Gammasphere first with 36 and later with 72 Ge detectors. Yields and neutron multiplicities were measured directly for Sr-Nd, Zr-Ce Mo-Ba, Ru-Xe, and Pd-Te correlated pairs. A new hot fission mode was discovered going via only 108Mo-144Ba,107Mo-145Ba, and/or 106Mo-146Ba pairs where one or more of 144,145,146Ba are
The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron... more The data of Independent yields of secondary fission fragment pairs (emerging after prompt neutron emission from primary fragment pairs) obtained by detecting coincidences between gamma rays following the spontaneous fission of 252Cf have been expanded. Our approach to estimate characteristics of the primary fragments pairs (mass and excitation energy distributions) by unfolding the yields of secondary fragment pairs is discussed. Mew model parameters were introduced and results are presented here. The new results confirmed our old assumption that in case of Mo-Ba charge split the two fission modes differing with average total kinetic energy on ~36 MeV are realized.
Ternary spontaneous fission of 252Cf has been studied in two experiments with the Gammasphere det... more Ternary spontaneous fission of 252Cf has been studied in two experiments with the Gammasphere detector array with light charged particle detectors surrounding the source. From alpha-gamma double gated spectra, neutron multiplicity distribution were determined for related alpha ternary fission pairs. In going from binary to alpha ternary SF for approximately the same mass splittings (A≈104-146) the average neutron multiplicity decreases
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