Prompt neutron emission in ^(250)No spontaneous fission associated with ground and isomeric state decays

The complete-fusion reaction^(204)Pb(^(48)Ca,2n)^(250)No was used to study two activities of^(250)No with distinct half-lives.A total of 1357 events were observed in the SFiNx neutron detection system.The average number of neutrons emitted per spontaneous fission of^(250)No was determined to be(4.1±0.1).The unusually symmetrical shape of the prompt neutron multiplicity distribution was restored and presented for the first time.Statistical tests were performed to compare the prompt neutron multiplicity distributions associated with the ground state and K-isomer state decays.

Sequential decay analysis of^(235)U(n^(th),f)reaction using fragmentation approach

Numerous experimental and theoretical observations have concluded that the probability of the three fragment emission(ternary fission)or binary fission increases when one proceeds towards the heavy mass region of nuclear periodic table.Many factors affect fragment emission,such as the shell effect,deformation,orientation,and fissility parameter.Binary and ternary fissions are observed for both ground and excited states of the nuclei.The collinear cluster tripartition(CCT)channel of the^(235)U(n^(th),f)reaction is studied,and we observe that the CCT may be a sequential or simultaneous emission phenomenon.To date,different approaches have been introduced to study the CCT process as a simultaneous or sequential process,but the decay dynamics of these modes have not been not fully explored.Identifying the three fragments of the sequential process and exploring their related dynamics using an excitation energy dependent approach would be of further interest.Hence,in this study,we investigate the sequential decay mechanism of the^(235)U(n^(th),f)reaction using quantum mechanical fragmentation theory(QMFT).The decay mechanism is considered in two steps,where initially,the nucleus splits into an asymmetric channel.In the second step,the heavy fragment obtained in the first step divides into two fragments.Stage I analysis is conducted by calculating the fragmentation potential and preformation probability for the spherical and deformed choices of the decaying fragments.The most probable fragment combination of stage I are identified with respect to the dips in the fragmentation structure and the corresponding maxima of the preformation probability(P0).The light fragments of the identified decay channels(obtained in step I)agree closely with the experimentally observed fragments.The excitation energy of the decay channel is calculated using an iteration process.The excitation energy is shared using an excitation energy dependent level density parameter.The obtained excitation energy of the identified heavy fragments is further used to analyze the fragmentation,and the subsequent binary fragments of the sequential process are obtained.The three identified fragments of the sequential process agree with experimental observations and are found near the neutron or proton shell closure.Finally,the kinetic energy of the observed fragments is calculated,and the middle fragment of the CCT mechanism is identified.

Construction of high-resolution energy-time-of-flight spectrometer for determination of fission fragmentmass distributions

Purpose With the aim of determining mass yield distributions of primary fission products,a one-arm spectrometer was developed based on kinetic energy and time-of-flight correlation measurement technique.Methods An axial grid ionization chamber(GIC)was designed for energy detecting.In order to minimize energy losses and straggling,a thin silicon nitride film with a thickness of 100 nm was performed as the entrance window of the GIC.The energy resolution is 0.38%for 80 MeV ^(63)Cu particles.Two-timing detectors based on the detection of secondary emission electrons by microchannel plates(MCPs)constitute the time pick-off system,and the time-of-flight resolution is better than 200 ps(FWHM)measured with a ^(241)Amαsource.With a flight path length of 47.6 cm,the path length resolution is 0.21%.Results and conclusion The first result of mass distribution from ^(252)Cf spontaneous fission was reported.Energy losses of fragments in dead layers of the spectrometer were corrected event-by-event depend on the Monte Carlo calculation.The mass resolution for light fission fragments peak A107 amu is 1.3 aum.

Study of various ground state decay mechanisms of Actinide nuclei

The special property of the actinide mass region is that nuclei belonging to this group are radioactive and undergo different ground state processes,such as alpha decay,cluster radioactivity(CR),heavy particle radioactivity(HPR),and spontaneous fission(SF).In this study,the probable radioactive decay modes of the heavy mass region(Z=89−102)are studied within the framework of the preformed cluster model(PCM).In the PCM,the radioactive decay modes are explored in terms of the preformation probability(P0)and penetration probability(P)at the turning point Ra,where the penetration of fragments is initiated[Ra=RT(touching state)+ΔR(neck length parameter)].First,the alpha decay half-lives are calculated for light and heavy nuclei,and Ra points are obtained by optimizing the neck length parameter.These Ra points are further employed to fix the Q-value dependent turning point(Ra(Q)).Then,using the(Ra(Q))relation,the decay half-lives are computed,and the calculated results are compared with the available theoretical and experimental data.The isotopical trend of P0 and P is studied with respect to the mass number of the parent and daughter nucleus,respectively.The CR and HPR channels are also explored,and a comparison of calculated data is conducted with the available literature.Comparative analysis of the fragmentation potential and preformation probability is carried out for alpha decay and SF.The mass distribution of the nuclei is studied as a function of fragment mass(A2)by considering the spherical and hot-compact deformation of the decaying fragments.Finally,the most probable fission fragments are identified using the fragmentation structure,and the corresponding fission fragment total kinetic energy of the identified fragments is calculated and compared with available data,wherever applicable.

Calculations of theα-decay properties of Z=120,122,124,126 isotopes

Theα-decay properties of even-Z nuclei with Z=120,122,124,126 are predicted.We employ the generalized liquid drop model(GLDM),Royer's formula,and universal decay law(UDL)to calculate theα-decay half-lives.By comparing the theoretical calculations with the experimental data of known nuclei from Fl to Og,we confirm that all the employed methods can reproduce theα-decay half-lives well.The preformation factor Pαandα-decay energy Qαshow that ^298,304,314,316,324,326,338,348120,^304,306,318,324,328,338122,and ^328,332,340,344124 might be stable.Theα-decay half-lives show a peak at Z=120,N=184,and the peak vanishes when Z=122,124,126.Based on detailed analysis of the competition betweenα-decay and spontaneous fission,we predict that nuclei nearby N=184 undergoα-decay.The decay modes of ^287−339120,^294−339122,^300−339124,and ^306−339126 are also presented.

Predictions of decay modes for the superheavy nuclei most suitable for synthesis

The competition between α-decay and spontaneous fission of superheavy nuclei（SHN） is investigated by the generalized liquid drop model（GLDM） and the modified Swiatecki＇s formula respectively. The theoretical decay modes are in good agreement with the experimental results. Predictions are made for as-yet unobserved superheavy nuclei. The theoretical calculations show that the nuclei^298 120,^295 119,^290 118,^291 117,^287 117,^294 116,^289 116,^286 116,^285 116,^284 115,^283 115,^283 114,^282 114,^280 113,^276 112,^275 112,^274 112,^273 111,^272 110,^265 109 may be synthesized experimentally in the near future since they not only have relatively large predicted cross sections but can also be identified via α-decay chains.

High-spin states in neutron-rich ^(102)Mo nucleus

High-spin states in neutron-rich 102Mo nucleus have been studied by measuring the prompt γ-rays in the spontaneous fission of 252Cf. The previous level scheme has been updated and some new levels and transitions are identified. The one-phonon γ-band is expanded and a band head level of the two-phonon γ- band is proposed. The systematic characteristics of yrast bands, one-phonon γ-bands, two-phonon γ-bands and quasi-particle bands in 102Mo, 104Mo and 106Mo are discussed.

Observation of a new rotational band in ^(104)Nb nucleus

The high spin states in neutron-rich 104Nb have been investigated from study of prompt γ-rays in spontaneous fission of 252Cf with the Gammasphere detector array. A new rotational band has been identified for the first time. This band is proposed as a semi-decoupled band based on the configuration π5/2-[303]ν1/2-[541].

Extended collective bands in neutron-rich ^(109)Ru

Levels in the neutron-rich 109Ru have been studied by observing the prompt γ-rays following the spontaneous fission fragments of 252Cf. The ground state band and the negative parity bands have been confirmed and extended. A positive parity band with the band head level at 332.5 keV is newly identified and suggested as a single-neutron excitation band built on the 7/2+[404] Nilsson orbital. Some structural characteristics of these bands are discussed.

High spin states in neutron-rich ^(106)Tc nucleus

The high spin states of the neutron-rich odd-odd 106Tc nucleus have been reinvestigated by observing prompt γ-rays from the spontaneous fission of 252Cf. A previously known collective band is confirmed and expanded, and a new collective band is newly identified. Several levels in previous report in 106Tc are reexamined and they belong to the members of a band in 107Tc. The total Routhian surface (TRS) calculations show that the 106Tc has triaxial shape. The spins and parities as well as the configurations for these bands have been tentatively assigned according to the analysis of the angular momentum alignments.