4n Channels Research Articles

The effect of deformation and orientation of colliding nuclei on synthesis of superheavy elements

In this paper, we study the evaporation residue cross section for superheavy elements 120295−304 using the phenomenological model taking into account the deformation and orientation effects of the target and the projectile. Calculations are done for the 3n and 4n channels in the reactions 54Cr+244−248,250Cm, 50V+245−250Bk, 55Mn+240−244Am, and 58Fe+240−242,244,246Pu. To test this model, we compared results of the 3n channel cross section in the reactions 48Ca+243Am, 48Ca+248Cm, 48Ca+249Bk and 48Ca+249Cf and the 4n channel cross section in the reactions 48Ca+243Am, 48Ca+248Cm, and 48Ca+249Bk with the experimental data. The agreement between the experimental data and the theoretical results based on deformed target and projectile is better than theoretical results for spherical target and projectile. Using this model, we predicted the maximum value and the corresponding energy of the 3n and 4n channel cross sections for spherical and deformed colliding nuclei for synthesizing Z=120. By applying the deformation effect and averaging over orientation, it is found that the maximum value of the 3n channel is 70.14 fb at 26.04 MeV for the reaction 54Cr+247Cm, whereas the maximum value of the 4n channel is 0.47 fb at 34.61 MeV for the reaction 54Cr+250Cm.

Theoretical studies on the synthesis of SHE 290-302Og (Z=118) using 48Ca, 45Sc, 50Ti, 51V, 54Cr, 55Mn, 58Fe, 59Co and 64Ni induced reactions

Using the phenomenological model for production cross section (PMPC), the production cross sections for the synthesis of isotopes of superheavy element Og (Z = 118) using the fusion reactions 48Ca+249-254Cf $\rightarrow$ 297-302Og, 45Sc+247,249Bk $ \rightarrow$ 292,294Og, 50Ti + 242-248,250Cm $ \rightarrow$ 292-298,300Og, 51V+241,243Am $\rightarrow$ 292,294Og, 54Cr + 238-242,244Pu $ \rightarrow$ 292-296,298Og, 55Mn + 235-237Np $ \rightarrow$ 290-292Og, 58Fe + 232-236, 238U $\rightarrow$ 290-294,296Og, 59Co + 231Pa $\rightarrow$ 290Og, and 64Ni + 228-230,232Cm $\rightarrow$ 292-294,296Og in $x\mathrm{n}$ $(x=3,4,5)$ evaporation channel have been systematically studied at energies near and above the Coulomb barrier. We have predicted most suitable projectile-target combinations for the synthesis of isotopes 290-302Og among these reactions. Our calculated evaporation residue (ER) cross section values for the reaction 48Ca + 249Cf $\rightarrow$ 297Og is in excellent agreement with available experimental values. For the synthesis of Og, among all the reactions mentioned above, the 3n channel cross section (2458 fb) is larger for 48Ca + 251Cf $\rightarrow$ 299Og; 4n channel cross section (212 fb) is larger for 48Ca + 252Cf $ \rightarrow$ 300Og and 5n channel cross section (34 fb) is larger for 48Ca + 253Cf $\rightarrow$ 301Og. The second largest 3n channel cross section (1143 fb) is obtained for the reaction, 50Ti + 245Cm $\rightarrow$ 295Og. Our studies will be useful for the future experiments to synthesize the isotopes of element Og which are not synthesized so far. We have also studied the effect of the use of mass values and shell correction of the Warsaw group which leads to a smaller ER cross section compared to the Moller group.

Fusion-Barrier Distributions Will Unveil Most Probable Reaction Energies to Synthesize Isotopes of Superheavy Elements Beyond Z = 118

To investigate the correlations between barrier distributions and excitation functions of neutron-evaporation channels (xn channels) in nuclear reactions, researchers have measured fusion-barrier distributions in reaction systems in which superheavy isotopes are synthesized. They found that the excitation functions of 3n and 4n channels in the system 48Ca+248Cm are strongly affected by the deformation of the target nucleus. This finding will enhance our ability to quantitatively predict the most probable reaction energies for further searches of superheavy elements.

Predictions of probable projectile-target combinations for the synthesis of superheavy isotopes of Ts

Taking the Coulomb and proximity potential as the interaction barrier, we have studied the production cross section of probable projectile-target combinations for the synthesis of superheavy element $^{297}\mathrm{Ts}$. The cold reaction valley of $^{297}\mathrm{Ts}$ is studied to identify the possible projectile-target combinations for the synthesis of $^{297}\mathrm{Ts}$. The entrance channel Coulomb barrier, the quasifission barrier, and barrier positions for all these combinations are calculated. The fusion probability and survival probability of the excited compound nucleus are evaluated. At energies near and above the Coulomb barrier, the excitation function [capture, fusion, and evaporation residue (ER) cross sections] of these combinations leading to superheavy element (SHE) $^{297}\mathrm{Ts}$ is investigated. It is found that the production cross sections of $^{297}\mathrm{Ts}$ in cold fusion reactions are very small compared to hot fusion reactions. The combinations $^{40}\mathrm{S}+^{257}\mathrm{Md}, ^{42}\mathrm{S}+^{255}\mathrm{Md}, ^{43}\mathrm{Cl}+^{254}\mathrm{Fm}, ^{44}\mathrm{Ar}+^{253}\mathrm{Es}, ^{46}\mathrm{Ar}+^{251}\mathrm{Es}, ^{48}\mathrm{Ca}+^{249}\mathrm{Bk}, ^{50}\mathrm{Ca}+^{247}\mathrm{Bk}, ^{67}\mathrm{Co}+^{230}\mathrm{Th}, ^{68}\mathrm{Ni}+^{229}\mathrm{Ac}, ^{70}\mathrm{Ni}+^{227}\mathrm{Ac}$, and $^{72}\mathrm{Ni}+^{225}\mathrm{Ac}$ are observed to be the most favorable projectile-target pairs for the production of SHE $^{297}\mathrm{Ts}$. Our calculated results are compared with experimental data and with other theoretical studies for the reaction $^{48}\mathrm{Ca}+^{249}\mathrm{Bk}$ leading to $^{297}\mathrm{Ts}$, and are in good agreement with experimental observation of Oganessian et al. Furthermore, the ER cross section for the synthesis of isotopes $^{291\ensuremath{-}296}\mathrm{Ts}$ and $^{298\ensuremath{-}299}\mathrm{Ts}$ using $^{48}\mathrm{Ca}$ induced reactions are studied. Among these isotopes, the isotope $^{298}\mathrm{Ts}$ has larger cross section in the 3n channel using the reaction $^{48}\mathrm{Ca}+^{250}\mathrm{Bk}$, and $^{299}\mathrm{Ts}$ has larger cross section in the 4n channel using the reaction $^{48}\mathrm{Ca}+^{251}\mathrm{Bk}$. Therefore, our theoretical predictions to produce isotopes of the element Ts will be helpful for future experiments, as the isotopes have not been synthesized so far.

Influence of hexadecapole deformation on production cross sections of superheavy nuclei

The current heaviest superheavy nuclei (SHN) are experimentally synthesized by using 48Ca to bombard actinide nuclei via fusion reactions. Actinide nuclei often have considerable hexadecapole deformation in addition to quadrupole deformation, which was not considered in previous theoretical studies. With the dinuclear system concept, and by taking the hexadecapole deformation in to consideration in addition to the quadrupole deformation, the hot fusion probability leading to the synthesis of SHN is investigated systematically. Synthesis of superheavy elements 296118 and 295118 by using the 48Ca+251Cf reaction channel is evaluated and discussed, and the maximal evaporation residue cross sections (ERCSs) of the 3n and 4n channels are predicted to be 1.90 and 0.11 pb, respectively. The predicted maximum ERCSs in 3n and 4n evaporation channels of the 249Bk(50Ti,xn) reaction are 0.12 and 0.04 pb, respectively. The most favorable reaction to synthesize the element Z = 120 turns out to be 251Cf(50Ti,xn)120, but the predicted maximum cross section for this reaction is only 67 fb. Therefore, superheavy element 119 may be the most hopeful new element for to be synthesized under some improved experimental conditions in the near future.

A new high-spin isomer in 195Bi

A new high-spin isomer has been identified in 195Bi at the focal plane of the HYbrid Recoil mass Analyser (HYRA) used in the gas-filled mode. The fusion evaporation reactions 169Tm (30Si, x n) 193, 195Bi were used with the beam energies on targets of 168 and 146MeV for 6n and 4n channels, respectively. The evaporation residues, separated from the fission fragments, and their decays were detected at the focal plane of HYRA using MWPC, Si-Pad and clover HPGe detectors. The half-life of the new isomer in 195Bi has been measured to be 1.6(1)μs. The configuration of the new isomer has been proposed and compared with the other isomers in this region. The Total Routhian Surface (TRS) calculations for the three-quasiparticle configurations corresponding to the new isomer suggest an oblate deformation for this isomeric state. The same calculations for different configurations in 195Bi and for the even-even 194Pb core indicate that the proton i 13/2 orbital has a large shape driving effect towards oblate shape in these nuclei.

Polymeric N-stage cascaded five-port optical router with scalable 4N channel wavelengths for wideband signal routing

As basic routing element, structure and principle of cross-coupling two-ring resonator are presented, and waveguide parameters are optimized for phase-matching and single-mode propagation. Using eight-group basic elements, a new one-stage five-port polymer optical router is proposed, and it can optically route four channel wavelength data streams along definite-path in 2-D plane. Under the selected four channel wavelengths, the insertion losses along all routing paths are within 0.03–0.62dB, the maximum crosstalk of all routing operations is less than −39dB, and the device footprint size is about 0.31mm2. A universal novel structure and routing scheme of N-stage cascaded five-port optical router are presented, and it contains 4N channel wavelengths that can be routed by the device. Compared with the previously reported silicon optical routers, this polymer device possesses similar ring radius (~10μm) and device size (<1mm2). Because of simple processing technology, low cost and good scalability, this device shows potential application of wideband signal routing in optical networks-on-chip (ONoC).

Predictions of the fusion-by-diffusion model for the synthesis cross sections ofZ=114–120 elements based on macroscopic-microscopic fission barriers

A complete set of existing data on hot fusion reactions leading to synthesis of superheavy nuclei of Z =114-118, obtained in a series of experiments in Dubna and later in GSI Darmstadt and LBNL Berkeley, was analyzed in terms of a new angular-momentum dependent version of the Fusion by Diffusion (FBD) model with fission barriers and ground-state masses taken from the Warsaw macroscopic-microscopic model (involving non-axial shapes) of Kowal et al. The only empirically adjustable parameter of the model, the injection-point distance (sinj), has been determined individually for all the reactions and very regular systematics of this parameter have been established. The regularity of the obtained sinj systematics indirectly points at the internal consistency of the whole set of fission barriers used in the calculations. Having fitted all the experimental excitation functions for elements Z = 114-118, the FBD model (with the new sinj systematics) was used to predict cross sections for synthesis of elements Z = 119 and 120. Regarding prospects to produce the new element Z = 119, our calculations prefer the 252Es(48Ca,xn)300-x119 reaction, for which the synthesis cross section of about 0.2 pb in 4n channel at Ec.m.= 220 MeV is expected. The most favorable reaction to synthesize the element Z = 120 turns out to be 249Cf(50Ti,xn)299-x120, but the predicted cross section for this reaction is only 6 fb (for 3n and 4n channels).

Combined in-beam electron andγ-ray spectroscopy ofHg184,186

By exploiting the SAGE spectrometer a simultaneous measurement of conversion electrons and {gamma} rays emitted in the de-excitation of excited levels in the neutron-deficient nuclei {sup 184,186}Hg was performed. The light Hg isotopes under investigation were produced using the 4n channels of the fusion-evaporation reactions of {sup 40}Ar and {sup 148,150}Sm. The measured K- and L-conversion electron ratios confirmed the stretched E2 nature of several transitions of the yrast bands in {sup 184,186}Hg. Additional information on the E0 component of the 2{sub 2}{sup +}{yields}2{sub 1}{sup +} transition in {sup 186}Hg was obtained.

Possible Way to Synthesize Superheavy Element Z = 117

Within the framework of the dinuclear system model, the productionof superheavy element Z = 117 in possible projectile–targetcombinations is analysed systematically. The calculated results showthat the production cross sections are strongly dependent on thereaction systems. Optimal combinations, corresponding excitationenergies and evaporation channels are proposed, suchas the isotopes 248,249Bk in 48Ca induced reactions in 3nevaporation channels and the reactions 45Sc+246,248Cm in 3nand 4n channels, and the system 51V+244Pu in 3n channel.

Highly selective studies of GDR inEr

Exclusive measurements of high energy γ-rays in the decay of164Er, formed in the reaction40Ar+124Sn, have been performed to study angular momentum dependence of the giant dipole resonance (GDR) strength function. The γ-ray spectra were measured in coincidence with A=160 evaporation residues (4n channel at Ebeam = 163 MeV and 187 MeV. A statistical model analysis, incorporating a two-component GDR strength function, shows increase in the GDR width as the average spin of the compound nucleus increases from 26ħ, (at 163 MeV to 54ħ (at 187 MeV). This is consistent with the predictions of a thermal shape fluctuation model.

Highly selective studies of GDR inEr

Exclusive measurements of high energy γ-rays in the decay of 164 Er, formed in the reaction 40 Ar+ 124 Sn, have been performed to study angular momentum dependence of the giant dipole resonance (GDR) strength function. The γ-ray spectra were measured in coincidence with A=160 evaporation residues (4n channel at E beam = 163 MeV and 187 MeV. A statistical model analysis, incorporating a two-component GDR strength function, shows increase in the GDR width as the average spin of the compound nucleus increases from 26ħ, (at 163 MeV to 54ħ (at 187 MeV). This is consistent with the predictions of a thermal shape fluctuation model.

Highly selective studies of GDR in 164Er

Exclusive measurements of high energy γ-rays in the decay of 164Er, formed in the reaction 40Ar+ 124Sn, have been performed to study angular momentum dependence of the giant dipole resonance (GDR) strength function. The γ-ray spectra were measured in coincidence with A=160 evaporation residues (4n channel at E beam = 163 MeV and 187 MeV. A statistical model analysis, incorporating a two-component GDR strength function, shows increase in the GDR width as the average spin of the compound nucleus increases from 26ħ, (at 163 MeV to 54ħ (at 187 MeV). This is consistent with the predictions of a thermal shape fluctuation model.

Symmetric fission of 24Mg following inelastic scattering

Symmetric fission into two 12C nuclei has been observed from states at high excitation energy in 24Mg excited in inelastic scattering. Fission to the 10B+ 4N channel has also been observed and indirect evidence for the 16O+ 8Be channel noted. The same experiment also reveals fission into 16O+ 12C from states in 28Si populated by alpha-particle pickup onto the 24Mg projectile. The correlation of the states in 24Mg observed in this experiment with those previously observed in 12C+ 12C scattering is discussed.

Experimental study of 136Nd at high angular momentum

Abstract The γ-ray multiplicities following 100 Mo ( 40 Ar , x n γ) Nd have been studied by several methods. The measured width of the multiplicity distribution and the shape of the multiplicity spectrum as a function of transition energy suggest a broad region of feeding into the 4n channel. The dependence of the multiplicity on transition energy, for the sum of all reaction channels and for only the 4n reaction channel, is well reproduced by a calculation which suggests that the products become deformed rotors at spins above 30ħ.

A study of γ-decay modes from high angular momentum nuclear states by high order multiplicity measurements

Reactions between 18O and 16O ions, with energies well above the Coulomb barrier, and 148, 150Nd target nuclei were used to study the cascades of γ-rays in the residual nuclei 161, 162Er. A multi-counter setup was used in which the γ-rays were detected by a Ge(Li) counter coupled in coincidence with up to 9 NaI(Tl) counters. The γ-multiplicity has been studied for γ-rays cascading through states above and along the yrast line. Higher moments of the multiplicity distributions (shape parameters) were deduced from the data. These moments allow the construction of the spin distribution for the entry states. The difference between these spin distributions from reactions induced by 16O and 18O ions was studied. Also the fusion cross section was measured for the two systems as a function of bombarding energy and compared to the multiplicity results at two different excitation energies ( E x = 49.5 and 56.2 MeV). A subtraction technique has been applied in the data analysis with the intention to study the decay of a selected part of the high-spin region, and the results show besides the 4n channel an unexpected large contribution of the 5n channel from this region. The sidefeeding patterns of the multiplicity distributions are extracted and show a significant difference for the 16O and 18O induced reactions, especially at the lowest bombarding energies. The results are compared with statistical model calculations.