Input Angular Momentum Research Articles

Low Energy Incomplete Fusion and the Role of Input Angular Momenta

Low Energy Incomplete Fusion and the Role of Input Angular Momenta

Study of the \(^{nat}\)Sm\((\gamma ,xn)^{143m,g}\)Sm Reactions Induced by Bremsstrahlung with End-point Energies Just above GDR Region

We investigate the energy dependence of the isomeric yield ratios for the \(^{nat}\)Sm\((\gamma ,xn)^{143m,g}\)Sm reactions with bremsstrahlung energies of 40-, 45-, and 50-MeV, just above the giant dipole resonance (GDR) region by the off-line $\gamma $-ray spectrometric method. The bremsstrahlung photons were produced from the 100 MeV electron linear accelerator (linac) at the Pohang accelerator laboratory (PAL), Pohang, Korea. In order to improve the accuracy of the experimental results the necessary corrections were made. The present results are compared with similar literature data of the $^{nat}$Sm($\gamma $,xn)$^{143m,g}$Sm reactions measured at various photon energies and of the $^{nat}$Sm(n,2n)$^{143m,g}$Sm reaction induced by 14 MeV neutrons in order to examine the effects of an excitation energy and an input angular momentum.

Isomeric yield ratios of 148Pm from the natSm(γ, x) and the natNd(p, xn) reactions

The independent isomeric yield ratios of 148Pm from the natSm(γ, x) reaction at the end-point bremsstrahlung energy of 45–64 MeV have been determined using an off-line γ-ray spectrometric technique at the 100 MeV electron linac of Pohang accelerator laboratory, Pohang, Korea. We also have determined the isomeric yield ratios of 148Pm from the natNd(p,xn) reactions in the proton energy of 5.08–44.72 MeV by a stacked-foil activation and an off-line γ-ray spectrometric techniques at the MC-50 cyclotron of the Korean Institute of Radiological and Medical Sciences, Korea. The determined isomeric yield ratios of 148Pm were compared with literature data and theoretical values estimated by the TALYS 1.4. The present data along with the similar data from literature at other energies shows that the isomeric yield ratio of 148Pm increases with the excitation energy both in the natSm(γ, x) and the natNd(p, xn) reactions. The isomeric yield ratios of 148Pm from the natNd(p, xn) reactions are always higher than those from the natSm(γ, x) reactions at the same excitation energy, which indicate the role of input angular momentum besides excitation energy.

Isomeric yield ratios of 87m,gY from different nuclear reactions

The independent isomeric yield ratios of 87m,gY produced from the 93Nb(γ, α2n) and natZr(γ, pxn) reactions with the end-point bremsstrahlung energy of 45–70 MeV have been determined by an off-line γ-ray spectrometric technique using 100 MeV electron linac at the Pohang accelerator laboratory, Korea. The isomeric yield ratios of 87m,gY were also determined from the natZr(p, αxn) and the 89Y(p,p2n) reactions with EP = 15–45 MeV as well as those from the 89Y(α, α2n) reaction with Eα = 32–43 MeV using the MC-50 cyclotron at the Korea Institute of Radiological and Medical Science, Korea. The isomeric yield ratios of 87m,gY from the present work in the 93Nb(γ, α2n), natZr(γ, pxn), natZr(p, αxn), 89Y(p,p2n), and 89Y(α, α2n) reactions were compared with those of the literature data in the 85Rb(α, 2n), the 86,87,88Sr(d, xn), 89Y(n,3n), and the 89Y(γ, 2n) reactions to examine the role of target, projectiles, and ejectiles through compound nucleus excitation energy and input angular momentum. The isomeric yield ratios of 87m,gY in the above eleven reactions were also calculated using the computer code TALYS 1.4 and compared with the experimental data. The different behaviors between photon- and neutron-induced reactions and charged-particle-induced reactions are discussed from the viewpoint of compound and non-compound (pre-equilibrium) process.

Probing of complete and incomplete fusion dynamics in heavy-ion collision

Three different types of experiments have been performed to explore the complete and incomplete fusion dynamics in heavy-ion collisions. In this respect, first experiment for the measurement of excitation functions of the evaporation residues produced in the 20Ne + 165Ho system at projectile energy ranges ≈2–8 MeV /nucleon has been done. Measured cumulative and direct cross-sections have been compared with the theoretical model code PACE-2, which takes into account only the complete fusion process. It has been observed that, incomplete fusion fraction is sensitively dependent on projectile energy and mass asymmetry between the projectile and the target systems. Second experiment for measuring the forward recoil range distributions of the evaporation residues produced in the 20Ne + 165Ho system at projectile energy ≈8 MeV /nucleon has been done. It has been observed that, some evaporation residues have shown additional peaks in the measured forwardrecoil range distributions at cumulative thicknesses relatively smaller than the expected range of the residues produced via complete fusion. The results indicate the occurrence of incomplete fusion involving the breakup of 20Ne into 4He + 16O and /or 8Be + 12C followed by one of the fragments with target nucleus 165Ho. Third experiment for the measurement of spin distribution of the evaporation residues produced in the 16O + 124Sn system at projectile energy ≈6 MeV /nucleon, showed that the residues produced as incomplete fusion products associated with fast α and 2 α-emission channels observed in the forward cone, are found to be distinctly different from those of the residues produced as complete fusion products. The spin distribution of the evaporation residues also inferred that in incomplete fusion reaction channels input angular momentum (J0) increases with fusion incompleteness when compared to complete fusion reaction channels. Present observation clearly shows that the production of fast forward α-particles arises from relatively larger angular momentum in the entrance channel leading to peripheral collision.

Independent isomeric yield ratios of 95m,gNb in the natMo(γ, pxn) and natZr(p, xn) reactions

The independent isomeric yield ratios of 95m,gNb from the natMo(γ, pxn) reactions with bremsstrahlung end-point energies of 45, 50, 55, 60, and 70 MeV were determined by an activation and an off-line γ-ray spectrometric technique at the Pohang accelerator laboratory (PAL), Korea. The isomeric yield ratios of 95m,gNb from the natZr(p, xn) reactions were also determined in eight different proton energies within 19.4–44.7 MeV by a stacked-foil activation and an off-line γ-ray spectrometric technique using the MC-50 cyclotron of Korea Institute of Radiological and Medical Sciences (KIRAMS), Korea. The measured isomeric yield ratios of 95m,gNb from the present work and the literature data in the natMo(γ, pxn) and natZr(p, xn) reactions were compared with the similar literature data in the natMo(p, αxn) reactions. It was found that the isomeric yield ratio of 95m,gNb increases with projectile energy, which indicate the effect of excitation energy. However, at the same excitation energy, the isomeric yield ratios of 95m,gNb in the natZr(p, xn) and natMo(p, αxn) reactions are higher than those in the natMo(γ, pxn) reaction, which indicates the role of input angular momentum. The isomeric yield ratios of 95m,gNb in the natMo(γ, pxn), natZr(p, xn), and natMo(p, αxn) reactions were also calculated using computer code TALYS 1.4. The calculated isomeric yield ratios of 95m,gNb from three reactions increase with excitation energy. However, in all the three reactions, the calculated values are significantly higher than the experimental data.

Measurement of isomeric yield ratios of the 104m,g,106m,gAg in the 45- and 55-MeV bremsstrahlung induced reactions of natural silver

The isomeric yield ratios for the natAg(γ,xn)104m,g,106m,gAg reactions with the end-point bremsstrahlung energies of 45- and 55-MeV have been determined by the off-line γ-ray spectrometric technique using 100 MeV electron linac at Pohang accelerator laboratory, Korea. The present data were compared with literature data in comparable compound nucleus from the natAg(γ,xn), natPd(p,xn), and 103Rh(α,xn) reactions to examine the effects of an excitation energy and an input angular momentum. It is observed that the isomeric yield ratios of 104,106Ag in natAg(γ,xn), natPd(p,xn) and 103Rh(α,xn) reactions increase with the end-point bremsstrahlung energy, proton and alpha energy, which indicate the role of excitation energy. It is also found that for the similar compound nucleus at same excitation energy, the isomeric yield ratio of 104m,gAg is higher in the natPd(p,xn) and 103Rh(α,xn) reactions than those in natAg(γ,xn) reaction, which indicate the effect of an input angular momentum.

Isomeric yield ratios for the natNd(γ, xn) 139m,g; 141m,gNd reactions in the bremsstrahlung energy region from 45 to 60 MeV

The independent isomeric yield ratios (IR) for the 139m,gNd and the 141m,gNd isomeric pairs produced from the natNd(γ, xn) reactions were determined by the activation and the off-line γ-ray spectrometric technique at the end-point bremsstrahlung energies of 45, 50, 55, and 60 MeV in the 100 MeV electron Linac of the Pohang accelerator laboratory, Korea. The present IR for the 141m,gNd isomeric pair were compared with those from the literature measured by the bremsstrahlung and the neutron to examine the role of excitation energy. The obtained IR for the 139m,gNd and the 141m,gNd isomeric pairs from natNd(γ, xn) reactions were compared with those from the 141Pr(p, x), the natCe(3He, x), and the 136Ce(α, n) reactions to examine the role of parameters in entrance channel i.e. excitation energy and the effect of the input angular momentum. The present IR of 139m,gNd and 141m,gNd were compared with those calculated by using the TALYS 1.4 code as well as those from the literature data of above mentioned reactions.

Independent isomeric-yield ratio of 89m,gNb from 93Nb(γ, 4n), natZr(p, xn), and 89Y(α, 4n) reactions

The independent isomeric-yield ratios of 89m,gNb for the 93Nb(γ, 4n) 89m,gNb reaction with bremsstrahlung energies of 45-, 50-, 55-, 60-, and 70-MeV were measured by the activation and the off-line γ-ray spectrometric technique at 100 MeV electron linac of the Pohang accelerator laboratory. The isomeric-yield ratios of 89m,gNb for the natZr(p, xn) 89m,gNb and the 89Y(α, 4n) 89m,gNb reactions were measured by using a stacked-foil activation technique with the proton energies of 19–45 MeV and alpha energies of 38.9-, 40.5-, and 42.5-MeV at the MC-50 cyclotron of Korea Institute of Radiological and Medical Sciences. The measured isomeric-yield ratio of 89m,gNb from the 93Nb(γ, 4n), natZr(p, xn), and 89Y(α, 4n) reactions were compared with the similar literature data in the 89Y(3He, 3n) reaction. It was found that the isomeric yield ratio of 89m,gNb increases with projectile energy, which indicate the effect of excitation energy. However, for the similar compound nucleus with the same excitation energy, the isomeric-yield ratios of 89m,gNb in the 89Y(α, 4n) and 89Y(3He, 3n) reactions are higher than those in the 93Nb(γ, 4n) and natZr(p, xn) reactions, which indicates the role of input angular momentum. The isomeric-yield ratios of 89m,gNb in the 93Nb(γ, 4n), natZr(p, xn), 89Y(α, 4n), and 89Y(3He, 3n) reactions were also calculated theoretically using computer code TALYS 1.4. The theoretical isomeric-yield ratios of 89m,gNb from four reactions increase with excitation energy. However, the theoretical value are significantly higher than the experimental data in the 93Nb(γ, 4n) and natZr(p, xn) reactions but slightly lower or comparable in the 89Y(α, 4n) rand 89Y(3He, 3n) reactions.

Low angular momentum flow model for Sgr A*

We examine the low angular momentum flow model for Sgr A* using two-dimensional hydrodynamical calculations based on the parameters of the specific angular momentum and total energy estimated in the recent analysis of stellar wind of nearby stars around Sgr A*. The accretion flow with the plausible parameters is non-stationary and an irregularly oscillating shock is formed in the inner region of a few tens to a 160 Schwarzschild radii. Due to the oscillating shock, the luminosity and the mass-outflow rate are modulated by several per cent to a factor of 5 and a factor of 2–7, respectively, on time-scales of 1 h to 10 d. The flows are highly advected and the radiative efficiency of the accreting matter into radiation is very low, ∼10−5 to 10−3, and the input accretion rate yr−1 results in the observed luminosities ∼1036 erg s−1 of Sgr A* if a two-temperature model and the synchrotron emission are taken into account. The mass-outflow rate of the gas originating in the post-shock region increases with the increasing input specific angular momentum and ranges from a few to 99 per cent of the input accreting matter, depending on the input angular momentum. The oscillating shock is necessarily triggered if the specific angular momentum and the specific energy belong to or are located just nearby the range of parameters responsible for a stationary shock in rotating inviscid and adiabatic accretion flow. The time variability may be relevant to the flare activity of Sgr A*.

Incomplete fusion dynamics by spin distribution measurements

Spin distributions for various evaporation residues populated via complete and incomplete fusion of $^{16}\mathrm{O}$ with $^{124}\mathrm{Sn}$ at $6.3$ MeV/nucleon have been measured, using charged particles ($Z=1,2$)-$\ensuremath{\gamma}$ coincidence technique. Experimentally measured spin distributions of the residues produced as incomplete fusion products associated with ``fast'' $\ensuremath{\alpha}$- and $2\ensuremath{\alpha}$-emission channels observed in the ``forward cone'' are found to be distinctly different from those of the residues produced as complete fusion products. Moreover, ``fast'' $\ensuremath{\alpha}$-particles that arise from larger angular momentum in the entrance channel are populated at relatively higher driving input angular momentum than those produced through complete fusion. The incomplete fusion residues are populated in a limited, higher-angular-momentum range, in contrast to the complete fusion products, which are populated over a broad spin range.

Studies of dissipative standing shock waves around black holes

We investigate the dynamical structure of advective accretion flow around stationary as well as rotating black holes. For a suitable choice of input parameters, such as, accretion rate ($\dot {\cal M}$) and angular momentum ($\lambda$), global accretion solution may include a shock wave. The post shock flow is located at few tens of Schwarzchild radius and it is generally very hot and dense. This successfully mimics the so called Compton cloud which is believed to be responsible for emitting hard radiations. Due to the radiative loss, a significant energy from the accreting matter is removed and the shock moves forward towards the black hole in order to maintain the pressure balance across it. We identify the effective area of the parameter space ($\dot {\cal M} - \lambda$) which allows accretion flows to have some energy dissipation at the shock $(\Delta {\cal E})$. As the dissipation is increased, the parameter space is reduced and finally disappears when the dissipation is reached its critical value. The dissipation has a profound effect on the dynamics of post-shock flow. By moving forward, an unstable shock whose oscillation causes Quasi-Periodic Oscillations (QPOs) in the emitted radiation, will produce oscillations of high frequency. Such an evolution of QPOs has been observed in several black hole candidates during their outbursts.

Spin-distribution measurement: A sensitive probe for incomplete fusion dynamics

Spin distributions of various reaction products populated via complete and/or incomplete fusion of {sup 16}O with {sup 169}Tm have been measured at projectile energy {approx_equal}5.6 MeV/nucleon. Particle (Z=1,2) {gamma}-coincidences have been employed to achieve the information about involved reaction modes on the basis of their entry state spin populations. The experimentally measured spin distributions for incomplete fusion products have been found to be distinctly different than those observed for complete fusion products. The driving input angular momenta associated with incomplete fusion products have been found to be relatively higher than complete fusion products, and increases with direct {alpha}-multiplicity. It has also been observed that incomplete fusion products are less fed and/or the population of lower spin states are strongly hindered, while complete fusion products indicating strong feeding over a broad spin range.

Flow Field in Swirl-Type Tabular Flame Burner

The flow field in swirl-type tubular flame burners was measured using a Particle Imaging Velocimetry (PIV) system with an easily controlled kerosene droplet tracer generator. Through characterization of the flow field in two burners with different swirl numbers, it was found that the flow is an axisymmetric vortex flow. The tangential component of the velocity is zero at the tube center, and increases proportionally with radius at first, and then falls slowly in a radial direction. The gradient of the tangential component near the vortex center depends significantly on the swirl number and the flow rate. The vortex center oscillates around the tube center in a roughly circular area, and this precession is significantly sensitive to the swirl number. The radius of the precession area shrinks as the swirl number increases. The radial distributions of the axial velocity take a plateau-shape for the weak swirl burner (swirl number S = 0.21), whereas they take an M shape for the strong swirl burner (S = 0.78) with reverse flow in the vicinity of the burner axis. The occurrence of the axial reverse flow is dominated by the swirl number, and is affected by the flow rate as well. Finally, a comparison was made between the swirl numbers calculated with the measured velocity profiles in a cross section and those calculated from the input angular momentum.

Some important aspects of fragment angular momentum in medium energy fission of 238U

Independent isomeric yield ratios of 131Te, 133T and 134I hava been determined at five different energies in the range of 25–44 MeV alpha particle induced fission of 238U using radiochemical and gamma spectrometric techniques. From the independent isomeric yield ratios, fragment angular momenta ( J rms) have been deduced using a statistical model analysis. The J rms were also calculated theoretically based on thermal equilibration of various collective modes after considering the occurrence of multichance fission. These data and the literature data for various fragments in the mass region 126–136 in 238U(α,f), 238U(p,f) and 238U(γ,f) show the following important features: (i) Both the entrance channel excitation energy and input angular momentum affect the fragment angular momentum in the exit channel. (ii) There are two groups of fission products from the point of view of change of fragment angular momentum with increase in excitation energy and input angular momentum. (iii) Fragment angular momentum depends on nuclear structure effect such as shell closure proximity and odd-even effect. (iv) The fragment angular momentum calculated theoretically based on statistical equilibration of various collective modes are in good agreement with the experimental values indicating the validity of such an assumption.

The feeding of the superdeformed band in 148Gd

The feeding pattern of the superdeformed band in 148Gd has been found to remain essentially the same, using the 122Sn ( 30Si, Xn) 152-xGd reaction, by varying the energy of the incident 30Si between 150 and 166 MeV in steps of around 5 MeV, leading to different input angular momenta and excitation energies in the compound nuclear system. This similarity as well as the relative yields of the superdeformed states as a function of beam energy may be understood in terms of the nuclear level density dependence on deformation and the onset of fission. In addition, it has been shown that, at beam energies, the selection of high-energy gamma-rays does not enhance the yield of the superdeformed states.

Effect of entrance channel parameters on fission fragment angular momentum in medium energy fission

Independent isomeric yield ratios of132I were radiochemically determined in alpha particle induced fission of238U in the energy range 25–44 MeV. Fission fragment angular momenta were deduced from the measured isomeric yield ratios using spin dependent statistical model analysis. It was seen that angular momentum of132I increases with increase of excitation energy and angular momentum of the fissioning nucleus. Comparison of the present data on132I in238U(α,f) with the literature data for the same product in238U(p, f) and238U(γ, f) at various excitation energies show that fragment angular momentum strongly depends on the input angular momentum in the range of excitation energy considered. Experimental fragment angular momentum at all excitation energies were seen to be in agreement with the theoretical values calculated based on thermal equilibration of the various collective rotational degrees after considering the occurence of multichance fission. Thus, strong effect of input angular momentum as well as the statistical equilibration among the various collective rotational degrees of freedom in medium energy fission is corroborated.

Studies of superdeformation in the [formula omitted] region

Recent advances in the physics of superdeformed nuclei in the A⋍ 150 mass region are reviewed. Topics covered include the intensity and the feeding pattern of yrast bands as a function of i) compound nucleus excitation energy and input angular momentum, ii) the mass of Gd isotopes and iii) beam-target combinations. Recent data on excited bands in 149Gd and on the deexcitation of the 152Dy band are presented. Plans for new γ-ray spectrometers are discussed and future directions of the field are briefly outlined.

Feeding of the superdeformed yrast band in 149Gd

Abstract The feeding pattern of the superdeformed yrast band in 149 Gd has been found to remain essentially the same, using the 124 Sn+ 30 Si reaction at beam energies of 150, 155 and 160 MeV leading to different input angular momenta and excitation energies in the compound nuclear system. This similarity as well as the relative yields of the superdeformed states as a function of beam energy may be understood in terms of the nuclear level density dependence on deformation and the onset of fission. In addition, it has been shown that, at all three beam energies, the selection of high-energy gamma rays does not enhance the yield of the superdeformed yrast states.

Feeding of discrete-line superdeformed bands at very high spin.

The superdeformed band in $^{149}\mathrm{Gd}$ has been populated with various input angular momenta and excitation energies. These, together with all other available data, indicate that the necessary criterion for populating superdeformed bands is to form cold residual nuclei at spins higher than those where the superdeformed states become yrast. In addition, the decrease in the superdeformed band intensity as it is gated by higher-energy $\ensuremath{\gamma}$ rays does not support the predictions based on a recently proposed feeding mechanism of these states.