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Dongwoo Cha

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School of the Art Institute of Chicago

Duke University

Kansas State University

Armando Marques-Guedes

UNL - New University of Lisbon

Field Museum

Oxford Brookes University

Mohammad Javad Ahmadian

University of Leeds

Suresh Muthusamy

Kongu Engineering College

Titika Dimitroulia

National and Kapodistrian University of Athens

State University of Jakarta

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Papers by Dongwoo Cha

Systematics of theστ−strength in nuclei

Physical review, Aug 1, 1981

The structure of the o~strength function is studied with a zero range interaction. The systematic... more The structure of the o~strength function is studied with a zero range interaction. The systematics of the giant Gamow-Teller state requires an interaction strength for V of about 200-240 MeV fm. While most of the strength goes to a state at high excitation, we find that-20-30% of the strength remains at low excitation energy. The L = 1 states show considerable J splitting, with a major peak at =20 MeV excitation. This peak contains components of J = 0, 1, and 2. Comparison with the experimental L = 1 energy shows that the momentum dependence of the ov interaction is small. NUCLEAR STRUCTURE. Gamow-Teller states and L = 1 states in adjacent odd-odd mass nuclei of double closed shells. TDA and RPA calculation with zero range interaction.

Transverse electromagnetic form factor inC12

Physical review, Apr 1, 1980

We calculate the contribution from the convection current to the recently measured transverse for... more We calculate the contribution from the convection current to the recently measured transverse form factor of the /sup 12/C 2/sup +/ level at 4.44 MeV. The convection current dominates for small momentum transfer and is determined by the B (E2). In this region, theory agrees with experiment. At intermediate momentum transfer, agreement with experiment is only possible assuming a coherent sum of the convection current and magnetization density contributions.

Δ-isobar effects onM2strength inPb208

Physical review, Feb 1, 1984

The strength distribution of the 2/sup -/ states in /sup 208/Pb is calculated including the ..del... more The strength distribution of the 2/sup -/ states in /sup 208/Pb is calculated including the ..delta..-isobar quenching effects. The theoretical B(M2) values up to 8 MeV are dominated by the orbital angular momentum part of the M2 operator. Therefore we find only little quenching in this energy region owing to the ..delta..-particle nucleon-hole admixtures.

GiantM1states in Zr isotopes within the simple shell model

Physical review, Sep 1, 1981

The newly observed M1 states in the (p, p') experiment on the Zr isotopes are considered within t... more The newly observed M1 states in the (p, p') experiment on the Zr isotopes are considered within the simple shell model. The calculation with a constant strength 5 function interaction reproduces the excitation energies and the slight increase of the M1 strength at small momentum transfer with mass number. We need about a factor of 2 quenching to reproduce the cross sections at small angles, which is in accordance with the general finding for magnetic transitions. NUCLEAR STRUCTURE Zr; shell model calculations, 1+ states. Very recently Anantaraman et al. have performed a

The OT₊ strength in nuclei

Nucleon tunnelling model of mass diffusion in deep inelastic heavy ion collisions

Physics Letters B, 1978

We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, ba... more We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, based on a proximity formulation of nucleon tunnelling. The predicted value of the coefficient is consistent with empirical data. The mass diffusion coefficient has a negligible dependence on excitation energy in the physically interesting domain.

Στ+ Strength in Nuclei

Physical Review C, 1983

The sigmatau/sub +/ strength function is studied with the quasiparticle random phase approximatio... more The sigmatau/sub +/ strength function is studied with the quasiparticle random phase approximation. The residual interaction modifies the pairing theory strength function in two ways. The particle-hole interaction reduces the overall strength by about a factor of 2, without shifting strength between different levels. The particle-particle interaction does not affect the overall strength, but shifts part of the strength from the lowest excitation to a higher excitation energy region. By comparing the theory with the observed log(ft) values of the ..beta../sup +/ decay in medium heavy nuclei, we find that an additional quenching is required for the sigmatau/sub +/ mode, similar in magnitude to the additional quenching present in other isovector spin-flip transitions. Finally, we predict that there is a large concentration of the sigmatau/sub +/ strength at higher excitation energy which cannot be observed by the ..beta../sup +/ decay.

Nuclear fission with diffusive dynamics

Physical Review C, 1992

We investigate the dynamics of nuclear fission, assuming purely diffusive motion up to the saddle... more We investigate the dynamics of nuclear fission, assuming purely diffusive motion up to the saddle point. The resulting Smoluchowski equation is solved for conditions appropriate to the ' 0+' Nd~'"Er reaction at 207 MeV. The solution is characterized by an equilibration time~0 for the system to reach steady state, and the fission decay rate in steady state, A. We find that the equilibration time~0 plays a very small role in determining the number of prescission neutrons. The diffusion coefficient extracted from the experimental data is larger than the theoretical in the work of Bush, Bertsch, and Brown by a factor of 5-11.

Implications of the recently discovered Pb208(1+, Ex=5.845 MeV) state for the spin-dependent nuclear interaction

Physical Review C, 1983

Measurements on the newly discovered 1+ state at E"=5. 845 MeV in Pb provide an opportunity to ex... more

Light particle emission in induced16 reactions on C12, Al27, and Au197 at E/A=25 MeV

Physical Review C, 1986

ABSTRACT

Is there evidence of simple relationship among measured yrast energies in even-even nuclei?

Bulletin of the American Physical Society, Feb 14, 2010

The Low-Lying Quadrupole Strength of 30Ne and 32Mg Is Revisited

Journal of the Korean Physical Society, Feb 1, 2006

Spin-dependent Empirical Formula for the Yrast Excitation Energies of the Unnatural Parity States in Even-even Nuclei

새물리, Feb 27, 2010

Empirical predictions of yrast energies in even-even nuclei

arXiv (Cornell University), Jul 19, 2010

The lowest excitation energies of the given multipole J π state (the J π yrast energies) are give... more The lowest excitation energies of the given multipole J π state (the J π yrast energies) are given for even-even nuclei throughout the entire periodic table. The yrast energies were calculated using the recently proposed empirical formula that depends only on the mass number A, and the valence nucleon numbers N p and N n. We provide a complete tabulation and plots of the yrast energies calculated using the empirical formula together with the ones measured for the natural parity states up to 10 + and for the unnatural parity states up to 10 − with the hope of encouraging active study on the possible origin of the relationship between the yrast energies, as revealed by the empirical formula.

The “missing” Gamow-Teller strength and the continuous (p,n) spectra

Springer eBooks, 1985

Microscopic analyses of complete forward angle intermediate energy (p,n)-spectra are presented fo... more Microscopic analyses of complete forward angle intermediate energy (p,n)-spectra are presented for the reactions 90Zr(p,n), 208Pb(p,n) and 42Ca(p,n). It is shown that the whole spectra up to an excitation energy of Ex = 70 MeV are the result of correlated one-particle-one-hole (1p1h) spin-isospin transitions only. The spectra reflect, therefore, the linear spin-isospin response of the target nucleus to the probing (p,n) field. We find a large amount of the “missing” Gamow-Teller strength in the continuum part of the O0 spectrum. Then the total amount of Gamow-Teller strength observed in these nuclei is close to the lower sum rule limit of 3(N-Z).

Implications of Recent Data on Non-mesonic Decay of Light Lambda-hypernuclei

arXiv (Cornell University), Aug 5, 1996

We analyze the recent data on the non-mesonic decays of light Λ-hypernuclei up to 12 Λ C using th... more We analyze the recent data on the non-mesonic decays of light Λ-hypernuclei up to 12 Λ C using the phenomenological model of Block and Dalitz. Fitting the spin-isospin dependent ΛN → N N reaction rates to six data points, we predict the remaining data in reasonable consistency. We find that despite the short-range nature of the ΛN → N N interaction, the non-mesonic decay of p-shell hypernuclei seems to be strongly induced by the p-shell neutrons. Also, the recent data indicate that the ∆I = 1 2 rule, well-proved at the hadronic level, may not be sacred in the nuclear medium and the ∆I = 3 2 interactions seem to be needed to describe the non-mesonic decays of Λ-hypernuclei.

C28fusion reactions at high energies

Physical review, Apr 1, 1987

We present a model based on the direct reaction concept which is able to describe the fusion cros... more We present a model based on the direct reaction concept which is able to describe the fusion cross section consistently throughout the entire range of the measured energies from the sub-barrier region to the very high energies where the cross section decreases linearly as the inverse of the center of mass energy. The model is applied to the fusion reaction of $^{28}\mathrm{Si}$ with $^{12}\mathrm{C}$ where Harmon et al. measured the cross section at energies up to three times the Coulomb barrier.

Theoretical investigation of the 48Ca(n, p)48K and 48Ca(p, n)48Sc reactions at E=200 MeV

Physics Letters B, Jun 1, 1987

Title: Theoretical investigation of the 48 Ca(n, p) 48 K and 48 Ca(p, n) 48 Sc reactions at E=200... more

Macroscopic theory of heavy-ion fusion reactions

Physical review, May 1, 1989

We have studied the heavy-ion fusion reactions by a macroscopic model which was proposed by Berts... more We have studied the heavy-ion fusion reactions by a macroscopic model which was proposed by Bertsch several years ago. It employed the Newtonian dynamics and was constructed in such a way that the essential features of time-dependent Hartree-Fock results could be reproduced. We have applied the model to fusion of light heavy-ion systems leading to the same compound nucleus /sup 56/Ni. It is shown that the model, being incorporated with the angular-momentum-dependent extra-push energy of Swiatecki, can account well for the fusion cross sections up to very high energies where cross section decreases as energy increases, and that the main reason for the decrease is the opening of the low angular momentum window.

Theoretical analysis ofPb208(p,n) spectra at 200 MeV

Physical review, Feb 1, 1989

Forward angle spectra of the /sup 208/Pb(p,n) reaction at E/sub p/ = 200 MeV are analyzed within ... more Forward angle spectra of the /sup 208/Pb(p,n) reaction at E/sub p/ = 200 MeV are analyzed within a microscopic model assuming that the measured cross section is a result of correlated one-particle--one-hole spin-isospin transitions only. We find that the data are essentially in agreement with the strength predictions of the random-phase approximation. We also find that the observed shapes of the spectra can only be explained by introducing a strongly asymmetric damping of the collective spin-flip modes.

Systematics of theστ−strength in nuclei

Physical review, Aug 1, 1981

The structure of the o~strength function is studied with a zero range interaction. The systematic... more The structure of the o~strength function is studied with a zero range interaction. The systematics of the giant Gamow-Teller state requires an interaction strength for V of about 200-240 MeV fm. While most of the strength goes to a state at high excitation, we find that-20-30% of the strength remains at low excitation energy. The L = 1 states show considerable J splitting, with a major peak at =20 MeV excitation. This peak contains components of J = 0, 1, and 2. Comparison with the experimental L = 1 energy shows that the momentum dependence of the ov interaction is small. NUCLEAR STRUCTURE. Gamow-Teller states and L = 1 states in adjacent odd-odd mass nuclei of double closed shells. TDA and RPA calculation with zero range interaction.

Transverse electromagnetic form factor inC12

Physical review, Apr 1, 1980

We calculate the contribution from the convection current to the recently measured transverse for... more We calculate the contribution from the convection current to the recently measured transverse form factor of the /sup 12/C 2/sup +/ level at 4.44 MeV. The convection current dominates for small momentum transfer and is determined by the B (E2). In this region, theory agrees with experiment. At intermediate momentum transfer, agreement with experiment is only possible assuming a coherent sum of the convection current and magnetization density contributions.

Δ-isobar effects onM2strength inPb208

Physical review, Feb 1, 1984

The strength distribution of the 2/sup -/ states in /sup 208/Pb is calculated including the ..del... more The strength distribution of the 2/sup -/ states in /sup 208/Pb is calculated including the ..delta..-isobar quenching effects. The theoretical B(M2) values up to 8 MeV are dominated by the orbital angular momentum part of the M2 operator. Therefore we find only little quenching in this energy region owing to the ..delta..-particle nucleon-hole admixtures.

GiantM1states in Zr isotopes within the simple shell model

Physical review, Sep 1, 1981

The newly observed M1 states in the (p, p') experiment on the Zr isotopes are considered within t... more The newly observed M1 states in the (p, p') experiment on the Zr isotopes are considered within the simple shell model. The calculation with a constant strength 5 function interaction reproduces the excitation energies and the slight increase of the M1 strength at small momentum transfer with mass number. We need about a factor of 2 quenching to reproduce the cross sections at small angles, which is in accordance with the general finding for magnetic transitions. NUCLEAR STRUCTURE Zr; shell model calculations, 1+ states. Very recently Anantaraman et al. have performed a

The OT₊ strength in nuclei

Nucleon tunnelling model of mass diffusion in deep inelastic heavy ion collisions

Physics Letters B, 1978

We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, ba... more We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, based on a proximity formulation of nucleon tunnelling. The predicted value of the coefficient is consistent with empirical data. The mass diffusion coefficient has a negligible dependence on excitation energy in the physically interesting domain.

Στ+ Strength in Nuclei

Physical Review C, 1983

The sigmatau/sub +/ strength function is studied with the quasiparticle random phase approximatio... more The sigmatau/sub +/ strength function is studied with the quasiparticle random phase approximation. The residual interaction modifies the pairing theory strength function in two ways. The particle-hole interaction reduces the overall strength by about a factor of 2, without shifting strength between different levels. The particle-particle interaction does not affect the overall strength, but shifts part of the strength from the lowest excitation to a higher excitation energy region. By comparing the theory with the observed log(ft) values of the ..beta../sup +/ decay in medium heavy nuclei, we find that an additional quenching is required for the sigmatau/sub +/ mode, similar in magnitude to the additional quenching present in other isovector spin-flip transitions. Finally, we predict that there is a large concentration of the sigmatau/sub +/ strength at higher excitation energy which cannot be observed by the ..beta../sup +/ decay.

Nuclear fission with diffusive dynamics

Physical Review C, 1992

We investigate the dynamics of nuclear fission, assuming purely diffusive motion up to the saddle... more We investigate the dynamics of nuclear fission, assuming purely diffusive motion up to the saddle point. The resulting Smoluchowski equation is solved for conditions appropriate to the ' 0+' Nd~'"Er reaction at 207 MeV. The solution is characterized by an equilibration time~0 for the system to reach steady state, and the fission decay rate in steady state, A. We find that the equilibration time~0 plays a very small role in determining the number of prescission neutrons. The diffusion coefficient extracted from the experimental data is larger than the theoretical in the work of Bush, Bertsch, and Brown by a factor of 5-11.

Implications of the recently discovered Pb208(1+, Ex=5.845 MeV) state for the spin-dependent nuclear interaction

Physical Review C, 1983

Measurements on the newly discovered 1+ state at E"=5. 845 MeV in Pb provide an opportunity to ex... more

Light particle emission in induced16 reactions on C12, Al27, and Au197 at E/A=25 MeV

Physical Review C, 1986

ABSTRACT

Is there evidence of simple relationship among measured yrast energies in even-even nuclei?

Bulletin of the American Physical Society, Feb 14, 2010

The Low-Lying Quadrupole Strength of 30Ne and 32Mg Is Revisited

Journal of the Korean Physical Society, Feb 1, 2006

Spin-dependent Empirical Formula for the Yrast Excitation Energies of the Unnatural Parity States in Even-even Nuclei

새물리, Feb 27, 2010

Empirical predictions of yrast energies in even-even nuclei

arXiv (Cornell University), Jul 19, 2010

The lowest excitation energies of the given multipole J π state (the J π yrast energies) are give... more The lowest excitation energies of the given multipole J π state (the J π yrast energies) are given for even-even nuclei throughout the entire periodic table. The yrast energies were calculated using the recently proposed empirical formula that depends only on the mass number A, and the valence nucleon numbers N p and N n. We provide a complete tabulation and plots of the yrast energies calculated using the empirical formula together with the ones measured for the natural parity states up to 10 + and for the unnatural parity states up to 10 − with the hope of encouraging active study on the possible origin of the relationship between the yrast energies, as revealed by the empirical formula.

The “missing” Gamow-Teller strength and the continuous (p,n) spectra

Springer eBooks, 1985

Microscopic analyses of complete forward angle intermediate energy (p,n)-spectra are presented fo... more Microscopic analyses of complete forward angle intermediate energy (p,n)-spectra are presented for the reactions 90Zr(p,n), 208Pb(p,n) and 42Ca(p,n). It is shown that the whole spectra up to an excitation energy of Ex = 70 MeV are the result of correlated one-particle-one-hole (1p1h) spin-isospin transitions only. The spectra reflect, therefore, the linear spin-isospin response of the target nucleus to the probing (p,n) field. We find a large amount of the “missing” Gamow-Teller strength in the continuum part of the O0 spectrum. Then the total amount of Gamow-Teller strength observed in these nuclei is close to the lower sum rule limit of 3(N-Z).

Implications of Recent Data on Non-mesonic Decay of Light Lambda-hypernuclei

arXiv (Cornell University), Aug 5, 1996

We analyze the recent data on the non-mesonic decays of light Λ-hypernuclei up to 12 Λ C using th... more We analyze the recent data on the non-mesonic decays of light Λ-hypernuclei up to 12 Λ C using the phenomenological model of Block and Dalitz. Fitting the spin-isospin dependent ΛN → N N reaction rates to six data points, we predict the remaining data in reasonable consistency. We find that despite the short-range nature of the ΛN → N N interaction, the non-mesonic decay of p-shell hypernuclei seems to be strongly induced by the p-shell neutrons. Also, the recent data indicate that the ∆I = 1 2 rule, well-proved at the hadronic level, may not be sacred in the nuclear medium and the ∆I = 3 2 interactions seem to be needed to describe the non-mesonic decays of Λ-hypernuclei.

C28fusion reactions at high energies

Physical review, Apr 1, 1987

We present a model based on the direct reaction concept which is able to describe the fusion cros... more We present a model based on the direct reaction concept which is able to describe the fusion cross section consistently throughout the entire range of the measured energies from the sub-barrier region to the very high energies where the cross section decreases linearly as the inverse of the center of mass energy. The model is applied to the fusion reaction of $^{28}\mathrm{Si}$ with $^{12}\mathrm{C}$ where Harmon et al. measured the cross section at energies up to three times the Coulomb barrier.

Theoretical investigation of the 48Ca(n, p)48K and 48Ca(p, n)48Sc reactions at E=200 MeV

Physics Letters B, Jun 1, 1987

Title: Theoretical investigation of the 48 Ca(n, p) 48 K and 48 Ca(p, n) 48 Sc reactions at E=200... more

Macroscopic theory of heavy-ion fusion reactions

Physical review, May 1, 1989

We have studied the heavy-ion fusion reactions by a macroscopic model which was proposed by Berts... more We have studied the heavy-ion fusion reactions by a macroscopic model which was proposed by Bertsch several years ago. It employed the Newtonian dynamics and was constructed in such a way that the essential features of time-dependent Hartree-Fock results could be reproduced. We have applied the model to fusion of light heavy-ion systems leading to the same compound nucleus /sup 56/Ni. It is shown that the model, being incorporated with the angular-momentum-dependent extra-push energy of Swiatecki, can account well for the fusion cross sections up to very high energies where cross section decreases as energy increases, and that the main reason for the decrease is the opening of the low angular momentum window.

Theoretical analysis ofPb208(p,n) spectra at 200 MeV

Physical review, Feb 1, 1989

Forward angle spectra of the /sup 208/Pb(p,n) reaction at E/sub p/ = 200 MeV are analyzed within ... more Forward angle spectra of the /sup 208/Pb(p,n) reaction at E/sub p/ = 200 MeV are analyzed within a microscopic model assuming that the measured cross section is a result of correlated one-particle--one-hole spin-isospin transitions only. We find that the data are essentially in agreement with the strength predictions of the random-phase approximation. We also find that the observed shapes of the spectra can only be explained by introducing a strongly asymmetric damping of the collective spin-flip modes.