OAKTrust :: Browsing by Author "Mukhamedzhanov, AM"

Browsing by Author "Mukhamedzhanov, AM"

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Astrophysical factor for the radiative capture reaction alpha+d->Li-6+gamma
(American Physical Society, 1995) Mukhamedzhanov, AM; Schmitt, R. P.; Tribble, Robert E.; Sattarov, A.
We consider the radiative capture process alpha+d-->Li-6+gamma at energies, E(c.m.)less than or equal to 300 keV, that are relevant for astrophysical processes. Due to the peripheral character of the reaction, the overall normalization of the astrophysical factor S-24 is entirely governed by one quantity, the asymptotic normalization coefficient C-01 for Li-6-->alpha+d. Using the recently well established value for this constant C-01=2.3+/-0.12 fm(-1/2), we calculated S-24 taking into account both E1 and E2 contributions. Our recommended value for S-24 is 2.57 MeV nb at the most effective energy for the capture reaction in astrophysical processes, E(c.m.)=70 keV, which gives a reaction rate 0.036 cm(3) mole(-1) s(-1) at the temperature 0.8x10(9) K. We found a significant energy dependence of S-24 at astrophysical energies. At energies of less than 110 keV, the E1 component dominates over the E2 component. AtE(c.m.)=70 keV, the E1 contribution to the total transition is about 58%.
Astrophysical S factor for Be-9(p,gamma)B-10
(American Physical Society, 1999) Sattarov, A.; Mukhamedzhanov, AM; Azhari, A.; Gagliardi, Carl A.; Trache, L.; Tribble, Robert E.
The Be-9(p, gamma) B-10 reaction plays an important role in primordial and stellar nucleosynthesis of light elements in the p shell, but the energy dependence of S(E) has not been well understood. We reanalyze the existing Be-9(p, gamma) B-10 experimental data within the framework of the R-matrix method. The direct capture part of the S factor is calculated using the experimentally measured asymptotic normalization coefficients for B-10 --> Be-9 + p. The fitted parameters of the low-lying B-10 resonances are also required to be consistent with previous measurements of Li-6(alpha, gamma) log. A good simultaneous fit to both radiative capture reactions is found, in contrast to previous analyses. These results demonstrate that experimentally measured asymptotic normalization coefficients, coupled to the R-matrix method, can provide a reasonable determination of direct radiative capture rates, even when the captured proton is tightly bound in the final nucleus. [S0556-2813(99)03608-0].
Astrophysical S factor for C-13(p,gamma)N-14 and asymptotic normalization coefficients
(American Physical Society, 2002) Mukhamedzhanov, AM; Azhari, A.; Burjan, V.; Gagliardi, Carl A.; Kroha, V.; Sattarov, A.; Tang, X.; Trache, L.; Tribble, Robert E.
We reanalyze the C-13(p,gamma)N-14 radiative capture reaction within the R-matrix approach. The low-energy astrophysical S factor has important contributions from both resonant and onresonant captures. The normalization of the nonresonant component of the transition to a particular N-14 bound state is expressed in terms of the asymptotic normalization coefficient (ANC). In the analysis we use the experimental ANC's inferred from the C-13(N-14,C-13)N-14 and C-13(He-3,d)N-14 reactions. The fits of the calculated S factors to the experimental data are sensitive to the ANC values and are used to test the extracted ANC's. We find that for transitions to all the states in N-14, except the third excited state, the ANC's determined from the transfer reactions provide the best fit. The astrophysical factor we obtain, S(0)=7.7+/-1.1 keV b, is in excellent agreement with previous results.
Asymptotic normalization coefficients and the Be-7(p, gamma)B-8 astrophysical S factor
(American Physical Society, 2001) Azhari, A.; Burjan, V.; Carstoiu, F.; Gagliardi, Carl A.; Kroha, V.; Mukhamedzhanov, AM; Nunes, FM; Tang, X.; Trache, L.; Tribble, Robert E.
We consider the results of two proton transfer reactions, B-10(Be-7, B-8)Be-9 and N-14(Be-7, B-8)C-13, to obtain a weighted average of the measured asymptotic normalization coefficients for the virtual transition 7Be +pB-8. These coefficients specify the amplitude of the tail of the B-8 overlap function in the Be-7+p channel, and are used to calculate the astrophysical S factor for the direct capture reaction Be-7(p, gamma)B-8 at solar energies, S-17(0) In light of recent improvements in the determination of optical-model potentials, including detailed understanding of the correlations between the DWBA analyses of the two experiments, and a new experimental measurement of the asymptotic normalization coefficients for the virtual transition C-13+pN-14, we report a weighted average asymptotic normalization coefficient of C-p3/2(2)= 0.388+/-0.039 fm(-1) for B-8Be-7+p, which implies S-17(0)= 17.3+/-1.8 eV b.
Asymptotic normalization coefficients for 14N+p -> O-15 and the astrophysical S factor for N-14(p, gamma)O-15
(American Physical Society, 2003) Mukhamedzhanov, AM; Bem, P.; Brown, BA; Burjan, V.; Gagliardi, Carl A.; Kroha, V.; Novak, J.; Nunes, FM; Paskor, S.; Pirlepesov, F.; Simeckova, E.; Tribble, Robert E.; Vincour, J.
The N-14(p,gamma)O-15 reaction, which controls energy production in the CNO cycle, has contributions from both resonance and direct captures to the ground and excited states. The overall normalization of the direct captures is defined by the corresponding asymptotic normalization coefficients (ANCs). Especially important is the ANC for the subthreshold state in O-15 at -0.504 keV since direct capture through this state dominates the reaction rate at stellar energies. In order to determine the ANCs for N-14+p-->O-15, the N-14(He-3,d)O-15 proton transfer reaction has been measured at an incident energy of 26.3 MeV. Angular distributions for proton transfer to the ground and five excited states were obtained. ANCs were then extracted from comparison to both distorted-wave Born approximation and coupled-channels Born approximation calculations. Using these ANCs, we calculated the astrophysical factor and reaction rates for N-14(p,gamma)O-15. Our analysis favors a low value for the astrophysical factor.
Asymptotic normalization coefficients for B-10->Be-9+p
(American Physical Society, 1997) Mukhamedzhanov, AM; Clark, HL; Gagliardi, Carl A.; Lui, YW; Trache, L.; Tribble, Robert E.; Xu, HM; Zhou, XG; Burjan, V.; Cejpek, J.; Kroha, V.; Carstoiu, F.
The differential cross sections for the reactions Be-9(B-10, B-10)Be-9 and Be-9(B-10,Be-9)B-10 have been measured at an incident energy of 100 MeV. The elastic scattering data have been used to determine the optical model parameters for the Be-9+B-10 system at this energy. These parameters are then used in distorted-wave Born approximation (DWBA) calculations to predict the cross sections of the Be-9(B-10,Be-9)B-10 proton exchange reaction, populating the ground and low-lying states in B-10. By normalizing the theoretical DWBA proton exchange cross sections to the experimental ones, the asymptotic normalization coefficients (ANC's), defining the normalization of the tail of the B-10 bound state wave functions in the two-particle channel Be-9+p, have been found. The ANC for the virtual decay B-10(g.s.)-->Be-9+p will be used in an analysis of the B-10(Be-7,B-8)Be-9 reaction to extract the ANC's for B-8-->Be-7+p. These ANC's determine the normalization of the Be-7(p,gamma)B-8 radiative capture cross section at very low energies, which is crucially important for nuclear astrophysics.
Asymptotic normalization coefficients for B-8 -> Be-7+p from a study of Li-8 -> Li-7+n
(American Physical Society, 2003) Trache, L.; Azhari, A.; Carstoiu, F.; Clark, HL; Gagliardi, Carl A.; Lui, YW; Mukhamedzhanov, AM; Tang, X.; Timofeyuk, N.; Tribble, Robert E.
Asymptotic normalization coefficients (ANCs) for Li-8-->Li-7+n have been extracted from the neutron transfer reaction C-13(Li-7,Li-8)C-12 at 63 MeV. These are related to the ANCs in B-8-->Be-7 + p using charge symmetry. We extract ANCs for B-8 which are in very good agreement with those inferred from proton transfer and breakup experiments. We have also separated the contributions from the p(1/2) and p(3/2) components in the transfer. We find the astrophysical factor for the Be-7(p, gamma)B-8 reaction to be S-17( 0) = 17.6+/-1.7 eV b. This is the first time that the rate of a direct capture reaction of astrophysical interest has been determined through a measurement of the ANCs in the mirror system.
Asymptotic normalization coefficients for C-13+p -> N-14
(American Physical Society, 1998) Trache, L.; Azhari, A.; Clark, HL; Gagliardi, Carl A.; Lui, YW; Mukhamedzhanov, AM; Tribble, Robert E.; Carstoiu, F.
The C-13(N-14,C-13)N-14 proton exchange reaction has been measured at an incident energy of 162 MeV. Angular distributions were obtained for proton transfer to the ground and low-lying excited states in N-14. Elastic scattering of N-14 On C-13 also was measured out to the rainbow angle region in order to find reliable optical model potentials. Asymptotic normalization coefficients for the system C-13+p --> N-14 have been found for the ground state and the excited states at 2.313, 3.948, 5.106, and 5.834 MeV in N-14. These asymptotic normalization coefficients will be used in a determination of the S factor for Be-7(p, gamma)B-8 at solar energies from a measurement of the proton transfer reaction N-14(Be-7,B-8)C-13. [S0556-2813(98)03111-2].
Asymptotic normalization coefficients for N-14 C-13+p from C-13(He-3,d)N-14
(American Physical Society, 2000) Bem, P.; Burjan, V.; Kroha, V.; Novak, J.; Piskor, S.; Simeckova, E.; Vincour, J.; Gagliardi, Carl A.; Mukhamedzhanov, AM; Tribble, Robert E.
The C-13(He-3,d) N-14 proton transfer reaction has been measured at an incident energy of 26.3 MeV. Angular distributions for proton transfer to the ground state and excited states at 2.313 and 3.948 MeV in N-14 are analyzed within the framework of the modified DWBA. Asymptotic normalization coefficients (ANC's) defining the amplitude of the tails of the N-14 bound-state wave functions in the C-13+p channel are extracted that are in excellent agreement with values found previously with the C-13(N-14,C-13)N-14 reaction. We conclude that C-p1/2(2)=18.2(9) fm(-1) and C-p3/2(2) = 0.91(14) fm(-1) for the virtual decay N-14(g.s.) --> C-13+p. These are necessary for the analysis of the N-14(Be-7, B-8)C-13 and N-14( C-11, N-12) C-13 reactions to extract the ANC's far Be-7+p --> B-8 and C-11+p-->N-12, which determine the direct radiative capture cross sections Be-7(p,gamma)B-8 and C-11(p,gamma)N-12 at astrophysical energies.
Asymptotic normalization coefficients from the (20)Ne((3)He, d)(21)Na reaction and astrophysical factor for (20)Ne(p,gamma)(21)Na
(American Physical Society, 2006) Mukhamedzhanov, AM; Bem, P.; Burjan, V.; Gagliardi, Carl A.; Irgaziev, BF; Kroha, V.; Novak, J.; Piskor, S.; Simeckova, E.; Tribble, Robert E.; Vesely, F.; Vincour, J.
The (20)Ne(p,gamma)(21)Na reaction rate at stellar energies is dominated by capture to the ground state through the tail of a subthreshold resonance state at an excitation energy of 2425 keV in (21)Na. Both resonant and direct capture contribute to the reaction rate while direct captures to other bound states are negligible. The overall normalization of direct capture to the subthreshold state is determined by the asymptotic normalization coefficient (ANC). Simultaneously this ANC determines the proton partial width of the subthreshold resonance state. To determine the ANC, the (20)Ne((3)He,d)(21)Na proton transfer reaction has been measured, at an incident energy of 25.83 MeV. Angular distributions for proton transfer to the ground and first three excited states were measured, and ANCs were then extracted from comparison with distorted-wave Born approximation calculations. Using these ANCs, we calculated the astrophysical factor for (20)Ne(p,gamma)(21)Na. Our total astrophysical factor is S(0)=5900 +/- 1200 keV b. Our analysis confirms that only nonresonant and resonant captures through the subthreshold state are important.
Asymptotic normalization coefficients, spectroscopic factors, and direct radiative capture rates
(American Physical Society, 2001) Mukhamedzhanov, AM; Gagliardi, Carl A.; Tribble, Robert E.
We compare the use of asymptotic normalization coefficients (ANC's) and spectroscopic factors determined from peripheral transfer reactions for determining the overall normalization of peripheral direct radiative capture reaction processes. We demonstrate that ANC's provide a natural way to parametrize the rates of both peripheral transfer and direct capture reactions. Furthermore, ANC's inferred from one reaction may be used in the analysis of a second reaction without further knowledge regarding their origin, and independent measurements of a given ANC may be combined to give an overall "best value" in a straightforward manner. In contrast, a spectroscopic factor derived from analysis of a peripheral transfer reaction can only be used in subsequent calculations if one has detailed knowledge of the single-particle bound state orbital that was assumed when the spectroscopic factor was obtained.
Connection between asymptotic normalization coefficients, subthreshold bound states, and resonances
(American Physical Society, 1999) Mukhamedzhanov, AM; Tribble, Robert E.
We present here useful relations showing the connection between the asymptotic normalization coefficient (ANC) and the fitting parameters in K- and R-matrix theory methods which are often used when analyzing low energy experimental data. It is shown that the ANC of a subthreshold bound state defines thr normalization of both direct radiative capture leading to this state and resonance capture in which the start: behaves like a subthreshold resonance. A determination of the appropriate ANC(s) thus offers an alternative method for finding the strength of these types of capture reactions, both of which are important in nuclear astrophysics. [S0556-2813(99)01006-7].
Determination of the astrophysical S factor for C-11(p,gamma)N-12 from the N-12 -> C-11+p asymptotic normalization coefficient
(American Physical Society, 2003) Tang, XD; Azhari, A.; Gagliardi, Carl A.; Mukhamedzhanov, AM; Pirlepesov, F.; Trache, L.; Tribble, Robert E.; Burjan, V.; Kroha, V.; Carstoiu, F.
The evolution of very low-metallicity, massive stars depends critically on the amount of CNO nuclei that they produce. Alternative paths from the slow 3alpha process to produce CNO seed nuclei could change their fate. The C-11(p,gamma)N-12 reaction is an important branch point in one such alternative path. At energies appropriate to stellar evolution of very low-metallicity, massive stars, nonresonant capture dominates the reaction rate. We have determined the astrophysical S factor for the C-11(p,gamma)N-12 reaction using the asymptotic normalization coefficient for N-12-->C-11+p to fix the nonresonant capture rate. In our experiment, a 110 MeV C-11 radioactive beam was used to study the(14)N(C-11,N-12)C-13 peripheral transfer reaction and the asymptotic normalization coefficient, (C-peff(12N))(2)=(C-p1/2(12N))(2)+(C-p3/2(12N))(2)=1.73+/-0.25 fm(-1), was extracted from the measured cross section. The contributions from the second resonance and interference effects were estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest value for Gamma(gamma). We find the S factor for C-11(p,gamma)N-12 is significantly larger than previous estimates. As a result, the required density for it to contribute is reduced, and more CNO material may be produced.
Determination of the direct capture contribution for N-13(p,gamma)O-14 from the O-14 -> N-13+p asymptotic normalization coefficient
(American Physical Society, 2004) Tang, XD; Azhari, A.; Fu, CB; Gagliardi, Carl A.; Mukhamedzhanov, AM; Pirlepesov, F.; Trache, L.; Tribble, Robert E.; Burjan, V.; Kroha, V.; Carstoiu, F.; Irgaziev, BF.
N-13(p, gamma)O-14 is one of the key reactions which trigger the onset of the hot CNO cycle. This transition occurs when the proton capture rate on 13N is faster, due to increasing stellar temperature (greater than or equal to10(9) K), than the N-13 beta-decay rate. The rate of this reaction is dominated by the resonant capture through the first excited state of O-14 (E-r=0.528 MeV). However, through constructive interference, direct capture below the resonance makes a non-negligible contribution to the reaction rate. We have determined this direct contribution by measuring the asymptotic normalization coefficient for O-14 --> N-13+p. In our experiment, an 11.8 MeV/nucleon N-13 radioactive beam was used to study the N-14(N-13, O-14)C-13 peripheral transfer reaction, and the asymptotic normalization coefficient, (C-p1/2(14O))(2)=29.0+/-4.3 fm(-1), was extracted from the measured cross section. The radiative capture cross section was estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest resonance parameters. We find the S factor for N-13(p, gamma)O-14 to be larger than previous estimates. Consequently, the transition from the cold to hot CNO cycle for novae would be controlled by the slowest proton capture reaction N-14(p, gamma)O-15.
Determination of the S-18 astrophysical factor for B-8(p,gamma)C-9 from the breakup of C-9 at intermediate energies
(American Physical Society, 2002) Trache, L.; Carstoiu, F.; Mukhamedzhanov, AM; Tribble, Robert E.
We have used existing data on the one-proton-removal cross section of C-9 at 285 MeV/nucleon and Glauber model calculations to extract the asymptotic normalization coefficient for the wave function of the last proton in the ground state of C-9. The calculations are done first using folded potentials starting from two different effective nucleon-nucleon interactions and second in the optical limit using three nucleon-nucleon interactions, and the results are found to be consistent, with no new parameters adjusted. We find C-2(p(3/2))+C-2(p(1/2))=1.22+/-0.13 fm(-1). From this result we obtain the astrophysical factor for the proton radiative capture reaction B-8(p,gamma)C-9 as S-18(0)=46+/-6 eV b. The calculated energy dependence of the astrophysical S factor for the energy region E-c.m.=0-0.8 MeV and the reaction rates for T-9=0-1 are included.
Elastic scattering of the proton drip-line nucleus F-17
(American Physical Society, 2005) Blackmon, JC; Carstoiu, F.; Trache, L.; Bardayan, DW; Brune, CR; Gagliardi, Carl A.; Greife, U.; Gross, CJ; Jewett, CC; Kozub, R. L.; Lewis, TA; Liang, JF; Moazen, BH; Mukhamedzhanov, AM; Nesaraja, CD; Nunes, FM; Parker, PD; Sahin, L.; Scott, JP; Shapira, D.; Smith, MS; Thomas, JS; Tribble, Robert E.
Precision data have been obtained for the elastic scattering of F-17 on C-12 and N-14 at 10 MeV/nucleon to clarify the reaction mechanism for loosely bound nuclei at low energies and to assess the validity of a double-folding procedure to predict optical model potentials for use in indirect methods for nuclear astrophysics. The double-folding procedure incorporates density and energy-dependent effective nucleon-nucleon interactions with realistic densities consistent with experimentally determined asymptotic normalization coefficients. The derived potentials provide an excellent description of the data and point to a complete dominance of absorption at the barrier. A semiclassical analysis in terms of multireflection barrier-internal barrier series expansion of the scattering amplitude shows that only the barrier component survives in the scattering process, pointing to the peripheral character of the reactions.
Long-range behavior of the optical potential for the elastic scattering of charged composite particles
(Physical Review A - Atomic, Molecular, and Optical Physics, 1995) Alt, EO; Mukhamedzhanov, AM
The N-14(Be-7,B-8)C-13 reaction and the Be-7(p,gamma)B-8 S factor
(American Physical Society, 1999) Azhari, A.; Burjan, V.; Carstoiu, F.; Gagliardi, Carl A.; Kroha, V.; Mukhamedzhanov, AM; Tang, X.; Trache, L.; Tribble, Robert E.
The N-14(Be-7,B-8)C-13 reaction was studied using an 85 MeV Be-7 radioactive beam. The asymptotic normalization coefficients for the virtual transitions Be-7+pB-8 were determined from the measured cross section. These coefficients specify the amplitude of the tail of the B-8 overlap function in the Be-7+ p channel, and were used to calculate the astrophysical S factor for the direct capture reaction Be-7(p,gamma)B-8 at solar energies S-17(0). We find that S-17(0) = 16.6 +/- 1.9 eV b. [S0556-2813(99)01111-5].
Optical model potentials involving loosely bound p-shell nuclei around 10 MeV/nucleon
(American Physical Society, 2000) Trache, L.; Azhari, A.; Clark, HL; Gagliardi, Carl A.; Lui, YW; Mukhamedzhanov, AM; Tribble, Robert E.; Carstoiu, F.
We present the results of a search for optical model potentials for use in the description of elastic scattering and transfer reactions involving stable and radioactive p-shell nuclei. This was done in connection with our program to use transfer reactions to obtain data for nuclear astrophysics, in particular for the determination of the astrophysical S-17 factor for Be-7(p, gamma)B-8 using two (Be-7,B-8) proton transfer reactions. Elastic scattering was measured using Li-7, B-10, C-13 and N-14 projectiles on Be-9 and C-13 targets at or about E/A = 10 MeV/nucleon. Woods-Saxon type optical model potentials were extracted and are compared with potentials obtained from a microscopic double folding model. Several nucleon-nucleon effective interactions were used: M3Y with zero range and finite range exchange term, two density dependent versions of M3Y and the effective interaction of Jeukenne, Lejeune, and Mahaux. We find that the latter one, which has an independent imaginary part, gives the best description. Furthermore, we find the renormalization constant for the real part of the folding potential to be nearly independent of the projectile-target combination at this energy and that no renormalization is needed for the imaginary part. From this analysis, we are able to eliminate an ambiguity in optical model parameters and thus better determine the asymptotic normalization coefficient for B-10-->B-9 +p. Finally we use these results to find optical model potentials for unstable nuclei with emphasis on the reliability of the description they provide for peripheral proton transfer reactions. We discuss the uncertainty introduced by the procedure in the prediction of the distorted wave Born approximation cross sections for the (Be-7,B-8) reactions used in extracting the astrophysical factor S-17(0).
Possibility to Determine the Astrophysical S-Factor for the Be-7(p,gamma)b-8 Radiative-Capture from Analysis of the Be-7(he-3,d)b-8 Reaction
(American Physical Society, 1995) Mukhamedzhanov, AM; Tribble, Robert E.; imofeyuk, N. K.