Proton Capture

Atomic nuclear clusters play a crucial role in nucleosynthesis in the universe, especially in the main sequence of heavy element synthesis. Cluster aspects in nucleosynthesis are briefly discussed based on a Cluster-Nucleosynthesis Diagram proposed here. Two recent topics on critical a-induced thermonuclear reactions are reviewed; the first one is the 12C(~, ~)160 reaction for the He burning stage and the other one is the 8Li(e, n)llB reaction for the big bang nucleosynthesis. A new field of nuclear astrophysics using radioactive nuclear beams is also discussed. As the stars evolve, the nucleosynthesis processes go faster, and finally they come to the point of a gravitational collapse if the mass of the star is large, which leads to a supernova explosion. Or, it may stop by becoming a white dwarf if the mass is small. Each step of the stellar evolution is characterized by a specific nucleosynthesis. Thus, one can test critically the standard model of the stellar evolution by studying the nuclear reaction processes which are not well known yet. These works eventually give enough nuclear physics information to deduce the information on the stellar environment of interest. These are the main subjects of nuclear astrophysics. Of course, the nucleosynthesis scenarios have been checked by the astronomical observations, meteorite studies, cosmic rays, etc.

Nuclear reactions playa crucial role in the evolution of the universe. Various astronomical observations of nuclear effects provide important clues and tests for understanding of the mechanism of stellar events and the evolution of the universe. The explosive phenomena in the universe inevitably involve radioactive nuclei. Nucleosynthesis in big bang models and stellar models are discussed critically, in particular the key nuclear reactions that involve radioactive nuclei. Also discussed is how new facets recently attained in the nuclear physics of unstable nuclei alter the nucleosynthesis scenarios. The scope of the new research field developed with radioactive nuclear beams in nuclear astrophysics is also discussed. Contents 6.1. Hot-eND cycle 6.2. Onset of the rp-process 6.3. Early stage of the rp-process 6.4. High temperature rp-process § 7. Isotopic anomalies and gamma ray observations § 8. Heavy element synthesis and cosmochronology § 9. Prospects of nuclear astrophysics with radioactive nuclear beams 9.1. The new technology of radioactive nuclear beams 9.2. The scope of the physics with radioactive nuclear beams

Measurements of scattering of 7 Be at 87 MeV on a melamine (C3N6H6) target and of 8 B at 95 MeV on C were performed. For 7 Be the angular range was extended over previous measurements and monitoring of the intensity of the radioactive beam was improved. The measurements allowed us to check and improve the optical model potentials used in the incoming and outgoing channels for the analysis of existing data on the proton transfer reaction 14 N(7 Be, 8 B) 13 C. The results lead to an updated determination of the asymptotic normalization coefficient for the virtual decay 8 B → 7 Be + p. We find a slightly larger value, C 2 tot (8 B) = 0.466 ± 0.047 fm −1 , for the melamine target. This implies an astrophysical factor, S17(0) = 18.0 ± 1.8 eV•b, for the solar neutrino generating reaction 7 Be(p,γ) 8 B.

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which specify the normalization of the tail of the nuclear overlap function, determine S-factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions involving both stable and radioactive beams have been used to measure ANCs. Tests have demonstrated that ANCs determined from proton transfer reactions can be used to calculate astrophysical direct capture rates to within 9%. The 10 B(7 Be, 8 B) 9 Be and 14 N(7 Be, 8 B) 13 C reactions have been used to measure the ANC appropriate for determining the 7 Be(p, γ) 8 B rate, and the 14 N(11 C, 12 N) 13 C reaction has been used to measure the ANC required to calculate the 11 C(p, γ) 12 N rate.

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which specify the normalization of the tail of the nuclear overlap function, determine S-factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions involving both stable and radioactive beams have been used to measure ANCs. Tests have demonstrated that ANCs determined from proton transfer reactions can be used to calculate astrophysical direct capture rates to within 9%. The 10 B(7 Be, 8 B) 9 Be and 14 N(7 Be, 8 B) 13 C reactions have been used to measure the ANC appropriate for determining the 7 Be(p, γ) 8 B rate, and the 14 N(11 C, 12 N) 13 C reaction has been used to measure the ANC required to calculate the 11 C(p, γ) 12 N rate.

The 22Na(3He,d)23Mg reaction has been investigated at E~ = 30 MeV using a 22Na implanted foil target and a Q3D spectrograph of high energy resolution. The angular distributions of 23 deuteron groups corresponding to nineteen Mg levels between E x = 6236 and 8076 keV have been measured at angles 01a b = 7.5 ° to 31 ° and lead to their proton spectroscopic factors using DWBA analysis. The 22Na(p,,y)23Mg resonance strengths for unbound states near the proton threshold have been deduced. The resulting reaction rates significantly reduce previous uncertainties.

It is known from the scattering theory that the phase-shift of elastic collision does not provide a unique potential to describe the bound state of the two-particle system. The bound state wave function is the most crucial input for various nuclear processes bearing astrophysical significance. In this paper, we emphasize on the important role of the asymptotic normalization coefficients for description of the $^{13}\rm{N}\longrightarrow {^{13}\rm{C}}+\beta^++\nu_e$ reaction. Using experimental data of the elastic scattering phase-shift of proton and neutron on $^{12}\rm{C}$ nucleus, we find the asymptotic normalization coefficients which determine the tail of bound state wave function. This allows us to correctly calculate the wave functions of $^{13}\rm{N}$ and $^{13}\rm{C}$ nuclei within the cluster model approach. These wave functions are applied to determine the nuclear matrix element for calculation of the ${\rm log} ft$ values and half-life of $\beta^+$ decay of $^{13}\rm{N}$....

The 12 C(12 C, 2n) 22 Mg reaction was measured with the CLARION array and the RMS separator at the Holifield Facility of Oak Ridge National Laboratory. This experiment was performed to gather more information on the excited states in 22 Mg, which might be of relevance to recent radioactive ion beam measurements of the astrophysically important 21 Na(p, c) 22 Mg reaction. The results are compared to direct measurements, transfer experiments and a competing experiment performed with Gammasphere.

The 12 C(12 C, 2n) 22 Mg reaction was measured with the CLARION array and the RMS separator at the Holifield Facility of Oak Ridge National Laboratory. This experiment was performed to gather more information on the excited states in 22 Mg, which might be of relevance to recent radioactive ion beam measurements of the astrophysically important 21 Na(p, c) 22 Mg reaction. The results are compared to direct measurements, transfer experiments and a competing experiment performed with Gammasphere.

Beams extracted from ECR ion sources are a mixture of several ions and many charge states. Solenoid focusing of such beams can maintain cylindrical symmetry and allow longitudinal motion of secondary electrons for full space charge compensation. Electrostatic focusing does not create multiple intermediate focii of ions with differing charge-to-mass ratios, yet locally destroys space charge compensation. To explore these issues, an electrostatic triplet was installed in place of the present solenoid lens as the first focusing element of the "Artemis" ECR ion source (RT-ECR) beam line. It was then removed and re-installed under the superconducting ECR ion source (SC-ECR) for more extensive testing. This test installation was successful with significant beam intensity gains achieved over the solenoid configuration. Motivations for and results of these tests are discussed.

The masses of the radioactive nuclei 22 Mg and 22 Na have been measured with the Canadian Penning trap on-line mass spectrometer to a precision of 3 ϫ 10 −8 and 1 ϫ 10 −8 , respectively. A Q EC value of 4124.39͑73͒ keV for the superallowed ␤ decay of 22 Mg is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision and is found to be consistent with the existing precision data set of superallowed Fermi emitters. This provides an important test of the isospin symmetry-breaking corrections. If the mass of 22 Mg determined here is used in the calibration of a recent 21 Na͑p , ␥͒ 22 Mg measurement, part of the discrepancy observed in that measurement is removed.

We discuss the importance of the spectroscopic properties of the resonances of 12C just above the 3a-threshold, and review the existing experimental information of this region with emphasis on O+ and 2+ states. A new experimental approach for studying the @-decays of 12B and 121V is presented based on techniques developed in the context of R.adioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given.

An excitation function for resonance elastic scattering of ␣ particles on 18 O and 18 Ne was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7 MeV in 22 Ne. Twelve of them are new. General features of ␣-cluster bands in 22 Ne are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11 − level in 22 Ne, as well as for the isotopic shift of the cluster levels in 22 Mg, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of ␣-cluster states in mirror N Z nuclei.

An excitation function for resonance elastic scattering of ␣ particles on 18 O and 18 Ne was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7 MeV in 22 Ne. Twelve of them are new. General features of ␣-cluster bands in 22 Ne are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11 − level in 22 Ne, as well as for the isotopic shift of the cluster levels in 22 Mg, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of ␣-cluster states in mirror N Z nuclei.

An excitation function for resonance elastic scattering of ␣ particles on 18 O and 18 Ne was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7 MeV in 22 Ne. Twelve of them are new. General features of ␣-cluster bands in 22 Ne are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11 − level in 22 Ne, as well as for the isotopic shift of the cluster levels in 22 Mg, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of ␣-cluster states in mirror N Z nuclei.

The strengths of low-energy resonances in 14 N(␣,␥) 18 F at 573 keV and 1136 keV have been measured using an activation method. In addition, their relative strength and the energy of the lower resonance have been determined in a prompt ␥-ray experiment. The results of these measurements are used to reevaluate the stellar reaction rate of 14 N(␣,␥) 18 F. The present reaction rate at temperatures of astrophysical interest is a factor of 2 smaller than previously reported.

The excitation energy of the first excited state in 23AI was determined by the 24Mg(7Li, 'He) reaction. The state is observed to be at 460 i 60 keV and belongs to the first excited A = 23 isospin quartet. The results are used to compute the coefficients of the isobaric multiplet mass equation. The influence of this state, a resonance in the **Mg(p, y) channel, on the reaction flow in rp-process nucleosynthesis is discussed in detail. NUCLEAR REACTIONS 24Mg(7Li, 'He), E = 191 MeV; measured v(E(s(He)); deduced E '*Mg(p, Y)'~AI stellar reaction rate, isobaric mass multiplet equation parameters. 23Al deduced levels.

Ë-factors for direct capture reactions can be found at astrophysical energies from asymptotic normalization coefficients which provide the normalization of the tail of the overlap function. For example the overlap for B Be + Ô defines the Ë-factor for Be (Ô) B. Peripheral transfer reactions offer a technique to determine these asymptotic normalization coefficients. As a test of the technique, the ½ O(¿ He, µ ½ F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ½ F. The Ë-factors for ½ O(Ô) ½ F calculated from these ½ F ½ O + Ô asymptotic normalization coefficients are found to be in very good agreement with recent measurements. Following the same technique, the ½¼ B(Be, B) Be and ½ N(Be, B) ½¿ C reactions have been used to measure the asymptotic normalization coefficient for Be(Ô) B. This result provides an indirect determination of ˽ (0).

The 14 N(7 Be, 8 B) 13 C reaction was studied using an 85 MeV 7 Be radioactive beam. The asymptotic normalization coefficients for the virtual transitions 7 Beϩp↔ 8 B were determined from the measured cross section. These coefficients specify the amplitude of the tail of the 8 B overlap function in the 7 Beϩp channel, and were used to calculate the astrophysical S factor for the direct capture reaction 7 Be(p,␥) 8 B at solar energies S 17 (0). We find that S 17 (0)ϭ16.6Ϯ1.9 eV b. ͓S0556-2813͑99͒01111-5͔

The 14 N(p,␥) 15 O 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 ͑ANCs͒. Especially important is the ANC for the subthreshold state in 15 O at Ϫ0.504 keV since direct capture through this state dominates the reaction rate at stellar energies. In order to determine the ANCs for 14 Nϩp→ 15 O, the 14 N(3 He,d) 15 O 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 14 N(p,␥) 15 O. Our analysis favors a low value for the astrophysical factor.

The '8Ne(a,p)21 Na reaction is of great importance to Nuclear Astrophysics as it provides a route to breakout from the hot-CNO cycle, possibly leading to the formation of the elements up to A100. This particular reaction has been studied using a '8 Ne beam, available at Louvain-la-Neuve, together with a helium gas target system previously developed for the investigation of (a,p) reactions with a radioactive beam. This study covered an energy region from-1.7-2.9 MeV in the centre of mass frame of the '8Ne+c system. A change in the detector geometry resulted in an increase in the detection efficiency and significantly reduced the proton background that hindered the previous measurement. A direct measurement of the energy loss of the '8Ne beam, as it passed through He gas, was undertaken to reduce a major source of uncertainty in the determination of the stellar reaction rate. This showed a linear relationship, between beam energy and distance traversed within the gas, over an energy scan of 8-16 MeV and gave an energy loss of (1.55 ± 0.01) MeV/cm and (15.96 + 0.02) MeV for the energy of the 18Ne beam upon entry into the gas. Firstly I would like to thank my supervisor, Alan Shotter for his support and patience throughout this project. My thanks go to my second supervisor, Phil Woods for his support. Special thanks go to Tom Davinson whose guidance and encouragement was greatly appreciated. I would also like to thank Will Bradfield-Smith for our useful discussions and Gordon Turnbull for his technical help with the experimental preparation. My thanks also go to our collaborators in Belgium, especially Pierre Leleux, for their invaluable contribution to this work. Special thanks go to my closest friend, Mandeep for her continuous support and encouragement throughout my time in Edinburgh. Thanks go to my other friends, especially Alessia, Alison, Chris, Fred, Karsten and Steve for creating a good working atmosphere and to my former flatmate, David for making life outside work entertaining. Thanks also go to my family (Mum, Dad and Daniel) for all their support. I wish to thank Gene Roddenberry for creating Star Trek which inspired me to study physics. Finally I wish to acknowledge the Engineering and Physical Sciences Research Council (EPSRC) for funding this project.

Coupled Reaction Channel Calculations have been performed for transitions to ground and first excited states of 17 F and 17 O at deuteron incident energies from E d =2.279 MeV up to 3.186 MeV. The n+ 16 O and p+ 16 O astrophysical direct capture cross sections have been calculated using the spectroscopic factors obtained from 16 O(d,p) 17 O and 16 O(d,n) 17 F transfer reactions. The astrophysical S-factors are compared to recent experimental data. The Maxwellian-averaged neutron capture cross section at kT=30 keV is obtained as 22(3)µ barn.

Various beams of short-and long-lived radioactive nuclei have recently been produced at the ATLAS accelerator at Argome NationalLaboratory,using either the so-calledIn-Flightor the 'IWo-Accelerator method.The productiontechniques,as wellas recentresults with %1 (T1/2=60y)and 17F('I'1/2=64s) beams,whichare of interestto nucleosynthesis in supernovaeand X-ray bursts, are discuss&i.

Various beams of short-and long-lived radioactive nuclei have recently been produced at the ATLAS accelerator at Argome NationalLaboratory,using either the so-calledIn-Flightor the 'IWo-Accelerator method.The productiontechniques,as wellas recentresults with %1 (T1/2=60y)and 17F('I'1/2=64s) beams,whichare of interestto nucleosynthesis in supernovaeand X-ray bursts, are discuss&i.

It is known from the scattering theory that the phase-shift of elastic collision does not provide a unique potential to describe the bound state of the two-particle system. The bound state wave function is the most crucial input for various nuclear processes bearing astrophysical significance. In this paper, we emphasize on the important role of the asymptotic normalization coefficients for description of the $^{13}\rm{N}\longrightarrow {^{13}\rm{C}}+\beta^++\nu_e$ reaction. Using experimental data of the elastic scattering phase-shift of proton and neutron on $^{12}\rm{C}$, we find the asymptotic normalization coefficients which determine the tail of bound state wave functions. This allow us to modify the wave functions of $^{13}\rm{N}$ and $^{13}\rm{C}$ within the single-particle approach using the inverse scattering theory. These wave functions are used to determine the nuclear matrix element for calculation of the half-life and log{\textit ft} values of $\beta^+$ decay of $^{13}...

It is known from the scattering theory that the phase-shift of elastic collision does not provide a unique potential to describe the bound state of the two-particle system. The bound state wave function is the most crucial input for various nuclear processes bearing astrophysical significance. In this paper, we emphasize on the important role of the asymptotic normalization coefficients for description of the $^{13}\rm{N}\longrightarrow {^{13}\rm{C}}+\beta^++\nu_e$ reaction. Using experimental data of the elastic scattering phase-shift of proton and neutron on $^{12}\rm{C}$ nucleus, we find the asymptotic normalization coefficients which determine the tail of bound state wave function. This allows us to correctly calculate the wave functions of $^{13}\rm{N}$ and $^{13}\rm{C}$ nuclei within the cluster model approach. These wave functions are applied to determine the nuclear matrix element for calculation of the ${\rm log} ft$ values and half-life of $\beta^+$ decay of $^{13}\rm{N}$....

In our letter-of-intent, INTC-I-051, we discussed the physics case for scattering and transfer reactions involving light nuclei in the break-out region of the rp-process. The committee found the physics case compelling and supported the letter-of-intent under the premise that beams of proper quality were developed and that an adequate detector setup was presented. As these two requirements have been met recently we now propose to study resonant proton scattering of 22 Mg to identify the states at 1.733 MeV and 2.575 MeV in 23 Al that have been reported from the 24 Mg(7 Li, 8 He) 23 Al reaction but that remained unobserved in the only resonant proton scattering experiment performed with 22 Mg sofar. In particular we should be able to investigate the character of the proton emission of the 2.575 MeV state which may also have a significant inelastic branch. We also propose to perform resonant proton scattering on 21 Na above α particle threshold with 18 Ne to study states in 22 Mg. States above α threshold are generally of interest for the 18 Ne(α,p) 21 Na reaction. The experiment aims to study the decay of the states at 8.31 MeV, 8.18 MeV and potentially also of the 8.51 MeV state.

The '8Ne(a,p)21 Na reaction is of great importance to Nuclear Astrophysics as it provides a route to breakout from the hot-CNO cycle, possibly leading to the formation of the elements up to A100. This particular reaction has been studied using a '8 Ne beam, available at Louvain-la-Neuve, together with a helium gas target system previously developed for the investigation of (a,p) reactions with a radioactive beam. This study covered an energy region from-1.7-2.9 MeV in the centre of mass frame of the '8Ne+c system. A change in the detector geometry resulted in an increase in the detection efficiency and significantly reduced the proton background that hindered the previous measurement. A direct measurement of the energy loss of the '8Ne beam, as it passed through He gas, was undertaken to reduce a major source of uncertainty in the determination of the stellar reaction rate. This showed a linear relationship, between beam energy and distance traversed within the gas, over an energy scan of 8-16 MeV and gave an energy loss of (1.55 ± 0.01) MeV/cm and (15.96 + 0.02) MeV for the energy of the 18Ne beam upon entry into the gas. Firstly I would like to thank my supervisor, Alan Shotter for his support and patience throughout this project. My thanks go to my second supervisor, Phil Woods for his support. Special thanks go to Tom Davinson whose guidance and encouragement was greatly appreciated. I would also like to thank Will Bradfield-Smith for our useful discussions and Gordon Turnbull for his technical help with the experimental preparation. My thanks also go to our collaborators in Belgium, especially Pierre Leleux, for their invaluable contribution to this work. Special thanks go to my closest friend, Mandeep for her continuous support and encouragement throughout my time in Edinburgh. Thanks go to my other friends, especially Alessia, Alison, Chris, Fred, Karsten and Steve for creating a good working atmosphere and to my former flatmate, David for making life outside work entertaining. Thanks also go to my family (Mum, Dad and Daniel) for all their support. I wish to thank Gene Roddenberry for creating Star Trek which inspired me to study physics. Finally I wish to acknowledge the Engineering and Physical Sciences Research Council (EPSRC) for funding this project.

The 22 Mg nucleus plays an important role in nuclear astrophysics, specially in the 22 Mg(α,p) 25 Al and proton capture 22 Mg(p,γ) 23 Al reactions. It is believed that 22 Mg is a waiting point in the αp-process of nucleosynthesis in novae. We proposed a direct measurement of the 22 Mg+α resonance reaction in inverse kinematics using a radioactive ion (RI) beam. A 22 Mg beam of 3.73 MeV/u was produced at CRIB (Center for Nuclear Study (CNS) low-energy RI Beam) facility of the University of Tokyo located at RIKEN (Japan) in 2011. In this paper we present the results about the production of the 22 Mg beam used for the direct measurement of the scattering reaction 22 Mg(α,α) 22 Mg, and the stellar reaction 22 Mg(α,p) 25 Al in the energy region concerning an astrophysical temperature of T 9 ¼ 1-3 GK.

We present the details of the construction and commissioning of the Texas-Edinburgh-Catania Silicon Array (TECSA). TECSA is composed of up to 16 Micron Semiconductor Ltd. type-YY1 silicon strip detectors and associated electronics, which is designed for use in studies of nuclear astrophysics and nuclear structure with rare isotope beams. TECSA was assembled at the Texas A&M University Cyclotron Institute and will be housed there for the next few years. The array was commissioned in a recent experiment where the d( 14 C,p) 15 C reaction at 11.7 MeV/u was measured in inverse kinematics. The results of the measurement and a discussion of the future use of this array are presented.

The elements between iron and strontium are largely produced by the weak sprocess occurring in massive stars during the late stages of convective core He burning and the convective shell carbon burning with the primary source of neutrons coming from the reaction 22 Ne(α,n) 25 Mg. However, shell carbon burning may produce hot enough temperatures to activate 12 C( 12 C,n) 23 Mg as a significant neutron source. Few studies have been done on this reaction, and the extrapolation from experimental data down to the relevant astrophysical energies is uncertain. Recent studies performed at the Nuclear Science Laboratory of Notre Dame aim to improve the existing reaction data using new experimental techniques as well as provide a more reliable extrapolation to the low energies not accessible by experiment. Preliminary results will be presented and the astrophysical implications will be discussed.

the gas cell were made of havar foil of 4 μm each and the pressure in the cell was p=1.5 atm. Due to the large negative Q-value of the reaction Q(p,n)=-18.12 MeV, the energy of the primary beam has to be large. Therefore the energy of the recoiling products, which is larger than needed for the secondary proton transfer reaction (10-12 MeV/u), needs to be degrade it behind the production target. A 250-μm-thick Al foil was put behind the target cell as an energy degrader. Various production scenarios such as charge exchange around 0° (forward angle solution), around 180° (backward angle solution) or the fusion- evaporation mechanism were considered and the production was measured for each. To quantify the influence of the multiple scattering in the Al degrader foil, we have determined the production rate with and without it in place. We have found its influence to be marginal. MARS was tuned for each case and the 12N production was determined by counting the 12N yield in the target de...

The cross section of the radiative proton capture reaction on the drip line nucleus 12 N was investigated using the Asymptotic Normalization Coefficient (ANC) method. We have used the 14 N( 12 N, 13 O) 13 C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13 O → 12 N + p and calculate from it the direct component of the astrophysical S factor of the 12 N(p, γ ) 13 O reaction. The optical potentials used and the DWBA analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time with the transfer measurement. From the transfer, we determined the square of the ANC, 2 2 / 1 p C ( 13 O g.s. ) = 2.53 ± 0.30 fm -1 , and hence a value of 0.33(4) keV⋅b was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of S total (0) = 0.42(5) keV⋅b. The 12 N(p, γ ) 13 O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.

The strengths of low-energy resonances in 14 N(␣,␥) 18 F at 573 keV and 1136 keV have been measured using an activation method. In addition, their relative strength and the energy of the lower resonance have been determined in a prompt ␥-ray experiment. The results of these measurements are used to reevaluate the stellar reaction rate of 14 N(␣,␥) 18 F. The present reaction rate at temperatures of astrophysical interest is a factor of 2 smaller than previously reported.

Experimental work has been carried out at Louvain-la-Neuve to study the reactions 13N(a, p) 160 and 18Ne(c, p) 21 Na in inverse kinematics with a gaseous helium target. The experimental method devised was tested using the reaction 13N(c, p) 160, as the cross section was calculable from data on the inverse reaction, 16 0(p, a) 13N [1-4]. This test experiment showed that the experimental error obtainable in the deduction of the resonance strengths, 'ys, was 30%, making the technique of practical use in the investigation of (cr, p) reactions of interest to Nuclear Astrophysics. The reaction 18Ne(c, p) 21 Na, which is important as a break-out mechanism from the hot CNO cycle into the rp-process during explosive hydrogen burning, has been investigated, and values for the resonance strengths have been extracted from the experimental data. A stellar reaction rate, based only upon the observed resonances, has been calculated and compared with theoretical predictions [5]. A good agreemen...

Coupled Reaction Channel Calculations have been performed for transitions to ground and first excited states of 17 F and 17 O at deuteron incident energies from E d =2.279 MeV up to 3.186 MeV. The n+ 16 O and p+ 16 O astrophysical direct capture cross sections have been calculated using the spectroscopic factors obtained from 16 O(d,p) 17 O and 16 O(d,n) 17 F transfer reactions. The astrophysical S-factors are compared to recent experimental data. The Maxwellian-averaged neutron capture cross section at kT=30 keV is obtained as 22(3)µ barn.

The 12 C(α,γ) 16 O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for SE1(300) and 7 to 120 keVb for SE2(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi-elastic α scattering on 12 C, α-transfer reactions to 16 O, and 16 N decay are usually included in the analysis. Here the β-delayed α decay of 16 N is used to infer information on the 12 C(α,γ) 16 O reaction and a new experimental technique is suggested.

We have measured levels in 18 Ne by the 16 O(3 He,n) reaction at the FN tandem accelerator of University of Notre Dame in order to measure the rate of the waiting point reaction 14 O(α,p) in the hot CNO cycle. This is one of the breakout reaction in the CNO cycle where the signatures are that the temperatures are high enough to bypass the beta decay of the waiting points breaking out of the hot CNO cycle by a thermonuclear runaway in some explosive environments like Novae and X-ray bursts. One of the two paths to breakout of the hot CNO cycle is the reaction chain 14 O(α,p) 17 F(p,γ) 18 Ne(α,p). The starting (α,p) reaction on the waiting point nucleus 14 O proceeds through resonant states above α-decay threshold in 18 Ne. The rate of this reaction is therefore very sensitive to the partial and total widths, excitation energies and spins of the resonances in 18 Ne. We studied the relevant states in 18 Ne using an array of liquid scintillators with time-of-flight and pulse-shape-discrimination techniques to measure the neutrons while decaying charged particles were detected by a silicon detector array. Coincidences of n-p/α were used to measure α and proton decay branching ratios. DWBA calculations were carried out to constrain the possible spins of the new states. We will include this new information in reaction network calculations to determine the impact of this breakout path on the nuclear energy generation and nucleosynthesis in explosive hydrogen burning environments. * Speaker.

We discuss the importance of the spectroscopic properties of the resonances of 12C just above the 3a-threshold, and review the existing experimental information of this region with emphasis on O+ and 2+ states. A new experimental approach for studying the @-decays of 12B and 121V is presented based on techniques developed in the context of R.adioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given.

We discuss the importance of the spectroscopic properties of the resonances of 12C just above the 3a-threshold, and review the existing experimental information of this region with emphasis on O+ and 2+ states. A new experimental approach for studying the @-decays of 12B and 121V is presented based on techniques developed in the context of R.adioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given.

We have updated and recalculated the ZlNa(p,T)ZZMg and 22Na(p, 7)Z3Mg reaction rates for temperatures 107-109K relevant for explosive hydrogen burning in stellar environment. We find the 21Na(p, 7)ZZMg rate lower than recently suggested. Considering various uncertainties in spin and parity assignments of the low energy ZeNa+p resonances we present upper and lower limits for the 22Na(p, 7)23Mg reaction rate which, however, allows for a meaningful discussion of the consequences of the new rates on the Ne-Na cycle under various stellar conditions.

Two-proton relative momentum distributions from the break-up channels 23 Al→p+p+ 21 Na and 22 Mg→p+p+ 20 Ne at an energy of 60-70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component from single-step 2 He for highly excited 23 Al and 22 Mg. diproton emission, proton-rich nuclei 23 Al and 22 Mg

We discuss the use of one-nucleon removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. The breakup reactions are proved to be good spectroscopic tools and can be used to study a large number of loosely bound proton-or neutron-rich nuclei over a wide range of beam energies. As peripheral processes, they can be used to extract asymptotic normalization coefficients (ANCs) from which non-resonant capture reaction rates of astrophysical interest can be calculated parameter free. In this talk, we present results of a proton-breakup experiment carried out at GANIL (France) with a cocktail beam centered around 23 Al at 50 MeV/nucleon. Momentum distributions of the breakup fragments, inclusive and in coincidence with gamma rays detected by EXOGAM Germanium clover array, were measured in the focal plan of SPEG energy-loss spectrometer. We present in particular the investigations of reaction rates for 22 Mg(p,γ) 23 Al and 23 Al(p,γ) 24 Si important for novae and X-ray bursts, respectively.

The '8Ne(a,p)21 Na reaction is of great importance to Nuclear Astrophysics as it provides a route to breakout from the hot-CNO cycle, possibly leading to the formation of the elements up to A100. This particular reaction has been studied using a '8 Ne beam, available at Louvain-la-Neuve, together with a helium gas target system previously developed for the investigation of (a,p) reactions with a radioactive beam. This study covered an energy region from-1.7-2.9 MeV in the centre of mass frame of the '8Ne+c system. A change in the detector geometry resulted in an increase in the detection efficiency and significantly reduced the proton background that hindered the previous measurement. A direct measurement of the energy loss of the '8Ne beam, as it passed through He gas, was undertaken to reduce a major source of uncertainty in the determination of the stellar reaction rate. This showed a linear relationship, between beam energy and distance traversed within the gas, over an energy scan of 8-16 MeV and gave an energy loss of (1.55 ± 0.01) MeV/cm and (15.96 + 0.02) MeV for the energy of the 18Ne beam upon entry into the gas. Firstly I would like to thank my supervisor, Alan Shotter for his support and patience throughout this project. My thanks go to my second supervisor, Phil Woods for his support. Special thanks go to Tom Davinson whose guidance and encouragement was greatly appreciated. I would also like to thank Will Bradfield-Smith for our useful discussions and Gordon Turnbull for his technical help with the experimental preparation. My thanks also go to our collaborators in Belgium, especially Pierre Leleux, for their invaluable contribution to this work. Special thanks go to my closest friend, Mandeep for her continuous support and encouragement throughout my time in Edinburgh. Thanks go to my other friends, especially Alessia, Alison, Chris, Fred, Karsten and Steve for creating a good working atmosphere and to my former flatmate, David for making life outside work entertaining. Thanks also go to my family (Mum, Dad and Daniel) for all their support. I wish to thank Gene Roddenberry for creating Star Trek which inspired me to study physics. Finally I wish to acknowledge the Engineering and Physical Sciences Research Council (EPSRC) for funding this project.

18F radioactive beams were used to measure the lSF(p,a) reaction in the c.m. energy ranges of 265-535 keV and 550-740 keV. In each case, a resonant level was clearly detected, of which the resonant strength and some other properties were deduced. The astrophysical reaction rate was calculated down to the novae peak temperature. Consequences for the hot CNO cycles were drawn. @ 1997 Elsevier Science B.V.

An excitation function for resonance elastic scattering of ␣ particles on 18 O and 18 Ne was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to 13.7 MeV in 22 Ne. Twelve of them are new. General features of ␣-cluster bands in 22 Ne are analyzed in the framework of the potential model with a deep potential well. Predictions for the 11 − level in 22 Ne, as well as for the isotopic shift of the cluster levels in 22 Mg, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of ␣-cluster states in mirror N Z nuclei.