[en] The (d,n) reaction of ⁷Be to form the ground state of ⁸B was studied for the first time. The reaction was performed with a 25.8 MeV/nucleon beam of ⁷Be ions from the A1200 fragment separator at the NSCL. The beam reacted in a CD₂ target in a large scattering chamber. The recoiling ⁸B nuclei were observed in a pair of position sensitive detector telescopes covering angles between 2 and 4.5 degrees (lab). A large array of neutron detectors was placed at angles ranging from 175 to 104 degrees (∼0 to ∼30 degrees COM) that was able to measure the energy of coincident neutrons by their time-of-flight. The efficiency of the neutron array was measured with a ¹⁷N source also produced in the A1200 separator. The overall response of the detector system was checked by performing the d(¹²C,¹³N)n reaction at 22 MeV/nucleon under identical, i.e., low intensity, conditions. The angular distribution of the ⁸B singles and the coincident neutrons were measured and will be presented

No abstract available

[en] The solar neutrino ''problem'' arises from the discrepancy between the observations of solar neutrinos fluxes in experiments at Homestake and Kamiokande and the solar model predictions of those fluxes. Both experiments, which are sensitive mainly to high-energy neutrinos, observe fewer neutrinos than predicted by solar models. Most of the expected high-energy solar neutrinos come from the beta-decay of ⁸B, which is produced in the reaction ⁷Be(p,γ)⁸B. A study of all of the measurements to date of the zero-energy S-factor for the reaction ⁷Be(p,γ)⁸B concludes that S₁₇(0) = 0.0224 +± 0.0021 keV-barn. Although a 10% error in S₁₇(0) alone wig not solve the solar neutrino problem, it would still be useful to nail down all of the inputs of the solar models as well as possible. This serves to guard against the possibility that a conspiracy among the errors might be the source of the discrepancy and provides tighter constraints on the ''new physics'' interpretations of the experimentally measured solar neutrino spectrum. In this paper, we examine several ways of improving this measurement. None appear to offer a significant improvement over past experiments

[en] The measured cross section for the ⁷Be(p,γ)⁸B reaction, extrapolated to energies relevant to the solar interior, in critical for estimating the flux of high energy neutrinos coming from ⁸B beta decay in the sun. The apparent reduction in high energy solar neutrinos observed in terrestrial experiments is the essential basis of the open-quotes Solar Neutrino Problemclose quotes which remains a question of intense investigation. While the ⁷Be(p,γ)⁸B cross section has been measured several times in the energy range from ¹²⁰ keV to several MeV, more precise data is clearly desirable. We have studied the feasibility of various schemes for improving our knowledge of this cross section, including new approaches with radioactive ⁷Be beams. The conclusions of our study will be presented

[en] In estimating the non-resonance nuclear reaction cross-sections σ(E) at low energies needed for astrophysical calculations it is customary to use the Gamow penetration factor T_G(E) in the conventional extrapolation formula, σ(E) = S(E)T(E)/E. Recently, it is shown that another choice of T _BW(E) based on a more realistic potential model of Blatt and Weisskopf consisting of the interior attractive nuclear square well and the exterior repulsive (Coulomb) potential can yield smaller extrapolated values of low-energy σ(E) for ⁷Be(p, γ)⁸B reaction. In the BW model, the interior wave function was chosen to be e^-iKr. We have developed an extended model in which a more general and realistic interior wave function, e^-iKr +re^iphie^iKr, is chosen with two real parameters, τ and φ. The resulting transmission coefficient, T_new(E), has a resonance structure with two parameters τ and φ which can be determined from the experimental resonance energy and width. Our new parameterization incorporates both the resonance and non-resonance contributions simultaneously. Comparison of the numerical results for low-energy φ(E) obtained from three different parameterizations using T_G(E), T_BW(E), and T_new(E) will be presented for ⁷Be(p,γ)⁸B

[en] OAK-B135 Tandem Terminal Ion Source. The terminal ion source (TIS) was used in several experiments during this reporting period, all for the(sup 7)Be((gamma))(sup 8)B experiment. Most of the runs used(sup 1)H(sup+) at terminal voltages from 0.3 MV to 1.5 MV. One of the runs used(sup 2)H(sup+) at terminal voltage of 1.4 MV. The other run used(sup 4)He(sup+) at a terminal voltage of 1.37 MV. The list of experiments run with the TIS to date is given in table 1 below. The tank was opened four times for unscheduled source repairs. On one occasion the tank was opened to replace the einzel lens power supply which had failed. The 10 kV unit was replaced with a 15 kV unit. The second time the tank was opened to repair the extractor supply which was damaged by a tank spark. On the next occasion the tank was opened to replace a source canal which had sputtered away. Finally, the tank was opened to replace the discharge bottle which had been coated with aluminum sputtered from the exit canal

[en] We report on a new measurement of the cross section of this reaction, following our previous experiment with an implanted ⁷Be target, a raster scanned beam and the elimination of the backscattering loss. Measurements were done at energies above and below the resonance as well as a detailed measurement of the resonance. We obtain an extrapolated value of S₁₇(0) 21.2 ± 0.7 from the entire set of measurements

[en] We measured the ⁷Be(p,γ)⁸B cross section from E_p = 221 keV to 1376 keV. A uniformly distributed beam that illuminated the whole area of a small diameter target was used to eliminate systematic error from ⁷Be target non-uniformity. The energy loss profile of the target to the incident beam was measured using the ⁷Be(α,γ)¹¹C resonance at E_α 1376 keV. The (α,γ) measurement also demonstrated that the target had a high ⁷Be atomic purity. The measured yield of the detected ⁸B was normalized to the activity of the target and the solid angle of the counting detector. Corrections for ⁸B decay during bombardment and arm rotation were applied. For the first time, the correction due to lost ⁸B from backscattering was determined experimentally. A new experiment is presently underway, extending to lower proton energy. Due to a problem in the determination of the α-detector solid angle in the first measurement, the solid angle in the new measurement will be determined by a different technique using a ¹⁴⁸Gd α source and a silicon detector whose distance to the source can be precisely adjusted

[en] The α-cluster transfer reactions have earlier been used as a potential tool to study the reactions in the helium burning phase of stars. The direct capture reactions with extremely small cross sections at low energies are difficult to measure in the laboratory. Hence, an indirect technique to study α-capture reactions is useful. This involves investigation of α-cluster transfer reactions to populate the relevant states in the residual nuclei. The technique has been extensively used on stable nuclei to investigate the astrophysical α-capture reactions. The loosely bound Lithium isotopes ⁶Li and ⁷Li are widely studied in this regard due to their α-cluster structure. Amro et al. carried out similar study on the radioactive mirror counterpart ⁷Be. However, the uncertainty in the optical model parameters (OMP) due to the limited angular distribution presented a serious problem in the study of transfer reactions. The study shows that α-cluster transfer reaction is more probable than breakup of ⁷Be. This low breakup yield makes the ⁷Be nucleus an excellent candidate for the study of high-excitation α-cluster states in the residual nuclei. We studied the α-cluster transfer reactions of ⁷Be to populate the states of ¹⁶O that dominantly contribute to the al- pha capture reaction ¹²C(α; γ)¹⁶O in helium-burning process in nuclear astrophysics

[en] The recent WMAP results tightly constrain the baryon density in the universe, which in turn constrains the light element abundance predicted in Standard Big Bang Nucleosynthesis (SBBN). There is a discrepancy in the ⁷Li abundance which cannot be explained by uncertainties in the main reactions included in the SBBN. Up to now, the influence of the reaction ⁷Be(d,p)2α has been neglected. We have investigated this reaction at SBBN energies using a radioactive ⁷Be beam and a (CD₂) _n self-supporting target at the CYCLONE RIB facility at Louvain-la-Neuve. The experimental method is briefly described. Preliminary results and consequences for primordial nucleosynthesis are discussed