Indirect techniques in nuclear astrophysics: a review.

In this review, we discuss the present status of three indirect techniques that are used to determine reaction rates for stellar burning processes, asymptotic normalization coefficients, the Trojan Horse method and Coulomb dissociation. A comprehensive review of the theory behind each of these techniques is presented. This is followed by an overview of the experiments that have been carried out using these indirect approaches.

ß decay of (38)Ca: sensitive test of isospin symmetry-breaking corrections from mirror superallowed 0+ → 0+ transitions.

We report the first branching-ratio measurement of the superallowed 0+→0+ß transition from Ca38. The result, 0.7728(16), leads to an ft value of 3062.3(68) s with a relative precision of ±0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed ß decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

FT values measured to ±0.1% for superallowed beta transitions: metrology at sub-second time scales.

Because of angular-momentum conservation, superallowed ß decay between 0(+) analog states involves only the vector part of the weak interaction, so its measured ft value can be used to determine the vector coupling constant, G(V). If many such transitions are measured, then the constancy of G(V) can be established and several important tests made on fundamentals of the electroweak Standard Model. We have developed apparatus that allows us to measure half-lives to ±0.03% and branching ratios to ±0.1% or better, for cyclotron-produced activities with half-lives as short as 100 ms. We present an overview of the equipment and a summary of more than 10 years of results.

Production of rare isotope beams at the Texas A&M University Cyclotron Institute.

The Cyclotron Institute at Texas A&M is currently configuring a scheme for the production of radioactive-ion beams that incorporates a light-ion guide and a heavy-ion guide coupled with an electron-cyclotron-resonance ion source constructed for charge-breeding. This scheme is part of an upgrade to the facility and is intended to produce radioactive beams suitable for injection into the K500 superconducting cyclotron. The current status of the project and details on the ion sources used in the project is presented.

Experimental validation of the largest calculated isospin-symmetry-breaking effect in a superallowed Fermi decay.

A precision measurement of the γ yields following the ß decay of (32)Cl has determined its isobaric-analogue branch to be (22.47(-0.18)(+0.21))%. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to 0+ → 0 + transitions for tests of the standard model.

Experimental constraints on left-right symmetric models from muon decay.

The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters ρ, δ, and P(µ)(π)ξ tests the standard model in a purely leptonic process and provides improved limits for relevant extensions to the standard model. Specifically, for the generalized left-right symmetric model |(g(R)/g(L))ζ|<0.020 and (g(L)/g(R))m(2)>578 GeV/c(2), both 90% C.L.

Measurement of angular distributions of Drell-Yan dimuons in p+p interactions at 800 GeV/c.

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a hydrogen target. The polar and azimuthal angular distribution parameters have been extracted over the kinematic range 4.5

Measurement of the 20 and 90 keV resonances in the 18O(p,alpha)15N reaction via the Trojan horse method.

The 18O(p,alpha)15N reaction is of primary importance in several astrophysical scenarios, including fluorine nucleosynthesis inside asymptotic giant branch stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus the indirect measurement of the low energy region of the 18O(p,alpha)15N reaction has been performed to reduce the nuclear uncertainty on theoretical predictions. In particular the strength of the 20 and 90 keV resonances has been deduced and the change in the reaction rate evaluated.

Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c.

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0

Measurement of angular distributions of Drell-Yan dimuons in p+d interactions at 800 GeV/c.

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a deuterium target. The muon angular distributions in the dilepton rest frame have been measured over the kinematic range 4.5

Measurement of the Michel parameter rho in muon decay.

The TWIST Collaboration has measured the Michel parameter rho in normal muon decay, mu(+)--> e(+)nu(e)nu (mu). In the standard model, rho = 3/4. Deviations from this value imply mixing of left- and right-handed muon and electron couplings. We find rho=0.750 80+/-0.000 32(stat) +/- 0.000 97(syst) +/- 0.000 23, where the last uncertainty represents the dependence of rho on the Michel parameter eta. This result sets new limits on the W(L)-W(R) mixing angle in left-right symmetric models.

J/psi polarization in 800-GeV p-Cu interactions.

We present measurements of the polarization of the J/psi produced in 800-GeV proton interactions with a copper target. Polarization of the J/psi is sensitive to the ccmacr; production and hadronization processes. A longitudinal polarization is observed at large x(F), while at small x(F) the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus p(T).

High precision measurement of the superallowed 0+ --> 0+ beta decay of 22Mg.

The half-life, 3.8755(12) s, and superallowed branching ratio, 0.5315(12), for 22Mg beta decay have been measured with high precision. The latter depended on gamma-ray intensities being measured with an HPGe detector calibrated for relative efficiencies to an unprecedented 0.15%. Previous precise measurements of 0+ --> 0+ transitions have been restricted to the nine that populate stable daughter nuclei. No more such cases exist, and any improvement in a critical Cabibbo-Kobayashi-Maskawa unitarity test must depend on precise measurements of more exotic nuclei. With this branching-ratio measurement, we show those to be possible for T(z)=-1 parents. We obtain a corrected Ft value of 3071(9) s, in good agreement with expectations.

Observation of polarization in bottomonium production at square root of s = 38.8 GeV.

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.

Asymptotic normalization coefficient of 8B from breakup reactions and the S17 astrophysical factor.

We show that asymptotic normalization coefficients (ANC) can be extracted from one-nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/nucleon. In particular, the breakup of 8B is described in terms of an extended Glauber model. The 8B ANC extracted from breakup data at several energies and on different targets, C(2)(tot) = 0.450+/-0.039 fm(-1), leads to the astrophysical factor S17(0) = 17.4+/-1.5 eV b for the key reaction for solar neutrino production 7Be(p, gamma)8B. The procedure described provides an indirect method to determine reaction rates of astrophysical interest with beams of loosely bound radioactive nuclei.

Is clamp and sew still viable for thoracic aortic resection?

OBJECTIVE: The authors reviewed the morbidity and mortality of surgical resection of the descending thoracic and thoracoabdominal aorta using the clamp-and-sew technique. BACKGROUND: Paraplegia remains a devastating complication after thoracoabdominal aortic resection, despite many strategies for spinal cord protection. Because of its simplicity, clamp and sew has been the preferred technique at the University of Virginia for the thoracoabdominal aortic resection when proximal control is possible. METHODS: Between 1987 and 1994, the authors reviewed 91 consecutive patients who underwent thoracic aortic resection using clamp-and-sew techniques without any additional adjuncts for spinal cord protection. RESULTS: The average age of patients was 60.8 years; 57.1% were male. No intraoperative deaths occurred. In-hospital mortality was 13% (12/91), with an overall incidence of postoperative spinal cord injury manifested as paraparesis or paraplegia of 9.9% (9/91). Eighty-nine percent (81/91) of all repairs were completed with aortic clamp times of 40 minutes or less, and nearly six out of ten were completed in 30 minutes or less (53/91). Cross-clamp times were not significantly different between those patients who sustained neurologic injury and those who had no deficits. CONCLUSIONS: The authors conclude that clamp and sew is still a viable technique for thoracoabdominal aortic resection. Nearly all resections can be completed within 40 minutes of aortic occlusion. However, the "safe" duration of thoracic aortic occlusion remains unknown, and spinal cord injury can occur even with short clamp times. Reproducible, safe, and technically simple means of spinal cord protection must be developed.

A simple technique for retrograde cerebral perfusion during circulatory arrest.

We describe a simple and safe technique for achieving retrograde cerebral perfusion via a small coronary sinus type catheter placed in the superior vena cava. This method is especially useful when the need for circulatory arrest is first recognized intraoperatively and a single two-stage venous cannula has already been placed for cardiopulmonary bypass. The advantages of this technique over other currently employed methods for retrograde cerebral perfusion are discussed.

Evolution of renal insufficiency in ischemic nephropathy.

This retrospective review of data collected during a recent 42-month period from 58 consecutive patients with ischemic nephropathy submitted to operative management in the authors' center was undertaken to report the rate of decline in their renal function during the period before intervention and to examine the impact of operation on their outcome. Based on serum creatinine values, immediate preoperative estimated glomerular filtration rates (EGFR) ranged from 0 to 46 mL/minute (mean, 23.85 +/- 9.76 mL/minute). Eight patients were dialysis dependent or anuric at the time of operation. Patients with at least three sequential measurements for calculations of EGFR changes during the 6 months before operation (n = 50) and the first 12 months after operation (n = 32) were used to describe the preoperative rate of decline in EGFR and the impact of operation on this decrease in the operative survivors. In addition comparative analyses of data from patients with unilateral versus bilateral lesions and patients classified as having improvement in EGFR versus no improvement after operation were performed. Comparison of the immediate preoperative EGFR with the immediate postoperative EGFR for the entire group showed significant improvement in response to operation. Likewise the rate of deterioration in EGFR for the total group was improved after operation. A similar improvement in the rate of deterioration in EGFR was seen in the subgroup of patients who received an immediate improvement in EGFR in response to operation. These data argue that ischemic nephropathy is a rapidly progressive form of renal insufficiency. Although individual responses to operation were heterogeneous, renal revascularization may provide both immediate improvement in renal function and an improvement in its rate of deterioration during follow-up in patients with ischemic nephropathy.

Renal duplex sonography: evaluation of clinical utility.

With the exception of conventional angiography, no previously proposed screening test has the necessary sensitivity/specificity to guide further evaluation for correctable renovascular disease. Recently, renal duplex sonography has been suggested as a useful substitute in such screening for renovascular disease. This report analyzes our data collected over the past 10 months in evaluation of renal duplex sonography to examine its diagnostic value. The study population for renal duplex sonography validity analysis consisted of 74 consecutive patients who had 77 comparative renal duplex sonography and standard angiographic studies of the arterial anatomy to 148 kidneys. Renal duplex sonography results from six kidneys (4%) were considered inadequate for interpretation. This study population contained 26 patients (35%) with severe renal insufficiency (mean 3.6 mg/dl) and 67 hypertension (91%). Fourteen patients (19%) had 20 kidneys with multiple renal arteries. Bilateral disease was present in 22 of the 44 patients with significant renovascular disease. Renal duplex sonography correctly identified the presence of renovascular disease in 41 of 44 patients with angiographically proven lesions, and renovascular disease was not identified in any patient free of disease. When single renal arteries were present (122 kidneys), renal duplex sonography provided 93% sensitivity, 98% specificity, 98% positive predictive value, 94% negative predictive value, and an overall accuracy of 96%. These results were adversely affected when kidneys with multiple (polar) renal arteries were examined. Although the end diastolic ratio was inversely correlated with serum creatinine (r = -0.3073, p = 0.009), low end diastolic ratio in 35 patients submitted to renovascular reconstruction did not preclude beneficial blood pressure or renal function response. We conclude from this analysis that renal duplex sonography can be a valuable screening test in the search for correctable renovascular disease causing global renal ischemia and secondary renal insufficiency (ischemic nephropathy). Renal duplex sonography does not, however, exclude polar vessel renovascular disease causing hypertension alone nor does it predict hypertension or renal function response after correction of renovascular disease.

Natural history of left anterior descending coronary artery obstruction: significance of location of stenoses in medically treated patients.

We examined the prognostic significance of an obstructive lesion in the proximal left anterior descending (LAD) coronary artery. Five-year or longer follow-up data were examined from 311 patients with greater than 70% obstruction of the LAD treated without surgery. Mortality was compared in subsets with lesions proximal to and distal to the first septal perforating artery. Survival curves were worse in patients with proximal than with distal LAD disease (p less than 0.05); lesion location remained a significant determinant of survival when ejection fraction, age, and sex were controlled using a Cox regression model. However, when patient subsets were examined, survival with proximal LAD disease was worse than with distal obstruction only in the presence of an associated right coronary artery lesion and an ejection fraction of less than 40% (p less than 0.01). Patients with proximal LAD plus right coronary lesions had a 5-year mortality rate (34.08 +/- 8.9%) that was not significantly (p greater than 0.05) different from that of a group of 66 patients with greater than 50% narrowing of the left main coronary artery (24.02 +/- 4.3%). Thus, proximal LAD disease is more significant than is a distal lesion only in the presence of right coronary obstruction. This two-vessel combination results in a mortality rate as high as that associated with left main coronary artery obstruction.