Signatures of the Giant Pairing Vibration in the 14C and 15C atomic nuclei.

Giant resonances are collective excitation modes for many-body systems of fermions governed by a mean field, such as the atomic nuclei. The microscopic origin of such modes is the coherence among elementary particle-hole excitations, where a particle is promoted from an occupied state below the Fermi level (hole) to an empty one above the Fermi level (particle). The same coherence is also predicted for the particle-particle and the hole-hole excitations, because of the basic quantum symmetry between particles and holes. In nuclear physics, the giant modes have been widely reported for the particle-hole sector but, despite several attempts, there is no precedent in the particle-particle and hole-hole ones, thus making questionable the aforementioned symmetry assumption. Here we provide experimental indications of the Giant Pairing Vibration, which is the leading particle-particle giant mode. An immediate implication of it is the validation of the particle-hole symmetry.

Experimental study of the two-body spin-orbit force in nuclei.

Energies and spectroscopic factors of the first 7/2-, 3/2-, 1/2-, and 5/2- states in the (35)Si21 nucleus were determined by means of the (d, p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the Si35 and S37 isotones, a reduction of the p3/2-p1/2 spin-orbit splitting by about 25% is proposed, while the f7/2-f5/2 spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei.

Breakdown of the Z=8 shell closure in unbound 12O and its mirror symmetry.

An excited state in the proton-rich unbound nucleus 12O was identified at 1.8(4) MeV via missing-mass spectroscopy with the 14O(p,t) reaction at 51 AMeV. The spin-parity of the state was determined to be 0+ or 2+ by comparing the measured differential cross sections with distorted-wave calculations. The lowered location of the excited state in 12O indicates the breakdown of the major shell closure at Z=8 near the proton drip line. This demonstrates the persistence of mirror symmetry in the disappearance of the magic number 8 between 12O and its mirror partner 12Be.

Decay pattern of pygmy states observed in neutron-rich 26Ne.

Coulomb excitation of the exotic neutron-rich nucleus (26)Ne on a (208)Pb target was measured at 58 MeV/u in order to search for low-lying E1 strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of B(E1)=0.49+/-0.16e(2) fm(2) is deduced, corresponding to 4.9+/-1.6% of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.

1n and 2n transfer with the Borromean nucleus 6He near the Coulomb barrier.

Angular distributions for 1n and 2n transfer are reported for the 6He+65Cu system at E_{lab}=22.6 MeV. For the first time, triple coincidences between alpha particles, neutrons, and characteristic gamma rays from the targetlike residues were used to separate the contributions arising from 1n and 2n transfer. The differential cross sections for these channels, elastic scattering, and fusion were analyzed using a coupled reaction channels approach. The large measured ratio of the 2n-to-1n cross section and the strong influence of 2n transfer on other channels indicate that the dineutron configuration of 6He plays a dominant role in the reaction mechanism.

First measurement of the giant monopole and quadrupole resonances in a short-lived nucleus: 56Ni.

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the 56Ni unstable nucleus by inducing the 56Ni(d,d') reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3+/-0.5 MeV and 16.2+/-0.5 MeV, respectively. The corresponding angular distributions are extracted from 3 degrees to 7 degrees . A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.

Reduction of the spin-orbit splittings at the n = 28 shell closure.

The N = 28 shell closure has been investigated via the 46Ar(d,p)47Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p(3/2), p(1/2), and f(5/2) states in 47Ar were determined and compared to those of the 49Ca isotone. We deduced a reduction of the N = 28 gap by 330(90) keV and spin-orbit weakenings of approximately 10(2) and 45(10)% for the f and p states, respectively. Such large variations for the f and p spin-orbit splittings could be accounted for by the proton-neutron tensor force and by the density dependence of the spin-orbit interaction, respectively. This contrasts with the picture of the spin-orbit interaction as a surface term only.

N = 14 shell closure in 22O viewed through a neutron sensitive probe.

To investigate the behavior of the N = 14 neutron gap far from stability with a neutron-sensitive probe, proton elastic and 2(1)+ inelastic scattering angular distributions for the neutron-rich nucleus 22O were measured using the MUr à STrip detector array at the Grand Accélérateur National d'Ions Lourds facility. A deformation parameter beta(p,p') = 0.26 +/- 0.04 is obtained for the 2(1)+ state, much lower than in 20O, showing a weak neutron contribution to this state. A microscopic analysis was performed using matter and transition densities generated by continuum Skyrme-Hartree-Fock-Bogoliubov and quasiparticle random phase approximation calculations, respectively. The ratio of neutron to proton contributions to the 2(1)+ state is found close to the N/Z ratio, demonstrating a strong N = 14 shell closure in the vicinity of the neutron drip line.

Evidence for a three-phonon giant resonance state in 40Ca nuclei.

Inelastic scattering of 40Ca on 40Ca at 50 MeV/A has been measured in coincidence with protons at the GANIL facility. The SPEG spectrometer was associated with 240 CsI(Tl) scintillators of the INDRA 4pi array, allowing for the measurement of complete decay events. The missing energy method was applied to these events. For events with excitation energy between 42 and 55 MeV, a direct decay branch by three protons towards the low energy states of 37Cl gives the first evidence for a 3-phonon state built with giant resonances.

(68)(28)Ni(40): Magicity versus superfluidity.

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.

Strong enhancement of extremely energetic proton production in central heavy ion collisions at intermediate energy.

The energetic proton emission has been investigated as a function of the reaction centrality for the system (58)Ni + (58)Ni at 30A MeV. Extremely energetic protons (E(NN)(p) > or = 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.

On the validity of language: speaking, knowing and understanding in medical geography.

This essay examines methodological problems concerning the conceptualization and operationalization of phenomena central to medical geography. Its main argument is that qualitative research can be strengthened if the differences between instrumental and apparent validity are better understood than the current research in medical geography suggests. Its premise is that our definitions of key terms and concepts must be reinforced throughout the design of research should our knowledge and understanding be enhanced. In doing so, the paper aims to move the methodological debate beyond the simple dichotomies of quantitative vs qualitative approaches and logical positivism vs phenomenology. Instead, the argument is couched in a postmodernist hermeneutic sense which questions the validity of one discourse of investigation over another. The paper begins by discussing methods used in conceptualizing and operationalizing variables in quantitative and qualitative research design. Examples derive from concepts central to a geography of health-care behavior and well-being. The latter half of the essay shows the uses and misuses of validity studies in selected health services research and the current debate on national health insurance.

Help-seeking behavior, use, and satisfaction among frequent primary care users in Santiago de Chile.

PIP: A survey of 140 low-income, urban consumers of primary health care services provided by the public sector at Santiago, Chile's Villa O'Higgins Clinic suggested that organizational factors are more significant predictors of frequency of clinic use and patient satisfaction than demographic characteristics of the clinic population. 73% of respondents interviewed were female; the mean family size was 5, most were from families that fell well below the official poverty level, and 76% of household income went toward food. 29% of the households represented lacked adult men or had unemployed male workers. 66% were acute care patients; the remainder were receiving treatment for chronic conditions such as diabetes, high blood pressure, and alcoholism. 70% had been attending the clinic for the past few years; the mean number of visits per year was 6.4. 53% indicated a preference for a public rather than a private doctor, even if the latter were affordable. Only 51% expressed a dislike of any aspect of the clinic (long waits, 24%; discourteous staff, 19%; and lack of cleanliness, 5%). 84% perceived the quality of the care they received as good; this perception was strongly associated with satisfaction with the physician and receipt of prescription drugs. Multiple regression analysis indicated that 4 organizational variables (travel time to clinic, distance from home to clinic, waiting time at clinic, and travel time-travel distance) and 3 demographic factors (mother bringing child for care, presence of children under 5 years of age, and acute rather than chronic illness) were the best predictors of the frequency of clinic visits. Changes in clinic management by Chile's military government may jeopardize this pattern of high satisfaction with public health services by the poor.^ieng

DRG calculation and utilization patterns: a review of method and policy.

This paper examines methodological and policy issues of interest to medical geographers who use diagnosis-related groups (DRGs) in their research. Methodological issues are studied in terms of the calculation of DRGs and variation in the utilization of surgical and medical DRGs. It is argued that a shift to a single DRG price system should first address the (i) regional disparities that currently exist and the need for large-scale indices of medical wages and labor costs; (ii) severity of illness measurements other than the present nominal ones; and (iii) wide variation among medical versus surgical procedures. The Department of Commerce's Economic Analysis Area is recommended to remedy the problem of geographic scale. Policy issues of interest to medical geographers center around the shift to greater hospital specialization which is likely to continue across the country. Inner-city, rural and teaching hospitals may continue to be inadequately reimbursed by DRGs, treat more medically indigent, or both. Medical geographers should be aware of the policy and methodological issues involved not only in DRGs, but in proposed prospective payment systems for ambulatory and long-term care.

HMO promotion and the privatization of health care in Chile.

Since 1973 the Chilean junta has privatized sectors of the national economy. This paper analyzes the country's policy process of promoting private medical programs through HMO-like plans (ISAPREs, or Institutes of Provisional Health). These plans have captured less than half of their originally anticipated market share. It is argued that the future performance of ISAPREs will be undermined by their limited maternal benefits, their targeting to a small upper-income group which cannot sustain many private medical programs, and competition with less expensive yet equally competent public medical programs. The paper briefly compares privatization in Chile with the experiences of other countries, and specifically contrasts the restructuring of health services under military rule in Chile with those of Argentina and Uruguay. The paper concludes that the Chilean experience with HMOs epitomizes the perils of planning health care during short-term periods of economic prosperity as well as failing to consult medical care providers and consumers.

Restructuring health care financing in Chile.

The current Chilean government adopted a neoclassical model of development and subsequently introduced various incentives for the privatization of medical care. This paper analyzes health care financing in Chile during the last decade and evaluates government efforts to minimize state-financed medical care. In so doing, this paper provides a framework for analyzing private vs public medical care delivery systems in developing countries. For this reason, the first section discusses the major attributes and issues of public and private delivery systems followed by a case study examining the origins, effectiveness and impact of the restructured health system in Chile.

A methodological note on location-allocation models.

Three conditions render the use of standard methodologies inappropriate in solving location-allocation problems. This paper presents one alternative method for assigning an emergency aircraft to one of three hospitals in northern Chile when standard approaches are not suitable. Graph analyses and the demographic potential measures are used in the case presented. The main advantages of this alternative approach are its computational ease and the use of more than one method.