626 research outputs found

### Nuclear surface diffuseness revealed in nucleon-nucleus diffraction

Nuclear surface provides useful information on nuclear radius, nuclear
structure as well as properties of nuclear matter. We discuss the relationship
between the nuclear surface diffuseness and elastic scattering differential
cross section at the first diffraction peak of high-energy nucleon-nucleus
scattering as an efficient tool in order to extract the nuclear surface
information from limited experimental data involving short-lived unstable
nuclei. The high-energy reaction is described by a reliable microscopic
reaction theory, the Glauber model. Extending the idea of the black sphere
model, we find one-to-one correspondence between the nuclear bulk structure
information and proton elastic scattering diffraction peak. This implies that
we can extract both the nuclear radius and diffuseness simultaneously, using
the position of the first diffraction peak and its magnitude of the elastic
scattering differential cross section. We confirm the reliability of this
approach by using realistic density distributions obtained by a mean-field
model.Comment: 12 pages, 12 figures, to appear in Phys. Rev.

### Improved parametrization of the transparency parameter in Kox and Shen models of total reaction cross sections

The total reaction cross section is an essential quantity in particle and heavy-ion transport codes when determining the mean free path of a transported particle. Many transport codes determine the distance a particle is transported before it collides with the target or is stopped in the target material, with the Monte Carlo (MC) method using semiempirical parametrization models for the total reaction cross sections. In order to improve the well-known Kox and Shen models of total reaction cross sections and allow the models to be used at energies below 30 MeV/nucleon, we propose a modified parametrization of the transparency parameter. We also report that the Kox and Shen models have a projectile-target asymmetry and should be used so that the lighter nucleus is always treated as the projectile

### Nuclear transparencies for nucleons, knocked-out under various semi-inclusive conditions

Using hadron dynamics we calculate nuclear transparencies for protons,
knocked-out in high-$Q^2$, semi-inclusive reactions. Predicted transparencies
are, roughly half a standard deviation above the NE18 data. The latter contain
the effects of binned proton missing momenta and mass, and of finite detector
acceptances. In order to test sensitivity we compare computed transparencies
without restrictions and the same with maximal cuts for missing momenta and the
electron energy loss. We find hardly any variation, enabling a meaningful
comparison with data and predictions based on hadron dynamics. Should
discrepancies persist in high-statistics data, the above may with greater
confidence be attributed to exotic components in the description of the
outgoing proton.Comment: 13 pages + 3 figsin appended PS file, report # WIS-94/43/Oct-P

### Absolute accuracy in membrane-based ac nanocalorimetry

To achieve accurate results in nanocalorimetry a detailed analysis and
understanding of the behavior of the calorimetric system is required. There are
especially two system-related aspects that should be taken in consideration:
the properties of the empty cell and the effect of the thermal link between
sample and cell. Here we study these two aspects for a membrane-based system
where heater and thermometer are both in good contact with each other and the
center of the membrane. Practical, analytical expressions for describing the
frequency dependence of heat capacity, thermal conductance, and temperature
oscillation of the system are formulated and compared with measurements and
numerical simulations. We finally discuss the experimental conditions for an
optimal working frequency, where high resolution and good absolute accuracy are
combined

### Field-induced Bose-Einstein Condensation of triplons up to 8 K in Sr3Cr2O8

Single crystals of the spin dimer system Sr3Cr2O8 have been grown for the
first time. Magnetization, heat capacity, and magnetocaloric effect data up to
65 T reveal magnetic order between applied fields of Hc1 ~ 30.4 T and Hc2 ~ 62
T. This field-induced order persists up to ~ 8 K at H ~ 44 T, the highest
observed in any quantum magnet where Hc2 is experimentally-accessible. We fit
the temperature-field phase diagram boundary close to Hc1 using the expression
Tc = A(H-Hc1)^v. The exponent v = 0.65(2), obtained at temperatures much
smaller than 8 K, is that of the 3D Bose-Einstein condensate (BEC) universality
class. This finding strongly suggests that Sr3Cr2O8 is a new realization of a
triplon BEC where the universal regimes corresponding to both Hc1 and Hc2 are
accessible at He-4 temperatures.Comment: 4 pages, 3 figures, accepted by PR

### Proton-nucleus total reaction cross sections in the optical limit Glauber theory: Subtle dependence on the equation of state of nuclear matter

We calculate the proton-nucleus total reaction cross sections at different
energies of incident protons within the optical limit approximation of the
Glauber theory. The isospin effect has been taken into account. The nucleon
distribution is obtained in the framework of macroscopic nuclear models in a
way depending on the equation of state of uniform nuclear matter near the
saturation density. We find that at an energy of order 40 MeV, the reaction
cross section calculated for neutron- rich isotopes significantly increases as
the parameter L characterizing the density dependence of the symmetry energy
increases, while at energies of order 300 and 800 MeV, it is almost independent
of L. This is a feature of the optical limit Glauber theory in which an
exponential dependence of the reaction cross section on the neutron skin
thickness remains when the total proton-neutron cross section is small enough.Comment: 5 pages, 4 figure

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