Showing papers by "Peter Möller published in 2009"

Heavy-element fission barriers

Abstract: We present calculations of fission properties for heavy elements. The calculations are based on the macroscopic-microscopic finite-range liquid-drop model with a 2002 parameter set. For each nucleus we have calculated the potential energy in three different shape parametrizations: (1) for 5 009 325 different shapes in a five-dimensional deformation space given by the three-quadratic-surface parametrization, (2) for 10 850 different shapes in a three-dimensional deformation space spanned by epsilon(2), epsilon(4), and gamma in the Nilsson perturbed-spheroid parametrization, supplemented by a densely spaced grid in epsilon(2), epsilon(3), epsilon(4), and epsilon(6) for axially symmetric deformations in the neighborhood of the ground state, and (3) an axially symmetric multipole expansion of the shape of the nuclear surface using beta(2), beta(3), beta(4), and beta(6) for intermediate deformations. For a fissioning system, it is always possible to define uniquely one saddle or fission threshold on the optimum trajectory between the ground state and separated fission fragments. We present such calculated barrier heights for 1585 nuclei from Z=78 to Z=125. Traditionally, actinide barriers have been characterized in terms of a "double-humped" structure. Following this custom we present calculated energies of the first peak, second minimum, and second peak in the barrier for 135 actinide nuclei from Th to Es. However, for some of these nuclei which exhibit a more complex barrier structure, there is no unique way to extract a double-humped structure from the calculations. We give examples of such more complex structures, in particular the structure of the outer barrier region near Th-232 and the occurrence of multiple fission modes. Because our complete results are too extensive to present in a paper of this type, our aim here is limited: (1) to fully present our model and the methods for determining the structure of the potential-energy surface, (2) to present fission thresholds for a large number of heavy elements, (3) to compare our results with the two-humped barrier structure deduced from experiment for actinide nuclei, and (4) to compare to additional fission-related data and other fission models. . (Less)

β-decay half-lives and β-delayed neutron emission probabilities of nuclei in the region A≲110, relevant for the r process

Abstract: Measurements of $\ensuremath{\beta}$-decay properties of $A\ensuremath{\lesssim}110$ r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory at Michigan State University. $\ensuremath{\beta}$-decay half-lives for $^{105}\mathrm{Y}$, $^{106,107}\mathrm{Zr}$, and $^{111}\mathrm{Mo}$, along with $\ensuremath{\beta}$-delayed neutron emission probabilities of $^{104}\mathrm{Y}$, $^{109,110}\mathrm{Mo}$ and upper limits for $^{105}\mathrm{Y}$, $^{103\ensuremath{-}107}\mathrm{Zr}$, and $^{108,111}\mathrm{Mo}$ have been measured for the first time. Studies on the basis of the quasi-random-phase approximation are used to analyze the ground-state deformation of these nuclei.

Global Calculation of Nuclear Shape Isomers

Abstract: To determine which nuclei may exhibit shape isomerism, we use a well-benchmarked macroscopic-microscopic model to calculate potential-energy surfaces as functions of spheroidal (epsilon(2)), hexadecapole (epsilon(4)), and axial-asymmetry (gamma) shape coordinates for 7206 nuclei from A=31 to A=290. We analyze these and identify the deformations and energies of all minima deeper than 0.2 MeV. These minima may correspond to characteristic experimentally observable shape-isomeric states. Shape isomers mainly occur in the A=80 region, the A=100 region, and in an extended region centered around Pb-208. We compare our model to experimental results for Kr isotopes. Moreover, in a plot versus N and Z we show for each of the 7206 nuclei the calculated number of minima. The results reveal one fairly unexplored region of shape isomerism, which is experimentally accessible, namely the region northeast of Pb-208(82). (Less)

Loss of HLA-DR expression and immunoblastic morphology predict adverse outcome in diffuse large B-cell lymphoma – analyses of cases from two prospective randomized clinical trials

Abstract: Background Research on prognostically relevant immunohistochemical markers in diffuse large B-cell lymphomas has mostly been performed on retrospectively collected clinical data. This is also true for immunohistochemical classifiers that are thought to reflect the cell-of-origin subclassification of gene expression studies. In order to obtain deeper insight into the heterogeneous prognosis of diffuse large B-cell lymphomas and to validate a previously published immunohistochemical classifier, we analyzed data from a large set of cases from prospective clinical trials with long-term follow-up.Design and Methods We performed morphological and extensive immunohistochemical analyses in 414 cases of diffuse large B-cell lymphoma from two prospective randomized clinical trials (NHL-B1/B2, Germany). Classification into germinal center and non-germinal center subtypes of B-cell lymphoma was based on the expression pattern of CD10, BCL6, and IRF4. Multivariate analyses were performed adjusting for the factors in the International Prognostic Index.Results Analyzing 20 different epitopes on tissue microarrays, expression of HLA-DR, presence of CD23+ follicular dendritic cell meshworks, and monotypic light chain expression emerged as International Prognostic Index-independent markers of superior overall survival. Immunoblastic morphology was found to be related to poor event-free survival. The non-germinal center subtype, according to the three-epitope classifier (CD10, BCL6, and IRF4) did not have prognostic relevance when adjusted for International Prognostic Index factors (relative risk=1.2, p=0.328 for overall survival; and relative risk=1.1, p=0.644 for event-free survival).Conclusions The previously reported International Prognostic Index-independent prognostic value of stratification into germinal center/non-germinal center B-cell lymphoma using the expression pattern of CD10, BCL6, and IRF4 was not reproducible in our series. However, other markers and the morphological subtype appear to be of prognostic value.

The tumor antigens RHAMM and G250/CAIX are expressed in head and neck squamous cell carcinomas and elicit specific CD8+ T cell responses.

Abstract: Despite advances in surgery, radio- and chemotherapy, therapeutic approaches for patients with head and neck squamous carcinoma (HNSCC) need to be improved. Immunotherapies eliciting tumor specific immune responses might constitute novel treatment options. We therefore investigated the expression and immunogenicity of two tumor-associated antigens (TAA) the receptor for hyaluronic acid mediated motility (RHAMM) and carboanhydrase IX (G250/CAIX) in HNSCC patients. Twenty-two HNSCC samples were examined for the expression of RHAMM and G250 by Western blotting and immunohistochemistry, 14/22 samples were tested for HLA-A2 expression by flow cytometry. For 8/22 samples single tumor-cell suspensions were generated, and mixed lymphocyte peptide cultures (MLPC) were performed to evaluate the frequencies of cytotoxic T cells specifically recognizing RHAMM and G250 using Tetramer staining/multi-color flow cytometry and enzyme linked immunosorbent spot (ELISPOT) assays. RHAMM and G250 were expressed in 73 and 80% of the HNSCC samples at the protein level. A co-expression of both TAAs could be detected in 60% of the patients. In 4/8 HLA-A2 + patients, 0.06-0.13% of CD8 + effector T cells recognized Tetramers for RHAMM or G250 and secreted IFNy and granzyme B in ELISPOT assays. RHAMM and G250 are expressed at high frequency and high protein level in HNSCCs and are recognized by cytotoxic CD8 + effector T cells. Therefore both TAAs constitute interesting targets for T cell based immunotherapies for HNSCC.

Combinatorial nuclear level-density model

Abstract: A microscopic nuclear level-density model is presented. The model is a completely combinatorial (micro-canonical) model based on the folded-Yukawa single-particle potential and includes explicit treatment of pairing, rotational and vibrational states. The microscopic character of all states enables extraction of level distribution functions with respect to pairing gaps, parity and angular momentum. The results of the model are compared to available experimental data: neutron separation energy level spacings, data on total level-density functions from the Oslo method, cumulative level densities from low-lying discrete states, and data on parity ratios.

Origin of the narrow, single peak in the fission-fragment mass distribution for 258Fm

Abstract: We discuss the origin of the narrowness of the single peak at mass-symmetric division in the fragment mass-yield curve for spontaneous fission of $^{258}\mathrm{Fm}$. For this purpose, we employ the macroscopic-microscopic model and calculate a potential-energy curve at the mass-symmetric compact scission configuration, as a function of the fragment mass number, which is obtained from the single-particle wave-function densities. In the calculations, we minimize total energies by varying the deformations of the two fragments, with constraints on the mass quadrupole moment, and by keeping the neck radius zero. The energies thus become functions of mass asymmetry. Using the obtained potential, we solve the one-dimensional Schr\"odinger equation with a microscopic coordinate-dependent inertial mass to calculate the fragment mass-yield curve. The calculated mass yield, expressed in terms of the microscopic mass density, is consistent with the extremely narrow experimental mass distribution.