14 research outputs found
Level density of Fe and low-energy enhancement of -strength function
The MnFe differential cross section is measured at
MeV\@. The Fe level density obtained from neutron evaporation spectra is
compared to the level density extracted from the
FeHe,Fe reaction by the Oslo-type technique.
Good agreement is found between the level densities determined by the two
methods. With the level density function obtained from the neutron evaporation
spectra, the Fe -strength function is also determined from the
first-generation matrix of the Oslo experiment. The good agreement
between the past and present results for the -strength function
supports the validity of both methods and is consistent with the low-energy
enhancement of the strength below MeV first discovered by the
Oslo method in iron and molybdenum isotopes.Comment: 7 pages, 5 figure
Recommended from our members
Level densities of iron isotopes and lower-energy enhancement of y-strength function
The neutron spectrum from the {sup 55}Mn(d,n){sup 56}Fe reaction has been measured at E{sub d} = 7 MeV. The level density of {sup 56}Fe obtained from neutron evaporation spectrum has been compared to the level density from Oslo-type {sup 57}Fe({sup 3}He, a{gamma}){sup 56}Fe experiment [1]. The good agreement supports the recent results [1, 8] including an availability of a low-energy enhancement in the {gamma}-strength function for iron isotopes. The new level density function allowed us to investigate an excitation energy dependence of this enhancement, which is shown to increase with increasing excitation energy
Recommended from our members
Bulk Properties of Iron Isotopes
Nuclear level densities and radiative strength functions (RSF) in {sup 56}Fe and {sup 57}Fe were measured using the {sup 57}Fe({sup 3}He,{alpha}{gamma}) and {sup 57}Fe({sup 3}He, {sup 3}He{prime}{gamma}) reactions, respectively, at Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4 MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the {sup 56}Fe(n,2{gamma}) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSF. In a third experiment, the neutron evaporation spectrum from the {sup 55}Mn(dn,N){sup 56}Fe reaction was measured at 7-MeV deuteron energy at John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of {sup 56}Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft {gamma} rays is supported by the last experiment
Double beta decay: present status
The present status of double beta decay experiments (including the search for
, EC and ECEC processes) are reviewed. The results of
the most sensitive experiments are discussed. Average and recommended half-life
values for two-neutrino double beta decay are presented. Conservative upper
limits on effective Majorana neutrino mass and the coupling constant of the
Majoron to the neutrino are established as eV and , respectively. Proposals for future double beta decay
experiments with a sensitivity for the at the level of (0.01-0.1)
eV are considered.Comment: 33 pages included 7 figures and 14 tables; an extended version of the
invited talk at 13th Lomonosov Conference of Elementary Particle Physics,
23-29 August, 2007, Moscow, Russi
Urine from Treated Cattle Drives Selection for Cephalosporin Resistant Escherichia coli in Soil
The U.S. Food and Drug Administration recently issued new rules for using ceftiofur in food animals in part because of an increasing prevalence of enteric bacteria that are resistant to 3(rd)-generation cephalosporins. Parenteral ceftiofur treatment, however, has limited effects on enteric bacteria so we tested the hypothesis that excreted ceftiofur metabolites exert significant selection pressure for ceftiofur-resistant Escherichia coli in soil. Test matrices were prepared by mixing soil with bovine feces and adding urine containing ceftiofur metabolites (CFM) (0 ppm, ∼50 ppm and ∼100 ppm). Matrices were incubated at 23°C or 4°C for variable periods of time after which residual CFM was quantified using a bioassay. Bla (CMY-2) plasmid-bearing ceftiofur resistant (cef(R)) E. coli and one-month old calves were used to study the selection effects of CFM and transmission of cef(R) bacteria from the environment back to animals. Our studies showed that urinary CFM (∼13 ppm final concentration) is biologically degraded in soil within 2.7 days at 23°C, but persists up to 23.3 days at 4°C. Even short-term persistence in soil provides a >1 log(10) advantage to resistant E. coli populations, resulting in significantly prolonged persistence of these bacteria in the soil (∼two months). We further show that resistant strains readily colonize calves by contact with contaminated bedding and without antibiotic selection pressure. Ceftiofur metabolites in urine amplify resistant E. coli populations and, if applicable to field conditions, this effect is far more compelling than reported selection in vivo after parenteral administration of ceftiofur. Because ceftiofur degradation is temperature dependent, these compounds may accumulate during colder months and this could further enhance selection as seasonal temperatures increase. If cost-effective engineered solutions can be developed to limit ex vivo selection, this may limit proliferation for ceftiofur resistant enteric bacteria while preserving the ability to use this important antibiotic in food animal production