285 research outputs found
Measurement of \u3cem\u3eγ\u3c/em\u3e-emission Branching Ratios for \u3csup\u3e154,156,158\u3c/sup\u3eGd Compound Nuclei: Tests of Surrogate Nuclear Reaction Approximations for (\u3cem\u3en,γ\u3c/em\u3e) Cross Sections
The surrogate nuclear reaction method can be used to determine neutron-induced reaction cross sections from measured decay properties of a compound nucleus created using a different reaction and calculated formation cross sections. The reliability of (n,γ) cross sections determined using the Weisskopf-Ewing and ratio approximations are explored for the 155, 157Gd(n,γ) reactions. Enriched gadolinium targets were bombarded with 22-MeV protons and γ rays were detected in coincidence with scattered protons using the Silicon Telescope Array for Reaction Studies/Livermore-Berkeley Array for Collaborative Experiments (STARS/LiBerACE) silicon and germanium detector arrays. The γ-emission probabilities for the 154, 156, 158Gd compound nuclei were measured at excitation energies up to 12 MeV. It is found that the approximations yield results that deviate from directly measured 155, 157Gd(n,γ) cross sections at low energies. To extract reliable cross sections, a more sophisticated analysis should be developed that takes into account angular-momentum differences between the neutron-induced and surrogate reactions
Calculation of energy levels and transition amplitudes for barium and radium
The radium atom is a promising system for studying parity and time invariance
violating weak interactions. However, available experimental spectroscopic data
for radium is insufficient for designing an optimal experimental setup. We
calculate the energy levels and transition amplitudes for radium states of
significant interest. Forty states corresponding to all possible configurations
consisting of the , and single-electron states as well as the
states of the , and configurations have been calculated.
The energies of ten of these states corresponding to the , ,
, and configurations are not known from experiment. Calculations
for barium are used to control the accuracy.Comment: 12 pages, 4 table
Double-beta decay Q values of 130Te, 128Te, and 120Te
The double-beta decay Q values of 130Te, 128Te, and 120Te have been
determined from parent-daughter mass differences measured with the Canadian
Penning Trap mass spectrometer. The 132Xe-129Xe mass difference, which is
precisely known, was also determined to confirm the accuracy of these results.
The 130Te Q value was found to be 2527.01(32) keV which is 3.3 keV lower than
the 2003 Atomic Mass Evaluation recommended value, but in agreement with the
most precise previous measurement. The uncertainty has been reduced by a factor
of 6 and is now significantly smaller than the resolution achieved or foreseen
in experimental searches for neutrinoless double-beta decay. The 128Te and
120Te Q values were found to be 865.87(131) keV and 1714.81(125) keV,
respectively. For 120Te, this reduction in uncertainty of nearly a factor of 8
opens up the possibility of using this isotope for sensitive searches for
neutrinoless double-electron capture and electron capture with positron
emission.Comment: 5 pages, 2 figures, submitted to Physical Review Letter
Report on 240Am(n,x) surrogate cross section test measurement
The main goal of the test measurement was to determine the feasibility of the {sup 243}Am(p,t) reaction as a surrogate for {sup 240}Am(n,f). No data cross section data exists for neutron induced reactions on {sup 240}Am; the half-life of this isotope is only 2.1 days making direct measurements difficult, if not impossible. The 48-hour experiment was conducted using the STARS/LIBERACE experimental facility located at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory in August 2011. A description of the experiment and results is given. The beam energy was initially chosen to be 39 MeV in order to measure an equivalent neutron energy range from 0 to 20 MeV. However, the proton beam was not stopped in the farady cup and the beam was deposited in the surrounding shielding material. The shielding material was not conductive, and a beam current, needed for proper tuning of the beam as well as experimental monitoring, could not be read. If the {sup 240}Am(n,f) surrogate experiment is to be run at LBNL, simple modifications to the beam collection site will need to be made. The beam energy was reduced to 29 MeV, which was within an energy regime of prior experiments and tuning conditions at STARS/LIBERACE. At this energy, the beam current was successfully tuned and measured. At 29 MeV, data was collected with both the {sup 243}Am and {sup 238}U targets. An example particle identification plot is shown in Fig. 1. The triton-fission coincidence rate for the {sup 243}Am target and {sup 238}U target were measured. Coincidence rates of 0.0233(1) cps and 0.150(6) cps were observed for the {sup 243}Am and {sup 238}U targets, respectively. The difference in count rate is largely attributed to the available target material - the {sup 238}U target contains approximately 7 times more atoms than the {sup 243}Am. A proton beam current of {approx}0.7 nA was used for measurements on both targets. Assuming a full experimental run under similar conditions, an estimate for the run time needed was made. Figure 2 shows the number of days needed as a function of acceptable uncertainty for a measurement of 1-20 MeV equivalent neutron energy, binned into 200 keV increments. A 5% measurement will take 3 days for U, but 20 days for Am. It may be difficult to be the sole user of the LBNL cyclotron, or another facility, for such an extended period. However, a 10% measurement will take 19 hours for U, and 5 days for Am. Such a run period is more reasonable and will allow for the first ever measurement of the {sup 240}Am(n,f) cross section. We also anticipate 40% more beam time being available at Texas A&M Cyclotron Institute compared to LBNL in FY2012. The increased amount of beam time will allow us to accumulate better statistics then what would have been available at LBNL
The WITCH experiment: Acquiring the first recoil ion spectrum
The standard model of the electroweak interaction describes beta-decay in the
well-known V-A form. Nevertheless, the most general Hamiltonian of a beta-decay
includes also other possible interaction types, e.g. scalar (S) and tensor (T)
contributions, which are not fully ruled out yet experimentally. The WITCH
experiment aims to study a possible admixture of these exotic interaction types
in nuclear beta-decay by a precise measurement of the shape of the recoil ion
energy spectrum. The experimental set-up couples a double Penning trap system
and a retardation spectrometer. The set-up is installed in ISOLDE/CERN and was
recently shown to be fully operational. The current status of the experiment is
presented together with the data acquired during the 2006 campaign, showing the
first recoil ion energy spectrum obtained. The data taking procedure and
corresponding data acquisition system are described in more detail. Several
further technical improvements are briefly reviewed.Comment: 11 pages, 6 figures, conference proceedings EMIS 2007
(http://emis2007.ganil.fr), published also in NIM B:
doi:10.1016/j.nimb.2008.05.15
Beta-delayed-neutron studies of Sb and I performed with trapped ions
Beta-delayed-neutron (n) spectroscopy was performed using the
Beta-decay Paul Trap and an array of radiation detectors. The n
branching ratios and energy spectra for Sb and I were
obtained by measuring the time of flight of recoil ions emerging from the
trapped ion cloud. These nuclei are located at the edge of an isotopic region
identified as having n branching ratios that impact the r-process
abundance pattern around the A~130 peak. For Sb and I,
n branching ratios of 14.6(11)%, 17.6(28)%, and 7.6(28)% were
determined, respectively. The n energy spectra obtained for Sb
and I are compared with results from direct neutron measurements, and
the n energy spectrum for Sb has been measured for the first
time
Wnt5a induces ROR1 to complex with HS1 to enhance migration of chronic lymphocytic leukemia cells.
ROR1 (receptor tyrosine kinase-like orphan receptor 1) is a conserved, oncoembryonic surface antigen expressed in chronic lymphocytic leukemia (CLL). We found that ROR1 associates with hematopoietic-lineage-cell-specific protein 1 (HS1) in freshly isolated CLL cells or in CLL cells cultured with exogenous Wnt5a. Wnt5a also induced HS1 tyrosine phosphorylation, recruitment of ARHGEF1, activation of RhoA and enhanced chemokine-directed migration; such effects could be inhibited by cirmtuzumab, a humanized anti-ROR1 mAb. We generated truncated forms of ROR1 and found its extracellular cysteine-rich domain or kringle domain was necessary for Wnt5a-induced HS1 phosphorylation. Moreover, the cytoplamic, and more specifically the proline-rich domain (PRD), of ROR1 was required for it to associate with HS1 and allow for F-actin polymerization in response to Wnt5a. Accordingly, we introduced single amino acid substitutions of proline (P) to alanine (A) in the ROR1 PRD at positions 784, 808, 826, 841 or 850 in potential SH3-binding motifs. In contrast to wild-type ROR1, or other ROR1P→︀A mutants, ROR1P(841)A had impaired capacity to recruit HS1 and ARHGEF1 to ROR1 in response to Wnt5a. Moreover, Wnt5a could not induce cells expressing ROR1P(841)A to phosphorylate HS1 or activate ARHGEF1, and was unable to enhance CLL-cell motility. Collectively, these studies indicate HS1 plays an important role in ROR1-dependent Wnt5a-enhanced chemokine-directed leukemia-cell migration
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