474 research outputs found
Absolute Determination of the 22Na(p,g) Reaction Rate in Novae
Gamma-ray telescopes in orbit around the Earth are searching for evidence of
the elusive radionuclide 22Na produced in novae. Previously published
uncertainties in the dominant destructive reaction, 22Na(p,g)23Mg, indicated
new measurements in the proton energy range of 150 to 300 keV were needed to
constrain predictions. We have measured the resonance strengths, energies, and
branches directly and absolutely by using protons from the University of
Washington accelerator with a specially designed beamline, which included beam
rastering and cold vacuum protection of the 22Na implanted targets. The
targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~ 20 C
bombardment as a result of protective layers. We avoided the need to know the
stopping power, and hence the target composition, by extracting resonance
strengths from excitation functions integrated over proton energy. Our
measurements revealed that resonance strengths for E_p = 213, 288, 454, and 610
keV are stronger by factors of 2.4 to 3.2 than previously reported. Upper
limits have been placed on proposed resonances at 198-, 209-, and 232-keV. We
have re-evaluated the 22Na(p,g) reaction rate, and our measurements indicate
the resonance at 213 keV makes the most significant contribution to 22Na
destruction in novae. Hydrodynamic simulations including our rate indicate that
the expected abundance of 22Na ejecta from a classical nova is reduced by
factors between 1.5 and 2, depending on the mass of the white-dwarf star
hosting the nova explosion.Comment: 20 pages, 18 figures; shortened paper, accepted in Phys. Rev.
The interaction of 11Li with 208Pb
Background: 11Li is one of the most studied halo nuclei. The fusion of 11Li
with 208Pb has been the subject of a number of theoretical studies with widely
differing predictions, ranging over four orders of magnitude, for the fusion
excitation function.
Purpose: To measure the excitation function for the 11Li + 208Pb reaction.
Methods: A stacked foil/degrader assembly of 208Pb targets was irradiated
with a 11Li beam producing center of target beam energies from above barrier to
near barrier energies (40 to 29 MeV). The intensity of the 11Li beam (chopped)
was 1250 p/s and the beam on-target time was 34 hours. The alpha-decay of the
stopped evaporation residues was detected in a alpha-detector array at each
beam energy in the beam-off period (the beam was on for <= 5 ns and then off
for 170 ns).
Results: The 215At evaporation residues were associated with the fusion of
11Li with 208Pb. The 213,214At evaporation residues were formed by the breakup
of 11Li into 9Li + 2n, with the 9Li fusing with 208Pb. The 214At evaporation
residue appears to result from a "quasi-breakup" process.
Conclusions: Most of 11Li + 208Pb interactions lead to breakup with a small
fraction (<= 11%) leading to complete fusion.Comment: 25 pages, 11 figure
Charge state studies of low energy heavy ions passing through hydrogen and helium gas
Studies of the charge state distribution of low energy (< 1.5 MeV/u), low Z (< 13) heavy ions passing through hydrogen and helium gas of varying target pressure have been performed using separate windowless gas target systems at TRIUMF and the University of Naples. Semi-empirical relationships have been deduced to estimate the equilibrium charge state distributions as a function of beam energy. From these distributions, cross-sections for the relevant charge changing reactions have been deduced. (C) 2002 Elsevier Science B.V. All rights reserved
Development of clinically relevant in vivo metastasis models using human bone discs and breast cancer patient-derived xenografts
Background
Late-stage breast cancer preferentially metastasises to bone; despite advances in targeted therapies, this condition remains incurable. The lack of clinically relevant models for studying breast cancer metastasis to a human bone microenvironment has stunted the development of effective treatments for this condition. To address this problem, we have developed humanised mouse models in which breast cancer patient-derived xenografts (PDXs) metastasise to human bone implants with low variability and high frequency.
Methods
To model the human bone environment, bone discs from femoral heads of patients undergoing hip replacement surgery were implanted subcutaneously into NOD/SCID mice. For metastasis studies, 7 patient-derived xenograft tumours (PDX: BB3RC32, ER+ PR+ HER2â; BB2RC08, ER+ PR+ ER2â; BB6RC37, ERâ PRâ HER2â and BB6RC39, ER+ PR+ HER2+), MDA-MB-231-luc2, T47D-luc2 or MCF7-Luc2 cells were injected into the 4th mammary ducts and metastases monitored by luciferase imaging and confirmed on histological sections. Bone integrity, viability and vascularisation were assessed by uCT, calcein uptake and histomorphometry. Expression profiling of genes/proteins during different stages of metastasis were assessed by whole genome Affymetrix array, real-time PCR and immunohistochemistry. Importance of IL-1 was confirmed following anakinra treatment.
Results
Implantation of femoral bone provided a metabolically active, human-specific site for tumour cells to metastasise to. After 4 weeks, bone implants were re-vascularised and demonstrated active bone remodelling (as evidenced by the presence of osteoclasts, osteoblasts and calcein uptake). Restricting bone implants to the use of subchondral bone and introduction of cancer cells via intraductal injection maximised metastasis to human bone implants. MDA-MB-231 cells specifically metastasised to human bone (70% metastases) whereas T47D, MCF7, BB3RC32, BB2RC08, and BB6RC37 cells metastasised to both human bone and mouse bones. Importantly, human bone was the preferred metastatic site especially from ER+ PDX (100% metastasis human bone compared with 20â75% to mouse bone), whereas ER-ve PDX developed metastases in 20% of human and 20% of mouse bone. Breast cancer cells underwent a series of molecular changes as they progressed from primary tumours to bone metastasis including altered expression of IL-1B, IL-1R1, S100A4, CTSK, SPP1 and RANK. Inhibiting IL-1B signalling significantly reduced bone metastasis.
Conclusions
Our reliable and clinically relevant humanised mouse models provide significant advancements in modelling of breast cancer bone metastasis
C+O sub-barrier radiative capture cross-section measurements
We have performed a heavy ion radiative capture reaction between two light
heavy ions, C and O, leading to Si. The present experiment
has been performed below Coulomb barrier energies in order to reduce the phase
space and to try to shed light on structural effects. Obtained -spectra
display a previously unobserved strong feeding of intermediate states around 11
MeV at these energies. This new decay branch is not fully reproduced by
statistical nor semi-statistical decay scenarii and may imply structural
effects. Radiative capture cross-sections are extracted from the data.Comment: 4 pages, 7 figures, to appear as proceedings of FUSION 2011
conference at St-Malo, Franc
The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the
nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the
emission of a characteristic 1.275 MeV gamma-ray line. This report provides the
first direct measurement of the rate of this reaction using a radioactive 21Na
beam, and discusses its astrophysical implications. The energy of the important
state was measured to be E= 205.7 0.5 keV with a resonance
strength meV.Comment: Accepted for publication in Physical Review Letter
pi-NN Coupling Constants from NN Elastic Data between 210 and 800 Mev
High partial waves for and elastic scattering are examined
critically from 210 to 800 MeV. Non-OPE contributions are compared with
predictions from theory. There are some discrepancies, but sufficient agreement
that values of the coupling constants for exchange
and for charged exchange can be derived. Results are and , where the first error is statistical and the
second is an estimate of the likely systematic error, arising mostly from
uncertainties in the normalisation of total cross sections and
.Comment: 21 pages of LaTeX, UI-NTH-940
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