Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0708.0218

Spin measurements for 147Sm+n resonances: Further evidence for non-statistical effects

P. E. Koehler·J. L. Ullmann·T. A. Bredeweg·J. M. O`Donnell·R. Reifarth·R. S. Rundberg·D. J. Vieira·J. M. Wouters
View original source ↗Read source document ↗Export metadata ↓

Abstract

We have determined the spins J of resonances in the 147Sm(n,gamma) reaction by measuring multiplicities of gamma-ray cascades following neutron capture. Using this technique, we were able to determine J values for all but 14 of the 140 known resonances below En = 1 keV, including 41 firm J assignments for resonances whose spins previously were either unknown or tentative. These new spin assignments, together with previously determined resonance parameters, allowed us to extract separate level spacings and neutron strength functions for J = 3 and 4 resonances. Furthermore, several statistical test of the data indicate that very few resonances of either spin have been missed below En = 700eV. Because a non-statistical effect recently was reported near En = 350 eV from an analysis of 147Sm(n,alpha) data, we divided the data into two regions; 0 < En < 350 eV and 350 < En < 700 eV. Using neutron widths from a previous measurement and published techniques for correcting for missed resonances and for testing whether data are consistent with a Porter-Thomas distribution, we found that the reduced-neutron-width distribution for resonances below 350 eV is consistent with the expected Porter-Thomas distribution. On the other hand, we found that reduced-neutron-width data in the 350 < En < 700 eV region are inconsistent with a Porter-Thomas distribution, but in good agreement with a chi-squared distribution having two or more degrees of freedom. We discuss possible explanations for these observed non-statistical effects and their possible relation to similar effects previously observed in other nuclides.

Explore related subjects

nucl-exnucl-th

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

P. E. Koehler, J. L. Ullmann, T. A. Bredeweg, J. M. O`Donnell, R. Reifarth, R. S. Rundberg, D. J. Vieira, J. M. Wouters. 2007-08-01. Spin measurements for 147Sm+n resonances: Further evidence for non-statistical effects. https://doi.org/10.1103/physrevc.76.025804

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Centrality dependence of charged-particle pseudorapidity density at midrapidity in Pb-Pb collisions at $\mathbf{\sqrt{\textit{s}_{\rm NN}} = 5.36}$ TeV

The ALICE Collaboration reports its first LHC Run 3 measurements of charged-particle pseudorapidity density at midrapidity in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV. Particle multiplicity in high-energy collisions characterises the system geometry, constrains particle-production mechanisms, and is used to estimate initial energy density. Multiplicity also acts as a reference for subsequent measurements as a function of centrality. In this letter, for the first time, charged particles are reconstructed using the upgraded ALICE Inner Tracking System and Time Projection Chamber, while the collision centrality is determined by measuring charged-particle multiplicities with the Fast Interaction Trigger system. Pseudorapidity density, ${\rm d}N_{\rm ch}/{\rm d}η$, is presented, averaged over events, for various centrality classes. Results are shown as a function of pseudorapidity and the average number of participating nucleons ($\langle N_{\mathrm{part}}\rangle$) in the collision. The average charged-particle pseudorapidity density ($\langle {\rm d}N_{\rm ch}/{\rm d}η\rangle$) at midrapidity ($|η|<0.5$) is 2010 $\pm$ 53 for the 5% most central collisions. The value of $\langle {\rm d}N_{\rm ch}/{\rm d}η\rangle$ normalised to $\langle N_{\mathrm{part}}\rangle/2$ as a function of $\sqrt{s_{\mathrm{NN}}}$ follows the trend established in previous measurements in heavy-ion collisions. Theoretical models based on mechanisms for particle production in nuclear collisions that involve the formation of quark-gluon plasma medium and models based on individual nucleon-nucleon interactions are compared to the data.

nucl-ex↗
arXiv2026

Observation of a magnetic shift in neutron whispering-gallery states

We developed experimental and theoretical methods to create and describe high-resolution whispering-gallery interference patterns and show the feasibility of measuring their small shifts by external interactions. Such experiments can be used to search for extra fundamental interactions, time parity violations, nonzero electric charges, precisely measuring the gravitational properties of (anti)matter, parity violations, neutron polarizability, quantum reflection, surface state effects, etc. Here, we measure a magnetic shift of such a neutron pattern $δg/g\sim (6.5 \pm 0.8_{st} \pm 1.2_{sys}) \cdot 10^{-4}$, and our sensitivity to spin-dependent differences between the scattering lengths was $δb_n/b_n \sim 10^{-4}$.

nucl-ex↗
arXiv2026

Photoneutron reactions on $^{165}$Ho and $^{169}$Tm in the giant dipole resonance region

Photoneutron reactions were investigated for the deformed $^{165}$Ho and $^{169}$Tm nuclei from the vicinity of the neutron emission threshold up to $\sim$40~MeV, well above the giant dipole resonance (GDR) region, using quasimonochromatic laser Compton scattering $γ$-ray beams provided at the NewSUBARU facility, Japan. A high-and-flat efficiency moderated array of $^3$He counters was used for the neutron detection and an associated neutron multiplicity sorting method for extracting the $(γ,\,1nX)$, $(γ,\,2nX)$, $(γ,\,3nX)$ and $(γ,\,4nX)$ reaction cross sections and average neutron emission energies. The present $^{165}$Ho cross sections were compared to existing data, revealing discrepancies with the Saclay multiplicity sorting results and an overall 10$\%$ strength difference with the Livermore ones. There are no other data for $^{169}$Tm. GDR parameters based on phenomenological Lorentzian models were extracted by fitting the present $σ(γ,\,Sn)$ data with adjustments for the missing contribution of charged-particle-only reactions not observed experimentally. For both nuclei we observed high energy structures at 20-25~MeV, matching giant quadrupole resonance KMFR predictions. Based on the present centroid energies of the first and second GDR peaks, hydrodynamic model predictions gave intrinsic electric quadrupole moments of +7.00(34)~b and +7.38(28)~b for the ground states of $^{165}$Ho and $^{169}$Tm, respectively. The present experimental excitation functions and photoneutron energies were compared to statistical model calculations. Using the EMPIRE code, we performed a sensitivity test to phenomenological models of photon strength functions and nuclear level densities. The TALYS code was used to reproduce the present experimental $(γ,\,inX)$ cross sections and average neutron energies using microscopic nuclear level density models.

nucl-ex↗