Mon·May 4, 2015Monday·May 4, 2015

1. 01*

   Energy dependence of space-time extent of pion source in nuclear collisions

   V. A. Okorokov (National Research Nuclear University "MEPhI")🇷🇺

   Energy dependence of space-time parameters of pion emission region at freeze-out is studied for collisions of various ions and for all experimentally available energies. The using of femtoscopic radii scaled on the averaged radius of colliding ions is suggested. This approach allows the expansion of the set of interaction types, in particular, on collisions of non-symmetrical ion beams which can be studied within the framework of common treatment. There is no sharp changing of femtoscopic parameter values with increasing of initial energy. Analytic functions suggested for smooth approximations of energy dependence of femtoscopic parameters demonstrate reasonable agreement with most of experimental data at $\sqrt{s_{NN}}\ge 5$ GeV. Estimations of some observables are obtained for energies of the LHC and FCC project.

   nucl-exhep-exeConf(2015)·2 citations
2. 02*

   Cross sections of $\alpha$-induced reactions for targets with masses $A\approx 20-50$ at low energies

   Peter Mohr🇭🇺

   A simple reduction scheme using so-called reduced energies $E_{\mathrm{red}}$ and reduced cross sections ${\sigma }_{\mathrm{red}}$ allows the comparison of heavy-ion induced reaction cross sections for a broad range of masses of projectile and target and over a wide energy range. A global behavior has been found for strongly bound projectiles whereas much larger reduced cross sections have been observed for weakly bound and halo projectiles. It has been shown that this simple reduction scheme works also well for $\alpha$-particle induced reactions on heavy target nuclei, but very recently significant deviations have been seen for $\alpha$+${}^{33}$S and $\alpha$+${}^{23}$Na. Motivated by these unexpected discrepancies, the present study analyses $\alpha$-induced reaction cross sections for targets with masses $A\approx 20-50$. The study shows that the experimental data for $\alpha$-induced reactions on nuclei with $A\approx 20-50$ deviate slightly from the global behavior of reduced cross sections. However, in general the deviations evolve smoothly towards lower masses. The only significant outliers are the recent data for ${}^{33}$S and ${}^{23}$Na which are far above the general systematics, and some very old data may indicate that ${}^{36}$Ar and ${}^{40}$Ar are below the general trend. As expected, also the doubly-magic ${}^{40}$Ca nucleus lies slightly below the results for its neighboring nuclei. Overall, the experimental data are nicely reproduced by a statistical model calculation utilizing the simple $\alpha$-nucleus potential by McFadden and Satchler. Simultaneously with the deviation of reduced cross sections ${\sigma }_{\mathrm{red}}$ from the general behavior, the outliers ${}^{23}$Na, ${}^{33}$S, ${}^{36}$Ar, and ${}^{40}$Ar also show significant disagreement between experiment and statistical model calculation.

   nucl-exastro-ph.IMnucl-thEPJA(2015)·32 citations
3. 03*

   Comment on "Neutron Skin of ${}^{208}$Pb from Coherent Pion Photoproduction"

   A. Gardestig🇺🇸 · C. J. Horowitz🇺🇸 · Gerald A. Miller🇺🇸

   We argue that the reaction mechanism for the coherent pion production is not known with sufficient accuracy to determine the neutron radius of 208Pb to the claimed precision of 0.03 fm.

   ↳ nucl-thhep-phnucl-ex8 citations
4. 04*

   Nonproportionality in the scintillation light yield of bismuth germanate

   T. R. Gentile🇺🇸 · M. J. Bales🇺🇸 · H. Breuer · T.E. Chupp🇺🇸 · K. J. Coakley🇺🇸 · R. L. Cooper🇺🇸 · J. S. Nico🇺🇸 · B. O'Neill

   We present measurements of nonproportionality in the scintillation light yield of bismuth germanate (BGO) for gamma-rays with energies between 6 keV and 662 keV. The scintillation light was read out by avalanche photodiodes (APDs) with both the BGO crystals and APDs operated at a temperature of approximately 90 K. Data were obtained using radioisotope sources to illuminate both a single BGO crystal in a small test cryostat and a 12-element detector in a neutron radiative beta-decay experiment. In addition one datum was obtained in a 4.6 T magnetic field based on the bismuth K x-ray escape peak produced by a continuum of background gamma rays in this apparatus. These measurements and comparison to prior results were motivated by an experiment to study the radiative decay mode of the free neutron. The combination of data taken under different conditions yields a reasonably consistent picture for BGO nonproportionality that should be useful for researchers employing BGO detectors at low gamma ray energies.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2015)·3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.