Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Calculation of radiation-induced DNA damage from photons and tritium beta-particles

Abstract: Yields of DNA single- and double-strand breaks (SSB and DSB) in nucleosomal DNA were calculated for 137Cs, 70 keV photons and tritium beta-particles by Monte Carlo means. Monte Carlo-generated electron tracks for liquid water were used to model energy deposition. Chemical evolution of a track and interactions between species and DNA following water radiolysis were modelled in an encounter-controlled manner. The calculated relative biological effectiveness (RBE) for DSB production for tritium against 137Cs was 1.2 for the total DSB yield. Tritium beta-particles were slightly more efficient compared to 137Cs in producing complex DSB, defined as DSB accompanied by additional strand breaks. The RBE for complex DSB formation was 1.3. Most complex DSB exhibited associated base damage; the extent of the base damage was similar for all the radiation types considered. Correlated DSB conforming to nucleosome periodicity were observed. However, their frequency was low, of the order of 2% of total DSB. For all the DNA damage endpoints considered and their response to variation of the scavenging environment or DNA conformation no difference was observed between 70 keV photons and tritium beta-particles.

Channeling of MeV He + Ions in Tungsten and Other Crystals: An Intercomparison of Rutherford Scattering and of Characteristic L and M X-Ray Yields

Abstract: Measurements of wide-angle (150\ifmmode^\circ\else\textdegree\fi{}) scattering and of $L$ and $M$ x-ray yields in tungsten single crystals are reported as a function of crystallographic orientation with respect to an incident beam of 1.4-MeV helium ions. Comparison of these yields establishes both lower and upper limits for the minimum impact parameter (${r}_{min}$) between a channeled ion and the tungsten-lattice atoms; these limits are consistent with Lindhard's estimate that ${r}_{min}\ensuremath{\sim}\mathrm{a}$, the Thomas-Fermi screening distance (i.e.,\ensuremath{\sim}0.11 \AA{} for He in W). A similar comparison between wide-angle scattering and x-ray yield curves is reported for several other lattices\char22{}Al, Si, GaP, GaSb, and U${\mathrm{O}}_{2}$; again the results are consistent with the predicted relationship: ${r}_{min}\ensuremath{\sim}\mathrm{a}$. Anomalies in published orientation studies of $K$, $L$, and $M$ x-ray yields are shown to be due to depth effects.

Observation of the Haldane gap in RbNiCl3.

Abstract: The Haldane gap is observed by neutron scattering in ${\mathrm{RbNiCl}}_{3}$. The three-dimensional-phase magnetic spectrum of ${\mathrm{RbNiCl}}_{3}$ is found to be very similar to that of ${\mathrm{CsNiCl}}_{3}$, even though the two materials differ significantly in the exchange parameters. Application of Affleck's field theory to ${\mathrm{RbNiCl}}_{3}$ shows that the theory is capable of explaining the dispersion of the gap mode and its relative intensity near the three-dimensional ordering wave vector (1/3,1/3,1). However, the theory does not provide a satisfactory explanation for the nearly degenerate magnon frequencies at (0,0,1). We argue that the degeneracy at (0,0,1) may not be related to the existence of the Haldane gap in integer-spin systems. Rather, it could be a general feature of certain antiferromagnetic materials.