Facility for preparation of gas mixture in muon catalyzed fusion experiments

A facility is described that allows safe handling of high tritium gas activity as dozens kilocuries in a regular laboratory environment. It is used to make and deliver into the target a mixture of specific isotopic composition with the contamination requirement of 10^-7 v.f. for Z>1 elements, and recover it upon completion of operation. With this facility, efforts have been accomplished to investigate into the muon catalyzed fusion on two targets – liquid tritium and high-pressure tritium types. Also, the operation range was 0.1–120 MPa for pressure and 20–800 K for temperature and the amount of tritium used was about 100 kCi. The facility showed reliability in operation without indications of radiation beyond the safety level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of ion-molecular reactions on μ-capture in hydrogen and on fusion in 3Hedμ muonic molecule

The de-excitation processes (J=1)→ (J=0) in muonic molecular ions (ppμ)⁺ and (³Hedμ)⁺ are studied. It is shown that the rate of such transitions substantially depends on the chain of ion-molecular reactions initiated by positively charged muonic ions. The probabilities of ortho-para transition in the [(ppμ)⁺H₂] and [(ppμ)⁺e] complexes formed as a result of chemical reactions in the pure hydrogen were estimated. Taking into account the ion-molecular processes in D₂ + He mixtures, the evaluation of the observed rate λ_f of nuclear fusion in the ³Hedμ muonic molecules was performed. The expected yield of fusion reactions per muon at the mixture density φ=0.1 and concentration C _He =0.05 was obtained to be equal to . This revised version was published online in August 2006 with corrections to the Cover Date.     

Aromatic 19F–13C TROSY—[19F, 13C]-Pyrimidine Labeling for NMR Spectroscopy of RNA

We present the access to [5-¹⁹F, 5-¹³C]-uridine and -cytidine phosphoramidites for the production of site-specifically modified RNAs up to 65 nucleotides (nts). The amidites were used to introduce [5-¹⁹F, 5-¹³C]-pyrimidine labels into five RNAs—the 30 nt human immunodeficiency virus trans activation response (HIV TAR) 2 RNA, the 61 nt human hepatitis B virus ϵ (hHBV ϵ) RNA, the 49 nt SAM VI riboswitch aptamer domain from B. angulatum, the 29 nt apical stem loop of the pre-microRNA (miRNA) 21 and the 59 nt full length pre-miRNA 21. The main stimulus to introduce the aromatic ¹⁹F–¹³C-spin topology into RNA comes from a work of Boeszoermenyi et al., in which the dipole-dipole interaction and the chemical shift anisotropy relaxation mechanisms cancel each other leading to advantageous TROSY properties shown for aromatic protein sidechains. This aromatic ¹³C–¹⁹F labeling scheme is now transferred to RNA. We provide a protocol for the resonance assignment by solid phase synthesis based on diluted [5-¹⁹F, 5-¹³C]/[5-¹⁹F] pyrimidine labeling. For the 61 nt hHBV ϵ we find a beneficial ¹⁹F–¹³C TROSY enhancement, which should be even more pronounced in larger RNAs and will facilitate the NMR studies of larger RNAs. The [¹⁹F, ¹³C]-labeling of the SAM VI aptamer domain and the pre-miRNA 21 further opens the possibility to use the biorthogonal stable isotope reporter nuclei in in vivo NMR to observe ligand binding and microRNA processing in a biological relevant setting.