Calculations of parity nonconserving s-d transitions in Cs, Fr, Ba II, and Ra II

We have performed ab initio mixed-states and sum-over-states calculations of parity nonconserving (PNC) electric dipole (E1) transition amplitudes between s-d electron states of Cs, Fr, Ba II, and Ra II. For the lower states of these atoms we have also calculated energies, E1 transition amplitudes, and lifetimes. We have shown that PNC E1 transition amplitudes between s-d states can be calculated to high accuracy. Contrary to the Cs 6s-7s transition, in these transitions there are no strong cancelations between different terms in the sum-over-states approach. In fact, there is one dominating term which deviates from the sum by less than 20%. This term corresponds to an s-p_{1/2} weak matrix element, which can be calculated to better than 1%, and a p_{1/2}-d_{3/2} E1 transition amplitude, which can be measured. Also, the s-d amplitudes are about four times larger than the corresponding s-s transitions. We have shown that by using a hybrid mixed-states/sum-over-states approach the accuracy of the calculations of PNC s-d amplitudes could compete with that of Cs 6s-7s if p_{1/2}-d_{3/2} E1 amplitudes are measured to high accuracy.Comment: 15 pages, 8 figures, submitted to Phys. Rev.

Eco-efficiency improvements in the propylene-to-epichlorohydrin process

BACKGROUND: Epichlorohydrin (ECH) production is an important industrial process, owing to its importance in windmill blade manufacture, but it suffers from several drawbacks such as high energy use, large wastewater production and low atom efficiency. This original study investigates a novel chlorohydrin-free technology with an enhanced separation system for ECH production. Rigorous process simulations were performed in Aspen Plus for the classic and novel processes, and a fair techno-economic and sustainability comparison was made between the new catalytic oxidation route and the classic chlorohydrin process. RESULTS: For the hydrogen peroxide (HP) process route, a novel separation system was developed using methanol as solvent, which enables high purity of ECH. Moreover, allyl chloride (ACH) purification was optimized using thermally coupled distillation to improve the energy efficiency of ACH production. The novel HP process provides 88% higher atom efficiency, about 10% higher yield and a smaller amount of by-products, as well as a 13% increase in production capacity and major savings of 98% in wastewater production, while also achieving lower energy use (<40 MJ kg−1 ECH) and reduced carbon dioxide emission (1.13 kg kg−1 ECH). CONCLUSION: The developed HP process route is feasible and economically viable. Also, it can be partly retrofitted to existing ECH plants based on the chlorohydrin route. As both processes use the same intermediate product, only the ECH part of a classic process would be replaced by the novel route, while keeping the common ACH part. This approach is the most profitable, as only 55% of capital expenditure is required for this modification, while the plant would benefit from all the improvements provided by the novel process.ChemE/Product and Process Engineerin

High-accuracy measurement of the differential scalar polarizability of a Sr+ 88 clock using the time-dilation effect

We report a high-accuracy measurement of the differential static scalar polarizability \u394\u3b10 of the 5sS1/22-4dD5/22 transition of the Sr+88 ion. The high accuracy is obtained by comparing the micromotion-induced positive scalar Stark shift to the negative time-dilation shift. Measurement of the trap drive frequency where these shifts cancel is used to determine \u394\u3b10 without the need to determine the electric field. \u394\u3b10 is a critical parameter for the operation of frequency standards as it determines the blackbody radiation frequency shift coefficient, the largest source of uncertainty in the Sr+88 ion clock. The measured value of \u394\u3b10 is -4.7938(71) 710-40Jm2/V2. Taking into account the dynamic correction, the blackbody shift at 300 K is 0.24799(37) Hz. The contribution of the blackbody shift coefficient to the uncertainty of the ion standard has been reduced by a factor of 24, from 2 710-17 to 8.3 710-19. The revised total uncertainty of our reference standard is 1.2 710-17, limited by the blackbody field evaluation. An additional benefit of the low uncertainty of \u394\u3b10 is the ability to suppress, by a factor of about 200, the net micromotion frequency shifts. \ua9 2014 Published by the American Physical Society.Peer reviewed: YesNRC publication: Ye

Time and frequency activities at NRC

The National Research Council of Canada (NRC) is currently involved in a number of research projects aimed at improving time and frequency realization based on the accurate and precise stabilization of microwave and optical sources on atomic and molecular transitions. Projects described in this summary will focus on the development of a primary standard for the realization of the SI second based on a cesium atomic fountain and a next generation standard based on an optical transition in a single trapped and laser cooled ion of strontium.The cesium fountain is undergoing evaluations of its systematic shifts for an eventual contribution to TAI and for a re-measurement of the absolute frequency of the strontium ion clock transition at the 10?15 level. The main contribution to the uncertainty budget of the fountain is thought to be caused by the inhomogeneity in the magnitude of the magnetic field in the drift region. The latest measurements of this field are presented. A new strontium ion trap of the endcap design was completed last year. This new system has compensation electrodes and access ports in three orthogonal directions to control the ion position and minimize micromotion. We report preliminary results indicating improved performance of this trap over our previous rf Paul trap. As part of an effort to reduce the systematics shifts to a minimum, the heights of the atomic standards above the geoid were measured with an accuracy of 5 cm, corresponding to a fractional frequency uncertainty of 5 7 10?18 for the gravitational redshift. \ua9 2011 SPIE.Peer reviewed: YesNRC publication: Ye