Direct measurement of nuclear magnetic moments of radium isotopes

Abstract

The nuclear magnetic moments of 213 Ra and 225 Ra have been measured at ISOLDE (isotope separator at the CERN synchrocyclotron) by observation of the Larmor precession of optically pumped atoms in a fast beam. The results ^/( 213 Ra) =0.6133(18)//^ and ^/( 225 Ra) = -0.7338(15)^* provide an accurate test of ab initio and semiempirical calculations from optical hyperfine structures in Ral and Rail. PACS numbers: 21.10.Ky, 27.80,+w, 27.90.+b, 32.80.Bx Over the past few years collinear fast-beam-laser spectroscopy on line with accelerators has proved to be a very fruitful technique for the study of exotic very unstable nuclei. x Nuclear magnetic moments, for instance, are deduced from hyperfine-structure (hfs) measurements through the magnetic interaction constant A and the nuclear spin /. This requires of course, the knowledge either of the magnetic field H e {0)-AIJ/iu(1) created by the valence electrons at the nucleus, or of the nuclear magnetic moment of at least one isotope. Moreover, this procedure implies that the hyperfine anomaly is negligible, and consequently the uncertainty on the nuclear results is rather large (1% typically) even if the hfs constants are known to a much better precision. Such measurements in a series of Ra isotopes were reported three years ago. 2 Since no direct measurement of the nuclear magnetic moment had been performed previously for any of the Ra isotopes, it was necessary to evaluate H e (0), and this is the main source of the estimated ± 5% error in the /ij values. There have been attempts to reduce this error by both theoretical ab initio calculations 3 " 5 and improved semiempirical analyses. 6 We report here the first direct measurement of the nuclear magnetic moments of 213225 Ra which eliminates the uncertainty about H e (0) in the determination of the Hi values for the whole isotopic sequence and also tests the atomic hfs theory.The experimental method consists of our measuring the Larmor precession of the ground-state magnetic moment in an external static magnetic field by observing the fluorescence of a fast atomic beam interacting with a collinear resonant laser beam. Such experiments were first performed with paramagnetic (J**0) neutral atoms 7 or ions. 8 When the experiment is performed with diamagnetic atoms (/-0 ground state), the gyromagnetic factor gj and thus the nuclear magnetic moment fii can be deduced directly from the precession frequency.The principle of the method has been described in a previous paper devoted to a pilot experiment on Ba isotopes 9 : The fast neutral atoms are first aligned (or oriented) by optical pumping through linearly (or circularly) polarized laser excitation (zone A in Fig. 1). Then, these aligned (or oriented) atoms precess at the Larmor frequency in a strong external magnetic field (zone B). In this region, the atoms are out of resonance with the laser because of the large Zeeman splitting of the upper level of the transition. At the exit of the magnet gap the fast atoms are reexcited by the laser light and the fluorescence ...

Calculation of energy levels and transition amplitudes for barium and radium

“…Compilation by Moore [10] based on these two works contains about forty energy levels of radium. There were few more experimental works on radiums studying Rydberg states [11], hyperfine structure and isotope shift [12,13], nuclear magnetic moments [14], etc. In the most recent work by Sielzo et al the lifetime and position of the 3 P o 1 state of Ra has been measured.…”

Atomic parity violation in a single trapped radium ion

“…Fig. 3) was only available from measurements at the ISOLDE facility at CERN, where the isotope shift (IS) and hyperfine structure (HFS) of the 7 2 S 1/2 , 7 2 P 1/2 , and 7 2 P 3/2 states were obtained by collinear spectroscopy over a large range of isotopes [25,26]. The only absolute measurement of the relevant wavelengths dates back to arc emission spectroscopy performed on 226 Ra + in 1933 [27].…”

“…701 (50) 248 (50) 453 (34) The measured values for the 6 2 D 3/2 state and a value extracted from [25,26] for the 7 2 P 3/2 HFS were used to obtain the IS with respect to the center-of-mass of the resonances in 213 Ra + equation model. We use the 6 2 D 3/2 F = 2 − 7 2 P 3/2 F = 1 resonance to determine the IS.…”

“…The most recent theoretical values were converted to 213 Ra + using the magnetic moment measured at ISOLDE [26]. The theoretical uncertainty is at the %-level (Timmermans, private communication) Fig.…”

Laser Trapping ofRa225andRa226with Repumping by Room-Temperature Blackbody Radiation

“…But over the time scale of 4 ms, the atoms will be recycled due to thermal radiation (as seen in Fig. 3 TABLE I: Measured hyperfine structure constants A in MHz for 225 Ra on the repump transition compared to a previous measurement and theory (obtained by scaling calculations for 213 Ra [7] and 223 Ra [16] by the ratio of nuclear magnetic moments and the inverse ratio of the nuclear spins [17,18] for 226 Ra) to the (F = 3/2) states and repumped. This effect can also be seen in Fig.…”