Charge-state distribution of Li ions from the β decay of laser-trapped He6 atoms

Abstract

The accurate determination of atomic final states following nuclear β decay plays an important role in several experiments. In particular, the charge state distributions of ions following nuclear β decay are important for determinations of the β − ν angular correlation with improved precision. Beyond the hydrogenic cases, the decay of neutral 6 He presents the simplest case. Our measurement aims at providing benchmarks to test theoretical calculations. The kinematics of Li n+ ions produced following the β decay of 6 He within an electric field were measured using 6 He atoms in the metastable (1s2s, 3 S1) and in the (1s2p, 3 P2) states confined by a magneto-optical trap. The electron shake-off probabilities were deduced including their dependence on ion energy. We find significant discrepancies on the fractions of Li ions in the different charge states with respect to a recent calculation.

Decay microscope for trapped neon isotopes

“…Observing table II, and provided that systematics and theoretical corrections are under control [6], the detection of 10 6 recoil ions from 23 Ne decay already improves on the state of the art. Nevertheless, to be competitive with ongoing and planned campaigns involving pure GT branches [31,32,[82][83][84][85], roughly 10 7 events are desired. 18 Ne decays mainly to the ground state of 18 F through a pure GT transition, and to an excited state by a superallowed Fermi transition.…”

“…To considerably reduce background counts, and distinguish between different charge-states of recoiling ions [19,32,103,119,120], coincidence detection is desired, allowing to measure the recoils TOF in parallel with their hit position. Similarly to [121], we opted to use shakeoff electrons as a start signal and detect recoil ions in coincidence.…”

Weak interaction studies at SARAF

“…As mentioned earlier, a competitive measurement requires acquisition of a few 10 7 decay events within the trap [29], and so for a reasonable beam time of under 100h, The average event rate should be at least 100/s. For a production rate of 10 9 isotopes of choice per second, the overall efficiency of transport, trapping and detection should be at least 10 −7 , which is easily obtained in the EIBT setup [19], and is regularly obtained in a state of the art, laser-cooling system for metastables [10]. At the present, a meaningful measurement can be accomplished at SARAF-I with the production capabilities shown in fig.…”

“…Whereas most laser-cooling systems require large flux [14], or a high density of atoms in the trap necessary to obtain a Bose-Einstein condensate, our most important quantity is the overall efficiency for cooling and trapping, namely the number of atoms which have decayed within the trap as a fraction of those which have entered the system. The excitation efficiency to the metastable state for light nobles is 10 −4 at most [28], and limits the efficiency of the such system to about 10 −7 [10], and so we are actively pursuing further developments for each part of the system such as the metastable RF source [22], and Zeeman-slower [20,21]. Recycling of the gas sample within the system system will be introduced in order to get a gain of up to 10 3 in efficiency [14] for stable isotopes, and our preliminary studies show that a gain of around 50 is obtainable owing to the relatively long half-life (37 s) of 23 Ne.…”

$β$-nuclear-recoil correlation from $^6$He decay in a laser trap

“…Details about the apparatus used in this measurement can be found in Refs. [21][22][23][24][25]. The 6 He atoms were produced via the 7 Li(d, t) 6 He nuclear reaction, bombarding a lithium target with an 18-MeV deuteron beam, delivered by the tandem Van de Graaff accelerator at the University of Washington.…”