Determination of the extraction efficiency for 233U source α-recoil ions from the MLL buffer-gas stopping cell

Abstract

Abstract. Following the α decay of 233 U, 229 Th recoil ions are shown to be extracted in a significant amount from the MLL buffer-gas stopping cell. The produced recoil ions and subsequent daughter nuclei are mass purified with the help of a customized quadrupole mass spectrometer. The combined extraction and mass-purification efficiency for 229 Th 3+ is determined via MCP-based measurements and via the direct detection of the 229 Th α decay. A large value of (10 ± 2)% for the combined extraction and mass-purification efficiency of 229 Th 3+ is obtained at a mass resolution of about 1 u/e. In addition to 229 Th, also other α-recoil ions of the 233,232 U decay chains are addressed.PACS. 27.90.+b A≥220 -23.60.+e α decay -07.75.+h mass spectrometers -23.35.+g isomer decay

Characterization of 233U alpha recoil sources for 229()Th beam production

“…The measured recoil efficiency of 2% for the LMU source is about a factor of two to three lower than that estimated for the same source (and also using the daughter activity) by L.v.d. Wense et al [15]. The value presented here is close to the recoil efficiency of ∼1.6% which was estimated by L.v.d.…”

“…These age estimations are purely from the measured activities and do not take into account the 229 Th that has not stayed within the uranium. Still, the ages match roughly with those expected for the source materials, and the 60 (11) year estimate matches also the previous estimation of 45(5) years [15]. By using a silicon charged-particle detector (Ortec U-017-300-500) with an intrinsic resolution of 17 keV, 500 µm depletion depth and 300 mm 2 detection area, a direct measurement of the alpha decay from the two sources was compared.…”

“…It is clear from our work and that of L.v.d Wense and colleagues [15], a thinner 233 U source layer is advantageous for a higher recoil ion efficiency. However, using exceedingly thin sources in order to achieve high recoil efficiencies (>20%) will not produce the highest recoil yield per unit area because it means that the thickness is smaller than the stopping distance of a recoil.…”

“…Nevertheless, the integration of the area of the 193.5 keV peak was possible suggesting a recoil ion efficiency of ∼3%, a factor of two lower than the estimate provided by L.v.d. Wense et al [15] for the same source. This direct measurement of the 229 Th recoil efficiency can be taken only as an upper limit because the gamma line is not clearly apparent.…”

“…The spectroscopic analysis was performed on two different types of 233 U source. One was provided by the Ludwig Maximilian University of Munich [15] and hereafter will be referred to as the LMU source. The source was made by evaporating uranium tetrafluoride on an aluminium backing until an activity of 230 kBq was accumulated within a circular area of 20 mm in diameter.…”