Modeling of electron emission processes accompanying radon-<i>α</i>-decays within electrostatic spectrometers

Wandkowsky, N.; Drexlin, G.; Fränkle, F. M.; Glück, F.; Groh, Stefan; Mertens, S.

doi:10.1088/1367-2630/15/8/083040

Cited by 19 publications

(29 citation statements)

References 37 publications

(102 reference statements)

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“…Besides the isomeric decay, low-energy electrons are also emitted as a by-product during radioactive α decays. Typically, two low-energy electrons (from atomic shell re-organization following the α decay) are emitted per radioactive decay event [40]. The intrinsic activity of 229 Th of ∼ 210 Bq will soon increase by a factor of about 10, due to daughter ingrowth, leading to expectedly about 4000 emitted electrons per second.…”

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confidence: 99%

A Laser Excitation Scheme for Th229m

et al. 2017

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Direct laser excitation of the lowest known nuclear excited state in 229 Th has been a longstanding objective. It is generally assumed that reaching this goal would require a considerably reduced uncertainty of the isomer's excitation energy compared to the presently adopted value of (7.8 ± 0.5) eV. Here we present a direct laser excitation scheme for 229m Th, which circumvents this requirement. The proposed excitation scheme makes use of already existing laser technology and therefore paves the way for nuclear laser spectroscopy. In this concept, the recently experimentally observed internal-conversion decay channel of the isomeric state is used for probing the isomeric population. A signal-to-background ratio of better than 10 4 and a total measurement time of less than three days for laser scanning appear to be achievable.Direct nuclear laser excitation has come closer into reach within the past years, partly due to the development of free-electron-laser technology. Such ideas are typically dealing with the excitation of nuclear states in the energy range of at least a few keV or above [1,2]. However, there is one exceptional nuclear state known for the last 40 years with a significantly lower energy of presumably below 10 eV [3,4]. An excitation energy of (7.8 ± 0.5) eV, corresponding to (159 ± 11) nm wavelength or ∼ 1900 THz, is by today the most accepted value for the isomeric first excited state of 229 Th [5,6]. This state conceptionally allows for direct nuclear laser excitation using solid-state laser technology and was proposed for the development of a nuclear clock of extremely high stability, due to an expected high resilience against external influences and a radiative lifetime in the range of minutes to hours [7][8][9][10]. It is generally assumed that direct nuclear laser excitation of 229m Th requires a considerably improved knowledge of the isomeric transition energy (see e.g. Ref.[11] and references therein). The reasons are that, first, the present uncertainty in the knowledge of the isomeric energy value is still rather large. The currently best energy value of 7.8±0.5 eV leads to an energy range of at least 1 eV (corresponding to 2.4·1014 Hz) to be scanned when searching for the isomeric excitation. Second, the radiative lifetime of 229m Th was theoretically predicted to be in the range of hours [12][13][14], leading to long required detection times when searching for a radiative decay channel. This has led to the assumption that the required time for laserbased scanning of the large energy range of 1 eV would be prohibitively long. In order to shorten the required scanning times, there are worldwide efforts ongoing to decrease the uncertainty of the transition energy, which would bring the isomeric state into realistic reach of direct laser excitation (see e.g. Refs. [15-18]). A recent review is found in Ref. [11].Here we propose a different approach, which allows for a direct laser excitation of 229m Th without the requirement of an improved knowledge of the transition energy. As the requi...

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A Laser Excitation Scheme for Th229m

et al. 2017

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“…This number, however, will grow soon after chemical purification by a factor of about 10, due to the ingrowth of short-lived daughter nuclei. As each radioactive decay will on average lead to the emission of two low-energy electrons [40], we estimate the total emission rate of low energy electrons of the target to 1 · 10 4 per second. As these electrons will be equally distributed in time, the number of detected electrons in a 5 µs time window amounts to 5 · 10 −2 .…”

Section: What Is the Expected Signal-to-background Ratio?mentioning

confidence: 99%

The concept of laser-based conversion electron Mössbauer spectroscopy for a precise energy determination of 229mTh

et al. 2019

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229 Th is the only nucleus currently under investigation for the development of a nuclear optical clock (NOC) of ultra-high accuracy. The insufficient knowledge of the first nuclear excitation energy of 229 Th has so far hindered direct nuclear laser spectroscopy of thorium ions and thus the development of a NOC. Here, a nuclear laser excitation scheme is detailed, which makes use of thorium atoms instead of ions. This concept, besides potentially leading to the first nuclear laser spectroscopy, would determine the isomeric energy to 40 µeV resolution, corresponding to 10 GHz, which is a 10 4 times improvement compared to the current best energy constraint. This would determine the nuclear isomeric energy to a sufficient accuracy to allow for nuclear laser spectroscopy of individual thorium ions in a Paul trap and thus the development of a single-ion nuclear optical clock.

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“…1). This dominant role of 219 Rn in generating background can be explained in the framework of our radon background model described in [13], and briefly summarized in the following subsection.…”

Section: Radon Emanationmentioning

confidence: 99%

“…Previous investigations [10,11] have revealed that the α-decay of 219,220 Rn atoms, emanated in small quantities from the installed non-evaporable getter (NEG) pump and from the inner surface of the stainless steel vessel, constitute a major source of background in KATRIN which cannot be shielded by electromagnetic fields. This background arises from electrons with energies from a few eV up to a few hundred keV [12,13] which accompany the primary α-decay of both radon isotopes. Subsequent investigations focus on actively removing trapped high-energy electrons [14] and on the signature of this background by detailed simulations [15] and specific measurements [10].…”

Section: Introductionmentioning

confidence: 99%

Impact of a cryogenic baffle system on the suppression of radon-induced background in the KATRIN Pre-Spectrometer

et al. 2018

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A : The KATRIN experiment will determine the effective electron anti-neutrino mass with a sensitivity of 200 meV/c 2 at 90% CL. The energy analysis of tritium β-decay electrons will be performed by a tandem setup of electrostatic retarding spectrometers which have to be operated at very low background levels of < 10 −2 counts per second. This benchmark rate can be exceeded by background processes resulting from the emanation of single 219,220 Rn atoms from the inner spectrometer surface and an array of non-evaporable getter strips used as main vacuum pump. Here we report on a the impact of a cryogenic technique to reduce this radon-induced background in electrostatic spectrometers. It is based on installing a liquid nitrogen cooled copper baffle in the spectrometer pump port to block the direct line of sight between the getter pump, which is the main source of 219 Rn, and the sensitive flux tube volume. This cold surface traps a large fraction of emanated radon atoms in a region outside of the active flux tube, preventing background there. We outline important baffle design criteria to maximize the efficiency for the adsorption of radon atoms, describe the baffle implemented at the KATIRN Pre-Spectrometer test set-up, and report on its initial performance in suppressing radon-induced background. K : KATRIN; non-evaporable getter; radon emanation; baffle; cold trap 1deceased 2Corresponding author arXiv:1808.09168v1 [physics.ins-det]

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Modeling of electron emission processes accompanying radon-α-decays within electrostatic spectrometers

Cited by 19 publications

References 37 publications

A Laser Excitation Scheme for Th229m

A Laser Excitation Scheme for Th229m

The concept of laser-based conversion electron Mössbauer spectroscopy for a precise energy determination of 229mTh

Impact of a cryogenic baffle system on the suppression of radon-induced background in the KATRIN Pre-Spectrometer

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