A new Channeltron-detector setup for precision mass measurements at ISOLTRAP

Yazidjian, C.; Blaum, Klaus; Ferrer, R.; Herfurth, F.; Herlert, A.; Schweikhard, L.

doi:10.1007/s10751-007-9555-y

Cited by 23 publications

(16 citation statements)

References 14 publications

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“…The resonance is detected by ejecting the trapped ions towards a channeltron detector [19] and measuring their time of flight. The timeof-flight resonance curve, as shown in Fig.…”

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confidence: 99%

Restoration of theN=82Shell Gap from Direct Mass Measurements ofSn132,134

et al. 2008

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A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of 134 Sn from the currently accepted value. The corrected mass assignment of this neutronrich nuclide restores the neutron-shell gap at N 82, previously considered to be a case of ''shell quenching.'' In fact, the new shell gap value for the short-lived 132 Sn is larger than that of the doubly magic 48 Ca which is stable. The N 82 shell gap has considerable impact on fission recycling during the r process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides. Shell effects are fundamental pillars upholding nuclear structure. The so-called ''magic'' numbers indicate closed shells, corresponding to spherical nuclei that provide important benchmarks for theoretical descriptions. The advent of radioactive beams has brought to light surprising evidence that shell closures lose their magicity far from stability, in regions of extreme isospin imbalance. The term ''shell quenching'' [1] has been used in cases where the effect of a magic number is eroded to the point of disappearance, as in the case of N 20 [2] and N 28 [3]. The nuclear ground-state binding energy, through the mass, has been a traditional observable for shell effects [4]. While these effects are small, especially considering the much larger volume and surface contributions to the binding energy, they can now be probed by mass measurements using high-precision techniques over large areas of the nuclear chart [5,6].The strength of the shell closures is important for nucleosynthesis via the rapid neutron capture process and consequently, masses have a considerable influence on the abundance distributions of heavy elements (see, for example, the work of Burbidge, Burbidge, Fowler, and Hoyle (BBFH) [7]). In their seminal work, BBFH elaborated the role of fission in the r process. This thread has been revived recently by who assert that the N 82 shell gap plays a pivotal role in the neutron-consumption rate during the r process.The strength of the 132 Sn shell, as derived from previous mass data, does not reflect a doubly magic nuclide whose vibrational (spherical) properties are well established from spectroscopy studies. One hypothesis, from -spectroscopy studies, was that the N 82 shell closure might be quenched [9]. The present letter reports on the resolution of this conflict. It turns out that the strength of the 132 Sn shell closure was mistakenly determined to be too small. Our new, direct mass measurement of 134 Sn has revealed a 0.5-MeV discrepancy with respect to previous Q measurements [10,11]. This finally restores the shell closure to that expected for a doubly magic nuclide.Mass measurements on the isotopes 127;131-134 Sn were performed with the Penning trap mass spectrometer ISOLTRAP [12,13], installed at the online isotope separator ISOLDE [14] at CERN. The short-lived tin nuclides were produced by imping...

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“…The resonance is detected by ejecting the trapped ions towards a channeltron detector [19] and measuring their time of flight. The timeof-flight resonance curve, as shown in Fig.…”

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confidence: 99%

Restoration of theN=82Shell Gap from Direct Mass Measurements ofSn132,134

et al. 2008

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“…The electric potential and the magnetic-field strength along the geometrical axis in the first part of the drift section of the mass spectrometer. Maximum retardation is applied in the region of the strongest magnetic-field gradient in order to achieve a large time-of-flight effect [71]. laxation method, which was found to give necessary precision, followed by a least-square fit to a pure quadrupole field, i.e., taking into account the sum of all higher multipoles.…”

Section: The Precision Penning Trap Of Isoltrapmentioning

confidence: 99%

“…In order to increase the detection efficiency and thus to minimize the required beamtime and to explore more exotic shorter-lived nuclides, the MCP detector for the time-of-flight ion cyclotron detection (MCP5(v)) was recently replaced by an off-axis channeltron detector with conversion dynode. This detector provides close to 100% detection efficiency which will thereby increase the accessibility to even shorter-lived nuclei [71]. A drawing of the new detection setup is shown in fig.…”

Section: The Time-of-flight Detection Sectionmentioning

confidence: 99%

ISOLTRAP: An on-line Penning trap for mass spectrometry on short-lived nuclides

et al. 2008

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Abstract. ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well below 100 ms. The mass-resolving power reaches 10 7 corresponding to 10 keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below 10 −8 . The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP.

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“…The existing micro channel plate (MCP) detector was replaced by a channeltron detector with a conversion dynode, where secondary electrons are monitored with an efficiency close to 100 %. With this setup an increase of the total efficiency by a factor of about 3 was obtained and nuclides with a lower production yield can be addressed [39].…”

Section: Present Status and Technical Development At Isoltrapmentioning

confidence: 99%

Penning trap mass spectrometry for nuclear structure studies

et al. 2006

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High-precision mass measurements as performed at the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN are an important contribution to the investigation of nuclear structure. Accurate nuclear masses with less than 0.1 ppm relative mass uncertainty not only allow stringent tests of mass models and mass formulas that are used to predict mass values of nuclides far from the valley of stability, but also to look for nuclear structure effects like shell or sub-shell closures, deformations, and halos. In addition to a sophisticated experimental setup for precise mass measurements, a radioactive ion beam facility is required that delivers a large variety of short-lived nuclides with sufficient yield. An overview of the results from the mass spectrometer ISOLTRAP is given and its limits and possibilities are described.

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A new Channeltron-detector setup for precision mass measurements at ISOLTRAP

Cited by 23 publications

References 14 publications

Restoration of theN=82Shell Gap from Direct Mass Measurements ofSn132,134

Restoration of theN=82Shell Gap from Direct Mass Measurements ofSn132,134

ISOLTRAP: An on-line Penning trap for mass spectrometry on short-lived nuclides

Penning trap mass spectrometry for nuclear structure studies

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