Torsten Radon

Schottky mass measurements of stored and cooled neutron-deficient projectile fragments in the element range of 57≤Z≤84

Abstract A novel method for direct, high precision mass measurements of relativistic exotic nuclei has been successfully applied in the storage ring ESR at GSI. The nuclei of interest were produced by projectile fragmentation of 930 MeV / u bismuth ions, separated in-flight by the fragment separator FRS, stored and cooled in the ESR. The mass values have been deduced from the revolution frequencies of the coasting cooled ions. We have measured 104 new mass values with a precision of about 100 keV and a resolving power of 3.5×10 5 for the neutron-deficient isotopes of the elements 57≤Z≤84 . This paper presents the experimental method, the mass evaluation and a table of the experimental mass values.

Schottky mass spectrometry at the ESR: a novel tool for precise direct mass measurements of exotic nuclei

Abstract Schottky mass spectrometry is a novel method of precision nuclear mass spectrometry based on the measurement of the revolution frequencies of ions in a storage ring. The measurements are performed by non-destructive detection and frequency analysis of the beam noise, the well-established Schottky diagnosis technique. Schottky mass spectrometry was applied for the first time at the Experimental Storage Ring ESR at GSI using electron-cooled, highly charged (mainly bare, H- and He-like) heavy ions at relativistic energies of up to 370 MeV/u. The performance of the method at the ESR is shortly reviewed and an overview of the results from our first mass measurements of radioactive neutron-deficient gold and bismuth fragments is given. Relative accuracies down to 3 × 10 −7 were achieved for the measured masses, corresponding to absolute uncertainties of 50 to 150 keV/ c 2 for these heavy isotopes (135 ≤ A ≤ 209). The typical mass resolving power of about 350 000 allows even the resolution of isomeric from ground state masses in some cases. Due to the required cooling time, the method is applicable, so far, to nuclei with half-lives of at least a few seconds.

Identification of Time-of-Flight spectra for Isochronous Mass Measurements

The Isochronous Mass Spectrometry (IMS) developed at GSI is a very effcient method for direct mass measurements of short-lived nuclides. By taking a recent IMS experiment as an example, the identification procedure of the Time-of-Flight (TOF) spectrum measured in this experiment is discussed.

SHIELDING OF THE TARGET AREA OF THE FRAGMENT SEPARATOR SUPER-FRS

Abstract The Super-FRS is designed as a versatile partially superconducting fragment separator for the planned international Facility for Antiprotons and Ion Research. It will be able to separate all kinds of nuclear projectile fragments of primary heavy-ion beams including uranium with energies of up to 1.5 GeV/u and intensities of up to 1012 particles/s. The primary beam power of up to 50 kW has to be dumped in six shaped beam catchers in accordance with the ion optical setting of the separator in order not to enter the main separator, which will have accordingly weaker shielding. A key issue for such a high-power facility is the activation of several components and thus their access by maintenance personnel. Both the prompt and the residual dose due to activation are calculated by means of the Monte Carlo particle transport code FLUKA. The biological shielding in the target area will be realized by massive iron blocks (thickness [approximate] 2 m) around the beam tube and the magnets. This will be surrounded by up to 6 m of concrete in order to reduce the dose rates below the design value of 0.5 μSv/h, which is in agreement with the German radiation protection ordinance for public access. A dedicated maintenance channel is foreseen in which the residual dose rates are tolerable for short time access after a certain cooling time.

Mass Measurements of Stored Exotic Nuclei at Relativistic Energies

Relativistic exotic nuclei produced via projectile fragmentation were separated in flight by the fragment separator FRS and injected into the storage ring ESR for precise mass measurements using Schottky spectrometry. Nuclei with half-lives shorter than the time required for electron cooling have been investigated by time-of-flight measurements with the ESR being operated in the isochronous mode. This novel experimental technique gives access to all nuclei with half-lives down to the μs-range.

Direct Observation of Bound State Beta Decay of Bare 207Tl at FRS-ESR

We observed the bound-state beta decay of fully ionized 2 0 7 Tl nuclei circulating in a storage ring. It is the first direct measurement of bound-state beta decay. 2 0 7 Tl nuclei were produced by the projectile fragmentation, separated by fragment separator and injected in the storage ring. Using the Schottky diagnostics the decay time spectrum of bare 2 0 7 Tl and hydrogen like 2 0 7 Pb ions which are the daughter nuclei of bound-state beta decay were measured. Observed decay-rate ratio between bound-state and continuous-state beta decay was 0.18(2). This value is consistent with the theoretical calculation.

First isochronous time-of-flight mass measurements of short-lived projectile fragments in the ESR

We present a new method for precise mass measurements of short-lived hot nuclei. These nuclei were produced via projectile fragmentation, separated with the FRS and injected into the storage ring ESR being operated in the isochronous mode. The revolution time of the ions is measured with a time-of-flight detector sensitive to single particles. This new method allows access to exotic nuclei with half-lives in the microsecond region. We report on first results from this novel method obtained with measurements on neutron-deficient fragments of a chromium primary beam with half-lives down to 50 ms. A precision of δm/m⩽5⋅10−6 has been achieved.

DESIGN DEVELOPMENT OF A PASSIVE NEUTRON DOSEMETER FOR THE USE AT HIGH-ENERGY ACCELERATORS

For the radiation survey at intermediate and high-energy accelerators, there is a need for a neutron dosemeter which provides reliable readings of the neutron dose in a wide energy range for continuous and pulsed radiation. The objective of this development is to find a dosemeter that fulfils the necessary requirements and can be reliably used to prove that the radiation levels in areas around accelerators are in accordance with the limits of the respective radiation protection legislation. A simple layout with small dimensions and light weight as well as the usage of common materials to lower the production costs is to be achieved.

Experiments with stored relativistic exotic nuclei

Beams of relativistic exotic nuclei were produced, separated and investigated with the combination of the fragment separator FRS and the storage ring ESR. The following experiments are presented: 1) Direct mass measurements of relativistic nickel and bismuth projectile fragments were performed using Schottky spectrometry. Applying electron cooling, the relative velocity spread of the circulating secondary nuclear beams of low intensity was reduced to below 10−6. The achieved mass resolving power of m/Δm=6.5⋅105 (FWHM) in recent measurements represents an improvement by a factor of two compared to our previous experiments. The previously unknown masses of more than 100 proton-rich isotopes have been measured in the range of 54⩽Z⩽84. The results are compared with mass models and estimated values based on extrapolations of experimental values. 2) Exotic nuclei with half-lives shorter than the time required for electron cooling can be investigated by time-of-flight measurements with the ESR being operated in ...

Radiation protection update for the FAIR APPA building

In 2011 the FAIR [1] application for construction approval was submitted to the radiation protection (RP) authorities based on -at that timeactual construction plans. In May 2014 the 11 and final part of the application was approved. However, since 2011 these plans underwent a series of changes due to ascertainment of additional needs by e.g. the scientific users, fire protection authorities or just the increasing grade of detail in the evolving FAIR project. These changes have to be reported to the RP authorities as an update of the 2011 application, because they might affect -to some gradethe radiation protection layout. This update-process requires a close monitoring and counseling of the necessary planning steps by the resident radiation protection at GSI, which is mandated to supervise all FAIR RP concerns. In a first step, the needs of all involved parties are acquired by the RP coordination team involving the architectural layout, requirements of the scientific user and of course the existing RP layout. The new layout is then tested by Monte Carlo calculations deploying FLUKA [2,3] following the basic principle that the new layout has to perform equally or better concerning RP needs. This maxim is laid out to achieve a smooth approval procedure of the updated construction application. These updates range from minor adjustment of shielding walls or niches therein to an entire new wall layout of a whole building like the APPA building “G50”. The original layout of the APPA cave is based on a double concrete wall design, where in-between the walls soil layers were used to improve the shielding effect (see Fig.1).