Using the high-resolution performance of the fragment separator FRS at GSI we have discovered 60 new neutron-rich isotopes in the atomic number range of 60 <= Z <= 78 . The new isotopes were ...unambiguously identified in reactions with a U 238 beam impinging on a Be target at 1 GeV/nucleon. The production cross-section for the new isotopes have been measured down to the pico-barn level and compared with predictions of different model calculations. For elements above hafnium fragmentation is the dominant reaction mechanism which creates the new isotopes, whereas fission plays a dominant role for the production of the new isotopes up to thulium.
Abstract A large-volume Time Projection Chamber (TPC) is the main tracking and particle identification (PID) detector of the ALICE experiment at the CERN LHC. PID in the TPC is performed via specific ...energy-loss measurements (d E /d x ), which are derived from the average pulse-height distribution of ionization generated by charged-particle tracks traversing the TPC volume. During Runs 1 and 2, until 2018, the gas amplification stage was based on multiwire proportional chambers (MWPC). Signals from the MWPC show characteristic long negative tails after an initial positive peak due to the long ion drift times in the MWPC amplification region. This so-called ion tail can lead to a significant amplitude loss in subsequently measured signals, especially in the high-multiplicity environment of high-energy Pb-Pb collisions, which results in a degradation of the d E /d x resolution. A detailed study of the signal shapes measured with the ALICE TPC with the Ne-CO 2 (90-10) and Ar-CO 2 (90-10) gas mixtures is presented, and the results are compared with three-dimensional Garfield simulations. The impact of the ion tail on the PID performance is studied employing the ALICE simulation framework and the feasibility of an offline correction procedure to account for the ion tail is demonstrated.
The neutron-rich lead isotopes, up to (216)Pb, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric ...states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond (208)Pb.
A thick neutron skin emerges from the first determination of root mean square radii of the proton distributions for 17−22N from charge changing cross section measurements around 900A MeV at GSI. ...Neutron halo effects are signalled for 22N from an increase in the proton and matter radii. The radii suggest an unconventional shell gap at N = 14 arising from the attractive proton–neutron tensor interaction, in good agreement with shell model calculations. Ab initio, in-medium similarity re-normalization group, calculations with a state-of-the-art chiral nucleon–nucleon and three-nucleon interaction reproduce well the data approaching the neutron drip-line isotopes but are challenged in explaining the complete isotopic trend of the radii.
We plan a semi-exclusive measurement of the 12C(p,dp) reaction to search for η'-mesic nuclei, aiming at investigating in-medium properties of the η′-meson. We employ a 2.5 GeV proton beam impinging ...on a carbon target to produce η′-mesic 11C nuclei via the 12C(p,d)η′⊗11C reaction. Using coincidence measurements of the forward going deuterons, important for missing-mass spectroscopy, and decay protons emitted from the η′-mesic nuclei. for event selection will provide a high experimental sensitivity to observe η'-mesic nuclei. We will perform the measurements by combining the WASA detector system with the fragment separator FRS at GSI and also with the Super-FRS at FAIR in the future. The plan of the experiments and the present status are reported.
Time Projection Chambers with C-pads for heavy ion tracking Janik, R.; Prochazka, A.; Sitar, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2011, Letnik:
640, Številka:
1
Journal Article
Recenzirano
Time Projection Chambers with C-pads and integrated delay line readout were developed as position sensitive detectors for the Fragment separator at GSI Darmstadt. The main advantages of TPCs are a ...small amount of matter in the sensitive volume, high spatial resolution, and high tracking efficiency. Working parameters in experimental conditions are presented. Internal spatial resolutions of
σ
x
=
88
μ
m
and
σ
y
=
38
μ
m
were achieved. The tracking efficiency dependence on ion beam intensity was studied with
238U beam at 1
GeV/
u energy. Efficiency of more than 99% was achieved up to 40
kHz and over 90% for 250
kHz
238U beam intensity. Different kinds of ions from proton to uranium were measured in many experiments and confirmed the result obtained.
We measured the interaction cross sections (
σ
I
) of
10,11B,
12–20C,
14–23N,
16–24O and
18–26F on carbon targets at energies of around 950
A MeV. We then deduced the effective matter radii of the ...nuclei by a Glauber-model analysis. Based on the assumption of a core plus a valence neutron structure, we applied a Glauber-model analysis for a few-body system adapted for nuclei with an odd neutron number. We also deduced the effective nucleus-matter densities as well as some spectroscopic information for selected nuclei. Evidence for a one-neutron halo structure was found for
22N,
23O and
24F, as well as
19C.
The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles ...in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90m3 and is operated in a 0.5T solenoidal magnetic field parallel to its axis.
In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb–Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report.
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