0000000000652113
AUTHOR
H. Ohm
showing 29 related works from this author
The beta-decay of95Rb and97Rb
1983
Theβ-decay of 377 ms95Rb and 168ms97Rb has been thoroughly investigated by means ofγ-ray, conversion electron andβ-delayed neutron spectroscopy. More than 97% of theβ-decay to particle-bound states has been placed in level schemes of95Sr and97Sr. High-resolution neutron spectroscopic studies have allowed to extend the knowledge of the excitation spectra up to 9 MeV, respectively 10 MeV. The density of neutron-unbound levels in95Sr and97Sr has been derived from peak stripping analyses of the neutron spectra. Beta-strength functions (S β(E)) have been investigated in detail. They indicate that Gamow-Tellerβ-decay of both precursors is dominated by nuclear structure. The discovered pronounced …
Structure of the neutron-rich nucleus 37 94 rb57
1989
A level scheme has been established for 37 94 Rb57 based on studies at the fission-product separator JOSEF ofγγ coincidences following theβ- decay of94Kr. For the 190.7 keV level a half-life of 2.5(8) ns has been determined through the centroid-shift method. The majorβ-decay branch of94Kr proceeds with log ft=3.7 into the 988.4 keV state in94Rb. This transition must be of the 0+→1+ GT type involving the transitionνg7/2→πg9/2. IBFFM calculations have been performed for94Rb, starting from the parametrization used in the previous IBM investigations for the isotope93Rb and the isotone96Y. A theoretical interpretation of the low-lying levels including propositions for the spins is given in a com…
Level scheme ofZr101and structure of theN=61 Sr, Zr, and Mo isotones
1995
The neutron-rich nucleus $_{40}^{101}\mathrm{Zr}_{61}$ has been studied at the isotope separator ISOLDE via the \ensuremath{\beta} decay of $^{101}\mathrm{Y}$. A detailed level scheme has been obtained from \ensuremath{\gamma}-ray singles, \ensuremath{\gamma}-\ensuremath{\gamma}-t and \ensuremath{\beta}-\ensuremath{\gamma}-t coincidence measurements. The level structure of $^{101}\mathrm{Zr}$ is similar to that of its isotone $^{103}\mathrm{Mo}$ showing that, in contrast to their Sr neighbors, the Zr isotopes do not reach maximum of deformation immediately at its onset. This result is rather well reproduced by particle-rotor coupling calculations. A level systematics for the deformed N=61 i…
Delayed-neutron spectroscopy with 3He spectrometers
1977
Abstract The characteristics of a 3 He ionization chamber for high-resolution spectroscopy of β-delayed neutrons have been examined. The detector response function is given in the energy range 0.019–2.77 MeV. A considerably improved energy resolution has been achieved by minimizing effects due to pulse summing, detection of scattered neutrons, and microphonics, and is most evident in the low-energy part of the spectra.
Half-lives andP n values of delayed-neutron precursors in the mass chains 85?87, 92, 135, 136 and 145
1978
Further results are presented on half-lives and neutron emission probabilities (P n ) of short-lived delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145 obtained with the recoil focussing parabola-type mass separator for unslowed fission products LOHENGRIN installed at the Grenoble high-flux reactor. A newP n -value of (44±14)% is given for the (0.73±0.06)s87As; theP n -values of seven precursor nuclides have been redetermined: (1.9±0.1)s85As with (22±8)%, 0.9s86As with (10.5±2.2)%, (0.35±0.04)s92Br with (21±8)%, (1.6±0.15)s135Sb with (14±1)%, (0.9±0.1)s136Sb with (19±9)%, (17.5±0.2)s136Te with (2.0±1.0)% and 0.6s145Cs with (12.5±3.0)%. The results are compared with th…
The ground-state deformation of98Sr
1987
The half-life of the first excited state (21+) of98Sr has been determined through the measurement of delayed γ-γ coincidences at the fission product separator OSTIS to t1/2=2.74(12) ns. This value is smaller than those obtained earlier from β− — conversion electron delayed coincidences and it indicates a stronger collectivity of the 21+→01+ transition in98Sr [B(E2)=98 (3) spu] than in100Sr [B(E2)=79(3) spu] which is normally assumed to be the better rotor.
Feasibility study for the measurement of πN transition distribution amplitudes at P¯ANDA in p¯p→J/ψπ0
2017
The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is show…
Structure of theN=59 nucleus97Sr: coexistence of spherical and deformed states
1990
A band with a rotational pattern based on a state at 585.1 keV has been identified in theN=59 neutron-rich nucleus97Sr. Its properties lead to the [422] 3/2 Nilsson-orbital assignment for the band head. There is evidence for a second band with the head at 644.7 keV and the configuration [541] 3/2. Since the ground state and the lowest excited levels are spherical, shape coexistence is established for97Sr. A deformed nature of several levels at 500–600 keV results also from QRPA-model calculations. The structure of the low-lying spherical levels has been studied in the frame of the IBF model. The results of the present investigations lead to a better understanding of theN=59 isotones which c…
Shape coexistence in theN=59 isotone97Sr
1988
Experimental evidence for shape coexistence in the N=59 isotone97Sr is presented. The ground state and the lowest excited levels are confirmed to be spherical. At 585.1 keV, a K=3/2 rotational band built on the v[422 3/2] Nilsson configuration has been identified. Nilsson orbital assignments for three further levels of deformed origin are proposed. The results are compared to RPA shell-model predictions.
Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
2014
We present new data for angular distributions and on the cross section ratio of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q = 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.
IBMF and IBFFM Approach to Nuclei in the A≃100 Region
1988
An overview of the calculations in IBFM and IBFFM for nuclei in the A ≃ 100 region is presented. The application to these nuclei with a complex structure including the rapid transition from spherical to deformed nuclear shapes provides a stringent test for the capacities of this theoretical approach. From the result of the studies of the heavy Yttrium isotopes and the N=59 isotones it is concluded that it can account for the basic structure and the phase transition in these nuclei.
Beta-delayed neutron emission from93?100Rb to excited states in the residual Sr isotopes
1982
Beta-delayed neutron emission from the precursors93–100Rb to excited states in the residual nuclei92–99Sr has been measured by means ofγ-ray and neutron spectroscopy. In general, considerable neutron feeding of excited final states is observed. The experimental branching ratios (P ) are compared to predictions from statistical model calculations. It is demonstrated that the main parameter affecting theP -values is the shape of theβ-strength function (S β). For several Rb isotopes hindrance, respectively enhancement of neutron branches to specific final states is observed giving evidence for the persistence of intermediate structure of the neutron-emitting states. By the example of98Rb it is…
Spin dependence of {\eta} meson production in proton-proton collisions close to threshold
2018
Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} pp{\eta} has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves …
Study of doubly strange systems using stored antiprotons
2016
Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible …
Evidence for excited 0+ states in94Sr
1982
Beta-delayed neutron measurements on95Rb have indicated evidence for two heretofore unknown excited O+ states in94Sr which are not fed by s -decay from the Jπ = 3− ground state of94Rb.
Band Structures in 96Zr and 98Zr Studied Through the High-Spin Beta Decays of the Y Parents
1988
The isotopes 96Zr and 98Zr are presently subject to intensive studies since their properties play a key role in the understanding of the rapid transition from spherical to deformed nuclear shapes at N ∼ 60. An interesting question is the strength of the subshell closures at Z = 38,40 and N = 56 and to which extent the structure of 96Zr, 98Zr and of their immediate neighbours is influenced by these shell effects. There is evidence, although limited, for closed- shell-or individual-particle character of these nuclei, but more information on the nature of the excited states, especially those with sizeable spins is desired. This is expected to help clarifying the situation with respect to the p…
The neutron binding energy in the neutron-rich nucleus93Sr
1980
The neutron binding energy in93Sr has been determined to (5230±6) keV from energy correspondences between levels defined by γ-ray transitions and β-delayed neutron emission.
The deformedN=60 nucleus 41 101 Nb
1991
The β− decay of101Zr has been investigated at the fission-product separators JOSEF and LOHENGRIN. The half-life of101Zr has been determined to 2.5(1) s and a level scheme for101Nb has been established fromγ ray singles as well as X/3-γ and γ—γ coincidence measurements. Conversion coefficients for transitions in101Nb and level half-lives between 10 ps and 2 ns have been determined. Three rotational bands are identified among the low-lying levels with band heads at 0 keV, 206 keV and 208 keV. The bands are probably based on the Nilsson configurations [422 5/2+], [301 3/2−] and [303 5/2−], respectively. The deformation has been determined to βq=0.40(4) and 0.41(8) for the ground state band and…
Investigation of beta strength functions by neutron and gamma-ray spectroscopy
1979
Abstract Neutron spectra from the decay of the β− delayed neutron precursors 55.6 sec 87Br, 24.5 sec 137I, 2.05 sec 85As and 1.71 sec 135Sb have been studied with high resolution 3He ionization chambers. By γ-ray measurements, the partial neutron emission probabilities to excited states in 84Se and 134Te have been determined independently. For the neutron-emitter nuclei 87Kr and 137Xe, from which neutron decay proceeds only to the ground states of the final nuclei, 86Kr and 136Xe, unique information on the shape of the β− strength function Sβ(E) is obtained. For the emitter nuclei 85Se and 135Te, correlations between neutron transition energies and differences in level energies in 84Se and …
Beta-delayed neutrons and high-energy gamma-rays from decay of137I
1980
Beta-delayed neutrons and high-energyγ-rays following decay of137I have been studied in order to characterizeβ-decay to and deexcitation of neutron-unbound levels in137Xe. The totalγ-ray intensity observed accounts for at least 20% of theβ-intensity to levels aboveB n . No evidence was found for neutron andγ-ray emission from the same levels. With the experimentalβ-strength function aboveB n detailed tests were performed on the reproduction of the experimental neutron spectrum, the level density and Porter-Thomas fluctuations of the reducedβ-transition probabilities to highly excited states in137Xe.
Observation of beta-delayed neutron decay to excited 0+ states in the residual nucleus: The case
1981
Abstract Beta-delayed neutron emission from 97 Rb to excited 0 + states in 96 Sr has been observed. The experimental branching ratios ( P n i ) are compared to predictions from a statistical model. It is demonstrated that, considering the influence of the strength of β -decay preceding neutron emission, the ( P n i ) reflect the different structure of the two excited 0 + states, in agreement with conclusions drawn from the measurement of their lifetimes.
Experimental Evidence for Shape Coexistence in 97Sr59 and Implications for the Structure of the Odd-Odd Isotone 98Y
1988
Experimental evidence for shape coexistence in the odd-mass N=59 isotone 97Sr is presented. The ground state and the lowest excited levels of 97Sr are shown to be spherical, whereas a rotational band based on a state at 585 keV has been identified. Three further levels of deformed origin are proposed. Nilsson-orbital assignments are supported by RPA shell-model calculations. These findings lead to a better understanding of the structure of the odd-odd N=59 isotone 98Y.
An Isotensor Dibaryon in the $pp \to pp\pi^+\pi^-$ Reaction?
2018
Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been carried out at WASA@COSY by means of $pd$ collisions at $T_p$ = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region $T_p = 1.08 - 1.36$ GeV, which is the region of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly with a pion is able to overcome these deficiencies.
Search for Mesic He with the WASA-at-COSY facility in the And Reactions
2020
We report on the experimental search for the bound state of an η meson and He3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γ and pd→3He6γ channels have been analysed. These reactions manifest the direct decay of the η meson bound in a He3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a $^{3}$He-η nucleus width Γ above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with…
Search for the $��$ mesic $^3$He in the $pd\rightarrow d p ��^{0}$ reaction with the WASA-at-COSY facility
2020
The excitation function for the $pd\rightarrow$ $d p ��^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$��$ mesic nuclei. The measurement in the vicinity of $��$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $��$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $��$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspace{-0.03c…
Measurement of the $pn \to pp\pi^0\pi^-$ Reaction in Search for the Recently Observed Resonance Structure in $d\pi^0\pi^0$ and $d\pi^+\pi^-$ systems
2013
Exclusive measurements of the quasi-free $pn \to pp\pi^0\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $\sqrt s$ = (2.35 - 2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. No ABC effect, {\it i.e.} low-mass enhancement is found in the $\pi^0\pi^-$-invariant mass spectrum -- in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s-wave. At the upper end of the covered energy region $t$-channel processes for Roper, $\Delta(1600)$ and $\Delta…
Search for the $\eta$ mesic $^3$He in the $pd\rightarrow d p \pi^{0}$ reaction with the WASA-at-COSY facility
2020
The excitation function for the $pd\rightarrow$ $d p \pi^{0}$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$\eta$ mesic nuclei. The measurement in the vicinity of $\eta$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $\eta$-mesic Helium decays via the formation of an intermediate N$^{*}$(1535) resonance. No direct signal of the $\eta$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\rightarrow$ $(^{3}\hspa…
Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY
2014
Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd->4He{\pi}0 have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +- 13…
On the Production of an Isotensor Dibaryon in the $pp \to pp\pi^+\pi^-$ Reaction
2018
Exclusive measurements of the quasi-free $pp \to pp\pi^+\pi^-$ reaction have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 1.08 - 1.36$ GeV ($\sqrt s$ = 2.35 - 2.46 GeV), which includes the regions of $N^*(1440)$ and $\Delta(1232)\Delta(1232)$ resonance excitations. Calculations describing these excitations by $t$-channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor $\Delta N$ dibaryon resonance with $I(J^P) = 2(1^+)$ produced associatedly…