Munich Q3D Spectrograph Research Articles

High-resolution study of Er166 with the ( p, t ) reaction

Excited states in the deformed nucleus $^{166}\mathrm{Er}$ have been studied with high-energy resolution in the ($p,t$) reaction, with the Munich Q3D spectrograph. 143 states have been observed up to 4 MeV excitation, and spin and parity has been proposed for about 100 states, based on a DWBA analysis of their angular distributions, out of which 11 are excited ${0}^{+}$ states, and 39 ${2}^{+}$ states. The excitation pattern of these states (especially the ${0}^{+}$ ones) in $^{166}\mathrm{Er}$ is compared to that in $^{168}\mathrm{Er}$. Calculations were carried out with the $spdf$-IBM model, which gives a reasonable agreement with the observed number of ${0}^{+}$ states in $^{166}\mathrm{Er}$ and their excitation in the ($p,t$) reaction. The $2n$-transfer intensity pattern for the ${0}^{+}$ states in the $^{166}\mathrm{Er}(t,p)^{168}\mathrm{Er}$ reaction is also reasonably predicted. However, the $spdf$-IBM calculations do not explain the differences between $^{166}\mathrm{Er}$ and $^{168}\mathrm{Er}$, in the ($p,t$) transfer distribution of the ${0}^{+}$ states. The understanding of these differences, which appear to be related to a structure change at the $N=98$ deformed subshell closure, remains as an important issue of future, more elaborated model calculations.

Beautiful clusters – boron-9: simulations and decay

Monte-Carlo simulations for analysis of the9Be(3He, t)9B∗ reaction at 33 MeV using coincidences between the high-resolution Munich Q3D spectrograph and the large-acceptance Birmingham silicon detector array are presented. These focus on the identification of the proton break-up product and the application to evidencing the first excited1/2+ state. Identifying this state has posed a challenge for over 70 years, but would enable the mirror symmetry in this light system to be explored, giving insight into its possible clustered structure. Penetrabilities for the low excitation energy regime are calculated showing the efficacy of the proton-identification method.

Spectroscopy ofB9via high-resolution ejectile-tagged recoil break-up

An experiment has been carried out using the $^{9}\mathrm{Be}(^{3}\mathrm{He},\phantom{\rule{0.16em}{0ex}}t)^{9}\mathrm{B}^{*}$ reaction at a beam energy of 33 MeV. A large acceptance silicon-strip array was used to detect the $^{9}\mathrm{B}^{*}$ break-up in coincidence with the triton ejectiles in the high-resolution Munich-Q3D spectrograph. The excitation energy regime $<3$ MeV has been explored and the spectrum resulting from proton decaying states, isolated and characterized. Additional resonance strength is observed at 1.86 MeV $\ifmmode\pm\else\textpm\fi{}70$ keV(stat) $\ifmmode\pm\else\textpm\fi{}35$ keV(syst), in agreement with two other recent measurements at higher energies and different angles. The consequences for the ``missing'' ${\textonehalf{}}^{+}$ first excited state are discussed. Additionally, the branching ratios for the 2.36 MeV ${5/2}^{\ensuremath{-}}$ state have been measured as ${\ensuremath{\Gamma}}_{\ensuremath{\alpha}0}/\ensuremath{\Gamma}=0.98\ifmmode\pm\else\textpm\fi{}0.12$ and ${\ensuremath{\Gamma}}_{p0}/\ensuremath{\Gamma}=0.016\ifmmode\pm\else\textpm\fi{}0.008$, in close agreement with earlier work.

Absolute decay width measurements in 16O

The reaction 126C(63Li, d)168O* at a 6Li bombarding energy of 42 MeV has been used to populate excited states in 16O. The deuteron ejectiles were measured using the high-resolution Munich Q3D spectrograph. A large-acceptance silicon-strip detector array was used to register the recoil and break-up products. This complete kinematic set-up has enabled absolute α-decay widths to be measured with high-resolution in the 13.9 to 15.9 MeV excitation energy regime in 16O; many for the first time. This energy region spans the 14.4 MeV four-α breakup threshold. Monte-Carlo simulations of the detector geometry and break-up processes yield detection efficiencies for the two dominant decay modes of 40% and 37% for the α+12C(g.s.) and a+12C(2+1) break-up channels respectively.

Excited states of the150Pm odd-odd nucleus

The knowledge of excited states in the odd-odd ${}^{150}$Pm, completely unknown until recently, is important both for understanding double $\ensuremath{\beta}$ decay of ${}^{150}$Nd and for nuclear structure studies in mass regions with a quantum phase transition. A large number of excited states have been determined for the first time in this nucleus by measuring spectra of the ${}^{152}$Sm($d$,$\ensuremath{\alpha}$) direct reaction at 25 MeV with the Munich Q3D spectrograph and by $\ensuremath{\gamma}$-ray spectroscopy with the ($p,n\ensuremath{\gamma}$) reaction at 7.1 MeV at the Bucharest tandem accelerator. Some of these levels correspond to peaks recently observed with the ${(}^{3}$He,$t$) reaction at 140 MeV/u.

High-resolution measurement of absoluteα-decay widths inO16

By using a large-acceptance position-sensitive silicon detector array in coincidence with the high-resolution Munich Q3D spectrograph, unambiguous measurements have been made of the absolute {alpha}-particle decay widths from excited states in {sup 16}O* in the energy range 13.85 to 15.87 MeV. Carbon targets have been bombarded with 42-MeV {sup 6}Li beams to induce {sub 6}{sup 12}C({sub 3}{sup 6}Li, d){sub 8}{sup 16}O* reactions. The deuteron ejectiles were measured in the Q3D and the results gated by {sup 4}He+{sup 12}C breakup products detected in the silicon array, the efficiency of which was modeled using Monte Carlo simulations. By comparing total population and breakup-gated spectra, the following absolute {alpha}-decay widths have been measured with high resolution: {Gamma}{sub {alpha}}0/{Gamma}{sub tot} = 0.87{+-}0.11 (13.980 MeV), 1.04{+-}0.15 (14.302 MeV), 0.92{+-}0.10 (14.399 MeV), 0.59{+-}0.04 (14.815 MeV), 0.88{+-}0.18 (15.785 MeV), and {Gamma}{sub {alpha}}1/{Gamma}{sub tot}=1.14{+-}0.08 (14.660 MeV), 0.46{+-}0.06 (14.815 MeV).

Structure investigation with the (p,t) reaction onBa132,134nuclei

The low-lying excited states in $^{132,134}\mathrm{Ba}$ isotopes have been studied with high-resolution ($p,t$) reactions. The experiments were performed at the Munich Q3D spectrograph with a 25-MeV proton beam and the 1.5-m-long focal plane detector. The high-resolution triton spectra allowed the observation of levels up to $~4$ MeV. The experimental results revealed 75 excited states in $^{134}\mathrm{Ba}$ and 79 in $^{132}\mathrm{Ba}$, many of them observed for the first time. The measured angular distributions compared with distorted-wave Born approximation calculations allowed spin assignments for these levels in most cases. The systematics of the monopole and quadrupole two-neutron transfer strengths is compared with the prediction of the interacting boson approximation model. The results indicate a transitional structure in $^{132}\mathrm{Ba}$ and $^{134}\mathrm{Ba}$ and contribute additional evidence in favor of a description between the U(5) and O(6) symmetries of the model.

High-resolution particle spectroscopy of 186Re

The transfer reaction 187 75Re(p, d)186 75Re has been studied using the Munich Q3D spectrograph at a proton bombarding energy of 21 MeV. The excitation energy regime up to ≈2.5 MeV has been elucidated, over 30 states observed for the first time and a precision down to 0.5 keV achieved. Blocked BCS calculations are presented, in excellent agreement with the experimentally observed low-lying structures in 186Re. These calculations have been used to predict the structures of the strongly populated states above 1 MeV, and 4-quasiparticle configurations are suggested.

Role of cross-shell excitations in the reaction 54Fe( $$ \vec d $$ , p)55Fe

The reaction 54Fe(\( \vec d \), p)55Fe was studied at the Munich Q3D spectrograph with a 14MeV polarized deuteron beam. Excitation energies, angular distributions and analyzing powers were measured for 39 states up to 4.5MeV excitation energy. Spin and parity assignments were made and spectroscopic factors deduced by comparison to DWBA calculations. The results were compared to predictions by large-scale shell model calculations in the full pf -shell and it was found that reasonable agreement for energies and spectroscopic factors below 2.5MeV could only be obtained if up to 6 particles were allowed to be excited from the f 7/2 orbital into p 3/2 , f 5/2 , and p 1/2 orbitals across the N = 28 gap. For levels above 2.5MeV the experimental strength distribution was found to be significantly more fragmented than predicted by the shell model calculations.

Study of the 130Ba nucleus with the (p, t) reaction

Excited states in 130Ba have been studied with the 25MeV 132Ba(p, t)130Ba reaction with 8keV energy resolution, at the Munich Q3D spectrograph. 27 excited states were observed up to 2.6MeV excitation energy, for 21 of them spin and parity being confirmed or assigned. These results complement earlier measurements concerning the systematics of 0+ states in 132Ba and 134Ba , and allow a more detailed comparison with predictions of different nuclear-structure models. The comparison with interacting boson model calculations brings additional evidence in favor of a description of this nucleus by parameters close to the O(6) symmetry.

High-resolution study of 0+ and 2+ excitations in 168Er with the (p, t) reaction

Excited states in the deformed nucleus 168Er have been studied with high energy resolution in the (p, t) reaction, with the Munich Q3D spectrograph. A large number of excited 0+ states (25) and 2+ states (64) have been assigned up to 4.0-MeV excitation energy. This allows detailed investigations along two directions of current interest: first, an extension of microscopic model interpretations into the region of medium level density above the pairing gap; second, a first analysis of the statistical fluctuation (order/chaos) properties of pure sequences of levels, in one deformed nucleus. Predictions of two models (the quasiparticle-phonon model and the projected shell model) are compared to the data, and it is concluded that, in both cases, mixing of more configurations is required in the wave functions.

High-resolution study of 0+and 2+excitations inEr168with the (p,t) reaction

Excited states in the deformed nucleus $^{168}\mathrm{Er}$ have been studied with high-energy resolution, in the ($p,t$) reaction, with the Munich Q3D spectrograph. A number of 25 excited $0{}^{+}$ states (four tentative) and $63\phantom{\rule{0.3em}{0ex}}{2}^{+}$ states have been assigned up to 4.0 MeV excitation energy. This unusually rich characterization of the $0{}^{+}$ and $2{}^{+}$ states in a deformed nucleus, close to a complete level scheme, offers a unique opportunity to check, in detail, models of nuclear structure that incorporate many excitation modes. A comparison of the experimental data is made with two such models: the quasiparticle-phonon model (QPM), and the projected shell model (PSM). The PSM wave functions appear to contain fewer correlations than those of the QPM and than required by the data.

A new multiwire proportional chamber with fast single strip readout and individual analog to digital conversion

Abstract A new precision MWPC with an active length of 400 mm has been built for the Munich Q3D spectrograph. The readout method uses the individual amplitude signals of narrow cathode strips (3 mm width, 0.5 mm spacing). Each of these signals is converted into a digital word by an individual fast ADC. A newly developed hard wired logic calculates the position of the particle event by the center of gravity method with a dead time of about 108 μs. The position resolution in test measurements simulating particle events was better than 0.1 mm.

A light ion focal plane detector for the Q3D magnetic spectrograph with periodic cathode readout

For the Munich Q3D spectrograph a focal plane detector of 1.2 m length appropriate for polarized particle induced reactions has been developed. Improved position resolution of the resistive wire proportional detectors is achieved by additional readout of periodic cathode structures.

New MWPCs for the Munich Q3D spectrograph

A position sensitive detector - for light particles - of about 150 cm length and a resolution of ∼ 0.5 mm is needed for the Munich Q3D spectrograph. For high resolution this detector must follow the curvature of the Q3D s focal surface. As a substitute for the MWPC of Glässel two new detectors, a short one (∼28 cm) and a long one (2 m) of the same type were constructed. The main features are: wire-spacing 0.5 mm, wire thickness 8 φm, particle detection from each position separately, total energy measurement in a subsequent plastic scintillator and thus ΔE/ E particle discrimination. The design of the detectors, the associated electronics and their performance in measurements since spring 1981 (short detector) and spring 1982 (long detector) respectively are reported.

A multiwire proportional chamber system with digital read-out for the Munich Q3D-spectrograph

A position-sensitive MWPC system with digital read-out for magnetic spectrographs is described. The spatial resolution, as given by the wire spacing, is 0.5 mm. The counter can be used for coincidence experiments with a time resolution of ≈10 ns. A ΔE-signal from the counter allows gross particle identification. With 4 or 5 adjacent wires firing simultaneously because of inclined particle incidence, coincidence requirements between these wires are used to reduce the neutron and γ-sensitivity of the chamber.

The ion optical properties of the Munich Q3D-spectrograph investigated by means of a special experimental ray tracing method

The ion optical properties of the Munich Q3D-spectrograph were investigated using a special experimental ray tracing method. Cs +-ions produced in a thermal ion source were accelerated by means of a very stable dc-voltage and focused on the object point of the spectrograph (spot size 0.2 × 2 mm 2). From this ion beam a set of rays corresponding to those used in ray tracing calculations was obtained by a special collimator system. The positions of these rays were measured in the region of the focal plane with an accuracy of about 0.15 mm. From these measurements we have been able to determine the ion optical properties of the spectrograph including aberration coefficients up to 4th order. The results are compared to ray tracing calculations for the spectrograph. Within the accuracy of both the ray tracing calculations (due to uncertainties in field boundaries), and the measurements reasonable agreement is found.