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Andersson, M. & Bäck, T. (2023). Gamma-ray track reconstruction using graph neural networks. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1048, Article ID 168000.
Open this publication in new window or tab >>Gamma-ray track reconstruction using graph neural networks
2023 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 1048, article id 168000Article in journal (Refereed) Published
Abstract [en]

Since the advent of the new generation of germanium detector arrays for low-energy nuclear physics experiments utilizing gamma-ray tracking, the challenges associated with track-reconstruction methods have been extensively studied. In the present work an approach based on recent developments in machine learning was used to address the problem. Here, a graph neural network was constructed and trained on data simulated in Geant4 in order to attempt track reconstruction of gamma rays below 1 MeV in a spherical shell geometry of pure germanium. Using a thick-shell geometry, and simulated data without energy-and position uncertainties the network achieved a reconstruction rate above 80% for complete tracks, and a combined peak-to-total value of 85% for energy spectra with four discrete peaks. For data with added noise, i.e. finite resolution in interaction-point position and energy, the corresponding peak-to-total ratio dropped to 74%. The track reconstruction was stable across multiplicities 1-10 but showed an increased error frequency in the energy range between 50 keV and 250 keV. To specifically study the complication of gamma tracks lost by out -scattering from the detector volume, a thin-shell (9 cm thickness) geometry was used together with a modified version of the GNN framework. By letting the GNN code identify and discriminate the out-scatter events, an improvement of the P/T value from 66% to 75% was found for the packed, noisy data. For the sake of comparison the new GNN model with existing gamma-ray tracking methods, a separate instance of the network was trained on slightly higher energies (up to 1.5 MeV) and multiplicities (up to 15) to evaluate 1.332 MeV photon cascade data in terms of P/T and photo-peak efficiency. The results for this GNN data set, with P/T values at 85% for single tracks and 74% for multiplicity 15, show clear promise when compared to the existing tracking methods.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Gamma-ray spectroscopy, Gamma-ray tracking, Machine learning, GNN
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-328795 (URN)10.1016/j.nima.2022.168000 (DOI)000990168700001 ()2-s2.0-85145971036 (Scopus ID)
Note

QC 20230613

Available from: 2023-06-13 Created: 2023-06-13 Last updated: 2023-06-13Bibliographically approved
Ahlgren Cederlöf, E., Bäck, T., Qi, C., Ataç, A., Matta, S., Subramaniam, P., . . . et al., . (2023). Lifetime measurement of the yrast 2 + state in 118 Te. European Physical Journal A, 59(12), Article ID 300.
Open this publication in new window or tab >>Lifetime measurement of the yrast 2 + state in 118 Te
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2023 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 59, no 12, article id 300Article in journal (Refereed) Published
Abstract [en]

The electromagnetic transition probabilities of the yrast 2 + states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118Te and the missing data for 116Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast 2 + state in 118Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is τ2 += 7.46 (19) ps. In addition, the lifetime of the 4 + state was measured to be τ4 += 4.25 (23) ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations. The trend of the B(E2 ; 0 +→ 2 +) values in the midshell area is in good agreement with the calculations and the calculated B4 / 2 ratio provide evidence for 118Te as a near perfect harmonic vibrator.

Place, publisher, year, edition, pages
Springer Nature, 2023
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-341738 (URN)10.1140/epja/s10050-023-01212-3 (DOI)2-s2.0-85180133905 (Scopus ID)
Note

QC 20240103

Available from: 2024-01-03 Created: 2024-01-03 Last updated: 2024-03-13Bibliographically approved
Liu, X., Cederwall, B., Qi, C., Wyss, R. A., Aktas, Ö., Ertoprak, A., . . . et al., . (2022). Evidence for spherical-oblate shape coexistence in Tc-87. Physical Review C: Covering Nuclear Physics, 106(3), Article ID 034304.
Open this publication in new window or tab >>Evidence for spherical-oblate shape coexistence in Tc-87
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2022 (English)In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 106, no 3, article id 034304Article in journal (Refereed) Published
Abstract [en]

Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.

Place, publisher, year, edition, pages
American Physical Society (APS), 2022
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-320485 (URN)10.1103/PhysRevC.106.034304 (DOI)000863087400003 ()2-s2.0-85140633028 (Scopus ID)
Note

QC 20221031

Available from: 2022-10-31 Created: 2022-10-31 Last updated: 2024-01-04Bibliographically approved
Eliasson, L., Lillhök, J., Bäck, T., Billnert-Maróti, R., Dasu, A. & Liszka, M. (2022). Range-shifter effects on the stray field in proton therapy measured with the variance–covariance method. Frontiers in Oncology, 12
Open this publication in new window or tab >>Range-shifter effects on the stray field in proton therapy measured with the variance–covariance method
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2022 (English)In: Frontiers in Oncology, E-ISSN 2234-943X, Vol. 12Article in journal (Refereed) Published
Abstract [en]

Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissue- equivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 mm in tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance–covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance–covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3. 

Place, publisher, year, edition, pages
Frontiers Media SA, 2022
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-316219 (URN)10.3389/fonc.2022.882230 (DOI)000840998900001 ()35982965 (PubMedID)2-s2.0-85137003042 (Scopus ID)
Note

QC 20220912

Available from: 2022-08-10 Created: 2022-08-10 Last updated: 2024-01-17Bibliographically approved
Davi, F., Bäck, T., Cederwall, B. & Zmeskal, J. (2022). Technical design report for the endcap disc DIRC. Journal of Physics G: Nuclear and Particle Physics, 49(12), Article ID 120501.
Open this publication in new window or tab >>Technical design report for the endcap disc DIRC
2022 (English)In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 49, no 12, article id 120501Article in journal (Refereed) Published
Abstract [en]

PANDA (anti-proton annihiliation at Darmstadt) is planned to be one of the four main experiments at the future international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. It is going to address fundamental questions of hadron physics and quantum chromodynamics using cooled antiproton beams with a high intensity and and momenta between 1.5 and 15 GeV/c. PANDA is designed to reach a maximum luminosity of 2 × 1032 cm−2 s. Most of the physics programs require an excellent particle identification (PID). The PID of hadronic states at the forward endcap of the target spectrometer will be done by a fast and compact Cherenkov detector that uses the detection of internally reflected Cherenkov light (DIRC) principle. It is designed to cover the polar angle range from 5° to 22° and to provide a separation power for the separation of charged pions and kaons up to 3 standard deviations (s.d.) for particle momenta up to 4 GeV/c in order to cover the important particle phase space. This document describes the technical design and the expected performance of the novel PANDA disc DIRC detector that has not been used in any other high energy physics experiment before. The performance has been studied with Monte-Carlo simulations and various beam tests at DESY and CERN. The final design meets all PANDA requirements and guarantees sufficient safety margins.

Place, publisher, year, edition, pages
IOP Publishing, 2022
Keywords
technical design report, particle identification, Cherenkov detector, PANDA
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-336833 (URN)10.1088/1361-6471/abb6c1 (DOI)000928188400001 ()2-s2.0-85144811850 (Scopus ID)
Note

QC 20230921

Available from: 2023-09-21 Created: 2023-09-21 Last updated: 2023-09-21Bibliographically approved
Barucca, G., Atac, A., Bäck, T., Cederwall, B., Zmeskal, J. & et al., . (2021). Feasibility studies for the measurement of time-like proton electromagnetic form factors from (p)over-barp -> mu(+)mu(-) at PANDA at FAIR. European Physical Journal A, 57(1)
Open this publication in new window or tab >>Feasibility studies for the measurement of time-like proton electromagnetic form factors from (p)over-barp -> mu(+)mu(-) at PANDA at FAIR
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2021 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 57, no 1Article in journal (Refereed) Published
Abstract [en]

This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, vertical bar G(E)vertical bar and vertical bar G(M)vertical bar, using the (p) over barp -> mu(+)mu(-) reaction at PANDA (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at PANDA, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is (p) over barp -> pi(+)pi(-), due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.

Place, publisher, year, edition, pages
Springer, 2021
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-304904 (URN)10.1140/epja/s10050-020-00333-3 (DOI)000608062500001 ()2-s2.0-85100155048 (Scopus ID)
Note

QC 20211116

Available from: 2021-11-16 Created: 2021-11-16 Last updated: 2022-06-25Bibliographically approved
Zhang, W., Cederwall, B., Qi, C., Ertoprak, A., Aktas, Ö., Liu, X., . . . Cullen, D. (2021). Identification of excited states in Te55 52107. Physical Review C. Nuclear Physics, 104(6), Article ID A156.
Open this publication in new window or tab >>Identification of excited states in Te55 52107
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2021 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 104, no 6, article id A156Article in journal (Refereed) Published
Abstract [en]

Excited states in the extremely neutron-deficient nucleus Te107 have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of γγ-coincidence relations and tentatively assigned as built on the mixed-parentage νg7/2d5/2 and νh11/2 intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the νh11/2 band of Te107 which highlights the shape-polarizing effect of a single valence neutron occupying the h11/2 intruder orbit as the N=50 shell closure is approached.

Place, publisher, year, edition, pages
American Physical Society, 2021
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-310608 (URN)10.1103/PhysRevC.104.064305 (DOI)000730824600005 ()2-s2.0-85121118174 (Scopus ID)
Note

QC 20220620

Available from: 2022-04-05 Created: 2022-04-05 Last updated: 2023-04-14Bibliographically approved
Ding, B., Petrache, C. M., Bäck, T., Cederwall, B. & Zikhali, B. R. (2021). Signature splitting of the g(7/2)[404]7/2(+) bands in Ba-131 and Ce-133. Physical Review C: Covering Nuclear Physics, 104(6), Article ID 064304.
Open this publication in new window or tab >>Signature splitting of the g(7/2)[404]7/2(+) bands in Ba-131 and Ce-133
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2021 (English)In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 104, no 6, article id 064304Article in journal (Refereed) Published
Abstract [en]

Excited states in Ba-131 and Ce-133 were studied using in-beam gamma-ray spectroscopy through the Sn-122(C-13, 4n) Ba-133 and Te-125(C-12, 4n) Ce-133 reactions, respectively. A strongly coupled band, associated with the nu g(7/2) [404]7/2(+) configuration, was identified in Ba-131 and Ce-133. It is the first time to observe the nu g(7/2) [404]7/2(+) bands in the N = 75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the pi g(7/2) [404]7/2(+) bands in the odd-A Ta and Re isotopes. Extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low- j orbitals.

Place, publisher, year, edition, pages
American Physical Society (APS), 2021
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-306858 (URN)10.1103/PhysRevC.104.064304 (DOI)000730839900001 ()2-s2.0-85121154713 (Scopus ID)
Note

QC 20220105

Available from: 2022-01-05 Created: 2022-01-05 Last updated: 2022-06-25Bibliographically approved
Barucca, G., Davì, F., Lancioni, G., Mengucci, P., Montalto, L., Natali, P. P., . . . Zmeskal, J. (2021). The potential of Λ and Ξ- studies with PANDA at FAIR. European Physical Journal A, 57(4), Article ID 154.
Open this publication in new window or tab >>The potential of Λ and Ξ- studies with PANDA at FAIR
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2021 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 57, no 4, article id 154Article in journal (Refereed) Published
Abstract [en]

The antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss ground-state hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: p¯ p→ Λ¯ Λ and p¯ p→ Ξ¯ +Ξ-. The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA.

Place, publisher, year, edition, pages
Springer Nature, 2021
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-309243 (URN)10.1140/epja/s10050-021-00386-y (DOI)000645914600001 ()2-s2.0-85105147608 (Scopus ID)
Note

QCR 20220302

Available from: 2022-03-02 Created: 2022-03-02 Last updated: 2022-06-29Bibliographically approved
Ertoprak, A., Cederwall, B., Qi, C., Aktas, Ö., Doncel, M., Hadinia, B., . . . Wyss, R. A. (2020). Evidence for octupole collectivity in 172Pt. European Physical Journal A, 56(2), Article ID 65.
Open this publication in new window or tab >>Evidence for octupole collectivity in 172Pt
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2020 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 56, no 2, article id 65Article in journal (Refereed) Published
Abstract [en]

Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of  ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing direct evidence for octupole collectivity in 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3- state as a collective octupole-vibrational state.

Place, publisher, year, edition, pages
Springer, 2020
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-271657 (URN)10.1140/epja/s10050-020-00071-6 (DOI)000517208400001 ()2-s2.0-85079637616 (Scopus ID)
Funder
Swedish Research Council, 621-2014-5558
Note

QC 20200427

Available from: 2020-04-03 Created: 2020-04-03 Last updated: 2024-03-18Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1996-0805

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