NEDA—NEutron Detector Array Valiente-Dobón, J.J.; Jaworski, G.; Goasduff, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2019, Letnik:
927
Journal Article
Recenzirano
Odprti dostop
The NEutron Detector Array, NEDA, will form the next generation neutron detection system that has been designed to be operated in conjunction with γ-ray arrays, such as the tracking-array AGATA, to ...aid nuclear spectroscopy studies. NEDA has been designed to be a versatile device, with high-detection efficiency, excellent neutron-γ discrimination, and high rate capabilities. It will be employed in physics campaigns in order to maximise the scientific output, making use of the different stable and radioactive ion beams available in Europe. The first implementation of the neutron detector array NEDA with AGATA 1π was realised at GANIL. This manuscript reviews the various aspects of NEDA.
Understanding the evolution of level densities in the crossover from spherical to well-deformed nuclei has been a long-standing problem in nuclear physics. We measure nuclear level densities for a ...chain of neodymium isotopes 142,144−151Nd which exhibit such a crossover. These results represent the most complete data set of nuclear level densities to date for an isotopic chain between neutron shell-closure and towards mid-shell. We observe a strong increase of the level densities along the chain with an overall increase by a factor of ≈150 at an excitation energy of 6 MeV and saturation around mass 150. Level densities calculated by the shell model Monte Carlo (SMMC) are in excellent agreement with these experimental results. Based on our experimental and theoretical findings, we offer an explanation of the observed mass dependence of the level densities in terms of the intrinsic single-particle level density and the collective enhancement.
In this work we present a comparison between the two liquid scintillators BC-501A and BC-537 in terms of their performance regarding the pulse-shape discrimination between neutrons and γ rays. ...Special emphasis is put on the application of artificial neural networks. The results show a systematically higher γ-ray rejection ratio for BC-501A compared to BC-537 applying the commonly used charge comparison method. Using the artificial neural network approach the discrimination quality was improved to more than 95% rejection efficiency of γ rays over the energy range 150 to 1000 keV for both BC-501A and BC-537. However, due to the larger light output of BC-501A compared to BC-537, neutrons could be identified in BC-501A using artificial neural networks down to a recoil proton energy of 800 keV compared to a recoil deuteron energy of 1200 keV for BC-537. We conclude that using artificial neural networks it is possible to obtain the same γ-ray rejection quality from both BC-501A and BC-537 for neutrons above a low-energy threshold. This threshold is, however, lower for BC-501A, which is important for nuclear structure spectroscopy experiments of rare reaction channels where low-energy interactions dominates.
Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and ...recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2;41+→21+)/B(E2;21+→0gs+) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.
Energy differences between analogue states in the T = 1/2 Mg-23-Na-23 mirror nuclei have been measured along the rotational yrast bands. This allows us to search for effects arising from ...isospin-symmetrybreaking interactions (ISB) and/or shape changes. Data are interpreted in the shell model framework following the method successfully applied to nuclei in the f(7/2) shell. It is shown that the introduction of a schematic ISB interaction of the same type of that used in the f(7/2) shell is needed to reproduce the data. An alternative novel description, applied here for the first time, relies on the use of an effective interaction deduced from a realistic charge-dependent chiral nucleon-nucleon potential. This analysis provides two important results: (i) The mirror energy differences give direct insight into the nuclear skin; (ii) the skin changes along the rotational bands are strongly correlated with the difference between the neutron and proton occupations of the s(1/2) "halo" orbit.
Electric quadrupole matrix elements, Mp, for the Jπ=2+→0+, ΔT=0, T=1 transitions across the A=46 isobaric multiplet 46Cr-46V-46Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows ...direct insight into the isospin purity of the states of interest by testing the linearity of Mp with respect to Tz. Pairs of nuclei in the T=1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The Mp values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for 46Cr and 46Ti; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in 46V and 46Ti. A constant value of Mp across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T=1 isospin triplets is presented.
Proton inelastic scattering on 68,70,72Ni Galtarossa, F; Scomparin, L; de Angelis, G ...
Journal of physics. Conference series,
09/2023, Letnik:
2586, Številka:
1
Journal Article
Recenzirano
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The proton inelastic scattering on 68,70,72Ni isotopes was measured at the NSCL at MSU, employing the S800 spectrometer coupled to the GRETINA γ-ray array. The aim of the experiment was to determine ...the degree of collectivity in these neutron-rich Z = 28 isotopes. The use of a hadronic probe allows to complement previous Coulomb excitation measurements of the reduced transition probability B(E2; 0+ → 2+) and deduce the neutron-to-proton transition matrix elements ratio. The high resolution in γ-ray energy achievable with GRETINA gives large control on feeding transitions, thus reducing possible systematics errors in the determination of transition strengths.
Precise measurements of the lifetimes of the first excited 2+ states in the stable even-A Sn isotopes 112–124Sn have been performed using the Doppler shift attenuation technique. For the isotopes ...112Sn, 114Sn and 116Sn the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously reported values and indicate a shallow minimum at N=66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the s1/2 neutron orbital in generating collectivity when near the Fermi level.
Abstract
The electromagnetic transition probabilities of the yrast
$$2^+$$
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
118
Te and the missing data for
116
Te 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
$$2^+$$
2
+
state in
118
Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is
$$\tau _{2+}=7.46(19)$$
τ
2
+
=
7.46
(
19
)
ps. In addition, the lifetime of the
$$4^+$$
4
+
state was measured to be
$$\tau _{4+} = 4.25(23)$$
τ
4
+
=
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
$$B(\textrm{E2};0^+\rightarrow 2^+)$$
B
(
E2
;
0
+
→
2
+
)
values in the midshell area is in good agreement with the calculations and the calculated
$$B_{4/2}$$
B
4
/
2
ratio provide evidence for
118
Te as a near perfect harmonic vibrator.
The Oslo Cyclotron Laboratory Görgen, A.; Guttormsen, M.; Larsen, A. C. ...
European physical journal plus,
02/2021, Letnik:
136, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Research at the Oslo Cyclotron Laboratory at the University of Oslo is focused on spectroscopy experiments for nuclear structure and nuclear astrophysics using the Oslo Scintillator Array OSCAR. ...Light-ion beams from the
K
=
35
cyclotron are furthermore used for studies in radiation biology and medical physics, for research and development related to medical isotope production, and for irradiation of materials and electronics components. Here we present an overview of the laboratory and its research infrastructure, give a brief discussion of the respective research programs and methods, and present recent highlights.
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