The fusion evaporation reaction 40Ca(58Ni,p3n)94 Ag has been used to study the odd-odd N=Z nucleus 94Ag at JYFL-ACCLAB using the MARA recoil separator and the JUROGAM 3 HPGe detector array. The recoil-β-tagging technique has allowed the observation of γ rays de-exciting states in 94Ag for the first time. Shell model calculations using the JUN45 interaction including multipole and monopole electromagnetic effects are presented. Comparison with analog states observed in neighbor isobar nucleus 94Pd is also discussed.

A recoil-beta-tagging experiment has been performed to study the excited T = 0 and T = 1 states in the odd-odd N = Z nucleus Ag-94, populated via the( 40)Ca(Ni-58,1p3n)Ag-94 reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyv & auml;skyl & auml;. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt gamma rays emitted at the reaction target, a number of transitions between excited states in Ag-94 have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived T = 1 ground state of Ag-94. The transitions are proposed to proceed within and between the sets of states with T = 0 and T = 1. Possible correspondence between some of these transitions from analog states in( 94)Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the T = 0 and T = 1 states and to allow a theoretical set of Coulomb energy differences to be calculated for the A = 94 T = 1 analog states.

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.

The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental "smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope La-116(57)59, 23 neutrons away from the only stable isotope La-139(57)82, is reported. La-116 nuclei were synthesised in the fusion-evaporation reaction Ni-58(Zn-64, p5n)La-116 and identified via their proton radioactivity using the mass spectrometer MARA (Mass Analysing Recoil Apparatus) and the silicon detectors placed at its focal plane. Comparisons of the measured proton energy (E-p = 718 +/- 9 keV) and half-life (T-1/2 = 50 +/- 22 ms) with values calculated using the Universal Decay Law approach indicate that the proton is emitted with an orbital angular momentum l = 2 and that its emission probability is enhanced relative to its closest, less exotic, odd-even lanthanum isotope (La-117(57)60) while the proton-emission Q-value is lower. We propose this to be a possible signature for the presence of strong neutron-proton pair correlations in this exotic, neutron deficient system. The observations of. decays from isomeric states in La-116 and La-117 are also reported.

This doctoral thesis consists of two parts: the experimental study of the neutron-deficient atomic nuclei 88Ru and 87Tc, and the computational study on the diagonalization of general pairing Hamiltonian. In the first part, which constitutes the main content of the thesis, the low-lying excited states in the N = Z nucleus 88Ru and N = Z + 1 nucleus 87Tc were studied via fusion-evaporation reactions induced by 115 MeV 36 Ar ions bombarding6 mg/cm 2 thick metallic 54 Fe target foils at the Grand Accélérateur Nationald’Ions Lourds (GANIL), Caen, France. The prompt γγ-neutron and charged-particle coincidences from the de-excitation of the reactions were measured by the AGATA γ-ray spectrometer coupled to the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays. The results for 88 Ru confirmed and extended the previous level scheme to a tentative (14+) state. The constructed level structure exhibits a moderately deformed rotational behavior but shows a band crossing at a significantly higher rotational frequency compared with neighboring nuclei with N > Z. Such band crossings are associated with quasiparticle alignment within the standard isovector pairing scheme. The observation of a “delayed” rotation alignment in the deformed N = Znucleus is consistent with theoretical predictions related to the existence of strong isoscalar neutron-proton pair condensate. The yrast band in 87 Tc from the (9/2+) state to the (33/2+) state was established based on six mutually coincident γ-ray transitions. The constructed yrast band exhibits a sharp backbending at ~ω ≈ 0.50 MeV. In the odd-A isotonic chains around N = 44, approaching the N = Z line, the observed decrease in alignment frequency and increase in alignment sharpness were proposed as an effect of the enhanced isoscalar neutron-proton interactions. In addition to the yrast band in 87 Tc, six new mutually coincident γ-ray transitions were identified by comparing the γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level scheme was compared with shell model and TRS calculations. The results indicate that these low-lying states exhibit spherical behavior different from the previously identified oblate yrast band, and the band might be built on a (7/2 +1 ) ground state.

In the second part, an OpenMP parallel Fortran program, PairDiag, for the diagonalization of the general pairing Hamiltonian in deformed systems was developed. In the program, the ‘01’ inversion algorithm is used to generate the seniority-zero basis vectors; all the non-zero Hamiltonian matrix elements are evaluated “on the fly” by the scattering operators and a search algorithm; the matrix diagonalization is achieved by the Lanczos + QR algorithm. The PairDiag program is packaged in a Fortran module and can be easily used to replace the BCS approximation in other nuclear structure programs.

Denna doktorsavhandling består av två delar: experimentella studier av de neutronfattiga atomkärnorna 8844Ru44 och 8743Tc44 och en beräkningsstudie av diagonalisering av Hamiltonfunktionen för parväxelverkan i ett mångkropparssystem. I denförsta delen, som utgör avhandlingens huvudsakliga innehåll, har de lägsta energitillstånden i kärnan rutenium-88 - med lika antal neutroner (N) och protoner (Z) -och kärnan teknetium-87 - med N=Z+1- studerats via fusionsreaktioner. Dessa inducerades av en argon-36-joner med kinetisk energi 115 MeV som fick bestråla tunnametallfolier av järn-54 (masstjocklek 6 mg/cm2) vid tungjonacceleratorlaboratorietGrand Accélérateur National d’Ions Lourds (GANIL), Caen, Frankrike. Gammafotoner, neutroner och lätta laddade partiklar som utsändes i reaktionerna detekteradesmed hjälp av γ-strålspektrometern AGATA, detektorsystemen NEDA, och NeutronWall samt detektorsystemet för laddade partiklar, DIAMANT. För atomkärnan 88Rukunde tidigare identifierade energitillstånd upp till spinn och paritet 8+ verifieras.Den rotationsliknande struktur som detta grundtillståndsband utgör kunde också utökas med ytterligare γ-övergångar och uppvisar en bandkorsning med en betydligthögre rotationsfrekvens jämfört med angränsande kärnor med N > Z. Sådana bandkorsningar är normalt sett förknippade med att par av kvasipartiklar (jfr. den s.k.BSC-teorin för parkorrelationer av isovektortyp) bryts och att deras spinn linjerarupp sig med kärnans rotationsriktning. Observationen av en “fördröjd” bandkorsning i den deformerade N=Z-kärnan överensstämmer med teoretiska förutsägelserom förekomsten av ett isoskalärt neutron-proton-parkondensat. Det starkast populerade, s.k. yraste, bandet av energitillstånd i atomkärnan teknetium-87 observeradessom en kaskad av sex γ-övergångar från tillståndet (33/2+1) ned till (9/2+1) Dennarotationsliknande struktur uppvisar en skarp bandkorsning vid rotationsfrekvensenω ≈ 0.50 MeV/~. I detta arbete noterades också att det i isotoniska kedjor av kärnor med udda masstal, runt N = 44, kan observeras skarpare bandkorsningar ochen systematisk minskning av bandkorsningsfrekvensen då neutrontal och protontalnärmar sig varandra. Detta föreslås vara en ny effekt av utökade isoskalära neutronprotoninteraktioner som uppstår i udda, deformerade atomkärnor nära N=Z-linjen.Förutom det rotationslika yraste bandet i 87Tc identifierades också sex nya ömsesidigt koincidenta γ-övergångar genom att jämföra γ-strålningsintensiteterna i spektrasom valts ut för olika kombinationer av detekterade partiklar. Det konstruerade nivåschemat jämfördes med skalmodell- och TRS-beräkningar. Resultaten tyder på attde tillstånd som sammanbinds av denna γ-kaskad kan utgöra grundtillståndsbandeti87Tc och att det har sfärisk karaktär medan det först identifierade rotationslikayraste bandet bygger på en nära oblat deformerad konfiguration.I andra delen av denna doktorsavhandling presenteras ett OpenMP parallelltFortran-program, PairDiag, som har utvecklats för diagonaliseringen av en generellHamiltonfunktion för parkorrelationer i deformerade system. I programmet användsinversionsalgoritmen “01” för att generera alla basvektorerna för senioritet noll. Allamatriselement skilda från noll utvärderas “i farten” av spridningsoperatorer och ensökningsalgoritm; matrisdiagonaliseringen uppnås med Lanczos + QR-algoritmen.PairDiag-programmet är förpackat i en Fortran-modul och kan lätt användas för attersätta BCS-approximationen i andra kärnstrukturberäkningsprogram

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.

We present a program for solving exactly the general pairing Hamiltonian based on diagonalization. The program generates the seniority-zero shell-model-like basis vectors via the ‘01’ inversion algorithm. The Hamiltonian matrix is constructed in this seniority-zero space. The program evaluates all non-zero elements of the Hamiltonian matrix “on the fly” using the scattering operator and a search algorithm. The matrix is diagonalized by using the iterative Lanczos algorithm. The OpenMP parallel program thus developed, PairDiag, can efficiently calculate the ground-state eigenvalue and eigenvector of the general pairing Hamiltonian for both the even-mass and the odd-mass system. The program is packaged in a Fortran module, which makes it easy to use the program to replace the BCS approximation in standard self-consistent mean field calculations. For systems with dimension around 108, the calculation can be done within hours on standard desktop computers. Program summary: Program Title: PairDiag. Program Files doi: http://dx.doi.org/10.17632/dzzspfszsh.1 Licensing provisions: CC by NC 3.0. Programming language: Fortran 95. Nature of problem: The numerically exact solution of general pairing Hamiltonian can be solved by diagonalization in configuration spaces of fixed seniority. Solution method: The program constructs the seniority-zero space by the ‘01’ inversion algorithm, and diagonalizes the general pairing Hamiltonian by the Lanczos plus QR algorithm. Restrictions: The total number of orbits involved must be less than 63, and the dimension that can be calculated is restricted by the local RAM condition. 

We present an efficient program for the exact diagonalization solution of the pairing Hamiltonian in spherical systems with rotational invariance based on the SU(2) quasi-spin algebra. The basis vectors with quasi-spin symmetry considered are generated by using an iterative algorithm. Then the Hamiltonian matrix constructed on this basis is diagonalized with the Lanczos algorithm. All non-zero matrix elements of the Hamiltonian matrix are evaluated "on the fly" by the scattering operator and hash search acting on the basis vectors. The OpenMP parallel program thus developed, PairDiagSph, can efficiently calculate the ground-state eigenvalue and eigenvector of general spherical pairing Hamiltonians. Systems with dimension up to 10(8) can be calculated in few hours on standard desktop computers. Program summary Program Title: PairDiagSph. CPC Library link to program files: https://doi.org/10.17632/t5txsg3s5g.1 Code Ocean capsule: https://codeocean.com/capsule/9159628 Licensing provisions: CC by NC 3.0. Programming language: Fortran 95. Nature of problem: The exact diagonalization of spherical pairing Hamiltonian can be achieved in the quasi-spin space. Solution method: The program generates the basis vectors via the adjacency excitation algorithm, and diagonalizes the spherical pairing Hamiltonian by the Lanczos + QR algorithm. Additional comments including restrictions and unusual features: The total number of spherical must be less than 64; The maximal dimension that can be handled is restricted by the local RAM capacity.

The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.

The low-lying excited states in the neutron-deficient N = Z + 1 nucleus 8743 Tc 44 have been studiedvia the fusion-evaporation reaction 54 Fe( 36 Ar, 2n1p) 87 Tc at the Grand Accélérateur National d’IonsLourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliaryNEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt γ-rays, neutrons, and charged particles emitted in the reaction. A level scheme of 87 Tc from the (9/2 +g.s. ) state to the (33/2 +)statewasestablishedbasedon6mutuallycoincidentγ-ray transitions. The con-1structed level structure exhibits a rotational behavior with a sharp back bending at ~ω ≈ 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.