Octupole collectivity in 220Rn and 224Ra

Collective properties of the radioactive nuclei 220Rn and 224Ra have been studied via Coulomb excitation of a 2.8 A.MeV radioactive ion beam (RIB) incident upon 60Ni, 112,114Cd and 120Sn targets. The experiments took place at the REX-ISOLDE RIB facility, CERN. De-excitation γ-ray yields following multiple-step Coulomb excitation were detected in coincidence with recoiling target nuclei in the Miniball spectrometer. For the first time, B(E3;3+ → 0+) values have been directly measured with a radioactive ion beam. In the process, 224Ra becomes the heaviest post-accelerated RIB to date at ISOLDE (with the possible exception of the quasi-stable 238U). The measurements presented in this thesis represent a tripling of the number of nuclei around Z ≃ 88 and N ≃ 134, for which direct measurements of the octupole collectivity have been performed. The only previous measurements being for the relatively long-lived 226Ra. The γ-ray yields, in conjunction with previously measured spectroscopic data, were used to determine electromagnetic matrix elements using the least-squares search code, Gosia. In total, nine E1, E2 and E3 matrix elements were measured in 220Rn (plus six upper limits) and 12 (plus four upper limits) in 224Ra. The measured B(E3; 3+ → 0+) values in 220Rn and 224Ra are 32±4 W.u. and 42±3 W.u., respectively. A new state has been observed at 937.8(8) keV in 220Rn and is proposed to be the 2+ member of the K = 2, γ-vibrational band. The results are interpreted in terms of the collectivity and deformation, and are compared with the predictions of self-consistent mean-field theory and cluster model calculations

Coulomb Excitation of Proton-rich N = 80 Isotones at HIE-ISOLDE

A projectile Coulomb-excitation experiment was performed at the radioactive ion beam facility HIE-ISOLDE at CERN. The radioactive ¹⁴⁰Nd and ¹⁴²Sm ions were post accelerated to the energy of 4.62 MeV/A and impinged on a 1.45 mg/cm²-thin ²⁰⁸Pb target. The γ rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL. The scattered charged particles were detected by a double-sided silicon strip detector in forward direction. Experimental γ-ray intensities were used for the determination of electromagnetic transition matrix elements. Preliminary results for the reduced transition strength of the B(M1;23+→21+)=0.35(19)μN2 of ¹⁴⁰Nd and a first estimation for ¹⁴²Sm have been deduced using the Coulomb-excitation calculation software GOSIA. The 2³₊ states of ¹⁴⁰Nd and ¹⁴²Sm show indications of being the main fragment of the proton-neutron mixed-symmetry 2⁺₁,ms state

Analysis methods of safe Coulomb-excitation experiments with radioactive ion beams using the GOSIA code

With the recent advances in radioactive ion beam technology, Coulomb excitation at safe energies becomes an important experimental tool in nuclear-structure physics. The usefulness of the technique to extract key information on the electromagnetic properties of nuclei has been demonstrated since the 1960s with stable beam and target combinations. New challenges present themselves when studying exotic nuclei with this technique, including dealing with low statistics or number of data points, absolute and relative normalisation of the measured cross-sections and a lack of complementary experimental data, such as excited-state lifetimes and branching ratios. This paper addresses some of these common issues and presents analysis techniques to extract transition strengths and quadrupole moments utilising the least-squares fit code, gosia.14 pages, 10 figures, to be published in European Physical Journal Astatus: publishe

GRIFFINCollaboration/GRSISort: Overdue Ozelot

<p><strong>New</strong></p> <ul> <li>grsiframe: Replacement for grsiproof, based on ROOT's RDataFrame instead of the obsolete PROOF. grsiframe uses "helpers" instead of "selectors" and a number of the latter that have been translated into the former can be found in the examples directory.</li> <li>FastTiminingHistSelector: A selector to create fast timing histograms from a prepared tree of fast timing information.</li> <li>checklog.sh script in examples is a quick script to check a log-file to see if the sort of a subrun ended successfully or not. Simply checks if the last line is "bye,bye" (good) or "Deleting thread" (bad).</li> <li>sort.sh script in examples can be used to sort files and can be run with multiple instances in parallel. Automatically saves the output of the sorting into log files which can be check with checklog.sh script to see if the sorting finished.</li> <li>TLevelScheme: New class to create, plot, and save level schemes. Includes some modification to the behavior of GCanvas if the canvas name is "LevelScheme".</li> <li>TEfficiencyCalibrator: New GUI to automatically take spectra created by the effiency helper to calculate efficiency curves, including summing in and summing out. The calculation of the latter still has some bugs in it.</li> <li>TRedirect class redirect stdout and stderr to a file as long as the object exists, i.e. until it goes out of scope or is deleted.</li> <li>EnableCrosstalkCorrection program allows enabling crosstalk correction for a list of analysis files.</li> <li>PlotVsRun allows plotting histograms vs the run number.</li> <li>ReadCalFromRoot loops over the provided root files and writes out a .cal file for each one of them.</li> <li>SetOdbFromData loops over the provided root files and checks if the PPG information read from the ODB matches the data. Writes out a line for each file whether the information was already correct, some error occured, or if it was updated.</li> <li>checkSort loops over the provided analysis root files and checks if any problem with repeated events occured (the bug making this check necessary has been fixed by now).</li> </ul> <p><strong>Improvements</strong></p> <ul> <li>TGRSIUtilities now provides a trim function and the separate versions in GValue, TChannel, and TRunInfo have been removed.</li> <li>GValue: It is now possible to provide a default value to <code>GValue::Value</code> which is used instead of <code>NaN</code> if the requested value is not found.</li> <li>Globals.h now provides a function <code>std::string hex(T val, int width = -1)</code> that formats the provided value in hexadecimal with lead 0x and if the provided width is positive pads it with zeroes up to that width. It also provides a <code>void SetGRSIEnv()</code> function to set the environment for grsisort, and for linux systems a <code>void PrintGdbStacktrace()</code> function to print the stack trace using gdb.</li> <li>TSinglePeak and all its children now have a working Sigma and FWHM function, and the <code>InitializeParameters</code> function can take a range which is used as limits for the centroid.</li> <li>TPeakFitter uses the range as limit for the centroid and doesn't include it when releasing all parameters if the fit failed to give good errors. Also returns the <code>TFitResultPtr</code> to allow users to access e.g. the covariance matrix.</li> <li>Made some adjustments to make grsisort work with ROOT 6.24 and 6.26.</li> <li>TCalibrationGraphSet: Added options to set marker type, as well as setting line colors and marker colors in one single function and adding axis titles. Also added functions to get minimum and maximum x- and y-values. When adding graphs to the set, the colors are initialized to the current size of the set.</li> <li>TChannel now supports multiple ranges for calibrations, corrections for time drifts (if digitizer clocks are not synched properly) and added GetTime function which is now called by <code>TDetectorHit</code> and simply calles the GetTime function of the mnemonic.</li> <li>TMnemomic warns if the base class is being used instead of the version defined in the data library. Also includes GetTime function that takes care of the different time stamp units of different digitizer etc.</li> <li>Instead of looping over the vector of fragments and adding the fragments on at a time to the <code>UnpackedEvent</code> class, we now simply set the raw data to the whole vector at once.</li> <li>TGRSIMaps includes a function to emplace elements.</li> <li>Added multiple new options to grsisort, mostly used by grsiproof and grsiframe.</li> <li>TGRSISelector includes a check for the size of object to warn if ROOT's limit of 1 GB is reached.</li> <li>Replaced (most?) uses of <code>printf</code> with <code>std::cout</code>.</li> <li>TNucleus offers option to get the transition sorted by energy or intensity. To that effect two lists of transitions are kept simultaneously.</li> <li>TPulseAnalyzer has been ported to the latest version from SFU TIPSort code.</li> <li>Updated TScaler to get ratio of two variables of the last scaler entry (used in EMMA). Also scalers are now actually written to file at the end.</li> <li>TSortingDiagnostics now includes a map of channels missing in the calibration file.</li> <li>TSourceCalibration zooms graph and residual simultaneously, had some bugs fixed as well.</li> <li>Improved and unified <code>Print</code> statements for detectors.</li> <li>TRunInfo now has a function <code>CreateLabel</code> that returns a string created using the run and sub-run numbers in it. Before this code was copied in multiple places of grsisort.</li> <li>Added new event building mode "Skip" that skips the step of sorting the fragments because they are already sorted.</li> <li>The makefile honors the c++ standard root-config returns and includes support for HIL data library.</li> <li>WriteCalToRoot output updated to show more clearly which files were update successfully and where problems occured.</li> </ul> <p><strong>Bug fixes</strong></p> <ul> <li>grsiproof: <code>--max-events</code> flag now works, additional options for PROOF added, log file names now include the run and sub-run number(s).</li> <li>The use of multiple threads to write the analysis file has led to problems with single events being repeated thousands of times, leading to spikes in the energy or time histograms. So we have reverted now to having TAnalysisWriteLoop write a single TFile directly instead of using the <code>TAnaysisWriteLoopClient</code> class.</li> <li>TPeakFitter used to crash when adding and removing peaks between fits.</li> <li>TSinglePeak and children now first set the parameter, then the limits, this avoids warnings that the parameter (which is 0 at that point) is outside the limits.</li> </ul&gt

Testing refined shell-model interactions in the sd shell: Coulomb excitation of 26Na

Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal sd interaction (USD) describing nuclei within the sd shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transitionmatrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus 26Na with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive beam experiment with 26Na (T1/2 = 1,07s) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with γ rays observed by the segmented MINIBALL array. Coulomb excitation cross sections of the beam have been obtained by normalization to the well known Coulomb excitation cross sections of the 104Pd target. Results: The observation of three γ -ray transitions in 26Na together with available spectroscopic data allows us to determine E2- and M1-transitional matrix elements. Results are compared to theoretical predictions. Conclusion: The improved theoretical description of 26Na could be validated. Remaining discrepancies between experimental data and theoretical predictions indicate the need for future experiments and possibly further theoretical improvements.status: publishe

Rb-97(37)60: The Cornerstone of the Region of Deformation around A similar to 100 (vol 115, 172501, 2015)

Excited states of the neutron-rich nuclei 97,99Rb were populated for the first time using the multistep Coulomb excitation of radioactive beams. Comparisons of the results with particle-rotor model calculations provide clear identification for the ground-state rotational band of 97Rb as being built on the πg9/2 [431] 3/2+ Nilsson-model configuration. The ground-state excitation spectra of the Rb isotopes show a marked distinction between single-particle-like structures below N=60 and rotational bands above. The present study defines the limits of the deformed region around A∼100 and indicates that the deformation of 97Rb is essentially the same as that observed well inside the deformed region. It further highlights the power of the Coulomb-excitation technique for obtaining spectroscopic information far from stability. The 99Rb case demonstrates the challenges of studies with very short-lived postaccelerated radioactive beams.nrpages: 172501status: publishe

Combined in-beam electron and γ -ray spectroscopy of 184,186Hg

By exploiting the SAGE spectrometer a simultaneous measurement of conversion electrons and γ rays emitted in the de-excitation of excited levels in the neutron-deficient nuclei 184,186Hg was performed. The light Hg isotopes under investigation were produced using the 4n channels of the fusion-evaporation reactions of 40Ar and 148,150Sm. The measured K- and L-conversion electron ratios confirmed the stretched E2 nature of several transitions of the yrast bands in 184,186Hg. Additional information on the E0 component of the 2+_2 → 2+_1 transition in 186Hg was obtained.status: publishe