<figure><img src="image_145.png" /></figure>

**Fig. 6.** Example of a pulse originating from R=24mm and z=23mm. The modulating effect of the response of the electronics is clearly seen. The effect of linear and derivative crosstalk is also shown. The netcharge segment is marked with a black circle.

<figure><img src="image_146.png" /></figure>

**Fig. 7.** Example of how the sensitivity of the pulse shapes to a specific parameter (in this case $\mu_{h^{<111>}}$) at a position in the detector is extracted.

<figure><img src="image_147.png" /></figure>

**Fig. 8.** Number of points in the crystal where a specific parameter had the largest influence

<figure><img src="image_148.png" /></figure>

**Fig. 9.** The average sensitivity for different parameters taken over points where they had the largest sensitivity.
<figure><img src="image_149.png" /><figcaption>**Fig. 10.** The influence of the electron mobility in the <100> direction on the pulse shapes as a function of position</figcaption></figure>

<figure><img src="image_150.png" /><figcaption>**Fig. 11.** The influence of the hole mobility in the <100> direction on the pulse shapes as a function of position</figcaption></figure>
<figure><img src="image_151.png" /><figcaption>**Fig. 12.** The influence of the electron mobility in the <111> direction on the pulse shapes as a function of position.</figcaption></figure>

<figure><img src="image_152.png" /><figcaption>**Fig. 13.** The influence of the hole mobility in the <111> direction on the pulse shapes as a function of position.</figcaption></figure>

<figure><img src="image_153.png" /><figcaption>**Fig. 14.** Extensive gridsearch on the simulated dataset. 2D projections of positions as determined by PSA. The level of noise have been varied in the interval .6%→12%. Note clustering close to segment boundaries for bad signal-to-noise ratio.</figcaption></figure>
<figure><img src="image_154.png" /><figcaption>**Fig. 15.** SVD Matrix PSA on the simulated dataset. 2D projections of positions as determined by PSA. The level of noise have been varied in the interval .6%→12%. Note how larger noise drives the results towards the center of the segments.</figcaption></figure>

<figure><img src="image_155.png" /><figcaption>**Fig. 17.** Position resolution as a function of interaction energy for simulated data, for different γ-ray energies [31], and for data from the 3D-scanning of S002 at Liverpool [32,33] using extensive gridsearch (GS) or matrix inversion after SVD (MI).</figcaption></figure>

<figure><img src="image_156.png" /><figcaption>**Fig. 16.** RMS values for different amounts of noise for a inclusive gridsearch on a 1x1x1 mm³ basis and using the SVD matrix method with the same basis. Results without crosstalk, with only linear crosstalk, or with linear and differential crosstalk added to the test signals are shown.</figcaption></figure>
7.12 Extended Geant4 simulations of the AGATA spec-
trometer

UNDER EDITING
# Extended Geant4 simulations of the AGATA spectrometer

J. Ljungvall¹

CSNSM, Univ Paris-Sud, CNRS/IN2P3, F-91405 Orsay, France

**Abstract.** The AGATA geant4 Monte Carlo code has been extended with several new reaction kinematics included as well as the possibility to use continuous time in the simulation allowing the study of background and pile-up within time gates. These new features have been applied to the planning and analysing of experiments performed at the AGATA@GANIL campaign.

**PACS.** 21.10.Tg In-beam γ-ray spectroscopy

## 1 Introduction

Monte Carlo simulations have become an important tool in all experimental physics and many other domains of science. High resolution γ-ray spectroscopy is no exception and simulations are extensively used to design experimental apparatus, to plan experiments, and to analyse the experiments. Simulations are used to estimate efficiencies and response functions of the detectors as well as to include effects that are difficult to model analytically, e.g. slowing down in the target, non-regular angular coverage of the detectors. In this paper development of the AGATA geant4 simulation code [1] are discussed, and examples of applications of these developments are given.

In section 2 a short description of the AGATA geant4 code is given, followed by the description of some implemented bench marks used to verify the correctness of the code for each new version of Geant4 [2] in section 3. Section 4 is devoted to the description of how one can include realistic time structures in the simulations allowing the modeling of build up of activity, pile-up in detectors etc. This is followed by section 5 that discuss the implementation of reaction kinematics in the code where examples of simulations and comparisons with experimental data is also give. Monte Carlo simulations are used within the AGATA collaboration to compare experimental and simulated efficiencies for source measurements, and for this reason many simulations of source measurements have been made. In section 6 examples are given with specialization to inclusion of the source strengths in the simulations. Finally conclusions and an outlook is given in section 7.

## 2 A short description of the AGATA geant4 code

The AGATA geant4 Monte Carlo Simulation code [1] was developed by Farnea et al. to design the AGATA array

and as a tool to develop γ-ray tracking algorithms. In the code the geometry of the detector system is defined using text input files giving the size and positions of the crystals, dead layers, aluminium in encapsulation and crystals. Scattering from material behind the crystals is modeled using a thicker than actual aluminum end of the triple clusters.

Photon transport and transport of charged particles and neutrons are done using the appropriate geant4 processes. The effect of the electrical segmentation, i.e. the possibility to read out deposited energy and corresponding position with a identified segment, is done in a schematic but accurate way.

The code has built in event generators and can read events generated externally from ascii files. This allows for several different ways of generating events. The output of the code is a list mode file, containing information of which detectors that have been hit, the segment with net energy for each deposited energy. How the energy is deposited depends on the "tracking mode", where either the primary interaction of photons are used or the secondary electrons are tracked. There are options in the code to post-process this interaction points to emulate the finite resolution and resolving power of the PSA.

## 3 Tools to validate of physics processes

As AGATA was to move from Legnaro to GANIL I got involved in the simulations of the expected performances. This included simulations to estimate the efficiency as well as simulations of Recoil Distance Doppler shift experiments. The first step in this process was to benchmark the physics of the simulations and of the event generators I added. To do this I added a "test" geometry consisting of a sphere. All particles are stopped and the energy deposited locally when they intersect the sphere. This feature is implemented via the inheritance of a geant4 G4VProcess class that kills all particles when they enter the volume
named "TestSpherePhys". This allows for simple investigation of quantities such as attenuation coefficients for γ rays, energy loss for heavy ions in materials etc. As examples I've included the validation of the attenuation of γ rays in Germanium in figure 1, the stopping power of ions in metals in figure 2 and finally the validation of the lifetime of excited states in an ion shown in figure 3. During this phase an error in the inclusion of Compton and photoelectric cross section were found. Note that this error was introduced in the stage of simulations for the GSI phase and were not present in the code described by Farnea et al. [1]. These tests allowed the validation of the physics

<figure><img src="image_157.png" /><figcaption>**Fig. 1.** Attenuation coefficient for γ rays in Germanium as given by different versions of geant4.</figcaption></figure>

<figure><img src="image_158.png" /><figcaption>**Fig. 2.** Stopping powers for six different combinations of ions. Geant4 simulations are compared to results from the LISE++ code [3].</figcaption></figure>

<figure><img src="image_159.png" /><figcaption>**Fig. 3.** Validation of the decay of excited states in $^{170}$Os. Note that the lifetimes are not taken from experiment but just realistic values.</figcaption></figure>

used in the AGATA simulations and the discovery of a few problems and bugs in the geant4 code [4, 5].

## 4 Wall time simulations - including reaction rates

In many experiments the limit in sensitivity is a result of random background events that leak through time gates, this as a result of either finite time resolution of the experimental or that the studies states have lifetimes that are long compared to the random reaction rate. For high reaction rates there is also the issue of pile-up in the detectors; this both from random events and multiple reactions with a time window too short for the detectors to resolve (in the case of AGATA this is about a few hundred nanoseconds). These situations are typically difficult to handle in Monte-Carlo simulations, especially the build up of activity, as one is dealing with 15 orders of magnitude in time scales. However, in the AGATA simulation code a continuous wall time clock has been included. This is controlled by giving the number of particles per second and the beam structure when simulating reactions, or by giving the source strength when simulating source measurements. The two can be combined. For beams the particles are assumed to be evenly distributed within the time bunches (this gives Poisson time statistics for a continuous beam). The list mode output file of the AGATA simulation then contains a universal time stamp allowing sorting the event and creating coincidences, pile-up events etc. If $\mathcal{N}(\beta)$ decay is simulated this typically requires a divide and conquer procedure for first sorting data into files containing time windows and then sorting events with in each file.
## 5 Simulation of reaction kinematics

In the preparation for experiments and proposals for AGATA I've performed a large range of simulations of Recoil Distance Doppler Shifts experiments. These simulations include the correct kinematics, the possibility to populate the excited states in the reaction product as wanted etc. In the step of analysing the simulations the acceptance of VAMOS was also included. Examples are given in figure 4 and figure 5 where an experiment performed in 2008 at GANIL with the EXOGAM γ-ray spectrometer combined with the VAMOS stood as example and the improvements that could be gained from AGATA. This was done by reproducing the experimental spectra from the 2008 experiment and after this replacing the EXOGAM spectrometer with AGATA in the simulations.

<figure><img src="image_160.png" /><figcaption>**Fig. 4.** Geant4 simulation of an experiment [6] where excited states in <sup>62</sup>Fe where populated using multi-nucleon transfer from a <sup>238</sup>U beam impinging on <sup>64</sup>Ni target. In the experiment the target like products where identified event by event in the VAMO Spectrometer. Gamma rays where detected in the EXOGAM γ-ray spectrometer. A plunger with a Mg degrader was used, giving rise to the double peak structure seen.</figcaption></figure>

As a final example of simulations of AGATA that I have done is the reproduction of experimental spectra while analysing the data from the experiment published by Klintefjord et al. [7]. In these simulations as many factors as possible where taken into account in order to reproduce the experimental spectra. This in order to estimate the peak shapes of the two components seen in the RDDS experiment. This was needed as the lifetimes of the 4<sup>+</sup>I states in the irons were not much longer than the transit time for the nuclei in the Mg degrader used. These simulations are shown in figure 6.

Having validated the basic physics of the simulations I've added to the already existing event generator to include the kinematics of fusion-fission reactions and Coulomb excitations. During this time I also introduced features to include radioactive sources with a specific source strength and model the experiments with given beam intensities

<figure><img src="image_161.png" /><figcaption>**Fig. 5.** Geant4 simulations comparing AGATA in different configurations for a lifetime measurement in <sup>62</sup>Fe using a plunger device with EXOGAM used in a previous experiment. The increased efficiency for similar peak separation is clear.</figcaption></figure>

<figure><img src="image_162.png" /><figcaption>**Fig. 6.** Realistic simulation of the first AGATA@GANIL experiment. In these simulations the populations and lifetime of levels have been adapted to reproduce experimental spectra as a function of distance between the target and the degrader foil. The purpose of the simulations was to determine the peak shape of the "slow" component.</figcaption></figure>

and beam structures. This work was done to a large extent for reason not related to AGATA in an effort to model an experiment performed at GANIL in 2012.

In figures 7 to 11 I show the result of a simulation of Coulomb excitation of the <sup>74</sup>Kr with an energy of 350 MeV on a <sup>208</sup>Pb target. The target and beam like particles were detected in a DSSSD detector. A beam intensity of 1000 pps was assumed with beam frequency of 100 MHz and a pulse width of 2 ns. The last sentence means that the start time for each event moves forward with an average 1 ms per event, but limited to windows of 2 ns each 10 ns. This time, i.e. the start time of the event is a part of the event header in the output file. For each individual interaction in an event there is also the time relative the event start. This data has then been time sorted, i.e. interactions that are in coincidence in a detector are treated together. For a simulated low number of particles per second this can be
<figure><img src="image_163.png" /><figcaption>**Fig. 7.** Geant4 geometry of a simulation of a Coulomb excitation of <sup>74</sup>Kr using a realistic time structure of the beam.</figcaption></figure>

<figure><img src="image_164.png" /><figcaption>**Fig. 8.** Count-rate as a function of time. The build up of β activity can clearly be seen.</figcaption></figure>

done by keeping a stack in memory but for more intense beams such as used in the simulation discussed in chapter intermediary steps such as writing files containing fixed times windows are needed. In this particular simulation the data was stored in the AGATA Data Flow format ADF, one file for each detector with time stamped data and analyzed using the tools used to analyse experimental data. As a consequence the number of γ rays that are detected per second increases due to the build up of <sup>74</sup>Kr in the target chamber as can be seen in figure 8. In figure 9 the energy versus angle in the DSSSD detector is shown, with the band of beam like particles and the target like particles at lower energies. If no coincidence gate is set on the time difference between the DSSSD and AGATA a γ-ray spectrum like what is shown in figure 10 is produced. If however a coincidence gate between the DSSSD and the tracked γ ray is used a clean γ-ray spectrum is produced, as shown in figure 11. While this feature of keeping track of the real time is rather neat it is not really useful. Consider

<figure><img src="image_165.png" /><figcaption>**Fig. 9.** Simulation of the detection of beam-like and target like particles in a silicon detector.</figcaption></figure>

<figure><img src="image_166.png" /><figcaption>**Fig. 10.** Gamma rays as detected in AGATA without time gate on prompt γ rays in coincidence with detected particles. Note the γ rays from β decay.</figcaption></figure>

<figure><img src="image_167.png" /><figcaption>**Fig. 11.** Gamma rays as detected in AGATA with time gate on prompt γ rays in coincidence with detected particles. Note that the γ rays from β decay are absent.</figcaption></figure>

a stable beam experiment with 10<sup>12</sup> pps. It is possible to simulate some 10<sup>4</sup> pps in the best case on a single CPU. The factor of 10<sup>8</sup> would indicate that we would need some 10<sup>10</sup> W of electric power to keep up with the experiment! Clearly one has to be more clever.
I've also performed similar simulations to show the expected increase in performance with AGATA for different type of experiments. In figure 12 the simulated comparison between an array representing JUROGAM and $1\pi$ of AGATA for a lifetime measurement using the RDDS technique with $^{186}$Pb populated using heavy-ion fusion reactions. The choice of $1\pi$ AGATA comes from the idea to show the increase in efficiency given the same peak separation.

<figure><img src="image_168.png" /><figcaption>**Fig. 12.** Simulation of a lifetime measurement with a Plunger device with excited states in $^{186}$Pb populated using heavy-ion fusion reactions. The background is estimated by reproducing experimental spectra from an experiment performed at Jyväskylä.</figcaption></figure>

## 6 Simulation of sources

In order to investigate differences between measured and simulated efficiency for the sub-array of AGATA used for the first AGATA campaign at GSI [8] I did complete simulations of AGATA using a chain of Monte Carlo simulations with $^{60}$Co sources of varying source strength. The energy deposition points were then fed into the pulse shape calculation code AGATAGeFEM that produces output files that can be read by the AGATA analyses tool chain. Noise, cross talk and realistic use of CFD threshold for the timing was applied before PSA being performed on the simulated traces. The same simulated interaction points were also treated in a more classic way where the PSA was simulated by packing and smearing (see for example explanation in Lopez et al. [9]). The conclusion from this work was, inline with all preliminary work done for AGATA and GRETA, that the tracking performance after PSA when using a correct data base of pulse shapes should be very good. Examples of simulations for $^{60}$Co sources are shown in figures 13,14,15,16, and 17.

<figure><img src="image_169.png" /><figcaption>**Fig. 13.** Singles spectra for simulations of $^{60}$Co with different source strengths (1 kBq, 100 kBq, and 10 MBq).</figcaption></figure>

<figure><img src="image_170.png" /><figcaption>**Fig. 14.** Gamma-gamma matrix of $^{60}$Co with different source strengths of 1 kBq.</figcaption></figure>

<figure><img src="image_171.png" /><figcaption>**Fig. 15.** Gamma-gamma matrix of $^{60}$Co with different source strengths of 100 kBq.</figcaption></figure>

## 7 Conclusions

Several new features have been added to the AGATA geant4 simulation packages. These include reaction kinematics for Coulomb excitation reactions and for induced fission reactions. Further more a mechanism to simulate the passing of time and hence also model time background and coincidences has been developed and tested. All these
<figure><img src="image_172.png" /><figcaption>**Fig. 16.** Gamma-gamma matrix of $^{60}$Co with different a source strengths of 10 MBq.</figcaption></figure>

<figure><img src="image_173.png" /><figcaption>**Fig. 17.** Gated spectra for simulations of $^{60}$Co with different source strengths (1 kBq, 100 kBq, and 10 MBq).</figcaption></figure>

features have been used to plan and analyze experiments during the AGATA@GANIL phase of the AGATA project.

## Acknowledgement

The author would like to give special thanks to Marc Labiche, Caterina Michelagnoli, and the AGATA collaboration.

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## 7.13 OASIS ANR

### Project summary

The OASIS project aims at optimizing the science production of the Advanced GAmmaray Tracking Array (AGATA) γ-ray spectrometer. Presently installed at the Grand Accélérateur National d'Ions Lourds (GANIL) at Caen, France, AGATA has passed the demonstrator phase of its early implementation (15 high-purity germanium detectors) and now contains 32 such detectors with infrastructure to accommodate 45 detectors covering 1π of solid angle.

AGATA is a new generation γ-ray spectrometer designed to overcome the inherent limitation of the previous generation of Compton suppressed HPGe detector arrays. By replacing the Anti-Compton shields, which occupy a significant amount of solid angle, with HPGe detectors solid angle coverage, and hence efficiency, can be increased. However, for this approach to produce high quality γ-ray spectra an alternative Compton suppression technique has to be developed. This is γ-ray tracking: The energy and position of individual γ-ray interaction points inside the HPGe is determined using highly segmented detectors combined with digital electronics and pulse-shape analysis. These interaction points are then tested for the hypotheses that they belong to a fully absorbed γ ray. For the γ-ray tracking to work the γ-ray interaction points have to be located to within 5 mm inside the detectors. A very important additional increase in performance comes from the very high effective angular granulation of AGATA given by knowing the interaction positions giving very good Doppler Correction capabilities, something very important in modern experimental nuclear structure research. Because of the high performance of AGATA it is considered a very important detector for the future and present nuclear structure research facilities in Europe, such as FAIR, HIE-ISOLDE, SPES, and SPIRAL2.

Since the first physics campaign with AGATA started has showed its high performance in experimental situation where the sensitivity is dominated by the Doppler broadening of the γ-ray peaks, for high-count rate situations, and when it is beneficial to have a very compact γ-ray spectrometer - AGATA has proven to be a technical success in many ways.

During the work analyzing experimental data the AGATA collaboration, and the γ-ray tracking community, has however seen that the performance of AGATA in terms of Compton suppression from the γ-ray tracking is not what simulations suggests it should be. It is believed in the γ-ray tracking community that cause for this is related to problems with the pulse-shape analysis. Although the nominal position resolution from the pulse-shape analysis is within the required limits several indications points to that the pulse-shape analysis does not perform as good as is needed. The OASIS project aims at carefully investigating the reasons for this using computer simulations to try to reproduce and understand the deficiencies seen in experimental data. One particular problem that will be addressed within the OASIS project is that of correctly determining the number of actual interaction that a γ-ray has had with the AGATA. Several novel ideas are to be investigated.

Finally, many aspects of analyzing γ-ray spectroscopy data have to be reviewed when using AGATA. This mainly comes from the fact that there is more detailed information to look at offering new possibilities. What was previously simple calibration procedures using source data, such as efficiency calibrations, now has complex dependencies on the experimental situation and choices made for the γ-ray tracking algorithms. Other methods, e.g. to determine angular correlations and distributions,
also need to be developed specifically for γ-ray tracking. A part of OASIS is dedicated to this work, making sure that the γ-ray tracking community will have thoroughly tested and quantifies procedures.

## Summary table of persons involved in the project:

<table><thead><tr><th>Partner</th><th>Name</th><th>First name</th><th>Current position</th><th>Involvement (person.month)</th><th>Role &amp; responsibilities in the project (4 lines max)</th></tr></thead><tbody><tr><td>CSNSM</td><td>Ljungvall</td><td>Joa</td><td>CR1</td><td>18</td><td>Scientific coordinator</td></tr><tr><td>CSNSM</td><td>Lopez-Martens</td><td>Araceli</td><td>DR2</td><td>6</td><td>Student supervisor<br>Coordination task 2</td></tr><tr><td>CSNSM</td><td>Korichi</td><td>Amel</td><td>DR2</td><td>6</td><td>γ-ray tracking expert</td></tr><tr><td>CSNSM</td><td>Dosme</td><td>Nicolas</td><td>IE1</td><td>1.5</td><td>Responsible Scanning CSNSM</td></tr><tr><td>CSNSM</td><td>Legay</td><td>Eric</td><td>IR2</td><td>1</td><td>Technical support</td></tr><tr><td>CSNSM</td><td>Grave</td><td>Xavier</td><td>IRHC</td><td>1.5</td><td>Scanning and computing</td></tr><tr><td>CSNSM</td><td>Linget</td><td>Dennis</td><td>IR1</td><td>1</td><td>"</td></tr><tr><td>CSNSM</td><td>Gibelin</td><td>Laurent</td><td>TCS</td><td>1</td><td>"</td></tr><tr><td>GANIL</td><td>Clément</td><td>Emanuel</td><td>CR1</td><td>9</td><td>"</td></tr><tr><td>IRFU/SPhN</td><td>Theisen</td><td>Christophe</td><td>E6</td><td>9</td><td>Supervisor Post doc 1<br>Coordination task 3<br>Work together with post-doc on task 1<br>γ-ray spectroscopy expert</td></tr><tr><td>IRFU/SPhN</td><td>Zielińska</td><td>Magda</td><td>E3</td><td>6</td><td>Supervisor Post doc 2<br>Coordination task 1</td></tr><tr><td>IRFU/SEDI</td><td>Karolak</td><td>Marc</td><td>E2</td><td>3</td><td>HPGe detectors expert</td></tr><tr><td>IPHC</td><td>Duchêne</td><td>Gilbert</td><td>DR1</td><td>6</td><td>Responsible Scanning IPHC<br>Coordination IPHC contribution task 1,2</td></tr><tr><td>IPHC</td><td>Sigward</td><td>Marie-Hélène</td><td>IE2</td><td>3</td><td>Perform Scanning</td></tr><tr><td>IPHC</td><td>Didierjean</td><td>François</td><td>IR2</td><td>3</td><td>γ-ray tracking</td></tr><tr><td>IPHC</td><td>De Canditiis</td><td>Bartolomeo</td><td>PhD</td><td>6</td><td>MC Simulations for PSA, Analyzing scanning data</td></tr></tbody></table>

## Any change that have been made in the full proposal compared to the pre-proposal

Change of strategy to acquire AGATA electronics. This is of no consequence for the science program, and a potentially less expensive solution. Also the need to renew the radioactive sources for the CSNSM scanning table and the IPHC scanning table has been lifted to scientific coordinators attention, and funds for this will be included in the OASIS.

### 7.13.1 Proposal's context, positioning and objective(s)

1. Objectives and scientific hypotheses Modern nuclear structure physics aims at bridging the gap between QCD and the effective in-medium force felt by nucleons in nuclei, on one hand, and on the other hand creating a uniformed view of all phenomena observed over the Segré chart. Not only important in its own
right, a detailed understanding of nuclear structure is very important for, e.g. astrophysical applications where small variations, such as the ordering of states, can create large changes in production rates, or to constrain nuclear matrix elements involved in neutrino-less double $\beta$ decay. It is therefore important to probe and understand terms in the nucleon-nucleon interaction that are "weak" for stable nuclei turning nuclear structure physics into a high-precision field, requiring high precision instrumentation with high sensitivity [290]. Gamma-ray spectroscopy is a very important part of this instrumentation, used in more than half of all nuclear structure physics experiments.

The OASIS project aims at greatly increasing the present performance of the Advanced GAmma Tracking Array (AGATA) [203] that is the next-generation $\gamma$-ray spectrometer for in-beam nuclear structure studies that is build in Europe. AGATA is recognized [290] as a key part of feature nuclear structure research in Europe, and our capacity to fully exploit the array will be of utmost importance to benefit from the opportunities given by new radioactive and high-intensity stable beam facilities being constructed in Europe such as FAIR, HIE-ISOLDE, SPES, and SPIRAL2. AGATA is presently installed at GANIL, Caen, France in a version that is about 1/5 of the full size of AGATA.

The conceptual design of AGATA, and its American counterpart GRETA, goes back to the end of the 1990's and the beginning of 2000's when simulations showed that a $\gamma$-ray spectrometer using so-called $\gamma$-ray tracking would provide unprecedented sensitivity, especially if combined with digital electronics allowing high count rates, i.e. high luminosity. For many physics cases the gain would be two orders in magnitude or more [291, 233]. This is illustrated in figure 7.1.

<figure><img src="image_174.png" /><figcaption>Figure 7.1: Figure showing the increased resolving power for $\gamma$-ray spectrometers. The resolving power is to be interpreted as inverse of the fraction of the total $\gamma$-ray intensity that can be seen.</figcaption></figure>

Therefore the development of $\gamma$-ray tracking arrays was started using segmented
HPGe detectors that are closely packed allowing the coverage of up to 80% of the solid angle. Gamma-ray tracking is, as the name suggests, the reconstruction of a γ ray's path in a detector by determination of the positions of its energy depositions. The tracking is done under the hypothesis that the γ ray was fully absorbed, and a track is accepted or rejected based on a figure of merit that should be high for truly absorbed γ rays and low for γ rays that were only partially absorbed and Compton scattered out of the detector. This way a high efficiency can be achieved while suppressing the Compton background. Simulations show that for γ-ray tracking to work the position of γ-ray interactions have to be determined within 5 mm. This also gives an effective angular opening for AGATA of 1° making the Doppler Correction capabilities excellent, important especially for experiments using inverse kinematics as is often the case for radioactive beam experiments.

Large resources have been invested in the AGATA project in Europe, and it is in many aspects a technical success. Both AGATA and GRETINA have proven to be excellent γ-ray spectrometers for physics were γ rays are emitted from nuclei moving faster than $v_c \approx 10\%$ of the speed of light. However, today the situation is that for experiments with high γ-ray multiplicity or when γ-ray coincidences are needed to identify the γ rays of interest both AGATA and GRETINA, scaled to the same solid angle coverage, perform worse than Gammasphere, i.e. the generation of γ-spectrometers they should replace. The expectations based on simulations is that AGATA should outperform Gammasphere with a factor of 2. This is understood within the γ-ray tracking community as due to a few specific issues that have not yet been resolved to satisfaction:

* The determination of the interaction positions within the detectors is not good enough.

**The first objective of OASIS is to resolve this issue.**

* The problem of correctly assigning the number of interactions inside a detector segment.

**The second objective of OASIS is to mitigate this problem.**

As the AGATA collaboration has started analyzing data from AGATA in detail it stands clear that data from a γ-ray tracking array challenges our understanding of γ-ray spectrometers. A striking example is the efficiency as a function of the multiplicity of detected γ rays where for a tracking array the situation is complex. Here the energy and geometrical separation of all absorbed γ rays have an impact on the actual efficiency. It therefore becomes important to be able to model the response of the detector array using simulations to deconvolute experimental data in a consistent way.

**The third objective of OASIS is to fully characterize AGATA to allow all γ-ray spectroscopy methods to be applied and apply this to data in order to extract more physics.**

**If the objectives of OASIS are realized AGATA would gain a factor of 2 in performance**

2. Originality and relevance in relation to the state of the art A block diagram of γ-ray tracking is shown in figure 7.2. It starts with highly segmented HPGe
detectors (in the case of AGATA the detectors are 36-fold segmented in 6x6 pat-
tern) where the signals from all 37 (36 outer segments and the central contact)
are digitized. The signals are then decomposed and the position and energy of
every individual interaction are extracted. After this step interactions from all
detectors that are in coincidence are used to perform the γ-ray tracking where
all reasonable combinations of interaction points are tested in order to recon-
struct fully absorbed γ rays. It is considered within the community that if the
signal decomposition can provide the correct positions and number of interac-
tion points in an event, the tracking algorithms will perform well.

<figure><img src="image_175.png" /><figcaption>Figure 7.2: Block diagram showing the ingredients needed for γ-ray tracking.</figcaption></figure>

The decomposition procedures, referred to as pulse shape analysis (PSA) are
based on comparing a pre-calculated (or measured) set of signals to the exper-
imental signals. This set, called the basis for the detector, contains signals for
a 3D grid of interaction points inside the detector, typically some tens of thou-
sands points for an AGATA crystal. In figure 7.3 an example is shown where a
basis signal (red) corresponding to the best position in the base is overlaid on
the experimental signal (black). The signals are composed of signals for each 36
segments and the central contact signal.
<figure><img src="image_176.png" /><figcaption>Figure 7.3: Example of pulse shape decomposition used in AGATA. The black signal is experimental and the red corresponds to the best match in the basis. The inset shows the distribution of interaction positions from grid search PSA.</figcaption></figure>

At the time of planning the OASIS project all steps in this chain have been extensively tested and used for producing results published in peer-reviewed journals [292]. Dedicated experiments have been performed to test the PSA [244, 245] showing that the achieved position resolution is within specifications. Experiments have also been performed to characterize the performance of AGATA [259]. There it is shown that the γ-ray tracking performance expected from Monte Carlo simulations are not reproduced using experimental data. A too low efficiency, and more important too low peak-to-total in the spectra are found. The differences can partly be explained by a difference in active volume for the detectors between simulation and experiment. However the low experimental peak-to-total reflects the need to assume a larger error than the nominal 5 mm FWHM in the positions used in tracking to get a good efficiency. This reflects large tails on the errors in the positions determined by the PSA. The suspicion that the lower than expected performance comes from problem with the PSA is further enhanced looking directly at the output of the PSA. As shown in the inset of figure 7.3, the distribution of interaction points in one AGATA crystal shows clustering of the interaction points. This is clearly not physical since over the solid angle of one detector the γ-ray flux is homogeneous. Different algorithms have been tested to perform the PSA [237, 239, 238, 240, 215]. This extensive testing has shown that independently of the algorithm used the basis has to have an excellent fidelity, requiring a perfect understanding of not only the detector but also the electronics response function (methods to circumvent this problems have been proposed [234]). Extensive work has been done on modeling detectors, characterizing detectors and electronics [217, 235, 227, 219, 220, 293, 221, 240, 222, 244, 245, 224] in order to achieve this high fidelity of the bases but up to date the results are not fully satisfactory. **Objective one of OASIS relates directly to this.** A second general conclusion that has been drawn is that the determination of the actual num-
ber of interaction points in a detector is a very complicated problem since the
signals of one large interaction often can be reproduced using two smaller in-
teractions (e.g. see [238]). A direct result of this is the difficulty to properly dis-
criminate between single Compton scattering events and Compton scattering
plus photo electric effect absorption, lowering the quality of the γ-ray spectra.
The improved treatment of this is objective 2 of OASIS.

3. Risk management and methodology To achieve the objectives described above this project has three well defined tasks:

(a) Understand and model detectors (objective 1).

(b) Improve algorithms for treating the signals from these detectors (objective 2).

(c) Understand the response function of a γ-tracking array. This will be very important as the complexity of spectroscopic work done with AGATA will increase (objective 3).

Task 1 will be addressed using numerical simulations. A code developed by
the scientific coordinator during the last decade, called AGATAGeFEM solves
the electric field and weighting potentials using Finite Element methods [294]
with tetrahedral cells. This allows a definition of the geometry only limited by
the numerical precision. The signals are generated using the Shockley-Ramo
theorem, where the transport of the charge carriers in the electric field is done
using an adaptive fourth order Runge-Kutta algorithm [228]. Examples of field
calculations and pulse shapes calculated with the code are shown in figure 7.4.

<figure><img src="image_177.png" /></figure>
Figure 7.4: To the left the weighting potential of an A slice segment inside an AGATA A type crystal calculated using the AGATAGeFEM code. The refinement in regions where the potential changes fast is clearly visible. To the right, example of pulse shapes calculated using AGATAGeFEM. The example shows the pulse shapes before applying the response of the electronics (black), with a low pass filter (red) and including only linear cross talk or linear+differential cross talk (green and blue)

The AGATAGeFEM code will be used to investigate what deficiencies in the pulse-shape data base that are responsible for the problems encountered by the PSA. This will be done by generating a set of interaction points in AGATA using the AGATA Monte Carlo simulation package [233], and then calculating the corresponding pulse shapes with varying parameters (detector geometry, electronic response functions etc). These pulses will then be analyzed using the same code as used for data analysis in AGATA. The data base used will be calculated assuming the geometrical and electrical properties of the crystals used to calculate the data based used to analyze experimental data. It is hoped that this way the discrepancies between the modeled and real HPGe detectors used in AGATA can be revealed. Finally, what has been learned will be applied on real AGATA detectors, testing with experimental data. It is foreseen to perform this last step using data from scanning tables equipped with AGATA electronics to be able to perform scanning in parallel with validation and this way be able to address problem regions in the detectors during the scanning. Whereas the computer modeling part of task 1 is rather risk free in terms of its feasibility the accessibility to an AGATA crystal for scanning (with corresponding cryostat) is not guaranteed. Our mitigation strategy in the case of failing to have access to an AGATA crystal is the use of already existing scan data. However, this solution will not allow targeted scanning of the crystal.

Task 2 will be addressed by adding information to the PSA algorithms. In general the idea is to add information to pulse-shape decomposition step to allow a better determination of the number of interactions inside single segments. One possibility is to let PSA suggest several solutions varying the number of interaction points in a segment, and then let γ-ray tracking choose the best solution. A second road to follow would be to combine the PSA and γ-tracking steps into one minimization problem. One could even imagine calculating the pulse shapes used as a part of the minimization this way allowing a correct modeling of the charge-carrier cloud extension and diffusion.

As pointed out, a considerable amount of effort has already been spent on modelling HPGe detectors, PSA, and γ-ray tracking development. The success of OASIS is therefore far from given. The scientific coordinator does however believe that he is in a good position to really advance the field given his experience in the field. Even in the case of failure to reach the objectives within the OASIS project a few question marks concerning our lack of understanding of the HPGe detectors will have been answered.

Task 3, which corresponds one-to-one to objective three, is to fill this lack of knowledge. The methodology will be the use of concatenation of experimental data to create high multiplicity events combined with geant4 Monte Carlo simulations+Pulse shape calculations. By assuring that we can reproduce the response of AGATA using simulations, these will be a good tool to deconvolute
experimental spectra. The first part of this task is considerably smaller and is less complicated than task 1-2, and a good starting point for a student. It is associated with a very small risk. As for the exploitation of AGATA data in order to extract physical results, this is important as such a result most likely would be a part of the PhD students work. The ambition of OASIS is to push the performance of AGATA so that physical results that were not accessible before OASIS will be after. However in the case that this fails the scientific coordinator is in possession of data from which physical results can be extracted given the present performance of AGATA allowing a mitigation strategy for this part of task 3.

### 7.13.2 Project organization and means implemented

1. Scientific coordinator The scientific coordinator Joa Ljungvall has worked with AGATA and related issues since his PhD (defended in spring 2005). During this decade he has performed detector characterization, Monte Carlo simulations, pulse-shape calculations, pulse-shape analysis, and proposed and performed experiments and published results from AGATA. Most of the technical work has been presented during the AGATA collaboration meetings (AGATA weeks) where he has given more than 15 presentation related to these topics. He was also the first to integrate a pulse-shape analysis code into the AGATA data acquisition system and has an excellent understanding of information technology aspects of AGATA, as well as the detector physics and the demands on its performance to fulfill the physics programs depending on it.

2. Consortium The consortium is created to give large contact surfaces between the student, the post-docs and the permanent staff involved in the OASIS project. A second criteria is to involve most of the french expertise in the field in such a way that the complementary aspect is not only in terms of different expertise but different experiences working on the same subject. The idea behind this is that the field of research addressed by OASIS is already well investigated and by collecting as much experience as possible it will be possible to avoid repeating already performed work. In figure 7.5 a mind chart of how the objectives of OASIS are connected to the tasks and the competences needed to finish the tasks and accomplish the goals. The last part of the figure shows the major (but unique) different contributions from the different partners. Table 7.1 summarizes the responsible person for each partner, the main resource that is asked for and to which task(s) the partner will mainly (but not uniquely) contribute.
<figure><img src="image_178.png" /><figcaption>Figure 7.5: Figure showing how the different objectives, tasks, needed competences and how different members of the consortium contribute</figcaption></figure>

<table><caption>Table 7.1: Table showing the partners of the consortium, the principal contact person and a first order distribution of the tasks and resources</caption><thead><tr><td>Partner</td><td>Person</td><td>Resources</td><td>Task</td></tr></thead><tbody><tr><td>CSNSM</td><td>Joa Ljungvall</td><td>Student+Equipment</td><td>1,2,3</td></tr><tr><td>GANIL</td><td>Emmanuel Clément</td><td>Post-doc 1</td><td>3</td></tr><tr><td>SPhN</td><td>Magda Zielińska</td><td>Post-doc 2</td><td>1</td></tr><tr><td>IPHC</td><td>Gilbert Duchêne</td><td>Equipment</td><td>1</td></tr></tbody></table>

The Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM) is a funding member of the AGATA collaboration which has been leading in the development of γ-ray tracking algorithms, pulse-shape analysis codes, and detector characterization using the Orsay Scanning table. A geographically close partner that has necessary complementary detector physics and "hands on" experience with AGATA type detectors is the Service de Physique Nucléaire/IRFU Cea (SPhN). They have a long time involvement in the AGATA project both in its conceptual phase, in the early and present exploitation phase and as one of the laboratories that are performing Customer Acceptance Tests (CAT's) for the AGATA collaboration. The SPhN also has an experienced γ-ray spectroscopy group. A post-doc working at SPhN will therefore profit from a strong local competence and close proximity to the CSNSM which should generate an excellent environment to advance OASIS towards its objectives. GANIL is the present host laboratory of AGATA and therefore a natural partner for a project that aims at pushing the exploration of AGATA data as far as possible. With a post-doc focusing on task 3, together with the student at CSNSM, a close to complete characterization of AGATA as a γ-ray spectrometer is possible. This will be combined with analyzing data with the goal of extracting nuclear-structure physics. The Institut Pluridisciplinaire Hubert CURIEN (IPHC) has a large experience in working with AGATA detectors, especially in comparing experi-
mental pulses coming from dedicated detector scanning setups with calculated
pulses, with a recent thesis. Their presence within the consortium is thus of
utmost value to ensure that to the work of especially task 1 can proceed from
an advanced point. IPHC is also one of two french laboratories (the second be-
ing CSNSM) equipped to scan AGATA detectors allowing to measure the pulse
shapes from a well defined location inside the crystal to allow a complete char-
acterization of the crystal. This complementary and redundancy drastically re-
duced the risks if the OASIS project will have the possibility to scan an AGATA
crystal.

3. Means of achieving the objectives

As has been described the three objectives of OASIS will be reached by solving three different tasks. Table 7.1 shows the course partitioning of the tasks. The tasks are subdivided into smaller parts according to the present understanding of the scientific coordinator. More details of the planning for each task are given under respective head line below. The only real estimation of success for objective one and two of OASIS is the improvement in performance of AGATA. Task 1 and task 2 corresponding to objective 1 and 2 can however be broken down into smaller steps, with the possibility to define whether it was successfully or not. Towards the end of the second year it will be very beneficial to organize an international workshop for γ-ray tracking and PSA. Funds are thus requested for this and this workshop is one of the deliverables of OASIS. Objective three is a bit different in that the first part is less exploratory and more production like and can be planned with clear objectives and deliverables. For the second part of objective 3, i.e. the application to experimental data to extract more physics the scope depends heavily on the outcome of all tasks and therefore has to be left open ended, e.g. without a well defined sub-task or deliverable.

The resources asked by each partner in the consortium to achieve the tasks are listed in table 7.2. The travel request are generic on the scale of 3.3 kEuro per year and partner. This is to allow frequent travel between the laboratories to be able to participate hands on in e.g. detector scanning or data taking with AGATA at GANIL (not experiments but to this project dedicated data, e.g. source data). Also it is our intentions to have 2 collaboration meetings per year of 2 days each. The assumption of four participants per laboratory is made in the cost estimation.

* Detailing Task 1 In table 7.3 the sub tasks of task 1 are shown together with the contributing members and deliverables. The approximate time span for the completion of each task is also shown. Considering the time needed to write publications and a PhD thesis the tasks are to be finished some time before the end of the OASIS project. As task number one is based on the use of computer simulations the first step is to achieve the coupling between the AGATA Monte Carlo code simulations package, the AGATAGeFEM pulse-shape calculation-code package and the AGATA on-line data acquisition part. This is work that is partly already performed by the scientific coordinator, but it has to be completed and upgraded to be compatible with the latest developments made on all the different codes. This is the first step and has to be done before the task can proceed, and is a first deliverable - a short report showing how computer simulations have been used to produce data that has been treated using the AGATA
<table><caption>Table 7.2: Resources asked for for each partner to accomplish tasks</caption><thead><tr><th>Partner</th><th>Resource</th><th>Demand [kEuro]</th></tr></thead><tbody><tr><td>CSNSM</td><td>PhD student</td><td>98</td></tr><tr><td>CSNSM</td><td>Collimated <sup>137</sup>Cs source</td><td>10</td></tr><tr><td>CSNSM</td><td>CPU for cloud computing</td><td>5</td></tr><tr><td>CSNSM</td><td>Equipment for CSNSM scanning table</td><td>10</td></tr><tr><td>CSNSM</td><td>Workshop+Travel</td><td>20</td></tr><tr><td>CSNSM</td><td>Open Access Publishing</td><td>10</td></tr><tr><td>SPhN</td><td>2 year post-doc</td><td>126</td></tr><tr><td>SPhN</td><td>CAT Lab equipment</td><td>20</td></tr><tr><td>SPhN</td><td>Travel</td><td>11</td></tr><tr><td>IPHC</td><td><sup>152</sup>Eu source and Equipment for IPHC scanning table</td><td>20</td></tr><tr><td>IPHC</td><td>Travel</td><td>10</td></tr><tr><td>GANIL</td><td>2 year post-doc</td><td>115</td></tr><tr><td>GANIL</td><td>Travel</td><td>10</td></tr><tr><td>Total</td><td></td><td>465</td></tr><tr><td></td><td><strong>ANR funding asked for</strong></td><td><strong>492</strong></td></tr></tbody></table>

online data acquisition and subsequent data analysis programs (already existing within the AGATA collaboration). The choice a FEM-based code to calculate the electric fields inside the AGATA crystal allows the possibility to investigate the effects of geometrical imperfection to an arbitrary small scale.

After this the computer modeling sub-tasks should be performed in parallel. This because much of the work analyzing the result of varying different aspect (i.e. detector geometry of the electronics response function) will be compared with each other. Typically the student and one of the post-docs will share this work with support from the scientific coordinator and permanent staff at CSNSM and SPhN. When all sub-tasks are finished short report will be written summarizing the influence of each change on position resolution, γ-ray tracking efficiency and peak-to-total in the γ-ray spectra. It will also clearly state if we have succeeded in pinning down the reasons for the less-than-perfect performance of the PSA algorithms, which is the measure of success for these sub-tasks. Here it should be noted the in2p3 project "Data flow for nuclear physics" will be able to provide the needed infrastructures for the computer based calculations. Therefore a small amount of money is asked for to contribute to the local computer infrastructure by buying additional computer power for the cloud. Access to a cloud computing facility is important as pulse-shape analysis and calculations are very CPU-time consuming activities.

If possible the result will be compared to and collaborated by the experimental scanning of an AGATA HPGe detector. Here is of extra interest the possibility to use a <sup>152</sup>Eu source as one will be able to study the impact of the charge carrier cloud size by using the different γ-ray energies available. Funds are therefore demanded for a <sup>152</sup>Eu source. This is work that has to be done on an ad-hoc time scale as it is impossible to foresee the availability of an AGATA crystal. An unavailability of an AGATA crystal during the project period is a real risk, with as only mitigation the use of
already existing scan data. It should here be pointed out that the access to two different scanning table setups and, via the consortium, different sets of scanning data, provides a very important redundancy to assure that the project can profit if a detector is available. However, for this redundancy there is a need to replace the collimated ¹³⁷Cs source at CSNSM, and funds will be asked for this within the OASIS project. There is also a request for funding to allow the use of an AGATA digitizer test-bench available at CSNSM together with the CSNSM scanning table make sure that the electronic response function is the correct one. The technical services of CSNSM (IT and electronics) will be solicited for this work. The possibility to scan the same detector using both the CSNSM and IPHC scanning table with different electronics would be of great interest and would enable us determining the pulse-shape alteration as a function of electronics.

<table><caption>Table 7.3: Table showing an overview of the sub tasks of task 1.</caption><thead><tr><th>Sub task</th><th>Leader</th><th>Partners/ Contribution</th><th>Success indicator</th><th>Deliverable</th><th>Start month</th><th>End month</th></tr></thead><tbody><tr><td>AGATAGeFEM<br>MC Sim coupling</td><td>CSNSM</td><td>CSNSM, IPHC</td><td>Data injected<br>in AGATA online<br>code</td><td>Full simulation</td><td>0</td><td>6</td></tr><tr><td>Investigate<br>geometrical effect</td><td>IRFU</td><td>CSNSM, SPhN,<br>IPHC</td><td>Effect seen<br>and quantified</td><td>Sensitivity estimate</td><td>6</td><td>30</td></tr><tr><td>Investigate effects<br>from electronics</td><td>IRFU</td><td>CSNSM, SPhN,<br>IPHC</td><td>Effect seen<br>and quantified</td><td>Sensitivity estimate</td><td>6</td><td>30</td></tr><tr><td>Implement and<br>investigate charge<br>carrier cloud effects</td><td>CSNSM</td><td>CSNSM, IPHC</td><td>Effect seen<br>and quantified</td><td>Sensitivity estimate</td><td>6</td><td>30</td></tr><tr><td>Scan AGATA detector<br>crystal</td><td>CSNSM</td><td>CSNSM, IPHC</td><td>Data taken</td><td>Data set</td><td>0</td><td>24</td></tr><tr><td>Publish</td><td>CSNSM</td><td>CSNSM, SPhN,<br>IPHC</td><td>Publication</td><td>Publication</td><td>18</td><td>36</td></tr></tbody></table>

* Detailing Task 2 In table 7.4 the sub tasks of task 2 are shown together with the contributing members and deliverables. The approximate time span for the completion of each task is also shown. Considering the time needed to write publications and a PhD thesis the tasks are to be finished some time before the end of the OASIS project. Task number two aims at better estimating the actual number of γ-ray interactions detected inside AGATA in each event, this way fulfilling the second objective of OASIS. Although this task of course is closely correlated to task 1, the principal difference is the abandoning of a logical separation between individual detectors and AGATA as a hole. This separation has no physical meaning and is a consequence of the assumption made that PSA (the subject of task 1 and objective 1) will not profit from any additional information outside the single crystal. It was therefore seen as not worth the considerable technical effort of the time when the electronics and DAQ of AGATA was design to consider all of AGATA at the level of PSA. The OASIS project takes the stand that this assumption should be questioned and that the inclusion of a global view into PSA will allow a better (although not exact) determination of the number of γ-ray interactions inside AGATA.

The first step of task 2 will be to connect what is today called "the local level" and "the global level" of data in AGATA. The "local level" refers to
data from one crystal without any time correlations to other detectors, whereas "the global level" unites time correlated data from all crystals, and if present, ancillary detectors. In the present form the codes used for PSA have only access to pulse-shapes from the crystals whereas γ-ray tracking only have access to the deduced positions and energy depositions. As a first step in this task the removal of the barrier between local and global level in the structure of the analysis is mandatory, and comes with a deliverable in form of reanalyzed data to prove that the new code is working.

Of utmost importance to reach the second objective of OASIS, and to finish task 2 is to have a reliable estimate of the position on an event by event basis from the PSA. Presently this information is not given by the PSA routines used in AGATA and the second sub-task of task 2, mandatory before continuing, is to implement a PSA routine that also provides errors. This can be done either using a classical $\chi^2 + 1$ approach in the case of using the present grid search method or using another PSA method where the errors also can be extracted, e.g. the Matrix method with Singular Value Decomposition. In order to see if the estimated errors are correct data with large Doppler Shifts will be used to correlate the error estimates to the Doppler Correction capability. The measure of success is to find such a correlation and that the increase in width of the Doppler Corrected peak corresponds to the given position uncertainties. There is potential technical risk here in that no reliable error estimate from the PSA can be found on an event-by-event basis. If this would be the case the project would have to proceed without but with a decreased chance of achieving objective 2. At the time of writing there is no reliable estimate to which extent.

As the sub-tasks related to joining the local and global level and the position error estimates have been finished the sub-tasks investigating different ways of improving the γ-ray tracking can be addressed. Although not separated as a sub-task there will be the need to put in place an efficient way of analyzing the results to access the success of each sub-task. These task will be performed in parallel if possible. If one proves to be the correct way this will quickly be discovered and the consortium force can be directed towards it. A worst case scenario would be that none of the ideas tested within the OASIS project improves the performance of the γ-ray tracking. However, even in such a case OASIS will have helped by removing some possible routes to explore.

* Detailing Task 3 Task 3 is detailed in table 7.5. The approximate time span for the completion of each task is also shown. Since a large part of task 3 will be centred around a 24 month post-doc it has a more compact schedule than task 1 and 2. Here the first step will be to identify existing experimental data suitable for the work in question and put in place the corresponding simulations. During the years that AGATA has been taking data suitable data sets for the suggested investigation have been taken and are becoming available to the entire AGATA collaboration. This first sub-task has therefore only a small risk associated to it.

The three consecutive named sub-tasks are to be performed in the enumerated order, as this in some way corresponds to the needs of the γ-ray
<table><caption>Table 7.4: Table showing an overview of the sub tasks of task 2.</caption><thead><tr><th>Sub task</th><th>Leader</th><th>Partners/ Contribution</th><th>Success indicator</th><th>Deliverable</th><th>Start month</th><th>End month</th></tr></thead><tbody><tr><td>Join local and global data flow</td><td>CSNSM</td><td>CSNSM</td><td>Reproduction of old result</td><td>Functional PSA+ γ-ray tracking code</td><td>0</td><td>12</td></tr><tr><td>Implement error</td><td>CSNSM</td><td>CSNSM</td><td>Correlation Doppler Broadening PSA error</td><td>PSA code</td><td>0</td><td>12</td></tr><tr><td>Gamma-ray tracking chooses solution</td><td>CSNSM</td><td>CSNSM, IPHC</td><td>Better figure of merit in γ-ray spectra</td><td>Functional code</td><td>12</td><td>30</td></tr><tr><td>PSA and γ-ray tracking in one step</td><td>CSNSM</td><td>CSNSM</td><td>Better figure of merit in γ-ray spectra</td><td>Functional code</td><td>12</td><td>30</td></tr><tr><td>Pre PSA estimation of number of hits</td><td>CSNSM</td><td>CSNSM</td><td>Better figure of merit in γ-ray spectra</td><td>Functional code</td><td>12</td><td>30</td></tr><tr><td>Publish</td><td>CSNSM</td><td>CSNSM, IPHC</td><td>Publication</td><td>Publication</td><td>18</td><td>36</td></tr></tbody></table>

spectroscopy community. For these tasks, as well as all of task 3, the indicators of success are reliable estimates of the errors made when extracting intensities from experimental spectra in different situations or deconvoluting a continuous spectrum. The tasks will be performed using standard γ-ray spectroscopy tools and are associated with a very small technical risk.

<table><caption>Table 7.5: Table showing an overview of the sub tasks of task 3.</caption><thead><tr><th>Sub task</th><th>Leader</th><th>Partners/ Contribution</th><th>Success indicator</th><th>Deliverable</th><th>Start month</th><th>End month</th></tr></thead><tbody><tr><td>Prepare data (sim and exp)</td><td>GANIL</td><td>GANIL, CSNSM</td><td></td><td>Data</td><td>0</td><td>6</td></tr><tr><td>Efficiency as function of fold and γ-ray energy</td><td>GANIL</td><td>GANIL, SPhN, CSNSM</td><td>Reliable error estimates</td><td>Recipe and code for collaboration</td><td>6</td><td>20</td></tr><tr><td>Determination of angular correlations and distributions</td><td>GANIL</td><td>GANIL, SPhN, CSNSM</td><td>Reliable error estimates</td><td>Recipe and code for collaboration</td><td>6</td><td>20</td></tr><tr><td>Deconvolution of continuous γ-ray distributions</td><td>GANIL</td><td>GANIL, SPhN, CSNSM</td><td>Reliable error estimates</td><td>Recipe and code for collaboration</td><td>6</td><td>20</td></tr><tr><td>Publish</td><td>GANIL</td><td>GANIL, SPhN, CSNSM</td><td>Publication</td><td>Publication</td><td>12</td><td>24</td></tr></tbody></table>

* CSNSM demand justification The CSNSM is asking for funds to finance one PhD student. Furthermore is the CSNSM asking for funds to complement existing AGATA electronics in order to have an AGATA electronics setup to perform detector scanning and to renew the collimated $^{137}$Cs source and, if needed, minor upgrades of the scanning table hardware. The AGATA electronics are needed to remove the ambiguity coming from different electronics when working with PSA. CSNSM will also organize an international workshop during the end of the second year of OASIS, and funds are asked for this. The estimated cost for a 3 day workshop with 20 participants is 1000 euros. We would like to invite participants from the Gretina collaboration in the USA with an estimated cost of 1300 Euro/person. This gives an estimation of about 5000 euros for the workshop.
As all results from OASIS are to be published with open access the CSNSM
is also asking for money to pay for this.

Finally the CSNSM asks for some money to be able to make a small con-
tribution to the local cloud computing infrastructure that will be solicited
by the OASIS project.

* GANIL demand justification GANIL is the present host-laboratory of AGATA and therefore an indispensable partner for OASIS. Having a qualified post-doc on site will allow rapid reaction, e.g., if complementary source data is needed. Physical access to AGATA will also help the post-doc in the understanding. Missions are required for the travel within the consortium for the post-doc and the permanent personnel.

* SPhN demand justification The tasks to be addressed by SPhN in OASIS is man hour demanding and hence the financing of a post-doc is asked for. The post-doc will work with the SPhN scientists on the PSA and simulation. He will be in close contact with the AGATA detector lab and therefore gain experience in the full readout chain from the crystals to the disks via the front-end electronics and digital electronics. Missions are required for the travel within the consortium for the post-doc and the two permanent physicists. Funds needed to upgrade and maintenance of the AGATA detector lab is also asked for.

* IPHC demand justification As one of the laboratories that can perform the complete scanning of a crystal IPHC are investigating the possibilities of performing scanning with a $^{152}$Eu source to be able to study the impact of the charge carrier cloud size on the pulse shape generation. IPHC therefore request money to acquire such a source. This will also require an upgrade of the collimator used at the IPHC scanning table and if needed some minor refurbish of the table, which is included in the request. Missions are required for the travel within the consortium for the IPHC personnel.

7.13.3 Impact and benefits of the project

The OASIS project has as main goal to improve the performance of AGATA. This will allow increased scientific production not only from future experiments but also passed experiments. In the perspective of the future use of AGATA at large scale nuclear physics installations in Europe, it is important that AGATA performs at the highest level possible, as anything else would be an unacceptable waste of resources.

The investigations performed within the OASIS project will move forward our knowledge about HPGe detectors as it has become clear that in order for PSA to perform according to our expectations a very detailed understanding of the detectors is needed. This knowledge will be used to improve the performance of AGATA. We will furthermore publish all results with open access. As the goal is to provide solution to the γ-ray tracking community world wide all computer codes will be licensed using appropriate licences (CeCILL) to allow the world wide use of the computer codes.

An interesting application of detailed knowledge about segmented HPGe detec-
tors is that of the detection of neutrino less double beta decay. Here HPGe detectors
are made by enriched ($^{76}$Ge) material and used as both source and detector. Pulse-
shape analysis is used to discriminate against background events.

If the improvements from OASIS for PSA and γ-ray tracking are substantial there
exists applications outside γ-ray spectroscopy for nuclear structure. Environmen-
tal monitoring in the case of very complex radioactive contamination where γ-ray tracking would allow both identification of the nuclei as well mapping of its spatial distribution. Also safe guards application where segmented germanium detectors combined with PSA could allow collimator less tomography of spent nuclear fuel to assure its integrity.
Chapter 8

List of Publications

* *Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus* <sup>88</sup>Ru B. Cederwall, X. Liu, Ö. Aktas, A. Ertoprak, W. Zhang, C. Qi, E. Clément, G. de France, D. Ralet, A. Gadea, A. Goasduff, G. Jaworski, I. Kuti, B. M. Nyakó, J. Nyberg, M. Palacz, R. Wadsworth, J. J. Valiente-Dobón, Al- H. Azri, A. Ataç Nyberg, T. Bäck, G. de Angelis, M. Doncel, J. Dudouet, A. Gottardo, M. Jurado, **J. Ljungvall**, D. Mengoni, D. R. Napoli, C. M. Petrache, D. Sohler, J. Timár, D. Barrientos, P. Bednarczyk, G. Benzoni, B. Birkenbach, A. J. Boston, H. C. Boston, I. Burrows, L. Charles, M. Ciemala, F. C. L. Crespi, D. M. Cullen, P Désesquelles, C. Domingo-Pardo, J. Eberth, N. Erduran, S. Ertürk, V. González, J. Goupil, H. Hess, T. Huyuk, A. Jungclaus, W. Korten, A. Lemasson, S. Leoni, A. Maj, R. Menegazzo, B. Million, R. M. Perez-Vidal, Zs. Podolyak, A. Pullia, F. Recchia, P. Reiter, F. Saillant, M. D. Salsac, E. Sanchis, J. Simpson, O. Stezowski, Ch. Theisen, and M. Zielińska, Phys.Rev.Lett. 124, 062501 (2020)

* Performance of the Advanced GAmma Tracking Array at GANIL J. Ljungvall, R.M. Pérez-Vidal, A. Lopez-Martens, C. Michelagnoli, E. Clément, J. Dudouet, A. Gadea, H. Hess, A. Korichi, M. Labiche, N. Lalović, H.J. Li, F. Recchia, Nuclear Instruments and Methods in Physics Research, Section A, volume 955, January 2020

* Lifetime measurements in $^{52,54}$Ti to study shell evolution toward N=32 A .Goldkuhle, C. Fransen, A. Blazhev, M. Beckers, B. Birkenbach, T. Braunroth, E. Clément, A. Dewald, J. Dudouet, J. Eberth, H. Hess, B. Jacquot, J.Jolie, Y.-H. Kim, A. Lemasson, S. M. Lenzi, H. J. Li, J. Litzinger, C. Michelagnoli, C. Müller-Gatermann, B. S. Nara Singh, R. M. Pérez-Vidal, D. Ralet, P. Reiter, A. Vogt, N. Warr, K. O. Zell, A. Ataç, D Barrientos, C Barthe-Dejean, G. Benzoni, A. J. Boston, H. C. Boston, P. Bourgault, I. Burrows, J. Cacitti, B. Cederwall, M. Ciemala, D. M. Cullen, G. De France, C. Domingo-Pardo, J.-L. Foucher, G. Fremont, A. Gadea, P. Gangnant, V. González, J. Goupil, C. Henrich, C. Houarner, M. Jean, D. S. Judson, A. Korichi, W Korten, M. Labiche, A. Lefevre, L. Legeard, F. Legruel, S. Leoni, **J. Ljungvall**, A. Maj, C. Maugeais, L. Ménager, N. Ménard, R. Menegazzo, D. Mengoni, B. Million, H. Munoz, D. R. Napoli, A. Navin, J. Nyberg, M. Ozille, Zs. Podolyak, A. Pullia, B. Raine, F. Recchia, J. Ropert, F. Saillant, M. D. Salsac, E. Sanchis, C. Schmitt, J. Simpson, C. Spitaels, O Stezowski, Ch. Theisen, M. Toulemonde, M. Tripon, J.-J. Valiente Dobón, G. Voltolini, and M. Zielińska, Phys. Rev. C 100, 054317
* *B(E2) anomalies in the yrast band of* $^{170}$Os A. Goasduff, **J. Ljungvall**, T. R. Rodríguez, F. L. Bello Garrote, A. Etile, G. Georgiev, F. Giacoppo, L. Grente, M. Klintefjord, A. Kuşoğlu, I. Matea, S. Roccia, M.-D. Salsac, and C. Sotty, Phys. Rev. C 100, 034302 (2019)

* Evidence of octupole-phonons at high spin in 207Pb D. Ralet, E. Clément, G. Georgiev, A.E. Stuchbery, M. Rejmund, P. Van Isacker, G. de France, A. Lemasson, **J. Ljungvall**, C. Michelagnoli, A. Navin, D.L. Balabanski, L. Atanasova, A. Blazhev, G. Bocchi, R. Carroll, J. Dudouet, E. Dupont, B. Fornal, S. Franchoo, C. Fransen, C. Müller-Gatermann, A. Goasduff, A. Gadea, P.R. John, D. Kocheva, T. Konstantinopoulos, A. Korichi, A. Kuşoğlu, S.M. Lenzi, S. Leoni, R. Lozeva, A. Maj, R. Perez, N. Pietralla, C. Shand, O. Stezowski, D. Wilmsen, D. Yordanov, D. Barrientos, P. Bednarczyk, B. Birkenbach, A.J. Boston, H.C. Boston, I. Burrows, B. Cederwall, M. Ciemala, J. Collado, F. Crespi, D. Cullen, H.J. Eberth, J. Goupil, L. Harkness, H. Hess, A. Jungclaus, W. Korten, M. Labiche, R. Menegazzo, D. Mengoni, B. Million, J. Nyberg, Zs. Podolyák, A. Pullia, B. Quintana Arnés, F. Recchia, P. Reiter, F. Saillant, M.D. Salsac, E. Sanchis, C. Theisen, J.J. Valiente Dobon, O. Wieland, Phys. Lett. B 797, (2019)

* Experimental determination of reference pulses for highly segmented HPGe detectors and application to Pulse Shape Analysis used in γ-ray tracking arrays H. J. Li, **J. Ljungvall**, C. Michelagnoli, E. Clément, J. Dudouet, P. Désesquelles, A. Lopez-Martens, G. de France, Eur. Phys. J. A (2018) 54: 198.

* Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the $^{78}$Ni Region: A Hint from Lifetime Measurements C. Delafosse, D. Verney, P. Marevic, A. Gottardo, C. Michelagnoli, A. Lemasson, A. Goasduff, **J. Ljungvall**, E. Clement, A. Korichi, G. De Angelis, C. Andreoiu, M. Babo, A. Boso, F. Didierjean, J. Dudouet, S. Franchoo, A. Gadea, G. Georgiev, F. Ibrahim, B. Jacquot, T. Konstantinopoulos, S.M. Lenzi, G. Maquart, I. Matea, D. Mengoni, D.R. Napoli, T. Niksic, L. Olivier, R.M. Perez-Vidal, C. Portail, F. Recchia, N. Redon, M. Siciliano, I. Stefan, O. Stezowski, D. Vretenar, M. Zielinska, D. Barrientos, G. Benzoni, B. Birkenbach, A.J. Boston, H.C. Boston, B. Cederwall, L. Charles, M. Ciemala, J. Collado, D.M. Cullen, P. Desesquelles, G. de France, C. DomingoPardo, J. Eberth, V. Gonzalez, L.J. Harkness-Brennan, H. Hess, D.S. Judson, A. Jungclaus, W. Korten, A. Lefevre, F. Legruel, R. Menegazzo, B. Million, J. Nyberg, B. Quintana, D. Ralet, P. Reiter, F. Saillant, E. Sanchis, Ch. Theisen, J.J. Valiente Dobon, Phys.Rev.Lett. 121, 192502 (2018)

* Lifetimes of excited states in triaxially deformed $^{107}$Tc and $^{109,111,113}$Rh T.W. Hagen, A. Gorgen, W. Korten, L. Grente, M.-D. Salsac, F. Farget, T. Braunroth, B. Bruyneel, I. Celikovic, E. Clement, G. de France, O.Delaune, A.Dewald, A.Dijon, M.Hackstein, B.Jacquot, J.Litzinger, **J. Ljungvall**, C. Louchart, C. Michelagnoli, D.R. Napoli, F. Recchia, W. Rother, E. Sahin, S. Siem, B. Sulignano, Ch. Theisen, J.J. Valiente-Dobon, Eur. Phys. J. A (2018) 54: 50

* Evidence for Coexisting Shapes through Lifetime Measurements in $^{98}$Zr P. Singh, W. Korten, T.W. Hagen, A. Gorgen, L. Grente, M.-D. Salsac, F. Farget, E. Clement, G. de France, T. Braunroth, B. Bruyneel, I. Celikovic, O. Delaune, A. Dewald, A. Dijon, J.-P. Delaroche, M. Girod, M. Hackstein, B. Jacquot, J. Libert, J. Litzinger, **J.Ljungvall**, C. Louchart, A. Gottardo, C. Michelagnoli, C. Müller-Gatermann, D.R. Napoli, T. Otsuka, N. Pillet, F. Recchia, W. Rother, E. Sahin, S. Siem, B.
Sulignano, T. Togashi, Y. Tsunoda, Ch. Theisen, J. J. Valiente-Dobon, Phys. Rev. Lett. 121, 192501 (2018)

* *Prompt-delayed γ-ray spectroscopy with AGATA, EXOGAM and VAMOS++* Y. H. Kim, A. Lemasson, M. Rejmund, A. Navin, S. Biswas, C. Michelagnoli, I. Stefan, R. Banik, P. Bednarczyk, S. Bhattacharya, S. Bhattacharyya, E. Clément, H., L. Crawford, G. De France, P. Fallon, J. Goupil, B. Jacquot, H. J. Li, **J. Ljungvall**, A. O. Macchiavelli, A. Maj, L. Ménager, V. Morel, R. Palit, R. M. Pérez-Vidal, J. Ropert, C. Schmitt, Eur. Phys. J. **A** (2017) 53: 162

* *Conceptual design of the AGATA 1π array at GANIL* E. Clément, C. Michelagnoli, G. de France, H.J. Li, A. Lemasson, C. Barthe Dejean, M. Beuzard, P. Bougault, J. Cacitti, J.-L. Foucher, G. Fremont, P. Gangnant, J. Goupil, C. Houarner, M. Jean, A. Lefevre, L. Legeard, F. Legruel, C. Maugeais, L. Ménager, N. Ménard, H. Munoz, M. Ozille, B. Raine, J.A. Ropert, F. Saillant, C. Spitaels, M. Tripon, Ph. Valler, G. Voltolini, W. Korten, M.-D. Salsac, Ch. Theisen, M. Zielińska, T. Joannem, M. Karolak, M. Kebbiri, A. Lotode, R. Touzery, Ch. Walter, A. Korichi, **J. Ljungvall**, A. Lopez-Martens, D. Ralet, N. Dosme, X. Grave, N. Karkour, X. Lafay, E. Legay, I. Kojouharov, C. Domingo-Pardo, A. Gadea, R.M. Pérez-Vidal, J.V. Civera, B. Birkenbach, J. Eberth, H. Hess, L. Lewandowski, P. Reiter, A. Nannini, G. De Angelis, G. Jaworski, P. John, D.R. Napoli, J.J. Valiente-Dobón, D. Barrientos, D. Bortolato, G. Benzoni, A. Bracco, S. Brambilla, F. Camera, F.C.L. Crespi, S. Leoni, B. Million, A. Pullia, O. Wiel, D. Bazzacco, S.M. Lenzi, S. Lunardi, R. Menegazzo, D. Mengoni, F. Recchia, M. Bellato, R. Isocrate, F.J. Egea Canet, F. Didierjean, G. Duchêne, R. Baumann, M. Brucker, E. Dangelser, M. Filliger, H. Friedmann, G. Gaudiot, J.-N. Grapton, H. Kocher, C. Mathieu, M.-H. Sigward, D. Thomas, S. Veeramootoo, J. Dudouet, O. Stézowski, C. Aufranc, Y. Aubert, M. Labiche, J. Simpson, I. Burrows, P.J. Coleman-Smith, A. Grant, I.H. Lazarus, P.S. Morrall, V.F.E. Pucknell, A. Boston, D.S. Judson, N. Lalović, J. Nyberg, J. Collado, V. González, I. Kuti, B.M. Nyakó, A. Maj, M. Rudigier, Nuclear Instruments and Methods in Physics Research, Section A, volume 855, February 2017, page 1-12

* 96 36 Kr$_{60}$-*Low-Z Boundary of the Island of Deformation at N=60* J. Dudouet, A. Lemasson, G. Duchêne, M. Rejmund, E. Clément, C. Michelagnoli, F. Didierjean, A. Korichi, G. Maquart, O. Stezowski, C. Lizarazo, R. M. Pérez-Vidal, C. Andreoiu, G. de Angelis, A. Astier, C. Delafosse, I. Deloncle, Z. Dombradi, G. de France, A. Gadea, A. Gottardo, B. Jacquot, P. Jones, T. Konstantinopoulos, I. Kuti, F. Le Blanc, S. M. Lenzi, G. Li, R. Lozeva, B. Million, D. R. Napoli, A. Navin, C. M. Petrache, N. Pietralla, D. Ralet, M. Ramdhane, N. Redon, C. Schmitt, D. Sohler, D. Verney, D. Barrientos, B. Birkenbach, I. Burrows, L. Charles, J. Collado, D. M. Cullen, P. Désesquelles, C. Domingo Pardo, V. González, L. Harkness-Brennan, H. Hess, D. S. Judson, M. Karolak, W. Korten, M. Labiche, **J. Ljungvall**, R. Menegazzo, D. Mengoni, A. Pullia15, F. Recchia, P. Reiter, M. D. Salsac, E. Sanchis, Ch. Theisen, J. J. Valiente-Dobón, and M. Zielińska, Phys. Rev. Lett. 118, 162501 (2017)

* Evolution of nuclear shapes in odd-mass yttrium and niobium isotopes from lifetime measurements following fission reactions T. W. Hagen, A. Görgen, W. Korsten, L. Grente, M.-D. Salsac, F. Farget, I. Ragnarsson, T. Braunroth, B. Bruyneel, I. Celikovic, E. Clément, G. de France, O. Delaune, A. Dewald, A. Dijon, M. Hackstein, B. Jacquot, J. Litzinger, **J. Ljungvall**, C. Louchart, C. Michelagnoli, D. R.
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*In-beam γ-ray spectroscopy of the neutron-rich platinum isotope* $^{200}$Pt toward the N=126 shell gap P. R. John, J. J. Valiente-Dobón, D. Mengoni, V. Modamio, S. Lunardi, D. Bazzacco, A. Gadea, C. Wheldon, T. R. Rodríguez, T. Alexander, G. de Angelis, N. Ashwood, M. Barr, G. Benzoni, B. Birkenbach, P. G. Bizzeti, A. M. Bizzeti-Sona, S. Bottoni, M. Bowry, A. Bracco, F. Browne, M. Bunce, F. Camera, L. Corradi, F. C. L. Crespi, B. Melon, E. Farnea, E. Fioretto, A. Gottardo, L. Grente, H. Hess, Tz. Kokalova, W. Korten, A. Kuşoğlu, S. Lenzi, S. Leoni, **J. Ljungvall**, R. Menegazzo, C. Michelagnoli, T. Mijatović, G. Montagnoli, D. Montanari, D. R. Napoli, Zs. Podolyák, G. Pollarolo, F. Recchia, P. Reiter, O. J. Roberts, E. Şahin, M.-D. Salsac, F. Scarlassara, M. Sferrazza, P.-A. Söderström, A. M. Stefanini, S. Szilner, C. A. Ur, A. Vogt, and J. Walshe, Phys. Rev. C 95, 064321 (2017)

*Anomalies in the Charge Yields of Fission Fragments from the* $^{238}$U(n, f) Reaction J. N. Wilson, M. Lebois, L. Qi, P. Amador-Celdran, D. Bleuel, J. A. Briz, R. Carroll, W. Catford, H. De Witte, D. T. Doherty, R. Eloirdi, G. Georgiev, A. Gottardo, A. Goasduff, K. Hadyńska-Klęk, K. Hauschild, H. Hess, V. Ingeberg, T. Konstantinopoulos, **J. Ljungvall**, A. Lopez-Martens, G. Lorusso, R. Lozeva, R. Lutter, P. Marini, I. Matea, T. Materna, L. Mathieu, A. Oberstedt, S. Oberstedt, S. Panebianco, Zs. Podolyák, A. Porta, P. H. Regan, P. Reiter, K. Rezynkina, S. J. Rose, E. Sahin, M. Seidlitz, O. Serot, R. Shearman, B. Siebeck, S. Siem, A. G. Smith, G. M. Tveten, D. Verney, N. Warr, F. Zeiser, and M. Zielińska, Phys. Rev. Lett. 118, 222501 (2017)

*Measurement of lifetimes in* $^{62,64}$Fe, $^{61,63}$Co, and $^{59}$Mn M. Klintefjord, **J. Ljungvall**, A. Görgen, S. M. Lenzi, F. L. Bello Garrote, A. Blazhev, E. Clément, G. de France, J.-P. Delaroche, P. Désesquelles, A. Dewald, D. T. Doherty, C. Fransen, A. Gengelbach, G. Georgiev, M. Girod, A. Goasduff, A. Gottardo, K. Hadyńska-Klęk, B. Jacquot, T. Konstantinopoulos, A. Korichi, A. Lemasson, J. Libert, A. Lopez-Martens, C. Michelagnoli, A. Navin, J. Nyberg, R. M. Pérez-Vidal, S. Roccia, E. Sahin, I. Stefan, A. E. Stuchbery, M. Zielińska, D. Barrientos, B. Birkenbach, A. Boston, L. Charles, M. Ciemala, J. Dudouet, J. Eberth, A. Gadea, V. González, L. Harkness-Brennan, H. Hess, A. Jungclaus, W. Korten, R. Menegazzo, D. Mengoni, B. Million, A. Pullia, D. Ralet, F. Recchia, P. Reiter, M. D. Salsac, E. Sanchis, O. Stezowski, Ch. Theisen, and J. J. Valiente Dobon, Phys. Rev. C 95, 024312 (2017)

*Lifetime measurements in* $^{100}$Ru T. Konstantinopoulos, P. Petkov, A. Goasduff, T. Arici, A. Astier, L. Atanasova, M. Axiotis, D. Bonatsos, P. Detistov, A. Dewald, M. J. Eller, V. Foteinou, A. Gargano, G. Georgiev, K. Gladnishki, A. Gottardo, S. Harissopulos, H. Hess, S. Kaim, D. Kocheva, A. Kusoglu, A. Lagoyannis, **J. Ljungvall**, R. Lutter, I. Matea, B. Melon, T. J. Mertzimekis, A. Nannini, C. M. Petrache, A. Petrovici, G. Provatas, P. Reiter, M. Rocchini, S. Roccia, M. Seidlitz, B. Siebeck, D. Suzuki, N. Warr, H. De Witte, T. Zerrouki, Phys. Rev. C 95, 014309 (2017)

*Low-energy Coulomb excitation of* $^{96,98}$Sr beams E. Clément, M. Zielińska, S. Péru, H. Goutte, S. Hilaire, A. Görgen, W. Korten, D. T. Doherty, B. Bastin, C. Bauer, A. Blazhev, N. Bree, B. Bruyneel, P. A. Butler, J. Butterworth, J. Cederkäll, P. Delahaye, A. Dijon, A. Ekström, C. Fitzpatrick, C. Fransen, G. Georgiev, R.
Gernhäuser, H. Hess, J. Iwanicki, D. G. Jenkins, A. C. Larsen, **J. Ljungvall**, R. Lutter, P. Marley, K. Moschner, P. J. Napiorkowski, J. Pakarinen, A. Petts, P. Reiter, T. Renstrøm, M. Seidlitz, B. Siebeck, S. Siem, C. Sotty, J. Srebrny, I. Stefanescu, G. M. Tveten, J. Van de Walle, M. Vermeulen, D. Voulot, N. Warr, F. Wenander, A. Wiens, H. De Witte, K., Phys. Rev C 94, 054326 (2016)

* Superdeformed and Triaxial States in ⁴²Ca K. Hadyńska-Klęk, P. J. Napiorkowski, M. Zielińska, J. Srebrny, A. Maj, F. Azaiez, J. J. Valiente Dobón, M. Kicińska-Habior, F. Nowacki, H. Naïdja, B. Bounthong, T. R. Rodríguez, G. de Angelis, T. Abraham, G. Anil Kumar, D. Bazzacco, M. Bellato, D. Bortolato, P. Bednarczyk, G. Benzoni, L. Berti, B. Birkenbach, B. Bruyneel, S. Brambilla, F. Camera, J. Chavas, B. Cederwall, L. Charles, M. Ciemala, P. Cocconi, P. Coleman-Smith, A. Colombo, A. Corsi, F. C. L. Crespi, D. M. Cullen, A. Czermak, P. Désesquelles, D. T. Doherty, B. Dulny, J. Eberth, E. Farnea, B. Fornal, S. Franchoo, A. Gadea, A. Giaz, A. Gottardo, X. Grave, J. Grebosz, A. Görgen, M. Gulmini, T. Habermann, H. Hess, R. Isocrate,, J. Iwanicki, G. Jaworski, D. S. Judson, A. Jungclaus, N. Karkour, M. Kmiecik, D. Karpiński, M. Kisieliński, N. Kondratyev, A. Korichi, M. Komorowska,, M. Kowalczyk, W. Korten, M. Krzysiek, G. Lehaut, S. Leoni, **J. Ljungvall**, A. Lopez-Martens, S. Lunardi, G. Maron, K. Mazurek, R. Menegazzo, D. Mengoni, E. Merchán,, W. Meczyński, C. Michelagnoli, J. Mierzejewski, B. Million, S. Myalski, D. R. Napoli, R. Nicolini, M. Niikura, A. Obertelli, S. F. Özmen, M. Palacz, L. Próchniak, A. Pullia,, B. Quintana, G. Rampazzo, F. Recchia, N. Redon, P. Reiter, D. Rosso, K. Rusek, E. Sahin, M.-D. Salsac, P.-A. Söderström, I. Stefan, O. Stézowski, J. Styczeń, Ch. Theisen, N. Toniolo, C. A. Ur, V. Vandone,, R. Wadsworth, B. Wasilewska, A. Wiens, J. L. Wood, K. Wrzosek-Lipska, and M. Ziebliński, Phys. Rev. Lett. 117, 062501 (2016)

* Pygmy dipole resonance in ¹⁴⁰Ce via inelastic scattering of ¹⁷O M. Krzysiek, M. Kmiecik, A. Maj, P. Bednarczyk, A. Bracco, F. C. L. Crespi, E. G. Lanza, E. Litvinova, N. Paar, R. Avigo, D. Bazzacco, G. Benzoni, B. Birkenbach, N. Blasi, S. Bottoni, S. Brambilla, F. Camera, S. Ceruti, M. Ciemala, G. de Angelis, P. Désesquelles, J. Eberth, E. Farnea, A. Gadea, A. Giaz, A. Görgen, A. Gottardo, J. Grebosz, H. Hess, R. Isocarte, A. Jungclaus, S. Leoni, **J. Ljungvall**, S. Lunardi, K. Mazurek, R. Menegazzo, D. Mengoni, C. Michelagnoli, B. Milion, A. I. Morales, D. R. Napoli, R. Nicolini, L. Pellegri, A. Pullia, B. Quintana, F. Recchia, P. Reiter, D. Rosso, M. D. Salsac, B. Siebeck, S. Siem, P.-A. Söderström, C. Ur, J. J. Valiente-Dobon, O. Wiel, K. Wrzosek-Lipska, M. Ziebliński, Phys. Rev. C 93, 044330 (2016)

* Spectroscopic Quadrupole Moments in ⁹⁶,⁹⁸Sr: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60 E. Clément, M. Zielińska, A. Görgen, W. Korten, S. Péru, J. Libert, H. Goutte, S. Hilaire, B. Bastin, C. Bauer, A. Blazhev, N. Bree, B. Bruyneel, P. A. Butler, J. Butterworth, P. Delahaye, A. Dijon, D. T. Doherty, A. Ekström, C. Fitzpatrick, C. Fransen, G. Georgiev, R. Gernhäuser, H. Hess, J. Iwanicki, D. G. Jenkins, A. C. Larsen, **J. Ljungvall**, R. Lutter, P. Marley, K. Moschner, P. J. Napiorkowski, J. Pakarinen, A. Petts, P. Reiter, T. Renström, M. Seidlitz, B. Siebeck, S. Siem, C. Sotty, J. Srebrny, I. Stefanescu, G. M. Tveten,, J. Van de Walle, M. Vermeulen, D. Voulot, N. Warr, F. Wenander, A. Wiens, H. De Witte, and K. Wrzosek-Lipska, Phys. Rev. Lett. 116, 022701 (2016)

* Performance of the AGATA $\gamma$-ray spectrometer in the PreSPEC set-up at GSI N. Lalović, C. Louchart, C. Michelagnoli, R.M. Perez-Vidal, D. Ralet, J. Gerl, D.
Rudolph, T. Arici, D. Bazzacco, E. Clément, A. Gadea, I. Kojouharov, A. Korichi, M. Labiche, **J. Ljungvall**, A. Lopez-Martens, J. Nyberg, N. Pietralla, S. Pietri, O. Stezowski, For PreSPEC and AGATA Collaborations, Nuclear Instruments and Methods in Physics Research, Section A, volume 806, January 2016, page 258-266

* Probing collectivity in Zn isotopes with one particle or hole outside the N=40 sub-shell closure I. Čeliković, A. Dijon, E. Clément, G. de France, P. Van Isacker, **J. Ljungvall**, A. Dewald, C. Fransen, G. Georgiev, A. Görgen, A. Gottardo, M. Hackstein, T. W. Hagen, C. Louchart, P. Napiorkowski, A. Obertelli, F. Recchia, W. Rother, S. Siem, B. Sulignano, P. Ujić, J. J. Valiente-Dobón, and M. Zielińska, Phys. Rev. C 91, 044311 (2015)

* Magnetism of an Excited Self-Conjugate Nucleus: Precise Measurement of the g Factor of the 2<sup>1</sup>State in <sup>24</sup>Mg A. Kusoglu, A. E. Stuchbery, G. Georgiev, B. A. Brown, A. Goasduff, L. Atanasova, D. L. Balabanski, M. Bostan, M. Danchev, P. Detistov, K. A. Gladnishki, **J. Ljungvall**, I. Matea, D. Radeck, C. Sotty, I. Stefan, D. Verney, D. T. Yordanov, Phys. Rev. Lett. 114. 062501 (2015)

* Shell evolution beyond N=40: <sup>69,71,73</sup>Cu E. Sahin, M. Doncel, K. Sieja, G. de Angelis, A. Gadea, B. Quintana, A. Görgen, V. Modamio, D. Mengoni, J. J. Valiente-Dobón, P. R. John, M. Albers, D. Bazzacco, G. Benzoni, B. Birkenbach, B. Cedlerwall, E. Clément, D. Curien, L. Corradi, P. Désesquelles, A. Dewald, F. Didierjean, G. Duchêne, J. Eberth, M. N. Erduran, E. Farnea, E. Fioretto, G. de France, C. Fransen, R. Gernhäuser, A. Gottardo, M. Hackstein, T. Hagen, A. Hernández-Prieto, H. Hess, T. Hüyük, A. Jungclaus, S. Klupp, W. Korten, A. Kusoglu, S. M. Lenzi, **J. Ljungvall**, C. Louchart, S. Lunardi, R. Menegazzo, C. Michelagnoli, T. Mijatović, B. Million, P. Molini, G. Montagnoli, D. Montanari, O. Möller, D. R. Napoli, A. Obertelli, R. Orlandi, G. Pollarolo, A. Pullia, F. Recchia, P. Reiter, D. Rosso, W. Rother, M.-D. Salsac, F. Scarlassara, M. Schlarb, S. Siem, Pushpendra P. Singh, P.-A. Söderström, A. M. Stefanini, O. Stézowski, B. Sulignano, S. Szilner, Ch. Theisen, C. A. Ur, and M. Yalcinkaya, Phys. Rev. C 91, 034302 (2015)

* Shape evolution in the neutron-rich osmium isotopes: Prompt γ-ray spectroscopy of <sup>196</sup>Os P.R.John, V.Modamio, J.J.Valiente-Dobon, D.Mengoni, S.Lunardi, T.R.Rodriguez, D.Bazzacco, A.Gadea, C.Weldon, T.Alexander, G.de Angelis, N.Ashwood, M.Barr, G.Benzoni, B.Birkenbach, P.G.Bizzeti, A.M.Bizzeti-Sona, S.Bottoni, M.Bowry, A.Bracco, F.Browne, M.Bunce, F.Camera, B.Cederwall, L.Corradi, F.C.L.Crespi, P.Desesquelles, J.Eberth, E.Farnea, E.Fioretto, A.Gorgen, A.Gottardo, J.Grebosz, L.Grente, H.Hess, A.Jungclaus, Tz.Kokalova, A.Korichi, W.Korten, A.Kusoglu, SLenzi, S.Leoni, **J.Ljungvall**, G.Maron, W.Meczynski, B.Melon, R.Menegazzo, C.Michelagnoli, T.Mijatovic, B.Million, P.Molini, G.Montagnoli, D.Montanari, D.R.Napoli, P.Nolan, C.Oziol, Zs.Podolyak, G.Pollarolo, A.Pullia, B.Quintana, F.Recchia, P.Reiter, O.J.Roberts, D.Rosso, E.Sahin, M.-D.Salsac, F.Scarlassara, M.Sferrazza, J.Simpson, P.-A.Soderstrom, A.M.Stefanini, O.Stezowski, S.Szilner, Ch.Theisen, C.A.Ur, J.Walshe, Phys. Rev. C 90, 021301 (2014)

* Musett: A segmented Si array for Recoil-Decay-Tagging studies at VAMOS Ch. Theisen, F. Jeanneau, B. Sulignano, F. Druillole, **J. Ljungvall**, B. Paul, E. Virique, P. Baron, H. Bervas, E. Clément, E. Delagnes, A. Dijon, E. Dossat, A. Drouart, F. Farget, Ch. Flouzat, G. De France, A. Görgen, Ch. Houarner, B. Jacquot, W.
Korten, G. Lebertre, B. Lecornu, L. Legeard, A. Lermitage, S. Lhenoret, C. Marry, C. Maugeais, L. Menager, O. Meunier, A. Navin, F. Nizery, A. Obertelli, E. Rauly, B. Raine, M. Rejmund, J. Ropert, F. Saillant, H. Savajols, Ch. Schmitt, M. Tripon, E. Wanlin, G. Wittwer, Nuclear Instruments and Methods in Physics Research, Section A, volume 747, May 21, 2014, page 69-80

* *Identification and rejection of scattered neutrons in AGATA* M. Şenyiğit, A. Ataç, S. Akkoyun, A. Kaşkaş, D. Bazzacco, J. Nyberg, F. Recchia S. Brambilla, F. Camera, F.C.L. Crespi, E. Farnea, A. Giaz, A. Gottardo, R. Kempley, **J. Ljungvall**, D. Mengoni, C. Michelagnoli, B. Million, M. Palacz, L. Pellegri, S. Riboldi, E. Sahin, P.A. Söderström, J.J. Valiente Dobon, Nuclear Instruments and Methods in Physics Research, Section A, volume 735, January 21, 2014, page 267-276

* *Direct determination of the hit locations from experimental HPGe pulses* P. Désesquelles, A.J. Boston, H.C. Boston, J.R. Cresswell, M.R. Dimmock, I.H. Lazarus, **J. Ljungvall**, L. Nelson, D.-T. Nga, P.J. Nolan, S.V. Rigby, J. Simpson, N.-T. Van-Oanh, Nuclear Instruments and Methods in Physics Research, Section A, volume 729, 21 November, 2013, page 198-206

* *Collectivity of light Ge and As isotopes* A.Corsi, J.-P.Delaroche, A. Obertelli, T.Baugher, D.Bazin, S.Boissinot, F.Flavigny, A.Gade, M.Girod, T.Glasmacher, G.F.Grinyer, W.Korten, J.Libert, **J.Ljungvall**, S.McDaniel, A.Ratkiewicz, A SIGNORacci, R.Stroberg, B.Sulignano, D.Weisshaar, Phys. Rev. C 88, 044311 (2013)

* *Collective nature of low-lying excitations in* $^{70,72,74}$Zn from lifetime measurements using the AGATA spectrometer demonstrator* C.Louchart, A. Obertelli, A. Gorgen, W. Korten, D. Bazzacco, B. Birkenbach, B. Bruyneel, E. Clement, P.J. Coleman-Smith, L. Corradi, D. Curien, G. de Angelis, G. de France, J.-P. Delaroche, A. Dewald, F. Didierjean, M. Doncel, G. Duchene, J. Eberth, M. N. Erduran, E. Farnea, C. Finck, E. Fioretto, C. Fransen, A. Gadea, M. Girod, A. Gottardo, J. Grebosz, T. Habermann, M. Hackstein, T. Huyuk, J. Jolie, D. Judson, A. Jungclaus, N. Karkour, S. Klupp, R. Krucken, A. Kusoglu, S. M. Lenzi, J. Libert, **J.Ljungvall**, S. Lunardi, G. Maron, R. Menegazzo, D. Mengoni, C. Michelagnoli, B. Million, P. Molini, O. Moller, G. Montagnoli, D. Montanari, D. R. Napoli, R. Orlandi, G. Pollarolo, A. Prieto, A. Pullia, B. Quintana, F. Recchia, P. Reiter, D. Rosso, W. Rother, E. Sahin, M.-D. Salsac, F. Scarlassara, M. Schlarb, S. Siem, P. P. Singh, P.-A. Soderstrom, A. M. Stefanini, O. Stezowski, B. Sulignano, S. Szilner, Ch. Theisen, C. A. Ur, J.J. Valiente-Dobon, M. Zielinska, Phys. Rev. C 87, 054302 (2013)

* *Investigation of high-* *K states in* $^{252}$No B. Sulignano, Ch. Theisen, J.-P. Delaroche, M. Girod, **J. Ljungvall**, D. Ackermann, S. Antalic, O. Dorvaux, A. Drouart, B. Gall, A. Görgen, P. T. Greenlees, K. Hauschild, R.-D. Herzberg, F. P. Heßberger, U. Jakobsson, P. Jones, R. Julin, S. Juutinen, S. Ketelhut, W. Korten, M. Leino, A. Lopez-Martens, M. Nyman, A. Obertelli, J. Pakarinen, P. Papadakis, E. Parr, P. Peura, J. Piot, P. Rahkila, D. Rostron, P. Ruotsalainen, J. Sarén, C. Scholey, J. Sorri, J. Uusitalo, M. Venhart, and M. Zielińska, Phys. Rev. C 86, 044318 (2012)

* *Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of the Z=104 Nucleus* $^{256}$Rf, P. T. Greenlees, J. Rubert, J. Piot, B. J. P. Gall, L. L. Andersson, M. Asai, Z. Asfari, D. M. Cox, F. Dechery, O. Dorvaux, T. Grahn, K. Hauschild, G. Henning, A. Herzan, R.-D. Herzberg, F. P. Hessberger, U. Jakobsson, P. Jones, R. Julin, S. Juutinen, S. Ketelhut, T.-L. Khoo, M. Leino, **J. Ljungvall**, A. Lopez-Martens, R. Lozeva, P. Nieminen, J. Pakarinen, P. Papadakis, E.
Parr, P. Peura, P. Rahkila, S. Rinta-Antila, P. Ruotsalainen, M. Sandzelius, J. Saren, C. Scholey, D. Seweryniak, J. Sorri, B. Sulignano, Ch. Theisen, J. Uusitalo, M. Venhart, Phys. Rev. Lett. 109, 012501 (2012)

• *N=50 core excited states studied in the* $^{96}_{46}\text{Pd}_{50}$ *nucleus*, M. Palacz, J. Nyberg, H. Grawe, K. Sieja, G. de Angelis, P. Bednarczyk, A. Blazhev, D. Curien, Z. Dombradi, O. Dorvaux, J. Ekman, J. Galkowski, M. Gorska, J. Iwanicki, G. Jaworski, J. Kownacki, **J. Ljungvall**, M. Moszynski, F. Nowacki, D. Rudolph, D. Sohler, D. Wolski, M. Zieblinski, Phys. Rev. C 86, 014318 (2012)

• *The Orsay Universal Plunger System, J. Ljungvall*, G. Georgiev, S. Cabaret, N. Karkour, D. Linget, G. Sedes, R. Chevrier, I. Matea, M. Niikura, M.-D. Salsac, B. Sulignano, Nuclear Instruments and Methods in Physics Research, Section A, volume 679, July 1, 2012, page 61-66

• *In-beam spectroscopy with intense ion beams: Evidence for a rotational structure in* $^{246}\text{Fm}$, J. Piot, B.J.-P. Gall, O. Dorvaux, P. T. Greenlees, N. Rowley, L. L. Andersson, D. M. Cox, F. Dechery, T. Grahn, K. Hauschild, G. Henning, A. Herzan, R.-D. Herzberg, F.P. Hessberger, U. Jakobsson, P. Jones, R. Julin, S. Juutinen, S. Ketelhut, T.-L. Khoo, M. Leino, **J. Ljungvall**, A. Lopez-Martens, P. Nieminen, J. Pakarinen, P. Papadakis, E. Parr, P. Peura, P. Rahkila, S. Rinta-Antila, J. Rubert, P. Ruotsalainen, M. Sandzelius, J. Saren, C. Scholey, D. Seweryniak, J. Sorri, B. Sulignano, J. Uusitalo, Phys. Rev. C 85, 041301 (2012)

• *AGATA-Advanced GAmma Tracking Array*, Nuclear Instruments and Methods in Physics Research, Section A, Volume 668, March 11, 2012, pages 26-58

• *First spectroscopy of* $^{66}\text{Se}$ and $^{65}\text{As: Investigating shape coexistence beyond the N=Z line*, A. Obertelli, T. Baugher, D. Bazin, S. Boissinot, J.-P. Delaroche, A. Dijon, F. Flavigny, A. Gade, M. Girod, T. Glasmacher, G.F. Grinyer, W. Korten, **J. Ljungvall**, S. McDaniel, A. Ratkiewicz, B. Sulignano, P. Van Isacker, D. Weisshaar, Phys. Lett. B. 701, issue 4 (2011)

• *Lifetime measurements in* $^{63}\text{Co}$ and $^{65}\text{Co}$, A.Dijon, E.Clement, G.de France, P.Van Isacker, **J.Ljungvall**, A.Gorgen, A.Obertelli, W.Korten, A.Dewald, A.Gadea, L.Gaudefroy, M.Hackstein, D.Mengoni, Th.Pissulla, F.Recchia, M.Rejmund, W.Rother, E.Sahin, C.Schmitt, A.Shrivastava, J.J.Valiente-Dobon, K.O.Zell, M.Zielińska, Phys. Rev. C 83, 064321 (2011)

• *Interaction position resolution simulations and in-beam measurements of the AGATA HPGe detectors*, P.-A. Söderström, F. Recchia, J. Nyberg, A. Al-Adili, A. Ataç, S. Aydin, D. Bazzacco, P. Bednarczyk, B. Birkenbach, D. Bortolato, A.J. Boston, H.C. Boston, B. Bruyneel, D. Bucurescu, E. Calore, S. Colosimo, F.C.L. Crespi, N. Dosme, J. Eberth, E. Farnea, F. Filmer, A. Gadea, A. Gottardo, X. Grave, J. Grebosz, R. Griffiths, M. Gulmini, T. Habermann, H. Hess, G. Jaworski, P. Jones, P. Joshi, D.S. Judson, R. Kempley, A. Khaplanov, E. Legay, D. Lersch, **J. Ljungvall**, A. Lopez-Martens, W. Meczynski, D. Mengoni, C. Michelagnoli, P. Molini, D.R. Napoli, R. Orlandi, G. Pascovici, A. Pullia, P. Reiter, E. Sahin, J.F. Smith, J. Strachan, D. Tonev, C. Unsworth, C.A. Ur, J.J. Valiente-Dobón, C. Veyssierea, A. Wiens and The AGATA Collaboration, Nuclear Instruments and Methods in Physics Research, Section A, volume 638, Issue 1, May 11, 2011, page 96-109
* *Onset of collectivity in neutron-rich Fe isotopes: Toward a new island of inversion?*, **J.Ljungvall**, A.Görgen, A.Obertelli, W.Korten, E.Clément, G.de France, A.Bürger, J.-P.Delaroche, A.Dewald, A.Gadea, L.Gaudefroy, M.Girod, M.Hackstein, J.Libert, D.Mengoni, F.Nowacki, T.Pissulla, A.Poves, F.Recchia, M.Rejmund, W.Rother, E.Sahin, C.Schmitt, A.Shrivastava, K.Sieja, J.J.Valiente-Doón, K.O.Zell, and M.Zielińska, Phys. Rev. C 81, 061301(R) (2010)

* *Lifetimes of odd-spin yrast states in* $^{182}$Hg, M.Scheck, T.Grahn, A.Petts, P.A.Butler, A.Dewald, L.P.Gaffney, M.B.Gomez Hornillos, A.Gorgen, P.T.Greenlees, K.Helariutta, J.Jolie, P.Jones, R.Julin, S.Juutinen, S.Ketelhut, T.Kroll, R.Krucken, M.Leino, **J.Ljungvall**, P.Maierbeck, B.Melon, M.Nyman, R.D.Page, J.Pakarinen, E.S.Paul, Th.Pissulla, P.Rahkila, J.Saren, C.Scholey, A.Semchenkov, J.Sorri, J.Uusitalo, R.Wadsworth, M.Zielińska, Phys. Rev. C 81, 014310 (2010)

* *Evolution of collectivity in* $^{180}$Hg and $^{182}$Hg, T.Grahn, A.Petts, M.Scheck, P.A.Butler, A.Dewald, M.B.Gomez Hornillos, P.T.Greenlees, A.Gorgen, K.Helariutta, J.Jolie, P.Jones, R.Julin, S.Juutinen, S.Ketelhut, R.Krucken, T.Kroll, M.Leino, **J.Ljungvall**, P.Maierbeck, B.Melon, M.Nyman, R.D.Page, Th.Pissulla, P.Rahkila, J.Saren, C.Scholey, A.Semchenkov, J.Sorri, J.Uusitalo, R.Wadsworth, M.Zielińska, Phys. Rev. C 80, 014324 (2009)

* *Position resolution of the prototype AGATA triple-cluster detector from an in-beam experiment*, F.Recchia, D.Bazzacco, E.Farnea, A.Gadea, R.Venturelli, T.Beck, P.Bednarczyk, A.Buerger, A.Dewald, M.Dimmock, G.Duchêne, J.Eberth, T.Faul, J.Gerl, R.Gernhaeuser, K.Hauschild, A.Holler, P.Jones, W.Korten, Th.Kröll, R.Krücken, N.Kurz, **J.Ljungvall**, S.Lunardi, P.Maierbeck, D.Mengoni, J.Nyberg, L.Nelson, G.Pascovici, P.Reiter, H.Schaffner, M.Schlarb, T.Steinhardt, O.Thelen, C.A.Ur, J.J.Valiente Dóbon and D.Weisshaar, Nuclear Instruments and Methods in Physics Research, Section A, Volume 604, Issue 3, 11 June 2009, Pages 555-562

* *γ-Ray Spectroscopy at the Limits: First Observation of Rotational Bands in* $^{255}$Lr, S.Ketelhut, P.T.Greenlees, D.Ackermann, S.Antalic, E.Clement, I.G.Darby, O.Dorvaux, A.Drouart, S.Eeckhaudt, B.J.P.Gall, A.Gorgen, T.Grahn, C.Gray-Jones, K.Hauschild, R.-D.Herzberg, F.P.Hessberger, U.Jakobsson, G.D.Jones, P.Jones, R.Julin, S.Juutinen, T.-L.Khoo, W.Korten, M.Leino, A.-P.Leppanen, **J.Ljungvall**, S.Moon, M.Nyman, A.Obertelli, J.Pakarinen, E.Parr, P.Papadakis, P.Peura, J.Piot, A.Pritchard, P.Rahkila, D.Rostron, P.Ruotsalainen, M.Sandzelius, J.Saren, C.Scholey, J.Sorri, A.Steer, B.Sulignano, Ch.Theisen, J.Uusitalo, M.Venhart, M.Zielińska, M.Bender, P.-H.Heenen, Phys. Rev. Lett. 102, 212501 (2009)

* *Shape evolution in self-conjugate nuclei, and the transitional nucleus* $^{68}$Se, A.Obertelli, T.Baugher, D.Bazin, J.-P.Delaroche, F.Flavigny, A.Gade, M.Girod, T.Glasmacher, A.Goergen, G.F.Grinyer, W.Korten, **J.Ljungvall**, S.McDaniel, A.Ratkiewicz, B.Sulignano, D.Weisshaar, Phys. Rev. C 80, 031304 (2009)

* *Shape of* $^{44}$Ar: *Onset of deformation in neutron-rich nuclei near* $^{48}$Ca, M.Zielińska, A.Gorgen, E.Clement, J.-P.Delaroche, M.Girod, W.Korten, A.Burger, W.Catford, C.Dossat, J.Iwanicki, J.Libert, **J.Ljungvall**, P.J.Napiorkowski, A.Obertelli, D.Pietak, R.Rodriguez-Guzman, G.Sletten, J.Srebrny, Ch.Theisen, K.Wrzosek, Phys. Rev. C 80, 014317 (2009)

* *Shape coexistence in light Se isotopes: Evidence for oblate shapes*, **J.Ljungvall**, A.Gorgen, M.Girod, J.-P.Delaroche, A.Dewald, C.Dossat, E.Farnea, W.Korten,
B.Melon, R.Menegazzo, A.Obertelli, R.Orlandi, P.Petkov, T.Pissulla, S.Siem, R.P.Singh, J.Srebrny, Ch.Theisen, C.A.Ur, J.J.Valiente-Dobon, K.O.Zell, M.Zielińska, Phys. Rev. Lett. 100, 102502 (2008)

* Neutron interactions in AGATA and their influence on gamma-ray tracking *Joa Ljungvall*, Johan Nyberg, Nuclear Instruments and Methods in Physics Research, Section A, volume 550, Issue 1-2, September 11, 2005, page 379-391

* A study of fast neutron interactions in high-purity germanium detectors, *Joa Ljungvall*, Johan Nyberg, Nuclear Instruments and Methods in Physics Research, Section A, volume 546, Issue 3, July 11, 2005, page 553-573

* Monte Carlo Simulations of The Neutron Wall detector system, *Joa Ljungvall*, Marcin Palacz, Johan Nyberg. Nuclear Instruments and Methods in Physics Research, Section A, volume 538, Issue 3, August 11, 2004, page 741-762

* Observation of core-excited E4 isomer in $^{98}$Cd, Blazhev, A., Gorska, M, Grawe, H, Nyberg, J., Palacz, M., Caurier, E., Dorvaux, O., Gadea, A., Nowacki, F., Andreoiu, C., de Angelis, G., Balabanski, D., Beck, Ch., Cederwall, B., Curien, D., Doring, J., Ekman, J., Fahlander, C., Lagergren, K., **Ljungvall, J.**, Moszynski, M, Norlin, L.-O., Plettner, C., Rudolph, D, Sohler, D, Spohr, K.M., Thelen, O., Weiszflog, M, Wisell, M, Wolinska, M, Wolski, W. Physical Review C (Nuclear Physics), volume 69, number 6, June 2004, page 64304-1-8

Conference proceedings

* Toward lifetime and g factor measurements of short-lived states in the vicinity of $^{208}$Pb D.Ralet, G.Georgiev, A.E.Stuchbery, E.Cement, A.Lemasson, C.Michelagnoli, M.Rejmund, L.Atanasova, D.L.Balabanski, G.Bocchi, R.Carroll, A.Dewald, J.Dudouet, B.Fornal, G.de France, S.Franchoo, C.Fransen, C.Muller-Gatermann, A.Goasduff, A.Gadea, B.Jacquot, P.R.John, D.Kocheva, T.Konstantinopoulos, A.Korichi, A.Kusoglu, S.M.Lenzi, S.Leoni, J.Ljungvall, R.Lozeva, A.Maj, A.Navin, R.Perez, N.Pietralla, C.Shand, O.Stezowski, D.Yordanov, Phys.Scr. 92, 054004 (2017)

* PRODUCTION AND STUDY OF NEUTRON-RICH NUCLEI USING THE LICORNE DIRECTIONAL NEUTRON SOURCE J.N. Wilson, M. Lebois, L. Qi, P. Amador-Celdran D. Bleuel, J.A. Briz, R. Carroll, W. Catford, H. De Witte, D. Doherty, R. Eloirdi, G. Georgiev, A. Gottardo, A. Goasduff, K. Hadynska-Klek, K. Hauschild, M. Hess, V. Ingeberg, T. Konstantinopoulos, J. Ljungvall, A. Lopez-Martens, G. Lorusso, R. Lozeva, R. Lutter, P. Marini, I. Matea, T. Materna, L. Mathieu, A. Oberstedt, S. Oberstedt, S. Panebianco, Z. Podolyak, A. Porta, P.H. Regan, P. Reiter, K. Rezynkina, S.J. Rose, E. Sahin, M. Seidlitz, R. Shearman, B. Siebeck, S. Siem, A.G. Smith, G.M. Tveten, D. Verney, N. Warr, F. Zeiser, M. Zielinska, Acta Phys.Pol. B 48, 395 (2017)

* LIFETIME MEASURMENTS OF EXCITED STATES IN NEUTRON-RICH FISSION FRAGMENTS T.W. Hagen, L. Grente, A. Görgen, M.-D. Salsac, W. Korten, F. Farget, T. Braunroth, B. Bruyneel, I. Celikovic, E. Clément, G. de France, O. Delaune, A. Dewald, A. Dijon, M. Hackstein, B. Jacquot, J. Litzinger, J. Ljungvall, C. Louchart, C. Michelagnoli, D.R. Napoli, A. Navin, F. Recchia, M. Rejmund, W. Rother, E. Sahin, S. Siem, B. Sulignano, Ch. Theisen, J.J. Valiente-Dobon, Acta Phys.Pol. B 47, 903 (2016)
* STUDY OF OCTUPOLE COLLECTIVITY IN <sup>146</sup>Nd AND <sup>148</sup>Sm USING THE NEW COULOMB EXCITATION SET-UP AT ALTO M. Komorowska, M. Zielińska, P. Napiorkowski, D.T. Doherty, K. Wrzosek-Lipska, P.A. Butler, L. Próchniak, W. Korten, R. Briselet, H. De Witte, L.P. Gaffney, G. Georgiev, A. Goasduff, A. Görgen, A. Gottardo, E.T. Gregor, K. Hadyńska-Klęk, H. Hess, M. Klintefjord, T. Konstantinopoulos, J. Ljungvall, R. Lutter, I. Matea, P. Matuszczak, G.G. O'Neill, W. Piatek, P. Reiter, D. Rosiak, M. Scheck, M. Seidlitz, B. Siebeck, M. Thürauf, N. Warr, *Acta Phys.Pol. B* 47, 923 (2016)

* Nuclear g-factor measurement with time-dependent recoil in vacuum in radioactive-beam geometry A.Kusoglu, A.E.Stuchbery, G.Georgiev, A.Goasduff, L.Atanasova, D.L.Balabanski, M.Bostan, M.Danchev, P.Detistov, K.Gladnishki, J.Ljungvall, I.Matea, D.Radeck, C.Sotty, I.Stefan, D.Verney, D.T.Yordanov, *Proc.NUBA Conference Series -1: Nuclear Physics and Astrophysics, Antalya, Turkey, 15-21 September 2014*, p.012041 (2015); J.of Phy.:Conf.Seri. 590

* LICORNE: A new and unique facility for producing intense, kinematically focused neutron beams at the IPN Orsay J.N. Wilson, M. Lebois, P. Halipre, B. Leniau, I. Matea, D. Verney, S. Oberstedt, R. Billnert, A. Oberstedt, G. Georgiev and J. Ljungvall, *EPJ Web of Conferences* 62, 05006 (2013)

* Onset of collectivity in neutron-rich Sr and Kr isotopes: Prompt spectroscopy after Coulomb excitation at REX-ISOLDE, CERN E. Clément, A. Görgen, A. Dijon, G. de France, B. Bastin, A. Blazhev, N. Bree, P. Butler, P. Delahaye, A. Ekström, G. Georgiev, N. Hasan, J. Iwanicki, D. Jenkins, W. Korten, A.C. Larsen, J. Ljungvall, K. Moschner, P. Napiorkowski, J. Pakarinen, A. Petts, T. Renstrom, M. Seidlitz, S. Siem, C. Sotty, J. Srebrny, I. Stefanescu, G.M. Tveten, J. Van de Walle, N. Warr, K. Wrzosek-Lipska, M. Zielińska, C. Bauer, B. Bruyneel, J. Butterworth, C. Fitzpatrick, C. Fransen, R. Gernhäuser, H. Hess, R. Lutter, P. Marley, P. Reiter, B. Siebeck, M. Vermeulen, A. Wiens and H. De Witte, *EPJ Web of Conferences* 62, 01003 (2013)

* Lifetime measurements on fission fragments in the A ~ 100 region, L. Grente, M.-D. Salsac, W. Korten, A. Görgen, T. W. Hagen, T. Braunroth, B. Bruyneel, I. Celikovic, E. Clément, O. Delaune, A. Dijon, A. Drouart, S. Ertürk, F. Farget, G. de France, A. Gottardo, M. Hackstein, B. Jacquot, J. Libert, J. Litzinger, J. Ljungvall, C. Louchart, C. Michelagnoli, D.R. Napoli, A. Navin, N. Pillet, A. Pipidis, F. Recchia, M. Rejmund, W. Rother, E. Sahin, C. Schmitt, S. Siem, B. Sulignano, J.J. Valiente-Dobon and K.O. Zell, *EPJ Web of Conferences* 62, 01002 (2013)

* Lifetime Measurements of Zn Isotopes Around N = 40 I.Celikovic, A.Dijon, E.Clement, G.de France, P.Van Isacker, **J.Ljungvall**, C.Fransen, G.Georgiev, A.Gorgen, A.Gottardo, M.Hackstein, T.W.Hagen, C.Louchart, P.Napiorkowski, A.Obertelli, F.Recchia, W.Rother, S.Siem, B.Sulignano, P.Ujic, J.J.Valiente-Dobon, M.Zielinska, *Acta Phys.Pol. B*44, 375 (2013)

* Odd-parity <sup>100</sup>Sn Core Excitations M.Palacz, J.Nyberg, H.Grawe, K.Sieja, G.de Angelis, P.Bednarczyk, A.Blazhev, D.Curien, Z.Dombradi, O.Dorvaux, J.Ekman, J.Galkowski, M.Gorska, J.Iwanicki, G.Jaworski, J.Kownacki, **J.Ljungvall**, M.Moszynski, F.Nowacki, D.Rudolph, D.Sohler, D.Wolski, M.Zieblinsk, *Acta Phys.Pol. B*44, 491 (2013)
* *Lifetime Measurements in Neutron-rich Fe and Co Isotopes*, A.Dijon, **J.Ljungvall**, E.Clement, G.de France, P.Van Isacker, A.Gorgen, A.Obertelli, W.Korten, J.P.Delaroche, A.Dewald, A.Gadea, L.Gaudefroy, M.Girod, M.Hackstein, J.Libert, D.Mengoni, T.Pissula, F.Recchia, M.Rejmund, W.Rother, E.Sahin, C.Schmitt, A.Shrivastava, J.J.Valiente-Dobon, K.O.Zell, M.Zielińska, Acta Physica Polonica B 42, 829 (2011)

* Onset of collectivity in Neutron-Rich iron isotopes: Toward a new island of inversion? **J. Ljungvall**, FRONTIERS IN NUCLEAR STRUCTURE, ASTRO-PHYSICS, AND REACTIONS: FINUSTAR 3. AIP Conference Proceedings, Volume 1377, pp. 386-388 (2011).

* *K Isomer in* 252 No, B.Sulignano, Ch.Theisen, **J.Ljungvall**, D.Ackermann, S.Antalic, O.Dorvaux, A.Drouart, A.Görgen, P.T.Greenlees, K.Hauschild, R.D.Herzberg, F.P.Hebetaberger, S.Hofmann, U.Jakobsson, P.Jones, R.Julin, S.Juutinen, S.Ketelhut, W.Korten, M.Leino, M.Nyman, A.Obertelli, J.Pakarinen, E.Parr, P.Papadakis, P.Peura, J.Piot, P.Rahkila, D.Rostron, P.Ruotsalainen, J.Saren, C.Scholeyb, J.Sorri, J.Uusitalo, M.Venhart, and M.Zielińska, AIP Conf. Proc. / Volume 1224, pp. 322-331, INTERNATIONAL SYMPOSIUM ON EXOTIC NUCLEI (2009)

* *Evolution Of Shapes And Collectivity In Exotic Nuclei*, Andreas Görgen and **Joa Ljungvall**, AIP Conf. Proc. / Volume 1224, pp. 54-63, INTERNATIONAL SYM-POSIUM ON EXOTIC NUCLEI (2009)

* *Lifetime Measurements and Coulomb Excitation of Light Hg Nuclei*, A.Petts, P.A.Butler, T.Grahn, A.Blazhev, N.Bree, B.Bruyneel, J.Cederkall, E.Clement, T.E.Cocolios, A.Dewald, J.Eberth, L.Fraile, C.Fransen, M.B. GomezHornillos, P.T.Greenlees, A.Gorgen, M.Guttormsen, K.Hadynska, K.Helariutta, R.-D.Herzberg, M.Huyse, D.G.Jenkins, J.Jolie, P.Jones, R.Julin, S.Juutinen, S.Ketelhut, S.Knapen, T.Kroll, R.Krucken, A.C.Larsen, M.Leino, **J.Ljungvall**, P.Maierbeck, P.L.Marley, B.Melon, P.J.Napiorkowski, M.Nyman, R.D.Page, J.Pakarinen, G.Pascovici, N.Patronis, P.J.Peura, E.Piselli, Th.Pissulla, P.Rahkila, P.Reiter, J.Saren, M.Scheck, C.Scholey, A.Semchenkov, S.Siem, I.Stefanescu, J.Sorri, J.Uusitalo, J.Van de Walle, P.Van Duppen, D.Voulot, R.Wadsworth, N.Warr, D.Weisshaar, F.Wenander, M.Zielińska, Proc.13th Intern.Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, Cologne, Germany, 25-29 Aug. 2008, J.Jolie, A.Zilges, N.Warr, A.Blazhev, Eds., p.414 (2009); AIP Conf.Proc. 1090 (2009)

* *Probing collectivity in the vicinity of neutron deficient Pb nuclei*, T.Grahn, A.Dewald, M.B.Gomez Hornillos, P.T.Greenlees, A.Gorgen, K.Helariutta, J.Jolie, P.Jones, R.Julin, S.Juutinen, S.Ketelhut, R.Krucken, T.Kroll, M.Leino, **J.Ljungvall**, P.Maierbeck, B.Melon, M.Nyman, R.D.Page, A.Petts, Th.Pissulla, P.Rahkila, J.Saren, C.Scholey, J.Sorri, J.Uusitalo, R.Wadsworth, M.Zielińska, Proc.Frontiers in Nuclear Structure, and Reactions (FINUSTAR 2), Crete, Greece, 10-14 Sept. 2007, P.Demetriou, R.Julin, S.V.Harissopulos, Eds. p.260 (2008); AIP Conf.Proc 1012 (2008)

* *Coulomb Excitation of Neutron-Rich* 44 Ar at SPIRAL, M.Zielińska, A.Goergen, A.Burger, W.Catford, E.Clement, C.Dossat, J.Iwanicki, W.Korten, **J.Ljungvall**, P.J.Napiorkowski, D.Pietak, G.Sletten, J.Srebrny, Ch.Theisen, K.Wrzosek, Acta Physica Polonica B 39, 519 (2008)

* *A Monte Carlo Simulation of the EUROBALL Neutron Wall detector system: How to identify scattered neutrons*, Marcin Palacz, Johan Nyberg. Acta Physica Polonica, Series B, volume 34, number 4, April 2003, page 2453-2456
# Chapter 9

## Shape of the rare-earth
nucleus $^{136}$Sm via sub-barrier
Coulomb excitation

### 9.1 Proposal (as sent to the GANIL PAC)
# GANIL
## PROPOSAL FOR EXPERIMENT

PAC date (fill in):

March, 2010

EXP # (Do not fill in):

E

* If Be or Ni production targets are to be used, indicate the maximum beam intensity the target can handle.

* Test runs which may be needed to commission new apparatus are encouraged, but should be presented as separate proposals.

**Title*: Shape of the rare-earth nucleus <sup>136</sup>Sm via sub-barrier coulomb excitation**

Is it a follow up experiment? [Yes/No]: **No**

If yes, experiment number: **E**

Is this just a TEST? [Yes/No]: **No**

**Spokespersons (if several, please use capital letters to indicate the name of the contact person):**

A. OBERTELLI (CEA Saclay), J. Ljungvall (CSNSM), E. Clément (GANIL)

Address of the contact person:

CEA Saclay, SPhN, 91191 Gif-sur-Yvette

Phone:01 69 08 74 86

Fax: 01 69 08 74 84

E-mail:alexandre.obertelli@cea.fr

Address of a backup contact person:

CSNSM, 91000 Orsay

Phone:

Fax:

E-mail: ljungall@csnsm.in2p3.fr

Other Participants or Organisations:

CEA Saclay: F. Dechery, A. Drouart, A. Goergen, W. Korten, C. Louchart, A. Obertelli, B. Sulignano, Ch. Theisen

GANIL: E. Clément, G. De France, H. Savajols, C. Stodel

CSNSM: J. Ljungvall

Short abstract:

We propose to investigate nuclear shapes in neutron-deficient rare earth nuclei below the N=82 shell closure by measuring the sub-barrier Coulomb excitation cross section of <sup>136</sup>Sm. By coupling the measured cross section with the experimentally known lifetime of the first 2<sup>+</sup> excited state in <sup>136</sup>Sm, we will determine its quadrupole moment. The nuclei with N=78 and Z=62 belong to one of the few regions of heavy nuclei in the nuclear chart where oblate-prolate coexistence near the ground state is predicted. Other models predict a triaxial ground state with γ=30°. Up to now, quadrupole moments in this region remain completely unexplored.

**Beam line (G1–G4, D1–D6, etc.): D6**

If LISE is requested, do you need the **Wien Filter**? [Yes/No]: **YES**

<table><tr><td><strong>Devices needed:</strong><br/>(Mark with an <strong>X</strong> or no. of detectors needed)</td><td>VAMOS</td><td>EXOGAM</td><td><strong>X</strong></td><td>DIAMANT</td><td>N-WALL</td><td>SPEG</td><td>MAYA</td><td>TIARA</td></tr><tr><td></td><td>MUST2</td><td>DEMON</td><td>INDRA</td><td>LISE2000</td><td>LISED4</td><td>LISED6</td><td><strong>X</strong></td><td>SIRA</td></tr><tr><td></td><td>NAUTILIS</td><td>CHARISSA</td><td>ECLAN</td><td></td><td></td><td></td><td></td><td></td></tr></table>

Other devices (specify):

<table><thead><tr><th><strong>Fill in completely:</strong></th><th><strong>Ion(s)</strong></th><th><strong>Energy (A.MeV)</strong></th><th><strong>Intensity (nAe)</strong></th><th><strong>UT/beam</strong></th></tr></thead><tbody><tr><td><strong>Primary beam(s)</strong></td><td><sup>126</sup>Xe</td><td>1.20</td><td>0.02</td><td>6</td></tr><tr><td></td><td><sup>82</sup>Kr</td><td>4.27</td><td>5800 (10<sup>12</sup> pps)</td><td>15</td></tr><tr><td><strong>Secondary beam(s)</strong><br/>if SISSI is requested</td><td>1.<br/>2.<br/>3.</td><td></td><td></td><td></td></tr><tr><td><strong>SPIRAL beam(s)</strong></td><td>1.<br/>2.</td><td></td><td></td><td></td></tr></tbody></table>

Will you need **SISSI**?

Yes/No: **NO**

If yes, SISSI Target(s) and Thickness(es):

LISE production target?

Yes/No: **YES**

If yes, LISE Target(s) and Thickness(es): <sup>58</sup>Ni, 1 mg.cm<sup>-2</sup>

**TOTAL number of beam UTs Requested:** 21

Time (UTs) required for setting up the apparatus: 21

If needed, to unlock this form, point to "Unprotect Document" on the Tools menu
If you need to accelerate more than one beam or energy (stable or SPIRAL), *include the beam-change tuning time* in your requested number of beam UTs. If not, the experiment may not be scheduled to run all at one time. **1 CSS1 Beam ($^{82}$Kr), 1 CIME beam ($^{126}$Xe).**

**Number of auxiliary (parasitic) beam UTs (if needed):**
**6**

If you wish to split beam UTs into more than one run, please specify UTs per run and period requested between runs:
**Auxiliary beam time should be scheduled at least 3 weeks before the experiment**

On what date would you be ready to run: **September 2010**

Excluded periods during next 3 years (if any already known):

Acquisition system: **GANIL**

Other (specify):

**SAFETY:** list any hazardous equipment or substances to be used, such as a radioactive target, liquid nitrogen, explosive gas, etc., even in SPEG chambers or germanium detectors:

**none**

**Go to Page 2**

Give the status of previous experiment(s) by this group in the last 3 years: e.g. results from of status of analysis of previous experiments at GANIL (or related experiments elsewhere):

**A. Drouart, E533 (2008), analysed, publication to be submitted**

**W. Korten, E553 (2008), analysed, publication to be submitted**

**A. Goergen, E393S (2006), published**

List publications, conference presentations, PhDs awarded, or other theses completed as a result of previous experiment(s) at GANIL (or related experiments elsewhere):

**J. Ljungvall et al., to be submitted (2010)**

**B. Avez et al., to be submitted (2010)**

**M. Zielinska et al., Phys. Rev. C 80, 014317 (2009)**

**E. Clément et al., Phys. Rev. C 75, 054313 (2007)**

**A. Chatillon et al., Phys. Rev. Lett. 98, 132503 (2007)**

**B. Avez, CEA Saclay, PhD thesis (2009)**

**E. Clément, CEA Saclay, PhD thesis (2006)**

**A. Chatillon, CEA Saclay, PhD thesis (2005)**

**A. Obertelli, CEA Saclay, PhD thesis (2005)**

List any NEW devices needed for this experiment which still have to be bought or manufactured:
**S2 Micron detector + mechanics (reaction chamber exists but needs some modifications)**

At what date do you expect these to be available? **September 2010**

List any special devices needed for this experiment which would require to be mounted prior to the experiment (special target chambers, detector arrays, etc.):

**1 mg.cm⁻² and 0.5 mg.cm⁻² ⁵⁸Ni targets to be built**

How long will it take to mount the particular device(s) once the area is available to you?

Will this require opening the roof beams above the area? [Yes/No]: **No**

Additional comments:
# Shape of the rare-earth nucleus <sup>136</sup>Sm via sub-barrier coulomb excitation

## 1-Motivations

The shape is one of the most fundamental properties of atomic nuclei. Calculations from deformed harmonic-oscillator potentials predict that prolate and oblate shapes should be equally probable across the nuclear chart. In the case of real nuclei, where the shell structure changes from a harmonic oscillator type to a Woods-Saxon+spin-orbit type with intruder orbitals, a strong dominance of prolate shapes is observed, which is related to the sharp surface of the nuclear potential [1]. Oblate shapes are expected when a major shell is almost filled due to the strong shape-driving effect of holes in the K=1/2 orbitals. This effect is seen for example in HFB calculations which predict oblate and prolate shapes to be equally favored just below the N=82 shell closure. Quadrupole deformation is not restricted to axial shapes: triaxiality may play an important role in connecting axially-deformed minima [2] or can even be prefered for the ground-state shape. The measurement of observables related to the nuclear shape represents a stringent test for theoretical models.

The HFB calculations with the Gogny D1S interaction predict deformed prolate shapes in the region above Z=50 and below N=82, except for a small region of oblate shapes for the most proton-rich N=78 and N=76 isotones [3]. The question of shape coexistence at low excitation energy, in the sense of two energy minima at different deformations, is raised but still unanswered in this mass region. Indeed, several studies in light Samarium nuclei showed several rotational bands associated to different intrinsic shapes. From lifetime measurements, a large deformation of β~0.3 has been deduced for the ground-state band of the lightest Sm isotopes [4].

To account for possible configuration mixing, correlations beyond the mean field have to be considered in the calculations. Such correlations can be accounted for through a mixing of HFB wave functions over collective degrees of freedom with the so-called Generator Coordinate Method (GCM). We have investigated HFB-based configuration mixing calculations for the chain of <sup>134-138</sup>Sm isotopes (i) using the Gogny D1S and the GCM with Gaussian overlap approximation (GOA) comprising axial and non-axial quadrupole degrees of freedom [5] and (ii) using the Skyrme Sly4 interaction and the GCM with axial symmetry and projected particle number and angular momentum [6]. In all cases, the total energy surfaces constrained to axial symmetry show almost degenerated minima at oblate and prolate shapes in both Gogny and Skyrme cases. The 5DCH (5-Dimension Collective Hamiltonian) approach predicts that these two minima are connected together via non-axial quadrupole shapes and therefore do not predict any oblate-prolate shape coexistence a low-excitation energy. In <sup>136,138</sup>Sm, a triaxial minimum is found, as suggested earlier from other models [7]. A purely triaxial nucleus with γ=30° has a much lower quadrupole moment than an axial oblate- or prolate-shaped nucleus. **The objective of this proposal is to determine the quadrupole moment of <sup>136</sup>Sm, as a representative nucleus of this region where oblate-prolate shape coexistence is expected from axial treatment but not from a 5DCH approach. As detailed later, the choice of <sup>136</sup>Sm, among neighboring nuclei presenting also two axial energy minima, is motivated by the feasibility of the experiment.**

<figure><img src="image_179.png" /><figcaption>**Figure 1:** (Left) Total energy surfaces for <sup>136</sup>Sm as a function of axial symmetry from calculations performed with the Skyrme Sly4 interaction and particle-number projection (PAV). (Middle) Total energy of <sup>136</sup>Sm (blue line) as a function of imposed axial deformation from HFB calculations with the Gogny D1S interaction. Dotted lines represent total-energy curves at I=2,4,6 angular momentum. (Right) Total energy surface in the (β,γ) plane calculated with the Gogny D1S interaction.</figcaption></figure>

In the case of <sup>136</sup>Sm, the resulting quadrupole moment is predicted to a rather small value of -99 efm<sup>2</sup> from 5DCH. Deformations where minima are observed in the energy surfaces restricted to axial symmetry occur at β =±0.3. This amplitude of deformation corresponds to a mean quadrupole deformation of Q=±255 efm<sup>2</sup>. A low-energy Coulomb excitation, as detailed in the next section, can distinguish between these scenarios. It appears
therefore as a sensitive test of the scenario of shape coexistence in $^{136}$Sm, and more generally in this mass region.

The neutron-deficient rare earth nuclei are accessible via heavy-ion induced fusion-evaporation reactions. However, experimental studies of shapes near the ground state are lacking completely in the considered region. Coulomb excitation experiments, which are sensitive to the spectroscopic quadrupole moments via the reorientation effect, are the most direct way to study shape transitions and shape coexistence. Some beams are expected to be soon available at REX-ISOLDE. The lightest Samarium isotope being accessible today for Coulomb excitation is $^{140}$Sm. The technique of combining lifetime and Coulomb excitation measurements has been successfully employed recently to obtain quadrupole moments, such as in $^{70}$Se [8].

In the rare-earth region where low-lying oblate deformations are expected, no Coulomb excitation has been performed due to the difficulty of producing such beams and identify incoming particles on an event-by-event method. The spectroscopy of $^{136}$Sm is known and its first $2^+$ excited state lies at 255 keV above the ground state. Its half-life has been measured at 88(9) ps [9]. The moment of inertia extracted from its high-spin spectroscopy [7,9,10] indicates a rather large deformation of $\beta\sim0.3$, but no information is known about the low excitation-energy deformation, sensitive to the details of the total energy surface (see Fig. 1).

We propose an innovative setup to measure the Coulomb-excitation of $^{136}$Sm produced by fusion evaporation and determine the number of incoming particles from a delayed measurement. This technique will allow to determine the absolute Coulomb-excitation cross section of $^{136}$Sm on $^{58}$Ni and, by combination with its known lifetime, one can estimate its quadrupole moment. This experiment, the first of its kind, can be seen as a pre-S3 experiment. The spectrometer S3 will indeed allow producing intense cocktail secondary beams via fusion-evaporation at SPIRAL2 with, unfortunately, no isobaric separation.

## 2-Experimental setup

The production of light Samarium isotopes via fusion-evaporation forbids to use a “heavy” primary beam (A>100) in order to ensure a clean rejection of beam particles with the LISE Wien filter. On the other hand, since we aim at using these fusion-evaporation products for a Coulomb-excitation secondary reaction, the residues should have a velocity large enough to use a high-Z target and reach a sizeable cross section.

These two reactions (fusion-evaporation for production and Coulomb excitation) are constrained in terms of incident energy: both should be performed around the Coulomb barrier.

<figure><img src="image_180.png" /><figcaption>Figure 2: Experimental setup.</figcaption></figure>

According to available stable beams at GANIL, we found that an optimized setup to study $^{136}$Sm is as follows. The fusion-evaporation residues will be formed from a $^{82}$Kr incident beam accelerated at 350 MeV (4.27 MeV/u) with the CSS1 cyclotron, at an intensity of $10^{12}$ pps, impinging on a $^{58}$Ni target (68 % abundance) of 1 mg.cm$^{-2}$. The Paquerette rotative target will be used to maintain the target temperature under 900 degrees. The maximum of the excitation function for $^{136}$Sm is found for an incident energy of 340 MeV. The total fusion-evaporation cross section is calculated with PACE4 to be 576 mb at the entrance of the production target, among which $^{136}$Sm is produced at 83 mb (purity of 15 %) via the alpha-evaporation channel. At the exit of the
target, the fusion-evaporation cross section is 294 mb and ¹³⁶Sm is produced at 64 mb (22 %). The incident energy is chosen to place the maximum of the excitation function in the middle of the target. Similar calculations performed with the HIVAP code from GSI predict that the maximum of the excitation function is at an incident energy close to the PACE4 value. The total fusion-evaporation cross section is also similar to the PACE4 prediction but the purity of the beam is 10% of ¹³⁶Sm. Finally, the compound-recoil velocity at the exit of the target ranges from 0.0492 c and 0.0534 c (beam=0.091 c at the exit of the target), which corresponds to energies from 154 MeV to 181 MeV for ¹³⁶Sm. The velocity spread will be reduced to ±5% (from 162 to 178 MeV) at the exit of the Wien filter with slits. In the following, we consider the most pessimistic predictions of a 10% purity and a mean fusion-evaporation cross section of 500 mb. The angular distribution of ¹³⁶Sm nuclei due to particle evaporation is calculated to be peaked around 1.5 degrees in the laboratory frame.

In the recent E533 experiment, Xe+Sn and Xe+Zr have been measured [12]. The LISE Wien filter was shown to reach a rejection of 2. 10⁻⁸, resulting in the present case to a 10⁴ pps contamination of beam particles in the secondary beam (i.e. 1%). From these experiments, we expect a transmission of ¹³⁶Sm better than 20%. Expectations from calculations are worst : Zgoubi calculations predict that the 27⁺ charge state has the larger transmission with 35%. The charge state distribution of ¹³⁶Sm convoluted with calculated transmissions give a global transmission of 10% for ¹³⁶Sm.

**The above uncertainties on (i) the primary beam rejection, (ii) transmission and (iii) relative production of ¹³⁶Sm lead us to request auxiliary beam in LISE to measure these quantities. Details on this preliminary test will be further exposed during the oral presentation.**

In the following, the intensity of the secondary beam is calculated assuming a total transmission of 20%. The total intensity on the secondary target is calculated to be around 1. 10⁶ pps containing 1. 10⁵ pps (lower limit of 10% for the purity) of ¹³⁶Sm at 1.25 MeV/nucleon. The time of flight from the production target to the secondary target will be of several hundreds of nanoseconds.

<table><caption>**Table 1: Coulomb-excitation cross sections for ¹³⁶Sm+⁵⁸Ni at 160 MeV (mid-target energy) integrated over the whole angular range covered by the annular Si detector.**</caption><thead><tr><td>Shape</td><td>Qs (efm²)</td><td>σ [50°; 160°] (mb)</td></tr></thead><tbody><tr><td>Spherical</td><td>0</td><td>542<sup>+62</sup><sub>-53</sub></td></tr><tr><td>Prolate</td><td>- 255 efm²</td><td>449<sup>+51</sup><sub>-40</sub></td></tr><tr><td>Oblate</td><td>+255 efm²</td><td>649<sup>+74</sup><sub>-57</sub></td></tr></tbody></table>

As mentioned earlier, the first 2⁺ excited state of ¹³⁶Sm has been measured at 255 keV with a lifetime of 88 (9) ps. Predictions for the Coulomb excitation cross section of ¹³⁶Sm on ⁵⁸Ni has been performed using the GOSIA code [13], assuming three different shapes for the first 2⁺ state of ¹³⁶Sm : (i) spherical, (ii) prolate and (iii) oblate. Integrated cross sections (from 50 to 160 degrees in the center of mass) have been calculated and are displayed in Table 1. All three values differ from each other with a sizeable difference of >20%. The quoted error bars contain uncertainties from the lifetime measurement. Note that multistep excitations vanish at such low incident energy. Only the first 2⁺ excited state will be populated.

<figure><img src="image_181.png" /><figcaption>**Figure 3: (Left) Kinematics of the inelastic Coulomb scattering ¹³⁶Sm+⁵⁸Ni at 170 MeV (1.25 MeV/nucleon) (Right) Differential angular distribution of the Coulomb excitation of ¹³⁶Sm on ⁵⁸Ni as a function of the scattering angle in the center of mass. The angular range covered by the Si stripped detector is shown.**</figcaption></figure>
Considering the experimental uncertainties on the lifetime of <sup>136</sup>Sm(2<sup>+</sup>) measured at 88(9) ps, an uncertainty of 15% in the cross section measurement should allow us to distinguish between a prolate, and an oblate shape for <sup>136</sup>Sm(2<sup>+</sup>) in case the deformation amplitude exceeds 150 e fm<sup>2</sup>.

Four Exogam clovers will be placed at 15 centimeters from the target center, leading to a total *photopeak efficiency* of 9% for a 300 keV transition. Depending on available electronics and mechanical constraints, we may add other clovers around the secondary target, increasing linearly the final statistics. Assuming a 0.5 mg.cm<sup>-2</sup> secondary <sup>58</sup>Ni target, one gets 1000 photopeak events per day of experiment. Considering the above-mentioned Coulomb-excitation cross section typical for all nuclei present in the beam, the low incident energy that prevent multiple scattering and a detection efficiency (Compton or photopeak) of 20% per clover for gamma-ray energies around 300 keV, we expect a rate of 1 Hz per crystal at the secondary target position. We plan to place a segmented Silicon annular detector (Micron S2 type, 48 mm inner radius, 96 mm outer radius) at 90 mm to detect scattered particles from 15<sub>lab</sub>° to 28<sub>lab</sub>°, which correspond to large center-of-mass angles from 50° to 160° (see kinematics in Fig. 3), where the differential cross section is more sensitive to the quadrupole moment, as displayed in Table 1 and the right panel of Fig. 3. At least three different angular bins will be made to increase the analysis sensitivity to the quadrupole moment. To give an idea of the sensitivity, we shall reach an uncertainty of about ±100 efm<sup>2</sup> in the range of discussed quadrupole moments including all uncertainties (mainly 15% from normalization, 10% from the lifetime measurement). The energy resolution of the Si detector will allow disentangling scattered Ni and Sm isotopes. The angular cone defined by the inner radius is large enough (15°) to let the secondary beam go through with no damage risk for the internal strips.

Incident <sup>136</sup>Sm nuclei will be implanted downstream the secondary target in an aluminium foil backed by three Exogam detectors. Appropriate shielding will be placed between the implantation foil and the Exogam detectors located around the secondary target. The counting of decay gamma-transitions of <sup>136</sup>Pm (daughter of <sup>136</sup>Sm via electron conversion, T<sub>1/2</sub>=47 s) will determine the incident rate of <sup>136</sup>Sm. This measurement will provide an absolute normalization for the Coulomb excitation cross section for <sup>136</sup>Sm. A 114.2 keV line in <sup>136</sup>Pm gathers 36% of the decay strength, leading to a clear identification of implanted <sup>136</sup>Sm. This absolute normalization to determine the Coulomb-excitation cross section is possible because the beta-decay of <sup>136</sup>Sm and all branching ratios are known. No nuclei populating <sup>136</sup>Sm via its radioactive decay is expected to be significantly produced in the secondary beam. The father nucleus <sup>136</sup>Eu has a half life of 3.3 s (an isomer with an half life of 3.8 s), short compared to <sup>136</sup>Sm. The residual influence, if any, of the implantation of <sup>136</sup>Eu could be corrected from time correlations between prompt and delayed gammas in the implantation Exogam detectors. We do not expect any line close to 114 keV in the decay chain of implanted nuclei that could pollute the rate estimate. The Exogam clovers for decay-tagging will be placed behind the reaction chamber where the implantation foil will be located. A geometrical efficiency close to 50% could be reached. Nevertheless, we plan to position the detector at 30 cm from the foil to reduce the solid angle and therefore the counting rate. Being at 30 cm from the implantation foil reduces also the effect the gamma efficiency of the implantation profile. We estimate the gamma counting rate produced in the detector by the decay of beam particles to be around 10<sup>3</sup>-10<sup>4</sup> Hz. The accumulated statistics will be extremely large and will allow γ-γ coincidences between crystals of the Exogam clovers to properly determine the number of implanted <sup>136</sup>Sm isotopes.

An additional separation from <sup>78</sup>Kr primary-beam not rejected via the Wien-Filter will be performed by a time-of-flight measurement between two Micro-Channel plates (MCPs). The MCP #2 will provide a start signals for time coincidences between prompt events and delayed signals from decays that will allow rejecting prompt gamma decays of nuclei excited during their implantation. In case a residual part of the beam particles impinging on the secondary target are not implanted on the Al foil, a correction factor to deduce the total <sup>136</sup>Sm will be determined from the ratio #MCP1/#MCP2.

A stable-beam measurement is required to tune and start operating the setup in “easy” conditions. We propose to perform the Coulomb excitation of the stable <sup>126</sup>Xe. The lifetime of its first 2<sup>+</sup> state (388 keV) has been measured at 40.8(13) ps. Its quadrupole moment is not known but it is expected to be well deformed at a prolate ground state. The beam will be delivered from the CIME cyclotron at a velocity close to the one expected for <sup>136</sup>Sm at the exit of the Wien filter (energy of 1.20 MeV/u). Since the two different stable beams are accelerated from separate cyclotrons (Kr in CSS1, Xe in CIME), no extra time is needed for the beam tuning. We expect an integrated cross section of about 500 mb. A one-day measurement at 10<sup>6</sup> pps gives about 2.10<sup>4</sup> photopeak events, enough for a differential cross section measurement. This reference measurement will provide a global validation of the efficiency of EXOGAM (around the Coulomb-excitation target), the
segmented silicon annular detector, the target thickness and the efficiency of the MCPs. The gamma spectrum obtained with the detector from the implantation area will give a reference for background. The eXe beam will be used also for a first tune of the Wien filter.

### 4-Beam-time request

We need for this experiment 2 days to tune the setup ($^{126}$Xe primary beam and $^{136}$Sm secondary beam), 1 day for the reference measurement with $^{126}$Xe and 4 days for the secondary beam experiment. The information used for beam time estimate are summarized in Table 2.

<table><caption>Table 2: Summary of ingredients considered for the beam time request.</caption><tr><td>Primary beam ($^{82}$Kr @ 350 MeV / CSS1)</td><td>10<sup>12</sup> pps</td></tr><tr><td>Production target ($^{58}$Ni, 1 mg.cm<sup>-2</sup>)</td><td>1.4 10<sup>19</sup> cm<sup>-2</sup></td></tr><tr><td>Mean fusion-evaporation cross section</td><td>400 mb (10 % of <sup>136</sup>Sm, lower limit)</td></tr><tr><td>Wien Filter transmission</td><td>30 %</td></tr><tr><td>Secondary beam intensity</td><td>1.5 10<sup>6</sup> pps (1.5 10<sup>5</sup> pps of <sup>136</sup>Sm)</td></tr><tr><td>Secondary target ($^{58}$Ni, 0.5 mg.cm<sup>-2</sup>)</td><td>5.2 10<sup>18</sup> cm<sup>-2</sup></td></tr><tr><td>Coulomb-excitation cross section</td><td>600 mb (from 50° to 160° deg. cm)</td></tr><tr><td>Photopeak efficiency @ 300 keV (4 clovers)</td><td>9 %</td></tr><tr><td>Beam time (fusion-evap. beam)</td><td>4 days</td></tr><tr><td>Statistics (photopeak events + <sup>136</sup>Sm in annular Si)</td><td>3. 10<sup>4</sup><br/>&gt;4 angular bins possible with &lt;2% statistical errors</td></tr></table>

Finally, we request 7 days of beam time to measure to perform the Coulomb-excitation of $^{136}$Sm and access the quadrupole deformation of its first excited $2^+$ state. The requested 21 UTs of beam time are decomposed in (i) 8 UTs of a $^{126}$Xe stable beam at 1.2 MeV/u delivered by CIME and (ii) 15 UTs of a $^{82}$Kr beam at 350 MeV delivered by CSS1.

Prior the experiment, we request 6 UTs of $^{82}$Kr at 350 MeV to verify the Wien-filter correct operation under our experimental conditions, and measure (i) the beam rejection, (ii) the beam purity in $^{136}$Sm and (iii) the Wien Filter transmission.

### References

[1] I. Hamamoto and B. R. Mottelson, ArXiv:0903.0973v1 [nucl-th] (2009).

[2] M. Girod et al., Phys. Lett. B 676, 39 (2009).

[3] http://www-phynu.cea.fr/science_en_ligne/carte_potentielmicroscopiques

[4] M. A. Coardona et al., Phys. Rev. C 44, 891 (1991).

[5] M. Girod, private communication (2010).

[6] J. Sadoudi, private communication (2010). Codes from M. Bender (CENBG).

[7] E. S. Paul et al., J. Phys. G: Nucl. Part. Phys. 20, 1405 (1994).

[8] J. Ljungvall et al., Phys. Rev. Lett. 100, 102502 (2008).

[9] F. Soramel et al., Phys. Rev. C 38, 537 (1988).

[10] F. Falla-Soleto, LNL annual report (2005).

[11] A. A. Sonzogni, Nuclear Data Sheets 95, 837 (2002).

[12] B. Avez, CEA Saclay, PhD thesis (2009).

[13] T. Czosnyka, D. Cline and C. Y. Wu, Bull. Am. Phys. Soc. 28, 745 (1983).
## 9.2 Experiment, a two stage rocket into the void

In order to validate the production rate of <sup>136</sup>Sm and the possibility to reject the primary beam an initial test was performed. The date from this test experiment was analyzed by me, and a report was written and send to GANIL in order to have the actual experiment programmed. The optimistic conclusions from this test was that the measurement was feasible.

### 9.2.1 Report on test experiment for E614
Results from the test part of E614, “Shape of rare-earth
nucleus <sup>136</sup>Sm via sub-barrier Coulomb excitation”

J. Ljungvall<sup>a</sup>, A. Obertelli<sup>b</sup>, B. Bruyneel<sup>b</sup>, L. Caceres<sup>d</sup>, E. Clement<sup>d</sup>, A. M. Corsi<sup>b</sup>, A. Drouart<sup>b</sup>, L. Gaudefroy<sup>c</sup>, B. Jacqout<sup>d</sup>, O. Kamalou<sup>d</sup>, C. Santamaria<sup>b</sup>, J.-C. Thomas<sup>d</sup>

<sup>a</sup>CSNSM

<sup>b</sup>CEA Saclay

<sup>c</sup>CEA DAM

<sup>d</sup>GANIL

# 1. Introduction

The experiment “Shape of rare-earth nucleus <sup>136</sup>Sm via sub-barrier Coulomb excitation” was accepted by the GANIL PAC in spring 2010, together with 6 UTs of beam time to test and verify some crucial aspects for the experiment to work:

1. Primary beam rejection.

2. Transmission of evaporation residues.

3. Production rate of <sup>136</sup>Sm.

Furthermore, we have, closely related to the question of rejection of the primary beam, the issue of the absolute count rate in the angular silicon detector that will be used to detect the scattered <sup>136</sup>Sm nuclei in the experiment.

# 2. Experimental setup

The setup used to perform the test part of the E614 experiment is shown in figure 1. The secondary target and the zero degree Silicon detector are removable. The main purpose of the MCP2 detector is to count the incoming particles and to allow for the determination of the scattering angle. MCP1 is used to estimate the amount of beam particles downstream the secondary target. The LaBr<sub>3</sub> detectors are used to identify the γ rays from the β decay of <sup>136</sup>Sm. The zero degree Silicon detector is used for the tuning of LISE.

Preprint submitted to Elsevier

January 14, 2013
Production

Particle detection

ID / Decay

<figure><img src="image_182.png" /><figcaption>Figure 1: Setup for the test experiment.</figcaption></figure>

### 3. Results from test experiment

#### 3.1. Rejection of primary beam/transmission of products

We did not manage to reject sufficiently the primary beam while transmitting the fusion residues.

During the test, we encountered issues to align the beam in the LISE beam line, upstream and inside the WF. After optics measurements performed after the test, it appeared that quadrupoles upstream the Wien Filter were dis-aligned by some millimeters. A PPAC was also off centered. We believe that these misalignments were responsible of our experimental difficulties to transmit the fusion products and reject the primary beam with the Wien Filter.

To identify the primary beam and transmission of ERs a silicon detector at zero degrees was used together with a time of flight measurement between the two MCP detectors. This identification is shown in figure 2. As the effective area of the zero degree silicon detector is much smaller than that of the two MCP detectors, there is a large fraction of events that has a zero
energy. In figure 2 a gate used to estimate the number of ERs is shown.
Everything outside this gate is considered to be scattered primary beam.

<figure><img src="image_183.png" /><figcaption>Figure 2: Identification of evaporation residues using in beam Si detector. Everything inside the black gate is considered to be ERs. A band corresponding to scattered beam can clearly be seen lower in energy as compared to the ERs.</figcaption></figure>

It was not possible to get a decent <sup>136</sup>Sm transmission when the primary
beam is fully rejected.
## 3.2. Count rates in Si detector

One limiting factor for the experiment is the amount of scattered primary beam that will hit the DSSD detector used for the Coulomb excitation. A large amount of time was used during the experiment to try to optimize, i.e. minimize, the count rate in the DSSD. These measurements were of course affected by the previously mentioned issues regarding the optics misalignment.

In figure 3 the hit pattern in the DSSD is shown together with the hit pattern in MCP2, without or with one of two different gates on the position in the DSSD. Gate 1 is interpreted as being fusion evaporation residues, whereas gate 2 is thought to be scattered beam. This data was taken with a primary beam intensity of 100 nAe and the DSSD trigger rate was 1500 Hz, with the most hit strip counting at 300 Hz. As can be seen they are physically separated. However, the situation shown in figure 3 is the best compromise that we could find. In figure 4 the energy as measured in the DSSD is shown, both total and when gated with gate 1 or 2. The distinctly different energy distribution supports the interpretation of the two different structures seen in figure 3. To further investigate the origin of the two structures seen in both figure 3 and 4 data that was taken without a secondary Coulomb excitation target was also analysed. In figure 5(a) the hit pattern on the Spider Si is shown, indicating a weaker scattered primary beam component. This can also be seen in the Spider energy spectra shown in figure 5(b). This suggest a large fraction of the scattered primary beam comes from interactions with the secondary target or its frame.

These results illustrate that we have difficulties producing an experimental condition that allows the use a primary beam intensity that is high enough. Again, these problems are believed to be a result from the alignment problems mentioned in section 3.1.
<figure><img src="image_184.png" /><figcaption>Figure 3: Hit pattern in Spider Si detector and MCP detector 2 (before secondary target). The two lower figures show the hit pattern of MCP2 with gate 1 (left) and gate 2 (right).</figcaption></figure>
<figure><img src="image_185.png" /><figcaption>Figure 4: Particle energy as measured by the Spider Si detector. The vertical line indicates the gate used when looking at events in the Spider and MCP 2 detectors. For the meaning of gate 1 and gate 2, see text and figure 3.</figcaption></figure>
<figure><img src="image_186.png" /><figcaption>(a) Hit pattern Spider Si without secondary target</figcaption></figure>

<figure><img src="image_187.png" /><figcaption>(b) Energy in Spider Si for different regions, see figure 5(a).</figcaption></figure>
### 3.3. Confirmation of the production of $^{136}$Sm

To make sure that we produced $^{136}$Sm during the experiment, $^{136}$Sm data was taken with and without primary beam in cycles of 10 minutes, corresponding to more than 10 halflives for $^{136}$Sm. During the off-beam periods $\gamma$ rays form the decays were detected using six LaBr$_3$ detectors. In figure 5 the decay chain of $^{136}$Sm is shown. Apart from being an ER, $^{136}$Pm is also populated from the decay of $^{136}$Sm, and it is the 114 keV line from this decay that is used to identify the $^{136}$Sm ions.

<figure><img src="image_188.png" /><figcaption>Figure 5: Decay scheme for the A=136 Isobars produced directly and via $\beta$ decay.</figcaption></figure>

In figure 6(a) the energy spectrum from LaBr$_3$ detectors is shown, clearly showing a strong peak at about 110 keV, and at 374 keV. The peak at 110 keV is a convolution of the 109 keV line from the decay of $^{136}$Pm and the 114 keV line from the decay of $^{136}$Sm.

In order to identify and quantify the nuclei decaying the detected $\gamma$ rays were binned in time bins of 20 s and put into histograms and the 109, 114, and 374 keV $\gamma$-ray lines were fitted, as shown in figures 6(b) and 6(c).

In figure 6 the number of counts per 20 s as function of time is shown for the 109, 114, and 375 keV $\gamma$-ray lines. The result is corrected for the difference in efficiency. Also shown are the solutions of the so-called Bateman equation with lifetimes taken from literature, but with the number of ions at $t = 0$
<figure><img src="image_189.png" /><figcaption>(a) γ-ray energy spectrum for the LaBr<sub>3</sub> detectors.</figcaption></figure>

<figure><img src="image_190.png" /></figure>

<figure><img src="image_191.png" /><figcaption>(b) Fit of the 109 and 114 keV γ-ray lines (c) Fit of the 374 keV γ-ray lines from the
from the β decay of <sup>136</sup>Nd and <sup>136</sup>Sm, respectively</figcaption></figure>

fitted. It is clear that production of <sup>136</sup>Sm and <sup>136</sup>Pm are comparable, in line
with the result from PACE4 calculations.
<figure><img src="image_192.png" /><figcaption>Figure 6: Decay curves for ¹³⁶Sm, ¹³⁶Nd, and ¹³⁶Pm taken after a cycle of beam off/beam on, each part for a period of 10 min.</figcaption></figure>
# 4. Conclusions

The test performed in July 2012 at GANIL was performed, allowing to answer some of the initial questions relative to the feasibility of the experiment. With regard to the initial questions prompting the test experiment the following conclusions have been drawn:

## 4.1. Primary beam rejection.

non-conclusive.

## 4.2. Transmission of evaporation residues.

non-conclusive.

## 4.3. Relative production of $^{136}$Sm.

The relative production of $^{136}$Sm with respect to other ERs are in line with the estimates used in the proposal.

## 4.4. Identification of $^{136}$Sm.

The gamma 114-keV line to identify $^{136}$Sm has been seen and could be separated from the 109 keV line coming from $^{109}$Nd as a function of time. For the physics experiment, high-resolution Ge detectors should be used for clean separation. **The physics experiment requests EXOGAM for both prompt and decay gamma spectroscopy.**

## 4.5. Comparison with ISOLDE

We would like to raise that the present physics case, given as a test case to prove the feasibility and power of the technique, is feasible at ISOLDE from recent beam developments of light Sm. The yield of $^{136}$Sm has not been measured but Thierry Stora from CERN estimates from recent developments for another coulex experiment on light Sm nuclei (spokesperson: A. Görgen) that the yield of $^{136}$Sm should be around 200 pps. Upgrades may be possible from 2017-2018. **The expected yields with the fusion technique proposed in our measurement exceeds CERN's estimates by a factor of 100 and is therefore competitive for the $^{136}$Sm case.**
4.6. Nutshell conclusions

The E614 experiment should be feasible with the allowed beam time if
the beam rejection and residue transmission is achieved. We think proper
working conditions could be reached with the re-alignment of the optical
elements of LISE performed since September 2012. A new test should be
performed.
9.2.2 The E614 experiment

During the spring of 2013 the experimental setup was prepared at GANIL. At the same time extensive calculations for LISE in terms of production and transmission to the secondary target points were made by members in the E614 collaboration. In figure 9.1 a drawing of the used setup is shown. The LISE Wien filter (not shown) is to the right of the figure. This is from where the evaporation residues arrive. They pass by the first MCP detector, impinge on the secondary target from where they either scatter or continue through the second MCP and are caught in the catcher foil in order to be counted using the 114 keV γ ray from β decay. Just after the target the double sided Silicon detector (referred to as Spider DSSD) was mounted to detect scattered ions. The idea was to detect γ rays from Coulomb excitation with a triple coincidence between the first MCP, the DSSD, and one of the EXOGAM detectors mounted close to the secondary target. By stopping and detecting the β decay downstream target an absolute number of ions on target was to be determined and with it the Coulex cross section and hence the electromagnetic matrix elements. In figure 9.2 and figure 9.3 photos of the setup are shown. Finally is the experimental setup as modeled in geant4 for simulations shown in figure 9.4.

<figure><img src="image_193.png" /><figcaption>Figure 9.1: Drawing of the E614 experimental setup</figcaption></figure>
<figure><img src="image_194.png" /><figcaption>Figure 9.2: Photos of the experimental setup for E614 without the HPGe detectors.</figcaption></figure>

<figure><img src="image_195.png" /><figcaption>Figure 9.3: Photos of EXOGAM HPGe detectors used in the E614 experiment</figcaption></figure>
<figure><img src="image_196.png" /><figcaption>Figure 9.4: The experimental setup as modelled in geant4 simulations.</figcaption></figure>

The experiment proved to be very complicated. Achieving good transmission of the fusion-evaporation residues combined with good rejection of the primary beam was very difficult. There were however $^{136}$Sm seen in the β-decay spectra. It was believed during the experiment that one of the problems we had was the bad quality of "secondary beam" as it impinged on the secondary target, adding not only to the ambient background from β decay but also making the kinematical selection in the DSSD complicated. To improve the situation a collimator was added upstream the secondary target (shown in figure 9.4).

<figure><img src="image_197.png" /><figcaption>Figure 9.5: Experimental scattered particle energy vs angle with simulations of scattered $^{136}$Sm (blue triangles) and $^{72}$Kr (black triangles). The cut was made to try to select $^{136}$Sm events as is also shown.</figcaption></figure>

In figure 9.5 the ion-energy vs scattering angle, as detected in the Spider DSSD,
is shown. It is overlaid with simulated distributions of scattered fusion-evaporation reaction products (blue triangles) and non-rejected primary beam of the same velocity (black triangles). Also shown is the gate used to select scattered secondary beam.

<figure><img src="image_198.png" /></figure>

Figure 9.6: TAC spectrum between Spider Particle detector and HPGe EXOGAM for prompt γ rays. The prompt peak (very weak) is between channel 10240 and channel 10630. The spectrum is in coincidence with the gate shown in figure 9.5. The full range is 2 μs.

Using this gate the time-difference between ions detected in the Spider detector and γ rays detected in the EXOGAM detectors close to the secondary target can be made. This time difference is shown as a spectrum in figure 9.6. The absence of a clear prompt peak is flagrant. However, using the peak of the $2_1^+ \rightarrow 0_1^+$ transition in the non-rejected primary beam one can deduce that there is a prompt peak. Using this peak the γ-ray spectra shown in figure 9.7 are produced. Overlaid on the background subtracted prompt spectrum is a simulation (described further down in this text) of the spectra from the $2_1^+ \rightarrow 0_1^+$ in $^{136}$Sm if produced by Coulomb excitation on the secondary target. The rather obvious conclusion is that we saw no Coulomb excited $^{136}$Sm in the experiment.
<figure><img src="image_199.png" /><figcaption>Figure 9.7: E614 γ rays. After background subtraction (in time domain) the only visible γ ray is the deexcitation of the $2_1^+$ state in the primary beam $^{82}$Kr. A Geant4 simulation of Coulomb excitation of the $2_1^+$ state in $^{136}$Sm is also shown as a reference. For the simulations see text for details.</figcaption></figure>

In figure 9.8 are shown spectra taken by the EXOGAM detectors placed at the catcher foil. After the primary beam was stopped, data was collected for one minute in order to see the γ rays from the decay products and to measure the γ-ray peak intensities as a function of time to assure that the correct ion species were produced. The peak at 114 keV shows that $^{136}$Sm was indeed produced and transported from the primary target to the secondary target (the direct production of more neutron deficient isobars form the $^{140}$Gd compound nuclei is much smaller). However, as no prompt Coulomb excitation peak from $^{136}$Sm could be seen no efforts were made to quantify the production of $^{136}$Sm.
<figure><img src="image_200.png" /><figcaption>Figure 9.8: Gamma-ray spectra from the decay station. Data taken during 60 s directly after that the primary beam was stopped. Spectra shown before and after a collimation of the secondary beam was introduced upstream the secondary target.</figcaption></figure>

A sophisticated simulation package based on the `geant4` code of AGATA [233] was created in order to simulate the experiment. The geometry of the experiment and an event generator was written as add-on libraries that can be used at execution time of the AGATA code (i.e. can be used without modifying the AGATA code). The event generator includes a simple $^{136}$Sm beam to simulate the most idealized case of a pure secondary beam with good beam optics. This mode was used to produce the simulated spectrum in figure 9.7. It also includes a mode simulating the cocktail beam of fusion evaporation products with beam optics as given by the calculations used to estimate transmission and rejection of the LISE Wien filter. In order to estimate the background from $\beta$ decaying nuclei the simulations are keeping track of the "wall clock" time. The time structure of the beam is also simulated. This is done by creating a large number of files (~50000), each file corresponding to a time slice of 15 s. Each interaction in an event is then written to the corresponding file on disk. All events in each time slice can then be time sorted and events can be created by reading the files in time order. These simulations are time consuming, on a single Intel(R) Xeon(R) CPU E5-2609 0 @ 2.40GHz CPU core about 500 events per second could be simulated, to be compared to the about 75000 pps assumed in "the experiment" - one second of experiment takes 2 minutes to simulate. The build up of activity in the simulations can clearly be seen in the counts per seconds in the EXOGAM detectors as function of time shown in figure 9.9.
<figure><img src="image_201.png" /><figcaption>Figure 9.9: Number of counts per 10 seconds in the EXOGAM detectors as a function of beam time. The build up of activity is clearly shown as well as the decay after the stop of the beam in the simulations (after around 15000 s). The spikes are from some minor issues chaining root files.</figcaption></figure>

Using simulated data corresponding to about one hour of experiment the time difference between scattered ions and γ rays in the EXOGAM detectors close to the secondary targets was made. The spectrum is shown in the upper panel of figure 9.10. It has a large resemblance with the experimental spectrum shown in figure 9.6. Also shown, from simulations including the Coulomb excitation of <sup>136</sup>Sm, the expected number of counts in the prompt peak. The γ-ray spectra for the two simulations are compared in the lower panel. The simulations shows that if the assumptions that went into the simulations, i.e. our best estimates before the experiment, would have been correct we could have seen the 2<sup>+</sup><sub>1</sub> → 0<sup>+</sup><sub>1</sub> γ ray in <sup>136</sup>Sm. However, the time resolution in the simulations (coming from the time binning used to create the histograms) were 8 ns, better than is expected from the experimental setup for γ rays at 255 keV. This is a possible explanation to the non observation in the experiment.
<figure><img src="image_202.png" /><figcaption>Figure 9.10: Upper panel: Simulated TAC between prompt γ rays and ions in the DSSD detector for simulations of all ion species and including β decay events (black) and only simulating the Coulex excitation events (red). Lower panel: Corresponding Dopper corrected γ-ray spectra when putting a condition on prompt coincidences corresponding to the interval [-8,0] ns.</figcaption></figure>

The simulated decay spectra are shown in figure 9.10, with shapes that are not very close to the experimental ones shown in figure 9.8. On the right panel in figure 9.10 the scaled experimental decay spectrum is also included. Apart from a missing peak, suggesting that the simulated cocktail is not correct, the intensity of the 114 keV line coming from the decay of <sup>136</sup>Sm is much smaller in the experimental data. This is the major part of the explanation of why we were not able to see any Coulomb exaction of <sup>136</sup>Sm in the experiment - the signal to noise ratio was just too low.
<figure><img src="image_203.png" /><figcaption>Figure 9.11: Simulated decay spectra. In the zoom on the decay of <sup>136</sup>Sm and <sup>136</sup>Pm the scaled experimental spectrum is also shown (in red). It is clear that in the experimental data the ratio of <sup>136</sup>Sm to everything else is much lower.</figcaption></figure>
# Chapter 10

## Lifetime measurements using
the RDDS method after
incomplete fusion

### 10.1 Proposal (as sent to the ALTO PAC)
TANDEM-ALTO
PROPOSAL FOR EXPERIMENT

PAC session :

February 2013

EXP # (Do not fill in):

Title: Lifetime measurements using the RDDS method after incomplete fusion

Is it a follow up experiment? [Yes/No]: No

If yes, experiment number:

Spokespersons (if several, please use capital letters to indicate the name of the contact person):

A. GOASDUFF, J. Ljungvall

Address of the contact person: CSNSM, bat. 108, 91405 Orsay – Campus, France

Phone:+33 169154564

Fax:

E-mail: alain.goasduff@csnsm.in2p3.fr

Address of a backup contact person:

Phone:+33169155528

Fax:

E-mail: joa.ljungvall@csnsm.in2p3.fr

Other Participants or Organisations:

G. Georgiev, Th. Konstaninopoulos, C. Sotty, CSNSM

S. Franchoo, I. Matea, M. Niikura, I. Stefan, D. Verney, IPN Orsay

A. Kusoglu – University of Istanbul, Turkeu

A. Blazhev, IKP Cologne

A. Gengelbacb, J. Nyberg, Uppsala University

M.-D. Salsac, IRFU CEA Saclay

E. Clément, GANIL

Short abstract:

We propose to measure the lifetimes of excited states in 71,72Zn using the RDDS method. The nuclei of interest will be populated using the reaction 7Li(70Zn, alphaxpyn), which we believe that the channels we will study will be produced mainly by incomplete fusion followed by particle evaporation. Particle transfer will also contribute to the cross sections. The experiment should allow us develop the use of incomplete fusion reaction together with the RDDS technique as a part of the preparation for future high-intensity radioactive beams. We should also be able to extract information on the interplay between collective and single particle degrees of freedom close to 68Ni.
**Beam line** (010, 110/PARRNe, 210, 320, 410, 420, 510.):

420

<table><tr><td><strong>Devices needed:</strong><br/>(mark with an X)</td><td>PARRNe</td><td>Bacchus</td><td>OSCAR</td><td>DIESE X</td><td>AGAT</td><td></td><td></td><td></td></tr><tr><td></td><td>Split Pole</td><td>ORGAM</td><td>X</td><td>DIESE</td><td>ESKIMO</td><td></td><td></td><td></td></tr><tr><td colspan="9">Other devices (specify):</td></tr></table>

<table><thead><tr><th>Fill in completely:</th><th>Ion(s)</th><th>Energy (MeV)</th><th>Intensity<br>(nAe or pps)</th><th>UT/beam</th><th>Pulsed beam<br>(yes/no<br>If yes specify time<br>structure)</th></tr></thead><tbody><tr><td>Tandem beam(s)</td><td>1.70Zn<br>2.<br>3.</td><td>190</td><td>10<sup>10</sup>pps</td><td>15</td><td>no</td></tr><tr><td>ALTO beam(s)</td><td>1.<br>2.<br>3.</td><td></td><td></td><td></td><td></td></tr><tr><td>ALTO source</td><td>1.<br>2.</td><td></td><td></td><td></td><td></td></tr></tbody></table>

<table><tr><td>Fill in completely:</td><td>Element / compound</td><td colspan="2">Target manufacturer</td></tr><tr><td>Targets</td><td>7Li – in what form to be decided</td><td>IPN<sup>1</sup></td><td>other<sup>2</sup></td></tr></table>

**TOTAL number of beam UTs Requested:**
(1 UT=8 hours):

Time (UTs) required for setting up the apparatus:
Time (UTs) needed for off-beam calibration and dismounting:

<table><tr><td>Acquisition<br>system:<br>(mark with an X)</td><td>Tandem</td><td>COMET</td><td>other</td><td>X</td><td></td><td></td><td></td><td></td></tr></table>

If other please specify:

<table><tr><td>SAFETY:</td><td>list any hazardous equipment or substances to be used, such as. radioactive target, liquid nitrogen, explosive gas, etc.,:</td></tr></table>

<table><tr><td>New devices:</td><td>List any NEW devices needed for this experiment which still have to be bought or manufactured:<br/>Liquid Nitrogen for HPGe filling<br/><br/>At what date do you expect these to be available?</td></tr></table>

<footnote n="1">¹ Please contact as soon as possible IPN target lab : petitbon@ipno.in2p3.fr</footnote>

<footnote n="2">² Please specify if empty target frames at Tandem standard are requested</footnote>
<table><tr><td>Special devices:</td><td>List any special devices needed for this experiment which would require to be mounted prior to the experiment (special target chambers, detector arrays, etc.):</td></tr><tr><td colspan="2">Oups plunger</td></tr><tr><td colspan="2">How long will it take to mount the particular device(s) once the area is available to you? 2 days</td></tr></table>

<table><tr><td>Status of previous Tandem/ALTO experiments:</td><td>Give the status of previous experiment(s) made by this group in the last 3 years at Tandem/ALTO: e.g. results from or status of analysis of previous experiments at Tandem/ALTO, list publications, conference presentations, PhDs awarded etc :</td></tr><tr><td colspan="2">ISI13 – “Test experiment for the CSNSM/IPNO/GANIL Plunger”, published NIM A N-SI-48, being analyzed<br/>N-SI-50 - “Probing the boundary of shape coexistence south of Z=82: Lifetime measurements of excited states in <sup>170</sup>Os using the RDDS method”, being analyzed</td></tr></table>

<table><tr><td>Additional comments:</td><td></td></tr><tr><td colspan="2"></td></tr><tr><td colspan="2"></td></tr></table>
# Lifetime measurements using the RDDS method after incomplete fusion.

## Abstract

We propose to measure the lifetimes of excited states in $^{71,72}$Zn using the RDDS method. The nuclei of interest will be populated using the reaction $^{7}$Li($^{70}$Zn,$\alpha$pyn), which we believe that the channels we will study will be produced mainly by incomplete fusion followed by particle evaporation. Particle transfer will also contribute to the cross sections. The experiment should allow us develop the use of incomplete fusion reaction together with the RDDS technique as a part of the preparation for future high-intensity radioactive beams. We should also be able to extract information on the interplay between collective and single particle degrees of freedom close to $^{68}$Ni.

## 1 Introduction

Large resources are presently invested into radioactive beam facilities around the world, with several such facilities already running and even more coming online in the decade to come. These radioactive beams will allow us to investigate excited states in nuclei that we hitherto have not been able to reach using combinations of stable targets and beams. Typical examples would be reactions with neutron-rich nickel or tin isotopes.

Model independent determination of electromagnetic transition probabilities has proved to be a very stringent test of nuclear structure models. As such it is important that the spectroscopy of poorly or completely unknown nuclei is not limited to that of the energy of excited states but that methods developed with stable targets and beams are transposed into the environment of radioactive beams. One of the most precise and reliable technique to measure lifetimes in the picosecond range is the recoil Distance Doppler Shift method (RDDS), also known as the plunger method. For this reason its use has been extended from the classical fusion-evaporation reactions to be used with several other production mechanisms such as multi-nucleon transfer[1], Coulomb excitation[2, 3] and induced fission reactions, often in inverse kinematics to be able to work with the expected target-beam combinations that are foreseen at the radioactive beam facilities. To the best of our knowledge, incomplete fusion reactions to reach neutron-rich nuclei using inverse kinematics have not yet been used together with the RDDS technique and $^{7}$Li target. Therefore there is an interest to develop this technique to widen the palette
of possible reaction mechanisms available at future radioactive beam facilities. Incomplete fusion reactions using $^{7}$Li have attracted a lot of attention in recent years for populating high-spin states in moderately neutron-rich nuclei[4, 5, 6, 7, 8, 9].

Using the combined target-beam planned for this proposal we expect to populate reaction channels such as $\alpha xn$ and $\alpha pxn$ with cross sections in the order of 1-2 mb, leading to slightly neutron-rich nuclei such as $^{71,72}$Zn. Lifetime measurements from this experiment can complement a fast-timing experiment performed in Bucharest 2010[10].

The neutron-rich even zinc isotopes are also of interest in the light of the increasing collectivity that has been noted as protons are removed from $^{68}$Ni, i.e. in moderately neutron-rich iron nuclei[11, 12], indicating a softness of the Z= 28 proton shell closure, but more importantly showing the importance of the $\nu d_{5/2}$ orbital for the development of collectivity in the region. It is of interest to see if the role of the $\nu d_{5/2}$ neutrons remains important on the other side of the proton shell-gap, i.e., for the zinc isotopes. Although several recent experiments have addressed this region conflicting results[13, 14] suggesting different structural interpretations motivates further measurements using different reaction mechanisms to populate the states of interests.

## 2 Goals of the experiment

The goal of the experiment is two fold:

* Development of the use of incomplete fusion reaction in inverse kinematics for RDDS measurements.

* To measure the lifetimes of excited states in $^{71}$Zn, and possible re-measure the $2_1^+$, $4_1^+$ in $^{72}$Zn using an alternative reaction mechanism to populate the states.

* Determine, with obvious experimental uncertainties, the different production cross sections.

## 3 Proposed experiment

### 3.1 Experimental details

We are proposing the reaction $^{7}$Li($^{70}$Zn,$\alpha$xpyn) with a beam energy of 190 MeV (10% higher than the Coulomb barrier) to populate excited states in Ga and Zn isotopes via incomplete fusion (higher Z nuclei will also be populated via $xn$ channels from complete fusion and will be the dominating channels). We will use the Orgam array consisting of 30 Compton suppressed HPGe detectors with a total efficiency of 3%. The Oups[15] will be used for the RDDS measurements. Particle detection is foreseen although an efficient way to detect alpha particles emitted during incomplete fusion is difficult due to their angular distribution which is shaded by the Plunger device[16]. We believe it is possible to detect $\alpha$ particles within the angular range $35^\circ \le \theta_{lab} \le 56^\circ$ using a segmented plastic detector available at CSNSM. Using a relatively low beam energy this detector
should be able to detect several tens of percent of the emitted $\alpha$ particles. We will use the plunger device together with a degrader foil rather than a stopper foil, this to allow a simple extrapolation to radioactive beams.

We will try to use both particle-$\gamma$, $\gamma\gamma$, and particle-$\gamma\gamma$ coincidences to clean the spectra from the dominating background from fusion-evaporation reactions, where dominating channels are of $xn$ type. Emitted $\alpha$ particles should also have lower energies.

In figure 1 $\gamma$-ray spectra for two different target-degrader distances are shown where $^{72}$Zn has been populated either via a fusion-evaporation reaction or via $2n$ transfer. Although the kinematics of these two reaction are not exactly that of an incomplete fusion reaction, together they should give an idea of the separation of $\gamma$-ray peaks that we can expect. A degrader of Mg has been used, this to allow the beam to exit the target area, an important feature for future use together with radioactive beams.

<figure><img src="image_204.png" /><figcaption>Figure 1: Gamma-ray spectra giving an idea of peak separation at $\theta = 46^\circ$ for two limiting reaction mechanisms in the reaction $^{7}$Li($^{70}$Se,$\alpha$p)$^{72}$Zn</figcaption></figure>

## 3.2 Count-rate estimates

The count-rate estimate is done for 1 mb, the expected cross section for the population of $^{72}$Zn. Assuming $1\text{mg/cm}^2$ of $^{7}$Li in the target and a beam intensity of $10^{10}$ particle per second gives a production rate of $100 \, ^{72}\text{Zn/s}$. Given the efficiency of about 3% and the need for using $\gamma\gamma$ coincidences we can expect about 0.1 good events per second.
For particle-γ coincidences we should get a factor of about 5 more cor-
responding to a detection efficiency of about 15 for the particle detection
that replaces the 3% of Orgam, giving about 1 good event per second.

For particle-γγ coincidences we can expect about 1 good event per
minute for the ⁷²Zn reaction channel.

3.3 Technical difficulties to overcome

There is a set of technical issues that makes this experiment difficult to
perform and requires additional investigations.

1. The target preparation: ⁷Li is usually prepared as LiF target, but such a target can not be used in a RDDS measurement. A suitable target therefore has to be developed.

2. The large background from pure fusion-evaporation reactions might, despite using γγ gating, drown the small signals we are looking for. Hence the use of a charged particle detector is envisaged and it should be incorporated in the experimental setup. We plan to use a segmented plastic detector already existing at CSNSM. However, in order to cover as large angles as possible for the α particle detection some modifications of the Plunger-plastic detector setup is foreseen.

4 Beam-time request

The beam-time request is made on the basis of extracting a result for
the lifetimes in ⁷²Zn. A statistical error of 5% would require at least 400
counts in each peak, or an optimistic 1000 good events. This suggest
that we should envisage to measure each Plunger distance for at least
1000 minutes, giving about 24 hours per distance. In order to be able to
judge the quality of a RDDS measurement there is a need for measuring
points at distances covering both short, long, and distances covering the
sensitive region. This can be done if at least 5 distances are measured.
We therefore ask for a total of five days of beam time. To summarize:
We ask for a total of 15 UTs, i.e. five days of a ⁷⁰Zn beam at
190 MeV.

References

[1] J. J. Valiente-Dobón *et al*, 2009 Phys. Rev. Lett. 102 242502

[2] A. Dewald et al., Phys. Rev. C 78, 051302(R) (2008)

[3] W. Rother et al. Nucl. Instrum. Methods A 654, 196 (2011).

[4] G.D. Dracoulis et al. J. Phys. G:Nucl. Part. Phys. 23, 1191 (1997)

[5] S.M. Mullins et al., Phys. Rev. C 61, 044315 (2000)

[6] A. Jungclaus et al., Phys. Rev. C 67, 034302 (2003)

[7] R.M. Clark et al., Phys. Rev. C 72, 054605 (2005)

[8] D.S. Judson et al., Phys. Rev. C 76, 054306 (2007)
[9] H. Watanabe et al., Phys. Rev. C 79, 024306 (2009)

[10] G. Georgiev, private communication

[11] J. Ljungvall et al. Phys. Rev. C 81, 061301(R) (2010)

[12] W. Rother et al., PRL 106, 022502 (2011)

[13] A. Obertelli, Private Communication.

[14] I. Celikovic, Zakopane 2012

[15] J. Ljungvall et al. Nucl. Instrum. Methods A 679, 61 (2012)

[16] B. Fornal, S. Leoni, et al. ISOLDE proposal
## 10.2 Experiment and outcome

The experimental setup was 17 HPGe detectors positioned in three rings at the angles 46.5°, 133.5°, and 157.7°. A segmented angular plastic detector downstream the target was used to detect the charged particles. This to have the γ-particle coincidence needed to select incomplete fusion in the background of fusion evaporation reaction channels.

### 10.2.1 Target issues

When the experiment was approved there was no clear decision taken on the target that was to be used. Based on experimentation at the target laboratory of IPN Orsay, the target used was finally a $Li_2SO_4$ target evaporated on a 0.8 mg/cm² Ni foil, with an uncertain thickness of the $Li_2SO_4$. Other failed attempts were

* Evaporation of LiF on 25 µm de Al: LiF attaches but Al too think for our measurement.

* Using Au (~2mg/cm2), the foils were destroyed or the LiF did not attach to the foil.

* Evaporation on Nd with a thickness 2 mg/cm2. The foils survived the evaporation but the LiF did not stick to the foils.

As a degrader a 5 mg/cm² Au foil was used.

### 10.2.2 Problems encountered during the experiment

There were some problems delivering the ⁷⁰Zn beam, making the effective time with beam on the target one day. Combined with problems with the Plunger feed back originating in the isolating qualities of the used $Li_2SO_4$ only data with long distances or with deliberate contact between the foils were taken.

### 10.2.3 Results and Conclusions

The experiment aimed at measuring lifetimes in ⁷²Zn populated via incomplete fusion. This in inverse kinematics to prepare for use with radioactive beams at, e.g., HEISOLDE, SPES or SPIRAL1/2 at GANIL. Without any particle-γ coincidence the γ-ray spectra are dominated by the Coulomb exaction of gold, nickel, and the ⁷⁰Zn beam. However, by demanding the prompt coincidence between the plastic detector and a HPGe detector (see figure 10.1), performing a background subtraction in time domain, and setting a gate on the energy detected in the plastic detector (see figure 10.2) γ-ray spectra containing reaction products are produced. As can be seen in figure 10.3 the spectra are dominated by fusion-evaporation products, in this case ⁷²Ga (106 keV, 165 keV, 393 keV...). Also shown in figure 10.3 are estimates of where γ rays from the first two excited states in ⁷²Zn should be seen. For the Ring 1, in the forward direction, the region of interest for the $2_1^+$ → $0_1^+$ transition (653 keV) is heavily contaminated with n,n' lines. However looking at ring 2 and ring 3, including the 847 keV from the ($4_1^+$) → $2_1^+$ transition a bit of imagination and there is some ⁷²Zn. It is however clear that in order to exploit the data a much better selection of events would have been needed.
<figure><img src="image_205.png" /><figcaption>Figure 10.1: Time difference between anular plastic detector and HPGe detectors</figcaption></figure>

<figure><img src="image_206.png" /><figcaption>Figure 10.2: Energy spectrum for Plastic detector in coincidence with prompt γ rays.</figcaption></figure>
<figure><img src="image_207.png" /><figcaption>Figure 10.3: Gamma-ray spectra for two distances separated by 750 µm. The arrows show the supposed location of the $2_1^+$ and $4_1^+$ in $^{72}$Zn before and after the Au degrader, respectively. Although it is not excluded that the lines are present they are too weak for lifetime analysis.</figcaption></figure>

As to how to improve the selection, this would go in the path of measuring the full kinematics of the outgoing particles and having discrimination between protons and $\alpha$ in the particle detector. As for the reaction products that were populated at a level to make lifetime measurements possible, the limited number of distances taken with the beam time given made limited these possibilities.