Astroparticles and Astrophysics

Experimental beam line
Experimental beam line

Counting setup
Counting setup
Relevant nuclear reactions for astrophysics
Contact persons: Tudor GLODARIU, Andreea OPREA

Majority of elements heavier than iron are synthesized via neutron capture processes known as s-(slow) and r-(rapid). However there are 35 p -nuclei along the valley of stability, between 74Se and 136Hg, that can't be produced by neutron those processes. These proton rich nuclei are produced by a combination of the (γ,n), (γ,p) and (γ,α) reactions on the existing s or r nuclei at temperatures around a few GK, characteristic of explosive environments.

To adequately describe the p-process nucleosynthesis, one needs reliable information on the thousands of reaction rates involved. In this respect, there is a considerable lack of experimental data on the relevant cross sections in the p-process energy range, because most γ -induced reactions are very difficult to measure directly. To overcome this difficulty, the charged particle induced reaction cross sections are measured and their inverse photodisintegration reaction cross sections are calculated using the detailed balance theorem. Experimental data for charged particle induced reaction cross sections are scarce above Fe. This is because for nuclei with Z>28 the energies of α -capture reactions are well below the Coulomb barrier, making the cross section very small and thus difficult to measure.

P-process studies are based mostly on the Hauser-Feshbach statistical model to predict the reaction rates which either over- or under-estimate the experimental data. Therefore, it is important to investigate the α -induced reaction cross sections experimentally to test the reliability of the statistical model prediction.

The main motivation of the present activity is to extend the experimental database by measuring with high precision the (α, γ) capture cross section on p-isotopes in the energy range close to the Gamow peak energy of each.

Activation technique consists in bombarding the target with α-particles to produce radioactive nuclei followed by the measurement of their specific activities after the irradiation has stopped.

The experiments are performed at 9MV Tandem Accelerator. The counting setup consists in two large volume high-pure germanium detectors (HPGe) with high relative efficiency (55% and 100%) placed head-on in a passive lead shielding. Due to the close detection geometry summing corrections are performed using the Monte Carlo simulation code GESPECOR.

References:
[1] I. Cata-Danil et al., Rom. Rep. Phys. 59, 1015 (2007).
[2] I. Cata-Danil et al., Phys. Rev. C 78, 035803 (2008).
[3] I. Cata Danil et al., Rom. Rep. Phys. 60, 555 (2008).
[4] M. Ivascu et al., Rom. Journal of Physics 55, 9 (2010).
[5] D. Filipescu et al., Phys. Rev. C 83, 064609 (2011).
[6] I. Gheorghe et al., Nuclear Data sheets 119, 245 (2014).

WILLI Detector
WILLI Detector

Analysis Tool Willi
Analysis Tool for WILLI Detector

Astroparticles - WILLI Detector
Contact persons: Bogdan MITRICA

Primary cosmic rays, penetrating from the outer space into the Earth's atmosphere initiate the development of a phenomena called Extensive Air Showers (EAS) by the multiple production of secondary particles due to cascading interactions of the primary particle with atmospheric nuclei. The secondary radiation establishes an essential feature of our natural environment and affects material and biological substances situated on the atmosphere, on the Earth surface or underground. The muons from the EAS are deeply penetrating long living particles which can influence natural and human made systems along their trajectory. While positive muons are merely scattered in matter by weak and electromagnetic forces, negative muons, after forming muonic atoms, can be absorbed by atomic nuclei and excite them in the continuum, thus emitting secondary nuclear products, in particular neutrons. Effects, which result in this way from the irradiation with the inclusive muon flux, produced by cosmic rays in the Earth's atmosphere, are a particular class of natural radiation effects in our environment and of cosmogenic isotope production. More general such effects comprise all influences of the various particle components of extended air showers (EAS) induced by primary cosmic rays.

The WILLI detector, built in IFIN-HH Bucharest measures the muon charge ratio by the effective lifetime of muons stopped in the detector.
The bulk of the detector consists of 16 scintillator modules for recording the energy and time signature of the muon and 4 scintillator modules in vertical position, on each side of the stack, acting as anticounters. Thus the muon trajectory and the electron produced by its dezintegration produce a clear signature used for determination of energy, direction and decay time of the muon. The anticounters are used to determine events which have the full history contained in the detector that is any time an anticounter fire the event is rejected.
All counters are made of a 1 cm thick aluminium plate and a plastic scintillator (NE 114) of 90 x 90 x 3 cm3 closed by an aluminium cover of 2 mm. All counters are installed in a rotatory frame such that the whole set-up can be used for measurements in all zenith and azimuthal directions.

WILLI detector applies an accurate method to specify the contributions of negative and positive muons. The charge ratio of muons contained in the detector is found using the total decay curve measured for all muons stopped in the detector. This decay curve is a superposition of several decay laws specific to materials of which the detector is build. The measurements are compared to a theoretic calculation based on CORSIKA and GEANT simulations. The muon charge ratio is obtained by fitting the measured decay spectrum with the theoretical curve. The results of the measurements are particularly robust due to the new detection system which reduce systematic errors and to a very good muon identification (90 % efficiency). These particular advantages of our detecting system are obtained due to the simplicity of our experimental method which need no monitoring for the detection components (e.g. magnetic fields in magnetic spectrometers) and respectively to the fine time sampling of 50 ns.

HPGe detector
Figure 1. Accelerator beam line for Cross Section Measurements

GammaSpec, NAG and μBq Laboratories
Figure 3. GammaSpec, NAG and μBq Laboratories

Nuclear Astrophysics Group
Contact persons: Livius TRACHE

NAG is a group in DFN working in experimental nuclear physics for astrophysics. To accomplish our work, we cooperate locally with colleagues from the accelerator department DAT, from DFNA, and with one theoretician from DFT. We also collaborate with fellow experimentalists and theoreticians from different laboratories outside Romania, on 3 continents: Texas A&M University (TAMU), Louisiana State University (LSU), Washington University at St. Louis (WU), ATOMKI Debrecen and RIKEN, Wako, INFN Pisa.

NA work in IFIN-HH is briefly described in a recent paper: http://iopscience.iop.org/article/10.1088/1742-6596/703/1/012028/pdf.
NAG was established and built after 2012. http://iopscience.iop.org/article/10.1088/1742-6596/703/1/012011/pdf
Activities are concentrated in two types of experiments and their interpretation:

  • A. Direct measurements using IFIN-HH's own installations.
  • B. Indirect measurements for Nuclear Astrophysics using RIBs in international nuclear physics centers
  • A. Direct measurements for Nuclear Astrophysics

    In 2013 and 2014 it became clear that doing direct measurements for nuclear astrophysics may be a possibility afforded by the newly installed 3 MV tandetron accelerator of IFIN-HH, which was just installed at the time. The idea of coupling it with the use of the ultra-low background laboratory that IFIN-HH has in the salt mine at Slanic-Prahova turned out to be a valuable one that makes the group competitive in this field. The accelerator tests of 2013 and the experiments of 2014, 2015 and 2016 proved the idea correct: this combination makes the group competitive for direct measurements with alpha particle and light ion beams [1, 2]. These "home experiments" turned out also to be an excellent training opportunity for the young students in the group. The main emphasis was on the experiment 13C+12C, which was done with groups from China (IMP Lanzhou, and CAS Beijing) and from the departments of IFIN-HH: DAT, DFNA and DFVM.

    During the experiment, the 13C beam in the laboratory energy range of Elab= 11.0 – 4.6 MeV (Ecm=5.28-2.21 MeV), with steps of 0.2 MeV, impinged on 1.5 mm thick natural carbon targets. Intensities in the range of 0.02-15 pµA were used in different runs. We did activation measurements (both in Magurele and in the salt mine in Slanic) and in-beam prompt gamma-ray measurements.

    The prompt emission spectra were measured using a spectroscopy system consisting of a coaxial high-purity germanium (HPGe) detector, signal amplifier and a multichannel analyzer. The experimental set-up is shown in Figure 1. The HPGe detector used is a 100% efficiency (relative to a standard 3”x 3” NaI crystal) detector. The detector was placed at 550 in extension of the reaction chamber of accelerator Cross Section Measurements line at 13 cm distance of Faraday cup. The radioactive sources and the targets were placed in an iron flange of 2.3 cm thickness. The HPGe detector was shielded along its length and on the front face with 5 cm thick lead bricks.

    The proton cross the 12C(13C, p)24Na fusion reaction was determined through the measurement of the gamma-ray yield following the beta-decay of 24Na (T1/2=15 h) at the low background laboratory GammaSpec (at ground level in IFIN-HH), in NAG's own setup and in the ultra-low background laboratory μBq in Unirea salt mine at Slanic [3, 4]. At μBq a significant reduction of radiation background compared with GammaSpec and NAG occurs (see Figure 2).

    Figure 2. Comparison between collected background from laboratories(NAG, GammaSpec and µBq)

    In these laboratories, the cascading gamma rays (1369 and 2754 keV) were detected with shielded HPGe detectors with 100% relative efficiency (at NAG), 30% (at GammaSpec) and 120% (at µBq in the salt mine). To calibrate the detectors in efficiency we used sources with well known activities, like: 153Eu, 133Ba, 60Co, 137Cs, 241Am.

    Schematic presentation
    Figure 4. Schematic presentation of the relation allowing the use of beta-delayed proton decay in resonant proton capture.

    B. Indirect methods

    B.1. Beta-delayed proton decay
    The resonant capture of protons is a two-step process where the proton incident on a nucleus populates first a metastable state in the compound nucleus (1st step) that then de-excites (2nd step) by gamma-ray emission. The corresponding astrophysical reaction rates are given by the properties of the narrow, isolated resonances only: spin and parity, energy and resonant strength ωγ. To study these resonances at astrophysical energies by direct measurements is not always easy or even possible. An alternative is to populate the same metastable states and determine their spectroscopic properties by other means. One way is the decay spectroscopy: we chose an exotic nucleus that will beta-decay to these same states. These are schematically illustrated in Figure 4.

    We have studied β-delayed proton decay (βp) at Texas A&M University using ASTROBOX2, an improved version of and early gas detector ASTROBOX-1, both developed with TAMU and CEA/IRFU Saclay. A clone of this new detector is being worked on at IFIN-HH, for use in European laboratories ASTROBOX2E.

    B.2. The breakup of 9C
    In 2001 we proposed to use nuclear breakup data to determine the ANC (Asymptotic Normalization Coefficients) for the breakup of nuclei Y->X+p and from there to evaluate the astrophysical S-factors for radiative proton capture reactions X(p,g)Y. Important NA reactions data like S17 [5,6] and S18 [7] were evaluated using data from literature. Later a dedicated experiment at GANIL was used to obtain NA data for the reactions 22Mg(p,γ)23Al [14] and 23Al(p,γ)24Si [9].
    In proposal NP1412-SAMURAI29R1 approved by the PAC of RIBF at RIKEN, Wako, Japan, we use the same scheme: the breakup of 9C at 300 MeV/nucleon to evaluate the astrophysical S-factor for radiative proton capture on 8B. The experiment is part of a group of four approved proton breakup measurements and scheduled, tentatively, in the fall of 2017.

    B.3. Trojan Horse Method measurements
    Trojan Horse Method was introduced and demonstrated as a valuable method for NA by the group of prof. Claudio Spitaleri from the University of Catania and INFN LNS. They have proposed and test measurements were done in collaboration in Bucharest, at the 9 MV FN tandem accelerator together with us to check if the reaction 12C + 12C can be studied using the Trojan Horse Method. The reaction proposed was 12C(16O,α20Ne)α. The test was done using an 16O beam on 12C targets, but the answer was NO, the method cannot be used for this reaction.

    B.4. Optical Model Potentials for nucleus-nucleus collisions
    We have a long-term program to understand and describe nucleus-nucleus collisions in terms of one interaction potential, the optical model potential (OMP). LT has worked on the problem for almost two decades with dr. F. Carstoiu. The motivation is that a good understanding of all phenomena occurring in the elastic nucleus-nucleus scattering, which are used typically to extract OMP, and the interpretation of the origin of different aspects, including the well know potential ambiguities, are of crucial importance for finding and justifying the procedures used for predicting nucleus-nucleus OMP in the era of radioactive nuclear beams (RNB) (see ours based on double folding in Ref. 10). The reliability of these potentials is crucial in the correct description of a number of reactions, from elastic to transfer, to breakup, at energies ranging from a few to a few hundred MeV/nucleon. Of particular interest for us is to support the absolute values of the calculated cross sections for reactions used in indirect methods for nuclear astrophysics, see references [11,12] for the most recent results.


    References:
    [1] Daniela Chesneanu, L. Trache, R. Margineanu, A. Pantelica, D. Ghita, M. Straticiuc, I. Burducea, A. M. Blebea-Apostu, C. M. Gomoiu, and X. Tang, AIP Conference Proceedings 1645, 311 (2015).
    [2] I. Burducea, M. Straticiuc, D.G. Ghita, D.V. Mosu, C.I. Calinescu, N.C. Podaru, D.J.W. Mous, I. Ursu, N.V. Zamfir, Nuclear Instruments and Methods in Physics Research B 359, 1219, 2015.
    [3] R. M. Margineanu, C. Simion, S. Bercea, O.G. Duliu, D. Gheorghiu, A. Stochioiu and M. Matei, Appl. Radiat. Isot. 66, 1501 (2008).
    [4] D. Tudor, A.I. Chilug, M. Straticiuc, L. Trache et al., in C. Spitaleri, L. Lamia and G.R. Pizzone (eds.), Proceedings of the 8th European Summer School of Physics on Experimental Nuclear Astrophysics (Santa Tecla School), J. of Phys: Conf Series, vol. 703 (2016) 012028.
    [5] L. Trache, F. Carstoiu, C.A. Gagliardi and R.E. Tribble, Phys. Rev. Lett. 87, 271102 (2001).
    [6] L. Trache, F. Carstoiu, CA Gagliardi and RE Tribble, Phys. Rev. C 69, 032802 (2004).
    [7] L. Trache, F. Carstoiu, CA Gagliardi and RE Tribble, Phys. Rev. C 66, 035801 (2002).
    [8] A. Banu et al., Phys. Rev. C 84, 015803.
    [9] A. Banu et al., Phys. Rev. C 86, 015806
    [10] L. Trache et al. Phys. Rev. C 61, 024612 (2000).
    [11] T. Al-Abdullah, F. Carstoiu, X. Chen, H. L. Clark, C. A. Gagliardi, Y.-W. Lui, A. Mukhamedzhanov, G. Tabacaru, Y. Tokimoto, L. Trache, R. E. Tribble, and Y. Zhai, Phys. Rev. C 89, 025809 (2014).
    [12] T. Al-Abdullah, F. Carstoiu, C. A. Gagliardi, G. Tabacaru, L. Trache, and R. E. Tribble, Phys. Rev. C 89, 064602 (2014).

    Carpathian Summer Schools of Physics
    NAG was also instrumental in the organization of the most recent editions of the Carpathian Summer Schools of Physics, a tradition that begun in 1964. Six out of the 7 latest editions were a series dedicated to nuclear and particle astrophysics, in relation to nuclei and to physics of exotic nuclei in particular. The Carpathian school is part of the European Network of Nuclear Astrophysics Schools (ENNAS), together with the European Summer School on Experimental Nuclear Astrophysics, ESSENA (Santa Tecla, Italy) and the Russbach School on Nuclear Astrophysics, RSNA (Russbach am Pass Gschütt, Austria). In agreement with those schools’ organizers, we created an established network of periodic events that responds to the need of preparing and educating the younger generations of physicists in the cross disciplinary fields of nuclear physics and astrophysics.
    Below are links to the latest editions of CSSP:
    CSSP 2012 , CSSP 2014, CSSP 2016



    Group leader: Dr. Livius Trache
    Senior Researcher 1
      Livius Trache
       
    Dr. Florin Carstoiu
    Senior Researcher 1 (Department of Theoretical Physics)
    The collaboration with dr. Carstoiu, which lasts for over 20 years, continued. LT and dr. Carstoiu continued working together on subjects from NA or on related projects. Of prime and immediate concern was to finalize by publication work which was done earlier, either at Texas A&M University or elsewhere. This resulted in 7 papers in 2013-2016.
       
    PhD Student Alexandra Chilug
    Research Assistant
      Alexandra Chilug
       
    PhD Student Dana Tudor
    Research Assistant
      Dana Tudor
       
    Ionut Catalin Stefanescu, MS
    Physicist
      Ionut Catalin Stefanescu
       
    Madalina Ravar
    Undergraduate student
      Madalina Ravar