Nuclear physics line

NUC beamline

Beam line at 45º . The beam comes from the right. The cross in front host the vacuum gauge and the collimator and Faraday cage

Inside chamber of Nuclear beamline

Inside the chamber, one can see the target holder with three positions mechanically centered, two DSSD detectors place at backward angles upstream and downstream the Si-Li ball detectors.

Responsible scientist: O. Tengblad (IEM), Mª J. G. Borge (IEM)

The main activity nuclear physics line is the study of relevant nuclear reactions for astrophysics. The reactions of interest have, in general, extremely low cross sections and the detection includes charge particles and gamma radiation.

The nuclear physics line has an approximate length of 5 m and it is placed at the –30º angle port of the switching magnet. It is fully equipped and maintained by the Nuclear Physics group of IEM-CSIC. One can distinguish two parts, a first part corresponding to the beam line that allow the transport of ion beam from the switching magnet to the chamber and the second part corresponding to the vacuum chamber that hosts the different experimental setups [1]. In the following we will describe briefly both parts. Part 1 includes a beam profile monitor (BPM) to measure the profile of the incoming beam, a collimator and a Faraday cup to measure the beam intensity. From switching magnet there is a straight section of 40 cm then a DN63CF valve, another straight tube of about 125 cm that connects to a cross with support structure that allocate a 250 L/s vacuum pump, and vacuum gauges, a collimator and a Faraday cup to measure the beam intensity. A long the line there is another straight section that includes a tombac to facilitate the alignment of the chamber so that the beam will reach the center of the chamber. Details of the beam line and connection with the chamber are shown on the photo on the right-hand side of the figure.

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Considering the required flexibility and the constraint due to Rutherford scattering, the end of the beamline is equipped with a big versatile reaction chamber. The chamber contains several mounting points for different type of set-ups, depending on the specific experiment. The fixed setup contains a generic target ladder: the sliding shaft enters through the top flange of the chamber, providing up to 3 different positions for different targets, plus a faraday cup. This position, when selected, place the current reading right in the beam-spot, thus ensuring the right alignment of the beam. The target ladder allows for rotation around the vertical axis, enabling to avoid the angles shadowed by the target-frame, or to adjust the target effective thickness. Additionally, at the entrance of this chamber, there is a collimator with three different apertures (0.8, 1, 1.2 cm), similarly moved through a shaft mounted in a side flange.

All set-ups share a design able to avoid the very strong signal from Rutherford scattering that would mask the reaction channel of interest. Besides, the detector set-ups are easily interchangeable. For charged particle detection at forward angles, a setup of 14 Si 5 x 5 cm2 detectors, each divided into 4 subdetectors of 6.25 cm2 [2], is mounted conforming one quarter of a 15 cm radius sphere. The so-called Silicon-Ball has an angular coverage of 27º – 87º, covering a solid angle of 11.6% of 4p. At backward angles, a tight set-up of three double sided Si strip detectors is placed, covering from 82º to 171º, with an angular resolution of 3 degrees and solid angle coverage of 12.5 % of 4p. Different types of gamma detection systems can be added via flanges in various directions. The segmentation of the detectors leads to a large number of electronic channels (200). Integrated electronics of advanced technology is being used for read-out. The signals are, in case of scintillators and Ge detectors, digitized at the source (Mesytec MDPP-16 module), while for Si detectors a multiplexed highly integrated analogue system is used (Mesytec MDI-2 module). All units are controlled and data transported by a VME controller to personal computer via USB3 connection with a sustainable event rate of 1 MHz with negligible deadtime.

  • [1] “Diseño y Montaje de una línea en el acelerador de 5MV de la UAM para física Nuclear Experimental” (Design and assembly of the Nuclear Physics beam Line at the CmAm-UAM 5 MV Ion Accelerator) by Adolfo Sabán Iglesias. DEA (Diploma de Estudios Avanzados), UCM, 2003.
  • [2] L.M. Fraile, J. Äystö, Nucl. Instrum. Methods Phys. Res. A 513(1), 287 (2003). https://doi.org/10.1016/j.nima.2003.08.049

The Nuclear Physics beamline has a branch at the 45º port, NUC_45º beamline:

NUC_45º

This line, with a shorter optimum focus, is composed of a small beam-diagnostic chamber (equipped with a faraday cup and a micrometric target ladder with up to 5 positions), a collimating slit with 4 independent micrometric blades with current reading, and a narrow extension tube ending in a target flange only 6 cm wide. The extension tube is designed to allow high solid-angle coverage with external detectors. The tube region is isolated from the rest of the line by a manual valve to allow quick target exchanges. This line hosts one of the two complementary movable neutron detection systems: MINIBELEN [MON22] that is a 4π neutron counter with nearly flat response up to 10 MeV, and MONSTER [MAR14] based on BC501/EJ301 liquid scintillator modules which operate as a time-of-flight spectrometer. Both systems are also complemented by γ-spectroscopy measurements for (α,xnγ) reactions using an array of fast scintillators. Both systems are operated by the MANY collaboration. The MANY (Measurement of Alpha Neutron Yields and spectra) collaboration is an effort by Spanish research groups (IFIC, UPC, UCM, CIEMAT, US, IEM) with the aim to carry out measurements of (α,xn) reactions using CMAM (Madrid) and CNA (Seville) α-beams with different  physical motivations.

  • [MAR2014] T. Martinez et al., Nuclear Data Sheets 120 (2014) 78.
  • [MON22] N. Mont et al., Proceedings XXII Chilean Symposium of Physics 2020, in press, 2022. arXiv:2205.02147

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