Nuclear physics facilities

The Accelerator Laboratory hosts two recoil separators mainly used in the study of nuclei produced in fusion-evaporation reactions. RITU is a gas-filled recoil separator suited to the study of heavy and superheavy nuclei, whilst MARA is a recoil-mass spectrometer better suited to the study of nuclei with masses below 150.

RITU gas-filled recoil separator: RITU is based on a standard DQQ magnetic configuration, with an extra vertically focusing quadrupole magnet in front of the dispersive element added, thus giving it a QDQQ configuration (see table opposite for detailed specifications). This gives an angular acceptance of 10 msr, the maximum rigidity is 2.2 Tm, the bending angle is 25 degrees, and the dispersion is 10 mm. The construction of the RITU separator was finished during 1994 and a wide-ranging experimental program was started. Alongside the strong experimental program, technical development work for the separator has continued. A differential pumping system was implemented, allowing windowless operation, hence improving beam focussing. Also a new dipole chamber was installed into RITU, which reduced the amount of scattered beam at the focal plane and therefore lowered the overall background.

MARA (Mass Analysing Recoil Apparatus): MARA is a vacuum mode recoil separator with the ion-optical configuration QQQEDMD. MARA complements the capabilities of the RITU gas-filled recoil separator and extends the region of accessible nuclei down to lighter masses, and to cases where mass resolving power is required to select the nuclei of interest. The mass resolving power is of the order of 1/350 (FWHM).

A number of devices are available which can be used for detection of gamma rays, internal conversion electrons and charged particles emitted from nuclei produced in nuclear reactions or from decay processes. The devices listed here are aimed at so-called "in-beam spectroscopy" whereby the devices are positioned surrounding the reaction target and detect prompt radiation from the reaction.

JUROGAM3: JUROGAM3 is an array of Compton-suppressed HPGe detectors which has been constructed for use at the target position of the RITU or MARA recoil separators. The detectors (Eurogam clover, Eurogam Phase I and GASP -type) have been provided by the GAMMAPOOL collaboration. The support structure and frame of the array are from the earlier implentations of EUROGAM, which was situated at Daresbury Laboratory in the U.K., and at IReS Strasbourg in France. The frame has been modified such that it can be opened in a direction perpendicular to the beamline and moved between the target positions of the two separators. This enables access to the target chamber, and allows the use of high intensity beams for decay spectroscopy.

A number of ancillary devices, can be used in combination with JUROGAM3:

• LISA (Light Ion Spectrometer Array)
• SAGE (Silicon And GErmanium) Spectrometer
• DPUNS plunger
• SPEDE (SPectrometer for Electron Detection)

There are three beamlines available for nuclear reaction studies and test experiments in the recently expanded LSC cavern. One line is equipped with a 1.5 m diameter Large Scattering Chamber. More information on our research is available here.

Selected papers with technical information on the LSC:

• W.H. Trzaska et al., High-resolution scattering experiments at the K130 cyclotron in Jyväskylä, NIMA 903 (2018), 241-245
• W.H. Trzaska et al., New experimental stopping power data of 4He, 16O, 40Ar, 48Ca and 84Kr projectiles in different solid materials, NIMB 418 (2018) 1–12

Focal plane outline

• GREAT spectrometer (Sub Directory)
• MARA focal plane (Sub Directory)
• RITU focal plane (Sub Directory)

The MARA-LEB facility is an extension to the MARA separator. It takes advantage of MARA's selectivity to study medium-heavy nuclei whose production is overwhelmed by other less exotic species. The main area of interest for MARA-LEB is the N=Z line, close to the proton drip line. This area is a fertile ground to test the predictions of the shell model, investigate the interaction between the proton and the neutron, and to further explore nuclear shape coexistence. 

Research performed using MARA-LEB will not only be of interest for fundamental nuclear physics, but will also be of importance for astrophysics, as the region of interest is at the heart of the rapid proton capture process that occurs in stars.  

Ion Transport System

The MARA-LEB transport system is a series of ion-optical devices that serve as the way of moving the ions produced by MARA and selected at the gas cell to the detector stations located on the second floor of the facility. 

The first stage of the transport system is a series of radio frequency quadrupole (RFQ) ion guides. These are linear Paul traps formed by a series of electrodes that combine direct and alternating currents to confine ions and direct them to acceleration electrodes downstream.

After the RFQ guides, an Einzel lens focuses the beam into an acceleration electrode that progressively increases the ions' velocity using an electric field of 30 kV. 

After acceleration, the ions are mass-selected by a very powerful dipole magnet, which also changes the ions' travelling direction upwards, through the vertical line and into an electrostatic deflector, which will again bend the ions by 90º into the experimental stations, while also providing additional mass and energy selectivity.