RITU

    RITU (Recoil Ion Transport Unit) is a gas-filled recoil separator used to select recoiling nuclei from primary beam like products after fusion evaporation reactions.

    RITU was proposed to be constructed at the end of the 1980’s when the new accelerator laboratory at JYFL was being planned. The ion optical design was based on experience from earlier gas-filled devices, mainly from SASSY at LBNL. The main goal was to increase the transmission of the traditional DQQ magnetic configuration even further by adding a small quadrupole magnet in front of the dispersive element. (See table opposite for detailed specifications). This led to 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 1993 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.


The GREAT Spectrometer

    Gamma:

Gammas arrays are detected either decaying from an isomeric state or subsequent to charged particle decay. They are detected in a segmented clover Ge detector and/or a planar Ge detector.

    Recoil:

The recoiling nuclei that pass through RITU are detected in a MWPC (multi-wire proportional counter) and are implanted in DSSDs (double -sided silicon strip detectors).

    Electron:

Conversion electrons are detected either decaying from an isomeric state or subsequent to charged particle decay. They are detected in the DSSDs or the PIN-diode box surrounding the DSSDs.

    Alpha:

Alpha decays are detected in the DSSDs.

    Timing:

A TDR (total data readout) trigger less data acquisition system was designed for this system.

    The GREAT spectrometer was a UK University funded project. The spectrometer was installed at the RITU focal plane in 2002. The official GREAT spectrometer homepage can be found by clicking on the picture opposite. This page contains a brief description of the spectrometer and its current status.

    The GREAT spectrometer is a composite array comprised of various Si and Ge detectors. The heart of the spectrometer is made of two DSSDs (double sided silicon strip detectors) for the implantation of recoiling nuclei and the detection of their charged particle decay, which is typically alpha decay or the more rare proton decay. The DSSDs are each 60×40 mm with a strip pitch of 1 mm giving a total of 4800 1 mm² pixels. The thickness of these detectors is dependent of the decay mode of the nuclei of interest. At present, three thicknesses are available: 100 µm for proton decay studies, 300 µm for alpha decay studies and 700 µm for beta decay studies.

 

    Directly up-stream (with respect to the beam direction) from the DSSDs is a box of PIN diodes. They are 28×28 mm in size with a thickness of 500 µm and form two rings of 14 detectors around the DSSDs. Their purpose is to detect either conversion electrons or escaping alpha particles. Up-stream from the DSSD by ~20 cm is a MWPC (multi-wire proportional counter) giving a position and energy loss signal, as well as being the start of a TAC, for which the DSSDs are the stop, hence giving a TOF (time of flight) between the two. Down-stream from the DSSDs by only 3 mm is a segmented planar germanium detector. It has a 500 µm Be entrance window so to minimise the attenuation of X-rays and low energy gamma rays. It is 12 cm wide, 6 cm high, 1.5 cm thick and has a strip pitch of 0.5 cm. Directly above the GREAT chamber is a segment Clover Ge detector used for the detection of higher energy gamma rays.