FOOT has been designed to be a fixed target experiment: the beams of interest, with an energy of hundreds of MeV , impinge on a material representative of the human tissue (mainly hydrogen, carbon and oxygen) and the produced fragments are detected and measured by a multi-purpose detector .

The FOOT electronic setup aims to experimentally measure the production cross section of Z > 3 fragments in an angular aperture of 20°; its components are described below

Start Counter

The Start Counter is a scintillator foil of EJ-204 plastic, placed 30 cm before the target, that monitors the primary particles rate, gives the trigger signal for event acquisition, counts the number of primary particles and provides the event initial time. This last information, together with the time reported by the scintillator in the downstream region, provides the time of flight (ToF) measurement. Since the ToF measurement is crucial to achieve the desired mass ID resolution, the Start Counter aims for a time resolution of about 30-40 ps for the incoming beam particles.

Beam monitor

The Beam Monitor is a drift chamber composed by 12 planes of alternated horizontal and vertical wires and filled with Ar/CO2 80/20% gas. Thanks to its low density material, the drift chamber represent the ideal detector, since it minimize the multiple Coulomb scattering and the production of fragments within it. The function of the Beam Monitor is to measure the direction and impinging point of the ion beam on the target, that is necessary to address the pile-up ambiguity in the Vertex detector.


The Vertex detector (VTX) is a stack of four MIMOSA28 (M28) silicon chips belonging to the family of the CMOS Monolithic Active Pixel Sensors (MAPS), which are commonly used for experiments in particle and heavy ion physics. This detector is placed right after the target (about 0.5 cm) as the first tracking station of the magnetic spectrometer, it contributes to reconstruct the particle track in the magnetic field in order to measure the particle momenta and it evaluate the vertex position for each event, i.e. the position inside the target where the beam interacted, originating the fragments.


The Inner Tracker is the second detector of the tracking system located between the two magnets. Like the Vertex, the Inner Tracker is made of M28 chips. The structure employed is composed by ladders similarly to the ones implemented in the PLUME project: in the FOOT setup, each ladder is composed by two modules housing four M28 pixel sensors each. Four of these ladders are disposed in a way to implementing a double plane tracker.


The Microstrip Silicon Detector consists of three layers of orthogonally oriented silicon miscrostrips placed downstream with respect to the magnets and about 35 cm away from the target. As the final station of the tracking system, the purpose of this detector is to give information about the track position to contribute to the momentum reconstruction, but it also provide a measurement of the fragments energy loss.


The Scintillator detector is composed of two layers of 20 orthogonally oriented plastic scintillator bars (EJ200), each one 40 cm long, 2 cm large and 3 mm thick , coupled at both ends to up to four silicon photomultipliers (SiPMs) by means of an optical glue. The SCN has the purpose of measuring both the energy loss and the crossing time, in order to stop the ToF measurement. The energy resolution obteined ranges between 6% and 13%, while the resolution on time measurement is about 30-40 ps for carbon ions and higher than 100 ps for protons.


The calorimeter is the most downstream detector and it is composed of 288 crystal of bismuth germanate (BGO) read-out by SiPMs. This detector is designed to measure the kinetic energy of the fragments which are supposed to stop inside it. Recent tests demonstrated that a relative energy resolution ranging between 1-3% can be achieved.

Emulsions Setup

In order to measure light fragments (Z<3), which are distributed with
a wider angular aperture than the heavier ones, another experimental setup, based on emulsion films, is employed.

This setup shares the pre-target region (Start Counter and Beam Monitor) with the electronic setup described above, while the target, the tracking system, the scintillator and the calorimeter are replaced by an
Emulsion Spectrometer that allows the detection of fragments produced with an emission angle up to 70° with respect to the axis of the incident beam. The emulsion spectrometer is composed of three sections .

  • Vertex and tracking

This section consists of several elementary cells made of emulsion films interleaved with carbon or C2H4 layers 1 mm thick. These passive layers act as targets, while the emulsions reconstruct the interaction vertex position with a micrometric resolution.

  • Charge measurement

The second section is entirely composed of emulsion films with the aim of reconstruct the charge of light fragments. The elementary cell is made of three emulsion films, each of which is treated with a different refreshing, a procedure that consists of keeping the emulsions for an appropriate time at a relatively high temperature and relative humidity, in order to partially or totally erase the tracks. This method allows to enlarge the
dynamical range of the detector and identify particles with very different energy release (H, He and havier nuclei).

  • Energy and mass measurement

In the last section the emulsion films are interleaved with layers of an high-Z material (such as lead or tungsten), in order to make the particles stop in the detector. The purpose of this section is to determine the kinetic energy and the momentum of the particles by measuring their entire track, evaluating the range and the multiple Coulomb scattering. The knowledge of energy and momentum leads to the identification of the particle mass.