Future Perspectives for Surrogate-Reaction Studies at Storage Rings
213
allowing to separate the different heavy “beam-like” products formed after γ-ray or
particle-emission by the compound nucleus and detect them in coincidence with the
target-like residues. Thanks to inverse kinematics, fission fragments and beam-like
products are emitted in forward direction, which results in detection efficiencies
that are close to 100%, much larger than in the traditional direct kinematics
measurements.
4 Developments Towards a New Set-up
The vast experience of CENBG with solar cells [5, 13] as fission and/or heavyion detectors has triggered the investigation of solar cells as heavy-ion detectors
at high energies. Indeed, the common solar cells found at the rooftops have been
used to detect heavy ions at low energies about 1 MeV/u for several decades [14–
16]. They are considered a good and cost-efficient alternative to Si detectors, due to
their radiation resistance properties [16], making solar cells an attractive detection
system. However, solar cells response to heavy ions of about 10 MeV/u and their
compatibility to UHV must be investigated.
The energy, time and radiation resistance response of solar cells to more energetic
heavy-ion beams were studied in three experiments carried out at the GANIL
facility in Caen, France. The beam isotopes of choice ( 84 Kr and 129 Xe) represented
examples of fission fragments and the energy of the beams ranged from 2 to
15 MeV/u, as expected in inverse kinematics. The studies considered several types
(common rooftop and for space applications) of cells of different sizes (from 5 × 5
mm 2 to 30 × 30 mm 2 ). The size of the cell has implications in the cell capacitance
influencing the electrical circuit that will follow, i.e. the impedance matching with
the pre-amplifier. The solar cells were placed in a rotating stainless-steel support
that could hold up to nine cells. The set-up containing the cells was placed just after
the GANIL cyclotron CIME. A gas profiler allowed us to evaluate the beam spot
size, typically of 5 mm and 7 mm in x and y directions, respectively. Each cell at its
turn was placed perpendicular to the beam.
The characterization of the solar cells included investigating energy and time
resolution and radiation resistance. The time resolution was measured by recording
the time difference between the frequency of CIME and the cell signal with a
Time to Digital Converter (TDC). Our preliminary results indicate that smaller cells
exhibit a better time and energy resolution. For example, a 5 × 5 mm 2 cell exposed
to 129 Xe beam of 10 MeV/u revealed an energy resolution E/E of 1.4% (RMS)
and a time resolution of 4.0 ns (FWHM) (Fig. 3). While the energy resolution is
lower when compared to a Si detector, the time resolution is indeed comparable.
One of the most interesting features of solar cells is their radiation hardness.
Several cells were irradiated at different rates from 1.5 kHz to 1.4 MHz and their
response with the number of events, as shown in Fig. 4. This figure shows the effect
of irradiating a 10 × 10 mm 2 cell with 703 k particles per second during 1 h with
an 84 Kr beam at 15 MeV/u. In the energy response, there is a decrease in amplitude
213
allowing to separate the different heavy “beam-like” products formed after γ-ray or
particle-emission by the compound nucleus and detect them in coincidence with the
target-like residues. Thanks to inverse kinematics, fission fragments and beam-like
products are emitted in forward direction, which results in detection efficiencies
that are close to 100%, much larger than in the traditional direct kinematics
measurements.
4 Developments Towards a New Set-up
The vast experience of CENBG with solar cells [5, 13] as fission and/or heavyion detectors has triggered the investigation of solar cells as heavy-ion detectors
at high energies. Indeed, the common solar cells found at the rooftops have been
used to detect heavy ions at low energies about 1 MeV/u for several decades [14–
16]. They are considered a good and cost-efficient alternative to Si detectors, due to
their radiation resistance properties [16], making solar cells an attractive detection
system. However, solar cells response to heavy ions of about 10 MeV/u and their
compatibility to UHV must be investigated.
The energy, time and radiation resistance response of solar cells to more energetic
heavy-ion beams were studied in three experiments carried out at the GANIL
facility in Caen, France. The beam isotopes of choice ( 84 Kr and 129 Xe) represented
examples of fission fragments and the energy of the beams ranged from 2 to
15 MeV/u, as expected in inverse kinematics. The studies considered several types
(common rooftop and for space applications) of cells of different sizes (from 5 × 5
mm 2 to 30 × 30 mm 2 ). The size of the cell has implications in the cell capacitance
influencing the electrical circuit that will follow, i.e. the impedance matching with
the pre-amplifier. The solar cells were placed in a rotating stainless-steel support
that could hold up to nine cells. The set-up containing the cells was placed just after
the GANIL cyclotron CIME. A gas profiler allowed us to evaluate the beam spot
size, typically of 5 mm and 7 mm in x and y directions, respectively. Each cell at its
turn was placed perpendicular to the beam.
The characterization of the solar cells included investigating energy and time
resolution and radiation resistance. The time resolution was measured by recording
the time difference between the frequency of CIME and the cell signal with a
Time to Digital Converter (TDC). Our preliminary results indicate that smaller cells
exhibit a better time and energy resolution. For example, a 5 × 5 mm 2 cell exposed
to 129 Xe beam of 10 MeV/u revealed an energy resolution E/E of 1.4% (RMS)
and a time resolution of 4.0 ns (FWHM) (Fig. 3). While the energy resolution is
lower when compared to a Si detector, the time resolution is indeed comparable.
One of the most interesting features of solar cells is their radiation hardness.
Several cells were irradiated at different rates from 1.5 kHz to 1.4 MHz and their
response with the number of events, as shown in Fig. 4. This figure shows the effect
of irradiating a 10 × 10 mm 2 cell with 703 k particles per second during 1 h with
an 84 Kr beam at 15 MeV/u. In the energy response, there is a decrease in amplitude