α-Particle Detection Systems Overview

α-particle detection

• The detector utilizes isobutane gas at a pressure of 4 Torr with an operating voltage of +540 V on the anode and −180 V on the cathode.
• The detector consists of holes of 1 mm diameter placed 5.08 mm apart in a rectangular matrix.
• Position resolution of ∼1.1 mm has been observed for α particles.
• The detector system is used for studying the fission mass distribution and fission-gated neutron multiplicity for various systems.
• The detector is operated at 1.5 Torr isobutane with an operating voltage of +400 V on the anode and −180 V on the cathode.
• At forward angles the count rates exceed 20 kHz.
• A timing resolution of ∼2.5 ns is observed for beam-like elastics.
• Time resolutions are expected to be better (∼1 ns) for fission fragments due to higher amplitude pulse.

HIRA and HYRA Focal Plane Detector Systems

• HIRA (electromagnetic separator) and HYRA (gas-filled separator) are used to detect fusion evaporation products or evaporation residues (ER).
• Multi-wire proportional chambers (MWPCs) are used at the focal plane of both spectrometers to detect ER's which focus the products and suppress primary beam-like particles.
• HIRA focal plane detector has a five-electrode geometry.
• HYRA focal plane MWPC uses four-electrode geometry by removing the last cathode.
• Both MWPCs are operated with isobutane gas at pressures between 1 to 3 Torr.
• The gas medium is isolated from the vacuum using a 0.5 μm Mylar entrance window, transparent to heavy recoils with A ∼200 and above.

HYRA Focal Plane Detector System

• A position-sensitive large-area silicon detector follows the HYRA MWPC.
• The silicon detector provides the energy of the implanted ER.
• The detectors can be stacked to create a larger detection area at the focal plane.
• The position-sensitive large-area silicon detector can be either a strip detector or resistive anode detectors.
• The Eurysis/Canberra resistive anode detectors are stacked to provide an active area of 15 × 5 cm2.

Time-Zero MWPC

• A transmission-type fast timing MWPC is used in combination with large-area position-sensitive MWPCs to obtain absolute timing of fission fragments and extract their mass-energy distributions.
• The detector can be used as a trigger in multidetector setups for measuring neutrons and γ rays in coincidence with fission fragments.
• The detector uses four electrodes made from wire frames, with a separation of 0.63 mm between adjacent wires.
• The detector is operated with isobutane gas at 2–4 mbar pressure.
• The anode is read using a fast timing amplifier and the cathode is read by a charge-sensitive preamplifier.
• The detector was tested offline with radioactive sources 241Am and 252Cf.
• The detector was operated with 3 mbar of isobutane gas pressure.
• A bias voltage of +450 V and −180 V was applied at the anode and the cathode, respectively.
• To evaluate the timing performance, TOF was set up between the time-zero and large-area MWPCs.
• The large-area MWPC acts as a stop detector.
• The distance between the two MWPCs is 15 cm.
• A neutron detector is placed at a distance of 1 m from the source to collect coincident neutrons and γ rays.
• The detector was used in an experiment to study the mass distribution for the 6,7Li + 238U system at 30–50 MeV energies.
• The start MWPC was placed at a distance of 7.5 cm from the target on one of the GPSC arms followed by a large-area position-sensitive MWPC.
• The second MWPC was placed on the other arm.
• The time-zero detector provided a master trigger for all timing signals such as TOF for the two position-sensitive MWPCs and their position signals.
• The electronic delay between the start and the stop detectors was determined using monoenergetic α particles from the 241Am source.

Hybrid Telescopes for Heavy-Ion Detection

• Hybrid telescopes, combining gas and silicon detectors, have been developed for heavy-ion detection and particle identification.
• The detector system is used for studying the angular distributions of fission fragments and can be used to identify projectile-like fragments to study transfer reactions.
• Silicon telescopes with very thin (10 μm) silicon detectors ( E) and thick (100–300 μm) (E) are used for particle identification.
• The 10 μm-thick detectors are opaque to low-energy heavy ions such as fission fragments.
• The telescope is composed of a gas ionization chamber, operating in the axial field geometry mode, which is followed by a silicon detector.
• The ionization chamber (IC) is composed of three wire frames of 10 mm active diameter.
• The wire frames consist of a cathode, a central anode frame and another cathode wire frame.
• The distance between adjacent wire frames is 10 mm.
• All wire frames are made from gold-plated tungsten wires of 20 μm diameter with 1 mm separation between adjacent wires.
• The two cathodes are grounded whereas the anode operates in the ionization region at 150 V with a gas pressure of 100 mbar isobutane (2.5 μm Si equivalent).
• The entrance foil is 1 μm Mylar (diameter 10 mm).
• The anode is read using CSPA with a gain of 90 mV/MeV (Si equivalent) and the silicon detector has a CSPA of 20 mV/MeV gain.