Low Pressure Multiwire Proportional Chamber Research Articles

The light charged particle detector array at the CSNS Back-n white neutron source

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) provides neutrons in the continuous energy region from 0.5 eV to 200 MeV. A spectrometer named Light charged Particle Detector Array (LPDA) is designed for the study of (n, lcp) reactions at Back-n. The main detector of the LPDA spectrometer, a 16-unit ΔE-ΔE-E telescope array, is composed of two arrays of 8-unit ΔE-ΔE-E telescope. Each telescope unit consists of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC), a Si-PIN detector, and a CsI(Tl) scintillator detector. In 2021, a neutron-proton (n-p) scattering reaction cross-section measurement experiment was accomplished as the first experiment of the telescope array. Protons can be clearly identified in the ΔE-E spectrum (LPMWPC + Si-PIN) and the ΔE-E spectrum (Si-PIN + CsI(Tl)). Cross sections of the n-p scattering reaction in the neutron energy range of several MeV are extracted. The ΔE-E method also provides new measurement opportunities for many-body neutron induced light charged-particle emission reactions.

Detection of low-energy charged-particle using the [formula omitted]E-E telescope at the Back-n white neutron source

The Back-n is a high luminosity white neutron beamline at the China Spallation Neutron Source (CSNS). It started running in 2018 for various nuclear data measurements. A Light charged Particle Detector Array (LPDA) is designed for (n, lcp) reaction experiments, which includes a group of detectors and supporting systems. The ΔE-E telescope, consisting of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC) and a Si-PIN detector, is the core detector of the LPDA. From the beginning of 2018, several measurements have been performed using the ΔE-E telescopes, and the light charged particles such as 1H, 3H, 4He, and 7Li, were identified successfully. At present, the LPMWPC can identify the protons with energy as low as 0.5 MeV. In the near future, combining with CsI(Tl) crystals, a system consisting of sixteen telescopes with an energy acceptance from 0.5 MeV to 100 MeV (proton) will be constructed for general purpose of (n, lcp) measurements.

Active Oxygen Target for Studies in Nuclear Astrophysics with Laser Compton Backscattered γ-ray Beams

An active target is being developed to be used in low-energy nuclear astrophysics experiments. It is a position- and time-sensitive detector system based on the low-pressure Multi Wire Proportional Chamber (MWPC) technique. Methylal ((OCH3)2CH2), at a pressure of a few Torr, serves as the working gas for MWPC operation, and in addition, the oxygen atoms of the methylal molecules serve as an experimental target. The main advantage of this new target detector system is that it has high sensitivity to the low-energy, highly-ionizing particles produced after photodisintegration of 16O and insensitivity to γ-rays and minimum ionizing particles. This allows users to detect only the products of the nuclear reaction of interest. The threshold energies for detection of α particles and 12C nuclei are about 50 keV and 100 keV, respectively. The main disadvantage of this detector is the small target thickness, which is around a few tens of μg/cm2. However, reasonable luminosity can be achieved by using a multimodule detector system and an intense, Laser Compton Backscattered (LCB) γ-ray beam. This paper summarizes the architecture of the active target and reports test results of the prototype detector. The tests investigated the timing and position resolutions of 30 × 30 mm2 low-pressure MWPC units using an α-particle source. The possibility of measuring the 16O(γ, α)12C cross-section in the 8–10 MeV energy region by using a LCB γ-ray beam is also discussed. A measurement of the 16O(γ, α)12C cross-section will enable the reaction rate of 12C(α, γ)16O to be determined with significantly improved precision compared to previous experiments.

Direct measurements of the lifetime of medium-heavy hypernuclei

The lifetime of a Λ particle embedded in a nucleus (hypernucleus) decreases from that of free Λ decay mainly due to the opening of the ΛN→NN weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. This paper presents a direct measurement of the lifetime of medium-heavy hypernuclei that were hyper-fragments produced by fission or break-up from heavy hypernuclei initially produced with a 2.34 GeV photon-beam incident on thin Fe, Cu, Ag, and Bi target foils. For each event, fragments were detected in coincident pairs by a low-pressure multi-wire proportional chamber system. The lifetime was extracted from decay time spectrum formed by the difference of the time zeros between the pairs. The measured lifetime from each target is actually a statistical average over a range of mass with mean about 1/2 of the target mass and appears to be a constant of about 200 ps. Although this result cannot exclude unexpected shorter or longer lifetimes for some specific hypernuclei or hypernuclear states, it shows that a systematic decrease in lifetime as hypernuclear mass increases is not a general feature for hypernuclei with mean mass up to A≈130. On the other hand, the success of this experiment and its technique shows that the time delayed fissions observed and used by all the lifetime measurements done so far on heavy hypernuclei could likely have originated from hyper-fragments lighter than the assumed masses.

Performance test of the low-pressure thin window multi-wire chamber

A flow gas low-pressure multi-wire proportional chamber (LPMWPC) with an active area of 180 mm × 80 mm has been developed for the flying time test of the recoil nuclei on super heavy nuclear experiments. The LPMWPC detector can be operated in single as well as double step operational modes. In the case of double step operational mode with a high gas amplification factor, signals from α-particles reside well above the electronic noise. The gas leakage rate and time resolution obtained from the α 239Pu source are shown and discussed at the condition of 3 mbar Isobutane gas. It was shown that the time resolution was better than 2.9 ns at the best work condition, and the detecting efficiency was larger than 98% at the low energy α particles. So the LPMWPC is fit to measure the flying time in the super heavy nuclear fragments experiment.

Performance of the low pressure MWPCs for fission fragments under a high background

Two couples of low pressure multi-wire proportional chambers (MWPC) were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory (Jlab). In the experiment, a continuous wave (CW) electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy (1.853 GeV) and high intensity (500 nA) primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.

Study and application of low pressure multi-wire proportional chambers

Low Pressure Multi-Wire Proportional Chambers (LPMWPC) were made in the laboratory and the systematic tests were carried out. The position resolution of the chamber is about 0.5mm and the time resolution is about 1.5ns. The detection efficiency is higher than 90% for light nuclei at low and intermediate energies, and for beam intensities lower than 105pps. This kind of detector is applicable for monitoring the radioactive ion beam which is in general characterized by low intensity and large spot. Application of new read-out techniques may allow to improve the beam intensity capability.

Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1–2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21×21 cm 2 was achieved.

Fission probabilities of Cu, Nb, Ag, Ho, Au and Bi nuclei excited by stopped antiprotons

The A dependence of nuclear fission induced by stopped antiprotons has been measured. An unambiguous identification of the binary fission decay mode was provided by a coordinate measurement of complementary fission fragments in coincidence using a large-acceptance fission detector based on low pressure multiwire proportional chambers. A deep fissility minimum was observed nearA=100, in agreement with the general behaviour predicted by the liquid-drop model. An unexpectedly low and high fission probability was found for the Ag and Cu nuclei, respectively.

Fissilities of 238U and 237Np nuclei measured with tagged photons in the energy range 60–240 MeV

The photofission cross sections of 238U and 237Np nuclei have been measured using bremsstrahlung tagged photons at the ROKK-2 facility of the storage ring VEPP-3 INR (Novosibirsk). Fission fragments were detected by the low-pressure multiwire proportional chambers. The behavior of the photofission cross sections and relative fissilities has been compared with theoretical evaluations based in the cascade evaporation and double-humped fission barrier model.

A nuclear fragment detector for experiments with backscattered laser photons

A new fission fragment detector (FD) was designed and built for the experiments with backscattered laser photons at intermediate energies. The FD is based on low-pressure multiwire proportional chambers to detect the trajectories and energy losses of fission fragments and ( ΔE− E) plastic scintillator modules to measure the energy of light charged particles such as protons, pions, etc. The results of calibrations with a spontaneous fission 252Cf source and first experiments on bremsstrahlung-induced photofission of 238U and 237Np nuclei at ( E γ ) max = 2 GeV are presented.

The performance of a UV sensitive multiwire proportional chamber filled with TMAE

We tested a low pressure multiwire proportional chamber filled with TMAE under various conditions. The asymptotic quantum efficiency (infinite thickness) for gaseous TMAE was measured to be 8% at 210 nm. No signal could be extracted from an adsorbed or condensed layer of TMAE. However, we expect that such a device with gaseous TMAE could be very efficient (> 50%) in the 100–180 nm range for detecting UV light, especially for astrophysical applications.

Experimental set-up for the measurement of ionization probabilities with a low pressure multiwire proportional chamber

The experimental set-up for ion-photon coincidence measurements with a multiwire proportional chamber (MWPC) operating at low gas pressures as position sensitive ion detector is described. The readout system is based on individual sense wire readout and allows to registrate about 100 × 100 different polar coordinates of the scattered ions. The performance of the system in studies of inner-shell ionization in ion-atom collisions is described.

A low pressure multiwire proportional chamber as a position sensitive detector of heavy ions: Construction and detection properties

A low pressure multiwire proportional chamber with two signal-wire planes and an active area of about 300 cm 2 has been developed as particle detector in heavy-ion X-ray coincidence experiments to study the impact-parameter dependence of inner-shell ionization processes. The construction of the chamber and its detection properties concerning heavy ions with energies of E/ A ≅ 0.1 to 1 MeV/u are described.

Properties of different counting gases for a low pressure multiwire proportional chamber

Test measurements with a MWPC with 20 μm diam. signal wires and 2 mm wire spacing were performed with 5.5 MeV alpha particles. Pulse height, timing characteristics, total efficiency and double hit efficiency were measured for several counting gases at pressures from 5 to 100 mbar.

A subnanosecond, low pressure MWPC for heavily ionizing particles

A multiwire proportional chamber (MWPC) having 10 μm wires and a wire spacing of 1 mm has been operated in gas pressures of 5–73 torr. Several gases and vapours were used. A time resolution better than 0.8 ns (fwhm) was reached with 5.5 MeV α-particles. The detection efficiency is nearly 100%. Some properties of low pressure MWPC are discussed.

The Operational Mode in a Buried-Channel Charge-Coupled Device

A flow gas low-pressure multi-wire proportional chamber (LPMWPC) with an active area of 180 mm× 80 mm has been developed for the flying time test of the recoil nuclei on super heavy nuclear experiments. The LPMWPC detector can be operated in single as well as double step operational modes. In the case of double step operational mode with a high gas amplification factor, signals from α-particles reside well above the electronic noise. The gas leakage rate and time resolution obtained from the α Pu source are shown and discussed at the condition of 3 mbar Isobutane gas. It was shown that the time resolution was better than 2.9 ns at the best work condition, and the detecting efficiency was larger than 98% at the low energy α particles. So the LPMWPC is fit to measure the flying time in the super heavy nuclear fragments experiment.

Low pressure multiwire proportional chambers with high time resolution for strongly ionizing particles

Multiwire proportional chambers have been tested in the range of pressures from 3 to 30 mm Hg of isobutane, pentane and heptane. With 5.5 MeV α particles, a time resolution of 2.5 nsec was obtained at 100% efficiency.