V. V. Parusov

A multichannel wire gas electron multiplier

A novel and relatively simple method of production of electrodes for a multichannel wire gas multiplier was developed. Two modifications of the multipliers have been tested: with a multiplication of electrons between two wire electrodes, MWGEM, and between a wire electrode and continuous anode, MWCAT. For both MWGEM and MWCAT detectors, filled with neon under pressure of 760 Torr and irradiated by β-particles (63Ni), the coefficient of proportional multiplication of electrons up to ∼104 was obtained. For the MWGEM detector irradiated by α-particles (239Pu), the coefficient of proportional multiplication of 300 was obtained. It is observed, that in contrast to the GEM detectors, produced by perforation of a metal-clad plastic foil, in a MWGEM the discharges do not destroy its electrodes even for the potentials above the threshold of discharges. The results on operation of the MWCAT filled with Ar, Ar + 20% CH4, and Ar + 1% Xe are also presented.

Multichannel gas electron multipliers with metal electrodes

Results of studying multichannel gas electron multipliers with 1-mm-thick metal electrodes, perforated over the entire working area by 1-mm-diameter holes with a 1.5-mm distance between them, and a 3-mm gap between the electrodes are described. The influence of N2 and H2O microadditives on operation of the neon-filled multiplier is studied. When β particles (63Ni) were detected, the maximal proportional electron multiplication factor in neon under pressure of 1 atm (abs.) with quenching additives of (H2O + N2) ≈ 100 mln−1, equal to Kmltcmpl = 3 × 104, is obtained.

Massive liquid Ar and Xe detectors for direct Dark Matter searches

A novel experiment for direct search for Dark Matter with liquid argon double-phase chamber with a mass of liquid Ar up to several hundred tons is proposed. To suppress the β, γ and n0 backgrounds, the comparison of scintillation and ionization signals for every event is suggested. The addition in liquid Ar of photosensitive Ge(CH3)4 or C2H4 and suppression of triplet component of scintillation signals ensures the detection of scintillation signals with high efficiency and provides a complete suppression of the electron background. For the detection of photoelectrons and ionization electrons, highly stable and reliable GEM detectors must be used.

Time-projection chamber with highdE/dz and energy resolutions

A time-projection chamber with high energy anddE/dz resolutions based on electron multiplication in a multiwire proportional chamber is described. The chamber is capable of operating at an up to 20-atm pressure of the filling gas.

Low-background shielding

A new method of ultradeep water purification from oxygen was developed. Water with a low concentration of radioactive impurities and oxygen can be used to produce ice shielding in low-background under-ground experiments.

Methods for detecting events in double-phase argon chambers

Multichannel wire gas electron multipliers in combination with pin anodes are proposed for detection of events in the gas phase of a double-phase argon chamber. Hydrogen with a concentration of 10 vol % is added to argon to eliminate feedbacks by photons emitted by excited argon molecules in avalanche development processes while detecting events in the argon gas. A maximum electron multiplication coefficient of ∼300 has been obtained for the multichannel wire gas electron multipliers with a 1-mm gap used to detect α particles in the Ar + 10% H2 mixture at a pressure of 1 atm (abs.). When a pin anode is used, the maximum electron multiplication factor is ∼2.5 × 105 for α particles and 3 × 106 for β particles (63Ni). It has been experimentally shown that adding H2 with a concentration of 100 ppm to liquid argon has no effect on the singlet component of the scintillation signal in the liquid argon and reduces the emission efficiency relative to the pure argon gas phase only slightly (by 20%).

A study of Ar + C2H4 and Xe + CF4 gas mixtures

Mixtures of Ar + 40 ppm C2H4 and 50% Xe + 50%CF4 have been investigated. The spatial distributions of photoelectron clouds produced by primary scintillations on α- and β-particle tracks, as well as the distributions of photoelectron clouds due to photons from avalanches at the pin anode, have been measured for the first time. For a mixture of 50% Xe + 50%CF4, it has been shown for the first time that CF4 is a photosensitive dopant in a mixture with Xe. For a mixture of Xe + CF4 (1: 1), the maximum electron multiplication factors at the pin anode are K(β)max = 3 × 104 and K(α)max = 3 × 103 at a pressure of 1 atm (abs.) and K(β)max = 104 and K(α)max = 4 × 103 at a pressure of 10 atm (abs.)

Multichannel wire gas electron multipliers

A simple technique for manufacturing electrodes of multichannel wire gas electron multipliers was developed. The maximum proportional multiplication factor of ionization electrons Kmax = 103 was obtained when the chamber containing a multichannel wire gas electron multiplier was filled with a mixture of Ar + 10%C2H4 at a pressure of 1 atm (abs.) and the drift (ionization) gap of the chamber was irradiated with β particles (63Ni). Under irradiation with α particles, Kmax = 103 at a pressure of 1 atm (abs.) and 3 × 103 at 0.4 atm (abs.). When the chamber was filled with a mixture of Ne + 10%C2H4 at a pressure of 1 atm (abs.) and exposed to β particles, Kmax = 4 × 103 was obtained.

A gas electron multiplier with metal electrodes

A gas electron multiplier with metal electrodes, which is characterized by simplicity and high manufacturing accuracy, reliability, and stability, has been fabricated and tested.

Studying the proportional discharge dynamics in mixtures of various gases using a chamber with preliminary electron multiplication

By using a chamber with preliminary multiplication of ionization electrons and extraction of the electron component of signals, the proportional discharge dynamics was studied in various gas mixtures, including mixtures of noble gases with gases, whose ionization potential is below the excitation energy of noble gas atoms (Penning mixtures). It was revealed that the main signals with durations of several microseconds, which are determined by the collection of electrons from primary avalanches, have “tails” of secondary avalanches with durations of up to tens of microseconds with a total charge comparable or exceeding the charge in the primary avalanches.