Lightweight organic scintillators have a moderate technical light yield as compared with inorganic scintillators. In order to obtain the highest luminescence intensity from p-terphenyl single crystal, we used the distinguishing feature of organic crystals consisting of the unit cell of the crystal lattice in the inequality of the axes lengths inside.

     The aim of this work is to study the scintillation properties of a small-sized detector of highly energetic charged particles based on the p-terphenyl single crystal along its characteristic axes a, b, and c. We have made a cubic-shaped detector with dimensions 6x6x6 mm² as well as measured and processed the energy spectra of conversion electrons using radioactive isotopes ¹³⁷Cs and ²⁰⁷Bi. We used silicon photomultiplier with total active area 6´6 mm² with the common number of pixels of 57600 as the photodetector. The measurements were conducted at a stabilized temperature of T = 15^°C and a depressed atmospheric pressure P ≈ 0.1 Bar. We analyzed amplitudes and energy resolutions of monoenergetic electron lines and characteristic X-ray radiation. We determined that the amplitude of the scintillation signal registered along the a axis of the crystal is less on ≈ 2--12 %, depending on the particle energy than the amplitude measured along the b axis, and even less on ≈ 15-20 % along the c axis.

     We conclude that 1) the best technical light yield of a small scintillation detector fabricated on the base of p-terphenyl single crystal of regular shape is reached when light flashes are registered along the axis b of crystallographic lattice; 2) the p-terphenyl single crystal should be oriented with respect to active area of the photodetector taking into account the described experimental studies while the manufacture of anti-coincident scintillation detector for high-energy charged particle monitor BPM of the solar X-ray spectrophotometer ChemiX of the interplanetary space mission "Interhelioprobe”.