Laboratory telescope for the study of secondary cosmic rays

The purpose of the lab

An initial investigation into main properties of secondary cosmic rays at the observation level.

Tasks

  1. Perform experimental measurement of the secondary cosmic rays intensity at the observation level.
  2. Identify the angular distribution of the secondary cosmic rays at the observation level.

Secondary cosmic rays

Primary cosmic rays are fluxes of high energy charged particles, mostly protons, coming to Earth from galactic and extragalactic sources. By studying these particles certain information about their sources and birth conditions can be obtained. Thereby it expands our perception of the universe structure.

Along with primary cosmic rays, it is agreed to distinguish secondary ones, which are particles generated by the interactions of primary rays with the atomic nuclei of the elements that constitute the Earth’s atmosphere. There are three components: hadronic, muon (“hard”) and electron-photon (“soft”). The first component involves nuclear-active particles which are almost fully absorbed by the atmosphere and nonexistent at the sea level. On the other hand, muons poorly interact with atomic nuclei what gives them high-penetration capability. This fact allows to carry out a study at relatively great depth of matter and receive qualitative information about cosmic rays. Finally, electrons and positrons from electron-photon component experience significant specific losses, however compound the major part of total flux at the sea level.

Intensity of charged particles at the sea level have the following values (for vertical flux):

Ih = 0,82 · 10−2 cm−2 s−1 sr−1

Is = 0,31 · 10−2 cm−2 s−1 sr−1,

where Ih , Is – intensity of hard and soft component respectively.

Angular distribution is also a characteristic of secondary cosmic rays. With an increase in the zenith angle, the distance that the particle travels from the moment of formation to the level of observation increases, and as a consequence, both ionization and radiation losses increase. Experimental data and computation show the dependence of the intensity of the rigid component from zenith angle θ:

Ih(θ) =Ih(0) cosγ(θ),

where Ih(0) — hard component intensity at θ = 0° and γ ̴1,6.

Experimental set-up

The flux of secondary cosmic rays in a given direction is detected by the telescope composed of two scintillation counters. Rotation mechanism sets telescope at chosen angle (with 15o step) within the range from –90° to +90°(Pic.1).

Pic.1. Laboratory telescope: 1 – scintillation counters, 2 – rotation mechanism, 3 – metal construction.

Each counter is an opaque pipe, inside which placed (Pic.2):

  • Cylindrical scintillator with R=10 cm, H= 5 cm. Scintillator material: polystyrene with addition 2% p-terphenyl and 0,02% POPOP.
  • Photomultiplier «ФЭУ-49Б».
  • High-voltage unit controller (from 0 up to 3000 V).
  • Coaxial cables, BNC connectors.
Pic.2. Scintillation counter structure: 1 – scintillator, 2 photomultiplier, 3 – high-voltage unit.

The operation principle of the telescope relies on the fact that charged particles by passing through scintillation counters produce voltage pulses in the anode circuits of the photomultipliers, which can be detected, processed and analyzed afterwards. Simultaneous operation of counters (1.5 μs coincidence window) means the passage of a charged particle at a solid angle θ (shown with blue lines on Pic.3).

Pic.3. Angle of aspect of telescope.

National Instruments ELVIS II+ station is used for obtaining and proceeding experimental data.

National Instruments ELVIS II+ is a software-hardware complex for laboratory works in technical and special disciplines. Software consists of sets of virtual instruments which serve as measuring devices. For example:

  • Function Generator;
  • Oscilloscope;
  • Dynamic Signal Analyzer;
  • Digital Multimeter;
  • Impedance Analyzer;

The workstation can be controlled via LabVIEW program, and in manual mode, with regulators located on the front panel.

Experimental data format

Experimental data from channels 0 and 1 (Channel 0 и Channel 1) is recorded on your computer in the form of oscillograms in text format (Pic. 4).

Pic.4. An example of registered event.

Each oscillogram contains 150 counts (1 count = 10 ns). Signal amplitudes from multipliers are written in a column after line “data:”.

Files with data have the following form «zenith angle θ ( 0°, 15°, 30°, 45°, 60°, 75°, 90°)_data acquisition time»

Oscillograms from channels 0 and 1 (ELVIS_Channel_0 и ELVIS_Channel_1) are saved on PC only if signal amplitudes from channel 0 (ELVIS_Channel_0) reach certain level (Trigger Level), chosen before taking measurements. In this case, the level is set at -30 mV.

Experimental data processing

  1. To estimate the intensity of secondary cosmic rays at the observation level, it is needed to calculate the number of pulses from channel 0 (ELVIS_Channel_0) which reached trigger level. Then divide this number by data acquisition time (zenith angle = 0o).
  2. To estimate the angular distribution of secondary cosmic rays at the observation level, it is needed to calculate the number of pulses from channel 1 (ELVIS_Channel_1) for each angle and then divide by data acquisition time respectively. Based on the results obtained, plot a graph of the dependence of the intensity on cosmic radiation I (θ) on cos (θ).
  3. Compare your results with theoretical predictions.
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