Cosmic radiation

Ana Bacelj[1], Kristina Hrastic[2], Tomislav Pelko[3], Denis Stogl[4], Suzana Galovic[5], Fran Hrzenjak[6]

  1. [1] III. gimnazija, Split, Croatia
  2. [2] Prirodoslovna skola Vladimira Preloga, Zagreb, Croatia
  3. [3] SS Oroslavje, Oroslavje, Croatia
  4. [4] Gimnazija Bjelovar, Bjelovar, Croatia
  5. [5] Prirodoslovna skola Vladimira Preloga, Zagreb, Croatia
  6. [6] Faculty of Science, Department of Physics, Zagreb, Croatia

Our main goal is to make a device which will detect cosmic rays and to determinate cosmic ray's density.

Cosmic rays

Cosmic radiation is emission of high-energy elementary particles traveling close to the speed of light. It is coming from every part of space such as Sun, supernovas, quasars, and galaxies, but because of their complex trajectories, it is difficult to determine exact place of their origin.

Primary cosmic radiation is a stream of "big" elementary particles (mostly protons) which travels through space to the Earth. Interaction of primary radiation and molecules (oxygen and nitrogen) in the upper layers of Earth's atmosphere produces stream of "smaller" particles with lower energy such as electrons, photons, neutrons and muons, which is called secondary radiation.

To determinate cosmic radiation, we will have to detect muons. Muons are the best choice because their big mass and energy make them able to get to the Earth's surface and they are not hard to detect.

Cosmic ray detector

Scheme with two GM tubes coincidence counter and measuring device.

Image 1: Scheme of cosmic ray detector

It is a device for detecting cosmic radiation. It is made of oscillator circuit, high voltage circuit, amplifier, Geiger – Müller tube, logical AND assembly and device for measuring output signal (voltmeter, oscilloscope or computer with interface).

GM counters detect the muon flux, which is around 5% to 10% of the total background radiation that is being picked up. Using only one GM tube is not an accurate way to find the muon flux rate. To make measurement more accurate we will use two GM counters at the same time and connect them with a coincidence counter (c-box). Only those muon particles that go through both GM counters at the same time are being counted with the help of the c-box.

Building a cosmic ray detector

We made schematics using PCB Express program, which we later printed on a transparency. We have pasted it on a copper board and heated it. Later we have put the board into the H2O2 and HCl. They "ate" all the copper except the one we marked as conductors. Then we have soldered the components (transistors, capacitors, diodes) on the board.

For counting signals from GM detectors, we programmed PIC16F877. For programming the chip, we used assembly program language. We have programmed virtual AND circuit into chip because we want to have direct input from detectors. Chip counts signals only if both detectors send them. For showing numbers, we used LED display.

Method of detection

For detection of muons we will use Geiger – Müller (GM) counter. We have only GM tubes and the rest of counter we have to build. For measuring, we will use different parameters. We will try to explore whether the number of detected muons depends on type and thickness of material, distance between tubes, angle on Earth normal and part of the day and try to make a conclusion how it depends on this parameters.