High energy electrons, protons, and complex nuclei can be produced in a number of astronomical environments. Such

particles travel throughout the universe and are called cosmic rays. Some of these particles reach our Earth. As these objects hit our atmosphere, other particles called pions and muons are produced. These particles then slow down or crash into other atoms in the atmosphere.

Natural atmospheric radiation influences sample count rates. This can be reduced through shielding of the counting environment. In order to reduce background level, anticoincidence shield can be used to add into the system. The shield is made of scintillator connected to a photo-multiplier tube.

A scintillant is a material which emits light when energy from a passing high-energy particle is deposited in it. Scintillators respond very quickly to the passage of a particle. The light generated inside scintillants is transmitted by total internal reflection to the edges of the scintillator and then converted into electric signal by photomultiplier tube. The signal output from this photomultiplier tube is then amplified by amplifier and filtered by discriminator and finally fed into time-pulse-converter as anticoincidence signal to reduce the background counting rate.

Fig.5.1, illustrates scintillator part of the instrumentation system. The scintillator shield can be put on top of the two PMTs in system Fig.3.8.





Fig. 5.1 Scintillator as Anticoincidence




Relating factors for detection of biophoton:

  1. Aperture size between PMTs
  2. The larger the aperture, the more counts output

  3. Transparent percentage of samples
  4. Samples are not perfectly transparent, in our instrumentation, transparent sample would be better in getting results. Because opaque sample may block one of the two photons from the photon pair and prevent output event.

  5. Absorption of container and water
  6. From the data, we can see water has large effect on counting rate. Possible reasons are absorption of water molecules and scattering.

  7. Light leakage of background
  8. Background counting rate is too high because of cosmic radiation, light leakage of room and electronic sources.

  9. PMT detection wavelength
  10. Because biophoton wavelength is in infrared region. The photomultiplier tube used in our experiment does not have highest sensitivity in infrared region, rather it is more sensitive to visible light. A detector especially designed for infrared light detection would be prefered.

  11. Time range of TAC and Delay time
  12. The time range of Time-to-Amplitude converter gives the duration of start and stop event. By choosing suitable time range, combining with suitable delay time, it could be possible to improve detection results.

  13. Cosmic radiation has large effect on background
Even when the two PMTS are blocked, the electrons from space hit the air between PMTs and photon is emitted. At some point, the photon may cause start at one PMT and a stop at the other PMT resulting an output count.

Relating Factors for random sequences collection:

In gathering physical random sequence, the method had large error. There are two reasons exist: First one is that because the multichannel analyzer and software we used had been designed to provide histogram record of counting rate, it can not provide real-time time sequence for each event. The sequence was recorded by human eyes. The second reason is that on multichannel analyzer screen, when we want to see the full range of channel numbers, one count could not be seen on the screen. The least count rate resolution is 2 counts. This also introduced error.

In order to improve this physical random sequence collecting method and reduce error, we can use newly designed software for analog-digital converter to record real-time counting event sequence.