Discussions
|
|
In principle the daily rotation of the earth about its axis and even annual rotation of the earth in its orbit about the sun enables us to distinguish variations of air shower rate in time. The experiment give you the chance to find out such variation even though practice complication araise in interpreting the data. In this experiment, you may face the following difficulties : 1. Problems in searching periodicity It is believed that there are many effects (e.g earth rotation, barometric effect) with different time length scale which will affect the rate of air showers. Hence, it may be hopeless to seek for the periodicity by event plot directly. The method suggested in the part of data analysis will be too rough for you. Actually, many numerical methods are available for you to investigate cosmic ray problems. There will be some references in Web. Another approach to tackle this problem is to isolate the unwanted effect in experiment. For example, temperature variation may affect the rate of air showers, you can lock you detectors in a room with air conditioner. 2. Problems of fluctuations in air showers People who are involved in calculations of an extensive air shower usually ignore the problem of fluctuations in the number of particles and consider average values only. However, this problem may draw your attention. The problem of fluctuations may be quite simply stated as follows. At some moment, a primary particle of a given energy can give rise to N subparticles at sea level by some cascading effect (e.g pair production). The arrival of subparticles are nearly independent.The heuristic argument holds because the history for each subparticle hitting your detector is nearly untraceable. You may know that independent counting process with increments highly depends on the given rate is always Poissonian. At a result, you expect the events form extensive air showers exhabit Poissonian fluctuation. There may be some technique problems which are not listed above. Such as computer software fails in taking long time measurement, Scientific event plots (including error bars) are hard to managed by EXCEL. You are wellcome to contact us for help or suggest any improvements about the experiment. In research field, people usually concern the extensive air showers with energy over 1013eV for the primary particle. Interest lies in the very high energy particles, but the frequency of these are very low. In order to detect one or two such events per day, apparatus must be capable of detecting the showers produced by primary particle falling in a effective area over several 10 km2. There are 3 ways in which a time variation is sought. Firstly, as you did in the project, the count rate of a given arrangement of appratus may be recorded as a function of time, using the rotation of the earth to direct the appratus to monitor different parts of the sky. Secondly, by assuming that the direction of shower particles indicates the direction of incoming primary particle. Plotting their direction as a point on the celestial sphere over time. This method clearly has an advantage over the first. It is because angular resolution is also included. If a point source of cosmic radiation exist at somewhere on the celestial sphere, we use method 1 to check the count rate variation, such source would tend to be obscured in an almost isotropic background. Thirdly, a cosmic ray telescope may be used to sweep a particular region of the sky to detect high energy particle in a more direct sense.
|