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Our Cosmic Ray scientists invite you to share in their discoveries and in their Search for Cosmic Rays. In Activity 1 students simulated Hess' balloon ride and discovered that the particle detection rate increases with altitude. The results from Hess' actual balloon ride led scientists to ask further questions, such as where are these particles coming from, from which direction, at what angles? In Activities 2 and 3 students investigated these questions and discovered that these particles were moving toward the Earth from outer space at very steep angles. Students began tracking the discovery and early understanding of what scientists had started to call Cosmic Rays. Many experiments similar to the first three activities were conducted by scientists around the world. It is our hope that the students working these activities are beginning to recognize the scientific processes that were used in the devising of these experiments. In Activity 4 students will begin to use their creativity to try and discover more about these mysterious Cosmic Rays. The two Geiger arrays used in activity 3 are now separated by a fixed distance of 1 meter. By clicking and dragging the mouse in the lab window, a protractor will form. Timers that measure the time between tube hits are provided (subtract the time on timer 1 from timer 2 for the time between hits). By using a little thought and a little class discussion, students should be able to realize that with a tiny bit of trigonometry (to measure the distance traveled between tubes) they can calculate the approximate velocity of a Cosmic Ray! (The velocity will be very close to the speed of light, 3 x 10^8 meters/second. Sometimes the calculated velocity of a Cosmic Ray will be faster than the speed of light. This is not physically possible. The reason that the calculation occasionally works out to be too fast is because the numbers being used in the calculation (recorded time and measured displacement) are not accurate enough to check the velocity precisely.) In Activity 5 students will finally get the chance to manipulate the arrangement of the detector. This activity, much more than the previous four, is geared toward letting students play around with the experiments that they've been running. The focus of this activity is to determine how to maximize the number of cosmic ray hits that they get through the Geiger array. Three major considerations in doing this: 1. A cosmic ray can yield no information with this lab setup unless it is seen by both rows of tubes. 2. How does the number of events through both rows of tubes change as the vertical distance between the rows increases? (number of events through both rows will decrease as the vertical separation increases.) 3. How does the number of events through both rows of tubes change as the horizontal distance between the rows increases? (number of events through both rows will decrease as the horizontal separation between the rows increases.) Teacher may want to let students play around for a while and determine these considerations for themselves.
Ask the students to think of other things, beside the things learned in the earlier activities, that could be discovered and scientifically measured with an experiment setup of two rows of Geiger tubes, timing devices, rulers, protractors, and other general science lab equipment. (velocity, frequency of hits...) Ask students to suggest the most practical setup of the detector in order to gain the most information (get the most cosmic ray hits). Ask the students to determine the type of scientific information important in learning about Cosmic Rays and the kind of information that it would be possible to gain with the equipment at hand. Remind students of the motion and angle information they gained in the previous labs.
As the students conduct the online lab, the teacher should act as a facilitator. Allow students as much freedom as possible. Ideally, they will discover the relationships on their own. It is best if students work in small groups, preferably two or three students per group. If this lab is to be done using a computer and projector in front of a class, ask questions and allow students to take turns running the computer. This will help to keep everyone involved. The teacher must conduct the lab activity prior to the students. This way the teacher will be able to answer student questions as they arise. Require that students read the instructions prior to proceeding to the next page. This will help them to learn more from the lab. Activities 4 and 5 should take about 1 classroom period, depending on technical problems and skill of students. It is worthwhile to discuss any possible technical problems with the technical specialist prior to beginning the lab. Such problems may include: whether or not all students have network access, the number of available computers with internet access, whether or not the local server is up and running on the day you wish to conduct the lab. A student lab packet is provided which includes student instructions, graph paper, and the questions from the lab. Teachers may wish to use this for classes that need extra support, or for classes with time constraints, or merely to facilitate the ease of conducting the investigation.
Students should discover that Hess' Cosmic Rays are flying toward the Earth
at almost the speed of light. It should be stressed that the energy required
to move these particles this fast is enormous. Millions of times more
energy per particle than humans have been able to create. (Some wonder and
amazement on the part of the teacher and the student would be appropriate
at this time.) Explain that modern scientists, with all their
supercomputers and equipment, are still unable to figure out what in
the universe would be powerful enough to give these cosmic rays their
energy. (more wonder and amazement) An average Cosmic Ray could circle the
Earth ten times in 1.5 seconds. Cosmic rays are a true unsolved mystery.
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