I have developed curriculum for providing instruction in the basics of
radiation chemistry to students from K4 up. Approximately 800 OSU
freshman Chemistry students participate in an Aluminum half-life lab each
year. We also get a number of classes from middle schools, high
schools and junior colleges in the region.
The OSU Radiation Center half-life experiment affords students the opportunity to view the nuclear decay process first hand. Aluminum samples are irradiated in the OSU TRIGA Mark II reactor. Radioactive 28Al samples are delivered to the GM workstations where students collect 15 data points as the radioactive atoms decay. Data can be manipulated manually utilizing a piece of 3 cycle semi-log paper. The same raw data may also be inserted in a computer spreadsheet for analysis. Using the 3 cycle semi-log graph permits younger students to solve the decay curve without using or understanding algebra and log functions. Documents selected from the aluminum lab exercise have been provided for your exploration.
The principle of half-life can be demonstrated by providing students with approximately 100 two sided objects like pennies, M&M (plain) or Skittles in a small 3 to 5 oz. drinking cup and a paper plate. The students are instructed to pour the items out onto the paper plate and remove and count all of the items that are either unlabeled or the pennies that come up tails. This group represents the decayed atoms. The items are set aside or eaten as appropriate for the item. The numbers are recorded by group for data analysis. The remaining objects are placed back into the cup and the process continues until all of the atoms have decayed. With a start point of 100 most will be out after 7 cycles.
For each "throw" or "roll" of items the probability that any one of the items will be eliminated (or decay) is 50%. For radioactive particles the time period in which 50% will decay is directly proportional to the instability of the nucleus. A very unstable atom has a higher probability of decay during a given time period; and conversely a slightly unstable atom has a very low probability of decay. The half life of any radioactive isotope is directly proportional to the degree of instability of the particular isotope. A copy of the exercise instructions may be found at the link below:
Building a GM detector may be to involved for the average hobbyist but it is possible. One web site already exists with diagrams of a detector at Build Your Own Geiger Counter page 1. Another recommended reference "The Boys' Second Book of Radio and Electronics" by Alfred Morgan is unfortunately out of print. The electronics are very simple but construction of an argon-methane (90/10) thin window tube could be a challenge.
A more reasonable project is construction of an electroscope. The BSA Atomic Energy Merit badge book has diagrams of a home-made electroscope as well as diagrams of a commercially built electroscope that one might find in a high school science lab.
This section is included because a cloud chamber is one of the most marvelous devices a science nerd will ever encounter. A cloud chamber is simply a super saturated alcohol environment that produces vapor trails when ionizing radiation passes through. If you want to make a cloud chamber just check out Andy Foland's web page. This individual has done an excellent job of explaining how to build a cloud chamber.
American Scientific at one time sold a simple commercially produced cloud chamber ($10) that consisted of half of a Plexiglas sphere like and inverted bowl with a radius of approximately 12 cm. The base was black plastic with a circle of felt fabric to absorb the alcohol. The base could be placed directly on a block of dry ice with the felt up. After soaking the felt with alcohol and placing an Americium source in the middle of the round base, the Plexiglas dome was placed over the base to trap alcohol vapor around the source. After about 15 minutes a strong flashlight beam would reveal a miniature fireworks like display of vapor trails shooting up from the source and arching back toward the base of the chamber.
I have a similar shaped dome from a popcorn popper that I suspect will also work for a cloud chamber. I plan to collect several common items I will test to see if other designs could work to build the supersaturated environment needed for a cloud chamber. If you have successfully built simple cloud chambers please send me a link or an email.
Multichannel Analyzers (MCA) coupled with high purity germanium detectors (HPGE) are used to measure gamma radiation. The more recent versions of MCAs often support networking protocols to enhance operation and management of the systems. Networking these MCAs presents challenges that network administrators typically would not deal with. This section is offered to assist installation of MCA networks. The section has been divided into three sections. The first two pertain to setting up Ortec DSpec and Canberra Genie analyzers. The third section will deal with setting up a local TCP/IP subnet.
The DSpec incorporates a 10 MBPS Thinnet port on the back panel using IPX/SPX as the transport protocol. Communication across this port is continuous at approximately 2 MBPS for each analyzer. Installing 5 or more analyzers on the same thin-net segment will generate more traffic than Thinnet is designed to accommodate. Larger installations will require installing multiple Thinnet segments or the use of 10base-2 to 10baseT transceivers and a 10/100 switch to connect multiple analyzers.
Canberra systems do not pose any particular problems during network setup except that some of the necessary documentation is not placed in obvious locations. In particular the installation of Ethernet support for the Multiport system requires a program "Multiport_II_Ethernet_Configuration.exe." This program can be found with the Geine2k software installation at "...Genie2k\Exefiles". Documentation is located in the "Multiport II Users Manuel" Appendix E. The MPII configuration software will facilitate entry of a network TCP/IP address into the Multiport PROM via the USB port.
The next issue is the addition of a Windows PC to a Vax/VMS installation of Genie. The trick here is to obtain a copy of the Canberra SNAP protocol. This driver rides on the TCP/IP transport to facilitate communication with the AIM and/or DSA analyzers.
Isolating MCA network from the larger LAN or WAN is useful to keep management of the analyzer system within the purview of the counting lab staff. In the case of DSpec analyzers it will also prevent user groups from renumbering of the analyzers every time a new analyzer is added to the system.
Start by selecting a non-routable subnet address like 192.168.10.0. If you have a computer or router that will be accessing the LAN or WAN assign this device the 192.168.10.1 address. This address will be the subnet gateway. The subnet mask becomes 255.255.255.0. Assign a fixed IP address to each node (not DSpec) on the network. Create a host file (or LMHosts optional for Windows PC) and copy it to the appropriate subdirectory on each computer (C:\Windows\System32\drivers\etc\hosts). When DHCP is not present the workstation will default to the hosts file for name resolution. Open the existing hosts file with "Notepad.exe" and follow the examples in the file. Don't forget that the hosts file can also restrict access to specific network address. Dynamic name resolution (DHCP) is also an option but is not required or recommended for this installation.
Use the Microsoft Windows XP Networking Wizard to add sharing features among the computers. Start with the gateway PC to establish "Microsoft Network Connection Sharing" for extended network access. On every other computer use the wizard to get network access through a network hub or gateway computer. Turn on Windows File and Printer sharing if desired. Make sure to enter the same Workgroup name (MSHOME is default) for computer that need peer to peer communication. If the windows computers are using LMHosts name resolution this must be selected in the Windows network NIC Properties page / TCI/IP / Properties / Advanced Network Protocol / WINS / LMHosts check box.
This site was last updated 07/06/06