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Lab #6 Minerals



Purpose: To introduce the student to methods and techniques used in identifying common minerals.


Apparatus: Mineral specimens, copper penny, plate glass, knife blade or nail, steel file, magnetic compass, magnifying glass, and ultraviolet lamp.

Introduction:


Minerals are solid, naturally occurring substances found in the Earth's crust. Minerals have a fairly definite composition and a crystalline structure (regular repeating arrangement of its components). Minerals can be identified via chemical analysis but this can be time consuming and expensive. A more common way to identify minerals is by the use of distinctive physical properties such as crystal form, hardness, cleavage, fracture (any breaks other than cleavage breaks), color, streak, luster, specific gravity, tenacity, magnetism, fluorescence and phosphorescence. Some of the physical properties are defined below.


hardness - a measure of the resistance of a mineral to being scratched. Mohs' scale is used as a reference when determining the hardness of minerals.


Modified Mohs' Scale


Hardness Mineral Example

1 Talc

2 Gypsum

2.5 Fingernail

3 Calcite

3 Copper Penny

4 Fluorite

5 Apatite Steel

5.5 Steel Knife, Plate Glass

6 Feldspar

6.5 Steel File

7 Quartz

8 Topaz

9 Corundum

10 Diamond


luster - the appearance of the mineral's surface in reflected light. Luster may be metallic (appears like a polished metal) or nonmetallic. Nonmetallic lusters are described below.


Luster Appearance of

adamantine diamond

greasy oily glass

pearly pearl

resinous yellow resins

silky silk

vitreous glass

earthy clay


tenacity - how well a mineral holds together (durable or brittle).


magnetism - the possession of a magnetic field. A magnetic mineral is attracted to a magnet and can be identified by the movement of a compass needle when the mineral is placed near a compass.


fluorescence - light emission resulting from the absorption of ultraviolet or x-ray radiation. This type of emission is short-lived and disappears very quickly after the radiation source is removed.


phosphorescence - light emission resulting from the absorption of ultraviolet or x-ray radiation that is long-lived and continues after the radiation source is removed.


Exercise:


Your instructor will give each student several mineral specimens. Using the tools available to you, examine each specimen and record their physical properties in the data table on Page 3.


References:


1. An Introduction to Physical Science , 10th Edition, James T. Shipman, Jerry D. Wilson, and Aaron W. Todd, Houghton Mifflin Company (2003).


2. Laboratory Guide for an Introduction to Physical Science, 8th Edition, J. T. Shipman and C. D. Baker, Experiment 49, "Minerals", Houghton Mifflin Company (1997).


Data Table


Mineral

Cleavage

Hardness

Color

Streak

Luster

Tenacity

Magnetism



























































































































Lab #7 Radioactive Materials



Purpose: To give the student experience with various properties of radioactive materials.


Apparatus and Materials: LabNet Geiger Interface (LGI), beta source, gamma source, ring stand, clamps, paper, plastic, lead, and meter stick (or other length measurement device).

Introduction:


Radioactive materials are ubiquitous. For example, some smoke detectors contain 241Am while bananas contain 40K. However, the radioactive nature of these materials cannot ordinarily be recognized by human senses. Hence, specialized detectors are needed to measure the presence of radioactive species.


Nuclei of radioactive substances are unstable and can therefore emit various types of radiation with differing properties. The type of radiation a particular nucleus emits will depend upon which decay process is energetically favorable. Sometimes more than one process may be energetically favorable and thus different particles can be emitted by a given quantity of radioactive material.


Alpha decay and beta decay are two common forms of radioactive decay. In alpha decay, the unstable parent nucleus emits an alpha particle which is simply a 4He nucleus (2 protons and 2 neutrons). The resulting daughter nucleus now has two less protons and therefore is a different chemical element.


In beta decay, the unstable parent nucleus emits a beta particle, which is an electron. In doing this, the resulting daughter nucleus has one additional proton.


As can be seen, these two radioactive decay mechanisms result in new elements being formed from the parent elements. Thus straw can be turned into gold!


Gamma rays, which have no mass, result as a consequence of a nucleus de-exciting. Gamma rays frequently are emitted after other decay processes such as beta decay that result in an excited nucleus.


The LGI is a self-contained alpha, beta, and gamma radiation detector. The power supply is also within the LGI. A phone cord is used to connect the LCI to a PC via a gameport card.


The radiation detector in the LGI consists of a Geiger-Müller (GM) tube. The end of the tube is a fragile sheet of mica approximately 0.01 inches thick. The GM tube will fail if the mica window gets punctured or experiences microscopic cracking. The GM tube operates at 450 DC volts.


Alpha particles, beta particles, and gamma radiation have different properties. For example, gamma rays are much more penetrating than alpha particles. In addition, the charges of these species differ.


The intensity of radiation drops off quickly as the distance between the source and the detector increases. Specifically, the intensity of radiation varies with the inverse square of the distance between the radiation source and the detector. So if one doubles the distance between the source and the detector, the detector will “see” only one forth of the radiation that it saw at the original distance.


In this experiment, your instructor will perform all of the measurements while you record the data. Only beta and gamma sources will be used for this experiment.


Exercise:


1. Move all radiation sources at least 5 meters from the LKG. Collect a background count for 3 minutes. Repeat this step two more times. Record the data in the table below.


Background Count #1

cpm

Background Count #2

cpm

Background Count #3

cpm

Average Background Count Rate

cpm


2. Using the beta source, determine the count rate at 4 distances from the detector. Record your data below.



Count Rate (cpm)

Distance from Source d (cm)


1/d2






































3. Plot count rate versus distance and make a separate plot of count rate versus 1/d2.


4. Move the beta detector to within 2 cm of the source. Record the distance between the source and the detector. Record the count rate of the beta source with nothing between the source and the detector. Place a sheet of paper between the beta source and the detector. Record the count rate. Remove the sheet of paper and place a sheet of plastic between the beta source and the detector. Record the count rate. Remove the sheet of plastic and place a sheet of lead between the beta source and the detector. Record the count rate.


5. Remove the beta source and replace it with a gamma source. Record the distance between the source and the detector. Record the count rate of the gamma source with nothing between the source and the detector. Place a sheet of paper between the gamma source and the detector. Record the count rate. Remove the sheet of paper and place a sheet of plastic between the gamma source and the detector. Record the count rate. Remove the sheet of plastic and place a sheet of lead between the gamma source and the detector. Record the count rate.



Source

Distance d (cm)

Count Rate

No shielding

Count Rate

Paper

Count Rate

Plastic

Count Rate

Lead

Beta
















Gamma

















Questions and Discussion:


  1. Why aren’t the three background count rates identical?



  2. Based on the results of this lab, which type of radiation is most penetrating?


3. What would be an appropriate first response to protect oneself from a spilled container of radioactive material?


4. Do nuclear weapons have a positive or negative impact on the environment? Why?


5. Does nuclear power have a positive or negative impact on the environment? Why?


6. Does the term “nuclear” generally have a positive or negative connotation in American Society?


References:


1. LabNet Geiger Interface User’s Manual, LabNet, Inc., IBM/MS-DOS, Version 2.0, 1994.


2. Principles of Instrumental Analysis, Douglas A. Skoog, F. James Holler, and Timothy A. Nieman, 5th Edition, Brooks/Cole (1998).


3. An Introduction to Physical Science Laboratory Guide, 10th Edition, James T. Shipman and Clyde D. Baker, “Radiation”, Experiment 26, Houghton Mifflin Company (2003).


Lab #8 Ten Day Forecast

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