D6347D6347M-Standard Test Method for Determination of Bulk Density of Coal Using Nuclear Backscatter Depth Density MethodsFull description
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Calibration of Bourdon Gauge
Determination of the field density by nuclear method Introduction:
Nuclear Density Gauge A nuclear density gauge is a tool used for measuring in-place density using gamma radiation. Gauges usually contain a small gamma source (about 10 mCi) such as Cesium-1! on the end of a retractable rod. Gamma rays are emitted from the source and interact "ith electrons in the pa#ement through absorption$ Compton scattering$ and the photoelectric effect. A Geiger-%ueller detector (situated in the gauge opposite opposite from the handle) handle) counts counts gamma gamma rays rays that that reach reach it from from the source. source. &a#ement density is then correlated to the number of gamma rays recei#ed by the detector. Nuclear %oisture Gauge A nuclear moisture gauge uses a neutron neutron source$ such as Americium Americium-'1* -'1*eryll eryllium$ ium$ placed inside the gauge. +he source emits high energy$ energy$ ,fast neutrons$ "hich then collide "ith #arious nuclei nuclei in the pa#ement pa#ement.. Due to moment momentum um conser# conser#atio ation$ n$ those neutrons neutrons that collide collide "ith "ith hydrogen nuclei slo" do"n do"n much uic/er than those that that collide "ith other$ larger larger nuclei. +he gauge detector counts only thermal (lo" energy) or ,slo" neutrons thereby ma/ing the detector count proportional to the number number of hydrogen atoms in the pa#ement. ince "ater contains many hydrogen hydrogen atoms ('2)$ ('2)$ the detector detector count is proportional proportional to moisture moisture content. content. A calibratio calibration n factor is used to relate thermal neutron count to actual moisture content. Objectives: •
Determine the in-place density and the moisture content.
Apparatus: •
&lease see Anne3-1.
Procedure:
After the calibration nuclear density gauges are typically operated in one of t"o modes. 1. Direct transmission +he retractable rod is lo"ered into the mat through a pre-drilled hole (this hole can be formed by pounding a steel rod "ith a similar diameter to that of the gauge4s retractable rod 5 6igure 1). +he source emits radiation$ "hich "hich then interact "ith electrons in the material and lose energy and7or are redirected (scattered). 8adiation that loses sufficient energy or is scattered a"ay from the detector is not counted. +he denser the material$ the higher the probability of interaction and the lo"er the detector count. +herefore$ +herefore$ the detector count is in#ersely proportional to material density. density. A calibration factor is used to relate the count to the actual density.
6igure 1. Direct transmission
6igure '. *ac/scatter
'. *ac/scatter +he retractable rod is lo"ered so that it is e#en "ith the detector but still "ithin the instrument (6igure '). +he source emits radiation$ "hich then interact "ith electrons in the material and lose energy and7or are redirected (scattered). 8adiation that is scattered to"ards the detector is counted. +he denser the material$ the higher the probability that radiation "ill be redirected to"ards the detector. +herefore$ the detector count is proportional to the density. A calibration factor is used to correlate the count to the actual density. Discussion: 1) What are the advantages and disadvantages of the nuclear density gauge Advantages
A nuclear density gauge offers the follo"ing /ey ad#antages o#er destructi#e density measurement (cores) •
&ortability. 2ne person can easily transport a typical nuclear density gauge.
9uic/ results. %ost nuclear gauges allo" both one and four minute readings. +hese are much uic/er than typical densities obtained from cores "hich could ta/e from se#eral days to se#eral "ee/s. •
:irtually non-destructi#e. ;sed in the bac/scatter mode$ the nuclear density gauge is entirely non-destructi#e. ;sed in the direct mode$ the gauge only reuires a small penetration into the finished mat appro3imately '0 mm (less than 1 inch) in diameter and about <0 mm (' inches) deep. •
=n addition to abo#e there are some other ad#antage as follo"s. %any de#ices are built to measure both the density and moisture content of material. +his is important to the Ci#il construction industry specifically as both are essential to creating suitable soil en#ironments to support structures$ streets$ high"ays$ and airport run"ays. •
+his density gauge is ease to operate and it is menu dri#en and prompts the user through the test procedure. •
>hen a pro?ect is acti#e$ all readings ta/en "ill be stored in memory under the pro?ect number for retrie#al at a later time. •
>hen printing the sa#ed data$ either all pro?ects or a single pro?ect can be printed. Data may be printed (uploaded) to a computer file or to a printer. •
Disadvantages
All use and possession is under the direction and super#ision of the 8adiation afety 2fficer. A radioacti#e source is located in this gauge can be harmful to the operator and general public if it is not handled in accordance "ith radiation safety plan. •
+he operater "ill e3ercise suitable control o#er the gauge at all time. At no time is it to be left unattended or in the possession of an unauthori@ed person. •
+he operator "ill stand no more than 10 feet from the gauge "hile a test is in progress. +he operator "ill ensure that no euipment or #ehicles are "ithin '0 feet of "here a gauge is being used to ta/e a test unless they are shut do"n. •
A special care must be ta/en during transportation. +he euipment shall be fully secured in the transporting #ehicle and located a"ay from personnel. •
+he gauge shall be stored in "ell protected location (cabinet or room) "ith a ,Caution$ 8adioacti#e %aterial sign. •
•
&eriodic maintenance must be carried out according to the safety guideline.
!) Discuss the modifications that you purpose to use the nuclear density gauge in order to use in "ri #an$an road industry
=t is #ery important to get appro#al from the Atomic nergy Authority of ri Ban/a to operate this nuclear density gauge in ri Ban/a. =f there is a possibility$ minimi@e the radiation amount that emits from the source. +ime to time carryout a medical chec/up for the persons "or/s "ith this instrument and periodically change those "or/ers. +hereby control the radiation effect to the human body. No" only the density and moisture content can be measured from this gauge. =t is #ery useful if "e can modify this gauge to measure the other parameters as "ell. %ost of our roads ha#e une#en rough surfaces. o it is #ery important to modify this instrument to use on those surfaces.
