For example, U-238 is an alpha source because U-238 => Th-234 + alpha
Beta sources are all nuclei capable of undergoing beta decay (as neutrons turn into protons, and some of the loss Part of the neutron becomes proton, the loss becomes electron escape)
For example, Th-234 is β radioactive source, because Th-234 => Pa-234 + β
γ radioactive source is all the atomic nuclei that can undergo γ decay (for some reason, a kind of electromagnetic wave with short wavelength is emitted. gt; Po-212 + γ (why the increase in mass?)
Fr-223 =& gt; Th-227 + γ
Pb-211 =& gt; At-215 + γ (why would there be a mass increase of 4?) A nucleon density meter or nucleon meter is short for nucleon density/moisture detector, which is an electronic instrument that utilizes the principle of isotope radiation to detect the density and moisture content of geotechnical construction materials in real time. Nucleon density is usually installed with a sealed 10 milli-curie cesium 137 gamma source and a sealed 50 milli-curie americium 241/beryllium neutron source, and the instrument is also installed with two types of radiation detectors for density and humidity, respectively, with the gamma source and the neutron source*** with the density and humidity measurements of the material under test. Industry, some cement factories, coal plants, etc., the use of thickness gauge, material level meter, density meter and nuclear scales, etc., also use the same type of radioisotopes, but such instruments used by the activity of the radioactive source is generally 10 to 500 curies, is the use of civil engineering on the nucleus meter of 1,000 to 50,000 times, the two are not in a completely on an order of magnitude. Although the two types of instruments have similar names and use approximate detection principles, they are used in completely different ways, protection methods and application purposes.
Edit the basic detection function and detection method of the nucleon density meter
The nucleon meter is used on the construction site to quickly detect the wet density (total density) and moisture content (humidity) of building materials. It usually takes 1 minute or less to complete a test. The functionality of the instruments varies from brand to brand and manufacturer to manufacturer. Some instruments detect only density or only moisture content, while most brands can detect both density and moisture content. Note 2: The Nucleus Instrument calculates the total density (wet density) of the material under test by detecting the sum of the atomic weights of all the elements contained in the material under test, so the density detection of the instrument is not affected by the particle size, gradation and homogeneity, as well as the physical state and chemical composition of the material under test. Unless the chemical composition of the material under test is very significantly different from that of conventional materials, the results of the density detection by the nucleon meter normally do not need to be corrected. When a nucleon meter measures moisture, it measures all the hydrogen atoms in the material being tested, which in most soils and aggregates are present in free water. However, serpentine, clay, organics, and lime-treated soils contain bound water, and the bound water in these materials has a slight effect on the moisture content of the material tested by the instrument. This problem can be corrected by the very simple method of entering a moisture bias into the instrument. For materials such as various soils and unconsolidated cement concrete, the transmission method is usually used. This method consists of drilling a vertical test hole in the material being tested with a steel drill, and then extending the probe rod of the instrument into the material being tested to check the density and moisture content of the material at various depths. For materials such as stone, concrete, etc., where holes cannot be made, the reflection method is usually used. This method involves placing the instrument on the surface of the material to be inspected, adopting the adapted detection gear according to the thickness and type of the material to be inspected, and directly inspecting the density, compaction and other indexes of the material. In addition to the above two basic detection methods, some nuclear instrument with more and more powerful detection functions, such as MC-3C and MC-4C nuclear instrument reflection method has BS and AC two gears, respectively, used for different testing materials and testing requirements, can be any thickness of the surface material, such as accurate detection.
Editorial construction materials that can be detected by the nucleon meter and applicable detection fields
Usually the nucleon meter can be used to detect various types of soil, stone, soil and stone mixtures and other geotechnical materials. Some instruments can detect cement concrete, but many cannot detect asphalt mixtures and concrete materials with relatively small layer thicknesses. Note 3: Usually when a nuclear instrument detects geomaterials, the material under test must be of a certain thickness and of sufficiently large volume or there will not be a sufficient number of ray counts to be used in calculating density or moisture. Asphalt mixtures are usually paved with each layer no more than 7-8 centimeters thick. When the instrument is testing, the rays will penetrate this layer thickness and test the other materials at the same time, so that the instrument will not only measure the density of the thin layer of material that we want to test, but the *** same density of the different layer thicknesses. Unless the instrument designers specifically for such testing purposes on the program and testing technology to modify and set up the thin layer detection function, otherwise the instrument can not be used to detect thin layers of asphalt mixture and other concrete materials. The nuclear instrument can be used for quality control, supervisory inspection and project acceptance of on-site construction of foundations, sub-base and surface layers of highways, railroad roadbeds, reservoir embankments, airport runways as well as ports, power plants, high-grade racing tracks, high-rise buildings and other civil engineering projects. The nuclear instrument can be used in various civil engineering maintenance testing and various research and development. It can be used in laboratory and engineering test section to obtain various construction reference data quickly and accurately. Note 4: Due to the accuracy, speed, safety and low cost of the nuclear instrument, there is no other method to replace the nuclear instrument in compaction testing. Especially in projects using asphalt concrete and cement concrete, it is impossible to ensure the quality and construction efficiency of the project without the application of nuclear instrument. Therefore, in the world, the nuclear meter is used and its widely used in almost all large and important civil engineering projects.
Edit the development history of the nucleon density meter
After the Second World War, many countries have carried out large-scale infrastructure construction one after another due to the needs of post-war reconstruction and economic development. Many research organizations around the world, research the use of nuclear technology to determine the density of building materials, water content and other indicators to ensure the quality of engineering projects and construction speed. Prior to 1968, there was only one standard method for determining the density of soil and aggregates in the field-the sand filling method. The operator of this equipment had to dig a hole in the ground, fill the hole with sand, calculate the density, and then take a sample to a laboratory to determine the moisture content. This method takes half an hour for each test, the operator needs to avoid many causes of error, and the test is destructive - leaving a hole that must be repaired. The results of the moisture content test were not available until the specimen had dried the next day, and until 1968 there was only one standard method for determining the density of asphalt pavements in the field. A core sample was obtained by drilling a hole in the pavement. The cored specimen was taken back to the laboratory, weighed on a balance, and its volume measured. The density is then calculated, which is the weight divided by the volume. By 1968, the Campbell (CPN) Company in the United States led the way in commercializing portable density/moisture testers and selling the instruments to U.S. state highway departments and private inspection companies. The CPN instruments provided adequate protection against radioactive sources, making the CPN density testing technology as safe as any other testing technology. By 1972, there were significant improvements in hardware design and software applications. Portable nuclear instruments allowed for highly accurate and rapid testing of soils and asphalt pavements, and they eliminated bias due to differences in soil type or chemical composition. New instrument designs, using modern, high-performance electronics, made the instruments lightweight, reliable, and easy to operate, and after the 1980s the instruments were fitted with field-programmable microprocessors that allowed the results to be read directly from the display, thus reducing the operator's workload in the field even further. Over the past three decades, the use of nuclear instruments for density and moisture testing of geomaterials has gained worldwide acceptance and has become the standard test method in the industry.
Editorial Classification of Nucleon Density Meters
Shallow Nucleon Meters
- Shallow nucleon meters are also known as surface nucleon meters. When we refer to nucleon meters, we usually mean shallow nucleon density/moisture detectors with a measuring depth of 30 centimeters, such as Model MC-3C and Model MC-4C nucleon meters. The most widely used and most common on the market in the construction of civil engineering projects such as highways, railroads and water conservancy dams are these shallow nuclei meters. This paper introduces the nuclear instrument mainly refers to this shallow nuclear instrument.
Layered nuclear instrument
(double rod nuclear instrument) - layered nuclear instrument is also known as the middle nuclear instrument, measuring depth of 60-90 cm, such as MC-S-24 and MC-S-36 type nuclear instrument. Layered nuclear instrument has two detection rods, so some places called double rod nuclear instrument, its radioactive source and detector were placed in the end of two different probe rods, along the horizontal level of the layer by layer detection of the compacted material, generally used in the case of thicker compaction layer, especially suitable for compaction testing of roller-compacted concrete (RCC) engineering projects.
Deep Nuclear Instruments
- Deep Nuclear Instruments are used to measure at depths ranging from several meters to hundreds of meters, such as the 501DR Nuclear Density Instrument and the 503DR Neutron Moisture Instrument. Deep nuclear instruments are generally used to detect the density and moisture content of deep landfill materials, as well as for long-term monitoring of the density and moisture content of highways and railroads, embankments and slopes, and for the detection of sand and mud content in water.
Asphalt content nuclear instrument
- nuclear asphalt content tester for non-polluting, rapid detection of asphalt content in asphalt mixtures, representative models have AC-2R asphalt content tester.
Other Nuclear Instruments
- In addition to the above various instruments, known as the nuclear instrument is also used for soil moisture detection of neutron moisture detector and for chemical pipeline insulation layer hidden moisture detection of nuclear pipeline moisture detector, such as MCM-2 pipeline detector.
Editing the working principle of the nuclear density/moisture detector
1. Principle of Total Density (Wet Density) Detection
A sealed 10-millicurie Cesium-137 gamma source radiates gamma rays to the tested material such as soil and the rays penetrating into the tested material will be detected by the density detecting tube in the instrument. If the density of the material is low and the material absorbs fewer gamma rays, then more gamma rays will pass through the material within a certain period of time, and the count of the detection tube will be higher: conversely, if the density of the material is high and the dense material absorbs more gamma rays, then fewer gamma rays will pass through the material within the same period of time, and the count of the detection tube will be lower. The behavior of gamma rays penetrating, reflecting and being absorbed in the material under test is only related to the mass of the nuclei of all the atoms that make up the constituents of the material under test. The total density measured by the nuclear meter is actually the total atomic weight per unit volume of the geomaterial. Only when the total atomic weight of the material to be measured changes, the results of the nuclear instrument will change accordingly.
2. Moisture (humidity) detection principle
A sealed 50 millicurie Americium-241/beryllium neutron source radiates high-energy neutron rays to the soil and other materials under test, and the high-energy neutrons collide with hydrogen atoms and quickly lose energy and become low-energy neutrons, and any other kind of atoms can't be as significant as hydrogen atoms to reduce the energy of high-energy neutrons. The higher the humidity in the material under test, the higher the moisture content, the more hydrogen atoms, and the more low-energy neutrons will be generated when neutron rays pass through; for the same reason, when the material under test is drier, the number of low-energy neutrons generated will be less. The moisture detector tube in the instrument only detects low energy neutrons. A higher count of low-energy neutrons indicates higher humidity in the material being measured; conversely, a lower count of low-energy neutrons indicates lower humidity. The nuclear meter measures the average moisture content of the material from the surface to 10 centimeters below the surface. The nuclear meter uses different radioactive sources, different ray receivers, and different data calculation systems for density and moisture measurements, so the two detection systems for density and moisture are independent of each other, and their detection data do not affect each other.
Edit the standard counting and checking (calibration)
Standard counting-radiation source attenuation, changes in the surrounding environment and background radiation will affect the instrument's detection data. The effect of these factors on the results can be cleared by placing the instrument on a standard counting block for counting every day or after a change in the detection environment to obtain a new counting reference result. The tool used for standard counting is the standard counting block. A standard counting block is a small rectangular plastic block, referred to as a standard block. Its density and hydrogen content are stable. The block is either 5.1 or 7.6 centimeters thick and has an area equivalent to that of the base of a nuclear instrument. Each instrument has its own corresponding standard block. Calibration of Nucleon Density Instruments - Nucleon instruments are able to accurately detect the density and moisture content of materials because they are calibrated at the time of manufacture. The method of calibration is to test the instrument against a set of standard blocks of material with different density levels (calibration blocks) in order to establish a correspondence between the number of rays and the standard density value. On a coordinate chart, a calibration curve is obtained by connecting the points corresponding to the different ray counts with the standard density, i.e., a proper correspondence is established between the ray count rate of the instrument and the results of the material test (density and humidity). The calibration data can be represented in graphs, tables, and equivalence factors or stored inside the instrument for use in converting the count rate to a density value for the material. Every nuclear instrument should have been calibrated when it left the factory. Existing instruments must be calibrated after repairs that may affect the structure of the instrument. Therefore, at most every other year, the instrument's calibration should be verified or re-established using standard density and humidity materials. If the validation reveals that the difference between the detection results of the nuclear instrument and the density or humidity of the standard material no longer meets the detection requirements, a new calibration relationship needs to be re-established.
Edit the safety of the nuclear instrument
As the nuclear instrument uses the principle of radiation to measure density and humidity, many people because they do not understand the size of the activity of the radioactive source and the human body is allowed to receive the dose of how much and the correct understanding, as long as the first time I heard of a radioactive source, it will produce a sense of fear, do not dare to use the instrument. In fact, no matter where we are, there is background radiation in the environment, and it is impossible for us to avoid radiation all the time in our daily life. Portable nuclear secret/moisture soil detectors have been in commercial use for more than 35 years, and there are now some tens of thousands of nuclear instruments applied worldwide in civil engineering, geology, agriculture and environmental testing. Owners and users of nuclear instruments are subject to laws and regulations set by government authorities. This may include the need to obtain a license and for operators to learn how to use the instrument properly. Operators of nuclear instruments can monitor the dose received using personal dose detection devices, most commonly dose films. No operator of a nuclear instrument has ever been exposed to a radiation dose exceeding the ICRP occupational threshold of 5 rem/year. In fact, operators are exposed to a very small fraction of this threshold, less than the annual average of background radiation we receive from nature. There has never been a case of long-term or short-term radiation injury due to the use of a nuclear densitometer. The effects of nuclear densitometers on the body are minimal compared to the harm caused to us by everyday behaviors such as smoking and drinking alcohol, which we often ignore. There has never been a leakage of a sealed radioactive source due to physical damage or fire, etc. Even though a number of nuclear instruments are accidentally and seriously destroyed every year during field construction, there has never been an accident of contamination to the operators or the general public. By special design, the surface dose rate of the instrument is below the level that requires special protection for the operator or the general public, and there is no need to publicize the transport vehicle or the location of the test. No additional protective clothing or equipment is required. In every country, radioactive products are subject to rigorous testing by the competent governmental authorities to confirm their safety. China's environmental protection department and commodity inspection department will carry out strict testing on every regular instrument imported into China, and the instruments that pass the test will certainly meet the safety regulations and requirements, so users can use them with confidence. As long as the acquisition is approved and recognized by the government authorities of the nuclear instrument and the instrument is used for normal testing, it will never cause any harm to the operator.
Edit this paragraph nucleon meter detection method and other density and moisture detection methods
The nucleon meter detection method is adapted to the detection of any particle size, grading, composition and composition of the structure of the soil, stone and other materials. ASTM International Standard D2922-04 "Standard Test Method for Field Detection of the Density of Soil and Soil-Stone Mixtures by the Nucleus Method (Shallow Layer)" stipulates that: This test method provides a rapid, non-destructive on-site determination of the density of soil and rock. It is suitable for construction quality control, acceptance testing of soils and rocks, and for research and development. The nondestructive nature of the test permits multiple repetitions at the same test site. Standards such as ASTM D2922, D2950, "Standard Method for Field Testing the Density of Asphalt Concrete by the Nucleus Method," and C1040, "Standard Method for Field Testing the Density of Concrete by the Nucleus Method," recognize that there is no other density testing method for testing materials such as soils, rocks, asphalt mixtures, concrete, etc., that has a sufficiently high level of accuracy to be compared with the nucleus method. If the chemical composition of the material to be tested is very significantly different from that of conventional materials, such materials can be used to prepare a block of material for field calibration in accordance with the regulations, which is tested, weighed, and calculated according to strict procedures and used to make adjustments to the actual results of the nucleon meter. ASTM Standard D3017, "Field Determination of Water Content of Soil and Rock by the Nucleon Method (Shallow)" states: The nucleon meter is suitable for the measurement of water content in soil and rock in the field by a rapid, nondestructive technique. It can be applied to quality control and acceptance inspection of compacted soil and rock during construction, research and development. The non-destructive nature of the method allows multiple repetitions of measurements at a single test point and statistical analysis of the results. If the tested material contains more bound water or organic matter than conventional soils, a comparative test with, for example, the drying method is required. So normally, a certified nuclear meter can accurately detect the density and moisture content of the material and does not need to be compared with other testing methods. Due to some uncertainties of doubt and history and other aspects of the reasons, some of China's industry standards require the use of nuclear instrumentation, whether density detection or humidity detection, are required to use the traditional density, humidity detection methods for nuclear instrumentation testing for comparison tests. But there are no specific requirements and guidance on the specimen acquisition method, the specific procedures of the comparison test. Therefore, comparison tests conducted by different technicians in different fields according to their own understanding of comparison tests often vary, and many of these cases are incorrect. There are many traditional methods for measuring density and moisture, each applicable to different test materials, so the appropriate method must be selected for comparison with the nuclear meter for different test materials. For example, for different materials such as fine-grained soils, coarse-grained soils, soil-stone mixtures, asphalt mixtures, cement mixtures, and rocks, the appropriate and correct method must be selected for comparison with the nuclear instrument, depending on the situation. When performing the comparison test, the specimens tested by the nuclear method and the conventional method must be identical. If the specimens of the materials being tested are different, i.e., if the same method is used for different operators to perform the comparison test, the results of the two may be very different.
Edit paragraph nucleon density meter advantages
Comparing the nucleon density meter with sand filling method or other destructive testing methods, the advantages are obvious, mainly including:
Non-destructive testing
A. Nucleon density meter testing of the soil, only need to test the surface is smooth, drilling a diameter of 20 millimeters of the test hole. Such a small hole does not need to be repaired. For sand filling method of detection, you need to dig a hole of 150 mm in diameter, so that large holes need to be backfilled to repair. B. For asphalt pavements, only the pavement needs to be leveled, and the nuclear instrument can be used for reflection method. However, the coring method will definitely leave a hole in the pavement that must be repaired.
Accuracy
A. The nuclear meter responds to the total weight of the material located between the radioactive source and the detector, and the detection is not affected by the chemical, mineral, or textural composition of the material being tested. Detection is very correct regardless of whether the material is homogeneous or not, or whether the particles are coarse or fine. B. Test results are better represented by the large volume of soil soil being tested. For a transmission density test with a test depth of 8 inches (20 CM), the specimen volume is approximately 25 cubic feet. For sand-filled tests, the specimen volume is approximately 10 cubic feet. C. Nucleometers are calibrated on standard, fixed, numerically constant soil and rock calibration blocks or other standard blocks of density and moisture material that are traceable to real soil. Testing protocols recommend calibration every one to two years. The operator can perform daily standard counts with a standard counting block to check the calibration status and detection capabilities of the instrument.
Speed of Detection
An instrumented test takes less than 5 minutes to complete, allowing the Nucleus to perform more tests and statistically analyze the quality of the project than the approximately 30 minutes it takes to complete a test by sand filling or coring. Simple and Safe Operation A. Operator error potential is virtually impossible. The instrument requires only minimal instructions to carry out a test. The instrument automatically calculates and displays test results and gives units. Unlike sand-filled tests, high humidity and vibrations from construction equipment do not affect the accuracy of a nuclear instrument in the vicinity. B. Unlike the sand-flooding operator, the nuclear meter operator can stand at all times, safely observe moving construction equipment if danger approaches, and quickly leave if there is danger.
"Real-Time" Inspection
The nuclear meter displays results minutes after the roller passes. It can provide immediate guidance on the need for additional rolling, and can help to adjust the construction method in time to ensure that the required results are obtained.