gamma-ray spectrometry - usdagamma radiation • emitted by naturally-occurring elements in rocks...
TRANSCRIPT
GAMMA-RAY SPECTROMETRY Cristine Morgan, Texas A&M University Jim Thompson, West Virginia University
Outline
• Gamma radiometrics? • Examples of applications in soil and earth science • Proximal sensors (field-scale examples) • Airborne sensors (regional-scale examples)
Gamma Radiation
• Emitted by naturally-occurring elements in rocks and soils
• Gamma rays have variable energies • Energy is characteristic of the radioactive isotope
• Measures from the upper 30 cm of soil or rock • Travel for up to 300 m through air • Little attenuation by vegetation
Gamma Radiation
• Potassium, Uranium, Thorium (and Cesium) • Relatively long half-lives • Relatively abundant in the environment • Produce gamma radiation of measurable intensity
40K 238U, 235U 232Th 137Cs
Gamma Radiation
Applications
• Related to mineralogy and geochemistry • Soil parent material • Weathering and pedogenesis • Geomorphic activity (source, age) • Erosion and deposition
What Properties Can Be Mapped?
• Parent materials • Soil texture (sand content, clay content) • Nutrients and other elements (Fe, K) • Soil organic matter, O horizon thickness • pH
• Bulk density • Water retention • Saturated hydraulic conductivity
The Mole The Soil Company Netherlands
Proximal Mobile Sensors
RS-700 Radiation Solutions
Canada
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
TC
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
K
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
U
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
Th
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
Cs
700950 701000 701050 701100 701150 701200 701250
3483850
3483900
3483950
3484000
3484050
3484100
3484150
Alt
158.5159159.5160160.5161161.5162162.5163163.5164164.5165165.5166166.5167167.5168168.5169169.5170
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13
182022242628303234363840424446485052545658
12131415161718192021222324252627282930313233343536373839
75
85
95
105
115
125
135
145
155
165
175
185
195
205
215
225
245
255
265
275
285
295
305
315
325
335
345
355
365
375
385
Elevation Cs
K
eTh
Total Count eU
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
TC
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
K
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
U
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
Th
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
Cs
700720 700740 700760 700780 700800 700820 700840
3483520
3483540
3483560
3483580
3483600
3483620
Alt
170.55170.6170.65170.7170.75170.8170.85170.9170.95171171.05171.1171.15171.2171.25171.3171.35171.4171.45171.5171.55171.6
0.511.522.533.544.555.566.577.588.599.51010.51111.512
343536373839404142434445464748495051525354555657
1516171819202122232425262728293031323334353637383940
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
346348350352354356358360362364366368370372374376378380382384386388390392
Elevation Cs
K
eTh
Total Count eU
Airborne Sensors
• Available data • USGS Aeroradiometric surveys of North America
• Product of the National Uranium Resource Evaluation (NURE) surveys (1975-1983)
• 2-km resolution raster data • Modeled from widely-spaced (5-10 km) flightlines
mrdata.usgs.gov/radiometric
Potassium
Equivalent Uranium
Equivalent Thorium
Dose
Sample Points (NCSS + FIA)
Preliminary Model
3.68 9.23
kg C m-2
SOC (0 - 20 cm)
Summary
• Positive • Fast • Quasi-continuous • Useful for large areas • Nearly non-destructive
• Negative • Only indirect
measurements • Need precise spatial and
non-spatial transfer functions
• Interpretation of geophysical results can be non-unique in terms of soil properties
Summary
• Combined with other environmental data, gamma has great potential as a tool for soils survey • Harmonization • Disaggregation
• Need a national strategy • How is gamma responding to soil variability in different
parent materials? • What scale of gamma data is needed to provide
effective information? • Best practices for harmonization and updating?