IIdI

INFORMATION CIRCULAR/l 9%

Evaluation of Several Natural Gamma

Radiation Systems-A Preliminary

Study

UNITED STATES DEPARTMENT OF THE INTERIOR

UNITED STATES BUREAU OF MINES
U.S. Department of the Interior

Mission Statement

As the Nation’s principal conservation agency, the Department of

the Interior has responsibility for most of our nationally-owned

public lands and natural resources. This includes fostering

sound use of our land and water resources; protecting our fish,

wildlife, and biological diversity; preserving the environmental

and cultural values of our national parks and historical places; and

providing for the enjoyment of life through outdoor recreation.

The Department assesses our energy and mineral resources and

works to ensure that their development is in the best interests of

all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility

for American Indian reservation communities and for people who

live in island territories under U.S. administration.
Information Circular 9434

Evaluation of Several Natural Gamma

Radiation Systems-A Preliminary

Study

By S. D. Maksimovic and G. L. Mowrey

UNITED STATES DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

BUREAU OF MINES

Rhea Lydia Graham, Director
CONTENTS

Abstract ...........................................................................

Introduction ........................................................................

General description of NGR systems.. ....................................................

RHC model 801 ...................................................................

RHC model 803 ...................................................................

AME models 1008 and 1016 ..........................................................

Eberline ESP-2 ...................................................................

EDAGRS-500.. ..................................................................

NGR evaluation tests .................................................................

Pittsburgh coal seam ...............................................................

Effect of airgap distance on NGR ....................................................

Underground coal thickness measurements .............................................

Variability of NGR readings for a given formation ........................................

Laboratory testing of coal and rock ...................................................

Kittanning coal seam ...............................................................

Underground testing .............................................................

Laboratory testing ;. .............................................................

Freeport coal seam .................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Clarion coal seam .................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Illinois No .5 coal seam .............................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Hiawatha coal seam ................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Wadge coal seam ..................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Additional NGR evaluation tests .........................................................

Pittsburgh coal seam ...............................................................

Underground testing .............................................................

Laboratory testing ...............................................................

Freeport coal seam .................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

Maxwell coal seam .................................................................

Underground testing .............................................................

Laboratorytesting ...............................................................

B coal seam ......................................................................

Underground testing .............................................................

Laboratory testing ...............................................................

Upper Left Fork coal seam ...........................................................

Underground testing .............................................................

Laboratory testing ................................................................

NGR systems in operation at mine sites ...................................................

Summary ..........................................................................

References .........................................................................

Appendix.-Technical specifications of several NGR systems .....................................

1

2

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4

5

8

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9

1 1

11

12

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1 8

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1 9

1 9

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21

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45
ILLUSTRATIONS

1 . RHC 801 NGR probe and coal thickness indicator unit .....................................

2. Coal thickness indicator unit for RHC 8O1 probe .........................................

3. Remote indicator unit for RHC 801 probe ..............................................

4 . Block diagram for RHC 801 NGR coal thickness indication system ............................

5. Physical size comparison between RHC 803 and RHC 801 NGR thickness indication systems .........

6. Gamma sensor for AME 1008 coal thickness measurement system ............................

7. Operator control and display unit for AME 1OO8 system.. ..................................

8. Block diagram for AME 1OO8 coal thickness sensor and display system .........................

9. Physical size comparison between the RHC 803, RHC 801, and AME 1008 NGR sensors ...........

10. Eberline ESP-2 unit ...............................................................

11. Eberline ESP-2 beii used underground ................................................

12. EDA GRS-5OO unit ...............................................................

13. Effect o fNGR rates as a function of distance as measured underground.. ......................

14. Variation of NGR rates along an underground coal face and adjacent ribs .......................

15. Effect of roof shale thickness on NGR count rates for different container diameters ...............

16. Effect of sample thickness on NGR count rates for 102-mm-diameter container ...................

17. Effect of coal sample thickness on NGR count rates for different container ......................

18. Effect of floor fireclay sample thickness on NGR count rates for different container diameters ........

19. Effect of sample thickness on NGR count rates for shale, coal, and fireclay, 102-mm container ........

20. Effect of samle thickness on NGR count rates for shale, coal, and fireclay, l52-mm container ........

21. Effect of sample thickness on NGR count rates for shale, coal, and fireclay, 190.5mm container ......

22. Effect of airgap on NGR count rates for shale, clay, and coal, 203- by 203-mm container, sample

thickness 76 mm ................................................................

23. Effect of airgap on NGR count rates for coal.. ..........................................

24. Effect o fairgap on NGR count rates for shale and parting ..................................

25. Effect of coal sample weight on NGR count rates Pittsburgh Coal Seam.. ......................

26. Effect of shale, parting, and coal sample weights on NGR count rates Pocohontas Coal Seam ........

27. Effect of shale and coal sample weight on NGR count rates No. 2 Gas Coal Seam ................

2 3

2 3

2 4

2 4

2 5

2 6

2 6

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28

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32

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3 9

4 0

41

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TABLES

1. Effect of airgap distance from a geological surface on NGR count rate as measured underground ..... 4

2. Effect of airgap distance on NGR count rate for various thicknesses of floor coal as measured

underground ................................................................... 5

3. Variation of NGR count rates as measured along underground coal face and adjacent ribs ........... 5

4. Effect of sample thickness on NGR count rate for different container diameters .................. 6

5. Effect of sample thickness on NGR count rate for 102-mm ID container.. ...................... 6

6. Effect of airgap on NGR count rates for 2O3- by 203-mm container, sample thickness 76 mm ......... 6

7. Effect of airgap on NGR count rates for coal.. .......................................... 7

8. Effect of airgap on NGR count rates for shale and parting .................................. 7

9. Effect of coal sample weight on NGR count rates.. ....................................... 7

10. Effect of shale, parting, and coal sample weights on NGR countrates.. ........................ 7

11. Effect of shale and coal sample weights on NGR count rates ................................ 8

12. Comparison of NGR count rates for different coal seams-underground tests ..................... 9

13. Comparison of NGR count rates for different coal seams-laboratory tests ...................... 1 0

14. Comparison of RHC 801 and ESP-2 NGR count rates for Kittanning coal seam-underground tests .... 1 0

15. Laboratory analyses of roof, coal, floor, and parting samples for different coal seams ............... 1 1

16. KUT radiometric and chemical laboratory analyses of roof samples ............................ 12

17. KUT radiometric and chemical laboratory analyses ‘of coal samples ............................ 13
TABLES--Continued

18. KUT radiometric and chemical laboratory analyses of floor samples ........................... 14

19. Underground and laboratory NGR measurements taken at five coal seams ...................... 1’7

20. Laboratory analyses of one sample from each of five coal seams .............................. 18

21. NGR sensors operating in U.S. mines ................................................. 2 1

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

Btu/lb British thermal unit per pound

c m centimeter

cpm count per minute

cps count per second

ft foot

ft/min foot per minute

g gram

h hour

in inch

keV kilo electron volt

kg kilogram

lb pound

MeV

m

m/min

mA

m m

S

s t

V

&i

W

“C

“F

mega electron volt

meter

meter per-minute

milliampere

millimeter

second

short ton

volt

microcurie

microsecond

degree Celsius

degree Fahrenheit

Reference to specific products does not imply endorsement by the U.S. Bureau of Mines.
EVALUATION OF SEVERAL NATURAL GAMMA RADIATION

SYSTEMS-A PRELIMINARY STUDY

By S. D. Maksimovic1 and G. L Mowrey1

ABSTRACT

An important element of the U.S. Bureau of Mines (USBM) mining research program is the

development and evaluation of reliable coal interface detection (CID) systems. Commercially available

CID sensors based on natural gamma radiation (NGR) are only applicable if the immediate roof is

composed of shaley material. The USBM has made numerous underground and laboratory measurements using several NGR systems approved for installation on mining machines by the Mine Safety

and Health Administration. In addition, two small handheld NGR instruments were used to make

comparative measurements. Underground NGR measurements in 10 different coal seams, potassiumuranium-thorium radiometric analyses on samples from 16 seams, and chemical analyses of coal and

rock for correlation with NGR counts were made. Laboratory test results on the effect of airgap and

sample thickness, size, and weight on the NGR measurements, as well as general results of the various

NGR systems, are discussed.

‘Electrical engineer, U.S. Bureau of Mines, Pittsburgh Research Center, Pittsburgh, PA.
2

To help evaluate the usefulness of the natural gamma

radiation (NGR) technique for the coal interface detection

(CID) project, the U.S. Bureau of Mines (USBM) collected data from various mining companies conducting

underground and surface operations in 15 major and 110

minor coal seams in the United States (1).2 This work was

done in support of the USBM goal to improve the method

of recovering coal from the nation’s mines in a safe and

economical manner. Field visits were made to eight mines

with underground operations in three major and four

minor coal seams in different coal regions. Underground

tests were made of three commercially available NGRbased coal thickness measurement systems (RHC 801,

RHC 803, and AME 1008) that have been approved

for installation on mining machines by the Mine

Safety and Health Administration (MSHA). A fourth

MSHA-approved sensor, the AME 1016, was not available

for testing. Over 200 coal and rock samples have been

collected from these mines for standard coal laboratory

analyses (i.e., ash, sulfur, and heating value). Project

personnel measured the NGR of these samples using two

handheld radiation survey instruments (ESP-2 and GRS500). Also, 45 coal and rock samples, representing 16 coal

seams, were analyzed for bulk density, potassium, uranium,

and thorium, using radiometric testing methods. It should

be noted that the handheld instruments can only be used

in fresh air since they have not been approved as intrinsically safe. General descriptions of these NGR systems and results of selected underground and laboratory

tests are given in this report.

GENERAL DESCRIPTION OF NGR SYSTEMS

The NGR technique measures naturally occurring

gamma radiation found in underground strata. Shales,

clays, silts, and muds typically have higher levels of naturally occurring radioactivity than coal, sandstone, and

limestone. This is because minute quantities of radioactive

potassium, uranium, and thorium are nearly always deposited during the formation of the shaley materials.

Therefore, overlying and/or underlying shale strata act as

the NGR source, and intervening coal is an NGR absorber

whose thickness can be determined by the amount of NGR

attenuation.

Two vendors, Rowe Hankins Components, Ltd. (RHC),

of Lancashire, England [formerly known as Salford Electrical Inc. (SEI)] and American Mining Electronics (AME)

of Huntsville, AL, fabricate MSHA-approved NGR systems for mining equipment. RHC currently manufacture

Models 801 and 803 natural gamma coal thickness indication systems. These RHC units have been used on

longwall shearers and continuous miners in underground

applications, and also on highwall miners in surface applications. The readouts of the two RHC units consist of

a column of light emitting diodes (LED’S), each of which

represents 20 mm (0.75 in) of roof coal. Over 150 of

these RHC systems are in use worldwide, the majority in

England but some are used in the United States on highwall miners and longwall shearers.

AME makes similar NGR systems, the AME 1008 and

AME 1016. The AME 1008 and AME 1016 use LED’s to

provide numerical output that directly gives the thickness

%lic numbers in parentheses refer to items in the list of references

preceding the appendix at the end of thii report.

in inches of roof coal remaining. They have been successfully used in numerous underground mining operations

in the United States on both continuous miners and longwall shearers (2).

Two small handheld radiation survey instruments

(Eberline ESP-2 and EDA GRS-500) were used at selected mine sites for evaluating the applicability of the

NGR technique. Since these units are not intrinsically safe

they must be used only in fresh air. They are also used

for NGR laboratory testing of coal and rock samples.

Details of specific sensors and radiation survey instruments

follow. Technical specifications of the NGR systems

evaluated in this report are given in the appendix.

RHC MODEL 801

The RHC Model 801 NGR sensor (probe) (3) uses a

scintillation detector [NaI (Tl) crystal] that is rugged and

can be mounted on the face side of any coal-cutting

machine (figure 1). According to the manufacturer, it can

reliably sense between 0 and 500 mm (0 and 19.5 in) of

coal thickness in the present or previous cut or prior to

cutting. The RHC SO1 coal thickness indicator (CTI) unit

is connected to the RHC 801 probe and provides the

machine operator with an indication of the deviation from

required roof or floor coal thickness (figure 2). The horizon (required coal thickness) can be set anywhere in the

range from 0 to 500 mm (0 to 19.5 in), the deviation being

indicated by LED’s in multiples of 20 mm (0.75 in) up to

a maximum of +&I mm (3.1 in). There are presently

three electrically identical intrinsically safe (IS) power

supplies. The mechanical arrangement of the components

is different to allow for fitting into different sired spaces.
An optional remote indicator unit provides a secondary

set of LED’s indicating any error in coal thickness from

the horizon setting (figure 3). This unit, powered by the

CI’I unit, can be added to the system if needed (e.g., for

double-ended longwall shearer machines).

A block diagram of the RHC 801 coal thickness system

is given in figure 4.

RHC MODEL 803

The RHC Model 803 unit looks basically identical to

the RHC 801, except that it is smaller (figure 5). It was

developed to fit on smaller mining equipment, e.g., continuous minersP

The main difference between the RHC 803 and the

original RHC 801 is a different method of isolation. Also,

a circuit board in the 801 unit for an analog and reverseanalog output that had never been used was removed from

the 803, both units now have only digital outputs. Both

units have been approved. by MSHA for intrinsic safety

(approval No. IA-371).

AME MODELS 1008 AND 1018

The AME Model 1008 coal thickness sensor uses a

scintillation detector [Nal (Tl) crystal]. It is a highperformance NGR system containing a large-area gamma

detector that accurately measures coal left on the roof or

floor when the seam-boundary material contains gammaproducing elements. The system works extremely well in

areas where gamma emissions are relatively constant at

the mining site and is applicable to both longwall and

continuous mining machines (4). The sensor assembly is

housed in an explosion-proof (X-P) enclosure that has a

window to receive NGR from the rock at the coal-seam

boundary. When the window is pointed at the roof or

floor area to be measured, the total gamma emission

entering the window is directly related to the thickness of

coal left at the rock boundary (figure 6).

An IS control and display unit converts gamma counts

from the sensor into inches of coal (figure 7). Figure 8 is

a block diagram of the AME 1008 coal thickness system

and figure 9 shows the physical size comparison between

the RHC 803, RHC 801, and AME 1008 natural gamma

sensors.

3

The larger system (AME 1016) has a sensitive NAl

crystal that is 33% larger and is capable of measuring up

to 890 mm (35 in) of coal with sufficient NGR counts It

can be connected to the existing system replacing only the

sensor unit on the boom (4). However, this system was

not available for evaluation for this report.

EBERUNE ESP-2

The Eberline Smart Portable (ESP-2) radiation survey

instrument, manufactured by Eberline Instrument Corp.,

Santa Fe, NM, is a handheld unit designed for routine

radiation surveys (figure 10). It can also be used in

remote areas, operated solely by a computer. The unit

utilizes a scintillation detector [NaI (Tl) crystal] to measure NGR in both the field and laboratory (figure 11). It

is also equipped with a single-channel pulse height analyzer (PI-IA). Information provided by this instrument is

used to determine if the NGR technique is applicable at

a given mine and seam (5). Because of the high voltage

(500 to 2,450 V) needed by the photomultiplier tube, the

ESP-2 is not intrinsically safe; therefore, it must only be

operated in fresh air when NGR measurements are taken

underground

EDA GRS_500

The GRS-500 differential gamma ray spectrometerscintillometer is manufactured by EDA Instruments Inc.,

Toronto, Canada (figure 12). This instrument is a compact, portable, lightweight, 5-channel field spectrometer

that uses both a wideband and a narrowband spectrometer. The wideband spectrometer (a sensitive scintillometer) is used for general reconnaissance. It measures total

gamma-ray activity from the uranium series, as well as

emitters from the naturally occurring thorium series and

potassium (6). Like the ESP-2, the information provided

by this instrument is used to determine if the NGR technique is applicable at a given mine and seam. Also, the

GRS-500 is not intrinsically safe because of the high

voltage (500 to 2,450 V) needed by the photomultiplier

tube; therefore, it must only be operated in fresh air when

NGR measurements are taken underground.

NGR EVALUATION TESTS

A series of NGR measurements and geological sam-, Mountain) at eight underground mines located in three

ple collections (coal, rock) have been made in the three major and four other coal seams. Results of potassiummain geological provinces (Eastern, Interior, and Rocky uranium-thorium (KUT) radiometric analyses and results

of chemical analyses of laboratory testing of coal and rock

‘Ptasnik, L (President, Mine and Process Setice Inc., Kcwance, IL) for possible correlation with NGR counts and other CID

personal communication, 1992. sensor measurements, are reported.
PITTSBURGH COAL SEAM

In the Pittsburgh Coal Seam, numerous NGR readings

have been made with three commercially available

machine-mounted NGR units (RHC 801, RHC 803, and

AME 1008), as well as two handheld units (Eberiine ESP2 and EDA GRS-500), at selected locations underground

at the roof mid-seam, floor, and air, in the USBM Safety

Research Coal Mine (SRCM). The coal seam in the study

area is about 1,674 mm (66 in) thick. The immediate roof

strata are composed of shale, up to 610 mm (24 in) thick,

followed by draw slate. Due to poor roof conditions, the

immediate roof is generally removed. The immediate

floor is water-sensitive soft fireclay. One parting of

variable thickness is typically found in the seam.

Effect of Airgap Distance on NGR

Underground testing using these NGR systems was

done to investigate the effect of the airgap between the

formation surface being measured and the NGR detector.

Readings were made at different points by locating the

NGR sensor at 76, 152, 305, and 1,219 mm (3, 6, 12, and

48 in) from the roof (shale), face (coal), and floor

(fireclay) surfaces and also in the middle of the entry (air).

Figure l3 shows the variation of the NGR readings in

the entry, as the NGR detector (ESP-2) is moved away

from the surface of roof, coal, and floor. At 76 mm (3 in)

from the coal on the right rib, the NGR reading increased

21% with respect to the reading taken with the unit at

contact with the coal. In general, for the coal, the NGR

reading increased most rapidly during the first 152 mm

(6 in), ranging from 16% to 31% increase. At 305 mm (12

in), the total increase ranged from 22% to 54%. For roof

shale, at 76 mm (3 in) from the surface, the reading

decreased 3%; at 152 mm (6 in), the reading decreased by

10%; and at 305 mm (12 in), the reading decreased by

17%. In general, the NGR readings decreased considerably during the first 305 mm (12 in), approaching the

background air reading at a distance of 1,219 mm (48 in).

For floor fireclay, the NGR reading decreased mostly

during the first 76 to 152 mm (3 to 6 in) from the surface.

For 152 to 305 mm (6 to 12 in), the decrease was insignificant (3% to 12%). By increasing the distance of the

detector from the coal or rock strata surface by 3% to

l2%, the influence of NGR from the surface was found to

decrease. At a distance of 305 to 381 mm (12 to 15 in)

from the source, the NGR rate was found to be similar to

the ambient background NGR rate (combined influence of

roof, coal, and floor strata) (table 1).

Underground Coal Thickness Measurements

Underground NGR readings in the SRCM were conducted using the RHC 801, RHC 803, AME 1008, ESP-2,

and GRS-500 sensors. Five slots of different coal thicknesses were prepared by leaving from 0 to 305 mm (0 to

12 in) of coal on the floor. Table 2 shows the general

trend of how the gamma-ray counts are attenuated as a

function of coal thickness left on the roof and floor, and

airgap below-the-roof coal or above-the-floor coal. As the

distance increased from 0 to 381 mm (0 to 15 in), the

NGR readings slightly increased during the first 229 mm

(9 in) when using the ESP-2, and then decreased as the

distance from the floor increased. The NGR readings for

the ESP-2 were not always consistent. For 0 to 76 mm

(0 to 3 in) of coal left on the floor, the NGR readings

using the RHC 801 decreased as the distance from the

floor clay and coal inaeased from 0 to 381 mm (1 to

15 in). For 152,229, and 305 mm (6,9, and 12 in) of coal

left on the floor the NGR readings for the RHC 801 unit

generally increased slightly as the airgap above the coal

increased from 0 to 229 mm (0 to 9 in). It should be

noted that for 0, 76, and l52 mm (0, 3, and 6 in) of coal

left on the floor and airgaps of 0 to 229 mm (0 to 9 in),

the NGR readings of the RHC 803 were from 10% to

20% higher than those of the RHC 801.

Table 1 .--Effect of alrgap distance from a geological surface

on NGR count rate (cpm) as measured underground

(Pittsburgh Coal Seam)

m&v, Roof coal Floor Backm m fin) shale fireclav around’

0 (0) . . . . . 10,267 3,670 a,377 6,@33

7 6

152

ii ***** 9,917 4,447 a,573 6,600

(12)’ : : : :

9,200 4,493 7,520 6,600

305 a,493 4,937 7,410 6,600

1,219 (48) . . . . 6,813 6,110 6,820 6,600

‘As measured in air in the middle between the floor and roof.

With airgap from 0 to 229 mm (0 to 9 in), the NGR for

the AME 1008 was 2.02 times greater than the RHC 803

for 152 mm (6 in) of coal left on the floor, to 2.73 times

for 0 mm (0 in) of coal on the floor. When compared

with the RHC 801, the NGR readmgs for the AME unit

were from 2.42 times to 3.16 times greater for the same

measurements. The NGR readings of the RHC 803 were

4% to 18% higher when compared with the RHC 801

(table 2).

Variability of NGR Readings for a Given Formation

Figure 14 shows the variation of the NGR rates along

a 8.53-m (28~ft) long entry of the SRCM. NGR readings

using the ESP-24 were done at 1.22-m (4ft) intervals for

*rhc FSP-2 unit was used with a 64mm (0.25-in) thick lead shield

on a detector. By using this lead shield on the detector, the roof-to-coal

ratio increased up to 38% and the floor-to-coal ratio increased up to

32%.
5 

the roof, coal, and floor strata of the left rib, face, and 

right rib (table 3). 

Table 2-Effect of airgap distance on NGR count rate (cpm) for 

various thicknesses of floor coal as measured underground 

(Pittsburgh Coal Seam) 

AkQaQ. ESPP RHC RHC AME GRS 

mm -’ iin) 801 803 1098 5uo 

0 mm (0 in) coal on floor 

0 (0) . . . 7,517 12,938 11,904 35,301 17,328 

78 (3) . . . 8,873 12,989 11,712 34,243 14,878 

229 (9) . . . 5,877 11,508 9,774 30,912 12,788 

381 (15) . . 4,930 10,888 9,818 27,500 11.874 

78 mm (3 in) coal on floor 

0 (0) . . . 5,187 9,584 8,898 24,833 12,839 

78 (3) . . . 3,233 9,300 8,940 24,919 11,892 

229 (9) . . . 3,059 9,188 8,472 23,352 10,522 

381 (15) . . 2,887 8.472 8.084 22,834 10.108 

152 mm (8.in) coal on floor 

0 (0) . . . 3,580 8,852 5,558 15,079 9,818 

78 (3) . . . 3,820 8,888 8,428 15,809 9,838 

229 (9) . . . 3,4T7 7,038 8,594 18,024 9,794 

381 (15) . . 3,437 7,805 8,780 17,791 9,918 

0 

78 

229 

229 mm (9 in) coal on floor 

(0) . . . 3,097 8,078 5,790 13,801 8,850 

(3) . . . 3,233 8,402 8,114 14,112 8,882 

(9) . . . 3,051 8,578 8,338 14,043 8,242 

381 (15) . . 2,887 7,044 8,758 14,285 8,078 

0 

78 

229 

305 mm (12 in) coal on floor 

(0) . . . 2,250 4,410 3,800 9,015 8,984 

(3) . . . 2,343 4,814 3,852 9,888 7,444 

(9) . . . 2,520 8,120 4,898 12,340 7,885 

381 (15) . . 2,409 8,342 5,228 15,481 8,098 

Backaround’ 

7,417 11,598 11,814 31,385 15,908 

‘As measured in air in the middle between the floor and roof. 

NOTE.--Measurements taken in the USBM SRCM. 

For the left rib, the mean reading for eight points was 

9,900 cpm for roof shale and 3,870 cpm for coal. The 

mean reading for the right rib over a corresponding 

distance for shale was 10,640 cpm and for coal was 

4,470 cpm. The right rib reading is 7% higher for the roof 

shale and 16% higher for coal. 

The mean ambient background air NGR rate at eight 

points in the center of the entry cross-section was 6,340 

cpm, which is about 15% lower than the mean value of 59 

readings of the surrounding roof, coal, and floor combined 

(7,280 cpm). 

For the face, the mean NGR reading obtained at five 

points was 9,820 cpm for roof shale, 3,440 cpm for coal, 

and 7,260 cpm for floor fireclay. For the right rib, the 

mean reading for floor fireclay was 8,300 cpm. 

Laboratory Testing of Coal and Rock 

Sample Thickness 

The mean NGR reading for the main roof at eight The effect of sample thickness on the NGR rates for 

points, which is about 0.61 m (2 ft) above the coal, was three different diameter plastic containers [i.e., 102-, l52-, 

6,030 cpm. The mean roof-to-coal (R:C) ratio for the left 

rib was 2.56, for the face it was 2.85, for the right rib it 

and 190.5mm (4.0-, 6.0-, and 7.5in)] ID was investigated 

empirically in the laboratory using the ESP-2. The results 

was 2.38. For the floor strata, the floor-to-coal (F:C) ratio are shown in figures 15 to 21. The data indicate that 

was lower, 2.11 for the face and 1.86 for the right rib. sample thickness of roof shale and floor Ereclay obtained 

When roof, coal, and floor samples obtained from the 

same area were measured in the laboratory, a R:C ratio 

of 235 and a PC ratio of 2.05 were indicated for the 

right rib, comparing favorably to the data obtained 

underground 

Tablo 3.-Variation of NGR count rates (cpm) as measured 

along underground coal faoe and adjaoent ribs 

(Pittsburgh Coal Seam) 

Distance from face, 

mm (ft) 

Roof coal Floor BaokRiaht rib 

ground’ 

0 (0) . . . . . . . 

1.22 (4) . . . . . . . 

2.44 (8) . . . . . . . 

3.88 (12) . . . . . . 

4.88 (18) . . . . . . 

8.10 

7.32 

yo; . . . . . * 

8.53 (28) : : : : : : 

L 

9,330 

10,059 

11,370 

10,380 

10,909 

11,039 

11,070 

11.100 

3,100 7,500 3.470 

4.200 8,370 5,909 

4,370 8,240 8,450 

4290 8,540 6,8M 

4,810 6,280 8,780 

4,830 8,130 7,190 

4,780 8,510 7,310 

5,380 8,620 7,020 

Face 

0 (0) . . . . . . . 10,870 3,050 ND ND 

0.91 (3) . . . . . . . 10,530 3,880 8,790 ND 

2.13 &‘:::::: 9,240 3,550 7,250 ND 

3.35 9320 

9:x30 

3830 

a:100 

7590 

7L580 

ND 

4.57 (15) . . . . . . ND 

Left rib 

0 ;; . . . . . . . 9,890 4,890 ND ND 

1.22 

2.44 (8) : : : : : : : 

9,890 4,130 ND ND 

9,180 3,590 ND ND 

3.88 (12) . . . ..I 11,170 3,900 ND ND 

4.88 (18) . . . . . . 9,980 3,950 ND ND 

8.10 (20) . . . . . . 9,380 3,950 ND ND 

7.32 (24) . . . . . . 9,020 3,810 ND ND 

8.53 (28) . . . . . . 10,870 3,059 ND ND 

ND No data. 

‘As measured in air in the middle between the floor and roof. 

NOTE.-Measurements taken in the USBM SRCM. 
6 

from two different coal seams (Pittsburgh and Coalburg) 

have a considerably greater influence on the NGR rates 

than pure coal. However, increasing the thickness of the 

material beyond 76 to 102 mm (3 to 4 in) caused changes 

in the NGR rates that were generally insignXcant (tables 4 

and 5). 

Table 4.-Effect of sample thlckneu on NGR count rate (cpm) 

for different container diameters 

(Pittsburgh Coal Seam) 

Sample thicknesq 

mm Cd 

Container ID, mm (in) 

(2% 102 152 190.5 

(4) (61 (7.5) 

Roof shale 

0 (01 . . . . . . 2,450 1,669 1,660 1,660 

12.7 

25.4 

36.1 

63.5 

66.9 

127.0 

139.7 

190.5 

(0.5) . . . . . 2.720 1,650 2,240 2,200 

(1.0) . . . . . 2.940 2,269 2,260 2,630 

(1.5) . . . . . 2,970 2/440 2,540 3,260 

3,070 3,469 

241.3 b.4.. . . . 3,266 2,960 ND ND 

cod 

0 

127 

25.4 

76.2 

152.4 229.0 

(0) . . . . . . 1,630 1,710 1,600 

(0.5) . . . . . 

f’z 

1,640 1,710 1,640 

(1.0) . . . . . k467 1,600 1,660 1,670 

(3.0) . . . . . 2,610 1,790 1,669 1,730 

(6.0) (9.0) . . . . . . . . . . 2,660 2,670 1,79064 1,920 ND ;; 

Floor firedav 

0 (0) . . . . . . 1,420 1,510 1,660 

12.7 (0.5) . . . . . 1,640 2,210 2,420 

25.4 (l.O)..... 2090 2,490 2,550 

36.1 (1.5) . . . . . 

:iz 

2,250 2,640 2,960 

63.5 2730 2,360 3,070 ND 

69.0 2,669 2,560 3,160 ND 

127.0 2,960 2,670 ND ND 

190.5 2290(7.5).90 . . . . . 2,9306 2,: /; ;; 

ND Nodata. 

‘NGR rates associated with the 7O-mm (2.75-in) ID container 

are higher than the other rates because the NGR readings were 

taken without fead shielding; lead shielding was used for the other 

three diameters. 

NOTE.-Samples obtained from USBM SRCM. 

Container Diameter 

The effect of container diameter on the NGR rates was 

investigated empirically in the laboratory using the ESP-2. 

The results are shown in figures I5 to 21 and tables 4 and 

5. The data indicate that NGR rates increase as the ID of 

the plastic container increases (roof shale-Pittsburgh Coal 

Seam). Also, the thickness of the material appears to be 

significant, particularly during the first 76 to 102 mm (3 to 

4 in), after which the thickness does not have much effect 

on the NGR rates (i.e., approaching an infinitely thick 

layer). 

Table 6.4ffect of sample thickness on NGR count rate (cpm) 

for lOZ-mm (4-h) ID container 

(Pittsburgh and Coaiburg Coal Seams) 

Sample Black Gray 

thickness, Shale’ shale2 Coal’ shale’ Rreclay’ Coal2 

mm (in) 

0 101 . . . 1.660 1.510 1.630 1.500 1,420 1,670 

12.7 (0.5) . . l&O 

25.4 (1.0) . . 2,260 

36.0 (1.5) . . 2,440 

63.5 (2.5) . . 2,660 

66.9 (3.5) . . 2,620 

139.7 (5.5) . . 2,810 

190.5 (7.5) . . 2,910 

241.3 (9.5) . . 2,960 

ND No data. 

‘Pittsburgh Coal Seam. 

%oalburg Coal Seam. 

Airgap 

1;650 1;f.W 1,750 1,640 1,770 

z=J 1,800 1,670 2,090 1,910 

2,530 1,600 2,110 2,250 1,820 

z= 1,790 2,250 2,360 l,=J 

3,070 ND 2,370 2,560 1,920 

3,120 1,790 2,490 2,670 l,=J 

3,090 ND 2,470 2,640 1,959 

3.260 1.640 2,560 ND 2,010 

Samples were also tested for NGR using the ESP-2 

while increasing the distance between the detector head 

and the sample material in the shielded enclosure [203- by 

203-mm (8- by 8-in) ID plastic container] with different 

sample weights. Preliminary results indicate that for rock 

samples, the maximum decrease in NGR readings within 

a distance of 25.4 mm (1 in) from the samples is 14% to 

24%. Within a distance of I27 mm (5 in), the total 

decrease ranged from 25% to 45%. From 127- to 229-mm 

(5 to g-in) distance, the decrease was in the range of 1% 

to 5%. Coal samples had from 3% to 5% decrease in 

NGR readings for a 229-mm (g-in) ‘distance from the 

sample (figures 22 to 24 and tables 6 to 8) (Pittsburgh and 

Pocahontas Coal Seams). 

Table S.-Effect of alrgap on NGR count rates (cpm) 

for 263- by 263-mm (6- by &In) container, 

sample thickness 76 mm (3 In) 

(Pittsburgh Coal Seam) 

Ww, Shale Coal Clay 

mm (in) 

0 (0) . . . . . . . 3643 l*=o 2,950 

25.4 (1.0) . . . . . . 3,107 1,663 2,967 

50.6 (2.0) . . . . . . 2,603 1,627 2,723 

76.0 g.0; . . . . . . 2,603 1,660 

127.0 

177.6 &O) : : : : : : 

2,370 1,647 

2,233 1,947 

Background’ : . . . . . . . 1,707 1,707 1,640 

‘As measured in air in the middle between the 

floor and roof. 
7 

Table 7. Effect of airgap on NGR 

count rates for coal’ 

(Pittsburgh Coal Seam) 

wPP, NGR count 

mm OnI rate, cpm 

0 (0) . . . . . . 2,273 

12.7 (0.5) . . . . 2,287 

25.4 (1.0) . . . . 2,237 

50.8 (2.0) . . . . 2293 

76.0 

E **-* 

2,310 

101.6 

127.0 (5:o) : : : : 

a90 

2,273 

152.4 (6.0) . . . . 2,277 

177.8 (7.0) . . . . 2,340 

203.2 (6.0) . . . . 2,197 

‘Coal weight 1,040 g (2.3 lb); NGR 

background count rate 2,027 cpm. 

Table &-Effect of alrgap on NGR count rates (cpm) 

for shali and parting 

(Pocahontas Goal Seam) 

Mm, Bottom shale, Parting, 

mm (in) 3,680 g (8.11 lb) 3,057 g (6.76 lb) 

0 (0) . . . . . . 5,200 4,900 

12.7 (0.5) . . . . . 4,660 ND 

25.4 ;;.cl; . . . . . 4,327 3,713 

50.8 

(3:o) : : : : : 

3,770 3,507 

76.0 3,343 3,197 

101.6 (4.0) . . . . . 3,077 2,973 

127.0 (5.0) . . . . . 2,917 2,753 

152.4 (6.0) . . . . . 2,953 2,763 

177.8 (7.0) . # . . . 2,857 2,697 

203.2 (8.0) . . . . . 2,783 2,613 

229.0 (9.0) . . . . . 2,647 2,650 

ND No data. 

Figure 22 shows the effect of distance of the NGR 

detector from the surface of the powdered material (60 

mesh) in a 203 by 203-mm (8- by &in) ID plastic container, 76 mm (3 in) sample thickness. NGR rates for 

both roof shale and floor fireclay samples were found to 

decrease considerably at distances of up to 76 mm (3 in) 

from the sample surface. In comparison, NGR rate 

changes for powdered coal were found to be insignificant. 

Sample Weight 

Pulverized samples from the SRCM of various weights 

[3,938 to 100 g (8.68 to 0.22 lb)] were tested for NGR 

using the EZSP-2. The results indicate that the NGR 

readings of rock samples decreased from 37% to 58% 

when the sample size was reduced 90% [to 100 g (0.22 

lb)]. For coal samples, the NGR reading decreased from 

8% to 20% when the size was reduced 90% (figures 25 to 

27, and tables 9 to 11). 

Table O.-Effect of coal sample weight 

on NGR count rates-laboratory tests 

(Pittsburgh Goal Seam) 

Weight, NGR count rate, 

Q Bb) wm 

1,020 (2.25) . . . . . . z200 

510 (1.12) . . . . . . 2,083 

255 (0.56) . . . . . . 2,150 

127 (0.28) . . . . . . a83 

Table lO.-Effect of shale, parting, and 

coal sample weights on NGR 

count rates 

(Pocahonfas Coal Seam) 

Weight, NGR count rate, 

g (Ib) wm 

Bottom shale: 

3,460 (7.63) . . . 

1,730 (3.81) . . . . 

870 (1.92) . . . 

430 (0.95) . . . 

223 (0.49) . . . 

110 (0.24) . . . 

Background’ . . . . . 

Bottom coal: 

2,081 (4.59) . . . 

1WQ (2.29) . . . 

520 (1.15) . . . 

260 (0.57) . . . 

130 (1.29) . . . 

Background . . . . . . 

Parting: 

3,087 (6.76) . . . 

1,533 (3.38) . . . 

767 (1.69) . . . 

383 (0.84) . . . 

192 (0.42) . . . 

Background . . . . . . 

5253 

4,343 

3,440 

2,863 

2,410 

2,243 

ND 

2,667 

z440 

x333 

2,133 

2,190 

2,075 

4,953 

3,940 

3,167 

2,683 

2,297 

2,040 

ND No data. 

‘As measured in air in the middle between the ffoor and roof. 

Effect of Sample Size and Thickness 

To find the relationship between the NGR reading and 

the size and thickness of the samples, pulverized material 

of four samples obtained from the SRCM (Pittsburgh Coal 

Seam) were used. For testing, plastic containers of 70, 

lOZ, l52, and 190 mm (2.75, 4.0, 6.0, and 7.5 in) ID were 

used. Pulverized material was added to the containers in 

various thicknesses [from I3 to 241 mm (0.5 to 9.5 in)] and 
8

NGR readings were made (figures 15 to 21 and tables 4

and 5).

Tabloll. Effectofshatoandcoal

sample weights on NGR

count r8tes (cpm)

(No.2Gascoalseam)

Weight, NGR count rate,

9 Cb) cpm

Rcof shah:

123

246 EZ **-**

2,170

492

984

g:; : : : : :

z200

2,462

l,w9 (4&a) :::::

2,617

2,890

3,938 (8.68) . . . . .

coal:

126 (0.28) . . . . .

261 (0.66) . . . . .

602 (1.11) . . . . .

l,w4 (2.21) . . . . .

2$308 (4.43) . . . . .

Backwound’ . . . . . .

3,290

2,170

2,203

2,220

tz

2,076

h measured in air in the middle between the floor and roof.

NGR readings taken of the samples from the main roof

(draw slate and coal) indicate that for material 76-mm

@-in) thick in plastic containers with an ID range of 70 to

190 mm (275 to 7.50 in), the NGR reading increased

above the background level from 21% to 40%.

The NGR reading of the sample from the immediate

roof (shale) indicates that for 89-mm (3.50-in) material

thickness and plastic container ID ranging from 70 to

190 mm (275 to 750 in), the NGR rate increased above

the background level from 32% to 116%.

The NGR reading of a coal sample indicates that for

material 76-mm (3-in) thick and plastic container ID

ranging from 70 to 190 mm (2.75 to 7.50 in), the count

rate increased above the background level from 9% to

19%.

For a floor sample (fireclay), NGR reading shows that

for material 89-mm (3.5-in) thick and plastic container ID

ranging from 70 to 190 mm (2.75 to 7.50 in), the NGR

rate increased above the background level from 40% to

120%.

By increasing the thickness of the pulverized material in

the plastic container above 76 or 89 mm (3.0 or 3.5 in), in

general the NGR rate increase was found to be insignificant.

Using the same thickness of the pulverized material in

l52- and 190-mm (6- and 7.5-in) ID plastic containers, the

NGR reading is relatively higher than for 70- and 102-mm

(2.75- and 4-in) plastic containers. For roof shale and

102-mm (4-in) plastic containers, the NGR reading ranged

from 14% to 30%.

Tables 12 to 15 show the results of underground and

laboratory testing analyses of samples from seven coal

seams.

Chemical Analyses

Three coal and five rock samples collected from the

Bruceton mine were analyzed for ash, sulfur, and heating

value. The ash content of the coal samples ranged from

5.27% to 6.29% (mean 5.80%); sulfur content ranged from

0.66% to 157% (mean 1.12%); heating value ranged from

14,053 to 14,426 Btu/lb (mean 14,258 Btu/lb) (table 15)

KllTANNlNG COAL SEAM

Two visits were made to a mine in Ohio to make a

series of underground NGR measurements of coal, roof,

and floor to determine if a sufficient NGR difference

existed between the coal and adjacent strata. Coal and

rock samples were also collected for laboratory analyses.

This particular mine operates in the Middle Kittanning

Coal Seam. The seam thickness ranges from 1,067 to

1,422 mm (42 to 56 in) with a mean thickness of 1,321 mm

(52 in). The immediate roof is composed primarily of

laminated hard draw slate. Two or more rock partings,

5 1 to 76-mm (2- to 3-in) thick, are typically found in the

coal 406 to 508 mm (16 to 20 in) below the roof. The

immediate floor strata are composed of relatively soft-tohard fireclay.

Underground Testing

During the first visit, NGR readings were made at four

different locations in the mine using the ESP-2. A total of

21 coal and rock samples were collected for laboratory

testing. NGR readings during the second visit were made

at eight points in the vicinity of the third location. A total

of 22 samples were collected during the second visit. The

results of the underground and laboratory tests are

summarized in tables 12 to 14.

Computed NGR ratios associated with the first visit are

as follows: underground roof-to-top coal (R:TC) ratio for

four locations ranged from 1.21 to 1.33 (mean 1.26); floorto-bottom coal (F:BC) ratio ranged from 1.60 to 236

(mean 2.03).

Underground tests during the second visit were made

with the RHC 801 and the GRS-500 at six locations, and

with the ESP-2 at eight locations. Slots were made in the

coal ribs at six of these locations leaving from 38 to 559

mm (1.5 to 22 in) of roof coal above each slot. Table 14

lists RHC 801 and ESP-2 readings as the roof coal

thickness varied and the position of the RHC 801 was

changed at these locations (ii the coal cut, outside the coal

at the same level, and near the immediate roof). The

RHC 801 data also showed that the airgap has little

influence on NGR readings of the immediate roof [about

8% difference for up to 330 mm (13 in) of airgap].
9 

Table 124omparison of NGR count rates for different ooal seamunderground tests 

coal seam 

ESP-2 

Count rate, cpm WiOS NGR sensor 

RHC801 GRS-500 to coal ESP-2 RHC6O1 GRS500 

Pittsburgh: 

......... 

coal ......... 

Floor ......... 

Background’ ... 

Kittanning: 

Roof ......... 

coal ......... 

Floor ......... 

Partings ....... 

Background .... 

Freeport: 

Roof ......... 

coal ......... 

floor ......... 

Partings ....... 

Back 

B 

round .... 

Clarion: 

Roof ......... 

Coal ......... 

Fioor ......... 

Partings ....... 

Background .... 

Illinois No. 5: 

Roof ......... 

Coal ......... 

Floor ......... 

Background .... 

Hiawatha: 

Roof ......... 

coal ......... 

Floor ......... 

Partings ....... 

Background .... 

Wadge: 

Roof ......... 

coal ......... 

Floor ......... 

10,160 11,446 16,066 

3,920 5,300 ND 

7,900 13,510 ND 

6,600 7,530 ND 

12,461 18,460 27,456 

8,856 11,667 22.162 

12,645 ND 26,508 

9,337 ND ND 

11,359 ND 25,740 

10,602 ND 25,545 

6,575 ND 2zo50 

12,733 ND 41,464 

9,097 ND 24,305 

8,686 ND 31,646 

5,044 ND ND 

3,216 ND ND 

6,913 ND ND 

3,606 ND ND 

5,342 ND ND 

20,880 ND ND 

6,790 ND ND 

12,409 ND ND 

14,650 ND ND 

6,337 ND ND 

2,345 ND ND 

5,595 ND ND 

4,644 ND ND 

3.564 ND ND 

9,588 ND ND 

W-56 ND ND 

6,331 ND ND 

1.57 

NAP 

2.15 

1.12 

w 

3.06 

NAP 

E 

2.70 

NAP 

2.39 

2.07 

NAP 

2.25 

NAP 

1.49 

Background . . . . 6,320 ND ND NAP NAP NAP NAP 

NAp Not applicable. 

ND No data. 

‘As measured in air in the middle between the floor and roof. 

*i-IA without shield. 

For ESP-2, computed ratios associated with the second 

visit were R:TC ratio ranged from 1.06 to 1.55 (mean 

1.37) and F:BC ratio ranged from 1.65 to 1.74 (mean 1.69). 

For the GRS-500, R:C ratio was 1.24 and F:C ratio was 

1.20. 

Laboratory Testing 

A total of 43 coal and rock samples collected during the 

two visits were tested in the laboratory using the ESP-2. 

Laboratory tests of 21 samples collected during the first 

visit indicate that the R:TC ratio ranged from 1.40 to 1.69 

(mean 1.55) and the F:BC ratio ranged from 1.83 to 2.27 

(mean 1.98). The mean NGR readings for 11 roof 

samples were 2,864 cpm; 14 top coal samples, 1,914 cpm; 

5 bottom coal samples, 1,572 cpm; 11 floor samples, 3,040 

cpm; and 2 partings, 2,063 cpm. The mean R:TC was 1.50 

and the mean F:BC was 1.93. Using the GRS-500, R:C 

ratio was 1.47 and F:C ratio was 1.55. 

KUT radiometric analysis of one roof sample indicates 

that the bulk density was 1.77 g/cc, RaeUS was 4.71 ppm, 

thorium (Th) was 18.10 ppm, and potassium (K-40) was 

331%. For one coal sample, bulk density was 0.94 g/cc, 

RaeU was 0.689 ppm, Th was 2.48 ppm, and K-40 was 

0.17%. One floor sample had a bulk density of 1.58 g/cc, 

RaeU of 5.33 ppm, Th of 19.u) ppm, and K-40 of 3.64% 

%aeU is the amount of uranium, under conditions of secular equilibrium, required to support the mcssurcd amount of radium daughters. 
10 

T8bh 134hnpukon of NGR count r&e8 for different coal 8eams-laboratory test8 

coalsearn 

Pbburgh: 

ESP-2 

Count rate, cpm RSUOS NGR sensor 

RtiC8O1 GRS-SW tooofd ESP-2 WC801 GFISSW 

z! .................. 

......... 

Background .... 

Kittanning: 

ii .................. 

......... 

Parungs ....... 

Background .... 

mw 

E .................. 

Floor ......... 

F+arungs ....... 

Background .... 

Clarion: 

E .................. 

......... 

Mnga ....... 

Background .... 

lllino& No. 5: 

iFi2 .................. 

Floor ......... 

Background .... 

Hhathai 

E 

floor.. 

....................... 

. 

Palungs ....... 

0ackground .... 

Wedge: 

z .................. 

Floor.. ....... 

Background .... 

5,754 

4,887 

5,718 

3,338 

2,518 

2,087 

3,258 

ND 

1.58 

NAP 

1.37 

NAP 

1.18 

NAP 

1.18 

NAP 

5,010 3,548 

4,396 2,409 

5,055 3,728 

ND ND 

3,842 1,928 

E 

1.80 

1.13 

NAP 

1.14 

w 

1.15 

ND 

MAD 

1 A7 

NAP 

1.55 

ND 

3,173 3,300 3,552 

1,923 3,137 2,905 

3,318 4,010 8,788 

3,330 3,113 3,840 

1,517 2.823 1,950 

2,444 5,004 3,898 

1,683 4,340 2,252 

3,224 5,894 3,948 

2,433 4,570 a43 

1,521 3,438 ND 

1.15 

KY 

e 

4,470 4,104 

3,984 2,496 

4,110 3,341 

2848 1.902 

1.12 

NAq 

E 

1.16 

NAP 

1.12 

1.13 

NAP 

2.568 4,778 3,444 

1,532 4,101 2254 

2,012 4,595 2,975 

1,982 3,960 2,280 

ND ND ND 

3,917 4,912 

2454 4,463 

ND ND 

Tabk 14.-Comparison of RHC 801 and ESP-2 NGR count rates (cpm) for Kittanning Coal Seam-underground tests 

Coal thickness, 

Location mm tin\ inside 

RHC 801 

Outside lmmed. Roof 

ESP-2 

Immed. Immed. Floor 

...... \"'I 

coal slot coal slot roof coal roof floor coal 

1 ........ 63.5 

8-*-- 

12,080 ND ND ND 11,333 11,033 ND 

1 ........ 152.4 

(G.0). : : : : 

11,460 17,340 18,300 8,693 11,333 ND ND 

1 ........ 330.2 11,520 16,880 ND ND 11,333 ND ND 

2 ........ 343.0 (13.5) .... 10,080 16,800 19,200 a,= 12,933 12,100 ND 

3 ........ 406.4 (18.0) .... 9,960 17,280 18,960 6,fm ND ND ND 

4 ........ 38.1 (1.5) ..... 15,360 17,450 18,180 12,ooa 12,887 13,433 ND 

4 ........ 88.9 (3.5) ..... 14,520 ND ND ND ND ND ND 

5 ........ 482.8 (19.0) .... 10,920 16,800 17,840 ND 11,700 11,967 8,957 

8 ........ 558.8 go) .... 9,300 17,340 18,800 ND 11,733 11,733 8,043 

7 ........ 0 

(0) :: :::: 

ND ND ND 10,587 12,433 12,287 7,063 

8 ........ 0 ND ND ND 10,887 13,700 15,833 9,613 

ND No data. 
11 

Table 15.Aaboratory analyses of roof, coal, fioor, and parting samples for different coal seams 

Coal seam and 

number of mines 

Chemical analyses NGR 

No. of Ash content, Sulfur 

samples 

Heating value, No. of Gamma ray, Ratio to 

% content, % Btu/ib samples 

cpm coal 

Mean SD Mean SD Mean SD Mean SD 

Pittsburgh (1): 

3 76.2 19.24 0.56 

3 5.8 0.50 1.12 

2 85.9 0.22 1.68 

5 88.6 4.15 3.24 

10 21.3 9.34 2.91 

5 93.6 1.38 0.45 

ND ND ND ND 

4 86.1 12.20 0.52 

13 13.7 7.65 3.34 

5 88.8 5.74 3.03 

2 81.4 6.20 0.53 

4 45.1 14.92 14.8 

7 10.2 11.42 4.33 

2 80.0 0.89 0.48 

4 83.7 3.92 2.31 

2 85.4 13.27 1.06 

3 12.0 7.63 2.74 

1 92.8 0 5.45 

ND ND ND ND 

6 

4 

1 

75.4 3.53 0.47 

8.4 3.54 0.59 

65.6 18.30 1.19 

51.0 0 0.14 

5 

7 

1 

91.5 0.57 

6.4 2.79 

49.1 0 

1.30 

0.54 

0.27 

3,106 7 2,446 700 

189 6 1,545 23 

245 4 2,110 406 

Roof- ........... 

Coal ......... 

floor ......... 

Kittanning (1): 

Roof ......... 

Coal ......... 

Fioor ......... 

Parting ....... 

Freeport (2): 

Hoof ......... 

Coal ......... 

Fioor ......... 

Parting ....... 

Clarion (1): 

Roof ......... 

Coal ......... 

Fioor ......... 

Parting ....... 

Illinois No. 5 (1): 

Roof .......... 

Coal .......... 

Floor .......... 

Parting ......... 

Hiawatha (1): 

Roof .......... 

Coal .......... 

Fioor .......... 

Parting ......... 

Wadge (1): 

Roof .......... 

Coal .......... 

Parting ......... 

0.69 

0 

2,550 

6,611 

0.45 14,258 

0.20 934 

2.53 655 

1.04 11,083 

0.21 82 

ND ND 

0.67 1,174 

5.61 13,354 

1.76 668 

0.61 1,493 

3.89 6,654 

3.84 12,665 

0.54 166 

1.82 1,264 

0.38 1,580 

1.19 12,552 

0 457 

ND ND 

0.26 2,113 

0.26 13,260 

1.34 4,472 

0 6,783 

0.44 524 

0.40 13,030 

511 11 2,970 198 

1,531 19 1,825 251 

124 11 3,284 398 

ND 1 2,064 0 

1.80 

ND 

1,949 8 3,173 433 

1,437 28 1,923 250 

943 13 3,318 483 

1,209 2 3,330 339 

s 

1.73 

1,053 13 2,718 615 

1,762 9 1,706 170 

0 6 3,330 1,025 

428 1 2,207 0 

ii: 

1.96 

1.30 

2,200 5 

546 7 

0 5 

ND ,l 

3,748 749 1.97 

1,905 461 NAP 

2,664 576 1.40 

4,647 0 2.44 

950 7 2,568 395 1.68 

588 7 1,532 112 NAI, 

2,688 6 2,012 363 1.31 

0 5 1,982 257 1.29 

130 5 3,917 645 1.606 

440 7 2,454 302 NAp 

0 1 3,740 0 1.52 

NAp Not applicable. 

ND 

SD 

No data. 

Standard deviation. 

(tables 16 to 18). No NGR testing of these samples were 

made because they were too small. 

Ten coal and ten rock samples were chemically analyzed for ash, sulfur, and heating value. The chemical 

analyses of four samples of the top coal and two samples 

of the bottom coal indicate that the ash content of the top 

coal ranged from 18.46% to 32.72% (mean 27.53%); sulfur 

content ranged from 2.15% to 3.35% (mean 2.87%); 

heating value ranged from 9,340 to 11,510 Btu/lb (mean 

10,190 Btu/lb). For the bottom coal, the ash content 

ranged from 7.90% to 8.37% (mean 8.14%); sulfur content 

ranged from 2.07% to 5.19% (mean 3.63%); and the mean 

heating value was 13,160 Btu/lb. Mean ash content of 10 

coal samples was 21.30%, mean sulfur content 2.91%, and 

mean heating value 11,083 Btu/lb (table 15). 

FREEPORT COAL SEAM 

The Upper Freeport Coal Seam in the study area had 

a mean thickness of 2,286 mm (90 in) and ranged from 

1,829 to 2,743 mm (72 to 108 in). One or two rock 

partings, from 51 to 914 mm (2 to 36 in) thick, are found 

in the middle of the seam. The immediate roof strata in 

the sampled areas are hard, dark gray, laminated shale up 

to 2.44 m (8 ft) thick. The immediate floor strata are 

hard, water-sensitive, gray shale, occasionally mixed with 

coal. 

Underground Testing 

Underground NGR measurements were conducted in 

two mines in the Upper Freeport Coal Seam in West 
12 

Table 16.4lJT’ radiometric and chemical laboratory analyses of roof samples 

Seam (State) 

Radiometric analysis Chemical analysis 

Sample Bulk FtaeU2 Thorium, Potassium, NGR, Sample Ash, Sulfur, Heating 

No. Density, fvm fvm % cm No. % % value, 

B seam ICOI . . . . . . . . . 

gl= BTU/lb 

1 1.71 3.97 16.70 2.70 2,133 NA NA NA NA 

Maxwell (CC) ......... 

No. 5 (IL) ............ 

No. 6 (IL) ............ 

Hazard (KY) .......... 

No. 9 (KYj ........... 

No.ll(Ky .......... 

upper Left Fork (NM) ... 

Clarion (OH) ......... 

Kittanning (OH) ....... 

Pittsburgh (PA) ........ 

Hiawatha (LtT) ........ 

Coalburg (WV) ........ 

Freeport (WV) ......... 

No.380.. ........ 

Mean ............. 

1 1.39 7.11 19.20 1.56 2,167 NA NA 

2 1.26 25.40 25.10 0.30 3,287 2 64.73 

1 1.33 35.80 9.50 2.82 2,863 1 73.64 

1 1.43 14.42 15.80 4.35 2,133 NA NA 

1 1.14 ‘148.00 5.70 1.80 NA 1 72.92 

4 1.45 3.34 15.50 3.09 2,003 NA NA 

1.62 

3(A) 1.20 

5.61 16.50 2.22 2,338 NA NA 

3.31 14.80 2.24 1,493 NA NA 

4 1.33 3.14 13.66 1.60 1,629 

4 

1.77 4.71 16.10 3.31 e, 4 87.01 

1.61 4.63 19.40 1.90 1,453 l(A) 89.70 

l(B) 1.64 5.38 19.59 1.57 1,550 1 (B) 60.25 

1 1.76 3.50 6.08 1.59 1,517 1 79.06 

1 1.64 4.13 14.40 2.80 2,023 1 91.78 

5 1.50 4.74 16.10 2.32 2,143 5 91.11 

2 1.43 4.97 12.80 1.78 1.240 NA NA 

NA NA 

0.79 25 

2.06 3,337 

NA NA 

2.79 3,567 

NA NA 

NA NA 

NA NA 

6.34 785 

0.62 460 

0.33 272 

0.59 2,216 

0.20 473 

0.35 1 354 

NA NA 

NAP 1.48 8.41 15.58 2.23 1,998 NAp NAp NAP NAI, 

Not available. 

& Not applicable. 

‘KUT = potassium/uranium/thorium. 

%aeU is the amount of uranium, under conditions of secular equilibrium, that would be required to support the measured amount of 

radium daughters. 

“ESP-2 unit used for lab testing. 

‘Not induded in mean value because results are 17.6 times higher than mean value. 

%arnple too small to measure. 

Virginia using the RHC 801, the ESP-2, and the GRS-500. 

The results indicate relatively large variations in the NGR 

readings at different sections in the mines. NGR readings 

were made at five locations at each mine and a total of 46 

coal and rock samples were collected for laboratory 

analyses. 

Underground NGR tests were made primarily with the 

ESP-2 The immediate roof strata at the first mine could 

not be measured (except at one location) because of the 

height of the roof. When using the ESP-2, R:C for both 

mines was 1.64 and F:C was 1.94. The parting-to-coal 

(PC) ratio was 1.38. When using the GRS-500, R:C was 

1.16, IX was 1.88, and PC was 1.10 (table 12). 

During a visit to a second mine, the RHC 801 unit was 

installed on a new Joy 6LS longwah shearer and was 

calibrated to leave about 76 mm (3 in) of coal on the roof 

to protect weak roof strata. The unit used two indicators, 

one of which was used by the operator for remote control. 

USBM personnel foliowed the shearer along the 213.4-m 

(700~ft) longwah face. In general, the RHC 801 indicator 

lights were on the proper horizon line. Occasionally, one 

yeUow light appeared, indicating thickening of the coal. At 

one point there was a minor roof cave-in during mining 

and a red Iight appeared on both indicators, which indicated that the roof coal was thinner than required, no coal 

was left on the roof, or more NGR was present in the roof 

rock. Longwali operators stated that the RHC unit operated satisfactorily for over four weeks without any major 

problems and appeared to work weli under adverse mining 

conditions. 

Laboratory Testing 

Fifty-one coal and rock samples were tested in the 

laboratory for NGR using ESP-2 and GRS-500. For the 

ESP-2, the mean R:C ratio was 1.65, and F:C and P:C 

ratios were each 1.73. For the GRS-500, the R:C ratio 

was 1.22, F:C was 3.02, and PC was 1.32 (table 13). 

KUT radiometric analysis of one roof sample indicates 

that the bulk density was 1.50 g/cc, RaeU was 4.74 ppm, 

Th was 18.10 ppm, and K-40 was 2.32%. For one coal 

sample, bulk density was 1.04 g/cc, RaeU was 1.42 ppm, 

Th was 3.21 ppm, and K-40 was 0.39%. One floor sample 

had bulk density of 1.71 g/cc, RaeU of 7.08 ppm, Th of 

13.50 ppm, and K-48 of 1.79%. Laboratory testing of 

these samples indicate that for roof, NGR was 2,143 cpm, 

for coal it was 1,317 cpm, and for floor it was 2,040 cpm 

(tables 16 to 18). 

Thirteen coal and eleven rock samples were analyzed 

for ash, sulfur, and heating value. The ash content of the 

13 coal samples ranged from 5.77% to 29.35% (mean 

X3.70%); the sulfur content ranged from 0.63% to 21.50% 
Table lT.-KUT’ radiometric and chemical laboratory analyses of coal Samples 

Radiometric analysis Chemical analysis 

Seam (State) 

Sample Bulk RaeU,2 Thorium, Potassium, NGR, Sample Ash, Sulfur, Heating 

No. density, wm wm % wm No. % % value, 

cl/= Btu/lb 

B seam (CO) . . . . . . 4 0.91 0.35 0.77 co.10 1,190 NA NA NA NA 

Maxwell &) . . . . . . 

Wadge (CO) . . . . . . . 

Hazard (KY) . . . . . . . 

No. 9 (KY) . . . . . . . . 

No.ll(KY) . . . . . . . 

Upper Left Fork (NM) 

Clarion (OH) . . . . . . 

Kittanning OH) . . . . . 

Pittsburgh (PA) . . . . . 

Hiawatha (UT) . . . . . 

Coalburg (WV) . . . . . 

Freeport (WV) . . . . . . 

No. 38 (WY) . . . . . . . 

2 0.88 1.25 3.33 co.10 11273 NA 

1 0.92 0.39 0.95 co.10 1,213 3 

6 0.92 0.33 0.70 co.10 1,223 NA 

4 0.99 1.31 2.57 0.43 1,210 3 

6 0.93 3.50 0.98 0.13 l,=J 6 

2 0.89 0.66 1.78 co.10 1,173 NA 

5 0.89 0.36 0.74 x0.10 1,197 NA 

5 0.94 0.68 2.48 0.17 0 5 

2 0.93 0.50 0.80 co.10 1,199 2 

3 1.04 1.43 4.61 0.32 1,246 3 

2 0.89 0.67 3.25 co.10 1,113 2 

3 

4 ‘1.48 ‘3.42 515.70 ‘2.16 ? ,740 2 

5 1.64 1.42 3.21 0.39 1,317 2 

1 0.89 0.68 1.03 co.10 1,183 NA 

2 0.92 1.39 1.22 co.10 1,246 

NA NA NA 

4.29 0.38 13,427 

NA NA NA 

13.42 4.34 12,414 

7.41 3.69 13,354 

NA NA NA 

NA NA NA 

12.88 3.03 12,434 

5.59 2.51 14,421 

3.87 1.12 14,517 

13.26 0.46 12,461 

4.84 0.63 13,825 

21.31 0.43 11,601 

8.91 1.95 14,236 

NA NA NA 

Mean . . . . . . . . . . NAp 0.93 0.99 1.99 60.29 1,297 NAp NAI, NAP NAI, 

Not available. 

/& Not applicable. 

‘KUT = potassium/uranium/thorium. 

2FIaeU is the amount of uranium, under conditions of secular equilibrium, that would be required to. support the measured amount of 

radium daughters. 

“ESP-1 unit used for lab testing. 

‘Sample too small to measure. 

‘Not included in mean value because results are much higher in the high ash coal. 

60nly the five samples above 0.1 were included in mean value. 

(mean 3.34%); and the heating value ranged from 10,021 

to 14,829 Btu/lb (mean 13,354 Btu/lb) (table 15). 

CLARION COAL SEAM 

A visit was made to a mine operating in the Clarion 

Coal Seam in Ohio. The immediate roof of the Clarion 

Coal Seam is hard limestone, up to 0.91 m (3 ft) thick, 

followed by sandy shale and sandstone. The mean coal 

seam thickness in this particular mine is 1.448 mm (57 in) 

and ranges from 1,219 to 1,676 mm (48 to 66 in). Two 

rock partings, 51 mm and 152 to 178 mm (2 in and 6 to 7 

in) thick, are found at different distances below the coal 

roof. To obtain the required entry height for the continuous mining machine, from 203 to 305 mm (8 to 12 in) of 

the floor fueclay must be removed during mining. 

Underground Testing 

Underground NGR readings were made at five different locations using the ESP-2, with a single-channel pulse 

height analyzer (PHA) option without the lead shield. The 

results indicated relatively large variations in the NGR 

rates underground. For the immediate roof (limestone 

and sandstone), the mean value was 5,044 cpm; for coal, 

the mean value was 3,216 cpm; for floor (fireclay), the 

mean value was 6,9l3 cpm; and for rock partings, the 

mean value was 3,606 cpm. The mean value for the 

underground ambient air measured at the center of the 

cross-sections was 4,800 cpm, which is similar to the mean 

value of the roof, coal, floor, and rock partings combined 

(4,695 cpm). The mean R:C ratio was 1.57 and mean F:C 

ratio was 2.15. For limestone roof, R:C ratio was 1.20, 

and for sandstone roof, R:C was 2.00. The P:C ranged 

from 0.90 to 1.33 (mean 1.12). Higher ambient air 

readings were noticed at one location where the floor 

strata are composed of shale and/or draw slate with high 

NGR readings (table 12). 

Laboratory Testing 

Laboratory tests of coal and rock samples collected at 

five locations underground showed similar trends in NGR 

readings. When using the ESP-2, the mean R:C ratio was 

1.45, the mean F:C ratio was 1.92, and the P:C was 1.45. 

For the limestone roof, R:C ranged from 1.40 to 1.70, and 

for the shale-draw slate floor, F:C ranged from 1.85 to 

2.40. When using the GRSJOO, the R:C ratio was 1.73, 

the F:C ratio was 1.75, and the P:C was 1.30 (table 1.3). 

KUT radiometric analysis of one sample of roof and 

one rock parting indicates that the bulk density was 1.20 

and 1.33 g/cc, RaeU was 3.31 and 3.!4 ppm, Th was 14.80 
14 

Table i8.4UT1 radiometric and chemical laboratory analyses of floor samples 

seam (state) 

Radiometric analysis Chemical analysis 

SamPlS Bulk ReeU,2 Thorium, Potassium, NGR: Sample Ash, Sulfur, Heating 

No. Density, wm fwm % wm No. % % value, 

g/a Btu/lb 

Wadge (CO) .......... 2 1.21 5.44 13.70 2.26 1,730 NA NA NA NA 

No.5(11). ........... 1 1.66 13.00 27.50 1.32 3,060 1 76.01 1.33 3,135 

No.661) ............ 2 1.54 2.47 15.00 2.22 1,573 2 94.76 0.65 19 

Hazard (KY) .......... 7 1.71 6.91 56.60 0.16 2,313 NA NA NA NA 

No.o(KY) ........... 6 1.54 3.67 14.60 3.40 1,607 5 94.52 1.13 5 

upper Left Fork (NM) ... 4 0.60 0.90 2.53 <O.lO 1,230 

Kittannlng (OH) ....... 6 1.58 5.33 lg.20 3.64 

Pittsburgh (PA) ........ 5 1.72 3.10 15.20 2.07 

(q ” gi 4 

NA 

9,132 

1,433 0.57 169 

6 1.50 7.16 14.60 1.67 1,667 6 93:73 2.16 155 

Hiawatha (UT) ........ 4 1.20 3.67 6.36 0.54 Nfl 4 66.26 1.40 4,534 

Coalburg (VW) ........ 5 1.40 3.67 15.60 3.20 1,667 5 g1.91 0.06 205 

Freeport (VW/) ......... 2 1.71 7.06 13.50 1.79 a4o 4 79.23 1.40 2,289 

Mean ............ NAp 1.47 5.24 17.66 2.03 1,836 NAI, NAPW NAP 

& E$Eie. 

‘KUT = potassium/uranium/thorium. 

%aeU k the amount of uranium, under conditions of secular equilibrium, that would be required to support the measured amount of 

radium daughters. 

‘ESP-2 unit used for lab testing. 

‘Sample too small to measure. 

and 13.60 ppm, and K-40 was 2.24% and 1.60%. One coal 

sample had bulk density of 0.89 g/cc, RaeU of 0.36 ppm, 

Th of 0.74 ppm, and K-40 of ~0.10%. Floor samples were 

not available for KUT testing. Laboratory testing indicates 

that roof and parting samples have NGR of 1,493 and 

l,620 cpm, and coal sample has 1,197 cpm (tables 16, 17). 

Seven coal and ten rock samples were analyzed for ash, 

sulfur, and heating vahre. The results of the coal samples 

indicate that the ash content ranged from 3.68% to 3551% 

(mean 1020%); sulfur content ranged from 2.08% to 

l2.92% (mean 433%); and heating value ranged from 

8,780 to 13,810 Btu/lb (mean l2,665 Btu/lb) (table 15). 

ILLINOIS NO. 5 COAL SEAM 

A visit was made to a mine operating in the No. 5 Coal 

Seam in Illinois. Seam thickness in this mine ranges from 

lJ70 to 1,829 mm (50 to 72 in), with a mean value of 

l,676 mm (66 in). The immediate roof is laminated, thin, 

hard black shale with limestone nodules and clay veins up 

to 2,438 mm (% in) thick. A lot of clay veins are also 

found in coal. The immediate floor is soft to relatively 

hard underclay, which is normally dry but water-sensitive. 

Limestone is generally found beneath the underclay. 

Underground Testing 

NGR data were obtained at seven locations near the 

active mining operations. Underground measurements 

indicated relatively small variations in the NGR readings 

at different sections as well as in the same entry (left or 

right rib). For the black roof shale, NGR readings were 

found to vary from 18,230 to 24,630 cpm, with a mean 

value of 20,880 cpm. For coal, NGR readings ranged from 

5,640 cpm in the western section to 7,900 cpm in the 

eastern section, with a mean value of 6,790 cpm. For floor 

underclay, NGR readings ranged from 11,030 cpm in the 

southern section to 13,700 cpm in the eastern section, with 

a mean value of 12.400 cpm. One reading taken on a clay 

vein was 9,108 cpm and a reading taken on a limestone 

nodule was 8,200 cpm. The mean NGR reading of the 

ambient air in the center of the entry cross-section was 

14,650 cpm, and ranged from 13,130 to 15,650 cpm, which 

is only about 9% lower than the mean value of the NGR 

readings of roof, noor, and coal combined. The R:C ratio 

varied from location to location and ranged from 2.47 to 

3.72, with a mean value of 3.08. The F:C ratio ranged 

from 1.52 to 2.07, with a mean value of 1.83 (table 12). 

Laboratory Testing 

Laboratory tests of 13 coal and rock samples collected 

in this mine at four locations showed similar variations in 

NGR readings. When using the ESP-2, NGR mean value 

of five black shale roof samples was 3,748 cpm; for seven 

coal samples the mean value was 1,905 cpm; for five floor 

samples the mean value was 2,664 cpm; and for one rock 

parting, it was 4,647 cpm. The mean R:C ratio was 1.97, 

and the mean F:C ratio was 1.40 (table 13). 

Laboratory testing of six other coal and rock samples 

obtained earlier from the same mine had a R:C ratio of 

3.17 and a F:C ratio of 1.34. When using the GRS-500, 

the R:C was 1.64, the F:C was 1.34, and the P:C was 1.39. 
KUT radiometric analysis of one roof sample indicates

that the bulk density was 1.28 g/cc, RaeU was 25.40 ppm,

Th was 25.10 ppm, and K-40 was 0.30%. For one floor

sample, the bulk density was 1.68 g/cc, RaeU was l3.00

ppm, Th was 27.50 ppm, and K-48 was 1.32%. No coal

sample was available for testing. NGR laboratory testing

of these samples showed that the roof sample has 3,287

cpm and the floor sample has 3,080 cpm (tables 16, 18).

Three coal and three rock samples were analyzed for

ash, sulfur, and heating value. Ash content of three coal

samples ranged from 7.86% to 15.73% (mean 12.00%);

sulfur content ranged from 1.69% to 4.03% (mean

2.74%); and heating value ranged from 12,069 to l3,144

Btu/lb (mean 12,552 Btu/lb) (table 15)

HIAWATHA COAL SEAM

A visit was made to a mine operating in the Hiawatha

Coal Seam in Utah. The immediate roof was gray to

black relatively soft shale, which was occasionally mixed

with coal and sandstone. The seam thickness ranged from

1,829 to 2,438 mm (72 to 96 in), with a mean value of

2,286 mm (90 in). In general, one rock parting of variable

thickness was found in the coal seam. The immediate

floor was soft fireclay or shale, occasionally mixed with

sandstone.

Underground Testing

NGR readings using the ESP-2 were made at six

underground locations and a total of 19 coal and rock

samples were collected. For roof shale, the NGR readings

ranged from 4,433 to 8,663 cpm, with a mean value

of 6,337 cpm. The NGR readings for coal ranged from

1,323 to 3,663 cpm, with a mean value of 2,345 cpm. For

floor fireclay, the NGR readings ranged from 5,133 to

6,711 cpm, with a mean value of 5,595 cpm. For rock

partings, the NGR readings ranged from 3,937 to 5,433

cpm, with a mean value of 4,844 pm. The mean NGR

reading of the ambient air was 3,564 cpm. The R:C ratio

at these locations ranged from 1.44 to 5.76, with a mean

value of 2.70; the F:C ratio ranged from 1.65 to 356, with

a mean value of 2.39; and the P:C ratio ranged from 1.47

to 3.08, with a mean value of 2.07 (table 12).

Laboratory Testing

Laboratory tests of 25 coal and rock samples obtained

from several locations in this mine showed small variations

in the NGR readings. When the ESP-2 was used, the

mean values were: seven roof samples, 2,568 cpm; seven

coal samples, 1,532 cpm; six floor samples, 2,012 cpm; and

five rock partings, 1,982 cpm. The mean R:C ratio was

1.68, the F:C ratio was 1.31, and the P:C ratio was 1.29.

Using the GRS-500, the R:C ratio was 1.53, the F:C ratio

was 1.32, and the P:C ratio was 1.01 (table 13).

KUT radiometric analysis of one roof sample indicates

that the bulk density was 1.76 g/cc, RaeU was 3.50 ppm,

Th was 8.08 ppm, and K-40 was 1.59%. For one coal

sample, bulk density was 0.89 g/cc, RaeU was 0.67 ppm,

Th was 3.25 ppm, and K-40 was <10% For one floor

sample, bulk density was 1.28 g/cc, RaeU was 3.87 ppm,

Th was 6.36 ppm, and K-40 was 0.54%. NGR testing in

the laboratory indicates that NGR for the roof sample was

1,517 cpm, for the coal sample it was 1,113 cpm, and the

floor sample was too small for testing (tables 16 to 18).

Six coal and ten rock samples were analyzed for ash,

sulfur, and heating value. Ash content of the coal samples

ranged from 4.84% to l3.26% (mean 8.40%); sulfur

content ranged from 0.43% to 1.10% (mean 059%); and

heating value ranged from 12,462 to 13,825 Btu/lb (mean

13,260 Btu/lb). One floor sample had 3.01% sulfur (table l5).

WADGE COAL SEAM

A visit was made to a mine in Wadge Coal Seam,

Colorado, to observe the RHC 801 unit in operation on a

longwall shearer, to collect coal, roof, and floor samples,

and to make NGR measurements of coal and surrounding

strata wherever possible. The immediate roof is relatively

hard, gray to dark gray laminated shale and silty mudstone

that becomes very fractured when exposed to air and

moisture. It is occasionally mixed with bony coal. The

mean seam thickness is 3,048 mm (120 in). Occasionally,

some rock partings up to 305 mm (12 in) thick are found

in the coal seam. The bottom of the coal is high in ash.

The immediate floor is composed of water-sensitive mudstone mixed with bony coal.

The mine was designed to produce about 3 million st

of coal/yr via longwall mining, with a computerized highcapacity conveyor belt system to maintain high production of clean coal (7). The dimensions of the longwall

panels are approximately 195 m (640 ft) wide by 2,743 m

(9,000-ft) long.

Underground Testing

Underground NGR measurements were made at six

locations using the ESP-2 For the roof shale, NGR

readings ranged from 7,787 to 10,333 cpm, with a mean

value of 9,588 cpm. For coal, the NGR readings ranged

from 3,183 to 4,803 cpm, with a mean value of 4,256 cpm.

For the floor mudstone, NGR readings ranged from 5,033

to 7,950 cpm, with a mean value of 6,331 cpm. [Note:

Because 152 to 305 mm (6 to 12 in) of coal was generally

left on the floor, direct NGR readings for the floor mudstone were not possible.] For ambient air, the mean NGR
16

reading was 6,320 cpm, which is only 6% less than the

mean value of roof, coaI, and floor combined. The mean

R:C ratio was 2.25 and F:C ratio was 1.49 (table 12).

The RHC 801 was successfully used on the longwall

shearer in the mine for over five months for the purpose

of controlling the thickness of the coal left on the roof.

The RHC indicator was calibrated to leave 203 mm (8 in)

of coaI, but it generally indicated that about 254 mm

(10 in) of coal was being left. After starting to use the

RHC 801 [leaving 203 to 254 mm (8 to 10 in) of roof

coal], roof control conditions at the face improved and the

ash content in the run-of-mine coal was reduced from

11.24% to 12.25% to approximately 10% as required by

the customer’s contract.

Laboratory Testing

Laboratory tests using the ESP-2 for 13 coal and rock

samples collected indicated that the mean R:C was 1.60

(excluding the bony coal roof) and was 1.58 (including the

bony coal roof). Using the GRS-500, the R:C was 1.48

and the F:C was 1.58 (table 13).

KUT radiometric analysis of one coal sample indicates

that the bulk density was 0.92 g/cc, RaeU was 0.39 ppm,

Th was 0.95 ppm, and K-40 was <0.10%. For one floor

sample, the bulk density was 1.21 g/cc, RaeU was 5.44 pm,

Th was 13.70 ppm, and K-40 was 2.28%. No roof sample

was available for testing. NGR testing in the laboratory

indicates that for the coal sample it was 1,213 cpm and for

the floor sample it was 1,730 cpm (tables 17, 18).

Seven coal and six rock samples were collected at six

locations near the longwah face and development entries.

Ash content of 7 coal samples ranged from 3.65% to

11.04% (mean 6.40%); sulfur content ranged from 0.34%

to 1.44% (mean 0.54%); and heating value ranged from

12,264 to l3,427 Btu/lb (mean 13,030 Btu/lb). The mean

R:C ratio was 2.50 (excluding the bony coal roof) and 2.21

(with the bony coal roof). For the mudstone floor mixture, the F:C ratio was 1.42 (table 15).

ADDITIONAL NGR EVALUATION TESTS

Additional underground, laboratory NGR, and KUT

measurements and geologic sample coIlections were made

in the Eastern and Rocky Mountain geological provinces

at five underground mines located in two major and three

other coal seams. The purpose of these measurements

was to determine if an NGR system can be used effectively

in these mines to control the roof coal thickness during

mining. The results of the underground and laboratory

NGR measurements for these five mines are given in table 19 and the chemical analyses are given in table 20.

For KUT radiometric analysis, the results are given in

tables 16 to 18.

PITTBURGH COAL SEAM

A visit was made to a mine operating in the Pittsburgh

Coal Seam in southwestern Pennsylvania. The immediate

roof is composed of draw slate and shale of variable

thicknesses. Roof parting occasionally thins from 635 mm

(25 in) to 30 mm (1.2 in) and appears to be squeezed and

fractured. Rider coal, which is above the parting, is of

variable thickness and ranges from 25 to 356 mm (1 to 14

in). The main coal seam is from 1,778 to 1,828 mm (70 to

72 in) thick. In most cases, the seam in the mine is

penetrated by clay veins (dikes) of variable thicknesses.

Occasionally, smaIl faults with clay veins are noted along

the longwaIl face. The immediate floor strata is hardpan,

152 to 203 mm (6 to 8 in) thick, beneath which is fireclay.

Underground Testing

Underground NGR data were obtained at three

locations using the ESP-2 and GRS-500 units (table 19).

Using the ESP-2 unit, the roof shale mean NGR reading

was 9,499 cpm; the roof coal was 6,445 cpm; the main coal

was 4,509 cpm; the roof parting was 9,101 cpm; and the

immediate floor was 10,796 cpm. The mean roof-to-toprider coal (R:TRC) ratio was 1.47. For the GRS-500 unit

(TCl level) the R:TRC ratio was 1.37. For the roof

parting-to-main coal (RP:MC) with ESP-2 unit, the mean

ratio was 2.02, with the GRS-500, the RP:MC ratio was

1.58. The mean floor-to-main coal (F:MC) ratio with

ESP-2 was 2.66 and with GRS-500 the F:MC ratio was

1.81.

Laboratory Testing

ESP-2 laboratory measurements of six samples obtained

from the mine indicate that the NGR reading for roof

shale was 3,940 cpm; for roof coal it was 2,240 cpm; for

main coal it was 2,283 cpm; for parting it was 4,020 cpm;

and for immediate floor it was 4,137 cpm. The R:TC and

RP:MC ratios were each 1.76, and the F:MC ratio was

1.53. Using the GRS-500 unit, the R:TC ratio was 1.49;

the RP:MC ratio was 1.34; and the F:MC ratio was 2.22

(table 19).

KUT radiometric analyses of two roof samples indicate

that the buIk density was 1.61 and 1.64 g/cc, RaeU was

4.83 and 5.38 ppm, Th was 19.40 and 19.50 ppm, and K-40

was 1.90% and 1.57%, respectively. For these two coal

samples, the bulk density was 0.93 and 1.04 g/cc, RaeU

was 0.50 and 1.43 ppm, Th was 0.80 and 4.61 ppm, and K40 was ~0.10% and 0.32%, respectively. Two floor

samples had bulk densities of 1.72 and 1.50 g/cc, RaeU

was 3.10 and 7.18 ppm, Th was 15.20 and 14.60 ppm, and

K-40 was 2.07% and 1.67%, respectively. NGR readings
17 

Table 19.4Jnderground and laboratory NGR measurements (cpm) taken at five coal seams 

Coal seam Location 

Underground Laboratory 

ESPP GRS-500 ESP-2 GRS-500 

TCl’ T& TCl’ Tc22 

Pittsburgh . . . . . . . 

Freeport ......... 

Maxwell ......... 

B Beam ......... 

Upper Left Fork . . . 

Imm. roof ....... 

Roof coal ....... 

coal ........... 

Parting ......... 

Imm. floor ...... 

Background ..... 

Imm. roof ....... 

Roof coal ....... 

coal ........... 

floor fireclay .... 

Background ..... 

lmm. roof ....... 

Roof coal ....... 

Main coal ....... 

Fioor shale ...... 

Background ..... 

Imm. roof ....... 

Top head coal ... 

Main coal ....... 

Parting ......... 

Fioor coal ....... 

Background ..... 

Imm. roof ....... 

Top coal ....... 

Roof coal below: 

Parting 1 ..... 

Main coal .... 

Parting 2 ..... 

Imm. floor .... 

Background ... 

9,499 21,832 3,828 3,940 4,502 1,248 

6,445 17,107 2,821 2,240 3,208 792 

4,509 13,706 2,029 z283 2,526 774 

9,101 21,605 3,958 4,020 4,703 1,212 

10,796 22,292 4,073 4,137 5,600 1,504 

7,809 19,334 3238 1,560 2,270 752 

9,761 19,283 3,552 2,817 ND ND 

7,026 17,513 3,113 2,317 3,314 894 

4,284 13.163 1,978 1,826 2,906 790 

12,289 24,929 4,605 3,420 4.270 lZ= 

8,271 17,777 3,037 1,668 z= 755 

9,336 22,034 4,057 2,977 4,145 1,094 

6,146 14,362 2,196 ND ND ND 

4,184 14,350 2,058 1,703 2,758 831 

10,933 22,955 4,037 ND ND ND 

7,162 17,509 2,881 1,637 2,234 708 

7,873 ND ND 3,227 4,640 1,245 

1,541 4,380 678 1,653 3,302 824 

1,653 4,533 615 1,633 3,305 840 

2,521 6,464 918 2,193 3,684 950 

2,231 5,478 822 ND ND ND 

1,845 5,052 744 1,453 2,186 695 

10,550 20,769 4,044 4,387 ND 1,416 

7,004 17,190 2,997 ND ND ND 

4,022 12,197 

3,858 12,923 

6,152 15,686 

9,763 20,547 

6,037 15,344 

1,823 ND 

1,894 1,963 

2,644 3,133 

3,875 4,080 

2,487 1,730 

ND ND 

3,614 876 

3,444 996 

6,642 1,662 

2,271 750 

ND No data. 

‘Total counts above 0.08 MeV. 

2Total counts above 0.40 MeV 

for two roof samples were 1,453 and 1,550 cpm, for two 

coal samples were 1,100 and 1,240 cpm, and for two floor 

samples were 1,433 and 1,667 cpm (tables 16 to 18). 

The results of chemical analyses of four coal and rock 

samples indicate that the ash content of the roof coal was 

5.97% and of the main coal was 12.53%; the sulfur content 

of the roof coal was 2.75% and of the main coal was 

5.00%; the heating value of the top coal was 14,297 Btu/lb 

and of the main coal was 12,843 Btu/lb (table 20). 

FREEPORT COAL SEAM 

A visit was made to a mine operating in the Lower 

Freeport Coal Seam in Ohio. The immediate roof strata 

are composed of laminated gray sandstone, occasionally 

mixed with shale. The mean seam thickness is about 1,778 

mm (70 in) and ranges from 1,422 to 1,905 mm (56 to 

75 in). The top 152 to 254 mm (6 to 10 in) of coal has up 

to 21% ash and up to 10% sulfur. Because of the high ash 

and sulfur content of the top coal, up to 254 mm (10 in) 

of coal is typically left on the roof. The immediate floor 

is made up of hard gray fireclay, beneath which is solid 

limestone. 

Underground Testing 

Underground NGR measurements were made at three 

locations (table 19). Using the RSP-2 unit, the NGR 

count rates were 9,781 cpm for roof shale; 7,026 cpm for 

roof coal; 4,284 cpm for main coal; and 12,289 cpm for 

floor fireclay. The mean R:TC ratio was 1.43; the mean 

R:MC ratio was 2.41; and the mean F:MC ratio was 3.00. 

For the GRSJOO unit (TCl level), the mean RTC ratio 

was 1.10, the mean R:MC ratio was 1.46, and the mean 

F:MC ratio was 1.89. 

Laboratory Testing 

Laboratory measurements of four samples using ESP-2 

indicate that the NGR count rate was 2,817 cpm for roof 

sandstone; 2,317 cpm for roof coal; 1,826 cpm for main 

coal; and 3,420 cpm for floor fireclay. The R:TC ratio was 
18 

Table 2O.-l&oratory analyses of one sample from each of ffve coal seams 

Chemical analyses NGR, cpm 

coal sesm Ash Sulfur Heating ESP-2 GRS5OO 

content, content, value, 

% % BTU/lb TCl’ TCZ? 

Pittsburgh: 

Roof ............................ 92.27 1.17 104 3,940 4,502 1,248 

Topcoal ......................... 5.97 2.75 14,297 2,240 3,028 792 

Parting .......................... 84.21 0.50 1,326 4,020 4,708 1,212 

Maincoal ........................ 12.53 5.00 12,843 2,283 3,528 774 

Fras$lOrt: 

............................ 90.87 3.09 558 1,817 ND ND 

Top coal ......................... 23.79 11.15 10,883 2,317 3,314 894 

Maincoal ........................ 7.87 4.08 13,386 1,828 2,908 790 

Floor fireday ...................... 92.74 0.88 320 3,420 4,270 1,222 

Msxwell: 

E ........................................................ 

70.28 0.18 3,744 2,977 4,145 1,094 

5.23 0.35 14,507 1,703 2,758 831 

Bseam 

............................ 

Hsadcoal ........................ 

Maincoal ........................ 

HnQ .......................... 

Upper l&t Fork 

Roof ........................... 

coal ............................ 

Parting .......................... 

............................ 

91.39 1.53 594 3,227 4,840 1,245 

5.11 0.83 13,572 1,653 3,302 824 

8.27 0.58 13,528 1,833 3,305 840 

79.51 0.17 1,789 2,193 3,884 950 

93.53 0.05 80 4,387 8,018 1,418 

12.02 0.45 13,185 1,983 3,824 878 

81.88 0.22 5,138 3,133 3,444 998 

90.80 0.21 578 4,080 8,842 1,882 

ND No data. 

‘Total counts above 0.08 MeV. 

%tal counts above 0.40 MeV. 

1.2% the RMC ratio was 1.42, and the F:MC ratio was 

1.89. When using GRS-500 unit (TCl setting), the RTC 

ratio was lm, the RMC ratio was 1.42; and the F:MC 

ratio was 1.89 (table 19). 

The results of chemical analyses of four coal and rock 

samples show that the ash content of the roof coal was 

23.79% and the main coal was 7.87%. The sulfur content 

of the roof coal was 11.15% and the main coal was 4.08%. 

The heating value for the roof coal was 10,883 Btu/lb and 

the main coal was 13,386 Btu/lb (table 20). 

MAXWELL COAL SEAM 

A visit was made to a mine operating in the Maxwell 

Coal Seam in Colorado. The immediate roof strata in 

the mine are composed of gray, soft slickensided shale, 

occasionally mixed with sandstone. The mean seam 

thickness is 2,134 mm (84 in) and ranges from 1,372 to 

2,743 mm (54 to 108 in). The seam occasionally has clay 

veins of different thicknesses. The immediate floor strata 

are made up of soft, water-sensitive fireclay. To protect 

the soft roof strata, from 203 to 305 mm (8 to 12 in) of 

coal are left on the roof. 

Underground Testing 

Underground NGR measurements were made at three 

locations (table 19). Using the ESP-2 unit, the mean 

NGR count rates were 9,336 cpm for roof shale; 6,146 cpm 

for roof coal, 4,184 cpm for main coal; and 10,933 cpm for 

floor shale. The mean RTC ratio was 1.52; the mean 

R:MC ratio was 2.23, and the mean F:MC ratio was 2.61. 

When using the GRS-500 (TCl setting), the mean R:TC 

ratio was 1.69 and the mean RMC and F:MC ratios were 

each 1.54. 

Laboratory Testing 

Laboratory measurements of two samples using the 

RSP-2 indicate that the NGR count rate for roof shale was 

2,977 cpm and for main coal was 1,703 cpm. The R:MC 

ratio was 1.75. When using the GRS-500 (TCl setting), 

the R:MC ratio was 1.54 (table 19). 

KUT radiometric analysis of one roof sample indicates 

that the bulk density was 1.30 g/cc, RaeU was 7.11 ppm, 

Th was 19.20 ppm, and K-40 was 1.56%. One coal sample 

had a bulk density of 0.88 g/cc, RaeU of 1.25 ppm, Th of 
19

333 ppm, and K-40 of < O.lO%. No floor sample was

available for testing. The NGR reading of that roof sample was 2,167 cpm and of that coal sample was 1,273 cpm

(tables 16,17).

The chemical analysis of one sample from the main

coal indicates that the ash content was 5.23%; the sulfur

content was 036%; and the heating value was 14,607

Btu/lb (table 20).

B COAL SEAM

A visit was made to a mine in the B Coal Seam in

Colorado. The immediate roof strata are composed of

dark gray shale, generally about 0.61 m (2 ft) thick. The

seam itself can be up to 7.62 m (25 ft) thick. The unmined (head) coal is up to 1,016 mm (40 in) thick and

includes banded and unbanded coal occasionally mixed

with pyrite. Between the head coal and main coal there is

a 76- to 102-mm (3 to 4-in)-thick rock parting with bony

coal (marker parting) that is normally left on the roof. Up

to 4.27 m (14 ft) of the upper coal will be mined during

the operation; the remaining coal [up to 3.09 m (10 ft)]

will be left on the floor. Occasionally, a rock parting of

variable thickness is found in the floor coal.

Underground Testing

Underground NGR measurements were made at five

locations (table 19). The results using the ESP-2 unit

indicate that the mean count rate was 7,873 cpm for the

immediate roof strata; 2,521 cpm for the roof parting near

the roof; 1,541 cpm for roof coal, 1,653 cpm for main coal;

2,321 cpm for floor coal; and 4,533 cpm for floor partings.

The mean R:TC ratio was 5.11; the R:MC ratio was 4.76;

and the RP:MC ratio was 1.53. Similar trends in the NGR

count rates were obtained when the GRS-500 unit was

used. However, ratios based on the GRS-500 measurements could not be computed because it was not possible

to take NGR readings of the immediate roof strata because it was inaccessible at the time. For GRS-500, the

RP:RC ratio was 148 and the RP:MC ratio was 1.43.

NGR measurements of the floor strata could not be made

with either unit.

Laboratory Testing

NGR laboratory measurements of four rock and coal

samples indicate that when using the ESP-2 unit the NGR

count rate was 3,227 cpm for the roof shale; 1,653 cpm for

roof coal; 2,193 cpm for a rock parting near the roof; and

1,633 cpm for the main coal. The R:TC ratio was 1.95;

the R:MC was 1.98; and the RP:MC was 1.34. When

using the GRS-500 (TCl setting), the R:TC ratio was 1.41

and the RP:MC was 1.11 (table 19).

KUT radiometric analysis of one roof sample indicates

that the bulk density was 1.71 g/cc, RaeU was 3.97 ppm,

Th was 16.70 ppm, and K-40 was 2.70%. For one coal

sample the bulk density was 0.91 g/cc, RaeU was

0.35 ppm, Th was 0.77 ppm, and K-40 was < 0.10%. NO

floor sample was available for testing. The NGR reading

of one roof sample was 2,133 cpm and of one coal sample

was 1,190 cpm (tables 16, 17).

Chemical analyses of one roof coal and one main coal

sample indicate that the ash content was 5.11% and

6.27%; sulfur content was 0.63% and 056%; and heating

value was 13,572 and 13,528 Btu/lb, respectively (table 20).

UPPER LEFT FORK COAL SEAM

A visit was made to a mine operating in the Upper Left

Fork Coal Seam in New Mexico. The immediate roof

strata are composed of shale and mudstone, occasionally

mixed with sandstone. The seam thickness ranges from

1,829 to 2,794 mm (72 to 110 in), with a mean value of

2,438 mm (% in). From one to three rock partings are

found in the seam, having a combined total thickness from

78 to 610 mm (7 to 24 in). The immediate floor is soft to

medium hard shale and mudstone. The mining company

would like to leave up to 508 mm (20 in) of coal on the

roof during mining to protect weak roof strata.

Underground Testing

Underground NGR measurements were made at three

locations. Using the ESP-2 unit, the results indicate that

the mean NGR count rate was 10,550 cpm for the immediate roof shale; 7,004 cpm for roof coal, 4,022 cpm for

roof coal below the parting; and 3,858 cpm for main coal.

For the roof parting the rate was 6,152 cpm and for the

floor shale the rate was 9,763 cpm. The mean R:TC ratio

was 1.50, for roof coal under the parting, the R:TC ratio

was 2.62; the R:MC ratio was 2.73; and the F:MC ratio

was 2.54. When using the GRS-500 unit (TCl setting), the

mean R:TC ratio was 1.21, for roof coalunder parting, the

R:TC ratio was 1.70; the R:MC ratio was 1.61; and the

F:MC ratio was 1.59 (table 19).

Laboratory Testing

Laboratory measurements of four samples indicate that

using the ESP-2 unit, the NGR count rate was 4,387 cpm

for roof shale; 1,963 cpm for main coal, 3,l33 cpm for

rock parting; and 4,080 cpm for floor shale. The R:MC

ratio was 2.23; the P:MC ratio was 1.60; and the F:MC

ratio was 2.08. When using the GRS-500 (TCl setting),

the R:MC ratio was 1.66, the F:MC ratio was 1.83, and the

P:MC ratio was 1.60 (table 19).
KUT radiometric analysis of one roof sample indicate sample had 1,173 cpm, and one floor sample had 1,230

that the bulk density was 1.62 g/cc, RaeU was 5.81 ppm, cpm (tables 16 to 18).

Th was 18.50 ppm, and K-40 was 2.22%. One coal sample Four coal and rock samples were analyzed for ash

had a bulk density of 0.89 g/cc, RaeU of 0.66 ppm, Th of content, sulfur content, and heating value. The ash con1.78 ppm, and K-40 of ~0.10%. One floor sample had a tent of the sample from the main coal was 12.02%, the

bulk density of 0.80 g/cc, RaeU of 0.90 ppm, Th of 253 sulfur content was 0.45%, and the heating value was

ppm, and K-40 of < 0.10%. NGR testing in the laboratory 13,185 Btu/lb (table 20).

indicated that one roof sample had 2,338 cpm, one coal

NGR SYSTEMS IN OPERATION AT MINE SITES

A number of NGR systems were used at underground

and highwall coal mines and also at a trona ash mine

during the period 1993 to 1995. As of August 1995, the

number of AME` units in the field was 34, of which two

were CM2000 systems (i.e., a new microprocessor-based

version of the AME 1008 with an inclinometer for continuous miner). Data obtained from 11 mines indicate

that the number of units fluctuated from 17 to 21. Of

these, 20 were AME units and 1 was a RHC unit. Table 21 lists known NGR systems installed on mining

machines in the United States as of August 1995.

These NGR systems were used in eight different coal

seams in seven states. One NGR unit is being used at a

trona mine to monitor up to 102 mm (4 in) of trona left

on the floor. One other trona mine has ordered two NGR

units.

Both the AME and RHC systems use scintillation

crystals and are capable of providing coal thickness

measurements on the order of 0 to 508 mm (0 to 20 in).

This must be left below the roof or above the floor to

protect poor roof or weak floor strata, or to avoid removal

of roof or floor coal with high ash and/or sulfur content.

In order to determine the feasibility of using the NGR

techniques in the United States, the USBM has analyzed

geological and mining data for over 460 underground and

surface mines. Information obtained indicated that approximately 90% of the mines have an immediate roof

and/or floor composed of shaley-type materials, which

typically have higher radioactive levels than coal.

NGR systems have been used successfully on both

longwall shearers and continuous miners in underground

operations and also on highwall miners in surface operations. The systems work best when the speeds are less

than 15 m/min (50 ft/min), and coal left is 152 to 203 mm

(6 to 8 in). If the speed of the shearer is 24 m/min

(80 ft/min) or higher, it is very difficult for the operator to

read the NGR data without a remote indicator. The units

are mounted between 203 to 406 mm (8 to 16 in) from the

roof or floor coal. The airgap between the NGR units and

the roof or floor coal ranges from 76 to 762 mm (3 to

30 in).

The NGR units have been used for measuring from 51

to 610 mm (2 to 24 in) of coal left on the roof and from

51 to 127 mm (2 to 5 in) or up to 610 m (24 in) on the

floor. When the thickness of the coal to be left on the

roof is thicker than 610 mm (24 in) or more [which is

beyond the normal 508- to 610-mm (20- to 24-in) range],

the NGR units cannot be applied. The best results are

obtained when the thickness of the coal left is in the range

of 152 to 305 mm (6 to 12 in), and the variation of the

thickness and geology of the immediate roof and floor

strata, as well as the variation in the seam thickness, is

small. Also, the seam should be flat or only with a small

dip. The NGR units can also be calibrated to indicate that

no coal is left on the roof.

Problems encountered when using the NGR units were

l nonshaiey roof or floor

l remnant coal too thick for sensor to read NGR

l geology too variable

l inadequate training of personnel

l decreased accuracy (due to decreased NGR counts)

l mining debris buildup on NGR sensor

l damaged cables and/or connectors of NGR system

l moisture accumulation in system due to -cleaning

equipment of high-pressure water spray

l longwall shearer * speed too high [> 15 m/mitt

(>50 ft/min)].
21 

Table Pl.-NGR sensors operating In U.S. mine8 (a8 of August 1995) 

Mine No. Coal seam State Miner type NGR system type Location Range, cm In use Comments 

1 ....... Pittsburgh PA CM 1006 F 20 Yes O.K. 

1 ....... Pittsburgh PA CM 1006 F 20 Yes O.K. 

1 ....... Pittsburgh PA CM F 20 Yes O.K. 

1 ....... Pittsburgh PA CM CMEE F 20 No Idle. 

2 ....... No. 36 WY Hw 1016 R 46-51 Yes 0.K 

2 ....... No. 36 WY l-w 1016 R 3lx36 No Standby. 

2 ....... No.36 WY Hw 1016 F 20-25 Yes O.K. 

3 ....... Hanna WY Ls 1016 R 46-91 Yes When -c61 cm. 

3 ....... Hanna WY CM CM2000 F 30 No Not installed. 

4 ....... Wadge co LS 1008 R 15-25 No High LB speed. 

5 ....... No.6 IL LS 1016 R 6-10 No Thin seam. 

5 ....... No.6 IL CM 1008 R 20 Yes 0 .K. 

5 ....... No. 6 IL CM 1008 R 20 Yes 0 .K. 

6 ....... Pittsburgh PA CM 1008 R 15-20 Yes O.K. 

6 ....... Pittsburgh PA CM 1008 R 15-20 No Standby. 

7 ....... O’Connor UT CM 601 R 61-91 No Thin seam. 

6 ....... No. 13 KY LS 1016 R 5-15 No Remote control. 

9 ....... Trona WY EBM 1008 F 2.510 Yes O.K. 

10 ...... Trona WY LS 1008 R 1525 No Not installed. 

10 ...... Trona WY EBM 

CMEE 

F 0+ No Not instailed. 

11 ...... Freeport OH CM F 2.515 Yes O.K. 

NOTE-Nomenclature: 

Location: Miner type: NGR system manufacturer: 

F floor CM continuous miner AME 1008, 1016, CM26C0 

Rroof EBM Eimco boring machine RHC 801 

HW highwail miner 

LS longwafl shearer 

SUMMARY 

Presently there are four commercially available NGR 

sensors that are MSHA approved for installation on 

mining machinery-the RHC 801, RHC 803, AME 1008, 

and the AME 1016. However, the AME 1016 was not 

available for testing. The physical dimensions of these 

sensors are basically similar, being approximately 635 

by 203 by 152 mm (25 by 8 by 6 in). The RHC 803 is 

designed for use on a continuous miner; however, all four 

units could be used on either longwall shearers or continuous miners. Both RHC units operate on either 440 to 

550 or 880 to 1,100-V, 3-phase, ac power, and can also 

operate on batteries. The AME units operate either on 

110 to 120 V, ac power, or batteries. 

All of the NGR sensors work best within a range of 

approximately 76 to 305 mm (3 to 12 in) of roof coal, although vendors claim sensors can work for up to 508 mm 

(20 in) of roof coal. These sensors should preferably have 

no more than 910 mm (3 ft) of airgap between the roof 

and the sensor to maintain adequate sensitivity. It was 

also found that the NGR values dropped rapidly during 

the first 305 mm (12 in) of airgap. 

For the NGR-based CID technique to work properly, 

the immediate roof or floor must be composed of a 

gamma-emitting material such as shale, draw slate, or 

fueclay. In addition, minimum thickness of the immediate 

roof or floor should be at least 76 mm (3 in), based on the 

results of laboratory tests. Also, the immediate roof or 

floor should remain relatively constant in geological 

composition for best results. 

Based on underground tests conducted at the USBM 

SRCM mine (Pittsburgh Coal Seam), the AME 1008 

appears to be about 2.4 times more sensitive than the 

RHC 801, and the RHC 803 is approximately 88% as 

sensitive as the RHC 801. The AME 1016 was not 

available for testing. The ESP-2 is about 53% as sensitive 

and the GRSJOO is approximately 1.4 times more sensitive 

than the RHC 801. Consequently, if the ESP-2 is used for 

preliminary underground tests, the values given by the 

ESP-2 can be multiplied by 1.89, 1.66, and 4.41, to obtain 

estimated values for the RHC 801, RHC 803, and AME 

1008, respectively. 

For testing in the laboratory, coal and rock samples 

should be at least 76 mm (3 in) thick, have at least 1613 

cm* (25 in*) of surface area exposed, and should weigh at 

least 1,814 g (4 Ibs) in order to get a reasonably good 

NGR measurement. In general, the larger the sample, the 

better the NGR reading. Ideally, the samples should be 

made identical in physical size and weight. Efforts are 
22

being directed toward determining a standard size sample

container so that all samples are identical in terms of

physical dimensions. The samples would be ground to at

least 60-mesh size and then poured into the sample

container.

Underground and laboratory NGR values as measured

by the ESP-2 were found to have a relatively wide range

for the coal seams studied in this report, e.g., the

underground/laboratory ratio values ranged from 1.53 to

5.58. Consequently, it is not yet possible to obtain a

general conversion factor for relating laboratory NGR

counts to underground counts, although a ratio value of 3.5

could be used as an initial approximation. More underground and laboratory measurements are needed to provide a more accurate ratio value for a given coal seam.

For the coal seams studied, the Illinois No. 5 had the

highest roof NGR count rate and the Hiawatha had the

lowest, based on underground measurements using the

ESP-2.6

Ratios of underground NGR readings were computed,

e.g., R:C and F:C. Basically, the higher this ratio, the

better likelihood that the NGR technique would work.

R:C values ranged from 1.41 (Kittanning) to 3.08 (Illinois

No. 5). F:C values ranged from 1.45 (Kittanning) to 2.39

(Hiawatha). Consequently, a roof NGR sensor appears to

have the best chance of success if used in the Illinois No. 5

coal seam and a floor NGR sensor is most likely to work

best if used in the Hiawatha coal seam.

Based on coal and rock data collected by USBM

personnel, it is currently believed that R:C and F:C ratios

on the order of at least 1.5 are needed for successful

implementation of the NGR technique. However, this

critical minimum value has not been able to be objectively

determined because there is very little underground

operational data available as yet.

KUT radiometric analysis of 17 roof rock, 16 coal, and

12 floor rock samples, obtained from 18 mines rep

resenting 16 coal seams in different coal regions, was done

by the U.S. Geological Survey, Branch of Isotope Geology,

Denver, Colorado. These samples were selected from

mines where the AME and RHC units were used (or

presently are in use), from mines where USBM personnel

have performed in-mine NGR testing for CID purposes,

and from those mines where laboratory or in-mine NGR

readings were significantly higher than normal.

The results of these 45 coal and rock samples are

listed in tables 16 to 18, with units being given in percent

for potassium and in part per million for uranium and

thorium; also, 29 of these samples also had a chemical

analysis done. It should be noted that the roof samples

from Illinois No. 5 and No. 6 Seams, and Kentucky No. 9

Seam, have higher than normal uranium concentration

(table 16). This was expected because these samples also

had higher NGR readings for both the underground and

laboratory testing.

REFERENCES

1. Maksiiovic, S. and G. L Mowrey. Basic Geological and

Analytical Properties of Selected Coal Seams for Coal Interface

Detection, USBM IC 92%, 1993,SS pp.

2 . Mowxy, G. L and S. Maksimovic. Investigation of the Feasibility

of Natural Gamma Radiation Coal Interface Detection Method in U.S.

Coal Mints, SME Preprint 90-127, SMEAnnual Meeting, Salt Lake City,

UT, Feb. 2GMar. 1,1990,11 pp.

tie Qarion Coal Seam had the lowest apparent NGR count rate;

however, the ESP-2 was operated in a narrow--window mode rather

than a widewindow mode for this particular seam. For that reason,

these values cannot be compared to the others.

3. Salford Electrical Instruments, Ltd. (Manchester, England).

Information Manual, Type 801 Natural Gamma Coal Thickness Indication System. Part I, 1%9,14 pp; Part II, 1990,32 pp.

4. American Mining Electronics Inc. (Huntsville, AL). AME Model

1008 Coal Thickness Sensor Manual, 1991,12 pp.

5. Eberline (Santa Fe, NM). Eberline Smart Portable Technical

Manual, Model ESP-2, 1986,114 pp.

6. EDA Instruments Inc. (Toronto, Ontario, Canada). Brochure,

Scintrex, GRS-500 Differential Spectrometer/Scintillometer, 1988.4 pp.

7. Hanna, K, K Haramy, and T. R Ritzel. Automated Longwall

Mining for Improved Health and Safety at the Foidel Creek Mine. SME

Annual Meeting, Denver, CO, Feb. 25-28, 1991, SME Preprint 91-165,

1991, 8 pp.






















45

APPENDIX.-TECHNICAL SPECIFICATIONS OF SEVERAL NGR SYSTEMS

RHC MODEL 801

The RHC Model 801 unit is comprised of three major

items and associated cables:

801 NGR Sensor

The 801 NGR sensor (probe) is ruggedly built and can

be mounted on the face side of any type of coal-cutting

machine. Depending on where it is mounted, the sensor

measures the thickness of the coal in the present cut,

previous cut, or prior to cutting (on continuous surface

miners). It can reliably sense between 0 and 500 mm (0

and 19.5 in) of coal thickness and is capable of accommodating machine speeds of up to 16.8 m/mm (55 ft/min)

at 254 mm (10 in) coal thickness.

The probe gives a pulsed digital output. The electronic

assemblies that produce the output are mounted in a high

‘g’ mount and wholly encased in a robust steel case with a

window in its top surface. This window is the entry port

for the gamma radiation. Strategically placed 12.5-mm

(0.5-in) thick lead shielding inside the sensor casing prevents radiation entering by any other way than the window.

The overall dimensions of the sensor are 640 mm long by

220 mm high by 170 mm wide (approximately 25 by 8.5

by 6.5 in) and weighs 52 kg (114.4 lbs). The electronic

assemblies are a scintillator unit and reforming circuit

(figure l).r

The assembly consists of the following components:

0 Scintillator Unit

This is the NGR detector. It is an integral unit

comprised of a 152-mm long by 76-mm ID (6- by

3-in) thallium doped caesium sodide (Nal) crystal

coupled to a nine-stage photomultiplier and highvoltage generator. A lead shield 12.5 mm (0.5 in)

thick, shields the crystal from all gamma radiation

except that coming from the selected area. NGR

enters the crystal and strikes an electron of the

crystal giving off a flash of light. The light flash is

seen by the photomultiplier which produces a voltage at its anode that is proportional to the energy

detected by the crystal.

l Photomultiplier

The photomultiplier requires high voltage (approximately 1,200 V). This is provided by a dc-to-dc

converter fed by the 10-V supply. Two-thirds of the

power required by the probe is consumed by the

‘Figure numbers refer to illustrations in the main text.

high-voltage generator. It converts the light flashing

from the caesium sodide crystal to voltage.

l Reforming Circuit

The reforming circuit receives the pulsed output

from the photomultiplier and reforms each pulse to

an amplitude of 10 V and a width of I20 ps.

Coal Thickness Indicator Unit

This is a microprocessor-based unit which, when coupled to a RHC 801 probe, provides the machine operator

with an indication of the deviation from required roof

or floor coal thickness. Its dimensions are 325 mm long

by 100 mm wide by 85 mm high (12.8 by 4 by 3.4 in) (figure 2).

The horizon (required coal thickness) can be set

anywhere in the range from 0 to 500 mm (0 to 19.5 in),

the deviation being indicated by LED’s in multiples of

20 mm (0.75 in) up to a maximum of f 80 mm (3.1 in).

Automatic calibration and test facilities are built in.

Power requirements are approximately 12.5 to 15 V dc at

140 mA.

The front panel from left to right has:

l a round display panel.

l test points, reset, and calibration control buttons

under a hinged security flap.

0 two Plessey connectors:

- top one is connected to 801 sensor.

- lower one connected to the remote indicator or

a data transmission system. A protective blank is supplied

to cover the connector when not in use.

Power Supply Units

There are presently three standard types of intrinsicallysafe (IS) power supplies. Electrically they are identical,

the mechanical arrangement of the components is different

to suit the space into which it must lit.

One power supply unit requires either a 440 to 550 or

880 to 1,100-V, 3-phase, ac input. An internal transformer

drops the output voltage to 16.5 V, 3-phase, ac.

The power supply unit (powered by 16.5 V, 3 phase, ac)

provides hvo isolated 15-V dc outputs rated at 140 mA

each.

Remote Indicator (optional)

A remote indicator unit, when connected to the coal

thickness indicator unit, will provide a secondary set of

LED’S indicating any error in coal thickness from the
46

horizon setting. The unit is powered by the coal thickness longwall shearing machines and can be added to the

indicator unit; it is normally used for double-ended system, if needed (figure 3).

RHC MODEL 803

The RHC model 803 is 555 mm long by 190 mm high

by 138 mm wide (approximately 22 by 7.5 by 5.5 in) and

that is rubber-isolated. The 803 unit has done away with

the suspension, and the basic cradle is covered with a

weighs 43 kg (95 lbs). This unit (figure 5) was developed stainless-steel alloy case.

to fit on smaller equipment such as a continuous miner.

Further, the original 801 unit

had the ability for an analog and a reverse analog output

The main difference between the RHC 803 and the that were never used. Consequently, one of the circuit

original RHC 801 unit is a different method of isolation. boards was removed from the 803 unit. Both models

In the 801 unit, all the components are held in a cradle today give only digital outputs.

AME 1008 AND 1016 UNITS

The AME Model 1008 coal thickness sensor is a highperformance system, containing a large-area gamma

detector, which accurately measures coal left on the roof

or floor when seam boundary material contains gammaproducing elements.

The sensor assembly, housed in the explosion-proof

(X-P) enclosure, has a window to receive “natural

background gamma radiation from the rock at the coal

seam boundary. When the window is pointed at the roof

or floor area to be measured, the total gamma emission

entering the window is relative to the thickness of coal left

at the rock boundary. The sensor has 305 by 102 by 51

mm (12 by 4 by 2 in) Nal crystal (figure 6). In most

applications, the sensor may be placed as much as 0.91 m

(3 ft) away from the coal surface.

An IS control and display unit converts gamma counts

from the sensor to inches of coal thickness, which are

displayed to the operator on the front panel (figure 7).

This unit requires a 12-V dc, 500~mA power supply source.

The AME 1008 system measures 25.4 to 406.4 mm (1

to 16 in) of coal, where adequate and consistent natural

radiation exists in the seam boundary rock. Figure 8

shows a block diagram and connection schematic of the

AME 1008. Measurement accuracy is within + 6.4 mm

(0.25 in) at 152.4 mm (6 in). Other beneficial features

are:

l High-sensitivity detector and electronics are minepermissible and housed in a rugged steel enclosure.

l Sensor can be easily calibrated by an operator onsite; it is simple to operate and requires minimal training.

It can be easily installed on mining machine for roof or

floor measurements.

l Sensor has ruggedized and moisture-sealed construction, and includes environmentally-sealed cable

connectors. It has extensive shielding to block unwanted

radiation background count; IS control-display unitoperated microprocessor; and continuous coal thickness

readout on a bright LED display.

l Available electrical outputs of the sensors include:

- coal thickness

- 0 to 5-v analog

- gamma counts.

l Ac-dc power supply, which is located in the

operator’s X-P power box, operates on lOO- to 130-V ac

power from the mining machine.

Components

supplied

Gamma sensor

Control and display

unit

IS barriers

Ac-dc power supply

Connecting cables

Dimensions

(L x W x H)

584.2 by 203.2 by 152.4 mm

(23 by 8 by 8 in)

203.2 by 152.4 by 88.9 mm

(8 by 8 by 3.5 in)

152.4 by 101.8 by 50.8 mm

(8 by 4 by 2 in)

101.8 by 152.4 by 78.2 mm

(4 by 6 by 3 in)

Lengths as required

Weight

90.72 kg

(200 Ibs)

4.54 kg

(10 Ibs)

0.45 kg

(1 lb)

2.27 kg

(5 Ibs)

The recently developed larger size AME 1016 system

measures up to 890 mm (35 in) of coal with sufficient

NGR counts. However, this system was not available for

evaluation for this report.
4 7

The Eberline Smart Portable (ESP-2) radiation survey

instrument is designed to be used for routine radiation

surveys. The ESP-2 unit may also be used in remote

areas, operated solely by a computer. It utilizes a

scintillation detector [51-mm long by 51-mm ID (2- by

2-in) Nal crystal] to measure NGR in both field and laboratory. It is also equipped with a single-channel pulse

height analyzer (PHA). Information provided by this

instrument is used to determine if the NGR technique is

potentially applicable in the field at a given mine and

seam. Figure 10 shows the Eberline Smart Portable

Model ESP-2 Unit.

Specifications

1. Mechanical:

a. Overall dimensions of this device are 267 mm

long by 127 mm high by 132 mm wide (10.5 by

5.0 by 5.2 in).

b. Weight of the unit (excluding probe) is

approximately 1.73 kg (3.8 lb).

2. Temperature:

a . Operating: -20 “C to +50 “C (-4 “F to 122 “I?).

EBERLINE ESP-2 UNIT

b. Storage: -30 “C to +80 ‘C (-22 “F to 176 “F).

3. Voltage:

a. Low voltage: 5 V dc.

b. High voltage (detector bias voltage): 500 to

2,450 V dc, adjustable from the keypad.

c . Battery supply voltage: 5.8 to 10.0 V dc.

4. Detectors:

The detectors connect to the ESP-2 unit via a

coaxial connector located on the front of the instrument.

5. Readout:

a. Two lines of 16 alphanumeric characters are

presented on liquid crystal display (LCD).

b. Character size: H = 4.45 mm (0.175 in); W =

3.15 mm (0.124 in).

c. Bar graph resolution: 1 in 48 (2.1%).

6. Power Supply:

The ESP-2 unit uses six C-cell batteries. Six

alkaline batteries provide approximately 300 h of

continuous use. The ESP-2 senses the low battery

condition at 0.95 V dc/cell and signals the user by

blinking the first character on the display.

EDA GRS-500 SYSTEM

The GRS-500 Differential Gamma Ray Spectrometer/

Scintillometer is manufactured by EDA Instruments Inc.,

Toronto, Canada. This instrument is a compact portable

field spectrometer with simplified operational controls. It

has two spectrometers that are used to measure the

gamma radiation emitted by various daughter isotopes in

the uranium decay series. The first of these is a sensitive

wide-energy-band spectrometer used for general reconnaissance. This is a sensitive scintillometer, or more correctly, a broadband spectrometer. This is a simple instrument which measures total gamma ray activity from the

uranium series, as well as emitters from the naturally

occurring potassium and thorium series.

The second instrument is an accurately-calibrated,

stable, sensitive spectrometer that detects gamma radiation

originating from certain discrete isotopes. These include

Bismuth-214, Thallium-208 and Potassium40 isotopes with

well-defined energy peaks from the uranium, thorium, and

potassium series, respectively. The GRS-500 is a lightweight 5-channel spectrometer (figure 12).

This instrument combines the functions of both spectrometers and serves in a variety of functions including:

l Rapid reconnaissance surveying.

l Ground follow-up of airborne anomalies.

l Detailed radio activity analysis of uranium, thorium,

and potassium.

l Detection of radioactive glacial float and detritus.

l Lithological and structural mapping.

l Systematic surveys and property evaluation.

l Qualitative screening of drill core, chip samples, and

slurry.

Specifications

Detector-Nal(Tl) crystal and high-stability photomultiplier tube with a mu-metal magnet shield. The detector

volume is 124 cm3 (75 in’). Mechanically ruggedized.

Energy Thresholds-!+vitch--selectable to:

TCl - Total count above 0.08 MeV.

TC2 - Total count above 0.40 MeV.

K - All gamma energies between 1.35 and 159

MeV.
48

U - All gamma energies between 1.65 and 1.87

MeV.

T - All gamma energies above 2.45 and 2.79

MeV.

Display-5-digit ruggedized low-temperature LCD. Displayed counts normalized to count per second. Flashing

count overflow and battery charge status indicators custom

designed into display.

Sample Rate-l.0 or 10.0 s, auto recycle, for all energy

levels, except for “CAL” position.

CalibrationSource-Barium-133 (13jBa) Isotope. Rated

activity 05 j&X

Power-Four alkaline “C” ceiis with an average continuous operation of 60 h without audio at 23 “C ambient

temperature.

Operating Temperature- -10 “C to +60 “C (+ 14 “F to

+ 140 OF).

Relative Humidity-O to 100%.

Weight-2.3 kg (5.0 lb).

Dimensions-235 by h by 64 mm (9.25 by 4.5 by 2.5

iIl).

INT.BU.OF MINES,PGH.,PA 30175

ti USGPO 709-009/20.049