1. Keating 1
Mary Kate Keating
Independent Study
Dr. Busch
01/10/2015
Analysis of Marcellus Shale Radiation:
Geiger-Muller Counter vs. Gamma Ray Spectrometer
When dealing with radiation, the three main types of ionizing radiation include
alpha, beta, and gamma (EPA, 2014). Ionizing radiation refers to radiation that contains
enough energy to remove electrons from atoms. Alpha (α) particles contain two protons
and two neutrons. The charge on the particle is therefore (+2). This is radiation
transmitted from the nucleus of an unstable atom. Most atoms emitting alpha particles
generally have a high atomic number. When the atom emits alpha particles, the result is a
decay product along with becoming a different element. Beta (β) particles are similar to
electrons. The nucleus of a radioactive atom emits subatomic particles called beta
particles. This results when the ratio of neutrons to protons is high. The charge on a beta
particle is (-1). What distinguishes the beta particle is the high amount of excess energy it
gives off. Lastly, there is the gamma ray (γ). On the electromagnetic spectrum, gamma
rays (photons) contain the highest amount of energy. Again, the nucleus of unstable
atoms can emit gamma rays. Gamma rays contain neither mass nor charge, and they
travel at the speed of light.
To determine the Marcellus radiation for our analysis, a Geiger counter (Geiger-
Muller counter) and a gamma ray spectrometer were used. First used to measure the
radiation was the Geiger counter. The Geiger counters detector consists of a “Geiger-
Muller tube” tube filled with an inert gas. When radioactive particles or gamma ray
photons penetrate the tube, they collide with the inert gas and release a pulse of electrons
that are registered on a meter that registers counts of the pulses of electrons. The counts

2. Keating 2
may be translated into an audible click of each count (NRC, 2014). Although alpha, beta,
and gamma radiation is detected by a Geiger counter, the specific element(s) giving off
the radiation is/are unknown. In this study, Geiger counter measurement was done for
each sample by recording the counts over a time interval of 10 minutes, then dividing by
ten to obtain counts per minute (CPM). First, the Geiger counter was run without a
sample, so the background radiation of the testing site could be determined. Then the
bulk radiation emitted from a sample (and the background around the sample) was
measured by placing the sample directly below and against the circular screen of the
Geiger counter. Background radiation was subtracted from this bulk CPM to determine
the actual radiation emitted by the sample in CPM.
Continuing the analysis, a Gamma Ray Spectrometer is then used. The device
measures the amount of gamma radiation emitted by the sample and gives an assay for
thorium (ppm), uranium (ppm), and potassium (%). A Terraplus RS-230 gamma ray
spectrometer was used in this study. Its detector is a. When a gamma ray interacts with its
bismuth germanate (BGO) crystal, a spectrum of energy levels is produced and can be
analyzed to determine the identity of the gamma emitter (primarily potassium, uranium,
and thorium). Over time (two minutes), the concentration of potassium (%), uranium
(ppm), and thorium (ppm) in the sample, plus counts per second of gamma radiation can
be determined. The RS-230 adjusts for background radiation. In this study, the RS-230
was used in the field. At each sample location, the instrument was directed parallel to
bedding and into the stratum being analyzed (and sampled for Geiger counter analysis in
the laboratory).

3. Keating 3
Once all the samples were analyzed, the results were made into an Excel
spreadsheet. From here correlations were determined between the Geiger counter and
gamma ray spectrometer. The gamma ray spectrometer data were used to calculate
readings in API (American Petroleum Institute) Units. For standard natural gamma-ray
logs (GR or SGR), the API value is calculated from thorium in ppm, uranium in ppm and
potassium in percent. API = 8 times the uranium concentration in ppm + 4 times the
thorium concentration in ppm + 15 times the potassium concentration in percent (Ellis
and Singer, 2008).
After the API values were calculated for each sample, the linear correlation
coefficient (r) and coefficient of determination (r2) were determined in a comparison of
sample API values versus their uranium, thorium, and potassium concentrations. The
linear correlation coefficient (r), also called the Pearson product-moment linear
correlation, is a measure of the strength and direction of a linear relationship between two
variables (in this case: API value versus the concentration of potassium, uranium, or
thorium). In this study, the CORREL function in Excel was used to calculate the linear
correlation coefficient (r). An r value of exactly +1 indicates a perfect positive
correlation, an r value of exactly -1 indicates a perfect negative correlation, and an r value
of exactly zero indicates that there is no linear relationship/correlation (i.e., the
relationship is purely random). The coefficient of determination (r2) is a measure of what
proportion of the values of one variable (in this case: API value) is predictable from the
values of the other variable (in this case: uranium concentration in ppm). In this study,
there was essentially no correlation between thorium and API (r = -0.01) or between
potassium and API (r = -0.31). However, there was a very strong positive correlation

4. Keating 4
between uranium and API (r=0.98) with a strong coefficient of determination (r2 = 0.95).
The coefficient of determination indicates that the correlation is so strong that 95% of the
API values are predictable from their corresponding values for uranium concentration.
Uranium is therefore identified as being the main source of gamma rays being
detected with the gamma ray spectrometer and thus driving the SGR (spectral gamma
ray) curve in API units. A fair relationship was observed between the Geiger Counter
values for total radiation emitted by each sample in CPM (counts per minute) versus
uranium concentration of each sample (r=0.76 and r2=0.58), so there are other isotopes
that are emitting the additional beta and alpha radiation detected by the Geiger counter.
Nevertheless, there is a good correlation (r = 80) between Geiger counter measures of
total radiation in CPM (counts per minute) and gamma radiation expressed in API values.
Therefore, a Geiger counter can be used in the field or laboratory to determine levels of
radiation emitted from Marcellus samples—radiation primarily emitted from uranium.
References
Ellis, Darwin V., and Singer, Julian M., 2008. Well Logging for Earth Scientists.
Springer, The Netherlands.
EPA (Environmental Protection Agency), 2014. Radiation: Non-Ionizing and Ionizing.
Retrieved January 10, 2015, from http://www.epa.gov/radiation/understand/
NRC (National Research Council), 2014. Geiger-Muller counter. Retrieved January 11,
2015, from http://www.nrc.gov/reading-rm/basic-ref/glossary/geigermueller-
counter.html