  Cosmic ray muons have emerged as a non-conventional high-energy radiation
probe to monitor dense and large objects. Muons are the most abundant cosmic
radiation on Earth, however, their flux at sea level is approximately 10,000
min^-1m^-2 much less than that of induced radiation. In addition, cosmic ray
muon flux depends on not only various natural conditions (e.g., zenith angle,
altitude, or solar activities) but also the geometric characteristic of
detectors. Since the low muon flux typically results in long measurement times,
an accurate estimation of measurable muon counts is important for muon
applications. Here we propose a simple and versatile semi-empirical model to
improve the accuracy in muon flux estimation at all zenith angles by
incorporating the geometric parameters of detectors, and we name this the
Effective Solid Angle model. To demonstrate the functionality, our model is
compared with i) the cosine-squared, ii) PARMA model, and iii) Monte-Carlo
simulations, and iv) measurements. Our results show that the muon count rate
estimation capability is significantly improved resulting in increasing a mean
C/E from 0.7 to 0.95. By selecting an appropriate intensity correlation, the
model can be easily extended to estimate muon flux at various altitude and
underground level.
