For a given detector, efficiency values depend on
the type and energy of the incident radiation
. … For incident charged particles such as alpha particles or beta particles, many detectors have a total efficiency that is close to 100 percent.
Does the efficiency of a gamma detector increase or decrease as the energy of the ray increases?
Eight different sources of gamma rays were used at different distances to calculate the efficiency of gamma rays. Efficiency was calculated by comparing the theoretical activity and observed activity of these radio isotopes. The results show that the efficiency of gamma
reduces
as the energy of gamma ray increases.
How is detector efficiency measured?
the efficiency of the detector for radiation from the sample must be calculated using
formula ε(E) = ω ε0(E)
, finding the value of the coefficient ω for the relation (2). For a cylindrical container l = H and for a complex-shaped container l = H – h.
Which detector has very good resolution and efficiency?
High purity germanium detector
has better resolution compared to the scintillation type of detector, Sodium iodide (NaI). The HPGe detector offers the advantage of resolving two closely located energy points and has the ability to detect a mixture of nuclear material.
What is the energy resolution of a detector?
Energy Resolution is
the ability of the Detector to accurately determine the Energy of the Incoming Radiation
. Since no camera system is perfect, no system is capable of determining precisely what energy photon struck the crystal.
What is the efficiency of a detector?
The detection efficiency is a
measure of the percentage of radiation that a given detector detects from the overall yield emitted from the source
.
What is scintillation efficiency?
Scintillation efficiency is defined as
the energy released as photons divided by the energy of the ionizing particle
. … Thus, 1 keV electrons produced only one-half as many photons per unit energy as 300 keV electrons.
Which detector has the best energy resolution?
1.
HPGe
is known for its high energy resolution. In Figures 1 through 3, the photopeaks are extremely sharp: the resolution is 1.8 keV FWHM (0.3%) at the 662 keV peak of 137Cs. Many distinct emission lines can be seen from the uranium sample.
Why is thallium used in NaI detector?
The doping of the NaI crystal with thallium
improves the scintillation efficiency by improving the light emission
due to the improved recombination by light emission of electrons and holes at the dopant site.
Which detector is useful for V ray spectroscopy?
Common detector materials include
sodium iodide (NaI) scintillation counters
and high-purity germanium detectors. To accurately determine the energy of the gamma ray, it is advantageous if the photoelectric effect occurs, as it absorbs all of the energy of the incident ray.
What influences the counting efficiency?
Several factors affect the counting efficiency:
The distance from the source of radiation
.
The absorption or scattering of particles by the medium (such as air)
between the source and the surface of the detector.
Which detector has more efficiency in photo conversion?
Photoemissive detectors
have an advantage over other detectors as they have faster speed, higher gain and low noise. However, their spectral range is somewhat limited as the incident photon must have sufficient energy to eject electrons from the photocathode.
How is detector resolution calculated?
It depends mainly on the thickness (x) of the detector material, according to the formula:
Det. eff. = 1 – e^(u.x)
, where u is the linear attenuation coefficient of the material, at a given energy. For the same x, the efficiency decreases for increasing energies.
What is the backscatter peak?
Backscattered peaks. Close inspection of a gamma-ray spectrum may reveal a wide peak with energy <250keV which does not correspond to a known photon from the source. Such a feature, termed a Backscatter peak, is
due to gamma-rays which first interact by Compton scattering with the shielding
.
How gamma rays are detected?
Like X-ray detection, gamma-ray detection is done photon-by-photon. Gamma rays are
detected by observing the effects they have on matter
. A gamma ray can collide with an electron and bounce off it like a billiard ball (Compton scatter) or it can push an electron to a higher energy level (photoelectric ionization).
How do you calculate FWHM?
FWHM can be determined as the
distance between the curve points at the peak half maximum level
. On a data graph, draw a vertical line from the peak maximum to the baseline. Measure the length of this line and divide it by 2 to find the center of the line.
