Radiation : The process of emitting energy in the form of waves or particles. Where does radiation come from?
Radiation: The process of emitting energy in the form of waves or particles.
Where does radiation come from?
Radiation is generally produced when particles interact or decay.A large contribution of the radiationon earth is from the sun (solar) or from radioactive isotopes of the elements .Radiation
By the end of the 1800s, it was known that certain isotopes emit penetrating rays. Three types of radiation were known:
Rn222Alpha Particles (a)
alpha-particle(a) is a Helium nucleus. It’s the same as the element Helium, with the electrons stripped off!
7 neutronsBeta Particles (b)
We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred:
n p + e ( + n)
Yes, the same neutrino we saw previously
In much the same way that electrons in atoms can be in an excited state, so can a nucleus.
+Gamma particles (g)
10 neutrons(in excited state)
10 neutrons(lowest energy state)
A gamma is a high energy light particle.
It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.
* m = E / c2
i) The type and energy of the incident radiation.
ii) The chemical and physical properties of the target material.
iii) The manner in which the incident radiation interacts with the material.
This section contains the mechanisms by which ionizing radiation interacts and loses energy as it moves through matter. This subject is extremely important for radiation measurements because the detection of radiation is based on its interactions and the energy deposited in the material of which the detector is made. Therefore, to be able to build detectors and interpret the results of the measurement, we need to know how radiation interacts and what the consequences are of the various interactions.
For the discussion that follows, ionizing radiation is divided into three groups:
Charged particles traveling through matter lose energy in the following ways:
Photons, also called X-rays or g rays are electromagnetic radiation, are considered as particles that travel with the speed of light c and they have zero rest mass and charge.
Shortly after the discovery of x-rays in 1885 by Professor Roentgen scientists began to notice the harmful effects of exposure to this radiation. There were many years before people realized how dangerous x-rays and other radiation could be. Quite number of pioneer radiologists suffered severe injuries, and some even died, as a result of prolonged exposure to dangerously high intensities of X-rays. These early workers in the field had no means of measuring the harm caused by radiation accurately and depended on unreliable effects such as the degree of skin reddening caused by the exposure, or on timing the exposure from a certain type of X-ray machine to establish quantity.
The SI unit of exposure is defined as 1 C / Kg air, without any new name proposed for it. Numerically
Where D is the absorbed dose and is the mean energy imparted by ionizing radiation to matter in a volume element and dm is the mass of matter in the volume element. The unit of the absorbed dose is rad defined as,
The first step toward that task was the introduction of a factor called the relative biological effectiveness (RBE), defined as
In 1963, the International Commission on Radiological Units and Measurements (ICRU) proposed the replacement of RBE by a new factor named the quality factor (QF). In 1973 the ICRU (82) recommended dropping "F" from QF, a suggestion that has now become practice. In 1977 the International Commission on Radiological Protection (ICRP) recommended that the dose equivalent (H) at a point in tissue be written as:
H = NQD
Where Q = Quality factor its values are given in Table 1.1.
D = absorbed dose
N= product of all the modifying factors. The suggested value of N is 1
When the unit of absorbed dose is multiplied by the corresponding Q value, the unit of dose equivalent (H) is obtained. The H units are
1 rem = Q x 1 rad
and the SI unit,
1 Sievert (Sv) = Q x 1 Gy
1 Sv = 100 rem.