2.2.6 Units of radioactivity

1.Conversion unit


#### 2. SI unit

2.2.3 Electron capture

2.2.4 The positron decay β<sup>+</sup>

2.2.5 Alpha decay

4 and 8 MeV.

isobaric.

Figure 9.

30

Electron capture decay: it is an inverted β�decay, whereas an orbital electron is

In other words, we can say that the electron capture is a process, in which a parent nucleus captures one of its orbital electrons and releases a neutrino. This neutrino is emitted from the nucleus and carries away some of the transitions energy. The remaining energy appears in the form of characteristic X-rays and Auger electrons, which are emitted by daughter product, whereas the resulting

In case of radioactive decay by positron emission, a proton in the nucleus is

proton ejected from the nucleus. A positron is an antiparticle of an ordinary electron:

After ejection from the nucleus, it loses its kinetic energy in collision with atoms

Radionuclide that decayed by a particle emission or by nuclear fission has rela-

Both of these decay modes occur primarily among very heavy elements that are

The particles, which are released with kinetic energy, are usually found between

Decay by alpha particle emission results in transmission of elements, but it is not

Activity: It is the total number of nuclei that are decaying per second. It is the probability that any individual atom will undergo decay during the same period:

of the surrounding matter and comes to rest; this usually happens within a few

transformed into a neutron and a positively charged electron (positron β<sup>+</sup>

tively little importance for direct usage as tracers in nuclear medicine.

p<sup>þ</sup> þ e� ! n þ υ þ energy (3)

p<sup>þ</sup> ! n þ β<sup>þ</sup> þ υ þ energy (4)

A ¼ λN (5)

) then a

captured by the nucleus and combines with a proton to form a neutron:

orbital electron vacancy is filled (as shown in Figure 9).

Use of Gamma Radiation Techniques in Peaceful Applications

millimeters from the site of its origin in body tissue [6].

of a little interest as physiological tracers [7].

The nucleus captures one of its orbital electrons and X-ray.


1 mCi = 3.7 � <sup>10</sup><sup>7</sup> dps = 37 MBq.

<sup>1</sup> <sup>μ</sup>Ci = 3.7 � <sup>10</sup> <sup>4</sup> dps = 37 kBq.

Half-life: It is the amount of time taken for the given quantity so as to be decreased to half of its initial value. As shown in Figure 10, the term is most commonly used in relation to atoms undergoing radioactive decay, but it can be used to describe other types of decay, whether exponential or not. One of the most well-known applications of half-life is:

$$\mathbf{T}\_{\forall i} = \mathbf{L}\mathbf{n}\mathbf{2}/\lambda\tag{7}$$

where T½ is the half-life of radionuclides; ln2 = 0.693 is the base of natural logarithms; λ is decay constant of radionuclides.

Figure 10. The time required for it to decay the number of radioactive nuclei to 50% of the (NO).
