20.08.2015   Fast Reactor Safety. (Nuclear science. and technology)

Damage to the Tissue

Damage to body tissue can be conveniently divided into that produced by direct and indirect action: the first being the case in which a particle of biological interest is struck by either the electron or nucleus of the ionized tissue hydrogen atom, and the other is the case in which the fragments of the ionized tissue may drift over to damage the more critical biological

+ The International Commission on Radiological Protection now prefers the nomen­clature Quality Factor QF for RBE when applied to protection rather than radiobiology.

TABLE 5.1

Average LET Values for Particles0

Particle

Mass

(amu)

Charge

Energy

(keV)

LET11

(keV/yii)

Tissue

penetration

(m)

Electron

0.00055

-1

1

12.3

0.01

10

2.3

1

100

0.42

180

1000

0.25

5000

Proton

1

+ 1

100

90

3

2000

16

80

5000

8

350

10,000

4

1400

200,000

0.7

300,000

Deuteron

2

+ 1

10,000

6

700

200,000

1

190,000

Alpha

4

+2

100

260

1

5000

95

35

200,000

5

20,000

Photons are

approximately equivalent to electrons of half the energy

Neutrons are approximately equivalent to protons of half the energy

0 See Frigerio (2).

6 Energy lost per unit track length.

molecules. Molecules which are of special interest are the DNA of the cell nucleus because damage to this molecule could have genetic consequences.

Figure 5.1 shows diagrammatically the linear energy transfer process in tissue and differentiates between the direct and indirect damage modes. Approximately, the LET values may be shown to correspond to the RBE values as shown in Table 5.2 (2).

Biological effects of body tissue damage can be separated into genetic effects, which may be transmitted to progeny, and somatic effects, which are bodily effects to the recipient itself.