Gamma radiation, absorption coefficients

We have limited our investigations to the action of gamma-rays and fast neutrons on aromatic, alicyclic, aliphatic, and ionic compounds. The absorption coefficients for these types of radiation have an order of magnitude of lO /cm which is particularly adequate. Shallow penetrating radiations would only alter the superficial layers and would obviously not be able to affect the intensity of the quadrupole line substantially. This is for instance the case for ultraviolet light which has been shown to be unable to produce any effect on the resonance line of iodoform (CHI3 3Sg)... 

Absorption Coefficient—Fractional absorption of the energy of an unscattered beam of x- or gamma-radiation per unit thickness (linear absorption coefficient), per unit mass (mass absorption coefficient), or per atom (atomic absorption coefficient) of absorber, due to transfer of energy to the absorber. The total absorption coefficient is the sum of individual energy absorption processes (see Compton Effect, Photoelectric Effect, and Pair Production). 

Absorption Coefficient, Linear—A factor expressing the fraction of a beam of x- or gamma radiation absorbed in a unit thickness of material. In the expression I=I0e+l x, I0 is the initial intensity, I the intensity of the beam after passage through a thickness of the material x, and p is the linear absorption coefficient. 

Irradiation Conditions and Dosimetry. All irradiations were carried out in the gamma-radiation field of either a nominally 10 or 18 kilocurie cobalt-60 source. Dosimetry of the gamma-radiation field was carried out using the Fricke method (ASTM test D 1671-59). Since the effective mass absorption coefficient for y-rays of this energy is nearly equal for the polymer and for the dosimetric solution, no correction was made for the change in media. 

Beta radiation has a finite range, whereas in theory x- and gamma rays are exponentially attenuated. It should be noted that x-radiation of each energy exhibits sharp changes in absorption coefficients for certain absorbers. 

Radiation exposure is defined as the energy deposited by radiation per unit mass. For a gamma ray emitted by a point source, the radiation exposure rate i is related to the gamma-ray decay fraction /, the gamma-ray energy E (in MeV), the activity of the radionuclide a(in Bq), the linear energy absorption coefficient /u-a, the density of air p, and the distance x ... 

In the latter case, D6.08 is the sum of the optical densities of the vinylidene and vinyl absorption bands in this region. An optical density ratio for these bands of approximately this value was found (1.75 to 3.3) for the products of thermal degradation of polypropylene. It is seen that only in the case of amorphous polypropylene irradiated with gamma-radiation from Co is the ratio (D11.23 + D10.99)/D6.08 close to the value calculated from the extinction coefficients of these bands. In the spectra of irradiated isotactic polypropylene, the intensity of the 6.08 pm band is greater than would be expected if only vibration of terminal double bonds contributes to absorption in this region. This increase in absorption in the 6.08-pm region can be related to absorption by the internal double bond in the allyl radical, the vibrational frequency of which is lowered by conjugation of the Jt-electrons of the double bond... 

The density of liquids can also be measured radiometrically, by the absorption of gamma-rays in the medium. The intensity of the exiting radiation depends on the density of the medium and is given according to the Beer-Lambert law [Eq. (28), where 7, Iq are the intensities behind and in front of the object, e the absorption coefficient, p the density of the medium and I the path length]. 

The photoelectric and Compton effects are applied in geoscience. Both effects result in an attenuation of the gamma radiation, which is expressed in Eq. (5.11). The absorption coefficient refers to the effect. 

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