Radioactive Isotopes

Laser media are not yet pumped by the radiation of radioactive isotopes. Radioac­tive isotopes were previously used for an auxiliary purpose—pre-ionization of the active media of CO2 lasers [62], as well as lasers at transitions of Xe [63] and Ne [64] atoms.

In the case of the use of radioactive isotopes directly for pumping of laser media, the specific power deposition will be higher for isotopes with short half-lives, which naturally reduces the lifespan of such a laser. As data from study [65] show, the most suitable isotopes for pumping gas NPLs are the a active isotopes Po, Cm, and the spontaneously fissionable isotope 52Cf. Some characteristics of these iso­topes are shown in Table 1.3.

Calculations of specific power deposition were made in [65] for cylindrical laser cells with internal diameters of 1-8 cm, on the internal surface of which layers of isotopes were deposited with a thickness equal to one-half the particle path length in the layer material. Calculations showed that depending on the cell diameter and the

210 242

argon pressure (0.25 and 0.5 atm), for the isotopes Po and Cm, the specific power depositions vary in a range of q = 0.06-0.1 W/cm3, and for 52Cf, q < 0.02 W/ cm3. With such small specific power depositions, it is possible to achieve lasing using only the most low-threshold active media of NPLs, for example, Ar(Kr)-Xe mixtures, radiating at the infrared transitions of the Xe atom (see Chap. 3, Sect. 3.1).

Study [66] examined the possibility of radioisotope pumping of a neon laser with a He-Ne-H2 mixture (X = 585.3 nm). When a 210Po layer 65 mg/cm2 thick used, and is deposited to the internal surface of a cylinder cell with a diameter of 15 mm, it is possible to obtain q < 0.6 W/cm3. However, the conclusion of the authors of [66] regarding the possibility of achieving lasing under such conditions appears

Table 1.3 Characteristics of radioactive isotopes

Isotope

(half-life)

Particle energy, MeV

Specific activity, Ci/g

Specific energy release, W/g

210Po (138 days)

5.3 (a particle)

4,490

140

242Cm (163 days)

6.1 (a particle)

3,300

120

252Cf (2.65 years, a decay);

(85 years, spontaneous fission)

6.1 (a particle)

540

20

180 (two fragments)

17

11

extremely optimistic, since NPLs with He-Ne-H2 mixture have a rather high lasing threshold (see Chap. 3, Sect. 3.2).

Apart from the thin radioisotope layers, for excitation of gas media it is possible to use gaseous isotopes, for example, p radiators 42Ar, 85Kr, etc. In this case, one should consider gas media having Ar or K as their basic components (for example, Ar-Xe or Kr-Xe). Calculations [54, 63] show that the isotopes 42Ar and 85Kr can for now be used only for pre-ionization of active media of gas-discharge lasers, since in this case the specific power deposition does not exceed 0.001 W/cm3.

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