Ce137 nelle TG

[Marc75]

Buongiorno a tutti
Qualcuno conosce l’attività originaria in uCi del Cs137 nelle valvole TG 57, TG58 e TG71?
Non riesco a trovare questo dato

I vari modelli usciti contenevano quantità molto variabili di Cs137 a seconda del modello di valvola. Non ho trovato niente su questi tre modelli

Grazie

Marco

[max56fe]

ciao forum, visto che a Marco non ha risposto nessuno ci provo io............. Glow Lamps or Spark Gap Tubes. According to NCRP No. 95, these devices have been used as starters for compact fluorescent lamps, and in electric blanket thermostats and other specialty products. The report (1987) claimed that the annual production of these devices was in the millions. The sources generally consisted of 1 to 9 uCi of Co-60, Ni-63, Kr-85, Pm-147, or Th-232. Today, most fluorescent lamp starters use about 5 pCi of Th-232 coated on the inside of a glass tube. The starter is actually a switch that applies the high voltage to the fluorescent lamp after that latter has been given time to warm up. This preheating of the lamp improves its ability to conduct.

Electron tubeElectron tube
NUREG-1717 provided the following NRC data regarding the annual distribution of electron tubes containing byproduct material during the period of 1970 to 1986.

Radionuclide Tubes per Year uCi per Tube
H-3 8.3 x 106 39
Co-60 3.2 x 104 0.29
Ni-63 7.4 x 104 1.0
Kr-85 7.4 x 107 0.28
Cs-137 1.7 x 104 1.0
Pm-147 2.1 x 106 5.6
Dose Estimates
Routine Use

NUREG-1717 estimated the doses to an occupant in a home from five electron tubes that contained either, H-3, Co-60, Kr-85, Cs-137, or Pm-147. It was assumed that for a given nuclide, each of the five tubes contained the activity presented in the previous table. For the calculations, it was assumed that the occupant spent 6,000 hours per year in the home. It was also assumed that the average distance to one tube was 1 meter, the average distance to two tubes was 3 meters and the average distance to the remaining two tubes was 6 meters. The dose was due to the emission of gamma rays and bremsstrahlung. In the case of tritium, the dose was due to airborne tritium—a leakage rate from the tubes of 2.5 ppm per hour was assumed.

Radionuclide uCi per Tube Effective Dose Equivalent
H-3 39 <0.001 mrem/year
Co-60 0.29 2 mrem/year
Kr-85 0.28 0.004 mrem/year
Cs-137 1.0 2 mrem/year
Pm-147 5.6 <0.001 mrem/year
NUREG-1717 also calculated the dose to an individual exposed to a single tube in a work environment. In this scenario, the individual was 1 meter away from the tube for 2,000 hours per year. In the case of a tritium containing tube, it was assumed that the equilibrium concentration in the air due to leakage was 4.9 pCi/m3. The resulting effective dose equivalents when the tube contained the maximum activity allowed by the exemptions were as follows:

Radionuclide uCi per Tube Effective Dose Equivalent
H-3 150 5 mrem/year
Co-60 0.29 2 mrem/year
Kr-85 0.28 0.1 mrem/year
Cs-137 1.0 2 mrem/year
Pm-147 5.6 0.001 mrem/year
Accidents and Misuse

NUREG-1717 estimated the doses due to a variety of non-routine situations (e.g., carrying a tube in a pocket, residential fires and warehouse fires), but the largest dose by far was due to the crushing of a microwave receiver protector tube containing the maximum activity of tritium permitted by the exemption (150 mCi). The potential dose to an individual crushing such a tube was estimated at 1000 mrem (1 rem).

Pertinent Regulations
30.15 Certain items containing byproduct material.

(a) Except for persons who apply byproduct material to, or persons who incorporate

byproduct material into, the following products, or persons who initially transfer for sale or distribution the following products containing byproduct material, any person is exempt from the requirements for a license set forth in section 81 of the Act and from the regulations in parts 20 and 30 through 36 and 39 of this chapter to the extent that such person receives, possesses, uses, transfers, owns, or acquires the following products:

. . . . .

(8) Electron tubes: Provided, Tthat each tube does not contain more than one of the following specified quantities of byproduct material:

(i) 150 millicuries of tritium per microwave receiver protector tube or 10 millicuries of tritium per any other electron tube;

(ii) 1 microcurie of cobalt-60;

(iii) 5 microcuries of nickel-63;

(iv) 30 microcuries of krypton-85;

(v) 5 microcuries of cesium-137;

(vi) 30 microcuries of promethium-147;

And provided further, that the levels of radiation from each electron tube containing byproduct material do not exceed 1 millirad per hour at 1 centimeter from any surface when measured through 7 milligrams per square centimeter of absorber.

For purposes of this paragraph ‘‘electron tubes’’ include spark gap tubes, power tubes, gas tubes including glow lamps, receiving tubes, microwave tubes, indicator tubes, pickup tubes, radiation detection tubes, and any other completely sealed tube that is designed to conduct or control electrical currents.

References

Data sheets for the Western Electric 346B and 346C electron tubes. AT&T 1962.
Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources. NCRP Report No. 95; 1987.
Nuclear Regulatory Commission. Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials. NUREG 1717. June 2001.
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