Average Energy of Allowed Beta-particle Spectra

Abstract

THE average P-particle energy per disintegration is a physical parameter of importance in the dosimetry of the radioisotopes, since the P-particle dose to biological materia'ls from a distribut'ed radioisotope source is proportional to this quantity. This paper presents the results of a systematic calculation of t'he ratio of average P-part'icle energy (E,) to the maximum P-particle energy (Eo), for the entire ranges of values of atomic number (2) and maximum P-part'icle energy which are likely to be of .biological importance. Values of E,;E', have been calculated for negatron spectra for the range Eo"O t o 4 xev and Z=O to 100, and for positron spectra for the range E0=0.2 t,o 4 BIev and Z=0 to 80.

Smith’s “Internal Dose Calculation for 99mTc”: An Excellent Paper with Approximate Methods (perspective on “Internal Dose Calculation for 99mTc” J Nucl Med. 1965;6:231–251)

“…The specific gamma-ray constant, G, for 99m Tc is 0.72 R-cm 2 /mc-hr; however, 29 per cent of this value is due to K a and k b x-rays which make up only 1.2 per cent of the total photon energy emitted by 99m Tc. Standard methods of calculating the gamma component of the absorbed dose for 99m Tc using the geometrical factor and G yield results which underestimate the absorbed dose by 16…”

Analysis of the atmospheric 14C record spanning the past 50,000 years derived from high-precision 230Th/234U/238U, 231Pa/235U and 14C dates on fossil corals

“…Hollow circles represent the corrected experimental data (Moljk and Curran, 1954). One energy unit in ''M 0 C 2 '' is approximately equal to 510.9 keV (Loevinger, 1957).…”

“…The average beta energy (Ē b ) can be computed from an actual, experimental spectrum or from Fermi-Kurie theory assuming the ''allowed'' distribution (Loevinger, 1957;Mantel, 1972). Most studies estimatedĒ b of 14 C in the range of 49-50 keV (Jenks and Sweeton, 1952;Caswell et al, 1954;Loevinger, 1957;Murthy, 1971;Mantel, 1972;Chu et al, 1999;Ekstro¨m and Firestone, 1999) (Table 2). According to Loevinger (1957), a calculatedĒ b would not change by more than 5% if the 14 C beta spectrum did not deviate from an ''allowed'' distribution appreciably.…”

“…Most studies estimatedĒ b of 14 C in the range of 49-50 keV (Jenks and Sweeton, 1952;Caswell et al, 1954;Loevinger, 1957;Murthy, 1971;Mantel, 1972;Chu et al, 1999;Ekstro¨m and Firestone, 1999) (Table 2). According to Loevinger (1957), a calculatedĒ b would not change by more than 5% if the 14 C beta spectrum did not deviate from an ''allowed'' distribution appreciably. At the time Jenks and Sweeton (1952) determined the 14 C half-life to be 6030 years, they assumed an ''allowed'' shape of the 14 C beta spectrum resulting in an average 14 Caswell et al (1954) 49.7 Allowed Loevinger (1957) 49.2 (unlikely to change by more than75%) Allowed Murthy (1971) 49 Allowed Mantel (1972) 49.3 Composite spectra; allowed Chu et al (1999) in Ekstro¨m and Firestone (1999) 50.1 Not mentioned…”