| 释义 |
ˈhalf-life
Also half life.
1. A life of half the full length; an unsatisfactory way of life. Also attrib., denoting a size of painting half life-size.
1864Atlantic Monthly XIII. 157 (title) A half-life and half a life. 1867D. G. Rossetti Let. 25 July (1965) II. 624 He would prefer a half-life scale. 1963Times Lit. Suppl. 31 May 393/4 The half-life which men were leading.
2. The time in which the quantity of a substance (or the number of similar objects) in a sample decreases by half, spec. (a) in Physics of a radioactive substance, (b) in Med. and Biol. of a substance accumulated in (an organ of) the body. Also half-life period.
1907Jrnl. Chem. Soc. XCI. ii. 1281 Rutherford and others have shown that whilst radium A, B, and C have a life-period of only a few hours, radium D has a half-life⁓period of forty years. 1954H. Semat Introd. Atomic & Nucl. Physics (ed. 3) xi. 363 The value of the half-life of the neutron was calculated from a determination of the density of the neutron beam and the number of neutrons decaying per unit time per unit volume. 1955Metabolism IV. 419 Two patients convalescing from recently active rheumatic fever..had hydrocortisone half-life values which were similar to those seen in the control subjects. 1955Sci. Amer. Aug. 37/1 So the hazard of a given radio⁓isotope depends basically on a composite quantity called the ‘biological half-life’—a measure of the duration of its activity within the body. 1964Times 31 Mar. 11/4 The extension of the half-life concept, familiar in the field of radioactivity, to the break-down of pesticide residues is very welcome. 1971Murphy & Mustard in J.-M. Paulus Platelet Kinetics ii. 26 The slope of the regression curve divided into -0·30103..is the estimated platelet half-life. 1971Nature 26 Nov. 233/3 The holes made in leaves by herbivorous insects, the half-life of leaves (four to nine months in most species) and a mass of interesting information about the roots and buttresses of tropical trees. 1972Ibid. 22 Dec. 465/1 Because 244Pu has an 82 m.y. half life, its presence today, 56 half lives after the formation of the Earth, is a most impressive accomplishment. |