【正文】 onuclides have been discovered in nature. The lightest have been mentioned. The heavier ones, not belonging to the natural radioactive decay series of uranium and thorium, are listed in Table . 50V is the nuclide of lowest elemental specific activity (~ Bq/g) while the highest are 87Rb and 187Re (each ~900 Bq/g). As our ability to make reliable measurements of low activities increases, the number of elements between potassium K and lead Pb with radioactive isotopes in nature can be expected to increase.Primordial radionuclidesv 由于這些核素的壽命特別長(zhǎng)，他們肯定是在太陽系和地球形成時(shí)（甚至更早）形成的。s injected large amounts of tritium into the geosphere。Th系U系錒系Primordial radionuclidesv thorium decay series Th系 —— consists of a group of radionuclides related through decay in which all the mass numbers are evenly divisible by four (the 4n series). It has its natural origin in 232Th which occurs with 100% isotopic abundance. Natural thorium has a specific activity S of MBq/kg, as itshalflife through α decay is 1010 y. The terminal nuclide in this decay series is the stable species 208Pb (also known as ThD). The transformation from the original parent to the final product requires 6 α and 4 βdecays. The longestlived intermediate is y 228Ra.Primordial radionuclidesv uranium decay series U系 —— consist of a group of nuclides that, when their mass number is divided by 4, have a remainder of 2 (the 4n + 2 series). The parent of this series is 238U with a natural abundance of %。該系名稱源于比 Bi重的 A＝ 4n+1的最長(zhǎng)壽命的核素 237Np，它是該系的母核，半衰期為 10 6y。它是迄今為止發(fā)現(xiàn)的最重要的天然放射性元素。高級(jí)別的礦石是鈾礦與其他礦物的混合物，所以在在壓碎的礦石中鈾的平均含量就低很多了：例如美國科羅拉多州高原的碎礦石中鈾含量 ≤ ％。v 三價(jià)的鈾離子能把水還原成氫，因此不可能制得穩(wěn)定的三價(jià)鈾水溶液。 2H2O的形式存在，它是一種難溶于水的酸性氧化物。 鈾能與所用的鹵素元素作用生成從＋ 3～ +6價(jià)的各種鈾鹵化物。 UF6還能與堿金屬氟化物反應(yīng)生成復(fù)鹽（如 ）。鈾的濃度越高， 其水解反應(yīng)析出的氫氧化物沉淀時(shí)的 pH值就愈低 。重鈾酸鹽 是一種重要的難溶性的鈾鹽，可以通過鈾酰鹽與氨水或堿反應(yīng)制備： 主要的重鈾酸鹽有 (NH4)2U2O Na2U2O7和 K2U2O7等，其中 (NH4)2U2O7俗稱“ 黃餅 ” yellow cake。 ）條件下能與氫、鹵素、硫、氮、碳和磷作用。由于 ThO2組成固定，且不易吸水，因此， 可以作為重量法測(cè)定 Th的基準(zhǔn)物質(zhì) 。釷的化合物 Th的氧化物：通常情況下， Th只能形成穩(wěn)定的四價(jià)化合物。 。 無水硝酸鈾酰的制備很困難，當(dāng)溫度升高到 180176。鈾的水解行為 各種鈾離子的水解能力取決于離子的電荷 Z與離子裸半徑 r0的比值，即離子勢(shì) Z/r0。 UF6在干燥的空氣中比較穩(wěn)定，一般不與氧或氮反應(yīng)。氫的分壓可用下式來計(jì)算：v式中 T為絕對(duì)溫度（ K）。 U3O8不溶于水和各種稀酸，但可與濃 HNO3作用生成 UO2(NO3)2溶液，也能與濃 H2SO4或 HCl作用，生成四價(jià)鈾鹽和鈾酰鹽的混合物：?其它鈾氧化合物 UO3為兩性鈾氧化合物，它與酸作用生成鈾酰鹽，與堿作用生成難溶性的鈾酸鹽如 Na2UO4或重鈾酸鹽如（ NH4)2U2O7。表 1 天然鈾同位素和 233U的一些核特性同位素 半衰期， a 衰變方式 粒子主要能量， MeV（％） 比活度，238U ?109 ? (77)， (23) 235U ?108 ? (57)， (18) 234U ?105 ? ()，() ?105233U ?105 ? ()，() ?105金屬鈾的性質(zhì)鈾的主要用途： 早期僅作為玻璃、陶瓷和琺瑯的著色劑。鈾在海水中的含量約為 34?g/L。如果這是原始 244Pu的殘存，那么只能剩余原始量的 1015％。Primordial radionuclidesv actinium decay series Ac系 —— consists of a group of nuclides whose mass number divided by 4 leaves a remainder of 3 (the 4n + 3 series). This series begins with the uranium isotope 235U, which has a halflife of 108 y and a specific activity of 8 104 MBq/kg. The stable end product of the series is 207Pb, which is formed after 7 α and 4 βdecays. The actinium series includes the most important isotopes of the elements protactinium Pa, actinium Ac, francium Fr, and astatine At. Inasmuch as 235U is a ponent of natural uranium, these elements can be isolated in the processing of uranium minerals. The longestlived protactinium isotope, 231Pa (t1/2 104 y) has been isolated on the 100 g scale, and is the main isotope for the study of protactinium chemistry. 227Ac (t1/ y) is the longestlived actinium isotope.釷系：以 232Th為起點(diǎn)，經(jīng)過了 10次轉(zhuǎn)化（ 6次 ?衰變， 4次 ?衰變 ），終點(diǎn)為 208Pd；為 4n系。v 仔細(xì)觀察這些天然長(zhǎng)壽命核素的衰變，其中某些顯示出 短衰變系 short decay series，例如： 152Gd→ 148Sm→ 144Nd→ 140Ce和 190Pt→ 186Os→ 182W。 ., between fast neutrons and nitrogen atomsv The yield for this reaction is about 2 500 atoms tritium per second per square meter