Radiokarbon bilan tanishish
Radiokarbonni aniqlash ( uglerodni aniqlash yoki uglerod-14 deb ham ataladi) - bu uglerodning radioaktiv izotopi bo'lgan radiokarbonning xususiyatlaridan foydalangan holda organik moddalar bo'lgan ob'ektning yoshini aniqlash usuli. Usul 1940-yillarning oxirida Chikago universitetida Willard Libby tomonidan ishlab chiqilgan. Bu radiokarbon ( 14</br> 14 ) Yer atmosferasida kosmik nurlarning atmosfera azoti bilan oʻzaro taʼsirida doimo hosil boʻladi. Natijada 14</br> 14 atmosfera kislorodi bilan birlashib, fotosintez orqali o'simliklarga kiritilgan radioaktiv karbonat angidrid hosil qiladi; hayvonlar keyin 14 ega bo'ladi14</br> 14 o'simliklarni iste'mol qilish orqali. Hayvon yoki o'simlik o'lganida, u atrof-muhit bilan uglerod almashinuvini to'xtatadi va keyin 14</br> Uning tarkibidagi 14 14 dan kamayishni boshlaydi14</br> 14 radioaktiv parchalanishga uchraydi. 14 miqdorini o'lchash14</br> Yog'och bo'lagi yoki suyak bo'lagi kabi o'lik o'simlik yoki hayvondan olingan namunadagi 14 hayvon yoki o'simlik qachon vafot etganini hisoblash uchun ishlatilishi mumkin bo'lgan ma'lumotlarni beradi. Namuna qanchalik katta bo'lsa, 14 dan kamroq14</br> 14 bor aniqlanishi kerak, va chunki yarimparchalanish davri 14</br> 14 (ma'lum bir namunaning yarmi parchalanib ketadigan vaqt) taxminan 5730 yilni tashkil etadi, bu jarayon orqali ishonchli o'lchanadigan eng qadimgi sanalar taxminan 50 000 yil oldinga to'g'ri keladi, ammo maxsus tayyorlash usullari vaqti-vaqti bilan aniq tahlil qiladi. eski namunalar mumkin. Libbi 1960 yilda qilgan ishlari uchun kimyo bo'yicha Nobel mukofotini oldi. Research has been ongoing since the 1960s to determine what the proportion of Andoza:Chem in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of Andoza:Chem in different types of organisms (fractionation), and the varying levels of Andoza:Chem throughout the biosphere (reservoir effects). Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the 1950s and 1960s. Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its Andoza:Chem to decay below detectable levels, fossil fuels contain almost no Andoza:Chem. As a result, beginning in the late 19th century, there was a noticeable drop in the proportion of Andoza:Chem as the carbon dioxide generated from burning fossil fuels began to accumulate in the atmosphere. Conversely, nuclear testing increased the amount of Andoza:Chem in the atmosphere, which reached a maximum in about 1965 of almost double the amount present in the atmosphere prior to nuclear testing. Radiouglerodni o'lchash dastlab beta-hisoblash qurilmalari tomonidan amalga oshirildi, ular parchalanish natijasida chiqarilgan beta-nurlanish miqdorini hisoblardi 14</br> Namunadagi 14 atomlari. Yaqinda tezlatgich massa spektrometriyasi tanlov usuliga aylandi; 14 ning hammasini sanaydi14</br> Namunadagi 14 atomlari va o'lchovlar paytida parchalanadigan bir nechta atomlar emas; shuning uchun u juda kichikroq namunalar bilan (alohida o'simlik urug'lari kabi) ishlatilishi mumkin va natijani ancha tez beradi. Radiokarbonli datingning rivojlanishi arxeologiyaga katta ta'sir ko'rsatdi. Arxeologik joylar ichida oldingi usullarga qaraganda aniqroq tanishish imkonini berishdan tashqari, u uzoq masofalardagi voqealar sanalarini solishtirish imkonini beradi. Arxeologiya tarixi ko'pincha uning ta'sirini "radiokarbon inqilobi" deb ataydi. Radiokarbon bilan tanishish tarixdan oldingi davrdagi asosiy o'tishlarni, masalan, so'nggi muzlik davrining oxiri va turli mintaqalarda neolit va bronza davrining boshlanishini aniqlashga imkon berdi.