Radiocarbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s at the University of Chicago by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960, it is based on the fact that radiocarbon is being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, incorporated into plants by photosynthesis; when the animal or plant dies, it stops exchanging carbon with its environment, thereafter the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calculate when the animal or plant died; the older a sample is, the less 14C there is to be detected, because the half-life of 14C is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods permit accurate analysis of older samples.
Research has been ongoing since the 1960s to determine what the proportion of 14C 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 14C in different types of organisms, the varying levels of 14C throughout the biosphere. Additional complications come from the burning of fossil fuels such as coal and oil, 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 longer than the time it takes for its 14C to decay below detectable levels, fossil fuels contain no 14C, as a result there was a noticeable drop in the proportion of 14C in the atmosphere beginning in the late 19th century. Conversely, nuclear testing increased the amount of 14C in the atmosphere, which attained a maximum in about 1965 of twice what it had been before the testing began.
Measurement of radiocarbon was done by beta-counting devices, which counted the amount of beta radiation emitted by decaying 14C atoms in a sample. More accelerator mass spectrometry has become the method of choice; the development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances. Histories of archaeology refer to its impact as the "radiocarbon revolution". Radiocarbon dating has allowed key transitions in prehistory to be dated, such as the end of the last ice age, the beginning of the Neolithic and Bronze Age in different regions. In 1939, Martin Kamen and Samuel Ruben of the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research, they synthesized 14C using the laboratory's cyclotron accelerator and soon discovered that the atom's half-life was far longer than had been thought.
This was followed by a prediction by Serge A. Korff employed at the Franklin Institute in Philadelphia, that the interaction of thermal neutrons with 14N in the upper atmosphere would create 14C, it had been thought that 14C would be more to be created by deuterons interacting with 13C. At some time during World War II, Willard Libby, at Berkeley, learned of Korff's research and conceived the idea that it might be possible to use radiocarbon for dating. In 1945, Libby moved to the University of Chicago, he published a paper in 1946 in which he proposed that the carbon in living matter might include 14C as well as non-radioactive carbon. Libby and several collaborators proceeded to experiment with methane collected from sewage works in Baltimore, after isotopically enriching their samples they were able to demonstrate that they contained 14C. By contrast, methane created from petroleum showed no radiocarbon activity because of its age; the results were summarized in a paper in Science in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin.
Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years; these results were published in Science in 1949. Within 11 years of their announcement, more than 20 radiocarbon dating laboratories had been set up worldwide. In 1960, Libby was awarded the Nobel Prize in Chemistry for this work. In nature, carbon exists as two stable, nonradioactive isotopes: carbon-12, carbon-13, a radioactive isotope, carbon-14 known as "radiocarbon
Bursa corrugata is a species of sea snail, a marine gastropod mollusk in the family Bursidae, the frog shells. The subspecies Bursa corrugata lineata Nowell-Usticke, 1959 has become a synonym of Bursa granularis This marine species occurs in the Atlantic Ocean off West Africa, the Canary Islands, Cape Verdes and Brazil; the maximum recorded shell length is 75 mm. Minimum recorded depth is 2 m. Maximum recorded depth is 137 m. Bernard, P. A.. Coquillages du Gabon. Pierre A. Bernard: Libreville, Gabon. 140, 75 plates Rosenberg, G. F. Moretzsohn, E. F. García. 2009. Gastropoda of the Gulf of Mexico, Pp. 579–699 in Felder, D. L. and D. K. Camp, Gulf of Mexico–Origins and Biota. Biodiversity. Texas A&M Press, College Station, Texas. Gofas, S.. P.. Conchas e Moluscos de Angola = Coquillages et Mollusques d'Angola.. Universidade Agostinho / Elf Aquitaine Angola: Angola. 140 pp. Rolán E. 2005. Malacological Fauna From The Cape Verde Archipelago. Part 1, Polyplacophora and Gastropoda. "Bursa corrugata corrugata". Gastropods.com.
Retrieved 15 January 2019
The Queen Mother Champion Chase is a Grade 1 National Hunt steeplechase in Great Britain, open to horses aged five years or older. As part of a sponsorship agreement with the online betting company Betway, the race is now known as the Betway Queen Mother Champion Chase, it is run on the Old Course at Cheltenham over a distance of about 2 miles, during its running there are thirteen fences to be jumped. The race is scheduled to take place each year during the Cheltenham Festival in March, it is the leading minimum-distance chase in the National Hunt calendar, it is the feature race on the second day of the Festival. The event was established in 1959, it was called the National Hunt Two-Mile Champion Chase, it was given its present title in 1980 – the year of the Queen Mother's 80th birthday – in recognition of her support to jump racing. The Queen Mother was a successful owner of National Hunt horses chasers, among these was Game Spirit – the runner-up in this race in 1976; the Queen Mother Champion Chase was not sponsored before 2007, between 2008 and 2010 it was backed by Seasons Holidays.
The sponsor from 2011 until 2013 was online gambling firm Sportingbet. BetVictor held naming rights for the 2014 season before the current sponsor, sports betting company Betway, took over. Horse racing in Great Britain List of British National Hunt races Recurring sporting events established in 1959 – this race is included under its original title, National Hunt Two-Mile Champion Chase. Racing Post: 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997 1998, 1999, 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 2019bbc.co.uk – "Royalty absent and present". Cheltenham.co.uk – Media information pack. Pedigreequery.com – Queen Mother Champion Chase – Cheltenham. Sportingchronicle.com – Queen Mother Champion Two Mile Steeple Chase Past Winners. The Breedon Book of Horse Racing Records. Breedon Books. 1993. P. 231. ISBN 1-873626-15-0. Race Recordings