Beta-active isotopes

But uranium-238 absorbed neutrons converting into uranium-239, a new isotope of uranium. This beta-active isotope gave rise to an isotope of the first transuranium element with an atomic number of 93. This was just what Fermi and his group thought. But the future neptunium was hard to distinguish among the multitude of fragments. This is why the experiments in mid-thirties yielded no results. 

Early measurements of " Th were on seawater samples and Th was co-precipitated from 20-30 L of seawater with iron hydroxide (Bhat et al. 1969). This procedure may not recover all of the " Th in the sample, and an alpha emitting Th isotope (e g., °Th or Th) is added as a yield monitor. Following chemical purification of the Th fraction by ion exchange chromatography, the Th is electrodeposited onto platinum or stainless steel planchets. The planchets are then counted in a low background gas-flow beta detector to measure the beta activity and subsequently with a silicon surface barrier detector to determine the alpha activity of the yield monitor. The " Th activity is thus determined as ... 

The actual discovery was made by Mile. Marguerite Perey at the Curie Institute in Paris. In 1939 she purified an actinium preparation by removing all the known decay products of this element. In her preparation she observed a rapid rise in beta activity which could not be due to any known substance. She was able to show that, while most of the actinium formed radioactinium, an isotope of thorium, by beta emission, 1.2 0.1 per cent of the disintegration of actinium occurred by alpha emission and gave rise to a new element, which she provisionally called actinium K, symbol AcK (35, 36). This decayed rapidly by beta emission to produce AcX, an isotope of radium, which was also formed by alpha emission from radioactinium. Thus AcK, with its short half-life, had been missed previously because its disintegration gave the same product as that from the more plentiful radioactinium. 

As shown in Table 17.9, the alpha activity in the leachate was 25 2 pCi/ml, and the beta activity was 98 lOpCi/ml. These activities are small when compared with the activities of their counterparts in the waste, which were in p-Ci/g. The very low activity in the leachate was attributed to the efficient stabilization of Ra as insoluble radium phosphate in the waste form. In particular, because Ra is water soluble, the leachate would provide a pathway for it, but the levels in the leachate are only in pCi/ml and, hence, much lower than the levels in the waste. This finding implies that radium and most other isotopes are stabilized in the waste forms. Thus, the Ceramicrete process is a good method to arrest leaching of even the most soluble Ra. 

The activities of some isotopes, in particular °Sr- °Y, can also be detected by liquid-crystal spectrometry with the use of the Cherenkov phenomenon [10, 11]. The Cherenkov effect is used to determine beta isotopes emitting particles whose iiniax IS above 500 keV [12]. The main advantage of beta activity determination by the Cherenkov effect is the use of analytical preparation used for another chemical analysis (e.g. calculation of recovery). Moreover, the addition of low energy beta or alpha radiation does not disturb the measurement, thereby lowering the cost of analysis. The weakness of this method is the decreased recovery registration and the decline in information about the realistic appearance of the beta spectrum [13]. The determination of beta isotopes in environmental samples is very difficult and requires their chemical isolation. The type of sample and the time of chemical analysis determine the choice of analytical method. Also, the time between contamination and sample collection is important procedures used for samples recently contaminated are different to those used for old samples in which the decay of short-lived radionuclides has aheady taken place [1, 5]. 

WHEN uranium with its natural mixture of isotopes is exposed to neutrons in a chain-reacting pile there is a competition by several processes for the absorption of the neutrons. One of the chief competitors to the absorption by to cause fission is the absorption by IP to produce the compound nucleus IP . This system may re-emit the neutron or emit a gamma ray. In the second case, the remaining beta active nucleus decays with a 24-min half-life. ... 

Just a year later three radiochemists from Vienna— S. Meyer, G. Hess, and F. Paneth—studied actinium-227, an isotope belonging to the family of uranium-235. They repeated their experiments and at last their sensitive instruments detected alpha particles of unknown origin. Alpha particles emitted by various isotopes have specific mean paths in air (of the order of a few centimetres). The mean path of the alpha particles in the experiments of the Austrian scientists was 3.5 cm. No known alpha-active isotope had such mean path of alpha particles. The scientists from the Vienna Radium Institute concluded that these particles were the product of alpha decay of the typically beta-active actinium-227. A product of this decay had to be an isotope of element 87. 

The isotope neptunium-239 was beta-active and had to convert regularly into an isotope of the next element (No. 94). McMillan and Abelson, of course, hoped to discover this element, too, but their dream did not come true. As found later, the isotope of element 94 with a mass number of 239 has a long half-life and its activity is low. The discoverers of neptunium only detected alpha particles of an unknown origin (later found to be emitted precisely by element 94) and discontinued their work. 

With beta emitting isotopes, the meter reading to surface activity ratio is sensitive to the beta energy which... 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Light-silver-colored element generated from a plutonium isotope (241Pu) by beta decay. Never detected in nature. Chemically similar to Europium. A few tons have been produced throughout the world through regeneration of fuel rods. Americium is a good source of alpha rays. Hence it is suitable to measure thicknesses, as a detector in smoke alarms, and for the activation analysis of the tiniest amounts of substances. 

The y particle is emitted virtually instantaneously on the capture of the neutron, and is known as a prompt y - it can be used analytically, in a technique known as prompt gamma neutron activation analysis (PGNAA), but only if such y s can be measured in the reactor during irradiation. Under the conditions normally used it would be lost within the nuclear reactor. In this reaction, no other prompt particle is emitted. The isotope of sodium formed (24Na) is radioactively unstable, decaying by beta emission to the element magnesium (the product nucleus in Figure 2.13), as follows ... 

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