Beta emissions

A beta particle is essentially an electron that s emitted from the nucleus. (Now 1 know what you re thinking — electrons aren t in the nucleus. Keep on reading to find out how they can be formed in this nuclear reaction.) Iodine-131 (1-131), which is used in the detection and treatment of thyroid cancer, is a beta particle emitter  

the Iodine-131 gives off a beta particle (an electron), leaving an isotope with a mass number of 131 (131 - 0) and an atomic number of 54 (53 - (-1)). An atomic number of 54 identifies the element as Xenon (Xe). 

Notice that the mass number doesn t change in going from 1-131 to Xe-131, but the atomic number increases by one. In the iodine nucleus, a neutron was converted (decayed) into a proton and an electron, and the electron was emitted from the nucleus as a beta particle. Isotopes with a high neutron/ proton ratio often undergo beta emission, because this decay mode allows the number of neutrons to be decreased by one and the number of protons to be increased by one, thus lowering the neutron/proton ratio. 

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The product nucleus, Al-28, is radioactive, decaying by beta emission ... 

Consider the new isotope JgX. Compare the product nuclides after beta emission and positron emission. 

Iodine-131 is used to treat thyroid cancer. It decays by beta emission and has a half-life of 8.1 days. 

WEB Chlorine-36 decays by beta emission. It has a decay constant of 2.3 X 10-6 y-1. How many /3-particles are emitted in one minute from a 1.00-mg sample of Cl-36 How many curies does this represent ... 

WEB Strontium-90 is a dangerous byproduct of atomic testing because it mimics the action of calcium in the body. It decays in two beta emissions to give zirconium-90 (Nudear mass = 89.8824 g). 

Th, Th and Po, all decay by alpha emission and are thus measurable by isotope dilution and alpha spectrometry (Ivanovich and Murray 1992). However, " Th is produced by the alpha decay of and in turn decays by beta emission to via the short-lived intermediate " Pa (half-life 1.18 m) ... 

The magic numbers which impart stability to a nucleus are 2, 8, 20, 28, 50, 82 or 122. The isotope, 39K, has a magic number equal to its number of neutrons, so it is probably stable. The others have a larger neutron-to-proton ratio, making them neutron-rich nuclei, so 40K and 41K might be expected to decay by beta emission. In fact, both 39K and 41K are stable, and 40K does decay by beta emission. 

K beta emission gK - 4oAr + °e (However, 41K is not unstable and does not decay.)... 

A radioactive isotope has a half-life of 6.93 years and decays by beta emission. Determine the approximate fraction of the sample that is left undecayed at the end of 11.5 years. 

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 ... 

Isotopes that are neutron-rich, that have too many neutrons or not enough protons, lie above the belt of stability and tend to undergo beta emission because that decay mode converts a neutron into a proton. 

A particular isotope may undergo a series of nuclear decays until finally a stable isotope forms. For example, radioactive U-238 decays to stable Pb-206 in 14 steps, half of these are alpha emissions and the other half are beta emissions. 

The electron capture detector is another type of ionization detector. Specifically, it utilizes the beta emissions of a radioactive source, often nickel-63, to cause the ionization of the carrier gas molecules, thus generating electrons that constitute an electrical current. As an electrophilic component, such as a pesticide, from the separated mixture enters this detector, the electrons from the carrier gas ionization are captured, creating an alteration in the current flow in an external circuit. This alteration is the source of the electrical signal that is amplified and sent on to the recorder. A diagram of this detector is shown in Figure 12.13. The carrier gas for this detector is either pure nitrogen or a mixture of argon and methane. 

Problem 1.14 Half-life of radioactive element is 2800 years. How many atoms of the element are required to produce an average of 10 beta emissions per hour ... 

Beta emission in which an electron, Je, is emitted from the nucleus. This is due to the conversion of a neutron into a proton plus the beta particle. 

Know that nuclear stability is best related to the neutron-to-proton ratio (n/p), which starts at about 1/1 for light isotopes and ends at about 1.5/1 for heavier isotopes with atomic numbers up to 83- All isotopes of atomic number greater than 84 are unstable and will commonly undergo alpha decay. Below atomic number 84, neutron-poor isotopes will probably undergo positron emission or electron capture, while neutron-rich isotopes will probably undergo beta emission. 

Element Symbol Half-life Beta emission Gamma emission... 

The end window of the tube must be thin enough to permit the weaker radiations to enter the tube (aluminium, 6-8 mg cm-2 mica, 2 mg cm-2) but even so alpha particles and very weak beta emissions are either completely or partially absorbed. The emissions from the biologically important isotopes of tritium and carbon-14 fall into this category and alternative detectors should be used for these isotopes. 

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