Decay schemes beta particle

The two fission-produced radio-strontium isotopes of interest in environmental samples are 90Sr and 89Sr. Sr-90 has a fission yield of 5.8 %, a half-life is 28.78 a, and the radioactive daughter 90Y with a half life of 2.67 d, to which it decays by beta-particle emission. Sr-89 has a fission yield of 4.7%, a half life of 50.52 d, and decays to the stable daughter89 Y. The decay schemes given in Figure 13.1 show that these two radio-strontium isotopes for practical purposes can only be measured by beta-particle counting. 

Similar to beta decay is positron emission, where tlie parent emits a positively cliargcd electron. Positron emission is commonly called betapositive decay. Tliis decay scheme occurs when tlie neutron to proton ratio is too low and alpha emission is not energetically possible. Tlie positively charged electron, or positron, will travel at higli speeds until it interacts with an electron. Upon contact, each of tlie particles will disappear and two gamma rays will... 

The most familiar radioactive element is uranium, which has two naturally occurring isotopes of mass numbers 235 and 238 that decay very slowly. Review the first few steps in the decay of uranium-238, which changes to lead-206 after the emission of 8 alpha and 6 beta particles. The earliest stages of the decay scheme involve only three elements, as shown in Figure 3-2. 

The salt used in this experiment is potassium chloride (KC1). Potassium-40 is a naturally-occurring isotope of potassium (abundance = 0.0117%) whose half life is 1.28 x 109 years. It emits a gamma ray at 1.461 MeV with a decay fraction of 10.7%, in addition to beta particles with a decay fraction of 89.3%. The decay scheme for 40K is given in Fig. 3.1. A tared container (see Experiment 2) is filled with solid KC1, closed, weighed, and counted. 

Each radionuclide among the more than one thousand that are known has a unique decay scheme by which it is identified. For this reason, among others, researchers have studied decay schemes over the years and their reported information has been compiled and periodically updated. The compiler surveys the reported information for each radionuclide and attempts to select the most reliable information for constructing a self-consistent decay scheme. The fraction of beta particles that feed an excited state must match the fraction of gamma rays plus conversion electrons emitted by the excited state. The energy difference between any two states must be consistent with the energies of the transition radiations plus the recoil energy of the atom that emitted the radiations. 

The Sr decay scheme in Fig. 9.3 is simple. For practical purposes, the radionuclide emits a beta particle group with a maximum energy of 1495 keV (plus the associated neutrino group discussed in Section 2.2.2). The half-life is 50.5 days. An obscure beta particle group of 590 keV maximum energy, followed by gamma rays of 909 keV with an intensity of about 0.01%, is of no practical consequence in radioanalytical chemistry. 

The Cs/ Ba decay scheme in Fig. 9.5 shows two beta-particle groups emitted by Cs. The 1176-keV maximum-energy beta-particle group decays to the ground state in 5.6% of the decays and the 514-keV maximum-energy beta-particle group decays in 94.4% of the decays to an excited state in The Ba is in secular equilibrium with Cs. This metastable state decays with a 2.55-min half-life. The decay of Ba is 85.1% by 661-keV gamma rays and 9.4% by conversion electrons. 

The decay scheme of the naturally occurring radionuclide (see Fig. 9.6) is 89.1% by beta-particle emission, 10.9% by electron capture, and 0.001% by positron decay. The 1311-keV maximum-energy beta-particle decay is to the ground state of " °Ca. Electron-capture decay is followed instantaneously by emission of a 1461-keV gamma ray from the excited state of °Ar to its ground state. Electron capture decay to the ground state is 0.2% per disintegration. 

Eq. (9.5) becomes complicated (NCRP 1985b) when some beta particles are counted in the gamma-ray detector or vice versa, or the decay scheme is more complex than for a beta particle followed by a single gamma ray. For example, conversion electrons may be in coincidence with beta particles and X rays, or... 

According to the decay scheme of the 4n + 2 series (Figure 1.3, later in the chapter), uranium-238 emits an alpha particle that is followed by two consecutive beta particle decays to form U-234 ... 

A method for estimating the residence time of tropospheric aerosol particles associated with radon decay product radionuclides is based on the radioactivity of a pair of genetically related radioisobars, such as Pb, Bi or Pb, Po according to the sequential disintegrations in the beta decay scheme, as... 

The shell model of deformed nuclei was verified for hundreds of nuclei and proved to be very successful. It can account for level schemes, moments, electromagnetic transition probabilities, single-particle transfer reactions, beta-decay properties, etc. in the deformed regions (A a 25, 150 < A < 190, A > 220). 

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