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Nuclear Structure and Decay
Published in Eric Ford, Primer on Radiation Oncology Physics, 2020
In general, any beta-minus decay can be written as , i.e. element “X” with Z protons decaying into element Y with Z + 1 protons. The decay scheme is also often shown graphically as in Figure 2.2.1 (bottom left, yellow) with the energy axis vertical and the number of protons increasing to the right. Often the axes in yellow are not included in such diagrams. Here the maximum energy of the beta-minus particle is labeled (1.71 MeV in the example decay shown here).
Short-Lived Positron Emitting Radionuclides
Published in Frank Helus, Lelio G. Colombetti, Radionuclides Production, 2019
Of the three known positron-emitting nuclides of oxygen the longest-lived is oxygen-15 with a half-life of 122 s. This radionuclide decays by positron emission for 99.9% and electron capture for 0.1% to stable nitrogen-15.159 The decay scheme is shown in Figure 13. The maximum positron energy is 1.72 MeV, corresponding to a range of 8 mm in water.
Radioactive Noble Gases for Medical Applications
Published in Garimella V. S. Rayudu, Lelio G. Colombetti, Radiotracers for Medical Applications, 2019
The 35-hr 79Kr isotope has a complex decay scheme, but its most abundant γ rays are of 261 keV and 398 keV which are of more appropriate energy than the 81-keV γ ray of 133Xe for imaging studies. The half-thickness in water54 for 79Kr γ rays is about 13.2 cm as compared to a half-thickness of only 7.7 cm for 133Xe, and therefore 79Kr should be a more useful tracer for studying interior regions of the body. Qaim et al.30 have prepared 79Kr by bombarding natural NaBr targets with deuterons. Since there are two stable isotopes of bromine, 79Br and 81Br, the excitation function has two maxima at 20 and 40 MeV, corresponding to the 79Br(d,2n)79Kr and 81Br(d,4n)79Kr reactions, respectively. A 79Kr yield of 3.9 mCi/μAh was reported at an incident deu-teron energy of 28 MeV. At this energy, 77Kr as the principal radionuclidic impurity produced. Since the half-life of 77Kr (75 min) is much shorter than that of 79Kr, the 77Kr contamination can be reduced by simply allowing the sample to decay. Clark and Buckingham54 have produced about 1 mCi/μAh of 79Kr with 16-MeV deuteron bombardments of NaBr. They observed that as the beam current and target irradiation time increase, the “on-target” yields decrease. Targets of melted NaBr resulted in higher and more reproducible yields as compared to those of powdered NaBr, primarily because the melted salt target was less prone to thermal damage during the irradiation. Observed radionuclidic impurities included 15-hr 24Na from the 23Na(d,p)24Na reaction and 35-hr 82Br produced from the 81Br(d,p)82Br reaction. Collé and Kishore55 have produced 79Kr at a rate of 2.8 mCi/μAh via the 79Br(p,n)79Kr reaction by bombarding KBr targets with 18-MeV protons. At higher proton energies, production of 79Kr is also possible through the 81Br(p,3n)79Kr reaction which has a threshold energy of 20.7 MeV. Alternatively, 79Kr can be produced by bombarding enriched 78Kr with thermal neutrons (σn = 4.7 b) by the 78Kr(n,y)79Kr reaction.53
Cellular dosimetry of 197Hg, 197mHg and 111In: comparison of dose deposition and identification of the cell and nuclear membrane as important targets
Published in International Journal of Radiation Biology, 2023
Zhongli Cai, Noor Al-saden, Constantine J. Georgiou, Raymond M. Reilly
We compared MCNP-6 calculated SN←CM, SN←Cy and SN←N of 111In, 197Hg and 197mHg to those calculated with MIRDcell using average electron spectra (Figure 2(A-C)). Under the selection of β full energy spectrum in MIRDcell, ‘Input Data for Calculation’ actually does not include all the radiations, except for β particles or AE, and only radiations which contribute greater than 0.1% to the total delta for that particular radiation type were retained. Moreover, the radiation data of β full energy spectrum and β average radiation spectrum was taken from MIRD: Radionuclide Data and Decay Scheme, 1st and 2nd editions, respectively (Vaziri et al. 2014). Since we used detailed spectra data of AE, CE, X-rays and γ-rays from MIRD: Radionuclide Data and Decay Scheme, 2nd edition (Eckerman and Endo 2008), we chose average instead of full electron spectra for MIRDcell calculation. All SN←N values obtained from both methods were in excellent agreements with the relative difference within 5%. The difference became larger for SN←Cy, but still was lower than 40%. This difference was larger at smaller RC, where MIRDcell calculated SN←Cy of 197Hg and 197mHg were larger than the MCNP6 estimated ones. In contrast, MIRDcell calculated SN←Cy of 111In were smaller than those for MCNP6. For SN←CM of 197Hg and 197mHg, the difference between MIRDcell and MCNP6 calculation remained modest, well below 55%. For SN←CM of 111In, the ratio between MIRDcell to MCNP6 calculated ranged from 0.61 to 1.90. The difference appeared to depend on the size of both the nucleus and cell, as well as the radionuclide. However, SN←CM, SN←Cy and SN←N of 111In calculated with MCNP6 were in good agreement with those of Monte Carlo codes PENELOPE (Falzone et al. 2015) and MCNP5 (Cai et al. 2010), with the difference within 8% and 12%, respectively Figure 2(D–F).