Implantation dose rate

In-beam Mossbauer spectroscopy is a source experiment and, as such, has three distinct advantages over conventional absorption experiments. First, the concentration of Mossbauer probe atoms in a sample is typically several orders of magnitude lower than that in absorption experiments. This makes source experiments more sensitive than absorption experiments and leads to a preponderance of radioactive sources for dilute systems. A concentration in the range 10 10 atoms cm is generally sufficient to observe the Mossbauer effect. It has recendy become possible to measure a Fe Mossbauer spectrum using an implantation dose rate of I O particles s of Mn nuclei by using a... 

Patients should be infection-free prior to pump implantation because the presence of infection may increase the risk of surgical complications. Moreover, a systemic infection may complicate attempts to adjust the pump s dosing rate. 

Figure 4.6 shows data that summarize the current knowledge about damage accumulation in SiC versus ion mass and implantation temperature. Almost all the experimental data that will be discussed from here on concerns the Si sublattice. In a first approximation, they can be considered representative of the whole SiC network because it has been observed that damage accumulations on the Si and C sublattices are rather similar (see Figure 4.4). The data in Figure 4.6 refer to both 3.5° off-axis 6H-SiC and 8° off-axis 4H-SiC wafers implanted at 60° off the wafer normal. The dose rate was in the range 1 X 10 cm" sec" to 8 x 10 cm secbut...

Figure 4.7 Influence of the dose rate on damage accumulation in 4H-SIC for fixed ion mass and ion energy (a) damage at the peak of the Si sublattice versus increasing dose rate and increasing implantation temperature (b) evaluation of the energy activation for the phenomenon responsible of the shift versus temperature shown in part (a). (From [26], 2003 American Institute of Physics. Reprinted with permission.)...

Ohno, T., and K. Amemiya, Influence of Implantation Temperature and Dose Rate on Secondary Defects Eormation in 4H-SiC, Mater. Sci. Forum, Vol. 389-393, 2002, pp. 823-826. 

Fig. 12.8. A model for the buildup of implanted concentration as a function of implantation dose. Assuming a very efficient atomic mixing, this model approximates the implanted profile with a constant shape, but with an increasing amplitude. The rate of increase of the implanted concentration is due to the difference between the flux of incident ions of species A, and that of the sputtered particles of species A, /A...

Ion beam processing provides an alternative and non-equilibrium method of introducing dopant atoms into the lattice. In typical applications, a beam of dopant ions is accelerated through a potential of 10-100 kV. The implantation system shown in Fig. 1.1 illustrates the basic elements required in this technique ion source, acceleration column, mass-separator, and target chamber. With different types of ion sources available, a wide variety of beams may be produced with sufficient intensity for implantation purposes for integrated circuit technology 10 " -10 ions cm (less than a monolayer see Sect. 1.4) is a representative ion dose. Ion dose is defined as the number of ions cm implanted into the sample. Alternatively, the term fluence is used instead of dose. The ion beam current density is expressed in units of A cm . The dose rate or flux is given in units of ions s cm . ... 

Low dose rate brachytherapy sources (except eye plaques and permanent implants) Industrial gauges that do not incorporate high activity sources Bone densitometers Static eliminators 1> A/D >0.01... 

Low dose rate brachytherapy eye plaques and permanent implant sources X ray fluorescence (XRF) devices Electron capture devices Mossbauer spectrometry sources Positron emission tomography (PET) check sources 0.01 > A/D and A > exempt ... 

In proton irradiation with MeV order energies, the major advantage is that it provides modest dose rate and damage depth, which allows hardness measurements at modest doses (0.1-10 dpa) within a reasonable irradiation period (a day or a week). Implanted H atoms are believed to have neghgible influence on material properties in Fe-based alloys at temperatures higher than room temperature. A minor limitation is radioactivation of irradiated specimens. 

Recently, permanent implants into the prostate with seeds have become increasingly popular. Typical implant seeds (1 mCi of per seed) are designed to deliver a dose of 160 Gy during the full decay. The initial dose rate is 7.72 cGy h and 87.5% of the full dose is dehvered over a period of 6 months (three half-lives). 

FIGURE 5 The resistance of a number of polymer compositions implanted at 50 keV to a dose of 1 X 10 ions/cm . Note that the resistance first increases with increasing dose rate, then decreases. The trend at higher dose rates is attributed to higher implant temperatures. 

Figure 19. Glass-roddosimeter insertion in cottonratsfSig/mM/on/rfjpiJujjandresults. (a) Subcutaneous insertion of glass-rod dosimeter in the field. The glass rod is in a nylon capsule held in the orifice of the implantation needle, (b) Average absorbed dose rate for 38 cotton rats on the radioactive White Oak Lake bed. (c) Exposure rate above the radioactive White Oak Lake bed. Toshiba low-Z rods were tied at 1-ft intervals to a nylon cord affixed normal to the soil surface. Each rod was contained in a small nylon capsule (wall thickness 0.047-inch). From Kaye (1%5). Copyright 1%5 by The Ecological Society of America.

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