Depth-dose profile

The absorption properties of the accelerated electrons in the processed materials are the absorbed dose, the depth dose profile, the penetration range, and the dose rate. 

Electron beam irradiation has been carried out with an electrocurtain accelerator manufactured by Energy Sciences, lnc.(model CB/150/15/180). The samples were placed on steel plates in aluminum trays and passed through the conveyor system of the electron beam apparatus. The maximum available dose per pass was 20 Mrad, hence, for the highest dose used in this study(40 Mrad), two passes were utilized. In light of the depth-dose profile at 175 kilovolts electron energy level of the EB system, the radiation dose will be nearly unifiorm throughout the sample thickness(3 mil). 

Figure 4. A calculated depth-dose profile in polypropylene for 70 kilovolt operation. A zero air path to the product Is assumed.

About one third of all localized tumors, which contribute to about 60% of all cancers, are cured by radiotherapy alone or by radiotherapy in combination with surgery [2]. For another one-third of the localized tumors, however, a failure of local control is observed, and this group is expected to benefit from the development of techniques allowing a better conformation of dose to the tumor. The compromise between tumor cure and minimal side effects is largely determined by the physical properties of the radiation type under consideration, namely the depth dose profile. The depth dose profile defines the ratio of the dose delivered to the tumor and the dose delivered to the healthy tissue. 

Within the framework of therapeutical applications of ion beams, this depth dose profile is often called inverted , because it shows low energy deposition at the entrance to tissue and high dose deposition in depth, in contrast to photon radiation, where in general the dose deposited in depth is lower than the dose deposited in the entrance region. The only exception to this general rule is the build-up effect for very high energetic photon beams, which can be explained by the forward... 

Fig. 13. Comparison of depth dose profiles for photon and carbon ion irradiation...

As will be explained later in more detail, the specific depth dose curve makes ion beams extremely suitable for radiotherapeutic applications to deep seated tumors because of the higher ratio of dose deposited in depth (and thus in the tumors) as compared to the dose deposited in the surrounding normal tissue. Besides the depth dose profile, further effects like, e.g., extremely small lateral and range straggling allow a very precise conformation of the dose to the tumor. 

The basic advantages of charged particle beams such as, e.g., carbon ion beams as compared to conventional photon and electron beams are the inverted depth dose profile (Bragg peak characteristics) and the Increased biological effectiveness. 

Proton beams only show the advantageous depth dose profile without the additional Increased effectiveness (see below). 

Warman, J. M. de Haas, M. R Luthjens, L. H. Horn, M. L. High-energy radiation monitoring based on radio-fluorogenic co-polymerization III Fluorescent images of the cross-section and depth-dose profile of a 3 MV electronbeam. Radial Phys. Chem. 2013,84, 129-135. 

The sputtering yields of SiC>2 and AI2O3 have been found to be similar (8). The abscissa is really in units of ion dose, but it was calibrated for depth by profiling through a 28-wt% coating thickness of 20 nm as measured by TEM. The calibration of ion dose to depth is then approximately 1 X 104 nm cm2 C-1. This calibration curve (compressed by a factor of 8) is shown,... 

Generally, the irradiation effects of polymers under vacuum or in an inert gas atmosphere are not different between gamma rays and accelerated EB irradiation. For PC, it was confirmed that the irradiation effects including hardness and wear resistance by EB were the same with those by gamma ray irradiation even at 150°C. However, the dose profile was different between gamma rays and EB for thick polymer materials, because the EB penetration depth into polymer materials depends on the EB acceleration voltage. 

Production of homogeneous solid-state standards is costly. Dynamic SIMS has the advantage that non-homogeneous ion implantation standards can also be used. Knowing the implantation dose of element (el), its RSF can be calculated by use of the integrated (summed) intensities of a depth profile according to Eq. (3.15) ... 

The depth profiles in Fig. 3.26 show that the typical flat channeling implantation profile is generated with low doses only. Increasing the dose superimposes the normal implantation profile shape. Undertaking such experiments with homogeneous wafers enables the production of calibrating models for semiconductor production. 

Implantation dose or fluence it controls the amount of dopant (i.e., its local concentration) introduced in the target per unit surface area. It is measured in ions/cm and it is the integral over the depth of the concentration profile. Typical values in the nanocluster synthesis are lO -lO ions/cm. For a comparison, the t5 pical fluence values for semiconductor doping processes are 10 -10 ions/cm. ... 

In related experiments by Johnson (1985), atomic deuterium was used instead of Hx to neutralize boron in Si. Similar results on spreading resistance were obtained. Furthermore, the distribution profile of D was measured by secondary-ion mass spectrometry (SIMS), as shown in Fig. 4. The distribution profile of D reveals 1) that the penetration depth of D is in good agreement with the resistivity profile and 2) that the D concentration matches the B concentration over most of the compensated region. In another sample, the B was implanted at 200 keV with a dose of 1 x 1014 cm-2, the damage was removed by rapid thermal anneal at 1100°C for 10 sec., and then D was introduced at 150°C for 30 min. As shown in Fig. 5, it is remarkable that the D profile conforms to the B profile. 

Fig. 2 Schematic diagram of a hydrogen depth profiling setup using a high efficiency BGO detector. A cooled sample holder is placed close to the front surface of the BGO scintillator in ultra-high vacuum. The sample holder can be moved perpendicular to the plane of the figure to bring different samples into the 15N beam and is surrounded by a Faraday cup arrangement to ensure accurate measurement of the analyzing beam dose.

DEPTH PROFILE. The secondary electrons produced by ionization processes from an incident beam of high-energy electrons are randomly directed in space. Spatial "equilibrium" is achieved only after a minimum distance from the surface of a polymer in contact with a vacuum or gaseous environment (of much lower density). Consequently, the absorbed radiation dose increases to a maximum at a distance from the surface (2 mm for 1 MeV electrons) which depends on the energy of the electrons. The energy deposition then decreases towards zero at a limiting penetration depth. 

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