[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

The fluctuation of the ti content is therefore

Info icon This preview shows pages 474–477. Sign up to view the full content.

only. The fluctuation of the Ti content is, therefore, related to the amount of the river water and to the amount of rain. 0.30 Ti [%] 0.15 0 0 20 ~AD 910 ~AD 860 ~AD 810 ~AD 760 16 6 47 3 42 9 40 Sample size [mm] Years 40 60 80 Fig. 7.8. Distribution of Ti-intensity in a bore core of the Cariaco basin [from 25]
Image of page 474

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

454 B. Kanngießer and M. Haschke From the distribution in Fig. 7.8 it may be concluded that in certain peri- ods of time—especially around 910, 860, 810, 760 (highlighted in the darker grey), the Ti-content is significantly lower for a few years than in other peri- ods. During these periods the amount of rain was reduced significantly. The population of the Mayas on Yucatan was already relatively high by approximately 12 million people on a small area. A high agricultural produc- tivity was needed to produce a sufficient food supply. If the amount of pre- cipitation was drastically reduced for long periods of time, then it could also be expected that the agricultural productivity suffered. During such periods there was not enough food available to feed the population. The multiple step collapse of the Maya civilization can be explained in terms of these food problems. This explanation is in agreement with other archaeological observations indicating that the Maya civilization collapsed in several steps, that there were no wars or other disastrous event that damaged the people. Mapping Mapping means that measurements are performed on a large matrix and the elemental distribution is displayed for an area. The combination of various elemental distributions may provide further information on material compo- sition, for example, phase distributions. Investigation of Malignant Cells Malignant cells are very similar to healthy cells. Destroying them in a se- lective way is very difficult. One way of killing malignant cells is irradiation with ionising radiation but radiation cannot distinguish between healthy and malignant cells. By marking malignant cells they can be identified. The mark- ing depends on the type of irradiation that is used. Currently, a new method has been developed—the Neutron Capture Can- cer Therapy (NCT) [26]. This method is a non-invasive therapy for malignant cells that is performed in two steps: 1. Injection of a substance that will preferentially adhere to cancerous cells. This substance contains an isotope with a large cross section for thermal neutrons producing, for example, α -particles. 2. The patient will be irradiated with thermal neutrons. In subsequent nuclear reactions α -particles are generated which destroy the surrounding malignant cells. Table 7.6. Cross sections for thermal neutrons Element 1 H 12 C 14 N 16 O 10 B 157 Gd cross section [barn] 0.333 0.0035 1.83 2 × 10 4 3.84 2.5 × 10 5
Image of page 475
Methodological Developments and Applications 455 For NCT, different elements can be used. An important selection criterion is a significant higher cross section for thermal neutrons than that for the typical elements of the cells and a nuclear reaction must be possible. The cross sections of some typical elements are summarised in Table 7.6.
Image of page 476

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Image of page 477
This is the end of the preview. Sign up to access the rest of the document.
  • Spring '14
  • MichaelDudley

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern