Experimental demonstration of a soft x-ray self-seeded free-electron laser.

The Linac Coherent Light Source has added a self-seeding capability to the soft x-ray range using a grating monochromator system. We report the demonstration of soft x-ray self-seeding with a measured resolving power of 2000-5000, wavelength stability of 10(-4), and an increase in peak brightness by a factor of 2-5 across the photon energy range of 500-1000 eV. By avoiding the need for a monochromator at the experimental station, the self-seeded beam can deliver as much as 50-fold higher brightness to users.

Cancer of the breast. Screening.

Screening is a more complicated issue than has been indicated in this chapter. Long-term followup is essential to exclude misleading initial impressions, and survival predictions must stand this test. The problem of interval cancers must be acknowledged, and methods of developing more cost-effective systems that might provide even broader coverage of the population at risk have to be considered. Suffice it to say that mass screening for breast cancer can be accomplished. Large numbers of American women are sufficiently concerned about this disease to participate, as evidenced by the success of the National Cancer Institute/American Cancer Society Breast Cancer Detection Demonstration Projects. It has been demonstrated that breast cancers so small that they would previously be considered a pathological curiosity are detected with surprising frequency. The ultimate effect on survival time by this screening can of course only be determined after passage of time, but there is every reason to believe that it represents one of the really great advances in detection-diagnosis in recent history. The chief detection modality is mammography, and it is to be expected that technological advances in this area will permit images of even greater reliability and resolution at a level of radiation exposure that will be acceptable to everyone. The definitive role of thermography in detection of breast disease has yet to be fully determined. The maximal scientific benefit and the true impact of the screening demonstration projects will be realized only after long-term followup of the 280,000 participants.