scientists play an essential role in this interdisciplinary effort, which blends biology, medicine, modern technology, and nuclear physics.

The years since 9/11 have seen important advances in nuclear forensics. An attack using a nuclear or radiological explosive device would of course be catastrophic, but it would also raise a set of urgent and crucial questions: What was exploded? Who did it? Do they have more? Was the device improvised or sophisticated? Did they steal it, and if so from where? Is the material reactor-grade or weapons-grade fuel? How old is it? Nuclear forensics refers to the techniques and capabilities needed to answer these questions. It can be likened to forensics-style exercises in nuclear astrophysics, whereby scientists analyze and evaluate the debris left behind by a stellar-scale nuclear explosion. Both efforts—nuclear astrophysics and nuclear forensics—are led by nuclear physicists.

The last decade has also seen major advances in the use of nuclear physics techniques to detect heavy nuclei like uranium or plutonium in a truck or cargo container—one such technique might detect the cosmic ray muons, elementary particles similar to electrons, that scatter off these elements at large angles. The techniques are based on well-understood basic nuclear physics, reminiscent of Rutherford’s early experiments, but their application to the detection of nuclear contraband crossing U.S. borders is new. The detector and computational challenges are related to very recent developments in basic nuclear physics.

Nuclear physics has long been a driver in the development of accelerators and computers, both of which are prevalent in our lives and in many sectors of the economy. Solving the design challenges associated with the building of very high energy accelerators being used to probe the fundamental nature of the matter in our universe will bring advances that improve the more than 30,000 accelerators used around the world for radiotherapy, for ion implantation to precisely embed dopants in semiconductor chips, and for other applications from developing new materials to improving food safety and benefiting other areas of industrial and biomedical research. Advancing nuclear science also drives innovations in computer architecture. For example, when IBM developed the Blue Gene line of computers that have become successful commercial machines with an impact on climate science, genomics, protein folding, materials science, and brain simulation, it employed a paradigm that had been developed first for lattice QCD machines—in fact, IBM employed people who had previously designed a computer called the QCDOC (QCD on a chip).

These examples all show how investment in nuclear physics has benefits beyond addressing the fundamental overarching questions earlier in this chapter. These investments are yielding progress on some of the nation’s biggest challenges as well as innovations that help to drive the economy.

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