Tech Tuesday: How Nuclear Physics Keeps You from Going Up in Smoke

  •  public_domain_smoke_detector_image

I’m lucky.  I’m part of a team of scientists, engineers and technicians that have been asked by our country to seek better understanding of the universe. Besides getting new insights into the nature of our universe, the things we learn while conducting research help to make our lives better. I mentioned in an earlier post that basic understanding of the universe gained by probing the mysteries of the atomic nucleus has led to life-saving devices from small smoke detectors to large medical centers that treat cancer. So read on to learn the nuclear physics origin of the invention of the smoke detector.

Like many at Thomas Jefferson National Accelerator Facility, I started out as a geeky kid who grew up to be a geeky adult. Luckily, I’ve found a home in Jefferson Lab to answer the nation’s call for probing the mysteries of nuclear physics that can lead to life improving innovations. All Americans should feel proud that, as taxpayers (or their tax-paying parents or grandparents), they played an essential part in making lives better and even saving lives. Some of those hard-earned tax dollars went to fund nuclear particle physics research that among other things unexpectedly lead to the development of smoke detectors that every American should have in their home.

The Nature of the Nucleus.

For nearly 75 years, Congress directed nuclear particle physicists to do basic research into the nature of the nucleus of the atom. We don’t know what mysteries will be uncovered and what these new findings will lead to. We also can’t predict what other uses will be found for the instruments and technology invented along this path. In fact, some pretty fantastic things have come out these efforts. An example of this all started in an American particle accelerator lab in 1945.

Discovering Seeds of Innovation.

The first smoke detector developed and widely used contains a manmade atom appropriately named Americium-241. This new atom was discovered in 1945 at the University of Chicago. The discovery came out of part of the US government’s investment in the Manhattan Project to construct an atomic bomb; however, it would take another 32 years until this cool seed found fertile ground for a life-saving application. It was in 1976 (America’s Bicentennial) when another American would file a U.S. patent on his Americium-241 based smoke detector.  I’ll describe the importance of patents and Jefferson Lab’s treasure trove of patents in a later post.

Innovation Reimagined.

This type of smoke detector makes use of ionization. [Geek Alert! I’m going to talk a little physics here. Feel free to jump right past this section if geek isn’t your thing.] This type of smoke detector uses a device called an ionization chamber. This chamber is a nuclear particle detector that was invented to detect several types of ionizing radiation such as alpha particles and is still used at particle accelerator research labs like Jefferson Lab. An alpha particle is just the nucleus of a helium atom (two protons and two neutrons) and is emitted by radioactive isotopes such as Americium-241. The alpha particle ionizes the air molecules (bumps off electrons) between two electrical plates in the top and bottom of a small pillbox-sized chamber that is open to room air. The electrical plates are part of an electrical circuit that can conduct a small current of electricity through the ionized air. If even a small number of smoke particles enter the chamber, the ionization is disturbed and the electrical current is broken. The electrical circuit detects the change and sounds the alarm.

There is another type of smoke detector referred to as a photoelectric-based smoke detector that also came out of nuclear particle accelerator research. Nuclear particle accelerators lead to another such seed: the understanding and ability to implant or insert atomic ions into types of crystals. The photoelectric-based smoke detector uses two different types of an electrical device called a diode. In this smoke detector, a light-emitting diode uses electricity to produce a beam of light. This beam of light is scattered by smoke, and the scattered light is then able to be detected by a light-sensitive photoelectric diode. This type of diode produces an electrical signal from the light that shines on it. Both the light-emitting diode and the light-sensing photodiode use a semiconductor that has been modified through ion implantation to make a diode.  I’ll talk more in other blog posts on the importance of ion implantation and how nuclear particle accelerator research gave us this powerful tool.

Benefits for the U.S. Economy.

While it is difficult to measure the economic impact of the discovery of Americium and the knowledge of ion implantation in this case, we can make estimates.  The National Fire Protection Association (NFPA) reports that most households (~96%) have smoke detectors. There are over a 125 million households in the U.S. If each household has at least one smoke detector, purchased for roughly $15, that’s almost $2 billion in sales. Throw in the fact that most houses have more than one smoke detector, and you replace them every ten years, then that’s a lot of money.

Saving Lives and Houses.

The NFPA reports that if your home is without a working smoke detector you are twice as likely to die in a house fire than if your home has a functional smoke detector. Almost 1500 deaths occur per year due to the lack of a working smoke detector.

Incidentally, a physicist at Jefferson Lab invented another way to detect certain types of fires before they actually start. There was a need at Jefferson Lab to make sure that many of the electrical cables used in the big Jefferson Lab experimental areas didn’t overheat under unexpected conditions. This scientist determined it was possible to optically detect the appearance of vapors that are released by the insulation of certain electrical cables when they heat up because of an overload.

We have all benefited from the early particle accelerator research that our parents and grandparents invested in. So go hug your folks and thank the geeky physicists.

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Questions? Email:

Drew Weisenberger
Chief Technology Officer
Jefferson Lab


Additional Information and Research.

  1. NFPA's "Smoke Alarms in U.S. Home Fires" Author: Marty Ahrens Issued: September 2015
  2. Number of households in the U.S. from 1960 to 2017
  3. AMERICIUM – FROM DISCOVERY TO THE SMOKE DETECTOR AND BEYOND, “ Keith Kostecka, 4’ Bull. Hist. Chem., VOL 33, number 2, 2008
  4. The two most commonly recognized smoke detection technologies are ionization smoke detection and photoelectric smoke detection.


Jefferson Science Associates, LLC, a joint venture of the Southeastern Universities Research Association, Inc. and PAE Applied Technologies, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science.DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit