Accelerator Radiation Safety Newsletter

(all articles are to be considered personal/professional in nature and do not reflect the opinions of the institutions described unless otherwise stated)

An Official Publication of the

Health Physics Society's Accelerator Section

Circulation: 493

Fourth Quarter 2014 /
Volume 24, Number 4



The Newsletter Editor’s Message
(Steve Frey introducing Patrick Bragg)


Everyone, Stewart Smith has resigned due to ongoing lack of sufficient internet access at his remote job location. We thank Stewart for willingness to serve and wish him well. In his place, we are happy to announce that Patrick Bragg, shown below, will now be filling the Newsletter Editor duties. Patrick is a CHP, a master’s degree candidate at Idaho State University, and is in good standing with our Section.

Welcome aboard, Patrick!

The President’s Message

Steve Frey


Hello friends, welcome to this edition of our Newsletter, and I hope you all have been treated to a wonderful holiday season. Our Section continues to prosper, thanks to all of you. 2015 promises to be a great year in our accelerator world, for both science and radiation safety.


In this issue, we feature a review of the latest in what’s going on in the world of particle and photon physics (from this writer), new member information from Linnea Wahl, and a sharing of some very interesting accelerator-based institutional knowledge about beamline targets and radiation safety considerations related to their operation and changeout at the Spallation Neutron Source from Scott Schwahn.

First, the science stuff: Particles, photons, and physics, oh my! Like Dorothy Gale experienced during her journey along the mysterious yet fascinating Yellow Brick Road, we are seeing a lot of interesting recent developments in accelerator-based physics coming our way. We’ve never lived in a better time for science and accelerators! Here’s some of the latest:



Steven Frey, Consultant



Elaine Marshall, Sandia National Laboratories


Past President:

Jason Harris, Idaho State University



Linnea Wahl, Consultant


Newsletter Editor:

Patrick Bragg, Idaho State University




Melissa Mannion (2015), Lawrence Berkeley National Laboratory


Robert May (2015), Thomas Jefferson National Accelerator Facility


Don Cossairt (2016), Fermilab


Reginald Ronningen (2016), National Superconducting Cyclotron Laboratory


• Accelerator Section Website

• HPS Website



-     Two new particles found at the Large Hadron Collider (LHC): They have been named  Xi_b’-  and Xi_b*-, and are identical except for having a difference in spin. Both particles are composed of the same three quarks: Down, Strange, and Bottom. It’s fascinating that these new particles are composed of three quarks that are all of the same “color” (quantum chromodynamically speaking), as shown by the yellow circle in the below chart of the Standard Model (Symmetry, 11/19/2014).


-     One hundred trillion of anything is bound to get attention. FermiLab is getting close to start producing that many neutrinos per second and shooting them 500 miles to the new NOvA detector in Minnesota. Construction of the NOvA Project’s detector, a state‑of‑the‑art device like no other, is now complete, and it use for studying neutrino morphing is to begin soon in earnest (Symmetry, 10/06/2014). Check out this cool video that’s all about the technical approach behind the NOvA detector: Detecting Neutrinos with the NOvA Detector


-    Plasma wakefield means of accelerating electrons Plasma wakefield means of accelerating electrons: Scientisat at SLAC National Accelerator Laboratory and the University of California, Los Angeles (USLA), have found advanced ways using plasma wakefield technology to push electrons to energies 400 to 500 times higher than otherwise possible. This technology promises to yield more powerful accelerators in smaller sizes that what we are used to seeing up to now. Who knows? Plasma wakefield teconology could make particle accelerators seemingly ubiquitous. (Symmetry, 11/05/2014) and Plasma Wakefield Aceleration: How it Works.

-     Axions may exist after all! In fact, they may help explain dark matter (, 10/20/2014). Recent analysis of x‑ray energies from deep space are producing hints that dark matter does indeed exist, indication of which is observed via energy patterns shown by those same  x-rays that seem to be mirroring those predicted for axions, a type of particle first suggested in 1977 by Dr. Helen Quinn of SLAC and Dr. Roberto Pecci of UCLA. Until recently, no proof that axions actually exist had been found. Now, proof may be at hand. Stay tuned for further developments.

-     Top Quark: why does it interact apparently more with Higgs Field than other quarks, especially with Top Quarks having rather similar rest energy-mass equivalence (173 GeV and 125 GeV, respectively (Symmetry, 10/15/2014).


-     (From Quarks to Quasars, 12/17/2014) A new proposal interjects the Higgs Boson into better understanding charge‑parity violation as the basis for why there is more matter than antimatter in the Universe. Here’s how:


In this illustration, two protons collide at high energy, producing a Higgs boson that instantly decays, producing two tau particles. The rest of the energy from the collision sprays outward in two jets (pink cones). Measuring the angle between these jets could reveal whether or not the Higgs is involved in charge-parity (CP) violation, which could help us understand matter and anti-matter. Image credit: SLAC National Accelerator Laboratory

In the above illustration, two protons collide at high energy, producing a Higgs boson that instantly decays, producing two tau particles. The rest of the energy from the collision sprays outward in two jets (pink cones). Measuring the angle between these jets could reveal whether or not the Higgs is involved in charge-parity (CP) violation, which could help us understand matter and anti-matter. Image credit: SLAC National Accelerator Laboratory

-     Interested in helping look for Higgs particles in the LHC data? All you have to do is go here to join the fun: Zooniverse Higgs Hunters.


And last, but certainly not least, the science surprise of the year: Supersymetry (SUSY) evidence has not been found at LHC, despite tailored efforts there to find it (Quanta, 1/22/2012). Here’s a description of SUSY:

Supersymmetry proposes that every particle in the Standard Model, shown at left, has a “superpartner” particle still awaiting discovery (illustration: CERN & IESde SAR). Source: Quanta Magazine.

Yow. Could the lack of proof at LHC mean that our faith in supersymmetry as the answer for resolving the underlying difference between fermions and bosons, with the possible difference being the driver behind the ongoing expansion of the universe (i.e., dark energy), is wrong? Since the date of this article in Quanta two years ago, the lack of proof continues; to date, none has emerged from any data anywhere. Let’s keep following this potential development as more information emerges, especially as LHC renews the search at higher energy levels in 2015.

In summary, all of the above point to an exciting year in 2015!

PS.   One more little reminder that the HPS Mid‑Year Meeting is coming up soon. It will feature a new, more versatile format that previous mid-year meetings. Please consider attending! The meeting will be held in beautiful Norfolk, VA, from February 1stthrough the 4th of 2015. You can access the meeting website at for more information.

From Linnea Wahl, The Secretary/Treasurer:
Linnea Wahl

You may know that like most professional organizations, the Health Physics Society (HPS) is concerned about dwindling membership. These days, radiation safety professionals have many ways to spend their time (and dollars!) and HPS must compete for their attention.

So it may come as a surprise that 2014 saw no fewer than 15 people joining both HPS and the Accelerator Section. Clearly the Accelerator Section has something special to offer new members.

Please join me in welcoming our newest members—new in 2014 to HPS and to the Accelerator Section.

Mark Balzer
Patrick Barron
Debra Bensen
Ian Byrnes
Elstan Desouza
Megan Harkins
Benjamin Kaurich
Uday Lanke
Abdul Mroue
Allen Pock
Staci Reed
Thomas Ruggieri
Adam Stavola
Silvia Surugiu
Sean Tanny
John Worthey
Fan Zhang



From Scott Schwahn, Spallation Neutron Source

Scott Schwahn

The Spallation Neutron Source (SNS) has experienced unplanned and previously unanticipated maintenance challenges since summer 2014. At the center of neutron production is a stainless steel target inside which circulates approximately 20 tons of liquid mercury. The nose of the target is struck by an approximately 1 GeV, ~1 MW (average) proton beam operating at 60 Hz. It is expected that the target will be damaged over time and it has to be replaced regularly. Internal cavitation damage is theorized to occur as approximately the cube of proton beam power. Up until recently, the target lifetime has typically been 6 months or more. With each target costing more than $1 million USD, quite a bit of research has gone into finding ways to extend the life of the targets.

There are multiple sensors inside the target to warn operators that the target is failing, to include mercury sensors and cooling water sensors, each in places where the mercury and water shouldn’t be. One sensor alarming could indicate a bad sensor; in fact, the target is declared inoperable when there is only one active sensor left unaffected. One target was declared inoperative after only one month of operation. The target put into place immediately afterward was declared inoperative after only one week of operation. After extensive troubleshooting, another target was put into place and has been operating since late November.

To make matters worse, and which put a severe strain on resources (and patience), a catastrophic water leak into the accelerator front end vacuum occurred at the same time as the second target failure. Electrical components that should never see water were soaked, and vacuum components that should never see significant air were brought not only to atmospheric pressure, but also soaked.


Large view of the front end cage, normally a Radioactive Material Area during maintenance. Usually posted as a Radiation Area during operations.

As far as radiological safety goes, these problems presented us with numerous challenges, although there was never any danger of contamination beyond the immediate area of the leak. The front end of the accelerator is normally defined by a relatively small “Radioactive Material Area (RMA)” – in the US Department of Energy scheme, that’s an area where any materials present have to be assumed to be radioactive unless they were personally brought in and carried out upon leaving. In fact, there is not normally a posted RMA outside of the access-controlled tunnel (the first 10 meters or so of the accelerator is outside of the tunnel). However, nearly every component of the beamline – every sensor, vacuum connection, beam pipe, magnet, radiofrequency cavity – had to be individually disconnected, labeled, evaluated, and treated for water and air intrusion. (This had never been performed or anticipated to be performed since the accelerator was first constructed, and included many one-of-a-kind items that could not be replaced!)


Accelerator section that had to be completely dismantled to address the water leak.

The RMA was expanded to take up a significant part of the building. Radiation Control Technicians were called upon to survey hundreds or perhaps thousands of individual items for both activation and contamination, to maintain postings and barriers, and to manage a radiological entry program with an order of magnitude greater entry frequency and expanded population of those normally entering the area. It should also be noted that due to the unusual electrical hazards (water in electrical components and disconnected electrical components), the electrical safety requirements such as extensive lock-and-tag activities were no small part of the work.



Typical size of a "staging RMA". During the front-end activities, the area was expanded by perhaps a factor of 6.


Everyone was quite pleased that in the end, not only were there no radiological safety violations of procedure, the entire accelerator was put back together properly and functioned properly. I could not begin to adequately describe the other work that was done to prevent damage to components and to dry out items that should have never seen water, but could not be taken apart. Of interest, there were items such as elastomeric washers that trapped water but could not experience significant heat or they would be damaged; and could not dry out under vacuum or the water would freeze. An interesting problem, solved by an external glycol bath held just a few degrees above 100 degrees C.

The targets provided unique challenges as well. When a target fails, it is emptied of all its mercury and is treated as a radioactive empty vessel. Normally, the vessel would be shipped within a shipping liner in the only approved shipping container to its approved burial site. The shipping container, however, is shared among several customers. The SNS target bay normally has room for two used targets with the third one in operation. While the used targets are awaiting transport, they can be analyzed with cameras or destructively with saws to analyze damage. However, when there were two unexpected target failures one right after the other, it presented a logistics issue in that the last target could not be replaced until room was made in the target bay. Expedient arrangements had to be made to ship the targets, while maintaining the discipline to ensure that there was no loss of appropriate radiological controls of these highly contaminated objects under perceived time constraints.

        SNSNews1     SNSNews2

Targets in temporary storage awaiting

shipment as waste. The lid on the spent target on the right is off.


              A close-up of mercury circulation channels in the spent target.


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