Any other ideas?

TO GET TO THE Los Alamos National Laboratory in New Mexico, you drive from Santa Fe through peach-parfait mesas and off into the sunset. Even on the public roads, there are checkpoints where security officers will ask to see your driver’s licence. The deeper you go, the more intense the screening gets, until finally you end up in a place employees just call “behind the fence”.

After the public roads but before “behind the fence” are the hot cells: 1,2- by 1-metre boxes where employees use robot hands controlled by joysticks to process non-weapons-grade isotopes. The isotopes are made on another mesa, by a linear particle accelerator that shoots rare metals with proton beams.

Just outside the hot cells, Eva Birnbaum, the isotope production facility’s programme manager, asks me if I know what a decay chain is. She points in the direction of an expanded periodic table that, despite a year of college chemistry, means about as much to me as a list of shipbuilding supplies from the 1600s. Birnbaum launches into a primer on radiochemistry: isotopes are chemical elements with too many or too few neutrons in their centres. Some of these are unstable and therefore release energy by shooting out various types of particles. Unstable isotopes are radioactive, and the particles they shoot out are known as ionising radiation.

As for what a decay chain is: when radioactive isotopes release radiation, they usually turn into another radioactive isotope, which releases radiation until it turns into another radioactive isotope, and so

on, until it hits on something stable. The pattern by which a particular isotope morphs is its decay chain. Today, in addition to whatever goes on behind the fence, Los Alamos National Laboratory is the primary producer of certain isotopes whose decay chains make them useful for medical scans, such as PET scans and heart-imaging techniques. Scientists at Los Alamos deliver the parent isotope in a container called a cow. As the parent decays, doctors “milk” the daughter isotope off to image patients’ hearts.

Decay chains present both an opportu- nity and a responsibility. You can’t just throw decaying radioactive isotopes into a landfill, so after the nuclear age and a half-century Cold War with the USSR, in the USA there are caches of radioactive uranium and plutonium isotopes sitting around gradually turning into other stuff. One of these caches is uranium-233, which was originally created for a reactor programme and is currently stored at the Oak Ridge National Laboratory in Tennessee. Over the last 40-some years, it has been slowly turning into thorium-229.

Thorium-229’s decay chain leads to actinium-225, which is of interest to cancer researchers for several reasons. For one thing, actinium-225’s decay chain goes on for several generations. It turns into francium-221, then astatine-217, then bismuth-213, then mostly polonium-213, then lead-209 before finally hitting a hard stop at bismuth-209, which is stable. In most of these generations, the radiation released consists of alpha particles, which can destroy cancer cells but have low tissue penetration; they leave the surrounding healthy cells mostly alone. Currently, all but one of the radioactive isotopes used in cancer treatment release beta radiation, which causes considerably more collateral damage.

If a drug company could attach an atom of actinium-225 to a targeting system – like, say, the kind in CAR-T cells – the actinium-225 could continuously attack cancer for days at a time, like an artificial, radioactive version of the immune system. Newer chemotherapy drugs called antibody-drug conjugates already use this

technique, directing chemotherapy agents that are too strong to give intravenously precisely where they are needed. At least two of these, Kadcyla and Adcetris, have already been approved by the FDA (for Her2-positive breast cancer and Hodgkin’s lymphoma, respectively).

The US system of national laboratories is already in talks with drug companies about making antibody-based radioactive drugs a reality. They seem promising; in a paper released last July in the Journal of Nuclear Medicine, one late-stage prostate cancer patient treated with three cycles of targeted actinium-225 at the University Hospital Heidelberg in Germany went into complete remission and another’s tumours disappeared from scans.

But of course, there’s a problem. Now that the reactor programme and the Cold War are both over, no one is making uranium-233 in the US (or anywhere). And because it takes more than 40 years for uranium-233 to turn into enough thorium-229 to be useful, it wouldn’t matter much even if they did. There are currently only about 1 500 to 1 700 millicuries of actinium-225 anywhere in the world, which would just treat one hundred to two hundred patients a year.

Which brings us to the reason Los Alamos has got deeply involved in actinium-225 at all: they’re going to figure out how to make more from scratch.

INTERLUDE

A roughshod man with bloodshot eyes rolls a cigarette outside a coffee shop in Taos, New Mexico. I can’t be sure if he is the backpacker who was playing a flute at this table earlier or a new person. “You a reporter?” he asks.

“Er, yeah. Just got off the phone with a drug company that thinks they can cure cancer.”

“A drug for cancer already exists,” the man says. “More people need to be looking at marijuana. It can cure all kinds of sicknesses, but the thing is, the government doesn’t want people knowing about it.”

A light breeze rustles the wind chimes. We are hiding from the sun under a pergola on the shop’s back porch. Another man attempts to come to my rescue: “But wasn’t Obama trying to change the rules about experimenting... ”

“Obama doesn’t want to change the rules because he’s not like us,” says the first man. “He’s got pharaoh DNA that they blend with lizard blood up in the mountains.” He inclines his chin towards Los Alamos.

“So he’s like a monster?” asks the second man.

“Nah, they’re physical, like us, but they only have three chakras, so they’re not as balanced.” He nods, sagely. “Highly carnivorous.”