What does HE stand for in "explosive force of the HE"?


I’ve been searching quite a while for the meaning of HE, as in “the explosive force of the HE” while reading up on the Manhattan Project. What does HE stand for? I look forward to your feedback.

It just means “High Explosive”. High explosives (like TNT) detonate and produce a shockwave, while low explosives (like gunpowder) basically just burn really fast.

The passage may have been referring to a simulation of the atomic bomb using conventional explosives, or the explosives that are used to drive the uranium/plutonium parts of the core together to initiate the reaction.

High explosive.

In the context of nuclear weapons, it is the chemical explosive that drove the subcritical “bullet” of U235 into the “target” (in the case of Little Boy) or compressed the hollow sphere of plutonium to criticality (in the case of Fat Man).


It’s impossible to read this post without hearing it said in Dr. Strangelove’s voice! :slight_smile: of course, the last word should be “erection.” And the ninth word should be “stimulation.”

To expound on this:

A “detonation” means that the reaction front passing through the explosive is traveling faster than the speed of sound; the supersonic shock wave passing through the explosive is the thing that triggers the chemical reaction at the front. For example, detcord has a detonation velocity of several kilometers per second (slo-mo video here). Most high explosives release less energy per unit mass than familiar combustible substances like gasoline/air, but because they release their energy so suddenly they can be much more destructive, generating a shock wave that creates very large local pressures (up to several thousand PSI) on nearby objects.

A “deflagration” means that the reaction front passing through the substance is traveling below the speed of sound; thermal effects at the reaction front are the thing that trigger the reaction to move through the mixture. You can generate large pressures in an enclosed space this way, but you won’t generate a shock wave (except if/when the enclosed space ruptures and suddenly releases built up pressure, e.g. when a bullet comes out of a gun muzzle; example, shock wave apparent on water when battleship fires main guns). This woosh bottle shows that deflagration can be very slow, on the order of centimeters per second if the combustible mixture remains quiescent. Any turbulence will stretch/distort the flame front, increasing its surface area and resulting in a faster overall reaction rate; this has much to do with why your car’s engine can run well over such a huge range of RPM (turbulence, resulting from the intake event, is much greater at higher RPM).

yes; as I understand it “low explosives” are only actually explosive if ignited inside a container. it’s the bursting of the container which does the damage.

Most excellent explanation. Thank you.

A slight expansion if I may. At the point of the two ellipses above, add “of the explosive material.”

IOW, what matters is the speed of sound within the C4, TNT, or whatever as a bulk material. Not the speed of sound in the surrounding atmosphere. There can be significant differences between those two values. The fact the SoS in, say, TNT is 2 or 3x the speed of sound in air further improves how violently the TNT shocks the air as it detonates.

Beyond that the speed of detonation of most common explosives is vastly higher than the SoS in the explosive. e.g. TNT detonates at 6900 meters/sec. Vice the speed of sound in air being very roughly 300 meters per second. So roughly 21 times faster.

Thanks LSLGuy. On page 579 of Richard Rhodes “The Making of the Atomic Bomb” it says:
“Initiator design has never been declassified, but irregularities machined into the beryllium outer surface that induced turbulence in the imploding shock wave probably did the job: the Fat Man initiator may have been dimpled like a golf ball.”
I’m reading the 25th Anniversary edition. Is the initiator design still classified?

Just to add this as an FYI: the standard artillery round (for the M-198 155mm towed howitzer is the HE round. It’s the cheap, basic round. High Explosive. It weighs 96 lbs.

I don’t happen to know, but if you want to learn more about the physical construction of Little Boy and Fat Man, get this book: Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man. It’s written by John Coster-Mullen, a truck driver and photographer who spent decades researching them, obtaining declassified documents and photographs, and examining the extant artifacts and sites. He and his son built the replica of Little Boy that is on display in Wendover, UT, at the site of the former AAF base where Col. Paul Tibbets trained the pilots and crews that would drop the bombs on Hiroshima and Nagasaki.

One of the things I learned from that book is that, contrary to what I had learned from other sources, the “bullet” in Little Boy was not a smaller piece of U235 fired into a stationary larger piece. It was exactly the other way around: the projectile was a large cylinder that was fired onto a stationary rod of four-inch-wide disks of U235.

Here’sa great New Yorker article from 2008 about the author and the book.

Thanks commasense, I’ll order the book.

I’d like to know how atomic physicists have responded to Mullen’s book.

From the Amazon page on the book:

“Most amazing document…In all first rate.” — Harold Agnew, Project Alberta and former Director of Los Alamos

“You have done a remarkable job.” — Philip Morrison, Manhattan Project Physicist

“Your detailed and unique research is very impressive.” — Henry Linschitz, Manhattan Project Chemist

“I am very favorably impressed by the amount of information you have gathered together and presented in an interesting fashion.” — Norman F. Ramsey, Project Alberta

Not physicists, but relevant:

“I was very much impressed.” — Paul W. Tibbets, Brig. General, USAF, Retired

“What you have now written is the best, I am sure, of any discussion on the subject I have seen.” — Frederick L. Ashworth, Vice Admiral, USN, Retired

“Your book contains the best description of the Nagasaki mission I have ever read.” — Dutch Van Kirk, Enola Gay Navigator

“I think your story is excellent. I don’t recall anything like it before.” — George Caron, Enola Gay Tail Gunner

If your concern is that it reveals information that could help terrorists, the fact is that the information has been available to anyone who really wanted it for at least 50 years. What really stops just anyone from making nuclear weapons (as in the 1986 movie “The Manhattan Project,” about a teenager who makes a bomb) is the difficulty of obtaining the fissile material, and the challenge of handling and machining it once you have it.

Indeed, Analog magazine printed an article on how to make a crude, fixed-in-place, bomb in the late 70s or early 80s.
Basically, a really complicated suicide device.

Apart from that, I was under the impression that there were restrictions on the technology used to make bombs, e.g. even if you know you need high-speed switches, you may have a hard time obtaining them.

Why would it be a suicide device? The weapons grade fissionable material, after processing, is only slightly radioactive and safe to handle with gloved hands and protection against inhaling the dust. If someone got their hands on some, they could assemble a crude bomb, set a timer, and get out of the blast radius before it goes off.

Now their lifespan after committing a crime against humanity like that would probably be shortened, depending on if they were caught or not (they probably would be, but the FBI is probably going to have a tough time finding fingerprints or serial numbers…), but they wouldn’t be killed in the process.

I wish I could say it was completely impossible, but apparently, Russia had a warehouse full of the stuff that was poorly guarded for several years following the fall of the Soviet Union. And I’ve read the total Materials Unaccounted For is enough to make at least 1 fission device. Russia also left several bombs worth lying completely unguarded in Mongolia as part of an experiment where they set nukes off and examined the effects on targets made of weapons grade fissionable material.

Sure. And they actually said that. But then, they also had you hand-machining weapons-grade fissile material. Which is incredibly dangerous from a heavy metals perspective, not to mention a powerful Alpha-emmitter. Chances of NOT getting some of that crap in your lungs and eyes, absent quite extreme protective* measures? Nil. Buh-bye.

*Especially so, considering the state of PPE at the time.

But didn’t the government consider that as conflicting with national security? Where would the line have been drawn at that time between the First Amendment and national security?

Thanks commasense. It’s surprising to me that Mullen’s book isn’t better known.

Not really. Their design was based on ‘first principles’ engineering - how to create a nuclear chain reaction isn’t all that arcane. OTOH, they didn’t have access to, or at least didn’t indicate access to, sophisticated fissile geometry. THAT would’ve made things dicey.