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March 11

Alpha particles and memory errors

I was reading in ECC memory about how alpha particles cause errors in computer memory (roughly 1 per 10GB per hour). But alpha particles are usually stopped by a sheet of paper. Most of the case on my computers is metal (plastic front and top). Also, my ECC memory is encased in a metal heat spreader. Shouldn't the case and heat spreader stop alpha particles? Bubba73 ^{You talkin' to me?} 06:20, 11 March 2019 (UTC)[reply]

I don't understand how a heat spreader or case is going to stop alpha particles emitted from the chip packaging hitting the internal circuitry of the same chip or that matter, other stuff on the same stick. (And alpha particle emissions from the chip packaging seem to be the only context in which the article discusses alpha particles.) I also don't understand how the heat spreader is going to stop alpha particles coming from the side of heat spreader exposed to the stick. (The packaging of the chips probably means alpha particles from the heat spreader are not a concern.) In any case, the section you must be referring to says that it's believed alpha particles are a very minor concern compared to secondary cosmic rays primarily neutrons

Electrical or magnetic interference inside a computer system can cause a single bit of dynamic random-access memory (DRAM) to spontaneously flip to the opposite state. It was initially thought that this was mainly due to alpha particles emitted by contaminants in chip packaging material, but research has shown that the majority of one-off soft errors in DRAM chips occur as a result of background radiation, chiefly neutrons from cosmic ray secondaries.

BTW, our soft error#Alpha particles from package decay discusses in more detail how attempts are made to reduce the risk of alpha particle emissions

Soft errors became widely known with the introduction of dynamic RAM in the 1970s. In these early devices, chip packaging materials contained small amounts of radioactive contaminants. Very low decay rates are needed to avoid excess soft errors, and chip companies have occasionally suffered problems with contamination ever since. It is extremely hard to maintain the material purity needed. Controlling alpha particle emission rates for critical packaging materials to less than a level of 0.001 counts per hour per cm2 (cph/cm2) is required for reliable performance of most circuits. For comparison, the count rate of a typical shoe's sole is between 0.1 and 10 cph/cm2. Package radioactive decay usually causes a soft error by alpha particle emission. The positive charged alpha particle travels through the semiconductor and disturbs the distribution of electrons there. If the disturbance is large enough, a digital signal can change from a 0 to a 1 or vice versa. In combinational logic, this effect is transient, perhaps lasting a fraction of a nanosecond, and this has led to the challenge of soft errors in combinational logic mostly going unnoticed. In sequential logic such as latches and RAM, even this transient upset can become stored for an indefinite time, to be read out later. Thus, designers are usually much more aware of the problem in storage circuits.

P.S. I'm not sure where in our article you got the figure you cited. The only figures I see are for all errors, rather than those attributed to alpha particles. As said, it says most of these appear to be caused by neutrons from cosmic rays. Nil Einne (talk) 09:30, 11 March 2019 (UTC)[reply]

P.P.S. As per Soft error#Cosmic rays creating energetic neutrons and protons, neutrons themselves being uncharged wouldn't generally affect the circuitry and it may be alpha particles emitted from neutron capture that do so.

Neutrons are uncharged and cannot disturb a circuit on their own, but undergo neutron capture by the nucleus of an atom in a chip. This process may result in the production of charged secondaries, such as alpha particles and oxygen nuclei, which can then cause soft errors.

So I guess in that way, you are right that it could be regarded as alpha particles at some ultimate level. But from what I read, alpha or other charged particles coming from neutrons coming from cosmic rays are normally considered separately from alpha particles coming from alpha decay of the chip packaging. And it's not clear to me if we even know what percentage of errors are likely to be coming from alpha particles compared to other charged particles, arising from neutron capture. Also, I still don't see the relevance of the heat spreader or case in stopping alpha particle emissions from neutron capture happening within the chip. Nil Einne (talk) 09:59, 11 March 2019 (UTC)[reply]

Sorry, I was thinking of them coming from outside the case. But more reading in alpha particles says that they are stopped by a few centimeters of air, so they aren't coming from a long way away. I also just found Soft_error#Alpha_particles_from_package_decay. Bubba73 ^{You talkin' to me?} 18:39, 11 March 2019 (UTC)[reply]

As far as the figure I gave, there is a range in the article and I did the calculations for something in that range. Bubba73 ^{You talkin' to me?} 21:14, 11 March 2019 (UTC)[reply]

Editing existing MS Word footers ... do I have to start by clicking 'Insert'?

In order to edit an existing MS Word footer I seem to need to go Insert >>> Header & Footer >>> Footer >>> Edit Footer. For years having to click 'Insert' to access an existing footer has irritated my obsessive compulsive behavior mode. Is there a more logical way? Hayttom (talk) 11:12, 11 March 2019 (UTC)[reply]

Hi, Hayttom! Have you tried to double-click the footer's contents? --CiaPan (talk) 11:17, 11 March 2019 (UTC)[reply]

Hi, CiaPan! I have now, thanks to your response. SPLENDID!! Hayttom (talk) 11:27, 11 March 2019 (UTC)[reply]