Hacker News Reader

Comment by batbomb | Hacker News Reader

Ha, we had this idea quite a long time ago (2008) when "apps" really started becoming a thing. I think this works if you were in a densely populated area and a significant fraction of the population was listening, but that was always a pipe dream.

On a related note, when a 10^19 or above event hit a densely populated area, there's a decent sized ionization column near the center of the shower that could likely lead to cancer. Theres probably 100 to 1000 or so events like that in an area the size of the Bay Area.

Edit: I took out a part talking about noise after I glanced at the paper, but I would still be worried about it because the area of the detector (aka camera sensor) is roughly equivalent to the area of the electronics (ADC, CPU, Memory, etc...) in a smart phone, whereas most surface detectors have a huge scintillation footprint compared to the electronics footprint.

View on HN

Actually the active area of the CMOS sensor is really quite small. Like ~0.1cm^2. It is the main reason we need so darn many phones (and, as you correctly point out, an appropriate density of phones) in order to have sensitivity.

The reason it's still interesting is that at the very very highest UHECR energies, like above 10^21 eV, the density of ionizing particles is so tremendous that it's almost impossible for a (tiny) camera not to see it, if it's close to the core. This is great because unlike the Pierre Auger observatory (which is already about 100% effective at detecting showers above 10^18 eV), we become better and better at detecting events the higher the energy. So while P-A has pretty much constrained the UHE spectrum up to about 10^20 eV, the limitations on its size (as in, how much area it covers on the ground) means it can't do any better, since the higher-energy events become so rare that the probability of them happening over their patch in the desert is quite small.

The hope with CRAYFIS is that, given global coverage, we can be the most sensitive measurement of these ultra-rare events at energies above what P-A has been able to observe.

  On a related note, when a 10^19 or 
  above event hits a densely populated 
  area, there's a decent sized ionization 
  column near the center of the shower 
  that could likely lead to cancer. 
  Theres probably 100 to 1000 or so 
  events like that in an area the size 
  of the Bay Area.

Ha! Oh man. That'd be the best alert a smart phone could ever show me.

  *beep* 
    You've just been irradiated by powerful 
    cosmic rays from outer space. Your risk 
    factor for certain forms of cancer has 
    increased by 0.013%.

I really would want to know if I was suddenly showered by cosmic rays, and my location within the crowd-sourced area-of-effect, but I wonder if an app could transmit it's sensor noise to a central server, and receive accurate results aggregated from all other app instances very quickly. I figure there'd be a lag of maybe a couple of hours or more.

Reminds me of this other site, which provides air quality stats:

https://plumelabs.com

And the alert tone could be ICQ's "Uh-oh".

> Theres probably 100 to 1000 or so events like that in an area the size of the Bay Area.

On what timescale?

So, to answer my own question, based on the graph of the rates at the wikipedia article[0] it looks as though you might see 100 to 1000 events per year, over an area the size of the Bay Area.

[0] https://en.wikipedia.org/wiki/File:Cosmic_ray_flux_versus_pa...

Yep, sorry for not responding, but about 100 per year. IIRC, 10^19 events have an electronic ionization column of about 6 feet wide close to sea level, which would be could be significant. I've been out of this area of physics for almost 7 years so my memory may be a little fuzzy.

Is this something that reasonable people should try to protect themselves from? I spend most of my time indoors. Will my house's roof protect me, or is this the kind of ray that penetrates everything?

Is there some simple insulation one could install to mitigate the risk? Specifically around one's sleeping quarters, where disproportionate time is spent.

Do cosmic rays disproportionately come from one direction? I realized that I'm somehow thinking of them coming down from straight up. However, they could come in at any angle I suppose, or even upwards through the earth if they're capable of passing through it. That being said, if atmosphere or matter degrade or deter cosmic rays, then I imagine they probabilistically come from straight up, since that requires passing through the least atmosphere.

Not much you can do to shield these events, it's mostly highly-penetrating gamma rays and muons. Maybe spend a lot of time a few dozen meters underground or the the basement of high-rise buildings. If it helps, you basically have to be within a meter of these things to really experience significant radiation (rough estimate; I don't know what dose actually corresponds to cancer). At a rate of 1/km^2/yr, that means the odds of one of these hitting within 1m of you in a year is 3e-6.

In other words, you can expect to get hit once about every 320,000 years. So I wouldn't worry about it personally. However it's interesting to note that the same logic implies that about 22,000 people are affected globally each year.

As for directionality, they can come from pretty much any direction, but as the angle deviates from zenith (straight up), the particles have to travel through more atmosphere, so the intensity is decreased. Neutrinos can travel upwards through the earth, but you don't have to worry about those causing health problems (for the same reason they are able to pass right through the earth).

yeah I was referring to the specific case where the observer is roughly close to x_max for a 10^19 or above event and quite literally in the ionization column. You can get rid of almost all of the electronic and gamma components in with about 10 feet sand, 5 feet concrete or 1 foot of lead, but that of course doesn't stop the muonic component.

(I worked on HiRes/Telescope Array for 4 years on muon detectors and bi-static radar techniques for UHECRs, but that was quite a while ago and some of my memory might be slightly off)

Not sure how much energy would be deposited, but I'm sure it's not insignificant. It's rare enough that no one person could expect it to happen but probably frequent enough that it does happen at least once a decade in a densely populated area.

Reply on news.ycombinator.com