There are many different detectors for different radiation,such as NaI,HpGe,CsI for $\gamma$ detection,and ionization chamber,proportional counter,Geiger counter for $\alpha$, $\beta$ detection,but how to select a suitable detector for different radiation?I mean compare between them,what is the advantages and defects of them?
[Physics] How to choose a $\alpha$, $\beta$, $\gamma$ measurement detector
experimental-physicsexperimental-techniqueparticle-detectorsradiation
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There are many reasons for this situation.
Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost.
(Mentioned by DumpsterDoofus) low power density. ${}^{63}\text{Ni}$ for instance produces ~5 W/kg (and kg here is just mass of radioactive material, the actual battery would be at least order of magnitude heavier). There are, of course isotopes with power densities much higher but they encounter other problems.
Semiconductor damage. If we try to increase power by using isotopes with higher decay energies we find that the high energy electrons damage semiconductors, reducing service life of batteries to times much shorter than isotope halflife. Alpha particles, especially, damage the p-n junctions, so even though (for instance) ${}^{238}\text{Pu}$ produces 0.55 W/g of alpha radiation, it is mainly used in the thermoelectric schemes rather than in direct energy converters.
Gamma radiation. Many isotopes has gamma emission as a secondary mode of decay. Since this type of radiation is difficult to shield, this means that the selection of isotopes usable for batteries is limited only to pure beta emitters.
Bremsstrahlung. Electrons braking produces this type of radiation, that had to be shielded. Again, this limits our selection of isotopes to those with relatively low decay energies.
Low volume of production / Economics. Many isotopes cost too much to be practical in wide array of applications. This is partly explained by low volume of production and partly by production process which will be costly at all volumes because it requires energy consuming isotope separation and special facilities for working with radioactive materials. For instance, tritium (one of the materials for betavoltaics) costs about $30 000 per gram and its world annual production is 400 g (from wikipedia).
All this means, that nuclear batteries are limited to a selection of niche applications, typically those with low power / long autonomous lifetime requirements. That is not to say that there can't be innovations expanding their use or reducing costs.
[1] Tsvetkov, L. A., et al. "Possible Way To Industrial Production of Nickel-63 and the Prospects of Its Use." (2005). online version
Update. Your updated calculations on power output from ${}^{63}\text{Ni}$ is essentially correct with one crucial distinction: 67 keV is total decay energy and approximately maximum energy of electron. But, since the decay also produces neutrino the mean energy of electron is much smaller: 17 keV (look at this NUDAT reference, or this java applet for electron spectrum). So the usable power from 1 mole of ${}^{63}\text{Ni}$ is: $$ W= {}^{63}\text{Ni specific activity} \times 17\,\text{keV} \times 63\,\text{g} = 0.36\,\text{W}, $$ where specific activity could be, for instance, taken from Wolfram Alpha. This is not sufficient to provide iPhone peak power consumption, which is about 1.5 W (see my reason 1).
Incidentally, we come to one more reason (though not, strictly speaking, related to physics):
- Safety / Regulations / Perception: 63 grams of ${}^{63}\text{Ni}$ constitute more than 3500 curie of radioactivity, which would definitely require regulations for handling and probably would not be allowed inside a single unit for unrestricted civilian use. We know that when properly used betavoltaics are safe. But what about im-proper use / improper disposal / potential for abuse? At any rate, current perception of nuclear power by general public is not that good, so marketing nuclear batteries will present certain challenge.
Best Answer
In some sense the question is simple too big. I mean, it always comes down to a balance between your ultimate goal, your budget and any engineering constraints imposed by the goal.
Consider the differences between
all the way up to things like
Like any other engineering situation we trade things off in order to get what we need (and maybe some of what we want) as easily as possible. In each case we consider things like