放射性元素每次只會有一粒原子進行衰變

放射性元素每次只會有一粒原子進行放射性衰變
I think you have misunderstood what your physics teacher has said.
He/she may mean each radionuclide can only decay once. Because after the decay, the radionuclide will have been changed to nuclide of another element, which may not be radioactive.
A sample of radioactive substance contains many many number of radioanuclides. In fact, you cannot tell exactly how many number of these radionuclide would decay in the next second, because radioactive decay is a random process. However, you can tell statistically the expected number of radionuclide which is going to decay in one second.
Take, cobalt-60, for example. The decay constant of cobalt-60 is 4.1x10^-9 s^-1. If you have, say, a sample containing 1000 million cobalt-60 radionuclides, there will be statisitcally about 4 cobalt-60 atoms decaying in 1 second.
That is to say, a single radionuclide can only decay once. But a radioactive smaple contains a large number of radionuclides, it can have several radionuclides decaying at the same time.
即每次只會發射出一粒放射物 , 不會同一時間射出兩粒放射物
Depending on the element, a single radionuclide of that element can only emit either an alpha or a beta particles, but not both. In some radionuclides, if the decayed nuclide is in an excited state, gamma rays will be emitted.
為什麼不能同一時間放出兩粒放射物??
A single radionuclide cannot emit alpha and beta are the same time because "alpha decay" and "beta decay" are in fact two "contradicting processes". Alpha decay occurs in heavy elements (i.e. elements with high atomic number) because of excess number of nuetrons present in the nucleus. Beta decay mostly occurs in light elements in which a neutron changes into a proton and a beta electron (plus a neutrino).


2009-07-12 14:11:20 補充：
那如果我把該樣本切開分成 2 塊 , 又會不會同時射出兩粒放射物?
Sure. Normally, in a sample of radioactive substance, there are many many particles emitting from it in every second.......(cont'd)

2009-07-12 14:12:18 補充：
... (cont'd) When you placed a radiation detector (e.g. a Geiger counter) near a radioactive sample, you could observe the count-rate recorded by the Geiger counter. ......(cont'd)

2009-07-12 14:12:49 補充：
....(cont'd) The number of counts in 1 second, in fact, indicates the the number of particles emitting from the sample and entering into the Geiger tube. Count-rates of several hundreds to several thousands counts in 1 second are not uncomon.

當你把該元素切成2塊，它就已經不是放射性元素了。(請給我分 please)