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  Physics Question Sergio <invalid@invalid.com> - 2016-07-07 08:28 -0500
    Re: Physics Question Poutnik <poutnik4nntp@gmail.com> - 2016-07-08 09:02 +0200
      Re: Physics Question Sergio <invalid@invalid.com> - 2016-07-08 09:19 -0500
      Re: Physics Question moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-07-08 15:06 +0000
        Re: Physics Question Odd Bodkin <bodkinodd@gmail.com> - 2016-07-08 10:11 -0500
          Re: Physics Question benj <benj@nobody.net> - 2016-07-08 17:12 -0400
            Re: Physics Question Odd Bodkin <bodkinodd@gmail.com> - 2016-07-08 16:32 -0500
              Re: Physics Question Sergio <invalid@invalid.com> - 2016-07-10 11:15 -0500
                Re: Physics Question Fabian Russell <fb@zen.info> - 2016-07-10 19:25 +0000
                  Re: Physics Question Odd Bodkin <bodkinodd@gmail.com> - 2016-07-10 15:43 -0500
                    Re: Physics Question Fabian Russell <fb@zen.info> - 2016-07-10 21:52 +0000
                      Re: Physics Question Odd Bodkin <bodkinodd@gmail.com> - 2016-07-11 07:50 -0500
                        Re: Physics Question Poutnik <poutnik4nntp@gmail.com> - 2016-07-11 17:04 +0200
                  Re: Physics Question moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-07-11 01:20 +0000
        Re: Physics Question Poutnik <poutnik4nntp@gmail.com> - 2016-07-08 19:01 +0200
          Re: Physics Question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-07-09 21:28 +0200
            Re: Physics Question moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-07-10 02:18 +0000
      Re: Physics Question Fabian Russell <fb@zen.info> - 2016-07-09 17:11 +0000

#588251 — Physics Question

1. A sample of radioactive nuclei of a certain element can decay only by 
gamma-emission and beta-emission. If the half-life for gamma-emission is 
24 minutes and that for beta-emission is 36 minutes, the half-life for 
the sample is

(A) 30 minutes
(B) 24 minutes
(C) 20.8 minutes
(D) 14.4 minutes
(E) 6 minutes

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#588327

Dne 07/07/2016 v 15:28 Sergio napsal(a):
> 1. A sample of radioactive nuclei of a certain element can decay only by 
> gamma-emission and beta-emission. If the half-life for gamma-emission is 
> 24 minutes and that for beta-emission is 36 minutes, the half-life for 
> the sample is
> 
> (A) 30 minutes
> (B) 24 minutes
> (C) 20.8 minutes
> (D) 14.4 minutes
> (E) 6 minutes
> 
F: Incomplete scenario definition without probabilities.

Aside of that, gamma emission itself is not radioactive decay,
it is releasing energy of excited kernel.

-- 
Poutnik ( The Pilgrim, Der Wanderer )
Knowledge makes great men humble, but small men arrogant.

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#588340

On 7/8/2016 2:02 AM, Poutnik wrote:
> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>> 1. A sample of radioactive nuclei of a certain element can decay only by
>> gamma-emission and beta-emission. If the half-life for gamma-emission is
>> 24 minutes and that for beta-emission is 36 minutes, the half-life for
>> the sample is
>>
>> (A) 30 minutes
>> (B) 24 minutes
>> (C) 20.8 minutes
>> (D) 14.4 minutes
>> (E) 6 minutes
>>
> F: Incomplete scenario definition without probabilities.
>
> Aside of that, gamma emission itself is not radioactive decay,
> it is releasing energy of excited kernel.
>

I was suprized one could determine a half life from what they stated in 
the problem. They did not show how, but said the answer was d or c, 
Perhaps it is a simple combining of the given half lifes,
the z = 1/(1/x+1/y)
they use that to combining of failure rates in probability of failure 
analysis.

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#588345

Poutnik <poutnik4nntp@gmail.com> writes:

>Dne 07/07/2016 v 15:28 Sergio napsal(a):
>> 1. A sample of radioactive nuclei of a certain element can decay only by 
>> gamma-emission and beta-emission. If the half-life for gamma-emission is 
>> 24 minutes and that for beta-emission is 36 minutes, the half-life for 
>> the sample is
>> 
>> (A) 30 minutes
>> (B) 24 minutes
>> (C) 20.8 minutes
>> (D) 14.4 minutes
>> (E) 6 minutes
>> 
>F: Incomplete scenario definition without probabilities.

The half-lives give the probabilities.

>Aside of that, gamma emission itself is not radioactive decay,
>it is releasing energy of excited kernel.

Some isotopes have "meta" (excited) states that can give off
a gamma to become the ground state.  Some of these isomers
can also decay radioactively to something else by giving off an
alpha or beta.  And sometimes the ground state can't decay
the same way the isomer can.

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#588346

On 7/8/2016 10:06 AM, Michael Moroney wrote:
> Poutnik <poutnik4nntp@gmail.com> writes:
>
>> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>>> 1. A sample of radioactive nuclei of a certain element can decay only by
>>> gamma-emission and beta-emission. If the half-life for gamma-emission is
>>> 24 minutes and that for beta-emission is 36 minutes, the half-life for
>>> the sample is
>>>
>>> (A) 30 minutes
>>> (B) 24 minutes
>>> (C) 20.8 minutes
>>> (D) 14.4 minutes
>>> (E) 6 minutes
>>>
>> F: Incomplete scenario definition without probabilities.
>
> The half-lives give the probabilities.

Right, and the answer is D, I believe.

>
>> Aside of that, gamma emission itself is not radioactive decay,
>> it is releasing energy of excited kernel.
>
> Some isotopes have "meta" (excited) states that can give off
> a gamma to become the ground state.  Some of these isomers
> can also decay radioactively to something else by giving off an
> alpha or beta.  And sometimes the ground state can't decay
> the same way the isomer can.
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#588403

On 7/8/2016 11:11 AM, Odd Bodkin wrote:
> On 7/8/2016 10:06 AM, Michael Moroney wrote:
>> Poutnik <poutnik4nntp@gmail.com> writes:
>>
>>> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>>>> 1. A sample of radioactive nuclei of a certain element can decay
>>>> only by
>>>> gamma-emission and beta-emission. If the half-life for
>>>> gamma-emission is
>>>> 24 minutes and that for beta-emission is 36 minutes, the half-life for
>>>> the sample is
>>>>
>>>> (A) 30 minutes
>>>> (B) 24 minutes
>>>> (C) 20.8 minutes
>>>> (D) 14.4 minutes
>>>> (E) 6 minutes
>>>>
>>> F: Incomplete scenario definition without probabilities.
>>
>> The half-lives give the probabilities.
>
> Right, and the answer is D, I believe.
>
>>
>>> Aside of that, gamma emission itself is not radioactive decay,
>>> it is releasing energy of excited kernel.
>>
>> Some isotopes have "meta" (excited) states that can give off
>> a gamma to become the ground state.  Some of these isomers
>> can also decay radioactively to something else by giving off an
>> alpha or beta.  And sometimes the ground state can't decay
>> the same way the isomer can.

As usual, amateur Boinker goes for the simplest answer which is wrong.

MM and Pouter have the correct information.

But then shooting off your mouth when you have insufficient information 
is what Boinker calls science.

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#588405

On 7/8/2016 4:12 PM, benj wrote:
> On 7/8/2016 11:11 AM, Odd Bodkin wrote:
>> On 7/8/2016 10:06 AM, Michael Moroney wrote:
>>> Poutnik <poutnik4nntp@gmail.com> writes:
>>>
>>>> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>>>>> 1. A sample of radioactive nuclei of a certain element can decay
>>>>> only by
>>>>> gamma-emission and beta-emission. If the half-life for
>>>>> gamma-emission is
>>>>> 24 minutes and that for beta-emission is 36 minutes, the half-life for
>>>>> the sample is
>>>>>
>>>>> (A) 30 minutes
>>>>> (B) 24 minutes
>>>>> (C) 20.8 minutes
>>>>> (D) 14.4 minutes
>>>>> (E) 6 minutes
>>>>>
>>>> F: Incomplete scenario definition without probabilities.
>>>
>>> The half-lives give the probabilities.
>>
>> Right, and the answer is D, I believe.
>>
>>>
>>>> Aside of that, gamma emission itself is not radioactive decay,
>>>> it is releasing energy of excited kernel.
>>>
>>> Some isotopes have "meta" (excited) states that can give off
>>> a gamma to become the ground state.  Some of these isomers
>>> can also decay radioactively to something else by giving off an
>>> alpha or beta.  And sometimes the ground state can't decay
>>> the same way the isomer can.
>
> As usual, amateur Boinker goes for the simplest answer which is wrong.

Then what's the answer and why?

>
> MM and Pouter have the correct information.

Poutnik said there was probability information missing, and Michael 
rightly pointed out that the probability information is expressed in the 
half-lives. Poutnik then agreed. So what information do you think is 
missing?

>
> But then shooting off your mouth when you have insufficient information
> is what Boinker calls science.
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#588596

On 7/8/2016 4:32 PM, Odd Bodkin wrote:
> On 7/8/2016 4:12 PM, benj wrote:
>> On 7/8/2016 11:11 AM, Odd Bodkin wrote:
>>> On 7/8/2016 10:06 AM, Michael Moroney wrote:
>>>> Poutnik <poutnik4nntp@gmail.com> writes:
>>>>
>>>>> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>>>>>> 1. A sample of radioactive nuclei of a certain element can decay
>>>>>> only by
>>>>>> gamma-emission and beta-emission. If the half-life for
>>>>>> gamma-emission is
>>>>>> 24 minutes and that for beta-emission is 36 minutes, the half-life
>>>>>> for
>>>>>> the sample is
>>>>>>
>>>>>> (A) 30 minutes
>>>>>> (B) 24 minutes
>>>>>> (C) 20.8 minutes
>>>>>> (D) 14.4 minutes
>>>>>> (E) 6 minutes
>>>>>>
>>>>> F: Incomplete scenario definition without probabilities.
>>>>
>>>> The half-lives give the probabilities.
>>>
>>> Right, and the answer is D, I believe.
>>>
>>>>
>>>>> Aside of that, gamma emission itself is not radioactive decay,
>>>>> it is releasing energy of excited kernel.
>>>>
>>>> Some isotopes have "meta" (excited) states that can give off
>>>> a gamma to become the ground state.  Some of these isomers
>>>> can also decay radioactively to something else by giving off an
>>>> alpha or beta.  And sometimes the ground state can't decay
>>>> the same way the isomer can.
>>
>> As usual, amateur Boinker goes for the simplest answer which is wrong.
>
> Then what's the answer and why?
>
>>
>> MM and Pouter have the correct information.
>
> Poutnik said there was probability information missing, and Michael
> rightly pointed out that the probability information is expressed in the
> half-lives. Poutnik then agreed. So what information do you think is
> missing?
>
>>
>> But then shooting off your mouth when you have insufficient information
>> is what Boinker calls science.
>>
>
>

found the orgional source, the answer is D, this came from example 
physics GRE question,
I think they are just using what I call the combing of failure rate 
equation

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#588623

On Sun, 10 Jul 2016 11:15:03 -0500, Sergio wrote:

> 
> found the orgional source, the answer is D, 
>

If the answer is 14.4 minutes, then the reaction
cannot be consecutive first-order reactions,
A --> B --> C

The reaction has to be a decay by two separate
and distinct processes:

A --> B, or A --> B'

But this make no sense for radioactive decay because
a nucleus does not "decay" by gamma emission.  In
gamma emission the number of protons and neutrons
does not change.

Gamma emission is usually the result of a previous decay
mode which leaves the nucleus in an excited state.  This
excited state will then emit a gamma photon.  But the
gamma emission is always a subsequent, or consecutive
reaction.

It seems to me that the problem statement is faulty.

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#588637

On 7/10/2016 2:25 PM, Fabian Russell wrote:
> On Sun, 10 Jul 2016 11:15:03 -0500, Sergio wrote:
>
>>
>> found the orgional source, the answer is D,
>>
>
> If the answer is 14.4 minutes, then the reaction
> cannot be consecutive first-order reactions,
> A --> B --> C
>
> The reaction has to be a decay by two separate
> and distinct processes:
>
> A --> B, or A --> B'
>
> But this make no sense for radioactive decay because
> a nucleus does not "decay" by gamma emission.  In
> gamma emission the number of protons and neutrons
> does not change.
>
> Gamma emission is usually the result of a previous decay
> mode which leaves the nucleus in an excited state.  This
> excited state will then emit a gamma photon.  But the
> gamma emission is always a subsequent, or consecutive
> reaction.
>
> It seems to me that the problem statement is faulty.
>

You may want to look up a little history here.
I believe Rutherford was the one to classify the three different 
radiations from nuclei as alpha, beta, and gamma, and all three of them 
are considered radioactive decay even though only two of them lead to 
transmutation of elements.

-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#588654

On Sun, 10 Jul 2016 15:43:55 -0500, Odd Bodkin wrote:

> I believe Rutherford was the one to classify the three different 
> radiations from nuclei as alpha, beta, and gamma,
>

There are more than these three (actually two).

There are also positron emission and electron capture.

But gamma emission is NOT a decay.

A better example would have been the alternative decay modes of
Potassium-40:

https://en.wikipedia.org/wiki/Potassium-40

One mode is beta emission and the other mode is electron capture,
with each mode producing different decay products.  That is what this
problem, based on the answer, is actually asking.

Gamma emission is not involved with alternative decay modes but only
with consecutive decay.

Again, IMO, the problem is poorly designed.

 

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#588750

On 7/10/2016 4:52 PM, Fabian Russell wrote:
> On Sun, 10 Jul 2016 15:43:55 -0500, Odd Bodkin wrote:
>
>> I believe Rutherford was the one to classify the three different
>> radiations from nuclei as alpha, beta, and gamma,
>>
>
> There are more than these three (actually two).
>
> There are also positron emission and electron capture.
>
> But gamma emission is NOT a decay.

According to whom?
https://en.wikipedia.org/wiki/Radioactive_decay
"Radioactive decay, also known as nuclear decay or radioactivity, is the 
process by which the nucleus of an unstable atom loses energy by 
emitting radiation, including alpha particles, beta particles, gamma 
rays and conversion electrons. A material that spontaneously emits such 
radiation is considered radioactive."

>
> A better example would have been the alternative decay modes of
> Potassium-40:
>
> https://en.wikipedia.org/wiki/Potassium-40
>
> One mode is beta emission and the other mode is electron capture,
> with each mode producing different decay products.  That is what this
> problem, based on the answer, is actually asking.
>
> Gamma emission is not involved with alternative decay modes but only
> with consecutive decay.
>
> Again, IMO, the problem is poorly designed.
>
>
>


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#588758

On 07/11/2016 02:50 PM, Odd Bodkin wrote:
> On 7/10/2016 4:52 PM, Fabian Russell wrote:

On 07/11/2016 02:50 PM, Odd Bodkin wrote:
 >
 >>
 >> A better example would have been the alternative decay modes of
 >> Potassium-40:
 >>
 >> https://en.wikipedia.org/wiki/Potassium-40
 >>
 >> One mode is beta emission and the other mode is electron capture,
 >> with each mode producing different decay products.  That is what this
 >> problem, based on the answer, is actually asking.

There is the 3rd, quite rare mode ( 0.001% )
of the 40K positron emission.

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#588679

Fabian Russell <fb@zen.info> writes:

>On Sun, 10 Jul 2016 11:15:03 -0500, Sergio wrote:

>> 
>> found the orgional source, the answer is D, 
>>

>If the answer is 14.4 minutes, then the reaction
>cannot be consecutive first-order reactions,
>A --> B --> C

>The reaction has to be a decay by two separate
>and distinct processes:

>A --> B, or A --> B'

>But this make no sense for radioactive decay because
>a nucleus does not "decay" by gamma emission.  In
>gamma emission the number of protons and neutrons
>does not change.

>Gamma emission is usually the result of a previous decay
>mode which leaves the nucleus in an excited state.  This
>excited state will then emit a gamma photon.  But the
>gamma emission is always a subsequent, or consecutive
>reaction.

>It seems to me that the problem statement is faulty.

See my previous reply on this topic.

Quite often when a nucleus decays, the initial daughter nucleus is an
isomer, an excited state.  Nearly all isomers emit a gamma within
nanoseconds or less, to become the ground state nucleus.  We interpret
this by the parent nucleus decaying by alpha or beta AND a gamma.
Nobody cares that the gamma was produced by a separate process a half a
nanosecond later.

However, there are a few isomers with a longer half-life before they
transmute into something else.  One that confused early nuclear physicists
was Protactinium-234 and Protactinium-234m.  Natural uranium-238 initially
decays via alpha decay to Th-234, which the early researchers called U-X1.  
Th-234/U-X1 decayed by beta into what they called U-X2 which beta decayed
with a 1.175 minute half-life into what they called U-II, which is U-234.

Except there was something wrong.  Some of the U-X2 didn't decay with a
1.175 minute half-life.  It had a longer half-life, over 6 hours. It was
otherwise identical to U-X2, it had the same chemical properties, the
same mass (as far as they could tell), and decayed the same way (beta
minus into U-234).  They called this strange substance U-Z. The decay of
Th-234/U-X1 was always a mix of two things, U-X2 and U-Z, identical except
for their half-lives.

Now we know that Th-234 beta decays into Pa-234m, which is one of those
odd isomers with a relatively long half-life (1.175 minutes).  It usually
beta decays into U-234. But 0.13% of the atoms emit a gamma and become
Pa-234 atoms (the ground state), and Pa-234 (which was the mysterious U-Z)
also beta decays into U-234, but with a half-life of 6.6 hours.

So, not only is the initial problem valid, Pa-234m could be the example
nuclide in the problem, except that the half-lives are wrong.  It does
make sense to state Pa-234m sometimes decays via gamma into Pa-234.
The two are almost the same, but have different half-lives.

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#588351

On 07/08/2016 05:06 PM, Michael Moroney wrote:
> Poutnik <poutnik4nntp@gmail.com> writes:
>
>> Dne 07/07/2016 v 15:28 Sergio napsal(a):
>>> 1. A sample of radioactive nuclei of a certain element can decay only by
>>> gamma-emission and beta-emission. If the half-life for gamma-emission is
>>> 24 minutes and that for beta-emission is 36 minutes, the half-life for
>>> the sample is
>>>
>>> (A) 30 minutes
>>> (B) 24 minutes
>>> (C) 20.8 minutes
>>> (D) 14.4 minutes
>>> (E) 6 minutes
>>>
>> F: Incomplete scenario definition without probabilities.
>
> The half-lives give the probabilities.

If they are real alternatives, and not subsequent processes.

>> Aside of that, gamma emission itself is not radioactive decay,
>> it is releasing energy of excited kernel.
>
> Some isotopes have "meta" (excited) states that can give off
> a gamma to become the ground state.  Some of these isomers
> can also decay radioactively to something else by giving off an
> alpha or beta.  And sometimes the ground state can't decay
> the same way the isomer can.

Yes, that is correct.

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#588511

Poutnik wrote:

> On 07/08/2016 05:06 PM, Michael Moroney wrote:
>> The half-lives give the probabilities.
> 
> If they are real alternatives, and not subsequent processes.

Half-life is the _time_ in which 50 % of the original specimen has decayed.

<https://en.wikipedia.org/wiki/Half-life>

>>> Aside of that, gamma emission itself is not radioactive decay,

True, because an emission is not a decay.  However, gamma decay is a type of 
radioactive decay.

<https://en.wikipedia.org/wiki/Gamma_ray#Sources_of_gamma_rays>

>>> it is releasing energy of excited kernel.
>>
>> Some isotopes have "meta" (excited) states that can give off
>> a gamma to become the ground state.  Some of these isomers
>> can also decay radioactively to something else by giving off an
>> alpha or beta.  And sometimes the ground state can't decay
>> the same way the isomer can.
> 
> Yes, that is correct.

No, the proper description of a nuclear isomer is “a _metastable_ state of 
an atomic nucleus (of an isotope of a chemical element)”.

<https://en.wikipedia.org/wiki/Nuclear_isomer>

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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#588552

Thomas 'PointedEars' Lahn <PointedEars@web.de> writes:

>Poutnik wrote:

>> On 07/08/2016 05:06 PM, Michael Moroney wrote:

>>>> it is releasing energy of excited kernel.
>>>
>>> Some isotopes have "meta" (excited) states that can give off
>>> a gamma to become the ground state.  Some of these isomers
>>> can also decay radioactively to something else by giving off an
>>> alpha or beta.  And sometimes the ground state can't decay
>>> the same way the isomer can.
>> 
>> Yes, that is correct.

>No, the proper description of a nuclear isomer is 'a _metastable_ state of
>an atomic nucleus (of an isotope of a chemical element)'

><https://en.wikipedia.org/wiki/Nuclear_isomer>

So why are you saying I am wrong? Because I wrote "meta" rather than
spelling out "metastable"?

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#588480

On Fri, 08 Jul 2016 09:02:48 +0200, Poutnik wrote:

>
> Incomplete scenario definition without probabilities.
> 

Nonsense.  The correct answer is A: 30 minutes

The problem is perfectly valid and represents what a chemist
would call consecutive first-order reactions:

A --> B --> C

In this case, B is a metastable nucleus that will "decay"
to a stable nucleus by gamma emission.

If we let k1 be the rate constant for A --> B, and k2 be the
rate constant for B --> C, then:

dA/dt = -k1 * A

dB/dt = k1*A - k2 * B

dC/dt = k2 * B

Solving simultaneously we get:

C = A0 * ( 1 + 1/(k1-k2) * (k2*exp(-k1*t) - k1*exp(-k2*t)) ) 

Letting C = 1/2 * A0, that is the initial amount of A,
we can then solve for the half life knowing that: 

k1 = ln(2)/36 min

k2 = ln(2)/24 min

The final answer is 29.8826999480768 min = 30 min

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