[seqfan] Re: Atomic number of n-th element in the "neptunium series"

[Marc LeBrun]

Maybe, rather than counting down, it should be increasing, with a(1) = the final stable decay product?  
That way, any "trans-neptunian" elements discovered in the future would simply extend the sequence.


> On Apr 19, 2018, at 9:52 AM, Allan Wechsler <acwacw at gmail.com> wrote:
> 
> The proposed sequence was not just counting down by fours. Every nucleus
> contains integral numbers of protons and neutrons. The mass number is the
> sum of these two; it is this that does not change (modulo 4) during
> radioactive decay. The atomic number is just the number of protons. Each
> decay event can change the atomic number by -2, -1, or +1, depending on
> what kind of decay it is. I believe Felix Fröhlich was proposing recording
> the atomic numbers in a sequence.
> 
> 
> On Thu, Apr 19, 2018 at 11:18 AM, Neil Sloane <njasloane at gmail.com> wrote:
> 
>> If the sequence is just counting down by 4's from 149, it probably is not
>> worth adding to the OEIS
>> 
>> Best regards
>> Neil
>> 
>> Neil J. A. Sloane, President, OEIS Foundation.
>> 11 South Adelaide Avenue, Highland Park, NJ 08904, USA.
>> Also Visiting Scientist, Math. Dept., Rutgers University, Piscataway, NJ.
>> Phone: 732 828 6098; home page: http://NeilSloane.com
>> Email: njasloane at gmail.com
>> 
>> 
>> On Thu, Apr 19, 2018 at 7:52 AM, Allan Wechsler <acwacw at gmail.com> wrote:
>> 
>>> Every nucleus has an integer mass number; radioactive decay either
>> doesn't
>>> change the mass number, or reduces it by 4. Therefore, there are four
>>> classes of radioactive nuclei. The Np-237 series all have mass number of
>>> the form 4n+1. It is called the Neptunium series because at the time of
>> its
>>> discovery, Neptunium was the earliest known member. Four prior members
>> are
>>> now known: Californium-249, Curium-245, Plutonium-241, and Americium-241
>>> (which decays into Neptunium-237).
>>> 
>>> The 4n series's earliest known member is Californium-252 and is called
>> the
>>> Thorium series; 4n+2 starts with Uranium-238 and is named after it; and
>>> 4n+3 starts with Californium-251 and is called the Actinium series.
>>> 
>>> I have no opinion on whether the atomic numbers of these series belong in
>>> OEIS; they seem like a borderline case to me.
>>> 
>>> On Thu, Apr 19, 2018 at 6:31 AM, Felix Fröhlich <felix.froe at gmail.com>
>>> wrote:
>>> 
>>>> "Why Neptunium 237?"
>>>> 
>>>> I chose it because it seems to have a long decay chain. There may be
>>> other
>>>> lements with longer chains, I am not sure. Also, I thought it was
>>>> interesting that the chain cannot have progressed past Bi-209 naturally
>>> due
>>>> to the extremely long half-life of Bi-209.
>>>> 
>>>> Thanks for your suggestion regarding making each term the number of the
>>>> most common element. That sounds like a good idea.
>>>> 
>>>> Regards
>>>> Felix
>>>> 
>>>> 2018-04-19 1:55 GMT+02:00 Frank Adams-watters via SeqFan <
>>>> seqfan at list.seqfan.eu>:
>>>> 
>>>>> If this is added, I think each term should be the atomic number of
>> the
>>>>> most common element at that step.
>>>>> This "stabilizes " the sequence: otherwise at step n, if you
>> discovered
>>>>> their was another decay product
>>>>> occurring only with, say, probability 0.001%, the sequence would have
>>> to
>>>>> be changed so that a(n) = 0.
>>>>> 
>>>>> Second, why Neptunium 237? Is there something special about it?
>>>>> 
>>>>> Franklin T. Adams-Watters
>>>>> 
>>>>> 
>>>>> -----Original Message-----
>>>>> From: Felix Fröhlich <felix.froe at gmail.com>
>>>>> To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
>>>>> Sent: Wed, Apr 18, 2018 7:41 am
>>>>> Subject: [seqfan] Atomic number of n-th element in the "neptunium
>>> series"
>>>>> 
>>>>> Dear SeqFans,here is an idea for a sequence related to radioactive
>>> decay
>>>>> of a chemical
>>>>> element:
>>>>> Atomic number of n-th element in the "neptunium series", the decay
>>> chain
>>>> of
>>>>> neptunium-237, or 0 if the n-th link of the chain consists of more
>> than
>>>> one
>>>>> element. For an overview, please see
>>>>> https://en.wikipedia.org/wiki/Decay_chain#Neptunium_series
>>>>> The sequence starts 93, 91, 92, 90, 88, 89, 87, 85, 83, 0, 82, 83,
>>>> 81a(10)
>>>>> (if the offset is 1) is 0, because bismuth-213 decays into
>>>>> polonium-213 and thallium-209, both of which in turn decay into
>>> lead-209.
>>>>> I don't know if this sequence is interesting. The "0" term may be a
>> bit
>>>>> unsatisfactory, but I am not sure of a better way to resolve the
>> issue
>>> of
>>>>> an
>>>>> isotope decaying into two daughter isotopes at the moment.
>>>>> 
>>>>> Best regardsFelix Fröhlich
>>>>> 
>>>>> --Seqfan Mailing list - http://list.seqfan.eu/
>>>>> 
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>>>>> Seqfan Mailing list - http://list.seqfan.eu/
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>>>> 
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