Nuclear Masses and Calculated
Ground-State Properties

Nuclear and atomic masses are needed to understand the energetics of nuclear reactions and the creation of the elements and isotopes that we observe in nature. Because of their importance, there have been extensive efforts over the years to measure masses and many theoretical efforts to understand the observations and to learn how to predict unmeasured masses.

Since more than half century tables of evaluated measured masses have regularly been published in an effort that for a long time was led by A. H. Wapstra. The most recent such evaluation is Wapstra, Audi, and Thibault (A. H. Wapstra, G. Audi, and C. Thibault, Nucl. Phys. A729 (2003), 129). Another repository of this evaluation and related data can be found here . A new evaluation has been advertised to appear in 2013. In the last decade or so new techniques, in particular trap measurements have allowed nuclear mass measurements of unprecedented accuracy. These new techniques have removed many ambiguities in previous evaluations. The individual groups performing these trap measurements maintain data bases (non-evaluated) of their results, which can be a useful resource between the more official evaluations. An exhaustive list of resources of such data bases and other mass-related resources is found here .

One of the most comprehensive and accurate models for predicting masses is the Finite Range Droplet Model (FRDM) as implemented in the work of Möller and Nix. See "Nuclear Ground-State Masses and Deformations," by P. Möller, J. R. Nix, W. D. Myers, and W. J. Swiatecki in Atomic Data and Nuclear Data Tables 59 (1995), 185-381. The report (and its extensive illustrations) is available on line from our site here. The version as published in Atomic Data and Nuclear Data Tables is available from sciencedirect .

The theoretical models for the ground-state properties of the nuclei also provide some other parameters of interest to nuclear physics and nuclear astrophysics, including lifetimes and energies for decay, particle separation energies, spins and parities, and pairing gaps. See "Nuclear Properties for Astrophysical and Radioactive-Ion-Beam Applications," by P. Möller, J. R. Nix, and K.-L. Kratz (Atomic Data and Nuclear Data Tables, 66 (1997) 131-345) is available from our site here and as published in ADNDT from sciencedirect.

All of this experimental and theoretical information can also be accessed on line using interactive forms.

Astrophysical Properties

One comprehensive online interface was created to give nuclear astrophysicists easy access to the experimental and computed masses and to the computed nuclear properties. These numbers are important for understanding nucleosynthesis in stars, especially the fast r-process that may explain the creation of heavy isotopes during supernova explosions.

The direct URL access is here .

It presents links to the ground-state masses and deformations, alpha-decay Q values and half-lives, ground-state odd-proton and odd-neutron spins and parities, ground-state proton and neutron pairing gaps, ground-state proton separation energies, ground-state neutron separation energies, beta-decay Q-values for beta-minus and EC decay, and beta-decay half-lives and beta-delayed neutron emission probabilities. When you click on the link to the desired data, the server will give you a form to enter the proton number Z and the mass number A for the desired nuclide. The results will then be returned to you in tabular form.

This interface provides a good display of the experimental and calculated masses, including plenty of significant figures and the error estimate.

The properties links also give you the option of downloading the complete data file for a particular property, for example all the alpha-decay Q values and half lives, in computer readable form. This is a convenient way to work if you want to feed the data into an astrophysics modeling code--you wouldn't want to have to select each material individually and transfer the results manually!

Reaction Q Values and Thresholds

As a byproduct of having complete files of experimental and calculated nuclear and atomic masses, we provide an online interface that can compute the reaction Q values and thresholds for all the reaction channels open for a given projectile and target up to some user-defined maximum energy. This is the qtool interface.

Simply enter the projectile and target (using the notation ZA=1000*Z+A) and EMAX (in MeV). The program will construct all open channels with up to six light outgoing particles and compute their Q values. Experimental masses will be used when available, and they will be backed up with calculated masses when necessary. The results will be sorted into energy order, and all the channels open below EMAX will be listed in an easy-to-read HTML table. Caution: if you set EMAX greater than about 50 MeV, you will start to loose some possible reactions.

The code makes no attempt to remove reactions that might be very improbable. It also keeps very short lived products like 8Be explicit. The user will have to use some judgement on how to use the results of qtool.

There is a link provided from qtool to the masses so that the user can have all the information needed to understand the displayed reaction Q values and thresholds.

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Created: Tue Mar 11, 1997
Last modified: Wed Feb 22 10:53:51 MST 2012