Semiempirical Shell Model Masses with Magic Number Z = 126 for Superheavy Elements

A semiempirical shell model mass equation applicable to superheavy elements up to Z = 126 is presented and shown to have a high predictive power. The equation is applied to the recently discovered superheavy nuclei Z = 118, A = 293 and Z = 114, A = 289 and their decay products.Comment: 7 pages, including 2 figures and 2 table

Social Security Money's Worth

This paper describes how three money's worth measures the benefit-to-tax ratio, the internal rate of return, and the net present value are calculated and used in analyses of social security reforms, including systems with privately managed individual accounts invested in equities. Declining returns from the U.S. social security system prove to be the inevitable result of having instituted an unfunded (pay-as-you-go) retirement system that delivered $7.9 trillion of net transfers (in 1997 present value dollars) to people born before 1917, and will deliver another$1.8 trillion to people born between 1918 and 1937. But young and future workers cannot necessarily do better by investing their payroll taxes in capital markets. If the old system were closed down, massive unfunded liabilities of $9-10 trillion would still have to be paid unless already accrued benefits were cut. Alternative methods of calculating these accrued benefits yield somewhat different numbers: the straight line calculation is$800 billion less than the constant benefit calculation we propose as the benchmark. Using this benchmark in a world with no uncertainty, we show that privatization without prefunding would not increase returns at all, net of the new taxes needed to pay for unfunded liabilities. These new taxes would amount to 3.6 percent of payroll, or about 29 percent of social security contributions. Prefunding, implemented by reducing accrued benefits or by raising taxes, would eventually increase money's worth for later generations, but at the cost of lower money's worth for today's workers and/or retirees. Computing money's worth when there is uncertainty is much more difficult unless four conditions hold prices into stocks and out of bonds has no effect whatsoever on money's worth when it i adjusted for risk: a dollar of stock is worth no more than a dollar of bonds. diversification can raise welfare for constrained households, but the exact money's worth must depend on specific assumptions about household attitudes toward risk. Calculations lik the Social Security Advisory Council that attribute over $2.85 of net present va$1 shifted from bonds to stocks completely overlook the disutility of risk. By estimate that a 2 percent of payroll equity fund carved out of social security w present value by about 59 cents per dollar of bonds switched into equities When the likely reductions in income and longevity insurance are factored in privatization and diversification is substantially less than popularly perceived

Would a Privatized Social Security System Really Pay a Higher Rate of Return

Many advocates of social security privatization argue that rates of return under a defined contribution individual account system would be much higher for all than they are under the current social security system. This claim is false. The mistake comes from ignoring accrued benefits already promised based on past payroll taxes, and from underestimating the riskiness of stock investments. Confusion arises because three distinct reforms are muddled. By privatization we mean creating individual accounts (which could, for example, be invested exclusively in bonds). By diversification we mean investing in stocks, and perhaps other assets, as well as bonds; diversification might be undertaken either by individuals in their private social security accounts, or by the social security trust fund. By prefunding we mean closing the gap between social security benefits promised to date and the assets on hand to pay for them. Any one of these reforms could be implemented without the other two. If the system were completely privatized, with no prefunding or diversification, the social security system would need to raise taxes and/or issue new debt in order to pay benefits already accrued. If the burden were spread evenly across all future generations via a constant proportional tax, the added taxes would completely eliminate any rate of return advantage on the individual accounts. We estimate that the required new taxes would amount to about 3 percent of payroll, or about a quarter of all social security contributions, in perpetuity. Unlike privatization, prefunding would raise rates of return for later generations, but at the cost of lower returns for today's workers. For households able to invest in the stock market on their own, diversification would not raise rates of return, correctly adjusted to recognize risk. Households that are constrained from holding stock, due to lack of wealth outside of social security or to fixed costs from holding stocks, would gain higher risk-adjusted returns and would benefit from diversification. If this group is large, diversification would raise stock values, thus helping current stockholders, but it would lower future stock returns, thus hurting young unconstrained households. Overall, since the number of truly constrained households is probably not that large, privatization and diversification would have a much smaller effect on returns than reformers typically claim.

The Origin of the Wigner Energy

Surfaces of experimental masses of even-even and odd-odd nuclei exhibit a sharp slope discontinuity at N=Z. This cusp (Wigner energy), reflecting an additional binding in nuclei with neutrons and protons occupying the same shell model orbitals, is usually attributed to neutron-proton pairing correlations. A method is developed to extract the Wigner term from experimental data. Both empirical arguments and shell-model calculations suggest that the Wigner term can be traced back to the isospin T=0 part of nuclear interaction. Our calculations reveal the rather complex mechanism responsible for the nuclear binding around the N=Z line. In particular, we find that the Wigner term cannot be solely explained in terms of correlations between the neutron-proton J=1, T=0 (deuteron-like) pairs.Comment: 10 RevTeX pages, 3 Postscript figures include

Social Security Money\u27s Worth

This paper describes how three money’s worth measures — the benefit-to-tax ratio, the internal rate of return, and the net present value — are calculated and used in analyses of social security reforms, including systems with privately managed individual accounts invested in equities. Declining returns from the U.S. social security system prove to be the inevitable result of having instituted an unfunded (pay-as-you-go) retirement system that delivered $7.9 trillion of net transfers (in 1997 present value dollars) to people born before 1917, and will deliver another$1.8 trillion to people born between 1918 and 1937. But young and future workers cannot necessarily do better by investing their payroll taxes in capital markets. If the old system were closed down, massive unfunded liabilities of $9–10 trillion would still have to be paid unless already accrued benefits were cut. Alternative methods of calculating these accrued benefits yield somewhat different numbers: the straight line calculation is$800 billion less than the constant benefit calculation we propose as the benchmark. Using this benchmark in a world with no uncertainty, we show that privatization without prefunding would not increase returns at all, net of the new taxes needed to pay for unfunded liabilities. These new taxes would amount to 3.6 percent of payroll, or about 29 percent of social security contributions. Prefunding implemented by reducing accrued benefits or by raising taxes, would eventually increase money’s worth for later generations, but at the cost of lower money’s worth for today’s workers and/or retirees. Computing money’s worth when there is uncertainty is much more difficult unless four conditions hold, namely optimization, time homogeneity, stable prices, and spanning. Under these conditions, the diversification of social security investments into stocks and out of bonds has no effect whatsoever on money’s worth when it is properly adjusted for risk: a dollar of stock is worth no more than a dollar of bonds. When spanning fails, diversification can raise welfare for constrained households, but the exact money’s worth must depend on specific assumptions about household attitudes toward risk. Calculations like those of the Social Security Advisory Council that attribute over $2.85 of net present value gain to each$1 shifted from bonds to stocks completely overlook the disutility of risk. By contrast, we estimate that a 2 percent of payroll equity fund carved out of social security would increase net present value by about 59 cents per dollar of bonds switched into equities, instead of $2.85. When the likely reductions in income and longevity insurance are factored in, the net advantage of privatization and diversification is substantially less than popularly perceived

Semiempirical Shell Model Masses with Magic Number Z=126 for Translead Elements with N smaller or equal to 126

A semiempirical shell model mass equation based on magic number Z=126 and applicable to translead elements with N smaller or equal to 126 is presented. For alpha decay energies the equation is shown to have a high predictive power and an rms deviation from the data of about 100 keV. The rms deviations for masses and other mass differences are between about 200 and 300 keV.Comment: 8 pages including 3 figures and 3 table

Microscopic structure of fundamental excitations in N=Z nuclei

Excitation energies of the $T$=1 states in even-even as well as $T$=0 and $T$=1 states in odd-odd $N$=$Z$ nuclei are calculated within the mean-field approach. It is shown that the underlying structure of these states can be determined in a consistent manner only when both isoscalar and isovector pairing collectivity as well as isospin projection, treated within the iso-cranking approximation, are taken into account. In particular, in odd-odd $N$=$Z$ nuclei, the interplay between quasiparticle excitations (relevant for the case of $T$=0 states) and iso-rotations (relevant for the case of $T$=1 states) explains the near-degeneracy of these fundamental excitations.Comment: 4 pages, 4 figure