J. B. Martins

Photodisintegration of light and medium-weight nuclei at intermediate energies I—Photoproduction of 18F, 22Na, and 24Na from targets with masses up to 40

Abstract Mean cross sections for the photoproduction of 18 F, 22 Na, and 24 Na have been determined from 23 Na, 27 Al, 28 Si, 31 P, 32 S, 35,37 Cl, 39 K, and 40 Ca targets using bremsstrahlung beams in the energy range 0·3–1 GeV. The results have been compared with a modified Rudstams CDMD formula and found to be consistent with the cross section dependence predicted on the basis of conventional spallation processes for 24 Na only. For 18 F and 22 Na, some deviations have been observed from the spallation patterns when target mass numbers exceed 31 and 37, respectively, thus suggesting other mechanisms different from spallation being effective in their production, such as fission and fragmentation.

Transparencies of complex nuclei to photoproduced pions and recoil nucleons

In the high-energy photonuclear research it is very important to study the probability that a pion and/or a recoil nucleon produced by the interaction of a high-energy photon with a complex nucleus, escape from the nucleus without any interaction, i.e. the transparency of the nucleus to the photopions and recoil nucleons. The only publication available in this field is the paper of Roos and PETERSON (1) on the photodissociation of complex nuclei at energies between the mesonic threshold and 1150 MeV. In their work, Roos and PETERSON used the transparency values of METROPOLIS et al. (2.3) for pionand nucleon-initiated cascades, with the simple modification of doubling those transparencies to account for the fact that in the case of photon-initiated cascades, pions and recoil nucleons originate within the nuclei and so have an average path length smaller than that for pions and nucleons impinging from the outside. Roos and PETERSON estimated that the path length in the latter case was two times that for particles originated by photons in the nucleus. The present paper reports the calculation of transparencies for pions and recoil nucleons originated by interaction of high-energy photons with complex nuclei (energy range (0.3-1.0) GeV). The calculation is based on the following assumptions:

Photodisintegration of light and medium-weight nuclei at intermediate energies—III: Spallation of vanadium, manganese, iron and cobalt

Abstract Cross sections per equivalent quantum, in the energy range 0.3–1.0 GeV, have been measured for spallation residuals from 51V, 55Mn, natural Fe, and 59Co targets. Mean cross sections per photon have been deduced in this energy range and the data analysed in terms of charge-dispersion curves and mass-yield distributions. The mean cross sections per photon have also been compared with a semiempirical Rudstams formula. A satisfactorily good agreement has been found with the calculated yields within a factor of two.

Nuclear fission of197Au,natPb and209Bi induced by polarized and monochromatic photons of 60 and 64 MeV

SummaryIn this paper we report experimental results on the fission cross-section and the fissionability of the197Au,natPb and209Bi nuclei at photons energies 60 and 64 MeV. The fissionability results agree satisfactorily with our estimate based on the statistical model and considerations on the mechanisms of nuclear disexcitation.RiassuntoSono riportati i risultati sperimentali sulla sezione d’urto di fissione e sulla fissionabilità dei nuclei di197Au,natPb e209Bi indotte dai fotoni monocromatici e polarizzati del fascio LADON dei Laboratori Nazionali di Frascati alle energie medie di 60 e 64 MeV. I risultati sulla fissionabilità sono in soddisfacente accordo con una stima che abbiamo ottenuto tenendo conto del modello statistico e di altre considerazioni sui meccanismi di diseccitazione nucleare.РезюмеВ этой статье мы приводим эспериментальные результаты по измерению поперечного сечения деления и расщепляемости ядер197Au,ectPb и209Bi фотонами с энергиями 60 и 64 МэВ. Результа.ы для расщепляемости удовлетворительно согласуются с оценками, основанными на статистической модели и на рассмотрении механизмов девозбуждения ядер.

Photodisintegration of light and medium-weight nuclei at intermediate energies—II Photoproduction of 11C and 7Be from 40Ca☆

Abstract Mean cross sections for the photoproduction of 11C and 7Be from 40Ca targets have been measured using bremsstrahlung beams in the energy range 0·3–1 GeV. The values obtained turned out to be much larger than those expected from a simple spallation mechanism. A fragmentation-like process has therefore been suggested to explain such a discrepancy.

Photoproduction of 18F from 27Al at energies between 0·3 and 1 GeV

Abstract Aluminium targets have been irradiated with bremsstrahlung beams at energies between 0·3 GeV and 1GeV and the cross-sections of the photoproduction of 18F have been measured by activation analysis.

On the isomeric-yield ratio of52Mng and52Mnm photoproduction from55Mn at intermediate energies

P h o t o n u c l e a r r e a c t i o n s y ie ld ing , as f inal p r o d u c t s , pa i r s of nuc l ea r i somer ic s t a t e s are v e r y use fu l in e s t i m a t i n g t h e r e l a t i ve p robab i l i t i e s of p r o d u c i n g each isomer . The knowledge of t h e i somer ic -y ie ld r a t i o s can p r o v i d e i n f o r m a t i o n a b o u t t he sp in dep e n d e n c e of t h e nuc lea r l eve l d e n s i t y in t h e nuc l eus u n d e r i n v e s t i g a t i o n a n d t he m e c h a n i s m of t h e r eac t ion . A n u m b e r of works h a v e b e e n ca r r i ed ou t on i somer ic pa i r s p r o d u c e d b y e i t h e r part ic le b o m b a r d m e n t s or low-energy p h o t o n i n d u c e d r eac t i ons (1.a). HUIZENGA a n d VANDEB0SCI~ (~.2) r e a c h e d t h e conc lus ion t h a t t h e r e l a t i ve y ie ld of t h e h igh sp in i somer increases w i t h i n c r e a s i n g i n c i d e n t energy . F o r p h o t o n i n d u c e d r e a c t i o n s a t low energies, W~LTE~S a n d HUMMEL (3) f o u n d a l a rge r y ie ld of t h e i somer w i t h spin closer to t h a t of t h e t a r g e t nucleus . No a t t e m p t s were m a d e in o rde r to d r a w up i n d i c a t i o n s a b o u t t h e genera l t r e n d of t h e i somer ic -y ie ld r a t ios a t t h e i n t e r m e d i a t e ( (0 .1 -1 ) GeV) and h i g h e r ( > 1 GeV) energies. D a t a on t h e i somer ic -y ie ld r a t i o s f r o m e x p e r i m e n t s u s ing i n t e r m e d i a t e e n e r g y photons are a t p r e s e n t v e r y scarce (6.G). Some resu l t s h a v e been r epo r t ed , in a p re l imi n a r y way, in ref. (s) as r ega rds t h e 52Mn i somer ic ra t io . The p r e s e n t p a p e r r epo r t s y ie ld m e a s u r e m e n t s of t h e p h o t o p r o d u c t i o n of 52Mng a n d 5~Mn~ f r o m 55Mn a t b r e m s s t r a h l u n g energies f rom 0.3 GeV u p to 1 GeV. A l r e a d y pub l i shed re su l t s for l~ a n d ~~ f r o m l~ (7.s) are also r e p o r t e d for t h e sake of comple t enes s a n d discussed.

SOME REMARKS ON THE TRANSPARENCY OF COMPLEX NUCLEI TO PHOTOPRODUCED CHARGED PIONS AT INTERMEDIATE ENERGIES.

I n a r e c e n t p a p e r (1) we r e p o r t e d t h e ca l cu la t ion of t r a n s p a r e n c i e s of c o m p l e x nuc le i to p h o t o p r o d u c e d p ions a n d recoil nuc l eons a t p h o t o n energies b e t w e e n 0.3 GeV a n d 1.0 GeV. Th i s ca l cu l a t i on was essen t i a l ly b a s e d u p o n t h e fol lowing a s s u m p t i o n s : i) t h e i n t e r a c t i o n b e t w e e n t h e p h o t o n a n d t h e nuc l eon in t h e nuc l eus p roduces a s ingle r . -meson a n d a recoil nuc l eon ; ii) in t e r m s r e p o r t e d iii) iv) v) t h e f ac t F r o m

Systematics of Spallation Yields with a Four-Parameter Formula

A semi-empirical four-parameter formula is proposed in order to systematize intermediateand high-energy proton-induced spallation yields of target nuclei covering the 5 0 1 0 0 mass number interval. It is shown that the measured yields are reproduced by the formula with a degree of accuracy which is comparable with or better than those obtained in previous proton-spallation systematics by other authors. The formula predicts reliable values for the most probable mass number of isotopie distributions. In addition, it allows one to derive in a simple way the mean nominal number of nucléons lost by the struck target nucleus, the chargeand mass-yield distributions for the spallation residuals, the total spallation reaction cross section, and the N / Z charge-dispersion curves.

Cross sections of (γ, xn) reactions in complex nuclei at intermediate energies☆

Cross sections per equivalent quantum, in the energy range 0.3–1.0 GeV, have been measured for 209Bi(γ, 2n), 209Bi(γ, 3n), 209Bi(γ, 4n), 59Co(γ, 2n), 509Co(γ, 3n), 59Co(γ, 4n) and 51V(γ, 3n) reactions. From the calculated mean absolute cross sections and the data already available in literature for (γ, xn) reactions (x ≥ 1), a cross section formula has been deduced which reproduces, within a factor of two, most of the experimental cross sections for target nuclei ranging between 9Be and 238U.