12 August 2002 Physics Letters A 300 (2002) 611–618 www.elsevier.com/locate/pla The primary target model of energetic ions penetration in thin botanic samples Yugang Wang ∗ , Guanghua Du, Jianming Xue, Feng Liu, Sixue Wang, Sha Yan, Weijiang Zhao Ion Beam Group, Institute of Heavy Ion Physics, Peking University, Beijing 100871, PR China Received 2 January 2002; received in revised form 3 July 2002; accepted 4 July 2002 Communicated by B. Fricke Abstract The ion transmission spectra of very low current MeV H + ions through two kinds of botanic samples, kidney bean slices and onion endocuticle, were carried out. The experimental spectra confirmed the botanic sample is inhomogeneous in mass density. A target model with local density approximation was suggested to describe the penetration of the energetic ions in such kind of materials. From the fitting of proton transmission spectra of two-energies, this target model was verified primarily. Including the influence of surface roughness and irradiation damage, this target model could be improved to predict the profile of penetration depth and range distribution of the energetic ions in the botanic samples.  2002 Elsevier Science B.V. All rights reserved. PACS: 61.82.-d; 34.50.Bw; 87.50.-a Keywords: Energetic ion penetration; Transmission spectrum; Biological membrane; Target model 1. Introduction The mutation effect of low energy heavy ions on crop seeds has gained more and more attentions since it was found in 1980’s due to its prospective application in biological study and agriculture [1]. However, the mechanism of this new application has not been well studied. Based on LSS theory [2], the range of such low-energy ions in condensed organic materials is not more than 1 μm, which is far less than the actual distance between the embryo and the surface of the seeds (usually 100 μm). One of the * Corresponding author. E-mail address: ygwang@pku.edu.cn (Y. Wang). possible explanations of this new phenomenon is that the penetration depth of a small part of those low- energy ions in the plant seed is much longer than that predicted by TRIM code assuming a homogeneous target material. In this case the DNA molecules in the embryo of the seed can be broken directly by the energetic incident ions. In order to understand the whole process happened during and after the low- energy ion irradiation of plant seeds, the first step—the physical process of the penetration of energetic ions in these samples should be studied carefully. To investigate the penetration process and the depth of the energetic ions in the botanic samples, in the past many analytic methods have been applied like particle induced X-ray emission (PIXE), positron annihilation and secondary ion mass spectrometry 0375-9601/02/$ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0375-9601(02)00938-6